SYNTHESIS AND REACTIVITY OF BIS(ETA-CYCLOPENTADIENYL) TRIMETHYLTIN DERIVATIVES OF NIOBIUM - CRYSTAL AND MOLECULAR-STRUCTURE OF [[NB(ETA-C5H5)2(SNME3)]2(MU-O)]

The reaction between [Nb(eta-C5H5)2H3] and LiBu followed by SnMe3Cl gives [Nb(eta-C5H5)2H2(SnMe3)] 2, also produced from [Nb(eta-C5H5)2H3] and SnMe3H. Heating 2 with styrene, PMe3, isoprene or but-2-yne gives [Nb(eta-C5H5)2L(SnMe3)] (L = eta-H2C = CH-C6H5, 3; PMe3, 4; eta-H2C = CHCMe = CH2, 5; or eta-C2Me2 6). Photolysis of complex 3 in the presence of CO, 2,6-Me2C6H3NC, MeCN, or PMe3 gives [Nb(eta-C5H5)2L(SnMe3)] (L = CO, 7; 2,6-Me2C6H3NC, 8; eta-2-MeCN, 9a and 9b; or PMe3, 4). Heating 3 with H-2 regenerates 2 and releases styrene. Compound 3, 5 or 6 reacts with SnMe3H to give the bis(stannyl) derivative [Nb(eta-C5H5)2H(SnMe3)2] 10, which is also formed by prolonged heating of [Nb(eta-C5H5)2H2(SnMe3)] with SnMe3H. Photolysis of 3 under CO2 gives a mixture of 7 and [{Nb(eta-C5H5)2(SnMe3)}2(mu-O)] 11 by cleavage of the CO2 molecule. Compound 11 crystallises in the orthorhombic space group Pbca with a = 8.409(3), b = 21.109(4) and c = 15.582(3) angstrom. The bridging oxygen atom sits on a crystallographic inversion centre giving a linear Nb-O-Nb group with Nb-O 1.9434(4) and Nb-Sn 2.8619(5) angstrom.