NEW HETEROSILOXANES OF BIVALENT GROUP-14 ELEMENTS AND THEIR REACTIONSWITH [MO(CO)(6)] - CRYSTAL-STRUCTURES OF [(M(MU-OBU(T))-(OSIPH(3)))(2)] (M=GE OR SN) AND [(SN(MU-OBU(T))(OSIPH(3)))MO-2(CO)(5)]

The protolysis of Ph(3)SiOH with a toluene solution of [{M(OBu(t))(2)} (n)] (M = Ge-II or Sn-II, n = 2; M = pb(II), n = 3) in 1:1 molar ratio at room temperature via alcohol elimination facilitated the isolation of high yields of heteroleptic alkoxosiloxides of the type [{M(mu-OBu (t))(OSiPh(3))}(2)] (M = Ge-II 1, Sn-II 2 or Pb-II 3). Crystal structu ral analyses of compounds 1 and 2 revealed them to be isomorphous and isostructural. Both the dimeric structures feature a perfect planar M( 2)O(2) (M = Sn 1 or Ge 2) core with a crystallographically imposed cen tre of inversion. Each metal atom is bound to two bridging tert-butoxi de ligands and one terminal triphenylsiloxide ligand resulting in a tr igonal-pyramidal co-ordination geometry around the metal atom. The ste reochemical activity of the lone pair of electrons present on the meta l atoms of 1 and 2 is demonstrated by their ability to form M-Mo bonds in [{M(mu-OBu(t))(OSiPh(3))}(2)Mo(CO)(5)] (M = Ge 4 or Sn 5) on their reaction with an equimolar amount of [Mo(CO)(6)] in refluxing toluene via displacement of CO from the inner co-ordination sphere of [Mo(CO) (6)]. The asymmetry in compound 5 was revealed by its crystal structur e. The structure consists of a four-co-ordinate tin(n) centre, bearing an Mo(CO), unit, linked via two bridging tert-butoxide groups to anot her Sn-II which exhibits (3 + 6) co-ordination with three normal Sn-O bonds and a weak tin(II)-arene (eta(6)) interaction originating from t he orientation of a phenyl ring of the OSiPh(3) ligand such that the t in to ring centre distance is 3.58 Angstrom. The identity of all the c ompounds in solution has been confirmed by multinuclear (H-1, C-13, Si -29, Sn-119 and Pb-207) NMR and IR spectra and elemental analyses.