HEXACOORDINATED GROUP-14 ELEMENTS WITH PHOSPHORUS DONOR LIGANDS - SYNTHESES AND STRUCTURES OF ME(2)E[C(PME(2))(2)(SIME(3))](2) (E=SI,GE,SN)

The dimethyl group-14 element dihalides Me(2)EX(2) (E = Si, Ge, Sn; X= Cl or Br) react with two equivalents of Li[C(P-Me(2))(2)(SiMe(3))] to give the cis-hexacoordinated complexes Me(2)E[C(PMe(2))(2)(SiMe(3))]( 2) (E = Si: 2a, E = Ge: 2b, E = Sn: 2c), which were characterized spec troscopically and by means of X-ray structure determinations. Whereas 2a and 2b are isotypic and crystallize in the space group P2(1)/c, 2c crystallizes in the space group C2/c with crystallographic C-2(2) mole cular symmetry. In all cases the diphosphanylmethanide ligands bind in an unisobidentate fashion. For compound 2c, this still can be attribu ted to the trans influence of the methyl group, but in 2a and 2b clear ly borderline cases between hexa- and tetracoordination are found. Com pound 2b (E = Ge) is much more on the side of tetracoordination than 2 a, thus underlining the importance of small polarity differences for t he actual coordination number achieved in compounds with relatively un polar bonds.