Ring functionalized cyclopentadienyl derivatives of niobium and tantalum: Molecular structures of (η5-C5H4-CO2CH3) M(CO)4 where M = Nb and Ta and (η5-C5H4-CO2CH2C6H5)Nb(CO)4

Article abstract of DOI:10.1016/S0022-328X(97)00225-8

Reaction of Na[M₂(μ-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 (η⁵-C₅H₄R)M(CO)₄, or (η⁵-C₉H₇)M(CO)₄ compounds in good yield. NaC₅H₄COCH₂C₆H₅, a new cyclopentadienyl synthon, was used to prepare TlC₅H₄COCH₂C₆H₅, and (η⁵-C₅H₄COCH₂C₆H₅)Mn(CO)₃. The latter was fully characterized as a model compound for the new ligand. The niobium and tantalum compounds are air-stable as solids but readily undergo oxidation in solution. Compounds were characterized by IR, ¹H and ¹³CNMR spectroscopies, and elemental analyses. Molecular structures of three compounds were determined. (η⁵-C₅H₄CO₂CH₃)Nb(CO)₄: monoclinic, P2₁/c, a = 12.664(6) A, b = 6,390(3) A, c,= 15.355(9) A, β = 97.81(4)°, V= 1231(1) A³, Z = 4, and A(F) = 3.90%. (η⁵-C₅H₄CO₂CH₃)Ta(CO)₄: monoclinic, P2₁/c, a = 12.612(4) A, b = 6.399(1) A, c, = 15.273(6) A, β = 97.89(3)°, V= 1220.9(4) A³, Z = 4, and R(F) = 5.67%. (η⁵-C₉H₇)Nb(CO)₄: monoclinic, P2¹/c, a = 16.353(2) A, b = 7.959(1) A, c, = 12.778(4) A, β = 106.14(2)°, V= 1597.7(6) A³, Z = 4, and R(F) = 2.48%.