4-LEGGED PIANO STOOL MOLYBDENUM(II) COMPOUNDS WITHOUT CARBONYL LIGANDS .2. REACTIONS OF (ETA-5-C5R5)MOCL(PME3)3 (R = H, ME) WITH NEUTRAL DONORS

Substitution of a PMe3 ligand of compound CpMoCl(PMe3)3 (1) with L affords CpMoCl(PMe3)2L molecules (L = N2 (2), C2H4 (3)). No analogous products are obtained with propene or butene. Neither does Cp*MoCl(PMe3)3 (1*) react in an analogous fashion with ethylene. NMR investigations show that the dinitrogen complex has a trans configuration of the monodentate ligands in the four-legged piano stool geometry, whereas the ethylene complex is present in solution as a mixture of cis and trans isomers, the cis isomer being the prevalent one (10:1 in benzene-d6; 33:1 in acetone-d6). The olefin ligand in the cis isomer does not freely rotate around the Mo-C2H4 bond on the NMR time scale, and its conformation has been established by a combination of selective decoupling, NOE, and H-1-C-13 COSY-NMR experiments. Interaction of 1 with butadiene affords CpMoCl(PMe3)(eta(4)-C4H6) (4), which can also be obtained directly from CpMoCl2, butadiene, PMe3, and Na/Hg. No analogous reactions occur with 2,3-dimethylbutadiene or cycloheptatriene. The corresponding Cp* compound, 4*, has been obtained by reduction of Cp*MoCl4(PMe3) with Na/Hg in the presence of butadiene. Compound 1 interacts with diphenylacetylene to afford the salt [CpMo(PMe3)2(PhCCPh)]+Cl- (5). Compound 3 reacts with LiEt3BH or EtMgBr to afford CpMoH(C2H4)(PMe3)2 (6), which is fluxional at room temperature and decoalesces into a 47:53 mixture of cis and trans isomers at low temperature. Compound 6 was also obtained from 1 and EtMgBr. Interaction of 6 with PMe3 results in C2H4 substitution rather than insertion into the Mo-H bond. Alkylation of 3 with MeLi generates CpMo(CH3)(C2H4)(PMe3)2 (7), which is stable at T less-than-or-equal-to 60-degrees-C and is present exclusively as the cis isomer. Warming transforms the latter compound into CpMo(eta(2)-CH2PMe2)(C2H4)(PMe3) (8) with elimination of methane.