Synthesis and oxidation reactions of the unsaturated anion [Mn-2(CO)(6)(mu-Ph2PCH2PPh2)](2-)

Chemical reduction of the unsaturated dihydride [Mn-2(mu -H)(2)(CO)(6)(mu - dppm)] (dppm = Ph2PCH2PPh2) with several reagents (Na-Hg, K, etc.) promotes dihydrogen elimination to yield the deep green anion [Mn-2(CO)(6)(mu -dppm )](2-). Oxidation of the latter with [FeCp2]PF6 (Cp = eta (5)-C5H5) gives t he GO-bridged species [Mn-2(mu-eta (1):eta (2)-CO)(CO)(6)(mu -dppm)] or, if PR3 is present, the related complexes [Mn-2(mu-eta (1):eta (2)-CO)(CO)(5)( PR3)(mu -dppm)] (R = Ph, OMe), Oxidation of the anion in the presence of ni triles or l-alkynes gives nitrile or vinylidene-bridged derivatives [Mn-2(m u-eta (1): eta (2)-L)(CO)(6)(mu -dppm)] with high yield (L = NCR or CCHR), The complexes having the (mu-eta (1):eta (2)-CO) ligand display dynamic beh avior in solution and react readily with CO to give the corresponding [Mn-2 (CO)(7)L(dppm)] (L = CO, PR3), Diazocompound CH(SiMe3)N-2 also adds readily to [Mn-2(mu-eta (1):eta (2)-CO)(CO)(6)(mu -dppm)], but the C-Si bond in th e initial product is easily hydrolyzed to yield the diazomethane complex [M n-2(mu -CO)(mu-eta (1):kappa (1)-CH2N2)(CO)(6)(mu -dppm)]. The structure of the new complexes is analyzed in the light of their IR and variable-temper ature NMR spectra, and possible reaction pathways for the above oxidation p rocesses are proposed on the basis of the nature of the compounds actually isolated and that of the detected intermediates. The structure of the new c ompounds [Mn-2(mu-eta1(:)eta (2)-CO)(CO)(5){P(OMe)(3)}(mu -dppm)] and [Mn-2 (CO)(7)(PPh3)(mu -dppm)] has been solved through single-crystal X-ray diffr action studies.