Terence N. Mitchell

Carbon-13 NMR investigations on organotin compounds

Abstract The carbon-13 NMR spectra of 49 organotin compounds have been recorded and analysed. Variation of the groups attached to tin causes variations in the chemical shift of carbons α to tin of almost 150 ppm. Large variations are also observed for the coupling constant 1 J( 119 Sn- 13 C), which, for the compounds investigated, lies between 240 and 1120 Hz; conclusions can readily be drawn from the magnitude of this coupling constant as to the hybridisation state and coordination number of the tin atom.

Palladium catalysis in organotin chemistry: addition of hexaalkylditins to alkynes

Abstract Tetrakis(triphenylphosphine)palladium(0) catalyses the cis-addition of hexaalkylditins R6Sn2 (R = Me, Et, Bu) to acetylene and 1-alkynes; for R = Bu, however, the reaction is not quantitative. With very few exceptions there is no reaction in the case of non-terminal alkynes. The (Z)-distannylalkenes can be partially or completely isomerised to the (E)-alkenes by UV irradiation. The 1,2-distannyl alkenes were characterised by NMR spectroscopy. Experimental details are given for the preparation of ditins R6Sn2 from tin hydrides R3SnH in the presence of tetrakis(triphenylphosphine)palladium(0).

Metalmetal spin coupling through chalcogenides. Correlation of 2J(119Sn, 119Sn) with molecular structure. Crystal structure of [(2-MeC6H4CH2)3Sn]2O and [(2-MeC6H4)3Sn]2O

The dependence of 2J(119Sn 119Sn) on the molecular structure of compounds containing the SnXSn moiety (where X = 0, S, Se, Te) has been investigated using new and earlier 119Sn solution and solid-state NMR and X-ray structural data for 46 linear and cyclic organotins. While 2J(119Sn, 119Sn) is found generally to vary with the size of the SnXSn angle for the chalcogenides, there is considerable scatter of the data. A plot of 2J(119Sn, 119Sn) (in Hz) vs. the angle SnXSn (in deg.) for compounds with X = O gives a straight line defined by the equation: angle SnOSn = 0.087 2J(110Sn, 119Sn) man(.6 with r = 0.990 and n = 8 (assuming no sign change in 2J(119Sn, 119Sn)). The quantity of data presently available does not permit regression analysis to be carried out for X = S, Se and Te. The range of SnX distances for a given X is small, and no meaningful relationships with 2J(119Sn, 119Sn) or the SnXSn angle were found. The X-ray crystal structures of [(2-methylbenzyl)3Sn]2O and (o-tolyl3Sn)2O are reported.

Palladium-catalysed addition of the silicon–tin bond to alk-1-ynes and 1,1-dimethylallene

(Trimethylsily)trimethylstannane adds regio- and stereo-specifically to alk-1-ynes in the presence of tetrakis(triphenylphosphine)palladium(0); regiospecific addition to 1,1-dimethylallene is also observed.

Synthesis of (Z)-1,2-bis(trimethylstannyl)-1-alkenes by platinum-catalysed addition of hexamethyldistannane to 1-alkynes

Abstract Addition of hexamethyldistannane to 1-alkynes in the presence of tetrakis(triphenylphosphine)palladium yields the title compounds, which can be photochemically isomerised to the corresponding ( E )-distannylalkenes.

α-Metallated vinyl carbanionoids: I. Formation of α-stannylvinyl anionoids from 1,1-bis(trimethylstannyl)alkenes☆

Abstract Hydrostannation of 1-stannyl-1-alkynes leads to the formation of 1,1- and 1,2-distannyl-1-alkenes. The former can undergo lithiation (by alkyllithium in THF) with varying degrees of stereospecificity. 1,1-Dilithio-1-alkenes cannot be prepared by double lithiation. The strongly basic α-stannyl vinyllithiums react with carbon electrophiles, but in some cases cause enolisation or dehydrohalogenation of the substrate. They can be readily converted into the corresponding vinyl Grignard reagents or vinylcopper derivatives.

Fourier transform NMR spectroscopy of organotin compounds : IX. Geminal tintin coupling constants of the type 2J(SntCSn)

Geminal tintin coupling constants 2J(SntCSn) are presented for a number of organotin compounds and discussed in terms of other coupling data. Chemical shift data have also been obtained; particularly noteworthy is the tin chemical shift difference of ca. 40 ppm between the two tin nuclei in 7,7-bis-(trimethylstannyl)norcarane.

PREPARATION OF VINYLPHOSPHINES BY MEANS OF FREE RADICAL ADDITION OF DIPHENYLPHOSPHINE TO ALKYNES AND ALLENES

Abstract Diphenylphosphine adds readily to alkynes and allenes under free radical conditions. Alkynes normally give E -vinylphosphines as the primary (kinetic) product, but Z -vinylphosphines are the main products isolated. Allenes generally give complex product mixtures in which the predominant components are vinyl phosphines formed via addition of the Ph 2 P . radical to the central carbon atom of the allene fragment.

Long-range tin-tin coupling constants: II. Two-bond coupling via carbon☆

Abstract Tin-119 and carbon-13 NMR data for a total of 34 compounds containing the grouping Sn-C-Sn (C is either sp3- or sp2-hybridised) are presented and discussed. In organotin derivatives of alkanes, 2J(Sn-C-Sn) can only be correlated with 1J(Sn-C2) if a sign change for the former coupling is assumed. In most of the compounds of this type studied, 1J(Sn-CH3) is, due to rehybridisation and in contrast to the usual situation, larger than 1J(Sn-C2); the same is true in some cases for distannylakenes, the behaviour of which is complicated by changes in the torsional angle about the carbon-carbon double bond. Thus correlation of 2J(Sn-C-Sn) with other spectral parameters is not possible in these cases. The total tin chemical shift range for compounds MenSn(CH2MME3)4-n (M  C, Si, Ge, Sn; n  0–4) is 140 ppm. Incorporation of a ditin fragment in a six-membered ring causes a downfield tin shift of 30 ppm.

On the relation between element NMR chemical shifts in the fourth main group

Abstract Regression analyses of representative chemical shift data for the isotopes carbon-13, silicon-29, tin-119 and lead-207 show a reasonable carbon-silicon shift correlation (r = 0.825) and very good silicon-tin (r = 0.990) and tin-lead (r = 0.975) correlations. In the latter two cases the observed shift ratios correspond fairly closely to the ratios for the element pairs. Pentacoordination at silicon may be more important than previously realised.