SYNTHESIS OF MONO(SILYL) AND BIS(SILYL) COMPLEXES OF TANTALUM

Thermal (ca. 110-degrees-C) or photochemical (350 nm) reaction of Cp2Ta(H)3 (Cp = eta-5-C5H5) or Cp2Ta(L)(H) (L = CO, PMe3, CH2 = CH2) with hydrosilanes (HSiR3) produces the tantalum (V) dihydride silyl complexes Cp2Ta(H)2(SiR3) (1-6; SiR3 = SiH3, SiMeH2, SiMe2H, SiMe3, SiMe2Cl, Si(OMe)3) in good to excellent yields. Two structural isomers of the complexes are observed. The major isomer has a symmetrical structure, with the silyl group occupying the central position between two equivalent hydride positions. In contrast, the silyl occupies a lateral position in the minor isomer, giving rise to two unique hydride environments (central and lateral). The tantalum(V) bis(silyl) complexes Cp2Ta(H)(SiR3)2 (7-11; SiR3 = SiMeH2, SiMe2H, SiMe3, SiMe2Cl, Si(OMe)3) can be prepared by treatment of the tantalum(III) methyl complexes Cp2Ta(L)(CH3) with excess hydrosilane. In most cases, only the symmetrical isomer with both silyls in lateral positions is observed, although both isomers have been observed for Cp2Ta(SiMeH2)2(H). Thermolysis of the bis(silyl) complexes in the presence of excess PMe3 leads to high yields of the corresponding tantalum(III) mono(silyl) complexes Cp2Ta(PMe3)(SiR3) (12-15; SiR3 = SiMeH2, SiMe3, SiMe2Cl, Si(OMe)3). Carbonyl derivatives Cp2Ta(CO)(SiR3) (17, 18; SiR3 = SiMe3, Si(t-Bu)2H) were prepared by ligand displacement from the corresponding phosphine complexes. Compounds 8 and 13 have been characterized by single-crystal X-ray diffraction studies. 8: orthorhombic space group P2(1)2(1)2(1) (Z = 4) with a = 7.989 (1) angstrom, b = 8.822 (1) angstrom, c = 23.100 (3) angstrom, and V = 1628.0 (6) angstrom 3. 13: orthorhombic space group P2(1)2(1)2(1) (Z = 4) with a = 8.131 (1) angstrom, b = 9.124 (2) angstrom, c = 25.004 (2) angstrom, and V = 1854.9 (8) angstrom 3.