John P. Oliver

X-ray crystal structure of trimethylsilylmethyllithium

Abstract The solid state structure of trimethylsilylmethyllithium has been determined by single crystal X-ray diffraction techniques. The compound crystallizes in the monoclinic system, space group P 2 1 / n . Cell dimensions were determined as follows: a 10.931(3), b 18.397(6), c 21.490(8) A, β 96.0(2)°, V 4298(2) A 3 , Z = 4, and a final R f 5.1% based on 2203 data with σ( I ) ≥ 2.5σ( I ). The compound is formed by hexameric units, {LiCH 2 Si(CH 3 ) 3 } 6 , with two distinct classes of LiLi distances of 2.46 and 3.18 A. There are also two LiC distances av 2.20 and 2.27 A. The LiH distances to the methylene H atoms have been determined and are short varying between 2.0 and 2.3 A to the closest lithium atom. The structure, including possible LiH interactions, is discussed and compared with the other known hexameric aggregates.

Studies on main group metal—transition metal bonded compounds ☆: II. THE crystal and molecular structure of π-C5H5(CO)3WGa(CH3)2 and evidence for mixed organozinc and organogallium transition metal derivatives

Abstract Metal—metal derivatives of the general formula (CH3)3—x]GaTmx (Tm = π-C5H5(CO)3Mo, π-C5H5(CO)3W) are obtained via reactions involving TmH and (CH3)3Ga in methylcyclohexane. For x = 1 and x = 3 the species are prepared by the combination of reactants in the appropriate molar ratios. The derivatives represented by x=2 may be obtained by heating the dimethyl derivatives under vacuum. NMR and IR data are presented for the molybdenum derivatives which show scrambling of the compounds in solution. Methyl exchange involving (CH3)3Ga and TmGa(CH3)2 is very rapid but the analogous exchange involving Tm2GaCH3 is considerably slower. NMR evidence indicates that methyl exchange between Tm2GaCH3 and TmGa(CH3)2 is slow or non-existent and that exchange of Tm is slow on the NMR time scale. The crystal structure of π-C5H5(CO)3WGa(CH3)2 has been determined from single-crystal X-ray data. This compound crystallizes in space group sol P 2 1 n with four molecules per unit cell of dimensions a = 8.707(2), b = 10.928(3), c = 13.04(3) A and β = 96.44(2)°. Full-matrix least-squares refinement gave final discrepancy factors R1 = 0.075 and R2 = 0.089 for 1936 data having I > 3σ(I).

Intramolecular metaldouble bond interactions : V. 1H NMR investigation of group II metalalkene compounds

1H NMR data are presented for a series of terminal alkenes and their respective halogen and Group II metal derivatives. The NMR parameters of the olefin functionality, with the exception of di-4-pentenylzinc, generally vary with the electron-donating or -attracting ability of the terminal substituent. The NMR parameters of di-4-pentenylzinc are interpreted in terms of an internal metaldouble bond interaction. This direct interaction leads to intramolecular cyclization in the di-5-hexenylmagnesium and -zinc derivatives.

Intramolecular metal—double bond interactions : VII. Intramolecular cyclization of alkenyl derivatives of lithium, aluminum, gallium and indium

Abstract The intramolecular cyclization reactions of tri-1-hex-5-enyl Group III derivatives and of 1-hex-5-enyllithium have been investigated and it is proposed that the reactions may be depicted as internal addition across the terminal double bonds of the alkenyl species. The cyclization reaction proceeds more readily for the 1-hex-5-enyl derivatives than for any other chain length and is dependent on temperature, concentration and solvent. 1H NMR data and cryoscopic molecular weight data are presented for several diisobutyialkenyl- and diisobutylalkyl-aluminum derivatives. These data have been interpreted in terms of a direct intramolecular interaction between the metal center and the π-electron system of the olefinic site. The intramolecular cyclization reactions for the 1-hept-6-enyl, 1-oct-7-enyl- and 1-undec-10-enylaluminum derivatives also were investigated and it was found that cyclization occurred only for the 1-hept-6-enyl derivative.

A proton NMR investigation of metalmetal bonding in trimethyltin-aluminium, -gallium, -indium and -thallium organometallic compounds

Abstract Proton NMR data for the Group III methyl derivatives, MMe 3 and LiMMe 4 are compared with NMR data for the novel tin—Group III-metal bonded species, Li[Me 3 SnMMe 3 ] (M  Al, Ga, In and Tl) and for Li[(Me 3 Sn) n -TlMe 4− n ] ( n = 0 to 4), reported here for the first time. The presence of tinmetal bonding in these derivatives is established by the observed tin-across-metal coupling constants and for the thallium derivatives by the additional observation of thallium-across-tin coupling. The variation in the magnitudes of 2 J (SnCH), 2 J (TlCH), 3 J (SnMCH) and 3 J (TlSnCH) are reported as a function of M and as a function of the number of Me 3 Sn groups bond to thallium in the [(Me 3 Sn) n TIME 4 − n ] − anions. Proposals concerning the factors governing the changes in these coupling constants and the chemical shifts are presented.

Silylcupration of acetylenes

Abstract Several organosilylcuprates have been prepared and their reactions with acetylenes examined. It has been shown that LiCu[Si(SiMe3)3]2 adds to acetylenes in only one manner, i.e. with cis addition and the Si(SiMe3)3 group in the least hindered cite as shown in the equation below. Similarly the sterically hindered LiCu(SiMePh2)2 LiCu[Si(SiMe3)2]2·LiI + RCCH → H+,H2O → trans-RHCCHSi(SiMe3)3 adds only in this fashion. If the less sterically hindered lithium compound, LiSiMe2Ph, is used to prepare the copper reagent, then, when the Li/Cu ratio is reduced to 1 1 a mixture of products, A and B (SiR3 = SiMe2Ph; R′ = n=Bu) is obtained in a ratio of 2 1 , but only one product, A (SiR3 = SiMe2Ph; R′ = n-Bu, t-Bu, Ph), is obtained when the ratio of Li/Cu is 2 1 . Only A is obtained when either diphenylmethylsilyllithium or tris(trimethylsilyl)silyllithium (SiR3 = SiMePh2, Si(SiMe3)3; R′ = n-Bu, t-Bu, Ph) is used regardless of the Li to Cu ratio.

Structures of Main Group Organometallic Compounds Containing Electron-Deficient Bridge Bonds

Publisher Summary This chapter discusses the structures of main group organometallic compounds containing electron-deficient bridge bonds. Main group metals that form electron-deficient bridged molecules are those with low electronegativity and small size. The structures of substantial numbers of simple organoaluminum species have been reported during the past few years. The structures of several other symmetrical organoaluminum compounds––which have important implications with regard to electron-deficient bonding––have been determined from X-ray data. Cryoscopic and spectroscopic evidence has been used to show that trivinylgallium, unlike the alkylgallium derivatives, is dimeric in solution, thus lending credence to the suggestion. A second class of unsymmetrically bridged systems is represented by pentamethyl dialuminum in which the bridging atoms are different—one providing an electron-deficient bridge bond and the other a normal bridge with two electron bonds. For several mixed vinyl–hydride systems, on the basis of nuclear magnetic resonance (NMR) spectral studies, the species are dimeric with one hydrogen and one vinyl bridge. Both trimethylgallium and -indium are monomeric in solution, and structural studies on the trimethylindium and triphenylindium and triphenylgallium show that these species are not bridged dimeric molecules in the solid state. There are a substantial number of systems in which electron-deficient bridge bonds have been reported to occur among dissimilar metals.

Proton magnetic resonance spectra of monosubstituted cyclopropanes

Abstract The proton magnetic resonance spectra of a series of monosubstituted cyclopropyl derivatives have been studied. The coupling constants have been shown to depend on the substituent electronegativity and equations have been developed which allow them to be predicted with a high confidence level. The chemical shifts have been discussed in terms of the substituent electronegativity and geometry of the molecule.

Studies on main group metal-transition-metal bonded compounds.6. The structure of η5C5H5(CO)3MoHgCl

The crystal structure of η 5 -C 5 H 5 (CO) 3 MoHgCl has been determined from single crystal X-ray data collected by counter methods. The compound crystallizes in space group P42 1 c with 8 molecules per unit cell and lattice constants of a  12.014(4), c  15.322(7). Full-matrix least squares refinement gave discrepancy factors R 1  0.058 and R 2  0.062 for 854 data with 1 3σ (1). The critical bond lengths and angles are MoHg  2.673(3)A, HgCl  2.437(8)A, and MoHgCl  160.0(2)°. Crystals of η 5 C 5 H 5 (CO) 3 WHgBr were shown to be isomorphous with lattice constants of a  12.068(4)A and c  15.643(7)A.

Fast Exchange Reactions of Group I, II, and III Organometallic Compounds

Publisher Summary This chapter deals with the exchange reactions of Group I, II, and III organometallic compounds. The actual degree of association depends on the alkyl group involved and the solvent. The nature of the association in these derivatives permits two types of exchange: group exchange between aggregates (intermolecular) and migration of groups within an aggregate. To account for the exchange, two alternate intramolecular paths were proposed in which rearrangement of the bridge bonds provides a mechanism for the transfer of the methyl groups. They also found that in the exchange of methyl groups between trimethylgallium or trimethylindium and trimethylaluminum the activation energy was within experimental error of that observed for the bridge-terminal exchange. The rates of exchange were the same in toluene solution but the methyl group exchange was a factor of ten slower than bridge-terminal exchange in cyclopentane solution. The main reason proposed for this is that the x-system of the unsaturated group interacts with the vacant nonbonding molecular orbitals of the aluminum atoms and this interaction stabilizes the bridge system.