NEW COORDINATION ENVIRONMENTS FOR YTTRIUM FORMED IN-SITU BY HETEROMETALLIC BRIDGING - CRYSTAL-STRUCTURES OF (C(5)H(4)SIME(3))Y[(MU-OCME(3))(MU-ME)ALME(2)](2) AND (ME(3)SICH(2))Y[(MU-CH2)(2)SIME(2)][(MU-OR)LI(THF)(2)](2)

The bimetallic yttrium complexes [(C(5)R(5))Y(mu-OCMe(3))(OCMe(3))](2) react with aluminum and lithium organometallic reagents to give complexes containing new combinations of ligands held together by heterometallic bridging atoms. [(C(5)H(4)SiMe(3))Y(mu-OCMe(3))(OCMe(3))](2), 1, reacts with AlMe(3) to form the mixed-metal mixed-ligand complex (C(5)H(4)SiMe(3))Y[(mu-OCMe(3))(mu-Me)AlMe(2)](2), 2, which contains a formally seven-coordinate yttrium linked to two four-coordinate aluminum atoms by bridging methyl and tert-butoxide ligands. Complex 2 contains two four-membered Y-O-Al-Me rings. [(C9H7)Y(mu-OR)(OR)](2), 3, reacts with LiCH(2)SiMe(3) to give a mixture of products from which (Me(3)SiCH(2))Y[(mu-CH2)(2)SiMe(2)][(mu-OR)Li(THF)(2)](2), 4, can be isolated by crystallization from hexane/THF. Complex 4 contains a pentacoordinate yttrium atom ligated by a terminal CH(2)SiMe(3) group, two bridging tert-butoxide ligands, and the two bridging methylene moieties of a (mu-CH2)(2)SiMe(2) group. Each lithium atom is coordinated to two molecules of THF and the alkoxide and methylene bridges. The bridging groups combine to make three fused four-membered metallacyclic rings, two Y-O-Li-C rings and one Y-C-Si-C ring. The structures of 2 and 4 were determined by single crystal X-ray diffraction studies.