Organolead chemistry : III. 207Pb chemical shifts in some organolead compounds

²⁰⁷Pb chemical shifts are reported for the compounds (CH₃)_4?nPb X_n, where n = 1 · 4, X = 4-FC₆H₄; n = 1, 2, 4, X = CH₃ CC; n = 1, 4, X = CH₂CH; n = 1, X = Cl, CH₃O, CH₃CO₂. A correlation between δ(²⁰⁷Pb) and δ(¹⁹F) for the 4-fluorophenyl derivatives is discussed, and solvent effects on δ(²⁰⁷Pb) for the propynyl derivatives are interpreted in terms of complex formation.     

Isomerization of olefins on hydride-halide compounds of titanium and aluminium of composition LmTiH2AlXX′. The role of the cocatalyst and the geometry of the ligand environment of the titanium atom in catalytic hydrogen transfer

Using bimetallic complexes of the compositions (C₅H₅)₂TiH₂MXX′ and (CH₂)_n(C₅H₄)₂TiH₂AlXX′ (M = B, Al; X,X′ = H,Hal, Alk, n = 1–3) as examples, the rate of homogeneous catalytic isomerization of α-olefins has been studied under the influence of the ligand environment, the nature of the transition metal, and the substituent at M. Only titanium and aluminium complexes with non-rigid ligand environments and involving terminal AlH bonds show catalytic activity in the reaction. An alkyl isomerization mechanism at the heterobinuclear centre is suggested. The first reaction step involves coordination of an olefin at the six-coordinate Al atom followed by the insertion of the olefin molecule in the terminal AlH bond.     

The chemistry and the stereochemistry of poly(n-alkyliminoalanes) : III. The crystal and molecular structure of the adduct (HalN-i-Pr)6AlH3

The crystal and molecular structure of the adduct (HAlN-i-Pr)₆AlH₃ has been determined from single-crystal and three dimensional X-ray diffraction data collected by counter methods. The cage-type molecular structure consists of two six-membered rings, (AlN)₃, joined together by four adjacent transverse AlN bonds; the loss of two of these bonds allows the complexation of one alane molecule, with five-coordination of the aluminum (trigonal bipyramidal geometry), through two AlN bonds and two AlHAl bridge bonds. The AlN bond lengths range from 1.873 to 1.959 Å; the average AlH bond length is 1.50(1) Å for the four-coordinated aluminum atoms; the average distance of the two apical hydrogens from the five-coordinated aluminum atom is 1.92(5) Å. Colourless prismatic crystals of the compound have the following crystal data: triclinic space group P$\text{1}$; a = 17.13(2); b = 10.78(2); c = 10.20(2) Å; α = 124.3(4), β = 92.0(4), γ = 92.1(5); Z = 2; calculated density 1.157 g/cm³. The structure has been refined by block-matrix, least-squares methods using 4358 independent reflections to a standard unweighted R factor of 4.9%.     

Electronic structure and geometry of the active centres in anionic polymerization of vinyl monomers

The charge distributions in the ions (CH₃CHR) and in the molecules CH₃CHRLi (RNO₂, CN, COOCH₃, C₆H₅, CHCH₂, H, NH₂ or OCH₃), modelling the active centres of the two extreme types in anionic polymerization, were calculated by the CNDO/2 method. The geometry of these compounds was partly optimized. Both the geometry and the charge distribution in anions were found to exhibit no strong dependence on R. This suggests that in free ion polymerization, the equality r₁r₂ = 1 holds. The active centres of the polarized bond type are fairly varied. Two reasons for their reactivity may exist: the polarity of their CLi bond and their geometry facilitating the insertion of a monomer. The electronic structure of the neutral molecules considered correlates with the low degree of association of the living chains.     

The strong,linear hydrogen bond in Al2H−7

Self-consistent field calculations have been used to determine the equilibrium structure of Al₂H^?₇. The unique AlHAl bond is confirmed to be linear and symmetric. Breaking the hydrogen bond to form AlH₃ and AlH₄ requires a hefty 37 kcal. Electron correlation plays a small role in the relative energetics, and so the nature of this strong hydrogen bond can be understood within a molecular orbital picture. The bridging proton acts as a bond stretcher to minimize electrostatic repulsion between the two halves of the ion.     

Infrared Spectroscopic and dielectrometric investigation of the molecular geometry of isocyanato- and isothiocyanato-silane derivatives

The molecular geometry of compounds of the series (CH₃)_nSi(NCX)_4-n, (where n  0, 1, 2, 3 X  S, O) were investigated with the objective of determining the magnitudes of the SiNC angles. Measurement of the infrared spectra and dipole moments were carried out. The infrared spectra unambiguously suggest linearity, and this is supported by dipole moment calculations. The deviation from linearity observed by electron diffraction is a consequence of shrinkage effects δ(SiNCX) resulting from low frequency, large amplitude vibrations. From the dipole moment values it is concluded that the N—Si—N angle in the di- and trifunctional isothiocyanates is larger than the tetrahedral angle. The structural differences between the silicon and carbon compounds can be attributed to (dp)π bonding in the former.     

Metalmetal bonded triazenido compounds : II. Compounds with M = RhI,IrI; R = Me,aryld and X = Cl,Br, I Cl,Br, I

Complexes

(M = Rh, X = Cl, M = Ir, X = Cl, Br, I and R = CH₃, R′ = CH₃, p-tolyl) have been made by the reaction of (Ph₃P)₂(CO)MX with

. The proposed structure is analogous to that of the related copper derivatives and contains a five-membered ring in which an M^I to Ag^I donor bond is bridged by an azenido group, while the halide atom X has migrated from M^I to Ag^I.Carbon monoxide at 1 atm reacts rapidly and quantitatively with the iridium compounds to give novel acyltriazenido compounds {Ph₃P(CO)₂ - Ir[OCN(R)N=NR′]} (R = CH₃, p-tolyl; R′ = CH₃, p-tolyl).     

Substituent effects and stereochemical mechanisms for substitution reactions of 18F for halogen atoms in CF3X, (CH3)3−n CHnX,and CH3X

No thermal substitutions of ¹⁸F for X (X  halogen atom) are observed with CF₃X and (CH₃)_3?nCH_nX substrates in excess SF₆. The absence of thermal yield increasing with weaker CX bond energies, as found with CH₃X substrates, is attributed to the much larger mass versus H of F and CH₃ substituents. The thermal substitution of ¹⁸F/X in CH₃X molecules probably occurs by an inversion mechanism.     

Etude de la réactivité du fluorure de potassium sur des esters polyhalogénés

Reactions of polyhalogenated esters with potassium fluoride in polar solvents have been studied. Two kinds of reactions are possible depending on the starting compound: the hydrochlorinated estersRCCl₂CH₂CHR′CO₂CH₃ (R=Cl, -CF₃ ; R′=H, -CH₃ give the corresponding α-β unsaturated derivatives. Moreover when using ethylene glycol as a solvent, a transesterification reaction occurs after the dehydrohalogenation. From perhalogenated esters, mainly decarboxylation products are formed; for example in DMSO as a solvent, the fluorination of the telomers Cl-(CFClCF₂)_n-CO₂CH₃ yields the corresponding perfluoroalkenes C_2nF_4n. Some mechanistic interpretations are given in order to explain the formation of the different compounds.     

Stannoboroxanes : III. Synthesis and reactions of 1,3-bis(boryloxy)tetraalkyldistannoxanes and related compounds

1,3-Bis(boryloxy)tetraalkyldistannoxanes,

, R = Me, Bu; G = CMe₂CH₂CHMe—, —CMe₂ —CMe₂ — and —CHMe—CH₂ — have been prepared from dialkyltin oxide and pyroborate, or directly from dialkyltin oxide, boric acid and glycol. A dimeric structure for these compounds is proposed on the basis of molecular weight, IR and PMR studies. The reactivity of the SnOB bond towards PhNCO and Me₃SiCl has been demonstrated.     

The molecular structure of the complex trimethylaluminium dimethyl ether, (CH3)3AlO(CH3)2, determined by gas phase electron diffraction

The molecular structure of (CH₃)₃AlO(CH₃)₂ has been determined by gas phase electron diffraction. The main molecular parameters are AlC = 1.973(11), AlO = 2.014(14), OC = 1.436(3) Å, OAlC = 98.7(1.5), AlOC = 122.6 (0.5) and COC = 114.5(1.7)°. The OC bond distance and the COC valence angle are significantly larger than those in free dimethyl ether. The three valencies of the oxygen atom appear to lie in one plane. It is suggested that the planarity of the oxygen atom is due to across-angle repulsion Al?C(O).     

A gas-phase anionic analog of the wittig reaction. An ion cyclotron resonance study of the gas-phase ion chemistry of silyl carbanions

Gas-phase ion–molecule reactions of a variety of fluorosilyl carbanions with compounds containing double bonds to oxygen, X?O, have been examined using pulsed ion cyclotron resonance spectroscopy. The predominant reaction channel observed for species not containing acidic hydrogens is a Wittig-like process involving Si? O bond formation and elimination of X?CH₂ species. The gas-phase acidity of F₃Si(CH₃) has been determined and those of F₂Si(CH₃)₂ and FSi(CH₃)₃ have been estimated. From the fluoride transfer reactions of F₃SiCH₂^? the fluoride affinity of F₂Si?CH₂ has been estimated and limits on the π bond strength in this silaethene obtained. Potential analytical applications of the Wittig reactivity have been discussed.     

Carbon-13 and proton NMR parameters of neopentyl-and trimethylsilylmethyl-thallium(III) derivatives and the x-ray crystal structure of bis(trimethylsilylmethyl)chlorothallium(III)

Carbon-13 and proton NMR spectra have been determined for organothallium (III) derivatives of the types RTlX₂ and R₂ TlX (R  (CH₃)₃CCH₂ or (CH₃)₃SiCH₂; X  Cl, Br or O₂CCH(CH₃)₂). The dependence of coupling of ¹³C and ¹H to thallium on the number and nature of R groups is discussed in terms of the Fermi contact mechanism for spinspin coupling.The crystal structure of [(CH₃)₃SiCH₂]₂ TlCl has been determined. The compound crystallises in the monoclinic space group P2₁/n, with a 10.618, b 24.492, c 6.017 Å, β 99.76°. The molecule is dimeric with each four-coordinate thallium atom bonded unequally to two bridging chlorine atoms. The CTlC angle is 168°.     

Reactions of xenon difluoride: Oxidative fluorination of methyl derivatives of the p-block elements

A survey has been carried out to determine how xenon difluoride reacts with methyl derivatives of p-block elements, Me_nX (n = 3, X = N, P, As, or Sb; n = 2, X = O, S, or Se; n = 1, X = Cl, Br, or I), on the basis of NMR measurements, tensimetric and IR analysis of the gaseous products, and mass balances. The reaction proceeds smoothly in most cases, although a Freon like CCl₃F may be needed as a moderator; the rate of the reaction seems to reflect the basicity of the substrate Me_nX. The difluoride Me_nXF₂ is formed in the cases where X = P, As, Sb, Se, or I. The scope of xenon difluoride in these conditions as a mild selective oxidative fluorinating agent is illustrated by the synthesis of the known compounds (CF₃)₂XF₂ (X = S or Se) and the novel compound Me(CF₃)SeF₂. By contrast, cleavage of CH bonds, with the formation of CH₂F derivatives, is the predominant path in the cases where X = N, O, or S, and cleavage of CX bonds, with the formation of MeF, occurs in the cases where X = Cl or Br.     

The chemistry and the stereochemistry of poly(N-alkyliminoalanes) : IV. The preparation and crystal structure of [H(HAlN-i-Pr)5AlH2]·LiH/Et2O

The compound [H(HAlN-i-Pr)₅AlH₂]·LiH/Et₂O has been prepared, and its crystal and molecular structure has been determined from single-crystal, three-dimensional X-ray diffractometer data. The molecular structure is a pseudohexameric cage, consisting of a five-membered fragment, AlNAlNAl, crosslinked to a six-membered cyclohexane type ring, (AlN)₃. The hydrogen atom of LiH is indistinguishable from the other hydridic hydrogens, so that the N-isopropyliminoalane part of the molecule may be considered as an anion with a formal charge of ?1. The lithium cation is linked to two adjacent molecules through three LiHAl bridges, the fourth position of its tetrahedral coordination being occupied by the oxygen of diethyl ether. Large distortions of the tetrahedral valence angles occur, both on the aluminum atoms and on the nitrogen atoms, together with a noticeable spread of the AlN bond lengths, averaging 1.919(4) Å. Colourless crystals of the compound have the following crystal data: orthorhombic space group Pna2₁; a = 19.76(2), b = 10.38(1), c = 16.60(2) Å; Z = 4; calculated density 1.048 g/cm³. The structure has been refined by block-matrix least-squares methods, using 2487 independent reflections, to an usual R factor of 5.9%.     

Alkylidenverbrückte diphosphane und dichlalkogenodiphosphorane als liganden in kationischen cyclopentadienyleisencarbonyl-komplexen

Oxidative cleavage of the FeFe bond in [C₅H₅Fe(CO)₂]₂ in the presence of alkylide-bridged diphosphanes LL (LL = (C₆H₅)₂P(CH₂)_n(P(C₆H₅)₂; n = 1–3), (C₆H₅)₂PCH₂As(C₆H₅)₂ and dichalcogenodiphosphoranes (X)LL(X) ((X)LL(X) = (C₆H₅)₂P(X)(CH₂)_n(X)P(C₆H₅)₂; X  O, S, Se; n = 1–3) yields the complexes [C₅H₅Fe(CO)₂L′]BF₄ (L′ = LL, (X)LL(X); X  S, Se) in high yield. the complexes react with Ni(CO)₄ under photochemical conditions to form [C₅H₅Fe(CO)₂(μ-L′)Ni(CO)₃]BF₄ in quantitative yield, and lose a CO group under irradiation (λ_max > 300 nm) to form the chelate compounds [C₅H₅Fe(CO)L′]BF₄, which are isolable for L′  LL (P,As ligand) and (X)LL(X) (X = S, Se). Some substitution reactions with phosphanes are described.     

Übergangsmetall-substituierte vb elementsysteme : VIII. Darstellung und komplexchemisches verhalten von cyclopentadienyl(tricarbonyl)viametall-dimethylstibinen

Starting with the cyclopentadienyl(carbonyl)metal anions [π-C₅H₅(CO)₃M]^? (M = Cr, Mo, W) and (CH₃)₂SbBr, transition metal-substituted stibines of the form π-C₅H₅(CO)₃MSb(CH₃)₂ are obtained. The nucleophilic character of the VB element primarily determines the reactivity of these species, and shows itself in alkyl halide quarternization (a) or ligand exchange on activated metal carbonyl complexes (b). (a) yields the trialkylstibine-substituted metal cations [π-C₅H₅-(CO)₃MSb(CH₃)₂R]X (R = CH₃, CH₂CH=CH₂, CH₂C₆H₅; X = Br, J), (b) leads to the formation of the metal carbonyl derivatives LM(CO)₅, L₂M(CO)₄ (M = Cr, Mo, W), LNi(CO)₃ and LFe(CO)₄ [L = (CH₃)₂SbM(CO)₃-π-C₅H₅] which are the first (CH₃)₂Sb-bridged polynuclear complexes. Phosphorus ylides cause heterolytic cleavage of the antimonytransition metal bond. Transfer of the (CH₃)₂Sb-group to the ylidic carbanion occurs via substitution/transylidation. All new compounds have been fully characterized by means of ¹H NMR, IR and mass spectroscopy     

Cleavage of the tintin bond in hexamethylditin by LiMR4 (M = B,Al, Ga,Tl; R = H,CH3) and the formation of MSn bonded intermediates

Evidence is presented for the cleavage of the tintin bond in hexamethylditin in 1,2-dimethoxyethane solution by Group IIIA derivatives of the form LiMR₄(M = B, Al, Ga, Tl; R = H, CH₃). In all cases where reaction occurs Me₃SnR is produced.The formation of SnM bonded intermediates in these reactions is supported by the observation of ¹H NMR spectra showing both tin and thallium satellites compatible with the formation of Li[(Me₃Sn)_nTlMe_4-n] derivatives in the reaction between Sn₂Me₆ and LiTlMe₄.The overall rate of reactivity of LiMR₄ with Sn₂Me₆ decreased as follows: LiTlMe₄ > LiAlH₄ ? LiGaMe₄ > LiAlMe₄ ? LiBH₄ and LiBMe₄. Neither LiBMe₄ or LiBH₄ reacted with Sn₂Me₆ even after heating for two weeks at 80°.     

Group IB Organometallic chemistry : XV. Arylcopper compounds ArnCun as intermediates in organometallic synthesis. One-step synthesis of triorganotin halides of the type Ar3SnX and Ar3-nRnSnX

A new method for the one-step preparation of triorganotin halides is described. Triphenyltin halides are synthesized via the reaction of pure phenylcopper with SnX₄ or with Ph₂SnX₂. Me₂NCH₂, Me₂N and OMe-substituted phenylcopper react with Me₂(or Ph₂)SnBr₂ to give novel (substituted-phenyl)-diorganotin bromides in high yields. The selective arylation of tin halides by organocopper compounds is based upon the low reactivity of RCu towards the SnX bond in triorganotin halides. The selectivity of the arylation by the corresponding phenyllithium derivatives is connected with intra- or inter-molecular SnN (or O) coordination and/or of steric factors exerted by substituents ortho to the SnC(phenyl) bond.     

Réactions d'addition-élmination à partir d'hétérocycles germaniés du type . III. Cas des diéthyl-2,2-germa-2-oxazolidines-1,3 (R = et; X = O; Y = NH,NMe)

Addition-elimination reactions from germanium heterocycles . III. 2,2-Diethyl-2-germa-1,-3-oxazolidines (R = Et; X = O; Y = NH, NMe) . The reactions of 2,2-diethyl-2-germa-1,3-oxazolidines with heterocumulenes (PhNCO, PhNCS, CS₂, CO₂, CH₂?C?O) and carbonyl compounds (aldehydes and ketones) are studied. Generally, monoinsertion derivatives are formed by addition of one molecule of the unsaturated compound accross the Ge? N bond. This bond is always the most reactive center of the molecule. In the case of the carbonyl compounds used, diinsertion may occur in a second step by a further addition across a Ge? O bond. Generally, this latter reaction is reversible. By thermal eliminat on of (Et₂GeO)_n or (Et₂GeS)₃ the monoaddition derivatives yield the corresponding oxazolidines and thiooxazolidines. The mechanisms of these reactions are discussed.