RING FUNCTIONALIZED CYCLOPENTADIENYL DERIVATIVES OF NIOBIUM AND TANTALUM - MOLECULAR-STRUCTURES OF (ETA(5)-C5H4-CO2CH3)M(CO)(4) WHERE M = NB AND TA AND (ETA(5)-C5H4-CO2CH2C6H5)NB(CO)(4)

Reaction of Na[M-2(mu-Cl)(3)(CO)(8)], where M = Nb or Ta, with NaC5H4R , where R = COCH3, CO2CH3, CO2C2H5, COC6H5, COCH2C6H5, LiC5H4C(CH3)CH2 , or NaC9H7 gives the corresponding (eta(5)-C5H4R)M(CO)(4), or (eta(5) -C9H7)M(CO)(4) compounds in good yield. NaC5H4COCH2C6H5, a new cyclope ntadienyl synthon, was used to prepare TlC5H4COCH2C6H5, and (eta(5)- C 5H4COCH2C6H5)Mn(CO)(3). The latter was fully characterized as a model compound for the new Ligand. The niobium and tantalum compounds are ai r-stable as solids but readily undergo oxidation in solution. Compound s were characterized by IR, H-1 and (CNMR)-C-13 spectroscopies, and el emental analyses. Molecular structures of three compounds were determi ned. (eta(5)-C5H4CO2CH3)Nb(CO)(4): monoclinic, P2(1)/c, a = 12.664(6) Angstrom, b = 6.390(3) Angstrom, c, = 15.355(9) Angstrom, beta = 97.81 (4)degrees, V = 1231(1) Angstrom(3), Z = 4, and R(F) = 3.90%. (eta(5)- C5H4CO2CH3)Ta(CO)(4): monoclinic, P2(1)/c, a = 12.612(4) Angstrom, b = 6.399(1) Angstrom, c, = 15.273(6) Angstrom, beta = 97.89(3)degrees, V = 1220.9(4) Angstrom(3), Z = 4, and R(F)= 5.67%. (eta(5)-C9H7)Nb(CO)( 4): monoclinic, P2(1)/c, a = 16.353(2) Angstrom, b = 7.959(1) Angstrom , c, = 12.778(4) Angstrom, beta = 106.14(2)degrees, V = 1597.7(6) Angs trom(3), Z = 4, and R(F) = 2.48%. (C) 1997 Elsevier Science S.A.