Synthesis and Oxidation Reactions of the Unsaturated Anion [Mn2(CO)6(μ-Ph2PCH2PPh2)]2-

Abstract

Chemical reduction of the unsaturated dihydride [Mn2(μ-H)2(CO)6(μ-dppm)] (dppm = Ph2PCH2PPh2) with several reagents (Na−Hg, K, etc.) promotes dihydrogen elimination to yield the deep green anion [Mn2(CO)6(μ-dppm)]2-. Oxidation of the latter with [FeCp2]PF6 (Cp = η5-C5H5) gives the CO-bridged species [Mn2(μ-η1:η2-CO)(CO)6(μ-dppm)] or, if PR3 is present, the related complexes [Mn2(μ-η1:η2-CO)(CO)5(PR3)(μ-dppm)] (R = Ph, OMe). Oxidation of the anion in the presence of nitriles or 1-alkynes gives nitrile or vinylidene-bridged derivatives [Mn2(μ-η1:η2-L)(CO)6(μ-dppm)] with high yield (L = NCR or CCHR). The complexes having the (μ-η1:η2-CO) ligand display dynamic behavior in solution and react readily with CO to give the corresponding [Mn2(CO)7L(dppm)] (L = CO, PR3). Diazocompound CH(SiMe3)N2 also adds readily to [Mn2(μ-η1:η2-CO)(CO)6(μ-dppm)], but the C−Si bond in the initial product is easily hydrolyzed to yield the diazomethane complex [Mn2(μ-CO)(μ-η1:κ1-CH2N2)(CO)6(μ-dppm)]. The structure of the new complexes is analyzed in the light of their IR and variable-temperature NMR spectra, and possible reaction pathways for the above oxidation processes are proposed on the basis of the nature of the compounds actually isolated and that of the detected intermediates. The structure of the new compounds [Mn2(μ-η1:η2-CO)(CO)5{P(OMe)3}(μ-dppm)] and [Mn2(CO)7(PPh3)(μ-dppm)] has been solved through single-crystal X-ray diffraction studies.