Protonation and oxidation chemistry of a pentaethylcyclopentadienyl-containing molybdenum(IV) trihydride complex

Compound (CpMoCl4)-Mo-Et (Cp-Et= eta(5)-C5Et5) (1) can be transformed into (CpMoH3)-Mo-Et(dppe) (2) and (CpMoD3)-Mo-Et(dppe) (2-d(3)) [dppe = 1,2-(dip henylphosphino)ethane] by reaction with LiAlX4 (X = H and D, respectively). The protonation and oxidation studies of these two compounds, in compariso n with previously reported studies on (C5Me5) analogs, show important diffe rences that may be attributed to a kinetic stabilization of the products, w hich is steric in nature. Protonation of 2 with HBF, in acetonitrile afford s [(CpMoH4)-Mo-Et(dppe)](+) (3), which only slowly decomposes to [(CpMoH2)- Mo-Et(MeCN)(dppe)](+) (4). Further protonation of the latter affords the mo nohydride species [Cp*MoH(dppe)(MeCN)(2)](2+) in three different forms, 5-7 . Direct protonation of 2 with 2 equiv, of HBF, shows the formation of all of the above compounds, plus a new compound, [(CpMoH3)-Mo-Et(dppe)(MeCN)](2 +) (8), to which a classical structure is assigned. The protonation of 2-d( 3) indicates reversibility for the proton transfer processes. The oxidation of 2 in MeCN affords [2](+), which decomposes slowly in MeCN to afford a m ixture of 4 and 5 as major products. No compound 8, on the other hand, is o btained by oxidation of 2, neither with 1 nor with 2 equiv. of oxidizing ag ent. Mechanistic schemes that rationalize all these observations are propos ed. (C) 2000 Elsevier Science S.A. All rights reserved.