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The sequential treatment of trans-(C6F5)(p-tol3P)2PtC≡CC≡CC≡CSiEt3 (2, acetone solution) with n-Bu4N+ F– in wet THF (to generate a PtC≡CC≡CC≡CH complex), ClSiMe3 (fluoride ion scavenger), excess HC≡CSiEt3, excess O2, and CuCl/TMEDA (0.20–0.25 equiv in acetone; Hay cross-coupling conditions) gives trans-(C6F5)(p-tol3P)2PtC≡CC≡CC≡CC≡CSiEt3 (4, 30%), as previously reported. When an analogous reaction is conducted with SiMe4 in place of ClSiMe3, the side-product trans-(C6F5)(p-tol3P)2PtC≡CC≡CC≡CC(Me)2OSiEt3 is obtained (ca 28%), the structure of which is established crystallographically. For comparison, crystal structures of three related complexes, 4, 2, and trans-(p-tol)(Ph3P)2PtC≡CC≡CC≡CSiEt3, are determined.

Low temperature stopped-flow methods together with diode array instrumentation have become extremely useful for studying reactions that are too fast at ambient temperatures and/or for detecting reactive intermediates that can only be observed at low temperatures. Furthermore, global analysis fitting methods are described that allow the analysis of complex reaction mechanisms. To illustrate the method the reaction of dioxygen with the tripodal copper(I) complex [Cu(Me2-uns-penp)(CH3CN)]ClO4 (Me2-uns-penp = (2-dimethylaminoethyl)bis(2-pyridylmethyl)amine) is discussed as an example.

In a one-pot reaction, the tetranuclear iron chelate complex [Fe4(L4)4] 6 was generated from benzene-1,3,5-tricarboxylic acid trichloride (4), bis-tert-butyl malonate (5a), methyllithium, and iron(II) dichloride under aerobic conditions. Alternatively, hexanuclear iron chelate complex [Fe(L5)6] 7 was formed starting from bis-para-tolyl malonate (5b) by employing identical reaction conditions to those applied for the synthesis of 6. The clusters 6 and 7 are present as racemic mixtures of homoconfigurational (delta,delta,delta,delta)/(lambda,lambda,lambda,lambda)-fac or (delta,delta,delta,delta,delta,delta)/(lambda,lambda,lambda,lambda,lambda,lambda)-fac stereoisomers. The structures of 6 and 7 were unequivocally resolved by single-crystal X-ray analyses. The all-iron(III) character of 6 and 7 was determined by Mossbauer spectroscopy.

The CuI-catalyzed reactions of trans-(Ph3P)2PtCl2 with HCCSiMe3 or HCCCCSiMe3 (greater than two equivalents, HNEt2), and trans-(p-tol)(Ph3P)2PtCl (4) or trans-(C6F5)(p-tol3P)2PtCl with HCCCCH, give trans-(Ph3P)2Pt(CCSiMe3)2 (2), trans-(Ph3P)2Pt(CCCCSiMe3)2 (3), trans-(p-tol)(Ph3P)2PtCCCCH (5), and trans-(C6F5)(p-tol3P)2PtCCCCH (7) in 74–81% yields. These compounds are characterized crystallographically, and their physical properties compared. A convenient three-step synthesis of 4 from (COD)PtCl2 is described.

A new strategy for the synthesis of biologically active quinoxalines by using versatile α-nitro epoxides as starting compounds has been developed. In addition, the in situ organocatalytic epoxidation of electron-poor nitro olefins followed by condensation with 1,2-phenylenediamines to provide quinoxalines in one pot has been demonstrated.

The synthesis of donor- (D) and/or acceptor (A)-expanded [4]radialenes has been developed on the basis of readily available dibromoolefin (7), tetraethynylethene (10 and 20), and vinyl triflate (12) building blocks. The successful formation of D/A radialenes relies especially on (1) effective use of a series alkynyl protecting groups, (2) Sonogashira cross-coupling reactions, and (3) the development of ring closing reactions to form the desired macrocyclic products. The expanded [4]radialene products have been investigated by spectroscopic (UV-vis absorption and emission) and quantum chemical computational methods (density functional theory and time dependent DFT). The combined use of theory and experiment provides a basis to evaluate the extent of D/A interactions via the cross-conjugated radialene framework as well as an interpretation of the origin of D/A interactions at an orbital level., NSERC; Deutsche Forschungsgemeinschaft (DFG-SFB 953); Interdisciplinary Center for Molecular Materials (ICMM); State Planning Organization (2008K120730)

A free-base porphyrin carrying two hexabenzocoronene (HBC) substituents in a trans arrangement and its zinc complex have been prepared. The compounds were characterized extensively and found to form tricationic dimers in the gas phase. X-ray crystallography confirms for the zinc complex a profound π-stacking of the HBC moieties. In contrast, the free-base porphyrin incarcerates n-heptane which essentially prevents π-stacking. Upon excitation of the HBC substituents, efficient energy transfer to the central porphyrin is observed.

The amino acid derived tertiary amide ligand tert-butoxycarbonyl-(S)-alanine-N,N-bis(picolyl)amide (Boc-(S)-Ala-bpa, 1) has been synthesized as a model for metal-coordinating peptide frameworks. Its reactions with copper(II) and cadmium(II) salts have been studied. Binding of Cu2+ results in amide bond cleavage and formation of [(bpa)(solvent)Cu]2+ complexes. In contrast, the stable, eight-coordinate complex [(Boc-(S)-Ala-bpa)Cd(NO3)2] (5) has been isolated and characterized by X-ray crystallography. An unusual tertiary amide nitrogen coordination is observed in 5; this gives rise to significantly reduced cis-trans isomerization barriers. Possible implications for metal-induced conformational changes in proteins are discussed.

Various fluorosubstituted benzoylchlorides 1a-c are transformed into the corresponding acylpyridinium triflates 2a-c by one equivalent of the reagent pair 4-dimethyl-aminopyridine/ trimethylsilyltriflate (DMAP/TMSOTf). Due to the combined electrostatic and mesomeric effect of the acylpyridinium function, fluorine substituents in o- and p-positions can be subsequently substituted with a pyridinio group by additional equivalents of DMAP/ TMSOTf via an SNAr mechanism. Whereas the p-substitution product can be isolated as the highly electrophilic dication salt 3b, the corresponding mono- and bis-orthosubstituted polycation salts 3a and 3c are transformed under the reaction conditions to the 7-azoniafluorenone derivatives 4a,c by a novel cyclo-acylation. Structural and electrochemical data of these compounds are presented.

Phenyl-terminated cis-oligodiacetylenes such as 18, containing a π-conjugated backbone with four triple and three double bonds, were synthesized using Pd-catalysed Sonogashira coupling reactions. Compound 18 represents the longest cis-oligoenyne system to date, but it suffers from the drawback of cis/trans isomerization observed in solution. In order to avoid cis/trans isomerization in such cis-oligodicacetylenes, the ene moieties within the oligomeric backbone were locked by incorporation into ring systems. 1,2-Dibromocyclopentene was used as an olefinic building block for this purpose, permitting the iterative synthesis of the cis-oligodiacetylenes 27 and 28, possessing the same π-conjugated backbone as 18. Unlike that compound, however, 27 and 28 are stable both in solution and in the solid state. Whereas X-ray crystallography revealed a completely planar structure for 27 in the single crystal, NMR and computational investigations suggest that a preferred helical conformation is likely in solution.

Reaction of achiral [Cu2(H3CCN)2(mu-pydz)3][PF6]2 (1) (pydz = pyridazine) with bidendate 1,3-bis(diphenylphosphanyl)propane (2) in acetonitrile at room temperature in a 1:1 ratio yielded the mononuclear copper(I) complex [Cu[CH2(CH2PPh2)2]2][PF6] (3) together with new one-dimensional coordination polymer 1 to infinity[[Cu(mu-pydz)2][PF6]] (4). Air-sensitive single crystals of 4, suitable for X-ray structure determination, were grown from a mixture of dichloromethane/ hexane [crystal system: monoclinic; space group: C2/c: a = 21.910(3), b = 12.130(2), c = 25.704(3) A,beta = 110.08(10) degrees, V = 6416.65(16) A3]. The one-dimensional coordination polymer 1 to infinity[[Cu(mu-pydz)2][PF6]] (4) exhibits as outstanding feature the rare structure of a meso-helix.

The broad applicability of the title reaction is established through studies of neutral and charged, coordinatively saturated and unsaturated, octahedral and square planar rhenium, platinum, rhodium, and tungsten complexes with cyclopentadienyl, phosphine, and thioether ligands which contain terminal olefins. Grubbs' catalyst, [Ru(=CHPh)(PCy3)2(Cl)2], is used at 2-9 mol% levels (0.0095-0.00042 M, CH2-Cl2). Key data are as follows: [(eta5-C5H4(CH2)6CH=CH2)Re(NO)(PPh3)-(CH3)], intermolecular metathesis (95 %); [(eta5-C5H5)Re(NO)(PPh3)(E(CH2CH=CH2)2)]+ TfO (E=S, PMe, PPh), formation of five-membered heterocycles (96-64%; crystal structure E = PMe); [(eta5-C5Me5)Re(NO)(PPh((CH2)6CH=CH2)2)(L)]n+ nBF4-(L/n = CO/1, Cl/0), intramolecular macrocyclization (94-89%; crystal structure L= Cl); fac-[(CO)3Re(Br)(PPh2(CH2)6CH=CH2)2] and cis-[(Cl)2Pt(PPh2(CH2)6CH=CH2)2], intramolecular macrocyclizations (80-71%; crystal structures of each and a hydrogenation product); cis-[(Cl)2Pt(S(R)(CH2)6CH= CH2)2], intra-/intermolecular macrocyclization (R=Et, 55%/24%; tBu, 72%/

Different electron-transfer pathways have been investigated in a three-dimensional redox system: tetrakis{4-[N,N-di(4-methoxyphenyl)amino]phenyl}phosphonium tetrafluoroborate 1+BF4- which comprises of four triarylamine redox centers arranged in a pseudo-tetrahedral geometry. Using a UV/Vis/NIR spectroelectrochemical setup we generated the mixed-valence species 12+, 13+, and 14+ and measured the UV/Vis/NIR spectra. These spectra were analyzed and interpreted according to a multi-dimensional Marcus−Hush approach. The analysis revealed that both the photoexcited as well as the thermal ET in 13+ are forbidden as a concerted two-electron transfer but allowed as two consecutive one-electron transfer steps.

A simple template-mediated route, starting from triethalolamine 1, sodium hydride or caesium carbonate, and iron(III) chloride led to the six- and eight-membered iron coronates [Na c [Fe6[N(CH2CH2O)3]6]]+ (2) and [Cs c (Fe8[N(CH2CH2O)3]8]]+ (3). In the reaction of N-methyldiethanolamine 4 (H2L1) or N-(2,5-dimethylbenzyl)iminodiethanol 6 (H2L2) with calcium hydride followed by addition of a solution of iron(III) chloride, the neutral unoccupied coronands [Fe6Cl6(L1)6] (5) and [Fe6Cl6(L2)6] (7) were formed. Subsequent exchange of the chloride ions of 7 by bromide or thiocyanate ions afforded the ferric wheels [Fe6Br6(L2)6] (8) or [Fe6(NCS)6(L2)6] (9), respectively. Titration experiments of solutions of dianion (L1)2- with iron(III) chloride in THF revealed interesting mechanistic details about the self-assembling process leading to 5. At an iron/ligand ratio of 1:1.5 star-shaped tetranuclear [Fe[Fe(L1)2]3] (11) was isolated. However, at an iron/ligand ratio of 1:2, complex 11 was transformed into the ferric wheel 5. It was shown, that the interconversion of 5 and 11 is reversible. Based on the mechanistic studies, a procedure was developed which works for both the synthesis of homonuclear 11 and the star-shaped heteronuclear clusters [Cr[Fe(L1)2]3] (12) and [Al[Fe(L1)2]3] (13). The structures of all new compounds were determined unequivocally by single-crystal X-ray analyses.

Reaction of enantiopure (S)-(η5-C5H5)Re(NO)(PPh3)(CH3) ((S)-1) with Ph3C+BF4- (1 equiv) and then the N,N‘-dimethyl 1,2-diamine HN(CH3)CH2CH2(H3C)NH (0.5 equiv) gives the diammonium salt (SReSRe)-[(η5-C5H5)Re(NO)(PPh3)(CH2NH(CH3)CH2CH2(H3C)HNCH2)(Ph3P)(ON)Re(η5-C5H5)]2+(BF4-)2 (94%) as a mixture of Re/N configurational diastereomers. Reaction with t-BuOK yields the title compound (SReSRe)-4 (66%) as an air-stable orange powder. Reaction with (PhCN)2PdCl2 gives a single diastereomer of a chelate complex, (80%), the configuration and approximate C2 symmetry of which has been established crystallographically. Racemic 1, Ph3C+BF4- (1 equiv), and the N,N‘-dimethyl 1,2-diamine HN(CH2CH3)CH2CH2(H3CCH2)NH (1 equiv) give [(η5-C5H5)Re(NO)(PPh3)(CH2NH(CH2CH3)CH2CH2NH(CH2CH3))]+BF4-, and the crystal structure of the SReSN,RReRN diastereomer is determined. The ReCH2N conformations of the preceding compounds, and their influence upon the diastereoselectivities, are analyzed in detail.

The reaction of N,N-dimethyl-1-naphthylamine with butyllithium agents is known to yield the peri lithiated product (3). The now reported structure of dimeric [1-(dimethylamino)-8-naphthyl]lithium with two molecules of THF (3·THF)2 shows a twist angle between the naphthyl-rings and the Li–Cipso–Li plane of ca. 38°. The magnitude of the 1J(13C,7Li) coupling constant as well as the line splitting pattern of the lithiated carbon atom in the 13C spectrum (THF-d8) demonstrate the existence of a dimeric species at −90 °C in solution. A previously published single crystal X-ray structure of dimeric [1-(dimethylamino)-8-naphthyl]lithium with two coordinating molecules of diethyl ether (3·Et2O)2 shows a smaller twist angle between the naphthyl-rings and the Li–Cipso–Li plane of ca. 11°. We assign this reduction of the twist angle to the weaker solvation properties of Et2O.

In an attempt to generalize the recently introduced concept of ‘auto-umpolung’, nitronyl nitroxides are identified as precursors of a special class of electron-excess carbenes. The latter can be formally derived from nucleophilic carbenes of the Wanzlick–Arduengo type by replacing redox-inactive N-substituents by lone-pair donor functions. A first systematic access to this class of compounds is achieved by lithiating the nitronyl nitroxide 11a at C(2), the central carbon position. The resulting radical anion equivalent 13 can be trapped in solution by various types of electrophiles to give C(2)-substituted nitronyl nitroxides 14, much in the same way as are trapped nucleophilic carbenes of the Wanzlick–Arduengo type. Carboxylation, addition to an aldehyde as well as silylation at the C(2)-position lead to novel types of functional nitronyl nitroxides. Elemental sulfur and selenium yield new types of anionic nitronyl nitroxides. The first characterized C(2)-derived heavy-metal complex of a nitronyl nitroxide 14g resulted, when Hg(OAc)2 was used as a trapping agent. More conveniently this complex could also be obtained directly from 11a and Hg(OAc)2. The X-ray structure of 14g is presented and analyzed in terms of cluster-forming secondary HgO interactions.

Reactions of methyl complex (η5-C5Me5)Re(NO)(P(4-C6H4CH3)3)(CH3) (2b) and the ferrocenium salt (η5-C5H5)2Fe + BArF− (BArF−=B(3,5-C6H3(CF3)2)4−) or the trityl salt Ph3C+ BArF− give the very air sensitive title radical cation 2b + BArF− or the robust methylidene complex [(η5-C5Me5)Re(NO)(P(4-C6H4CH3)3)(CH2)]+ BArF− (3b+ BArF−) as analytically pure powders in 80% yields. The crystal structures of 2b and 2b + BArF− are determined. With the aid of high level density functional calculations on model complexes, key structural, bonding, and dynamic properties are compared. Similar quantities are calculated for 3b+ BArF−, which could not be crystallized, and the ReCH2 rotational barrier is bounded by NMR (ΔG‡383 K>17.5 kcal mol−1). Special attention is given to structural manifestations of backbonding, particularly with the phosphine ligands. Cobaltocene and 2b + BArF− react to give 2b. However, no phosphine exchange or well-defined thermal decomposition products of 2b + BArF− are detected.

Reaction of 2-diazo-1,3-diketones with titanocene precursors can produce five-, six- or seven-membered 1-titana-2,n-diheterocyclic complexes with different coordination modes: whereas reaction with dicarbonyltitanocene is fast and furnishes either five-membered titanaoxazacycles or CC coupled seven-membered dioxochelates, decamethyltitanocene dicarbonyl reacts sluggishly to give a novel heteroleptic, trigonal-bipyramidal oxygen bridged Ti 5 O 6 -cluster containing six unsymmetric six-membered titanadioxacyclic ligands.

The objective of this study was to evaluate the efficacy and safety of low doses (50 and 100 microg b.i.d.) of hydrofluoroalkane-134a (HFA) beclomethasone dipropionate (BDP) extrafine aerosol in improving asthma control. Reformulation of BDP in a new chlorofluorocarbon (CFC)-free propellant (HFA) has produced an extrafine aerosol with increased delivery of the drug to the airways of the lung. The study population comprised 270 steroid-naive patients with mild to moderate asthma (mean baseline forced expiratory volume in 1 sec [FEV1] as a percentage of predicted normal of 65%-85%). This was a 6-week, blinded, placebo-controlled, multicenter study. Patients were randomized to receive 50 or 100 microg b.i.d. HFA-BDP or HFA-placebo. Treatment with either 50 or 100 microg b.i.d. HFA-BDP resulted in a significantly greater improvement compared with placebo in FEV1 (mean change from baseline as percentage of predicted normal of 6.7%, 8.6%, and 0.4%, respectively; por = 0.01 active treatment groups vs. placebo), with a significant trend toward increasing improvement with increasing doses (por = 0.0001). Treatment also resulted in significantly greater mean changes from baseline in morning peak expiratory flow compared with placebo (29.5, 33.8, and 5.0 L/min, respectively; por = 0.01 active treatment groups vs. placebo). All other pulmonary function and asthma symptom measures supported these data. The study treatments were well tolerated. These results show that low doses of HFA-BDP extrafine aerosol effectively improve asthma control in adult patients with mild to moderate asthma. However, it is important that inhaled corticosteroid therapy is still given at a dose high enough to control airway inflammation as well as asthma symptoms.

Selective C- over O-/N-acylation of acyclic, carbocyclic and heterocyclic carbonyl compounds bearing active α-CH groups is described. β-Ketoesters give the corresponding α-acylylidic derivatives in good yields. Likewise, tetronic acids and 4-hydroxycoumarins furnish the respective 3-acylylidic derivatives, and pyrazol-5-ones exclusively yield the corresponding 4-acylylidic compounds despite the possibility of tautomerism. X-Ray single crystal structure and NMR analyses of the product tricarbonyl ylides are presented and structure–reactivity interdependencies are discussed. As a rule, compounds with wide-spread conjugation of the π-system like 9/13 do not readily undergo Wittig olefination. Acylylides 11 with separated β-keto moieties react normally.

Reaction of methanolic copper(II) acetate solution with oxazolidine 21 (HL7) led to the formation of the one-dimensional coordination polymer 1D-∞1[CuL27] 23. On the contrary, reaction of copper(II) acetate in methanol with pyrrolidine 24 (HL8) yielded the two-dimensional coordination polymer 2D-∞2[CuL28] 26. A common feature of 23 and 26 are the C2h-symmetric coordinatively unsaturated building blocks 22 and 25. In 1D-∞1[CuL27] 23, the cyano groups are linked to copper in a side-on fashion and the monomers 22 are oriented parallel to one another, whereas in 2D-∞2[CuL28] 26 the cyano groups are bound to copper in the end-on mode and the monomers 25 are oriented at an angle of 117° to one another. In both 1D-23 and 2D-26, copper has a distorted octahedral coordination sphere. On the other hand, reaction of methanolic copper(II) acetate solution with enantiomerically pure (5S)-pyrrolidine 27 (HL9(S)) led to the formation of the diastereomeric helical strands (M)-/(P)-1D-∞1[CuL29] 29. (M)- and (P)-29 are present in pairs in the infinite unit cell. In helical 1D-29, copper is tetragonal-pyramidally coordinated and the C2-symmetric monomers 28 (CuL29) are linked through only one cyano group. Moreover, it has been shown that the reaction of chiral racemic pyrrolidine 30 (HL10(R,S)) with copper(II) acetate via the intermediate Ci-symmetric building blocks 31 (CuL10(R)L10(S)) furnishes one-dimensional 1D-∞1[CuL10(R)L10(S)] 32. Single-crystal X-ray diffraction analyses of the supramolecular species 23, 26, 29, and 32 unequivocally establish the structures of these coordination polymers.

Various types of mono- and binuclear ferracyclic (η 3 -allyl)iron complexes were prepared from unsaturated diols. Chelated tricarbonylironcarbene complexes 5 and 7 featuring a partially ligated (1,3-η 3 )-pentadienyl ligand were built up from the diene-1,2-diols 4 or 8 , respectively. 2-Hexyn-4-ene-1,6-diol ( 12 ) reacted with enneacarbonyldiiron to furnish the binuclear 1-lactonyl-(1,3-π:2-σ)-allyldiiron complex 13 under mild conditions. Its structural details are discussed. Similar complexes 17 with five- to seven-membered lactone substituents at the allyl ligand were prepared likewise from the corresponding 2-alkyne-1,n-diols ( 16 ).

Threefold ring-closing metatheses of mer,trans-Re(CO)3(X)(P((CH2)6CHCH2)3)2 (X = Cl, Br), followed by hydrogenations, yield the gyroscope-like species which react with NaI or Ph2Zn to give substitution products; crystal structures have been determined, and low-temperature NMR data indicate rapid rotation of the Re(CO)3(X) moieties.

Sulfonium salts [R2S-CH2-OTf]+ OTf- 1a,b are synthetically versatile 1,1-biselectrophiles featuring the sulfonio- and triflato-substituents as leaving groups of differential nucleofugic power. Reactions with a number of neutral nucleophiles |Nu yield a series of novel sulfoniom ethylated onium salts [R2S-CH2-Nu]2+ 2OTf- 2 - 8 under very mild conditions. Structures of salts 2a, 5a and 6b were confirm ed by X -ray analysis. With certain N -hetarenes exchange of both nucleofuges in la was achieved, yielding the symmetrical 1,1-bisonium salts 9 and 10. With pyridine(derivatives) selective substitution of the sulfoniofunction in 1,1-bisonium systems 2a and 5a was also realized. These reactions represent typical examples of nucleophilic substitutions at geminally bisonio substituted Csp3 centers, which we recently have introduced as a novel variant of Sɴ2 reactivity.

The arsonium salt [Ph3As-CH2-OTf]+ OTf- 11a contains a 1,1-biselectrophilic Csp3 center which permits to synthesize a wide range of symmetrical and unsymmetrical geminally bisonio-substituted methane derivatives. With neutral nucleophiles INu under mild condi- tions a series of 1.1-bisonium salts [Ph3As-CH2-Nu]2+ 2OTf- 12-23 is obtained in good yields. Under more stringent conditions the triphenylarsonio function in these salts can also be mobilized as a nucleofuge in a subsequent SN-reaction with a second nucleophile | Nu’, yielding a series of novel unsymmetrical 1,1-bisonium salts [Nu-CH2-Nu’]2+ 2OTf- 24-27. Structures 18, 23 and 26b were confirmed by X-ray analysis. For certain nucleophiles a discrete stepwise substitution of both nucleofuges in 11a cannot be realized and the corresponding symmetrical 1,1-bisonium salts (e.g. 28 and 30-32) are obtained directly. The experimental material can be rationalized on the basis of a simple MO model. The conclusion is that stabilization of a hypervalent SN2 transition state by an equatorial oniosubstituent parallels the stability of the underlying ylids. This is corroborated by model calculations. The geminal bisonium salts reported are potential precursors to mono- and 1,1-bisylids and, in special cases, to functional nucleophilic carbenes.

New chelating silylamido ligands with four `directing metalation donor groups' (DMGs), OMe, NMe 2 , CH 2 NMe 2 and CF 3 on aryl moieties have been synthesized. The X-ray crystal structures of the dimeric lithium derivatives [{ t -BuN–SiMe 2 – o -(C 6 H 4 )–DMG}Li] 2 ( 1 ) 2 (OMe), ( 2 ) 2 (NMe 2 ), ( 3 ) 2 (CH 2 NMe 2 ) and ( 4 ) 2 (CF 3 ) reveal Li–DMG contacts in all four cases and decreased lone pair-aryl conjugation for OMe and NMe 2 . In plane distortions are apparent for the alkyl and silyl substituents of the central (LiN) 2 rings in ( 1 ) 2 –( 4 ) 2 ; these give rise to short `agostic' Li⋯H 3 C– interactions with the t -Bu moieties. While the OMe, NMe 2 and CH 2 NMe 2 groups exhibit `side on' lithium–heteroatom contacts, lithium coordinates to a CF 3 fluorine atom significantly more `end on'. The ability of the chelating silylamido ligands to coordinate metal ions other than lithium is demonstrated by the X-ray crystal structures of the magnesium complexes [{ t -BuN–SiMe 2 – o -(C 6 H 4 )–OMe} 2 Mg] ( 9 ) and [{ t -BuN–SiMe 2 – o -(C 6 H 4 )–CH 2 NMe 2 }(OMe) 2 Mg 2 ] ( 10 ).

The conformational and dynamic behaviour of the 25,26,27,28-tetraalkoxycalix[4]arenes 1–7 (R = methyl, propyl) has been investigated by X-ray crystallography, dynamic 1D and 2D NMR spectroscopy, as well as with a series of force field (PIMM) and semiempirical (PM3, MNDO) calculations. The stereo-electronic effects of the upper rim substituents of tetramethoxycalix[4]arenes characteristically influence the preferred arrangement of the phenyl rings in the paco conformation. The in/out isomerisation (0001≈AAAA⇌0001≈AAAB) taking place in 4 is strongly hindered in 1 due to the smaller diameter of the upper rim. The ease of rotation of the methoxy group attached to the inverted ring in paco-4 can be altered by using a solvent (CD2Cl2), which is able to form a host–guest complex with the calixarene cavity. For 1–3 cone/paco and paco/paco equilibria have been observed by 2D EXSY spectroscopy. Gibbs activation energies for the cone(C2v)/cone(C2v) conversion were determined for 1, 2, 5 and 6. An NMR line shape analysis provided Arrhenius and Eyring activation parameters for the cone(C2v)/cone(C2v) conversion in 5 and 6.

Agostic Si−H···Li contacts (i.e. significantly less than ∼3.0 A) are not present in the solvent-free X-ray structure of [Li{Me2Si(H)N-t-Bu}]3; shorter (t-Bu)CH3···Li distances (∼2.8 A) are observed instead. The situation in solution is different. While the 1H−6Li HOESY spectrum of [Li{Me2Si(H)N-t-Bu}] in toluene at −80 °C evidently detects the same trimeric species (lacking Si−H···Li interactions, but with short (t-Bu)CH3···Li contacts), two major species with strong Si−H···Li interactions also are present. In the Li−HN−SiH3 computational model system, Si−H···Li interactions are favored energetically and result in increased Si−H distances and decreased Si−H frequencies. Agostic Si−H···metal contacts in the solid state are found in the X-ray crystal structure of [Mg2{Me2Si(H)N-t-Bu}4], where Li“+” is replaced by the more highly charged Mg“2+”. The two short agostic Si−H···Mg interactions (2.2, 2.5 A) which result also are shown by the two low ν(Si−H) frequencies (2040, 1880 cm-1) in the IR spectrum (Nujol ...

The synthesis and structural characterisation of two dinuclear iron(III) complexes are reported. The compounds of general structure [Fe2L] [8; L1 = dianion of 2,2′-dicyano-2,2′-isophthaloyldi(isopropyldicarboxylate)] and [K ⊂ Fe2L]+ (PF6)- [10; L2 = dianion of 1,1′-(2,6-pyridylene)bis-1,3-(4-dimethyl)-pentanedione] are formed by the deprotonation of ligands 7 and 9 with triethylamine and potassium hydride respectively, followed by addition of iron(III) chloride and work up with water or aqueous potassium hexafluorophosphate. X-ray crystallographic studies reveal that 8 is a racemic mixture composed of triple helicates with (Δ,Δ)-fac and (Δ,Δ)-fac configuration at the two iron bridgeheads. In contrast to racemic 8, the two iron centres in the meso-10 [(Δ,Δ)-fac] have opposite configuration. Investigations of the redox-active iron centres in {2}-metallacryptand 8 and {2}-metallacryptate 10 by cyclic voltammetry show slightly different behaviour. The peaks for the two consecutive reductions of the two iron centres of 8 can hardly be resolved, whereas 10 shows two well-separated peaks. Mossbauer measurements were performed on 8 and 10 between 4.2 and 300 K, with and without a field applied perpendicular or parallel to the γ-beam. All zero-field and 20 mT spectra exhibit a broad and unresolved absorption pattern. Application of 5.3 T at 4.2 K results in well-resolved magnetic hyperfine patterns which are practically the same for 8 and 10.

Although lithium−sulfur interactions should result if the thienyl groups in [Li−O−SiMe2(2-C4H3S)]6 ((6)6) and in [Li−O−CH(i-Pr)(2-C4H3S)]6 ((9)6) were rotated, no short distances between the lithiums of the (LiO)6 cores and the thiophene S atoms (Li−S > 3 A) are apparent in their X-ray crystal structures. Instead, the thienyl conformations in (9)6 benefit from Li (CC) π-interactions (Li1−C2 = 2.631(7) A, Li1−C3 = 2.845(7) A). DFT (B3LYP) computations show Li−S contacts to be only slightly favored over Li−C binding in Li−O−SiH2(2-C4H3S) (7) (1.4 kcal/mol) and in Li−O−CH2(2-C4H3S) (8) (1.7 kcal/mol). Semiempirical PM3 conformational analyses of thienyl groups on the (LiO)6 cores of the model hexamers [Li−O−SiH2-(2-C4H3S)]6 (7)6 and [Li−O−CH2(2-C4H3S)]6 ((8)6) show preferences for pyramidal Li−S(thiophene) contacts, whereas planar Li−O arrangements are favored for the furanyl analogues. Due to the higher aromaticity of thiophene, the σ “in-plane” Li+−S(thiophene) coordination energy (Li+−SC4H4, 16.9 kcal/mol...

Reaction of a methanolic copper(II) acetate solution of enantiomerically pure (5R)-/(4S)-methyl E-(4-ethyl-2-oxazolidinylidene)cyanoacetate 6 leads to the mononuclear chelate complexes (R, R)-/ (S, S)-7. Recrystallization of (R, R)-/(S, S)-7 from non-coordinating chloroform and asymmetric induction via the stereogenic centers, originating from (R)-/(S)-6, stereospecifically yield the right- and left-handed helical ID-coordination polymers (P)-/(M)-8. The structures of mononuclear complex (R, R)-7 and of helix (P)-8 and its mirror image (M)-8 have been characterised unequivocally by X-ray crystal structure analyses. (P)- and (M)-8 crystallize with chloroform to give the clathrates 1.{[CuLR2]. 2 CHCl3} and 1.{[CuLS2].2CHCl3}, respectively.

The title complexes 8 and 9 are easily prepared in two or three steps from iron carbonyls and isobutene diol 5 by Meerwein alkylation of the intermediate acyl complexes 6 and 7. With carbon and heteroatom nucleophiles like enolates and triphenylphosphane they form either stable 4-substituted alkene-carbene complexes 10 and 11, or substituted trimethylenemethane tricarbonyliron complexes like 12. Oxidation with H2O2/NaOH both of the alkene-carbene complexes 11 and of the less stable β-oxo-substituted trimethylene-methane complexes 13, as obtained from reaction of 8 with lithium enolates, yields the corresponding substituted allyl carbamates 15 or the allyl alcohols 14, which are formally bis- and monosubstituted derivatives, respectively, of the starting isobutene diol.

The synthesis, isolation, spectroscopic characterization, and computational investigations of the rod-shaped dicyanopolyynes 1–6 (C2nN2, n = 4–9), which are model substances for the hypothetical one-dimensional carbon allotrope carbyne sp-C∞, are described. Based on the trends in the spectroscopic behavior of 1–6 with increasing chain length, the electronic as well as the NMR properties of carbyne are predicted. For the investigation of the synthetic potential of this compound class, a first selected series of regioselective derivatizations is presented with the synthesis of the [4+2] and [3+2] cycloadducts 7–12.

The X-ray crystal structure of [Li−C⋮C−SiMe2−C6H4−OMe]6 (14)6 features nearly symmetric π-interactions between the lithium ions and the acetylide anions (Li1−Cβ = 2.353(9) A, Li1−Cα = 2.292(9) A). These π-contacts are facilitated by the chelating o-anisyl methoxy groups (Li1−Cα−Cβ = 77.6(4)°, Li1−O1 = 2.169(9) A). The Li−Cα distances in the (LiCα)6 core of (14)6 differ significantly (Li1α−Cα = 2.132(9) A, Li1b−Cα = 2.205(11) A). This Li−Cα distance differentiation is unique in organolithium hexamers, and is due to Li(C⋮C−R) “side-on-π” and “end-on-σ” contacts, as is shown computationally in H−C⋮C−Li(LiH)2 (20). A second X-ray crystal structure, [Li−O−CMe2−C⋮C−H]6 (22)6, reveals electrostatic π-interactions between the lithiums in the (LiO)6 core and the nonmetalated acetylene groups (Li1−C2 = 2.443(5) A, Li1−C3 = 2.749(6) A). These Li−C π-contacts shorten upon acetylene lithiation, as is shown computationally in Li−O−CH2−C⋮C−(H/Li) (24-H/Li). Additional computations reveal that the π-interactions in (HC⋮C...

Reaction of a methanolic copper(II) acetate solution with tetrazolyl enol derivatives 2a or 2b leads to the formation of the corresponding lD-coordination polymer 1 ∞[CuL2] 3a and pseudo 1D-coordination polymer [CuL2]2 3b, respectively. On the contrary, reaction of 2c with methanolic copper(II) acetate solution yields OH-bridged 1D-coordination polymer 1 ∞[CuL2(MeOH)2 3c. Single-crystal X-ray diffraction of the supramolecular species 3 established unequivocally the structures of the stairlike coordination compounds. Reaction of a methanolic copper(II) acetate solution with amidotetrazole derivative 6 leads to the formation of the lD-coordination polymer 1 ∞ [CuL2] 7. The structure of 7 has been established by X-ray structure analysis

Reactions of (R)-[(η5-C5H5)Re(NO)(PPh3)(CH2PPh2H)]+X-, mild base, and Pd(OAc)2 yield the novel Pd3(OAc)4-based palladacycle which has been characterized crystallographically and elaborated to dimeric halide-bridged and monomeric palladacycles that are effective catalyst precursors for the Heck reaction.

Threefold intramolecular ring-closing metatheses of trans-[MCl2(P{(CH2)(m)CH=CH2}3)2] are effected with Grubbs' catalyst. Following hydrogenation catalyzed by [RhCl(PPh3)3], the title complexes trans-[MCl2(P((CH2)n)3P)] (n=2m+2; M/n=Pt/14, 4 c; Pt/16, 4 d; Pt/18, 4 e; Pd/14, 5 c; Pd/18, 5 e) and sometimes isomers partly derived from intraligand metathesis, trans-[MCl2{P(CH2)n(CH2)n}P(CH2)n)] (4'c-e, 5'e), are isolated. These react with LiBr, NaI, and KCN to give the corresponding MBr2, MI2, and M(CN)2 species (58-99%). (13)C NMR data show that the MX2 moieties rapidly rotate within the diphosphine cage on the NMR timescale, even at -120 °C. The reaction of 4 c and KSCN gives separable Pt(NCS)2 and Pt(NCS)(SCN) adducts (13 c, 28%; 14 c, 20%), and those of 4 c,e and Ph2Zn give PtPh2 species (15 c, 61%; 15 e, 90%). (13)C NMR spectra of 13 c-15 c show two sets of CH2 signals (ca. 2:1 intensity ratios), indicating that MX2 rotation is no longer rapid. Reactions of 4 c or 4'c and excess NaC≡CH afford the free diphosphines P{(CH2)14}3P (91%) and (CH2)14P(CH2)14P(CH2)14 (90%). The latter has been crystallographically characterized as a bis(BH3) adduct. The crystal structures of eight complexes with P(CH2)14P linkages (PtCl2, PtBr2, PtI2, Pt(NCS)2, PtPh2, PdCl2, PdBr2, PdI2) and 15 e have been determined, and intramolecular distances analyzed with respect to MX2 rotation. The conformations of the (CH2)14 moieties and features of the crystal lattices are also discussed.

The use of cumulenes in synthetic transformations offers the possibility to form structurally interesting and potentially useful conjugated molecules. The cycloaddition reaction of a tetraaryl[5]cumulene with the electron-deficient olefin tetracyanoethylene affords unusual products, including functionalized dendralenes and alkylidene cyclobutanes, as well as a symmetric [4]radialene that shows unique solvatochromism, with λ(max) values approaching the near-IR region. These carbon-rich products have been investigated spectroscopically and by X-ray crystallographic analysis (five structures). The cycloaddition reaction sequence has also been explored by mechanistic and theoretical studies. The obtained results clearly demonstrate the potential of [5]cumulenes to serve as precursors for unprecedented conjugated structures.

Three series of regioisomeric bisadducts of C60, namely, C62(anisyl)4 and the mixed systems C62(anisyl)2-(COOEt)2, and C61(COOEt)2(NCOOEt), were synthesized starting from the 1,2-monoadducts C61(COOEt)2 (1), C61-(anisyl)2 (2), and C60(NCOOEt) (4) by using the Bingel and Bamford-Stevens reactions, and nitrene additions. In the case of C61(COOEt)2(NCOOEt) the complete series of nine possible regioisomers were isolated for the first time. For steric reasons the cis-1 isomers of C62(anisyl)4 and C62(anisyl)2(COOEt)2 were not formed. The transannular [6,6] bonds in the cis-1 isomer 42 of C61(COOEt)2(NCOOEt) are closed. The properties and regioselectivities of formation of these bisadducts and their monoadduct precursors were compared with those of the series C62-(COOEt)4 and C60(NCOOEt)2, which we synthesized previously. In the additions to 1, 2, and 4 the preferred positions of attack are e and trans-3 for sterically demanding addends (e.g., combinations of C(anisyl)2 and C(COOEt)2) and cis-1, e, and trans-3 for sterically less demanding addends (e.g., combinations of N(COOEt) and C(COOEt)2). A detailed analysis of the MO structures, the experimental and calculated geometries of monoadduct precursors, and the stabilities of reaction products leads to the conclusion that the addend-independent cage distortion itself is responsible for the observed regioselectivities of bisadduct formations.

The novel ferracyclic (η2-alkene)carbene complexes of type 3 and 9 are easily accessible either from the corresponding (ω-alkenyl)carbene complexes 1 or from the chelated (η2-olefin)acyl complex 8, depending on the central metal fragment and the heteroatom substituent X at the carbene carbon atom. X-ray structural data of 9 are provided and compared with those of 3 and similar metallacycles of the ‘earlier’ transition metals W and Mn. With nucleophiles, 9 yields new (η2-olefin) complexes bearing a substituted rearranged alkene ligand in an SN2′-type reaction, thus offering a new method for the α-allylation of carbon nucleophiles like enoxyborates.

Monomeric lithium bis(diphenylphosphino)amide, LiN(PPh2)2 (5), solvated with tetrahydrofuran, 5·3THF, was characterized by single-crystal X-ray analysis. The pentacoordinated lithium environment, a...