DIRECT OBSERVATION OF LIGAND MIGRATION IN THE REVERSIBLE ADDITION OF TRIMETHYLPHOSPHINE TO 1,2-MO2(CH2PH)2(O-I-PR)4 AND STRUCTURAL CHARACTERIZATION OF (PME3)(PHCH2)2(I-PRO)MO-EQUIVALENT-TO-MO(O-I-PR)3 AND 1,2-MO2(CH2PH)2(O-I-PR)4(DMPM), WHERE DMPM = BIS(DIMETHYLPHOSPHINO)METHANE

Addition of PMe3 (1-2 equiv) to hydrocarbon solutions of 1,2-Mo2(CH2Ph)2(O-i-Pr), (I) at 22-degrees-C leads to an equilibrium mixture of I, free PMe3, and (PMe3)(PhCH2)2(i-PrO)Mo=Mo(O-i-Pr)3 (II). Compound II is an orange crystalline solid that loses PMe3 upon heating in vacuo (slowly at room temperature and rapidly at +50-degrees-C) with the regeneration of I. Addition of 2 equiv of PMe3 to I in toluene-d8 at -80-degrees-C yields a bisphosphine adduct (PMe3)(PhCH2)(i-PrO)2Mo=Mo(O-i-Pr)2(CH2Ph)(PMe3) that yield II upon warming to +20-degrees-C by way of an intermediate. When the solution is cooled, an unsymmetrical bisphosphine adduct (PMe3)(PhCH2)2(i-PrO)Mo=Mo(O-i-Pr)3(PMe3) is formed at -80-degrees-C. The latter forms II reversibly by PMe3 loss upon warming. Addition of dmpm to I in hexane or toluene (at -60-degrees-C) yields 1,2-Mo2-(CH2Ph)2(O-i-Pr)4(mu-dmpm) (III), where dmpm = bis(dimethylphosphino)methane. Compound III was isolated at -25-degrees-C by crystallization. In toluene-d8 and at room temperature, the H-1 and P-31 NMR spectra indicate the presence of an isomeric form of III, (eta1-dmpm)(PhCH2)2(i-PrO)Mo=Mo(O-i-Pr)3. Addition of dmpe (1 equiv) to hydrocarbon solutions of I yields an insoluble crystalline material MO2(CH2Ph)2(O-i-Pr)r(dmpe) (IV), where dmpe = 1,2-bis(dimethylphosphino)ethane. Compound IV is sparingly soluble in tetrahydrofuran and upon photolysis in the presence of additional dmpe compound IV is converted to Mo2(O-i-Pr)4(dmpe)2 and bibenzyl. Crystal data: for II at -159-degrees-C a = 16.779 (3) angstrom, b = 10.104 (1) angstrom, c = 19.555 (4) angstrom, beta = 90.59 (10)-degrees, Z = 4, d(calcd) = 1.38 g cm-3 and space group P2(1)/c; for III at -168-degrees-C a = 14.952 (2) angstrom, b = 29.252 (4) angstrom, c = 17.637 (2) angstrom, beta = 111.05 (1)-degrees, Z = 8, d(calcd) = 1.38 g cm-3, and space group P2(1)/n.