IMPROVED SYNTHESIS OF (ETA(5)-CPR)M(CO)(4) COMPOUNDS AND THE NUJOL MATRIX PHOTOCHEMISTRY OF (ETA(5)-C5H5)M(CO)(4) AND (ETA(5)-C9H7)M(CO)(4), WHERE M = NB AND TA

Improved preparative routes for cyclopentadienyl (Cp) and substituted Cp(CO)(4) derivatives of niobium and tantalum and their precursors are described. New compounds are fully characterized by IR, NMR, and elem ental analysis. The molecular structures of five compounds were determ ined: (vinylCp)Nb(CO)(4): triclinic, P (1) over bar, a = 6.770(1) Angs trom, b = 6.937(1) Angstrom, c = 12.706(2) Angstrom, alpha = 90.42(1) Angstrom, beta = 91.07(1)degrees, gamma = 105,560(8)degrees, V = 574.7 1(12) Angstrom(3), Z = 2, R(F) = 2.82; (acetylCp)Nb(CO)(4): monoclinic , P2(1)/c, a = 10.316(2) Angstrom, b = 14.490(3) Angstrom, c = 7.957(3 ) Angstrom, beta = 94.68(2)degrees, V = 1185.4(4) Angstrom(3), Z = 4, R(F) = 2.58; (Cp)Ta(CO)(4): orthorhombic, Pnma, a = 7.756(1) Angstrom, b = 12.159(2) Angstrom, c = 10.580(1) Angstrom, V = 997.7(2) Angstrom (3), Z = 4, R(F) = 2.60; (indenyl)Ta(CO)(4): monoclinic, P2(1)/n, a = 6.602(2) Angstrom, b = 12.399(1) Angstrom, c = 7.4775(9) Angstrom, bet a = 92.05(2)degrees, V = 611.2(2) Angstrom(3), Z = 2, R(F) = 3.05; and (benzoylCp)Ta(CO)(4): monoclinic, P2(1)/c, a = 12.552(10) Angstrom, b = 6.5247(2) Angstrom, c = 18.4682(2) Angstrom, beta = 98.9152(4)degre es, V = 1494.24(5) Angstrom(3), Z = 4, RF) = 2.83 are reported. Photol ysis of CpMCO)(4) and indenyl)MCO)(4), where M = Nb and Ta, in Nujol g lass matrices were found to result in loss of one to three CO ligands as a function of the wavelength of the incident light. Annealing or re verse photolysis resulted in reversal of these CO-loss reactions. (C) 1998 Elsevier Science S.A. All rights reserved.