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RESEARCH PRODUCT

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

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International audience; Compound CpEtMoCl4 (CpEt=η5-C5Et5) (1) can be transformed into CpEtMoH3(dppe) (2) and CpEtMoD3(dppe) (2-d3) [dppe=1,2-(diphenylphosphino)ethane] by reaction with LiAlX4 (X=H and D, respectively). The protonation and oxidation studies of these two compounds, in comparison with previously reported studies on (C5Me5) analogs, show important differences that may be attributed to a kinetic stabilization of the products, which is steric in nature. Protonation of 2 with HBF4 in acetonitrile affords [CpEtMoH4(dppe)]+ (3), which only slowly decomposes to [CpEtMoH2(MeCN)(dppe)]+ (4). Further protonation of the latter affords the monohydride species [Cp*MoH(dppe)(MeCN)2]2+ in three different forms, 5–7. Direct protonation of 2 with 2 equiv. of HBF4 shows the formation of all of the above compounds, plus a new compound, [CpEtMoH3(dppe)(MeCN)]2+ (8), to which a classical structure is assigned. The protonation of 2-d3 indicates reversibility for the proton transfer processes. The oxidation of 2 in MeCN affords [2]radical dot+, which decomposes slowly in MeCN to afford a mixture of 4 and 5 as major products. No compound 8, on the other hand, is obtained by oxidation of 2, neither with 1 nor with 2 equiv. of oxidizing agent. Mechanistic schemes that rationalize all these observations are proposed.