Carbonylniobium Chemistry, IV [1] Derivatives of ^5-C5H5Nb(CO)4 with Tridentate Phosphines

Recent investigations into the coordinative properties of oligodentate phosphorus ligands towards carbonylvanadium and -niobium complexes in our laboratory have lead to a large body of systematic IR, 31P and metal NMR data, including those on CpV(C0)4 and CpNb(C0)4 derivatives with ditertiary [2-5] and tritertiary phosphines [6, 7]. In this communication, we report on the reaction pattern observed in the system CpNb(CO)4/Ph2P(CH2)2PR(CH2)2PPh2 (R = Ph: L1, R = Cy: L2), emphasizing the spectral properties of the new carbonylcyclopentadienylphosphineniobium complexes in the context of comparative studies within the vanadium triad. The data are collected in Table I ; data on representative complexes containing the ligands Ph2P(CH2)wPPh2 (n = 2: p2(2), n = 5: p2(5)) are included. The complexes a's-[CpNb(CO)2L] are formed during UV irradiation of THF solutions containing CpNb(CO)4 and L in equimolar amounts. The 31P NMR spectra clearly reveal that chelating fivemembered rings are formed exclusively: the sole