| Oxidative addition to compounds containing metal-metal triple bonds ((sigma)('2)(pi)('4)) results in complexes with an increased coordination number and a decrease in the metal-metal bond order. The results of adding X(,2) (X = Pr('i)O, PhCO(,2), Cl, Br, I, O, H) to M(,2)(OR)(,6)(M(TBOND)M) {M = Mo, W; R = Bu('t)(CMe(,3)), Pr('i)(CMe(,2)), Ne(CH(,2)CMe(,3))} are reported.;Mo(,2)(OPr('i))(,6) reacts with PhCO(,2)O(,2)CPh (benzoyl peroxide) to give Mo(,2)(OPr('i))(,6)(O(,2)CPh)(,2), a compound with a metal-metal bond order of two. Mo(,2)(OBu('t))(,6) reacts with PhCO(,2)O(,2)CPh to form the unstable product, Mo(,2)(OBu('t))(,6)(O(,2)CPh)(,2), which disproportionates to Mo(OBu('t))(,4)(O(,2)CPh)(,2) and an uncharacterized Mo(V) compound. A single crystal X-ray structure determination of Mo(,2)(OBu('t))(,4)(O(,2)CPh)(,2) is reported.;Mo(,2)(OPr('i))(,6) reacts with two equivalents of the halides (Cl(,2), Br(,2), I(,2)) to form Mo(,2)(OPr('i))(,6)X(,4). Single crystal X-ray structure determinations show that these molecules have a metal-metal bond order of one.;Molecular oxygen reacts with Mo(,2)(OR)(,6) to cleave the triple bond, forming MoO(,2)(OR)(,2) and alkoxy radicals. The initial cleavage is proposed to be asymmetric, giving MoO(,2)(OR)(,2) and Mo(OR)(,4). The steric bulk of the Mo(IV) alkoxide determines the next stage of the reaction. Bulky Mo(IV) alkoxides react with oxygen to give MoO(,2)(OR)(,2) and alkoxy radicals. With less bulky alkoxides, the oxy-alkoxy cluster compounds, Mo(,3)O(OR)(,10), Mo(,6)O(,10)(OR)(,12), and Mo(,4)O(,8)(OR)(,4)(py)(,4) are formed. Single crystal X-ray structure determinations on the latter cluster compounds, and on MoO(,2)(OPr('i))(,2)(bipy), are reported.;Mo(,2)(OPr('i))(,6) reacts with Pr('i)OOPr('i) to give Mo(,2)(OPr('i))(,8), a compound containing a metal-metal bond order of two. The bulkier peroxide, Bu('t)OOBu('t), does not react with Mo(,2)(OPr('i))(,6). Likewise, Mo(,2)(OBu('t))(,6) does not react with Pr('i)OOPr('i) or Bu('t)OOBu('t). A Lewis base coordination of Pr('i)OOPr('i) to Mo(,2)(OPr('i))(,6) is proposed, prior to electron transfer. The intermediate {Mo(,2)(OPr('i))(,6)(Pr('i)OOPr('i))}, is prohibited from forming when bulky alkoxides and/or bulky peroxides are present.;Molecular oxygen reacts with W(,2)(OR)(,6) to give W(,2)O(,3)(OR)(,6), compounds with no metal-metal bond. Intermediates in this reaction are proposed, which make this reaction consistent with the reaction pathway proposed for the reaction between Mo(,2)(OR)(,6) and oxygen.;Molecular hydrogen does not react with M(,2)(OR)(,6) or Mo(,2)(OPr('i))(,8). Thermochemical calculations show that the energy needed to break the H-H bond and reduce the metal-metal bond order is larger than the metal-ligand bond energy which would be gained by such a reaction. Mo(,2)(OBu('t))(,4)Me(,2) reacts with H(,2) to give CH(,4), presumably because of the strength of a carbon-hydrogen bond relative to a carbon-molybdenum bond. |
