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Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the λ4 Te dichloro derivative. Its crystal structure demonstrates that the heterocycle retains its ability to autoassociate by chalcogen bonding (ChB) forming macrocyclic tetramers. The corresponding Te⋅⋅⋅O ChB distances are 2.062 A, the shortest observed to date in aggregates of this type. DFT-D3 calculations indicate that while the halogenated molecule is stronger as a ChB donor it also is a weaker ChB acceptor; the overall effect is that the ChBs in the chlorinated homotetramer are not significantly stronger. However, partial halogenation or scrambling selectively yield the 2 : 2 heterotetramer with alternating λ4 Te and λ2 Te centers, which calculations identified as the thermodynamically preferred arrangement.

Wilkinson’s manganese(I) ethylene hydride complex trans-[(dmpe)2MnH(C2H4)] (1) reacts as a source of a low-coordinate manganese(I) ethyl complex. This is illustrated in the reactivity of 1 toward a variety of reagents. Reactions of 1 with primary silanes RSiH3 (R = Ph, nBu) at 60 °C afforded ethane and the disilyl hydride manganese complexes [(dmpe)2MnH(SiH2R)2] (4a, R = Ph; 4b, R = nBu). Additionally, reaction with H2 at 60 °C afforded ethane and the dihydrogen hydride complex [(dmpe)2MnH(H2)] (5), which has previously been prepared by an alternate route. The proposed low-coordinate intermediate, [(dmpe)2MnEt], was not observed spectroscopically but could be trapped using isonitrile ligands; reaction of 1 with CNR (R = tBu, o-xylyl) afforded the manganese(I) ethyl complexes [(dmpe)2MnEt(CNR)] (6a, R = tBu; 6b, R = o-xylyl). Ethyl complex 6a did not react further with CNtBu at 80 °C. In contrast, complex 6b reacted with excess o-xylyl isonitrile to form 1,1-insertion products, including the iminoacyl comp...

Addition of 3.05 equiv of dme (1,2-dimethoxyethane) to an n-pentane solution of [(XA2)U(CH2SiMe3)2] (1; XA2 = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) and LiCH2SiMe3 (∼1:1) precipitated the tris(alkyl) 'ate' complex, [Li(dme)3][(XA2)U(CH2SiMe3)3] (2-dme). Sterically encumbered 2-dme is thermally unstable in solution, eliminating SiMe4 to form [Li(dme)3][(XA2*)U(CH2SiMe3)2] (3-dme; XA2* = XA2 cyclometallated at the methine carbon of an isopropyl group) as the major product. Compound 1 did not react with PMe3, 2,2ʹ-bipyridine (bipy), or quinuclidine in benzene at 40 °C. However, 1 reacted with 2.1 equiv of 4-(dimethylamino)pyridine (DMAP) or 9-azajulolidine (AJ; a DMAP derivative featuring a fused tricyclic structure) at 22 °C to afford [(XA2)U(CH2SiMe3)(η2CN-DMAP*)(DMAP)] (4) and [(XA2)U(CH2SiMe3)(η2CN-AJ*)(AJ)] (5), respectively, where DMAP* and AJ* are DMAP and AJ ligands cyclometallated at the 2-position. Reaction of 1 with DMAP-d2 (deuterated in the ortho positions) confirmed that 4 is formed via a direct σ-bond metathesis mechanism. All newly-isolated uranium complexes (2–5) were crystallographically characterized.

Reaction of 4,5-bis(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H2XN2) with [Zr(NMe2)4], followed by crystallization from O(SiMe3)2, yielded [(XN2)Zr(NMe2)2]·{O(SiMe3)2}0.5 (1·{O(SiMe3)2}0.5). The zirconium dimethyl complex [(XN2)ZrMe2] (2) was subsequently accessed (a) by treatment of 1·(O(SiMe3)2)0.5 with excess AlMe3 or (b) via reaction of 1·(O(SiMe3)2)0.5 with excess Me3SiCl, affording [(XN2)ZrCl2] (3) followed by reaction of 3 with 2 equiv of MeLi. Reaction of [(XN2)ZrMe2] (2) with one equiv of B(C6F5)3 or [CPh3][B(C6F5)4] yielded cationic [(XN2)ZrMe][MeB(C6F5)3] (4) and [(XN2)ZrMe(arene)][B(C6F5)4] {arene = η6-benzene (5a), η6-toluene (5b), or bromobenzene (5c)}, respectively. Both 4 and 5b are active for ethylene polymerization under 1 atm of ethylene at 24 and 80 °C in toluene with activities ranging from 23.5–883 kg mol–1 atm–1 h–1, yielding polymers with weight-average molecular weights (Mw) of 70,800–88,100 g mol–1 and polydispersities (Mw/Mn) of 3.94–4.67.

The protonation of 2,3,4,5-tetraphenylcyclopentadienone (tetracyclone) yields 6,11-diphenyl-5H-benzo[a]fluoren-5-one (17) and 2,3,4,5-tetraphenylcyclopent-2-en-1-one (18) as the major products. This contrasts with the pyrolysis of tetracyclone that yields 5,6-diphenyl-11H-benzo[a]fluoren-11-one (22) a structural isomer of 17. Mechanisms are presented that rationalize these observations. The protonation of 4-hydroxy-2,3,4-triphenylcyclopentadienone, the precursor to 2,3,4-triphenylcyclo¬pentadienone, generates 2-(2′-oxo-3′,4′,5′-triphenylcyclopent-3′-enyl)-3,4,5-triphenyl-cyclopenta-2,4-dienone, (30) which has been unequivocally characterized by X-ray crystallography. The establishment of the conformation of molecule 30 in the solid state, which correlates with its structure in solution, provides a rationale for the subsequent formation of the tetrahydro-pentaphenyl-as-indacene-3,4-dione, 32, upon further protonation.

Reaction of the ethylene hydride complex trans-[(dmpe)2MnH(C2H4)] (1) with Et2SiH2 at 20 °C afforded the silylene hydride [(dmpe)2MnH(=SiEt2)] (2 a) as the trans-isomer. By contrast, reaction of 1 with Ph2SiH2 at 60 °C afforded [(dmpe)2MnH(=SiPh2)] (2 b) as a mixture of the cis (major) and trans (minor) isomers, featuring a Mn-H-Si interaction in the former. The reaction to form 2 b also yielded [(dmpe)2MnH2(SiHPh2)] (3 b); [(dmpe)2MnH2(SiHR2)] (R=Et (3 a) and Ph (3 b)) were accessed cleanly by reaction of 2 a and 2 b with H2, and the analogous reactions with D2 afforded [(dmpe)2MnD2(SiHR2)] exclusively. Both 2 a and 2 b engaged in unique reactivity with ethylene, generating the silene hydride complexes cis-[(dmpe)2MnH(R2Si=CHMe)] (R=Et (4 a), Ph (4 b)). Compounds trans-2 a, cis-2 b, 3 b, and 4 b were crystallographically characterized, and bonding in 2 a, 2 b, 4 a, and 4 b was probed computationally.

Reaction of NacNacAl (NacNac=[DippNC(Me)CHC(Me)NDipp]- ) with one equivalent of benzophenone affords a ketylate species NacNacAl(η2 (C,O)-OCPh2 ) that undergoes easy cyclization reactions with unsaturated substrates. The scope of substrates included benzophenone, aldimine (PhNC(Ph)H), quinoline, phenyl nitrile, trimethylsilyl azide, and a saturated cyclic thiourea. The latter substrate reacted by an unusual C-N cleavage that left the C=S functionality intact. The new products were characterized by NMR spectroscopy and X-ray diffraction analysis.

Iso-tellurazole N-oxides are promising supramolecular building blocks. While in neutral solutions, they form tetra- and hexameric macrocyclic aggregates linked by Te···O secondary bonding (σ hole interactions or chalcogen bonds), protonation of the oxygen atom in acidic media disrupts such supramolecular association. The process is reversible and, consequently, can be used to switch on and off the self-assembly process. Hammett acidity measurements gave pKa values of –3.2 for the protonated molecules. Adducts with HCl and HBr were isolated and structurally characterized. Protonation in solution led to the crystallization of a new polymorph of 3-methyl-5-phenyl-1,2-tellurazole N-oxide, which features a unique polymeric arrangement.

Iodine oxidation of bis[2-(hydroxyiminomethyl)phenyl] dichalcogenides yields benzo-1,2-chalcogenazole 2-oxides. Annulated derivatives of iso-tellurazole N-oxides spontaneously aggregate into cyclic tetra- and hexamers through Te⋯O chalcogen bonding; the structures of the co-crystals with benzene and CH2Cl2 illustrate the ability of these macrocycles to interact with small guest molecules. The selenium congener crystallizes forming a supramolecular polymer. VT NMR indicates that both compounds aggregate in solution but only at low temperature in the selenium case. The different abilities of these molecules to engage in supramolecular interactions are interpreted on the basis of their electronic properties evaluated with DFT-D3 calculations.

The synthesis of a rigid 4,5-bis(triphenylphosphinimino)-2,7-di-tert-butyl-9,9-dimethylxanthene {(Ph3PN)2XT} ligand is outlined, along with a modified synthesis for previously reported 1,8-bis(triphenylphosphinimino)naphthalene {(Ph3PN)2NAP}. Reaction of neutral (Ph3PN)2XT with [Y(CH2SiMe3)3(THF)2] resulted in double cyclometallation, yielding the base-free monoalkyl complex, [({Ph2(C6H4)PN2XT)Y(CH2SiMe3)] (1). Layering a concentrated THF solution of 1 with hexanes at −28 °C afforded THF-coordinated [({Ph2(C6H4)PN}2XT)Y(CH2SiMe3)(THF)]·2THF (1-THF·2THF), with a distorted pentagonal bipyramidal geometry and approximately meridional coordination of the pentadentate {Ph2(C6H4)PN}2XT dianion. Similarly, (Ph3PN)2NAP reacted with [Y(CH2SiMe3)3(THF)2] to afford a THF-coordinated monoalkyl complex, [{(Ph2(C6H4)PN)2NAP}Y(CH2SiMe3)(THF)] (2-THF). Layering a DME solution of 2-THF with hexanes at −28 °C afforded X-ray quality crystals of [[{(Ph2(C6H4)PN)2NAP}Y(CH2SiMe3)(κ2-DME)]·hexane (2-DME·hexane), with a highly distorted pentagonal bipyramidal geometry and a facial coordination mode of the tetradentate {Ph2(C6H4)PN}2NAP dianion.

The two title complexes as well as the dimeric complex [Ru(II)(η5-C5H5)(6,6′-diamino-2,2′-bipyridine)]2(OTf)2 have been synthesized and characterized by NMR and single-crystal X-ray crystallography. The direct structural comparison of the 2,2′-bipyridine and 6,6′-diamino-2,2′-bipyridine complexes suggests that the electronic and steric environments of the ruthenium centers in both complexes are essentially equivalent, providing for a unique opportunity to probe the influence of the noncoordinated amine substituent on the relative reactivity and catalytic activity of the complexes. Opposite to what would be anticipated on the basis of steric effects, the bulkier amine-substituted ligand results in a catalyst showing substantially higher activity in the hydrogenation of cyclohexanone in acidic medium, which is attributed to the operation of a metal–ligand bifunctional hydrogenation mechanism mediated by the amine substituents in their protonated form acting as proton shuttles.

Reaction of [(BDPP)ThCl 2 (dme)] ( 1 ) with 2 equivalents of MeMgBr in OEt 2 , followed by filtration and layering a toluene solution with hexanes at −30 °C yielded a single large crystal of [{(BDPP)ThX(μ-X) 2 Mg(OEt 2 )(μ-Me)} 2 ]·2 toluene (X = Br 0.73–0.87 /Cl 0.13–0.27 ; 3 ·2 toluene). This product is the result of halide exchange to form a partially brominated neutral thorium species, which is adducted with MeMgX(OEt 2 ). The complex is then tetrametallic as a result of Mg–Me–Mg bridges. The structure of complex 3 provides direct insight into the process by which halide exchange takes place between electrophilic metal halide complexes and Grignard reagents. This reactivity stands in stark contrast to the reactions of 1 and [(XA 2 )ThCl 2 (dme)] ( 2 ) with PhCH 2 MgCl. In these cases the expected dialkyl products, [LTh(CH 2 Ph) 2 ] [L = BDPP ( 4 ) and XA 2 ( 5 )], were formed under most conditions. However, addition of a PhCH 2 MgCl solution to 2 at −78 °C and warming to room temperature after 5 minutes gave [(XA 2 )Mg(dme)] ( 6 ), the product of ancillary ligand transfer from thorium to magnesium, in 30–50% yield.

Acetylferrocene readily forms an adduct with BF3. The product is a neutral model for protonated acetylferrocene, a species that is a crucial intermediate in the formation of 1,3,5-trisferrocenyl-benzene and other conjugated heterometallic derivatives by cyclocondensation. The title compound’s structure was determined in the solid state by X-ray diffraction and its spectroscopic properties were examined in detail, particularly the electronic excitation spectrum, which confirms the previous identification of the in situ generated protonated ketone.

Reaction of the neutral dialkyl complex [(XA2)Th(CH2SiMe3)2] {1; XA2 = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene} with [CPh3][B(C6F5)4] in benzene or toluene at room temperature resulted in the formation of [(XA2)Th(CH2SiMe3)(η6-arene)][B(C6F5)4] {arene = C6H6 (5) and toluene (5B)}, which were characterized by 1H, 13C, and 2D NMR spectroscopy and by X-ray crystallography (for 5). In close analogy, reaction of [(XA2)Th(CH2Ph)2] (3) with [CPh3][B(C6F5)4] in toluene at room temperature resulted in the formation of 1 equiv of Ph3CCH2R (R = Ph) and precipitation of an insoluble orange-brown oil, which upon layering with hexanes yielded crystals of [(XA2)Th(η2-CH2Ph)(η6-C6H5Me)][B(C6F5)4] (6). NMR investigation of the reactions of 1 and 3 with substoichiometric amounts of [CPh3][B(C6F5)4] provided no evidence for dinuclear monocation formation. By contrast, reaction of [(BDPP)Th(CH2Ph)2] {4; BDPP = 2,6-bis(2,6-diisopropylanilidomethyl)pyridine} with 0.5 equiv of [CPh3][B(C6F5)4] res...

Reaction of 2,7-di-tert-butyl-5-diphenylboryl-4-diphenylphosphino-9,9-dimethylthioxanthene (TXPB) with [PdCl2(COD)] resulted in the formation of [PdCl(μ-Cl)(TXPB)] (3), which can be reduced in a stepwise fashion, forming [Pd(TXPB)] (2) via [{PdI(μ-Cl)(TXPB)}2] (4). Dinuclear 4 could also be prepared through a comproportionation reaction of palladium(II) complex [PdCl(μ-Cl)(TXPB)] (3) with either [Pd(TXPB)] (2) or [Pd(dba)(TXPB)] (5). In complexes 3 and 4, the TXPB ligand is bound to palladium via the phosphine and thioether donors, with a chloride anion bridging between the metal and the borane unit of TXPB. By contrast, the TXPB ligand in 2 is bound to palladium not only via the phosphine and thioether donors but also through a Pd-(η3-BAr3) linkage involving boron and the ipso- and ortho-carbon atoms of one B-phenyl ring. The analogous nickel complex, [Ni(TXPB)] (6) also proved accessible by direct reaction of [Ni(COD)2] with TXPB. In both 2 and 6, short distances (2.02−2.33 A) between the metal and the ...

A new NON-donor ligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H2[XA2], 1), was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with the appropriate dibromoxanthene precursor. Stable K2(dme)2[XA2] (2) and Na2[XA2] (3) salts were accessible by deprotonation of H2[XA2] with KH in dme or NaH in toluene. The thermally unstable lithium salt of McConville's 2,6-bis(2,6-diisopropylanilidomethyl)pyridine ligand (Li2[BDPP], 4) was isolated by deprotonation with nBuLi or LiCH2SiMe3 in hexanes at low temperature. Reaction of [ThCl4(dme)2] with Li2[BDPP] or M2(dme)n[XA2] resulted in the formation of pentagonal bipyramidal [LThCl2(dme)] complexes (L = BDPP, 5; XA2, 6). Subsequent reaction of 5 or 6 with LiCH2SiMe3 gave base- and salt-free dialkyl complexes, [LTh(CH2SiMe3)2] (L = BDPP, 7; XA2, 8), which are stable for days in solution at 90 and 70 °C, respectively. Complexes 5, 7, and 8 were also accessible by initial combination of 2 or 4 equiv of LiCH2SiMe3 with [Th...

Reaction of [{RhCl(CO)2}2] with a phosphine/thioether/borane ligand (TXPB) gave [Rh(μ-Cl)(CO)(TXPB)] (1), a rare example of a complex containing a M−Cl−BR3 bridging interaction. Reaction of 1 with K[CpFe(CO)2] gave [(TXPB)Rh(μ-CO)2Fe(CO)Cp] (2), which contains an unprecedented η3-interaction between rhodium and the B−Cipso−Cortho unit of a triarylborane. DFT calculations suggest a bonding description intermediate between that expected for an isolated borane/alkene complex and a fully delocalized allyl-like complex.

Ethylene nanoextrusion polymerization has been demonstrated to be a novel nanofabrication concept for the preparation of polyethylene (PE) fibers directly from ethylene monomers without any post-processing procedures. For PE fibers, chain orientation is a critical parameter that affects performance and application of the fibrous materials. In this communication, we report an investigation on chain orientation in PE fibrous samples prepared through nanoextrusion polymerization using a two-dimensional wide angle X-ray diffraction (2D WAXRD) technique. Two types of fibrous samples, including individual microfibers and microfiber aggregates, were sampled randomly and studied. For individual PE microfibers, anisotropic diffraction patterns were observed, suggesting chain orientation along the microfiber axial direction. Some microfibers showed the most desired diffraction pattern often found in high-modulus high-strength PE fibers. These samples possessed a very high degree of chain orientation along the fiber axis. Owing to a random aggregation of anisotropic microfibers, microfiber aggregates exhibited isotropic diffraction patterns. This work provided further experimental evidence for the proposed nanoextrusion polymerization concept.

Hexaethylbenzene (HEB) and [(p-cymene)RuCl2]2 react in the melt to yield [(HEB)RuCl2]2 (6), the NMR spectra of which reveal the presence of [(HEB)2Ru2(µ-Cl)3]Cl in solution. In [(HEB)2Ru2(µ-Cl)3][C5(CO2Me)5] (7), the cation has D3h symmetry with alternating proximal and distal ethyl groups. Bridge cleavage of 6 with trimethyl phosphite or with trimethylphosphine gives (HEB)RuCl2[P(OMe)3] (9) or (HEB)RuCl2(PMe3) (10), respectively. The latter reaction also yields RuCl2(Me3P)4 (11), whose structure represents a relatively rare example of a crystallographically characterized trans isomer of this type. In 9, five of the ethyl ligands are distal, whereas in 10 all six substituents are distal. Attempts to prepare the sandwich dication [(HEB)2Ru]2+ gave instead [(HEB)Ru(H2O)3](BF4)2 (8), whose NMR and X-ray data reveal the 1,3,5-distal–2,4,6-proximal arrangement of ethyls both in the solid state and in solution. (HEB)Mn(CO)2Br (13) likewise adopts the 1,3,5-distal–2,4,6-proximal structure in the solid state but, surprisingly, there is no evidence for slowed ethyl rotation in solution.Key words: hexaethylbenzene conformations, hindered rotations, crystallography, NMR, ruthenium, manganese.

Both stereoisomers of disiloxane-bis(1-indenyl)-ansa-ferrocene, Fe(η5-inden-1-yl-SiMe2)2O, 1, were prepared by the reaction of disiloxane-bis-1,3-inden-1‘-yl anion with FeCl2; the diastereomers were separated by column chromatography and recrystallized from n-heptane. A single-crystal X-ray diffraction study confirmed that each stereoisomer, racemic 1r and meso 1m, involves parallel bis-indenyl coordination to the Fe metal center. These isomers were also characterized by 1H, 13C, and 29Si NMR and IR spectroscopy. Compounds 1r and 1m could each be transformed into the other diastereomer: the conversion was retarded by base, but accelerated under weakly acidic conditions. The mechanism of this process, investigated using deuterium labeling experiments, is consistent with a series of successive 1,5-suprafacial, sigmatropic silicon shifts. Compound 1 was also copolymerized with 1,1,3,3,5,5,7,7-octamethylcyclotetrasiloxane (D4) and 1,1,1,3,3,5,5,5-octamethyltrisiloxane (MDM) to produce green organometallic po...

A 15-member library of phosphaadamantane ligands has been prepared via P-arylation of 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phosphaadamantane. Screening of this tertiary phosphine collection has allowed for the rapid determination of the most suitable ligand, specifically 1,3,5,7-tetramethyl-6-(2,4-dimethoxyphenyl)-2,4,8-trioxa-6-phosphaadamantane, for facilitating Suzuki-type couplings of alkyl halides or tosylates containing β-hydrogens with either boronic acids or alkylboranes.

The attempted Diels-Alder reaction between 9-phenylethynylfluorene and tetracyclone yields instead three products resulting from the dimerization of the isomeric allene. The major product is 8,16-diphenyl-diindeno[1,2,3-de:1',2',3'-mn]naphthacene, in which each terminal ring is derived from a fluorenyl unit; aerial oxidation then yields a peroxide. A dihydronaphthacene bearing fluorenyl moieties spiro-bonded at the C(5) and C(11) positions was also identified. The structures of the naphthacenes were elucidated by X-ray crystallography, and a mechanistic rationale is offered. [reaction: see text]

3-Ferrocenyl-2,4,5-tri-(β-naphthyl)cyclopentadienone undergoes a Diels–Alder reaction with di-(β-naphthyl) acetylene to yield, after elimination of carbon monoxide, ferrocenyl-penta-(β-naphthyl)benzene (4). 1H and 13C variable-temperature NMR studies on 4 reveal the existence of multiple diastereoisomers at low temperature. These data are interpreted in terms of slowed rotation of the naphthyl groups, and are supported by the X-ray crystal structure of 4, which exhibits disorder at three of the naphthyl sites.Key words: sterically crowded molecules, hindered rotations, crystallography, NMR.

The reaction of phenylethynyllithium with 9-bromofluorene yields 9,9′-bifluorenylidene, 8 , 9,9′-bifluorenyl, 9 , and a molecule 10 , of formula C52H32, in which coupling has occurred between a 9,9′-bifluorenyl fragment and a 9,9′-bifluorenylidene moiety such that a C(9) position of the former is attached to a C(3) site of the latter. This parallels the unsymmetrical radical coupling of triphenylmethyl radicals, which leads to the Gomberg dimer, rather than hexaphenylethane. The structure of 10 has been elucidated by X-ray crystallography, and a mechanistic rationale is offered.

Two homoleptic Re(I) complexes of ortho and para-carborane isocyanide ligands were prepared as the first examples of a new class of metal-based BNCT and BNCS agents. The target compounds were prepared in low yield through the reaction of [Re2(O2CPh)4Cl2] and [Re2(OAc)4Cl2] with 3-isocyano-1,2-dicarba-closo-dodecaborane and a para-carborane azetidine derivative respectively. The desired product from the latter reaction was characterized crystallographically and is only the second reported molecular structure of a homoleptic Re(I) isonitrile complex.

In the solid state, [(acetylacetonate)-3,4-di(β-naphthyl)-2,5-diarylcyclopentadienone]rhodium(I) (4a, aryl=phenyl, 4b, aryl=m-xylyl) exist as head-to-tail dimers in which each rhodium is bonded to the γ-carbon of the acetylacetonate ligand in the other half of the molecule. These dimers are also favoured in solution at low temperature, and restricted naphthyl rotation results in the formation of numerous conformers whereby the naphthyls can adopt either proximal or distal orientations. These rotamers can be detected by observation of the 1H- and 13C-NMR methyl resonances in the acetylacetonate moiety. Triphenylphosphine cleaves the dimers (4a and 4b) to give the corresponding monomers, (C4Ar2(naphthyl)2CO)Rh(acac)PPh3 (5a and 5b), and the crystal structure of 5a exhibits a proximal/distal disorder of one naphthyl substituent. The rotamers of 5a and 5b are also present in solution, and the variable-temperature 31P-NMR spectra yield activation enthalpies of 8.2±0.5 kcal mol−1 for naphthyl rotation in each compound.

A nido-carborane analogue of tamoxifen, the widely employed breast cancer therapy agent, was prepared as an archetype of a potential new class of antiestrogen and boron neutron capture therapy agent in which the carborane is incorporated within the framework of the parent compound. The carborane was introduced through the reaction of 6,9-bis(acetonitrile)decaborane with a unique and highly conjugated ene-yne, which was prepared stereoselectively. NMR spectroscopy and a crystal structure of a key intermediate, the carborane analogue of chloro-tamoxifen, demonstrated the structural similarities between the tamoxifen carboranes and their corresponding phenyl analogues.

The reaction of (5-alkynylcyclopentadienol)Co2(CO)6 clusters with iron pentacarbonyl in acetone does not yield the expected product in which the hydroxyl substituent is lost and a tricarbonylcobalt vertex is replaced by an Fe(CO)3 group. Instead, the product contains an (η5-C5Ph2R2)Fe(CO)2H moiety that is bridged to one of the cobalt vertexes of the intact dicobalt-alkyne cluster. The process is rationalized in terms of a decarboxylation rather than a dehydroxylation process, and the relevance to the mechanism of substitution of one metal vertex by another is discussed.

Two corticosteroid–carborane esters were synthesized through the use of a BOP-Cl promoted esterification. The steroid–carborane conjugates are designed to selectively deliver boron to arthritic tissue for boron neutron capture synovectomy, a new therapeutic approach for rheumatoid arthritis.

The first nondisordered structure of a free tropylium cation has been unequivocally determined by single-crystal X-ray diffraction. The solid-state structure of the heptaphenylcycloheptatrienyl cation, C7Ph7+, in [C7Ph7+][CF3CO2−]⋅2 CF3CO2H reveals a severely crowded system in which the central ring is nonplanar, and the propeller blades (the peripheral phenyl substituents) are arranged in a slightly tilted fashion about the seven-membered ring (right).

The crystal structure of 3,4,7,8-tetramethylglycoluril (5) was determined by X-ray diffraction. The structure reveals a hydrogen-bonding motif in the crystal lattice that differs from that present in related glycolurils. The two sides of each molecule form part of two independent, but parallel, infinite helical chains. These chains are formed by the NH donor and C==O acceptor on one side of a glycoluril molecule, forming H-bonds to two different molecules at adjacent positions within the helix. On the other side of the same molecule, a similar motif generates another helix of opposite helicity to the first. The molecule has a crystallographic plane of symmetry through the two bridgehead carbon atoms and the two bridgehead methyl groups, which are syn-periplanar. Thus, 5 is similar to 3,4-dimethylglycoluril (3), but differs from some glycolurils, where there is a significant dihedral angle between the two bridgehead-to-bridgehead substituent bonds. Bond lengths and angles in 5 resemble those reported for 3, but bond lengths around the bridgehead positions are slightly lengthened relative to 3.Key words: glycoluril, 1,2,5,8-tetramethyl-2,6,7,8-tetraazabicyclo[3.3.0]octane-3,7-dione, X-ray diffraction, crystal structure, hydrogen-bond array.

The crystal structure of 3,4,7,8-tetramethylglycoluril (5) was determined by X-ray diffraction. The structure reveals a hydrogen-bonding motif in the crystal lattice that differs from that present in related glycolurils. The two sides of each molecule form part of two independent, but parallel, infinite helical chains. These chains are formed by the NH donor and CTO acceptor on one side of a glycoluril molecule, forming H-bonds to two different molecules at adjacent positions within the helix. On the other side of the same molecule, a similar motif generates another helix of opposite helicity to the first. The molecule has a crystallographic plane of symmetry through the two bridgehead carbon atoms and the two bridgehead methyl groups, which are syn-periplanar. Thus, 5 is similar to 3,4-dimethylglycoluril (3), but differs from some glycolurils, where there is a significant dihedral angle between the two bridgehead-to-bridgehead substituent bonds. Bond lengths and angles in 5 resemble those reported for 3, but bond lengths around the bridgehead positions are slightly lengthened relative to 3.

A free phosphine/thioether/borane ligand (5) suitable to position a Lewis acidic borane in close proximity to a coordinated late transition metal has been prepared. Reaction with 0.5 [Pd2(dba)3] gave a zwitterionic palladium(II) η3-boratoxypentadienyl complex with the empirical formula [Pd(dba)(5)].

N,N′-[Dimethyl-(2,2′-dithiobisacetyl)]ethylenediamine (1) has been synthesized in 30% overall yield from N,N′-dimethylethylenediamine and thioacetic acid by an improved procedure involving simultaneous deprotection and oxidative cyclization with iodine. This cyclic diamide disulfide exists in solution as a mixture of two Z,Z and one Z,E disulfide, and amide ring conformers and has been characterized by nuclear Overhauser effect (NOE), 1H–1H, 1H–13C shift-correlated 2D-NMR and molecular modelling studies. Among the Z,Z ring conformers Z,Z1 and Z,Z2, the former predominates and interconverts with the latter isomer by rotation about the S—S bond with an activation energy of 14.5 ± 1.3 kcal/mol. Coalescence of N-CH3 signals occurred at ca. 127 °C (500 MHz), which corresponded to an approximate barrier to amide rotation of 19.3 kcal/mol. Aromatic solvent-induced shifts in C6D6 corroborated molecular mechanics and NOE predictions of amide stereochemistry. The structure of the Z,E stereoisomer of 1 has been determined by single-crystal X-ray diffraction at 296 K. A large geminal N-CH2 inequivalence (>2 ppm in CDCl3) was observed for the Z,Z conformers. Proton chemical shifts have been calculated for the conformers of 1 and related molecular fragments with DFT/GIAO theory. Absolute chemical shifts are modelled within 0.2 ppm of experiment. The unusual nonequivalence of geminal N-CH2 and S-CH2 protons can be understood as a combination of shielding mechanisms derived from short N-methyl contacts, amide group orientation, and sulfur lone-pair disposition. An implication of these results is the possibility of using α-CH (and eventually α-CH) shifts to probe the local conformational space in cyclic peptides and other conformationally constrained rings. Keywords: amide/disulfide rotamers, conformational analysis, density functional theory, DFT/GIAO NMR shift calculations, methylene nonequivalence, molecular modelling.

[structure: see text] Phosphorinanes are presented as a class of phosphine ligand suitable for organopalladium cross-coupling chemistry. Prepared via a direct double Michael addition of a monoalkyl- or arylphosphine to phorone followed by a Wolf-Kishner reduction, phosphorinanes are relatively inexpensive to manufacture and allow modification of one of the alkyl moieties permitting steric and electronic fine-tuning of the ligands. Library screening and applications of these ligands in the Suzuki, Sonogashira, ketone arylation, and aryl amination reactions are presented.

The spectroscopic and structural properties of the perchlorate and triflate salts of N-n-butyl-retinylidene imine, 2 and 3, have been examined in solution and solid phases. In solution these salts were found to exhibit very similar UV and NMR spectroscopic properties. However, in the solid state marked differences in their absorption spectra (2, λmax = 504 nm; 3, λmax = 445 nm) and13C NMR spectra were found. The structures of the two salts were determined by X-ray crystallography. The cations in each of the salts were shown to have very similar conformations, detailed structures, and packing in their crystal lattices. The differences in the spectroscopic properties of the salts in the solid state could not be accounted for on the basis of any structural differences in the cations themselves. In terms of cation–anion interactions, a strong hydrogen bonding interaction was found in each case between the N-H proton and an oxygen atom of the counterion. However, there were significant differences between the two salts in terms of the [Formula: see text] internuclear distances (2, [Formula: see text] and in 3, 2.85(1) Å). The results are strongly suggestive that the wavelength and positive charge delocalization in retinylidène iminium salts are controlled by variation of the distance between the anion and the proton bonded to the Schiff base nitrogen atom. The work reported here represents the first examples of secondary retinylidene iminium salts containing an N-alkyl substituent to be successfully analyzed by X-ray crystallography. The relationship of these observations in the solid state to the spectroscopic properties of the natural visual pigments is explored. Key words: retinylidène iminium salts, iminium salts, cation–anion interactions.

1-Deoxy-D-xylulose (= 1-deoxy-D-theropentulose) is a precursor of thiamin (Vitamin B1) and of pyridoxine (Vitamin B6) in bacteria. The synthesis of a [2,3-13C2] bond-labeled sample of the compound, to be used for investigations of the biosynthesis of the two vitamins, is described. In aqueous solution 1-deoxy-D-xylulose exists mainly as the open chain ketone. In methanol solution the compound exists as a mixture of the open chain ketone and the two corresponding epimeric furanoses. In acid solution the compound yields a dimeric anhydride, di-β-1-deoxy-D-xylulofuranose 2,3′:3,2′-dianhydride, whose structure was established by X-ray crystallography. Keywords: [2,3-13C2]-1-deoxy-D-xylulose, di-β-1-deoxy-D-xylulofuranose 2,3′:3,2′-dianhydride, 5-O-benzyl-3,4-O-isopropylidene-1-deoxy-D-xylulose, 4-O-benzyl-2,3-O-isoproylidene-D-threose.

Pentaerythritol and trichloroacetyl chloride react to yield the tetrakis-trichloroacetate ester C(CH2-O2C-CCl3)4, 5, which crystallizes in the triclinic space group [Formula: see text] with a = 9.874(2) Å, b = 11.811(2) Å, c = 12.858(3) Å, α = 114.35(3)°, β = 95.63(3)°, γ = 99.11 (3)°, and V = 1326.5(5) Å3 for Z = 2. The molecule adopts a geometry in which the trichloroacetate chains fold to produce a flattened tetrahedron, giving a molecule of approximate D2d symmetry. Treatment of 5 with CO2(CO)8 gave, as the highest molecular weight product, the tris-cluster complex C[CH2-O2C-CCo3(CO)9]3(CH2-O2C-CCl3), 6, rather than the tetra-cluster C[CH2-O2C-CCo3(CO)9]4, 7. A space-filling model of 7, derived by replacing the CCl3 groups in 5 by CCo3(CO)9 moieties, exhibited considerable molecular crowding. Reaction of several 1,1,1-trichloroacetylacetonate salts with Co2(CO)8 gave the corresponding cluster complexes of Co(II), Co(III), or Al(III). The uncomplexed cluster ligand CH3C(O)CHC(OH)CCo3(CO)9, 9, crystallizes in the orthorhombic space group Pna21 with a = 16.226(2) Å, b = 11.6300(10) Å, c = 9.919(2) Å, V = 1871.7(4) Å3 for Z = 4. The direction of enolization of 9 has been studied by EHMO calculations. The tendency to enolize is also found in (benzoylacetone)Cr(CO)3, 17, which crystallizes in the tetragonal space group P43212 with a = 10.0840(10) Å, b = 10.0840(10) Å, c = 25.387(5) Å, V = 2581.5(6) Å3 for Z = 8. Keywords: inorganometallic clusters.

The reaction of D-penicillamine and benzaldehyde yielded 2-phenyl-5,5-dimethylthiazolidine-4-carboxylic acid. The structure was determined by single crystal X-ray diffraction. Crystals were monoclinic, P21, a = 9.785(2), b = 6.941(1), c = 10.399(2) Å, β = 114.06(3)°, Z = 2. Intensities were measured on a Rigaku AFC6R diffractometer with Cu Kα radiation and 1881 reflections were used to determine the structure. R = 0.076, wR = 0.048. The compound exists as an amino acid in the 2S,4S configuration. The conformation of the thiazolidine ring is determined by intermolecular hydrogen bonding. Bond lengths and angles are normal. 1H and 13C NMR spectra showed that epimerization takes place in d4-CH3OH solution, and the ratio of 2S,4S diastereomer to 2R,4S diastereomer at room temperature is 65:35.

The structures of chloro(triphenylmethyl)mono-, di-, and -trisulfanes were obtained. The monosulfane displayed a triclinic (P1) space group, a=10.792(2) A, b=15.090(2) A, c=10.027(2) A, α=100.15(1) o , β=103.13(1) o , γ=88.80(1) o , Z=4. The disulfane gave a triclinic (P1) space group, a=9.758(1) A, b=10.426(2) A, c=9.1691(6) A, α=97,52(1) o , β=90.116(1) o , γ=116.750(1) o , Z=2. The trisulfane gave an orthorhombic space group (Pna2 1 ), α=9.224(1) A, b=19.196(3) A, c=10.308(1) A, Z=4. The sulfenyl chlorides decompose above their melting points to mixtures consisting primarily of triphenylchloromethane and sulfur. The sulfur was determines to consist of several allotropes (S 6 , S 7 , S 8 and S 9 ). The di- and trisulfanes slowly decompose to the same products at room temperature; the decompositions are enhanced by light. The decomposition of the trisulfane in the presence of dienes gave adducts consistent with the transfert of a two-sulfur species. The disulfane and trisulfane undergo the normal nucleophilic substitution reactions of the monosul- fanes

The tetrakis(trimethylsilyl)ethynyl derivatives of Si, Ge, Sn, and Pb were prepared and examined spectroscopically. NMR and Mössbauer spectroscopy and X-ray crystal structure data clearly demonstrate an electronic interaction in the ground state between the distal SiMe3 groups and the central metal atom, leading to a strong shielding of the central metal atom; the respective nmr signals of the central metal are among the most shielded examples reported for a tetrahedral Group 14 metal centre with four carbon ligands. The nature of these electronic interactions is discussed.

Methyl and n-butyl thorium complexes of a rigid 2,6-bis(anilidomethyl)pyridine ligand have been prepared; the n-butyl complex is thermally stable, even at 60 degrees C, while the methyl complexes exhibit a high tendency to eliminate methane via sigma-bond metathesis.

Trimesitylgermylamine, Mes 3 GeNH 2 , prepared in high yield by the coupling of Mes 3 GeCl (Mes  2,4,6-Me 3 C 6 H 2 ) with NaNH 2 or LiNH 2 , has been fully characterized by 1 H and 13 C NMR, IR and mass spectrometry. It is a rare example of a stable primary germylamine, melting at 166°C, which is only slowly cleaved by H 2 O, CH 3 OH, HCl or phenol, indicating that the central Ge atom is protected from attack by the mesityl groups. Unlike other germylamines, Mes 3 GeNH 2 reacts with t BuCOCl to give the N -substituted amide, Mes 3 GeNHCO t Bu, rather than Mes 3 GeCl. Preliminary X-ray crystallographic analyses reveal that the Ge atom has approximate tetrahedral coordination with an average GeC bond length of 1.978(3) A and a GeN bond length of 1.854(3) A, and crowding around the Ge atom so that it is shielded from attack by approaching reactants.

In an analogous fashion to the preparation of ergosterol peroxide from singlet oxygen, the preparation of its sulfur analog was attempted via the Diels–Alder addition of diatomic sulfur to ergosterol. Two of the recently reported methods for generating and trapping diatomic sulfur were employed as well as "activated" sulfur. Although the desired target was not obtained, several interesting steroidal products were isolated including 3,5-cyclo-6,8(14),22-ergostatriene (12), ergosta-5,7,22-trien-3-thiol (13), and ergosta-4,6,8(14),22-tetraen-3-one (16). Mechanistic aspects are discussed. Keywords: diatomic sulfur, ergosterol, sulfur analog of ergosterol peroxide, ergosta-6,22-dien-5a,8a-epidisulfide-3-ol, ergosterol peroxide, 3,5-cyclo-6,8(14),22-ergostatriene, ergosta-5,7,22-trien-3-thiol, ergosta-4,6,8(14),22-tetraen-3-one.

[Co(PMe 3 ) 4 ]PF 6 reacts with formaldehyde to form [Co(CO)(PMe 3 ) 4 ]PF 6 , which is shown by X-ray diffraction P2 1 / n