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The combined use of theoretical and mathematical methods in the analysis of electron paramagnetic resonance data has greatly increased the ability to interpret even the most complex spectra reported for doublet state inorganic main group radicals. This personal account summarizes the theoretical basis of such an approach and provides an in-depth discussion of some recent illustrative examples of the utilization of this methodology in practical applications. The emphasis is on displaying the enormous potential embodied within the approach. peerReviewed

The recent discovery of a suitable synthesis of the monoanionic ditelluroimidodiphosphinate ligands [TePR 2 NPR 2 Te] − (R = Ph, i Pr, t Bu) has facilitated investigations of the fundamental chemistry of these chelating inorganic ligands. This article is focused on aspects of that chemistry in which the behaviour of this ditelluro PNP ligand differs from that of the well-studied dithio and diseleno congeners. The emphasis is on new tellurium-containing ring systems formed in: (a) redox transformations and (b) the synthesis of metal complexes.

The scattered electron paramagnetic resonance (EPR) spectroscopic data for binary sulfur–nitrogen (S,N) radicals have been compiled and critically assessed.Many of these are inorganic rings or cages.For each species, possible equilibrium structures in the gas phase and the EPR hyperfine coupling (hfc) constants have been calculated with DFT using the B3LYP functional and basis sets of triple-ζ (or better) quality.Good agreement is obtained between calculated and measured values for the well characterized [S3N2]+ , a planar π-radical for which the s-component of the orbitals is likely to be reasonably independent of minor geometrical changes between gas-phase and condensed-phase states.The cage compounds [S4N4]− and [S4N5]−2 , for which reliable experimental EPR spectra have been reported, show larger variation between calculated and measured hfc, as a consequence of the dependence of the s orbital content of the molecular orbitals on small structural changes.The very large disagreements between the DFT calculated and experimentally claimed hfc constants for [NS] , [SNS] and [S4N4]−3 in condensed phases lead us to question their assignment.Among binary S,N radicals, 33S hfc data has only been reported for [S3N2]+ (through isotopic enrichment).These values were essential for the correct identification of the EPR spectra of this important radical, which previously was misassigned to other species.Our results suggest that 33S data will be equally important for the correct identification of the EPR spectra of other binary S,N species, many of which are cyclic systems, e.g.[S3N3] , [S4N3] and[S4N5] .

X-ray structural investigations have shown that the products of the reaction of CuCl2·2H2O and OP[NH-t-Bu]3 are markedly dependent on solvent and temperature. The polymeric ionic complex [(t-BuNH3)2(Cu3(OH)(H2O)Cl7)]∞ (1), containing a trinuclear anionic repeating unit, is obtained from toluene at 80 °C, whereas the 2:1 adduct Cu(t-BuNH2)2Cl2 (4) is formed at 150 °C. By contrast, a neutral tetranuclear cluster Cu4[PO(NH-t-Bu)3]4(µ4-O)Cl6 (2) or the one-dimensional chain [Cu(Py)2Cl2]∞ (3) is produced when the reaction is carried out in hexane or pyridine, respectively, at 80 °C. The reaction of a mixture of CuCl and CuCl2·2H2O (2:1 molar ratio) with OP[NH-t-Bu]3 at 80 °C in toluene produces [t-BuNH3]5[Cu5Cl10] (5), in which the anion is a pentanuclear cluster with both terminal and bridging chloride ions. The removal of the chloride ions from the reaction mixture by the addition of AgNO3 yields the 2:1 adduct Cu[OP(NH-t-Bu)3]2(NO3)2 (6).Key words: copper halides, templation, P–N compounds, cluster complexes, one-dimensional framework

The boraamidinate ligand, [RB(NR′) 2 ] 2− , is isoelectronic with the corresponding and extensively studied amidinate ligand, [RC(NR′) 2 ] − . This review provides the first comprehensive account of the coordination chemistry of the boraamidinate ligand with s-, p- and d-block metals. The focus is on the methods available for the synthesis of metal complexes, as well as the variety of bonding modes exhibited by these dianionic ligands at metal centers. The properties and reactivity of individual metal boraamidinates are discussed and, where appropriate, compared with those of the related amidinate complexes. In particular, the formation of the radical anion, [RB(NR′) 2 ] − , by the oxidation of main group complexes is highlighted.

The reactions of MCl3 with Li2[PhB(NtBu)2] in 1:1, 1:1.5, and 1:2 molar ratios in diethyl ether produced the monoboraamidinates ClM[PhB(NtBu)2] (1a, M = As; 1b, M = Sb; 1c, M = Bi), the novel 2:3 boraamidinate complexes [PhB(NtBu)2]M-micro-N(tBu)B(Ph)N(tBu)M[PhB(NtBu)2] (2b, M = Sb; 2c, M = Bi), and the bisboraamidinates LiM[PhB(NtBu)2]2 (3a, 3a.OEt2, M = As; 3b, M = Sb; 3c.OEt2, M = Bi), respectively. The 2:3 complexes 2b and 2c were also observed in the reactions carried out in a 1:2 molar ratio at room temperature. All complexes have been characterized by multinuclear NMR spectroscopy (1H, 7Li, 11B, and 13C) and by single-crystal X-ray structural determinations. The molecular units of the mono-boraamidinates 1a-c are isostructural, but their crystal packing is distinct as a result of stronger intermolecular close contacts going from 1a to 1c. In the novel 2:3 bam complexes 2b and 2c, each metal center is N,N'-chelated by a bam ligand and these two [M(bam)]+ units are bridged by the third [bam]2- ligand. The structures of the unsolvated bis-boraaminidate complexes 3a and 3b consist of [Li(bam)]- and [M(bam)]+ monomeric units linked by Li-N and M-N bonds to give a tricyclic structure. Solvation of the Li+ ion by diethyl ether results in a bicyclic structure composed of four-membered BN2As and six-membered BN3AsLi rings in 3a.OEt2. In contrast, the analogous bismuth complex 3c.OEt2 exhibits a tetracyclic structure. Variable-temperature NMR studies reveal that the nature of the fluxional behavior of 3a-c in solution is dependent on the group 15 center.

The third member of the series of imidoselenium(II) chlorides ClSe[N(tBu)Se]nCl (n = 3) (9) has been isolated from the cyclocondensation reaction of tBuNH2 and SeCl2 in THF in a molar ratio of ca. 3:1 and characterized in the form of two polymorphs 9a and 9b by single crystal X-ray analysis. The unusual structural features of this nine-atom chain are explained satisfactorily in terms of a bonding model that invokes intra-molecular secondary bonding interactions and hyperconjugation. The reaction of the bifunctional reagent ClSe[N(tBu)Se]2Cl (8) with tBuNH2 in THF occurs via concurrent pathways to give 1,3,5-Se3(NtBu)3 (1) and 1,3-Se3(NtBu)2 (3a). The energetics of the reactions of tBuNH2 and SeCl2 in THF have been calculated at the PBE0/def2-TZVPP level of theory in order to assess the feasibility of ClSe[N(tBu)Se]nCl (7–9, n = 1–3) as intermediates in the formation of known cyclic selenium imides. DFT calculations were also employed to explore the energy profile of the pathway of the formation of the first member of the series ClSeN(tBu)SeCl (7) from tBuNH2 and SeCl2 in THF at 298 K. The neutral ligand ClSeN(tBu)SeCl (7) is Se,Se′-coordinated to the metal centre in the unusual adduct [PdCl2{Se,Se′-(SeCl)2N(tBu)}]·[PdCl2{Se,Se′-Se4(NtBu)3}]·MeCN (10·MeCN), which is the first metal complex of an imidoselenium(II) chloride.

T.C. thanks the NSERC (Canada) for continuing funding. J.D.W. is grateful to the University of St Andrews for support. A.N. thanks the EPSRC for financial support.

The complexes [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] [M = Cd (1), Hg (2)] were obtained in high yields by the reaction of tert-butylselenium diimide Se(IV)(N(t)Bu)2 with CdCl2 or HgCl2 in tetrahydrofuran. Recrystallization of 1 and 2 from acetonitrile (MeCN) afforded yellow crystals of 1·MeCN and 2·MeCN, respectively. Isomorphic 1·MeCN and 2·MeCN contain an unprecedented dimeric selenium diimide ligand, which is N,N'-chelated to the metal through exocyclic imido groups. In addition to the complexes 1 and 2, the (77)Se NMR spectra of acetonitrile solutions of 1·MeCN and 2·MeCN indicated the presence of the dimeric (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu, monomeric Se(IV)(N(t)Bu)2, and cyclic selenium imides. Density functional theory calculations at the PBE0/def2-TZVPP level of theory were used to assign the (77)Se resonances of the dimer. A comparison of Gibbs energies of formation of some metal dichloride complexes [MCl2{N,N'-Se(IV)(N(t)Bu)2}] and [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] (M = Zn, Cd, Hg) indicated that the formation of complexes containing a dimeric selenium diimide ligand is favored over those containing a monomeric ligand for the group 12 metals. In the case of the group 10 metal halogenides (M = Ni, Pd, Pt), the Gibbs energies of the complexes with monomeric Se(IV)(N(t)Bu)2 ligands are close to those containing dimeric (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu ligands. A plausible reaction pathway with a low activation energy involves the initial formation of [MCl2{N,N'-Se(IV)(N(t)Bu)2}] (M = Zn, Cd, Hg), which then reacts with another molecule of Se(N(t)Bu)2, leading to the final [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] complex. Without the presence of group 12 metal halogenides, the [2 + 2] cyclodimerization of Se(IV)(N(t)Bu)2 is virtually thermoneutral, but the activation energy is relatively high, which accounts for the kinetic stability of (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu in solution. A minor byproduct, [Cd7Cl14{N,N'-Se(II)(NH(t)Bu)2}6]·4CH2Cl2, was identified by X-ray crystallography as a heptanuclear cluster with selenium(II) diamide ligands N,N'-chelated to the cadmium centers.

T.C. thanks the NSERC (Canada) for continuing funding. J.D.W. is grateful to the University of St Andrews for support. A.N. thanks the EPSRC for financial support.

Review: [fundamental concepts necessary for an understanding of the unique structures and reactivities of tellurium compounds; 50 refs.

The cyclocondensation reaction of equimolar amounts of SeCl2 and (Me3Si)2NMe in THF affords 1,3,5,7-Se4(NMe)4 (5b) [δ((77)Se) = 1585 ppm] in excellent yield. An X-ray structural determination showed that 5b consists of cyclic, puckered crown-shaped molecules with a mean Se-N bond length of 1.841 Å typical of single bonds. A minor product of this reaction was isolated as unstable orange-red crystals, which were identified by X-ray analysis as the adduct 1,5-Se6(NMe)2·(1)/2Se8 (1b·(1)/2Se8), composed of cyclic 1,5-Se6(NMe)2 and disordered cyclo-Se8 molecules. A detailed reinvestigation of the cyclocondensation reaction of SeCl2 and (t)BuNH2 as a function of molar ratio and time by multinuclear ((1)H, (13)C, and (77)Se) NMR spectroscopy revealed that the final product exhibits one (77)Se resonance at 1486 ppm and equivalent N(t)Bu groups. The shielding tensors of 28 selenium-containing molecules, for which the (77)Se chemical shifts are unambiguously known, were calculated at the PBE0/def2-TZVPP level of theory to assist the spectral assignment of new cyclic selenium imides. The good agreement between the observed and calculated chemical shifts enabled the assignment of the resonance at 1486 ppm to 1,3,5,7-Se4(N(t)Bu)4 (5a). Those at 1028 and 399 ppm (intensity ratio 2:1) could be attributed to 1,5-Se6(NMe)2 (1b).

The authors are grateful to the EPSRC, the EPSRC National Mass Spectrometry Service Centre (NMSSC) Swansea, the School of Chemistry St. Andrews, EaStCHEM, and NSERC Canada for financial support. A comprehensive investigation of reactions of alkali-metal derivatives of the ditelluro dianion [TePV(NtBu)(μ-NtBu)]22– (L2–, E = Te) with p-block element halides produced a series of novel heterocycles incorporating P2VN2 rings, tellurium, and group 13–16 elements. The dianion engages in Te,Te′-chelation to the metal center in Ph2Ge and R2Sn (R = tBu, nBu, Ph) derivatives; similar behavior was noted for group 14 derivatives of L2– (E = S, Se). In the case of group 13 trihalides MCl3 (M = Ga, In), neutral spirocyclic complexes (L)M[NtBu(Te)PV(μ-NtBu)2PIIIN(H)tBu)] (M = Ga, In) comprised of a Te,Te′-chelated ligand L2– and a N,Te-bonded ligand resulting from loss of Te and monoprotonation were obtained. In reactions with RPCl2 (R = tBu, Ad, iPr2N) a significant difference was observed between Se- and S-containing systems. In the former case, Se,Se′-chelated derivatives were formed in high yields, whereas the N,S-chelated isomers predominated for sulfur. All complexes were characterized by multinuclear (1H, 31P, 77Se, 119Sn, and 125Te) NMR spectroscopy; this technique was especially useful in the analysis of the mixture of (L)(Se) and (L)(SeSe) obtained from the reaction of Se2Cl2 with L2– (E = Te). Single-crystal X-ray structures were obtained for the spirocyclic In complex (9), (L)GePh2 (E = Te, 10), (L)SntBu2 (E = Te, 12a); E = Se, 12aSe, E = S, 12aS) and (L)(μ-SeSe) (E = Te, 16). Postprint Postprint

The dichlorocyclodistib(lll)azane [ClSb(μ-N t Bu)] 2 (1) has been shown to exist as the cis isomer in the solid state. A series of bis(1°-amino)cyclodistib(lll)azanes [R'NHSb(μ-N t Bu)] 2 (2, R' = t Bu; 3, R' = Dipp; 4, R' = Dmp) has been prepared by the reaction of 1 with 2 equiv. of LiNHR'. On the basis of NMR solution spectra, all three derivatives are formed as a mixture of cis and trans isomers. In the case of 3, the structures of both the cis and trans isomers have been determined by X-ray crystallography; cis-3 adopts an endo, endo arrangement for the amido protons of the DippNH groups. Isomerization of trans-3 into cis-3 occurs slowly in solution. Deprotonation of 2 with 2 equiv. of n BuNa or trans-3 with n BuLi produces [Na 2 Sb 2 (μ-N t Bu) 4 ] (5) and [Li 2 Sb 2 (μ-N t Bu) 2 (μ-NDipp)2] (6), whose solvated cubane structures were established by X-ray crystallography. In contrast, the reaction of cis-3 with 2 equiv. of n BuLi produces the tricyclic compound [Li 2 Sb(μ-N t Bu) 2 (μ-NDipp)(μ-NHDipp)] (7).

Two-electron oxidation of the [N(PiPr2E)2]- anion with iodine produces the cyclic [N(PiPr2E)2]+ (E =Se, Te) cations, which exhibit long E-E bonds in the iodide salts [N(PiPr2Se)2]I (4) and [N(PiPr2Te)2]I (5). The iodide salts 4 and 5 are converted to the ion-separated salts [N(PiPr2Se)2]SbF6 (6) and [N(PiPr2Te)2]SbF6 (7) upon treatment with AgSbF6. Compounds 4-7 were characterized in solution by multinuclear NMR, vibrational, and UV-visible spectroscopy supported by DFT calculations. A structural comparison of salts 4-7 and [N(PiPr2Te)2]Cl (8) confirms that the long E-E bonds in 4, 5, and 8 can be attributed primarily to the donation of electron density from a lone pair of the halide counterion into the E-E sigma* orbital (LUMO) of the cation. The phenyl derivative [N(PPh2Te)2]I (9) was prepared in a similar manner. However, the attempted synthesis of the selenium analogue, [N(PPh2Se)2]I, produced a 1:1 mixture of [N(PPh2Se)2(mu-Se)][I] (10) and [SeP(Ph2)N(Ph2)PI] (11). DFT calculations of the formation energies of 10 and 11 support the observed decomposition. Compound 10 is a centrosymmetric dimer in which two six-membered NP2Se3 rings are bridged by two I- anions. Compound 11 produces the nine-atom chain {[N(PPh2)2Se]2(mu-O)} (12) upon hydrolysis during crystallization. The reaction between [(TMEDA)NaN(PiPr2Se)2] and SeCl2 in a 1:1 molar ratio yields the related acyclic species [SeP(iPr2)N(iPr2)PCl] (13), which was characterized by multinuclear NMR spectroscopy and an X-ray structural determination.

Tetrasulfur tetranitride and tellurium tetrachloride react in dichloromethane to form a 1:1 adduct TeCl4·S4N4 (1). The crystal structure of 1 shows that TeCl4 is bonded to the S4N4 ring through a Te–N linkage. As a consequence, the transannular S···S bonds in S4N4 are broken and the molecule assumes an open, monocyclic conformation. The Te–N bond of 2.16(1) A is slightly longer than the single bond. The S–N bonds span a range of 1.55(1)–1.67(1) A. The adduct 1 was also characterized by mass spectrometry and Raman spectroscopy. The bonding and spectroscopic properties of 1 are compared by DFT calculations at the B3PW91/(RLC ECP) level of theory with those of BF3·S4N4 (2), SO3·S4N4 (3), AsF5·S4N4 (4), SbCl5·S4N4 (5) for which experimental structural information is available. The structural and bonding trends in TeF4·S4N4 (6), TeBr4·S4N4 (7), and SeX4·S4N4 [X = F (8), Cl (9), Br (10)] are also discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The reactions of MAlH4 (M = Li, Na) with primary amines NH2R (R = t-Bu, i-Pr, p-tolyl) in a 1:4 molar ratio in THF produce the tetrakis(amido)aluminates, [M(THF)n][Al(NHR)4], in yields of 46%–82% together with secondary products. The extent of solvation of the alkali-metal cation varies from none (n = 0) for M[Al(NH-i-Pr)4] (2b, M = Li; 3b, M = Na) to n = 4 in the complex [Li(THF)4][Al(NH-p-tolyl)4] (2c), which exists as a solvent-separated ion pair. The complexes 2b, 3b, and [Na(THF)][Al(NH-p-tolyl)4]∞ (3c) all exhibit one-dimensional polymeric structures in which the bis-N,N′-chelating tetrakis(amido)aluminate anions are bridged by four- (2b, 3b) and five-coordinate (3c) metal ions, respectively. The structures of two of the secondary products, {[Na(THF)2][(NH-t-Bu)Al(H)(µ-N-t-Bu)]}2 (4) and {[Na(THF)3][(NH-p-tolyl)2Al(µ-N-p-tolyl)]}2 (5), were established by X-ray crystallography. Complex 4 is a dimer of the [HAl(NH-t-Bu)(N-t-Bu)]– anion, which forms a central Al2N2 ring with each monoanion N,N′-chelated to a [Na(THF)2]+ cation. Complex 5 is a dimer of the [Al(NR)(NHR)2]– (R = p-tolyl) anion in which the bridging p-tolyl groups are coordinated in an N-monodentate fashion to the trisolvated [Na(THF)3]+ cations. Key words: aluminohydrides, alkali metals, primary amines, tetrakis(amido)aluminates, structures.

The first magnesium and zinc boraamidinate (bam) complexes have been synthesized via metathetical reactions between dilithio bams and Grignard reagents or MCl2 (M = Mg, Zn). The following new classes of bam complexes have been structurally characterized: heterobimetallic spirocycles {(L)mu-Li[PhB(mu-NtBu)2]}2M (6a,b, M = Mg, L = Et2O, THF; 6c, M = Zn, L = Et(2)O); bis(organomagnesium) complexes {[PhB(mu3-NtBu)2](MgtBu)2(mu3-Cl)Li(OEt2)3} (8) and {[PhB(mu3-NtBu)2](MgR)2(THF)2} (9a, R = iPr; 9b, R = Ph); mononuclear complex {[PhB(mu-NDipp)2]Mg(OEt2)2} (10). Oxidation of 6a or 6c with iodine produces persistent pink (16a, M = Mg) or purple (16b, M = Zn) neutral radicals {Lx-mu-Li[PhB(mu-NtBu)2]2M}. (L = solvent molecule), which are shown by EPR spectra supported by DFT calculations to be Cs-symmetric species with spin density localized on one of the bam ligands. In contrast, characterization of the intensely colored neutral radicals {[PhB(mu-NtBu)2]2M}. (5c, M = In, dark green; 5d, M = B, dark purple) reveals that the spin density is equally delocalized over all four nitrogen atoms in these D2d-symmetric spirocyclic systems. Oxidation of the dimeric dilithio complex {Li2[PhB(mu4-NtBu)2]}2 with iodine produces the monomeric neutral radical {[PhB(mu-NtBu)2]Li(OEt2)x}. (17), characterized by EPR spectra and DFT calculations. These findings establish that the bam anionic radical [PhB(NtBu)2].- can be stabilized by coordination to a variety of early main-group metal centers to give neutral radicals whose relative stabilities are compared and discussed.

The use of trichloroiminophosphoranes Cl3P=NR to control the concurrent release of the templating cation [RNH3]+ and chloride ligand via in situ P—N and P—Cl bond cleavage produced two new copper(II) chloride oligomers. The nature of the organic substituent R was a factor in determining the chain lengths. For n-propyltrichloroiminophosphorane, the hexanuclear cluster [n-PrNH3]2[Cu6Cl14] (1) was obtained, while p-tolyltrichloroiminophosphorane generated the tetranuclear copper chloride salt [4-CH3C6H4NH3][2-Cl-4-CH3C6H3NH3][Cu4Cl10] (2). In both structures a two-dimensional framework displaying a herringbone arrangement is created by Cu—Cl secondary bonding interactions. The direct addition of the [n-PrNH3]+ cation to a CuCl2·2H2O solution under the same reaction conditions produced [n-PrNH3]2[CuCl4]. Key words: copper halides, templation, oligomers, two-dimensional frameworks.

Reaction of the secocuhane [Sn 3 (μ 2 -NHtBu) 2 (μ 2 -NtBu)(μ 3 -NtBu)] (1) with dibutylmagnesium produces the heterobimetallic cubane [Sn 3 Mg(μ 3 -NtBu) 4 ] (4) which forms the monochal-cogenide complexes of general formula [ESn 3 Mg(μ 3 -NtBu) 4 ] (5a, E=Se: 5b, E=Te) upon reaction with elemental chalcogens in THE. By contrast, the reaction of the anionic lithiated cubane [Sn 3 Li(μ 3 -NtBu) 4 ] with the appropriate quantity of selenium or tellurium leads to the sequential chalcogenalion of each of the three Sn I I centres. Pure samples of the mono- or dichalcogen-ides are, however, best obtained by stoichiometric redistribution reactions of [Sn 3 Li(μ 3 -NtBu) 4 ] and the trichalcogenides [E 3 Sn 3 Li(μ 3 -NtBu) 4 ] (E-=Se, Tc). These reactions are conveniently monitored by using 1 1 9 Sn NMR spectroscopy. The anion [Sn 3 Li(μ 3 -NtBu) 4 ] also acts as an effective chalcogentransfer reagent in reactions of selenium with the neutral cubane [(Snμ 3 -N-(dipp)} 4 ] (8) (dipp=2,6-diisopropyl-phenyl) to give the dimer [(thf)Sn{μ-N(dipp)] 2 Sn(μ-Se) 2 Sn{μ-N(dipp)} 2 Sn-(thf)] (9), a transformation that results in cleavage of the Sn 4 N 4 cubane into four-membered Sn 2 N 2 rings. The X-ray structures of 4, 5a, 5b, [Sn 3 Li(thf)-(μ 3 -NtBu) 4 (μ 3 -Se)(μ 2 -Li)(thf)] 2 (6a). [TeSn 3 Li(μ 3 -NtBu) 4 ][Li(thf) 4 ] (6b). [Te 2 Sn 3 Li(μ 3 -NtBu) 4 ][Li([12]crown-4) 2 ] (7b") and 9 are presented. The fluxional behaviour of cubic imidotin chalcogenides and the correlation between NMR coupling constants and tin-chalcogen bond lengths are also discussed.

Aerosol-assisted chemical vapour deposition (AACVD) studies using {M(μ-Te)[N(iPr2PTe)2]}3 (M = In, Ga) were carried out on glass and Si(100) substrates at deposition temperatures between 325–475 °C. Black, adherent films were obtained in all cases and characterized by XRD, SEM, EDAX and Raman spectroscopy. The indium precursor gave cubic In2Te3 exclusively, whereas the gallium complex generated a mixture of cubic Ga2Te3, monoclinic GaTe and hexagonal Te. Mass spectrometric studies indicate that fragmentation of the indium precursor to give In2Te3 is accompanied by the formation of In[N(iPr2PTe)2]2+ and [N(iPr2PTe)2]2−.

Treatment of Cl2Si(NH-t-Bu)2 (6a) with t-BuNH2 in boiling toluene yields trisamino(chloro)silane ClSi(NH-t-Bu)3 (7); formation of the tetraaminosilane Si(NH-t-Bu)4 is not observed. The reaction of SiCl4 with 4 equiv. of LiNHR produces the corresponding tetraaminosilanes Si(NHR)4 (2a, R = i-Pr; 2b, R = t-Bu; 2c, R = p-tol) in good yields. When the sterically demanding adamantyl derivative LiHNAd is employed, only disubstitution occurs to form Cl2Si(NHAd)2 (6b). Oxidation of the dimeric imidosilicates {Li3[Si(NR)3(NHR)]·THF}2 (3a, R = i-Pr; 3b, R = t-Bu) with 1 mol of iodine produces the persistent radicals {Li2[Si(NR)3(NHR)]·LiI·3THF}·, which, on the basis of EPR spectra, exist as SiN3Li3I cubes in solution. The spirocyclic tetraimidosilicate monoanion radical {[(THF)2Li(µ-Nnaph)2Si(µ-Nnaph)2Li(THF)2]}–· (10) is formed upon oxidation of the tetralithiated species {Li4[Si(Nnaph)4]·4Et2O} (1) and {[Li(12-crown-4)]2[(Et2O)2Li(µ-Nnaph)2Si(µ-Nnaph)2Li(Et2O)2]} (8) with iodine. The spectroscopic characterization of hexa(amino)disiloxane (t-BuNH)3SiOSi(NH-t-Bu)3 (14) formed from the reaction of Cl3SiOSiCl3 with 6 equiv. of LiNH-t-Bu is discussed. Key words: imido ligands, silicate, radicals, EPR spectra, lithium.

The aerosol-assisted chemical vapour deposition (AACVD) of CdTe has been carried out using Cd[(TePiPr2)2N]2 at substrate temperatures between 375 and 475 °C. XRD shows the formation of cubic CdTe between 425 and 475 °C. At low deposition temperature (375 °C), a mixture of hexagonal tellurium and cubic cadmium telluride is observed. SEM images reveal that the growth temperatures do not have a profound effect on the morphologies of films. Surface analysis by XPS of films deposited at 475 °C showed the growth of Te-rich films. The AACVD of Hg[(TePiPr2)2N]2 resulted in deposition of hexagonal tellurium.

n-Propylimidodiphosphonic anhydride [O(OH)P(μ-O)PO(OH)(μ-NnPr)]2·2NH2nPr (1) is prepared by hydrolysis of trichloro-n-propylimidophosphorane with three equivalents of water. X-ray analysis shows that 1 forms an eight-membered P4N2O2 ring in a chair conformation. These heterocycles are linked via extensive hydrogen-bonding to form a three-dimensional network. Hydrothermal reactions of 1 with zinc chloride give rise to P-N bond cleavage and the formation of the hydrated zinc phosphates, {Zn3(PO4)2·H2O}n and {Zn3(PO4)2·4H2O}n, whereas the solvothermal reaction in isopropyl alcohol produces the anionic network [ZnCl(HPO4)−]n with [nPrNH3]+ counter-ions.

The reaction of OP(NH-t-Bu)3 with 1 equiv. of ZnMe2 generates the dimeric eight-membered ring {MeZn[(µ-NH-t-Bu)(µ-N-t-Bu)P(NH-t-Bu)(µ-O)]}2 (5) and the cubane {[MeZn]3[OP(N-t-Bu)3][OP(NH-t-Bu)3]} (6), which contains the first known trisimidophosphate trianion. A related complex {Zn[ZnMe]2[OP(N-t-Bu)(NH-t-Bu)2][OP(N-t-Bu)3]} (7) is obtained by the reaction of OP(NH-t-Bu)3 with ZnMe2 in a 2:3 molar ratio. The treatment of OP(NHMe)3 with 1 equiv. of ZnMe2 produces the oxide-templated cluster {Zn4(µ4-O)[OP(NMe)(NHMe)2]4[OP(NMe)2(NHMe)]}2 (8). Each half of this centrosymmetric dimer contains a tetrahedral arrangement of four 4-coordinate Zn2+ ions surrounding the central µ4-O2- anion. The reaction of SP(NH-t-Bu)3 with ZnMe2 in a 1:1 molar ratio generates the dimer {MeZn(µ-S)(µ-N-t-Bu)P(NH-t-Bu)2}2 (10), which has a ladder-type structure. When a 2:1 molar ratio of the same reagents is employed, the bis(N,S)-chelated complex {Zn[(µ-S)(µ-N-t-Bu)P(NH-t-Bu)2]2} (11) is obtained. The monomeric N,N′-chelated complex {MeZn[(µ-N-t-Bu)(µ-NSiMe3)P(NH-t-Bu)2]} (12) results from the reaction of Me3SiNP(NH-t-Bu)3 with 1 equiv. of dimethylzinc. All new compounds have been characterized by multinuclear (1H, 13C, and 31P) NMR spectroscopy and, in the case of 5, 6, 7, 8, and 10, by X-ray structural determinations.Key words: zinc, phosphate, imido ligands, sulfur.

Reactions of (RNH)(3)PNSiMe(3) (3a, R = (t)()Bu; 3b, R = Cy) with trimethylaluminum result in the formation of {Me(2)Al(mu-N(t)Bu)(mu-NSiMe(3))P(NH(t)()Bu)(2)]} (4) and the dimeric trisimidometaphosphate {Me(2)Al[(mu-NCy)(mu-NSiMe(3))P(mu-NCy)(2)P(mu-NCy)(mu-NSiMe(3))]AlMe(2)} (5a), respectively. The reaction of SP(NH(t)Bu)(3) (2a) with 1 or 2 equiv of AlMe(3) yields {Me(2)Al[(mu-S)(mu-N(t)Bu)P(NH(t)()Bu)(2)]} (7) and {Me(2)Al[(mu-S)(mu-N(t)()Bu)P(mu-NH(t)Bu)(mu-N(t)Bu)]AlMe(2)} (8), respectively. Metalation of 4 with (n)()BuLi produces the heterobimetallic species {Me(2)Al[(mu-N(t)Bu)(mu-NSiMe(3))P(mu-NH(t)()Bu)(mu-N(t)()Bu)]Li(THF)(2)} (9a) and {[Me(2)Al][Li](2)[P(N(t)Bu)(3)(NSiMe(3))]} (10) sequentially; in THF solutions, solvation of 10 yields an ion pair containing a spirocyclic tetraimidophosphate monoanion. Similarly, the reaction of ((t)BuNH)(3)PN(t)()Bu with AlMe(3) followed by 2 equiv of (n)BuLi generates {Me(2)Al[(mu-N(t)Bu)(2)P(mu(2)-N(t)Bu)(2)(mu(2)-THF)[Li(THF)](2)} (11a). Stoichiometric oxidations of 10 and 11a with iodine yield the neutral spirocyclic radicals {Me(2)Al[(mu-NR)(mu-N(t)Bu)P(mu-N(t)Bu)(2)]Li(THF)(2)}(*) (13a, R = SiMe(3); 14a, R = (t)Bu), which have been characterized by electron paramagnetic resonance spectroscopy. Density functional theory calculations confirm the retention of the spirocyclic structure and indicate that the spin density in these radicals is concentrated on the nitrogen atoms of the PN(2)Li ring. When 3a or 3b is treated with 0.5 equiv of dibutylmagnesium, the complexes {Mg[(mu-N(t)()Bu)(mu-NH(t)()Bu)P(NH(t)Bu)(NSiMe(3))](2)} (15) and {Mg[(mu-NCy)(mu-NSiMe(3))P(NHCy)(2)](2)} (16) are obtained, respectively. The addition of 0.5 equiv of MgBu(2) to 2a results in the formation of {Mg[(mu-S)(mu-N(t)()Bu)P(NH(t)Bu)(2)](2)} (17), which produces the hexameric species {[MgOH][(mu-S)(mu-N(t)()Bu)P(NH(t)Bu)(2)]}(6) (18) upon hydrolysis. Compounds 4, 5a, 7-11a, and 15-17 have been characterized by multinuclear ((1)H, (13)C, and (31)P) NMR spectroscopy and, in the case of 5a, 9a.2THF, 11a, and 18, by X-ray crystallography.

The preparation of a new family of acyclic DippN(H)P(Ph)NRCR‘NR systems (2a−c) has been achieved by the reaction of the mono(amino)chlorophosphine PhP(Cl)N(H)Dipp (1; Dipp = 2,6-(iPr)2C6H3) with 1 equiv of Li[CR‘(NR)2] (2a, R = tBu, R‘ = nBu; 2b, R = Cy, R‘ = tBu; 2c, R = Cy, R‘ = nBu). Metalation reactions of 2a−c using nBuLi, Me3Al, and Bu2Mg have shown that the NPNCN backbone is susceptible to nucleophilic attack. Reactions of 2a or 2b with nBuLi or Me3Al, respectively, produce the complexes Li[DippNPhP−P(nBu)PhNDipp]·Et2O (3) and Al(Me)2[DippNPhP−P(Me)PhNDipp] (4). These complexes involve a new type of N,N‘ bidentate ligand with a chiral phosphorus center bearing bulky organic substituents on the nitrogen atoms. Reaction of 2c with Bu2Mg proceeds in a different manner, producing the amidinate complex Mg[CyNC(nBu)NCy][DippNP(nBu)Ph]·Et2O (5). A more direct route to 3 and the analogous methyl-substituted complex Li[DippNPhP−P(Me)PhNDipp]·Et2O (6), involving the reaction of 1 with the appropriate organol...

Several aspects of recent developments in the chemistry of multiply bonded selenium and tellurium compounds are surveyed in this article. These include (a) tellurium(IV)-nitrogen compounds, (b) complexes with two (or more) terminal Group 14–Group 16 linkages, and (c) a new approach to previously inaccessible ligands containing Group 15–Group 16 functionalities.

The hydrolysis of (t)BuNTe(mu-N(t)Bu)(2)TeN(t)Bu (1) with 1 or 2 equiv of (C(6)F(5))(3)B.H(2)O results in the successive replacement of terminal imido groups by oxo ligands to give the telluroxane-Lewis acid adducts (C(6)F(5))(3)B.OTe(mu-N(t)Bu)(2)TeN(t)Bu (2) and [(C(6)F(5))(3)B.OTe(mu-N(t)Bu)(2)Te(mu-O)](2) (3), which were characterized by multinuclear NMR spectroscopy and X-ray crystallography. The Te=O distance in 2 is 1.870(2) A. The di-adduct 3 involves the association of four (t)()BuNTeO monomers to give a tetramer in which both terminal Te=O groups [d(TeO) = 1.866(3) A] are coordinated to B(C(6)F(5))(3). The central Te(2)O(2) ring in 3 is distinctly unsymmetrical [d(TeO) = 1.912(3) and 2.088(2) A]. The X-ray structure of (C(6)F(5))(3)B.NH(2)(t)()Bu (4), the byproduct of these hydrolysis reactions, is also reported. The geometries and energies of tellurium(IV) diimides and imido telluroxanes were determined using quantum chemical calculations. The calculated energies for the reactions E(NR)(2) + Te(NR)(2) (E = S, Se, Te; R = H, Me, (t)Bu, SiMe(3)) confirm that cyclodimerization of tellurium(IV) diimides is strongly exothermic. In the mixed-chalcogen systems, the cycloaddition is energetically favorable for the Se/Te combination. The calculated energies for the further oligomerization of the dimers XE(mu-NMe)(2)EX (E = Se, Te; X = NMe, O) indicate that the formation of tetramers is strongly exothermic for the tellurium systems but endothermic (X = NMe) or thermoneutral (X = O) for the selenium systems, consistent with experimental observations.

A series of monochalcogenide derivatives of the seco-cubane [Sn3(μ2-NHtBu)2(μ2-NtBu)(μ3-NtBu)] has been prepared and characterized by NMR and X-ray crystallographic studies. These complexes exhibit different tin-chalcogen bonding modes. In the case of the monotelluride, a terminal Sn=Te bond was observed in solution and in the solid state, whereas for the monosulfide, a μ2 bridging mode was adopted by the sulfur atoms. The monoselenide was found to employ both bonding modes in solution, although only the terminal Sn=Se bonding mode was structurally characterized. The complexes undergo chalcogen exchange between tin atoms in solution, and this process was studied by variable temperature NMR. Chalkogenid-Derivate des seco-Cubans [Sn3(μ2-NHtBu)2(μ2-NtBu)(μ3-NtBu)] Eine Reihe von Monochalkogenid-Derivaten des seco-Cubans [Sn3(μ2-NHtBu)2(μ2-NtBu)(μ3-NtBu)] wurden dargestellt und durch NMR-Spektroskopie sowie Rontgen-Kristallstrukturanalysen charakterisiert. Diese Komplexe zeigen unterschiedliche Zinn-Chalkogen-Bindungen. Im Fall der Monotelluride wird in Losung und im festen Zustand eine endstandige Sn=Te-Bindung beobachtet, wahrend fur die Monosulfide, eine μ2-Brucke bei den Schwefelatomen angenommen wird. Fur die Monoselenide wurde gefunden, dass beide Bindungsarten in Losung vorliegen, obwohl nur die terminale Sn=Se-Bindung strukturell charakterisiert wurde. Die Komplexe zeigen in Losung Chalkogen-Austausch zwischen den Zinnatomen - dieser Prozess wurde durch NMR-Messungen bei verschiedenen Temperaturen untersucht.

The reaction of ((t)BuNH)(3)PNSiMe(3) (1) with 1 equiv of (n)BuLi results in the formation of Li[P(NH(t)Bu)(2)(N(t)Bu)(NSiMe(3))] (2); treatment of 2 with a second equivalent of (n)BuLi produces the dilithium salt Li(2)[P(NH(t)Bu)(N(t)Bu)(2)(NSiMe(3))] (3). Similarly, the reaction of 1 and (n)BuLi in a 1:3 stoichiometry produces the trilithiated species Li(3)[P(N(t)Bu)(3)(NSiMe(3))] (4). These three complexes represent imido analogues of dihydrogen phosphate [H(2)PO(4)](-), hydrogen phosphate [HPO(4)](2)(-), and orthophosphate [PO(4)](3)(-), respectively. Reaction of 4 with alkali metal alkoxides MOR (M = Li, R = SiMe(3); M = K, R = (t)Bu) generates the imido-alkoxy complexes [Li(3)[P(N(t)Bu)(3)(NSiMe(3))](MOR)(3)] (8, M = Li; 9, M = K). These compounds were characterized by multinuclear ((1)H, (7)Li, (13)C, and (31)P) NMR spectroscopy and, in the cases of 2, 8, and 9.3THF, by X-ray crystallography. In the solid state, 2 exists as a dimer with Li-N contacts serving to link the two Li[P(NH(t)Bu)(2)(N(t)Bu)(NSiMe(3))] units. The monomeric compounds 8 and 9.3THF consist of a rare M(3)O(3) ring coordinated to the (LiN)(3) unit of 4. The unexpected formation of the stable radical [(Me(3)SiN)P(mu(3)-N(t)Bu)(3)[mu(3)-Li(THF)](3)(O(t)Bu)] (10) is also reported. X-ray crystallography indicated that 10 has a distorted cubic structure consisting of the radical dianion [P(N(t)Bu)(3)(NSiMe(3))](.2)(-), two lithium cations, and a molecule of LiO(t)Bu in the solid state. In dilute THF solution, the cube is disrupted to give the radical monoanion [(Me(3)SiN)((t)BuN)P(mu-N(t)Bu)(2)Li(THF)(2)](.-), which was identified by EPR spectroscopy.

The dilithiated boraamidinate complexes [Li(2)[PhB(NDipp)(2)](THF)(3)] (7a) (Dipp = 2,6-diisopropylphenyl) and [Li(2)[PhB(NDipp)(N(t)Bu)](OEt(2))(2)] (7b), prepared by reaction of PhB[N(H)Dipp][N(H)R'] (6a, R' = Dipp; 6b, R' = (t)Bu) with 2 equiv of (n)BuLi, are shown by X-ray crystallography to have monomeric structures with two terminal and one bridging THF ligands (7a) or two terminal OEt(2) ligands (7b). The derivative 7a is used to prepare the spirocyclic group 13 derivative [Li(OEt(2))(4)][In[PhB(NDipp)(2)](2)] (8a) that is shown by an X-ray structural analysis to be a solvent-separated ion pair. The monoamino derivative PhBCl[N(H)Dipp] (9a), obtained by the reaction of PhBCl(2) with 2 equiv of DippNH(2), serves as a precursor for the synthesis of the four-membered BNCN ring [[R'''N(H)](Ph)B(mu-N(t)Bu)(2)C(n)Bu] (10a, R''' = Dipp). The X-ray structures of 6a, 9a, and 10a have been determined. The related derivative 10b (R''' = (t)Bu) was synthesized by the reaction of [Cl(Ph)B(mu-N(t)Bu)(2)C(n)Bu] with Li[N(H)(t)Bu] and characterized by (1)H, (11)B, and (13)C NMR spectra. In contrast to 10a and 10b, NMR spectroscopic data indicate that the derivatives [[DippN(H)](Ph)B(NR')(2)CR(NR')] (11a: R =( t)Bu, R' = Cy; 11b: R = (n)Bu, R' = Dipp) adopt acyclic structures with three-coordinate boron atoms. Monolithiation of 10a produces the novel hybrid boraamidinate/amidinate (bamam) ligand [Li[DippN]PhB(N(t)Bu)C(n)Bu(N(t)Bu)] (12a).

X]C (2a,X=Br; 2b,X=I)obtained bytheoxidationof1withhalogens.The derivative 2bhas been structurally characterized in thesolidstatebyX-raycrystallography.ThesolutionbehaviorofthesenovelradicalsystemshasbeeninvestigatedbyEPRandUV/Visspectroscopies.The reactions of the dimer1 with one equivalent ofbromineoriodineinamixtureoftolueneandTHFat295Kproduce deep blue solutions immediately. Removal of thesolventsgives2aor2b,respectively,asbluepowdersingoodyields. Crystals of 2b suitable for an X-ray structuraldetermination

The use of a mild, oxidative chlorination route for the synthesis of linear and cyclic carbophosphazenes is described. For example, chlorination of the linear PNCN chain Ph(2)P-N=C(Ph)-N(SiMe(3))(2) (1) with C(2)Cl(6) led to the clean formation of the previously known 8- and 6-membered rings [Ph(2)PNC(Ph)N](2) (2) and [Ph(2)PNC(Ph)NP(Ph)(2)N] (3), respectively. In a similar fashion, the N-alkyl-substituted PNCN derivatives, Ph(2)P-N=C(Ph)-N((t)Bu)SiMe(3) (4) and Ph(2)P-N=C(Ph)-N(i)Pr(2) (7) were readily converted by C(2)Cl(6) into the halogenated derivatives ClPh(2)P=N-C(Ph)=N(t)Bu (5) and [ClPh(2)P=N=C(Ph)-N(i)Pr(2)]Cl (8), respectively. Protonation of 5 was accomplished using HCl and gave the carbophosphazenium salt [ClPh(2)P=N-C(Ph)=N((t)Bu)H]Cl (6). In addition, the isolation of a rare 8-membered P(2)N(4)C(2) heterocycle [(Cl(3)P=N)ClPNC(Ph)NP(Cl)(2)NC(Ph)N] (9) from the reaction of PCl(5) and Li[PhC(NSiMe(3))(2)] is reported. Treatment of 9 with one equivalent of GaCl(3) led to the discovery of an unusual Lewis acid-induced ring contraction reaction whereby the (PNCN)(2) ring in 9 is converted into the novel 6-membered P(2)N(3)C heterocyclic adduct [(Cl(3)P=N)ClPNP(Cl)(2)NC(Ph)N].GaCl(3) (10) with concomitant release of PhCN. Structural characterization of compounds 1, 5, 6, and 8-10 by single-crystal X-ray diffraction is also provided.

The reactions of CdCl2 or HgCl2 with {Li2[Te(N-t-Bu)3]}2 in n-hexane–THF give rise to two distinctly different types of product. In the former case the complexes [Li(THF)x][(CdCl)3{Te(N-t-Bu)3}2] (7a (x = 4), 7b (x = 3)) are obtained. The tetrasolvated complex 7a is a solvent-separated ion pair. The trisolvated complex 7b is a contact ion pair in which the fourth coordination site at the Li+ centre is occupied by one of the Cl ligands of the anion. The polycyclic anion in 7a and 7b is comprised of two tripodal [Te(N-t-Bu)3]2– dianions that exhibit different coordination modes to the three CdCl+ units. One ligand is N,N′-chelated to all three metal centres, and each nitrogen atom bridges two Cd atoms, whereas the other is bonded in a tris-N-monodentate fashion in 7b. In 7a there is an additional weak Cd-N interaction. The reaction of HgCl2 with {Li2[Te(N-t-Bu)3]}2 produces the adduct [t-BuNTe(µ-N-t-Bu)2TeN-t-Bu]HgCl2 (8), in which the dimeric tellurium diimide ligand in its cis(exo,exo) configuration is N,N′-chelated to mercury. Polymeric strands parallel to the b axis are formed by weak Te•••Cl interactions (3.5248(16) Å, 3.5876(15) Å) involving both Cl atoms, but only one Te atom of the ligand. Key words: imido ligands, cadmium, mercury, tellurium.

The tellurium diimide dimer [tBuNTe(μ-NtBu)2TeNtBu] (1) and B(C6F5)3 form a 1:1 adduct which instigates THF ring-opening to give [tBuNTe(μ-NtBu)2TeN(tBu)(CH2)4OB(C6F5)3] (3) quantitatively; complex 3 is also formed rapidly when 1 is added to a THF solution of B(C6F5)3. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

In the solid state, OP[N(H)Me](3) (1a) and OP[N(H)(t)Bu](3) (1b) have hydrogen-bonded structures that exhibit three-dimensional and one-dimensional arrays, respectively. The lithiation of 1b with 1 equiv of (n)BuLi generates the trimeric monolithiated complex (THF)[LiOP(N(t)Bu)[N(H)(t)Bu](2)](3) (4), whereas reaction with an excess of (n)BuLi produces the dimeric dilithium complex [(THF)(2)Li(2)OP(N(t)Bu)(2)[N(H)(t)Bu]](2) (5). Complex 4 contains a Li(2)O(2) ring in an open-ladder structure, whereas 5 embraces a central Li(2)O(2) ring in a closed-ladder arrangement. Investigations of the lithiation of tris(alkyl or arylamido)thiophosphates, SP[N(H)R](3) (2a, R = (i)Pr; 2b, R = (t)Bu; 2c, R = p-tol) with (n)BuLi reveal interesting imido substituent effects. For the alkyl derivatives, only mono- or dilithiation is observed. In the case of R = (t)Bu, lithiation is accompanied by P-S bond cleavage to give the dilithiated cyclodiphosph(V/V)azane [(THF)(2)Li(2)[((t)BuN)(2)P(micro-N(t)Bu)(2)P(N(t)Bu)(2)]] (9). Trilithiation occurs for the triaryl derivatives EP[N(H)Ar](3) (E = S, Ar = p-tolyl; E = Se, Ar = Ph), as demonstrated by the preparation of [(THF)(4)Li(3)[SP(Np-tol)(3)]](2) (10) and [(THF)(4)Li(3)[SeP(NPh)(3)]](2) (11), which are accompanied by the formation of small amounts of 10.[LiOH(THF)](2) and 11.Li(2)Se(2)(THF)(2), respectively.

Monomeric complexes with two or three terminal M=Se bonds, Sn4Se2(NtBu)4 or Ge4Se3(NtBu)4, respectively, are produced by oxidation of (MNtBu)4 (M = Sn, Ge) with selenium in hot toluene. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The geometries and energetics of different conformations of sulfur and selenium diimides E(NR) 2 (E = S, Se; R = H, Me, 'Bu, C 6 H 3 Me 2 -2,6, SiMe 3 ) have been studied by using various ab initio and DFT molecular orbital techniques. The syn,syn conformation is found to be most stable for parent E(NH) 2 , but in general, the preferred molecular conformation for substituted chalcogen diimides is syn,anti. In the case of E(NH) 2 the present calculations further confirm that syn,syn and syn,anti conformations lie energetically close to each other. From the three different theoretical methods used, B3PW91/6.31G * proved to be the most suitable method for predicting the geometries of chalcogen diimides. The optimized geometrical parameters are in a good agreement with all available experimental data. While qualitative energy ordering of the different conformations is independent of the level of theory, the quantitative energy differences are dependent on the method used. The performance and reliability of higher level ab initio calculations and DFT methods using large basis sets were tested and compared with experimental information where available. All of the higher level ab inito methods give very similar results, but the use of large basis sets with the B3PW91 method does not increase the reliability of the results. The combination of CCSD(T)/cc-pVDZ with the B3PW91/6.31G*-optimized geometries is found to be the method of choice to study energetic properties of chalcogen diimides.

The reactions of [Li(2)[PhB(N(t)Bu)(2)]](2) with GaCl(3) in various stoichiometries yield [Li(thf)(4)][PhB(mu-N(t)Bu)(2)GaCl(2) x GaCl(3)] (1), [PhB(mu-N(t)Bu)(2)GaCl](2) (2), and [mu-Li(OEt(2))[PhB(N(t)Bu)(2)]Ga] (3a), a series of complexes in which the three chloride ligands are successively replaced by the dianion [PhB(N(t)Bu)(2)](2-). The X-ray structures of 1, 2, and 3a show that the boraamidinate ligand adopts an N,N'-chelating mode. In the ion-separated complex 1, one of the nitrogen atoms is coordinated to a GaCl(3) molecule. The related indium complexes [mu-LiCl(thf)(2)][PhB(mu-N(t)Bu)(2)InCl](2) (4) and [mu-Li(OEt(2))[PhB(mu-N(t)Bu)(2)]In] (3b) were obtained in a similar manner. Complex 4 is the indium analogue of 2 with the incorporation of a bissolvated LiCl molecule. In 3a and 3b the spirocyclic [[PhB(mu-N(t)Bu)(2)](2)M](-) (M = Ga, In) anions are N,N'-chelated to the [Li(OEt(2))](+) counterion. Prolonged reactions result in the formation of [PhB(mu-N(t)Bu)(2)GaCl][(t)BuN(H)GaCl(2)] (5) and [[PhB(mu-N(t)Bu)(2)InCl][(t)BuN(H)InCl(2)][mu-LiCl(OEt(2))(2)]] (6), respectively. The X-ray structures of 5 and 6 reveal bicyclic structures which formally involve the entrapment of the monomers (t)BuN(H)MCl(2) by a four-membered BN(2)M ring (M = Ga, In). The synthesis and X-ray structure of Cl(2)Ga[mu-N(H)(t)Bu](2)GaCl(2) are also reported.

The reaction of PhECl2 with 2 equiv of LiHN-t-Bu has been studied for the series E = As, Sb, and Bi to determine the effect of the phenyl group on subsequent amine condensation processes. For PhAsCl2, the metathesis product PhAs(NH-t-Bu)2 4 was obtained as a colourless oil. Similar reactions involving PhECl2, where E = Sb or Bi, yielded the cyclodipnict(III)azanes PhE(μ-N-t-Bu)2EPh 5 (E = Sb) and 6 (E = Bi), respectively. Treatment of 4 with 2 equiv of n-BuLi produced the dilithium salt Li2[PhAs(N-t-Bu)2] 7a. Products 4, 5, 6, and 7a were characterized by 1H, 7Li (7a), and 13C NMR spectra, while 5, 6, and 7a were also structurally characterized by X-ray crystallography. Compound 7a is dimeric in the solid state via intermolecular Li···N and η6-Li···Ph interactions. The cyclodipnict(III)azanes 5 and 6 have similar structures, with the exocyclic phenyl groups in trans positions relative to the E2N2 ring. This synthetic approach provides a new route to the four-membered rings RE(μ-N-t-Bu)2ER (E = Sb, Bi) and the first example of a bis(organyl)cyclodibism(III)azane.Key words: arsenic, antimony, bismuth, amides, imides.

The scant attention paid to tellurium in both inorganic and organic chemistry textbooks may reflect, in part, the very low natural abundance of the element. Such treatments commonly imply that the structures and reactivities of tellurium compounds can be extrapolated from the behaviour of their lighter chalcogen analogues (sulfur and selenium). In fact, recent findings and well-established observations clearly illustrate that this assumption is not valid. The emerging importance of the unique properties of tellurium compounds is apparent from the variety of their known and potential applications in both inorganic and organic chemistry, as well as materials science. With reference to selected contemporary examples, this Tutorial Review examines the fundamental concepts that are essential for an understanding of the unique features of tellurium chemistry with an emphasis on hypervalency, three-centre bonding, secondary bonding interactions, σ and π-bond energies (multiply bonded compounds), and Lewis acid behaviour.

Financial support from the EPSRC and NSERC (Canada) is acknowledged. Metathetical reactions of alkali–metal derivatives of the dianion [tBuN(Se)P(μ-NtBu)2P(Se)NtBu]2− (2Se2−) with Ag(NHC)Cl, Ag[BF4], AuCl(THT) and HgCl2, as well as the reaction of 2S2− with AuCl(THT) were investigated. The observed products all incorporate the monoprotonated ligands 2SeH− or 2SH− in a variety of structural arrangements around the metal centres, including tetrameric and trimeric macrocycles [Ag and Au (E = Se)], a ladder (Au, E = S) and a spirocycle (Hg); the ladder contains both the dianion 2S2− and the monoanion 2SH− as ligands linking three Au2 units. All complexes have been characterised in the solid state by single crystal X-ray analyses and in solution by multinuclear (1H, 31P and 77Se) NMR spectra. Postprint

The authors thank EPSRC and NSERC (Canada) for financial support. Reactions of the dianion [Te(tBuN)P(μ-NtBu)2P(NtBu)Te]2− with I2 or [Cp*RhCl2]2 unexpectedly produced complexes of the novel spirocyclic Te5 dianion [{tBuN(Te)P(μ-NtBu)2P(Te)NtBu}2μ-Te]2−, which is N,N′-coordinated to two Na+ ions in the disodium derivative and adopts a Te,Te′,Te′′-bonding mode in the Cp*Rh complex. Postprint

Deprotonation of bis(tert-butylamido)cyclophosph(III/III)azane with organolithium or organomagnesium reagents followed by oxidation with elemental tellurium is a viable approach to the preparation of metal cyclodiphosphazane mono- and ditellurides. The reaction of the cyclodiphosph(III)azane [tBu(H)NP(mu-NtBu)2PN(H)tBu] (1) with elemental tellurium in boiling toluene affords the monotelluride [tBu(H)N(Te)P(mu-NtBu)2PN(H)tBu] (9). A similar reaction involving the magnesium salt Mg[tBuNP(mu-NtBu)2PNtBu](THF)2 (2) also yields a monotelluride Mg[tBuN(Te)P(mu-NtBu)2PNtBu]-(THF)2 (10). By contrast, reaction of the lithium salt Li2[tBuNP(mu-NtBu)2PNtBu](THF)2 (3) with tellurium results in double oxidation and the formation of the ditellurides Li2[tBuN(Te)P(mu-NtBu)2P(Te)NtBu](THF)4 (11) and Li2-[tBuN(Te)P(mu-NtBu)2P(Te)NtBu](tmeda)2 (12). Compounds 9-12 have been characterized by multinuclear (1H, 7Li, 13C, 31P, and 125Te) NMR, while 9, 10, and 12 have also been characterized by X-ray crystallography. The structure of 9 reveals a typical cis/endo, exo arrangement, with no intermolecular contacts to tellurium. The seco-heterocubic structure, observed in 2, is retained in 10, with the ligand chelating magnesium in an N,N',N"-manner. Unique coordination behavior is exhibited by the ditelluride 12, in which the dianionic ligand is attached to the two lithium centers in both Te,Te' and Te,N bonding modes. Multinuclear NMR data are consistent with retention of the solid-state structures of 9-12 in solution at low temperatures. The reactivity of cyclodiphosph(III/III)azanes toward chalcogens is rationalized by using theoretical calculations (semiempirical PM3 level of theory), which show an inverse correlation between the charge at the phosphorus center and the ease of oxidation.

The dilithium salts of the phosphonate dianions [PhP(E)(N(t)Bu)(2)](2-) (E = O, S, Se) are generated by the lithiation of [PhP(E)(NH(t)Bu)(2)] with n-butyllithium. The formation of the corresponding telluride (E = Te) is achieved by oxidation of [Li(2)[PhP(N(t)Bu)(2)]] with tellurium. X-ray structural determinations revealed dimeric structures [Li(THF)(2)[PhP(E)(N(t)Bu)(2)]](2) in which the monomeric units are linked by Li-E bonds. In the case of E = Se or Te, but not for E = S, transannular Li-E interactions are also observed, resulting in a six-rung ladder. By contrast, for E = O, this synthetic approach yields the Li(2)O-templated tetramer [(THF)Li(2)[PhP(O)(N(t)Bu)(2)]](4).Li(2)O in THF or the tetramer [(Et(2)O)(0.5)Li(2)[PhP(O)(N(t)Bu)(2)]](4) in diethyl ether. The reaction of trimethylaluminum with PhP(E)(NH(t)Bu)(2) produces the complexes Me(2)Al[PhP(E)(N(t)Bu)(NH(t)Bu)] (E = S, Se), which were shown by X-ray crystallography to be N,E-chelated monomers.

Leak-before-break (1-b-b) safety cases depend on predictions of flow rate through postulated cracks. The calculated flow rates are dependent upon assumptions made about a number of features including fluid friction, and this in turn is influenced by surface roughness and flow regime. This paper considers the uncertainties associated with flow rate prediction in both the laminar and fully rough turbulent regimes as influenced by fluid friction. It shows how uncertainties can be bounded. In particular it discusses the maximum values for fluid friction that might arise in practice. The use of computational fluid dynamics in future analyses could significantly reduce the uncertainties associated with fluid friction in cracks.