Peter J. Davidson

Tris[bis(trimethylsilyl)methyl]tin(III), R3Sn·: an unusually stable stannyl radical, from photolysis of R2Sn

Photolysis of R2Sn [R =(Me3Si)2CH] with visible light in benzene at ambient temperature yields the stable radical R3Sn·, which has an e.s.r. solution spectrum showing coupling with the methine protons and 119Sn and 117Sn nuclei.

Subvalent Group 4B metal alkyls and amides. Part III Mössbauer spectroscopy studies of bis[bis(trimethylsilyl)methyl]tin(II) and its derivatives

Mossbauer spectra of SnR2[R = CH(SiMe3)2] and of 16 of its derivatives have been recorded. The latter fall into two classes: (i) the dialkylstannylene complexes such as [Cr(CO)5(SnR2)] in which bivalent Sn is three-co-ordinate: and (ii) dialkylstannylene insertion products into C–X, M–H, M–Cl, M–Me, or M–M bonds (M = a transition metal, X = halogen) such as [Fe(η-C5H5)(CO)2(SnR2Cl)], in which quadrivalent tin is four-co-ordinate. The compound SnR2 and class (i) complexes are characterised by isomer shifts of 2.15 ± 0.1 mm s–1 relative to BaSnO3 and large quadrupole splittings [2.31 (for SnR2) or 4.25 ± 0.2 mm s–1 for class (i)]. Class (ii) complexes show lower isomer shifts (1.49 ± 0.25 mm s–1) and quadrupole splittings (<2.37 mm s–1). Magnetic Mossbauer measurements on SnR2 and [Cr(CO)5(SnR2)] show that for both complexes the sign of the quadrupole coupling constant eQVzz, is negative and hence Vzz the principal component of the field gradient tensor, is positive.

Subvalent Group 4B metal alkyls and amides. Part I. The synthesis and physical properties of kinetically stable bis[bis(trimethysilyl)methyl]-germanium(II), -tin(II), and -lead(II)

Two methods are described for the synthesis of the unusual bivalent Group 4B metal alkyls M[CH(SiMe3)2]2(M = Ge, Sn,or Pb)from Li[CH(SiMe3)2] indiethyl ether at 0 to –20°C and (a) the metal(II) chloride (M = Sn or Pb) or (b) M[N(SiMe3)2]2(M = Ge or Sn). At ambient temperature in cyclohexane or benzene the solutions are yellow (Ge), red (Sn), or purple (Pb), and the compounds are monomeric and in a singlet electronic ground state. There are colour changes between the solid and the melt, and the compounds tend to become colourless at –196 °C. The crystal structure of the tin(II) alkyl shows a centrosymmetric dimer with a Sn–Sn bond (2.76 A) similar in length to that in Sn2Ph6, and the two pairs of geminal alkyl groups in a mutually trans arrangement. The solid germanium compound is inferred to be structurally similar because of the presence of a strong polarised Raman line at 300 cm–1. The monomer is believed to be angular with three approximately sp2 hybridised orbitals at the metal, one of which is non-bonding; the dimer. with a SnSn bent double bond, is formed by overlap of the non-bonding orbital of each monomer unit with the orthogonal vacant pz orbital of the other.

Stabilisation of metals in a low co-ordinative environment using the bis(trimethylsilyl)methyl ligand; coloured SnII and PbII alkyls, M[CH(SiMe3)2]2

(Me3Si)2CHLi and SnCl2 in ether at 0° give Sn[CH(SiMe3)2]2, which is diamagnetic at room temperature and behaves chemically as a singlet ‘stannylene’, yielding complexes such as R2SnM′(CO)5(M′= Cr or Mo).

Subvalent Group 4B metal alkyls and amides. Part II. The chemistry and properties of bis[bis(trimethylsilyl)methyl]tin(II) and its lead analogue

Bis[bis(trimethylsiiyl)methyl]tin, SnR2, has an extensive chemistry, behaving as (i) a Lewis base, (ii) a Lewis acid, or (iii) undergoing oxidative addition (insertion reactions). The following complexes have been isolated, many as well characterised crystals. For class (i), these include (M = Cr or Mo)[M(CO)5(SnR2)], trans-[M(CO)4-(SnR2)2], [Fe2(η-C5H5)2(CO)3(SnR2)], [RhCl(PPh3)2(SnR2)], and [PtCl(PEt3)(SnR2)(SnR2Cl)]: for class (ii), the readily thermally-dissociable 1 : 1 adducts with pyridine, 4-methylpyridine, or piperidine, and for class (iii), SnR2(A)B (AB = HCl,HF, MeI, RCl, Cl2, Br, O2, CH2:CMeCMe:CH2, [Mo(η-C5H5)(CO)3X](X = H or Me), [Fe(η-C5H5)(CO)2X](X = Cl or Me), [{Fe(CO)4}2]. and [PtCl2(PEt3)(SnR2)]). An interesting feature is the appearance in the 1H n.m.r. spectra of doublets characteristic of diastereotopicallv distinct SiMe3 groups in compounds of the form SnR2(A)B (A ≠ B). The complex [Mo(CO)5(PbR2)] has also been obtained.