Synthesis and characterization of arene, mono-and dihydrido-arene, monohydrido-cyclopentadienyl, and phosphite complexes of molybdenum containing the tridentate ligand PhP (CH2CH2PPh2)2

Article abstract of DOI:10.1016/s0020-1693(98)00162-5

The reduction of [MoCl₃(TRI)], where TRI = PhP(CH₂CH₂PPh₂)₂, with sodium amalgam in benzene, toluene or anisole resulted in the formation of the corresponding [Mo(η⁶-arene) (TRI)] complex. Each complex displayed a reversible one-electron oxidation in the cyclic voltammogram at ～ - 1.0 V versus the ferrocenium/ferrocene couple at 0.0 V, corresponding to the oxidation of Mo(0) to Mo(1+). A second pseudo-reversible oxidation occurred at ～0.7 V more positive. Monoprotonation of the arene complexes with CF₃COOH in THF resulted in the isolation of [Mo(H)(η⁶-arene)(TRI)][CF₃COO] (δ(MoH) ～ - 6 ppm). In neat CF₃COOH or HBF₄, evidence of diprotonation of the arene complexes was observed in the ¹H NMR spectra. Upon work-up, only the monoprotonated product was isolated. [Mo(TRI)(P(OMe)₃)] was formed by the reduction of [MoCl₃(TRI)] in the presence of a small excess of P(OMe)₃. Attempts to prepare [Mo(TRI)(PMe₃)₃] by a similar method resulted in a product that readily absorbed N₂ to form fac-[Mo(N₂)(TRI)(PMe₃)₂]. Yellow [Mo(H)(η⁵-C₅H₅)(TRI)] was formed by (i) the reduction of [MoCl₃(TRI)] with sodium amalgam in the presence of cyclopentadiene, or (ii) heating fac-[Mo(N₂)(TRI)(PMe₃)₂] with cyclopentadiene in heptane, or (iii) heating trans-[Mo(N₂)₂(TRI)(PPh₃)] with cyclopentadiene in THF.