In this paper, the mechanism of alkyne metathesis catalyzed by W/Mo alkylidyne complexes has been theoretically investigated with the aid of density functional theory calculations. Calculations on various model alkylidyne complexes M( CMe)(OR)(3) (M = W, Mo; R = Me, CH2F), W( CMe)(NMe2)(3), and W( CMe)(Cl)(3) allow us to examine the factors that influence the reaction barriers. In the reaction mechanism, metallacyclobutadienes are initially formed from a ring-closing step between alkynes and alkylidyne complexes. A ring-opening step then gives the metathesis products.
Treatment of OsHCl(PPh3)(3) with allenes CH2=C=CHR at room temperature in benzene produced the vinyl complexes OsCl(C(CH3)=CHR)(CH2=C=CHR)-(PPh3)(2), instead of eta(3)-allyl complexes as normally observed. DFT calculations show that the formation of the vinyl complex is favored kinetically.
B3LYP density functional theory calculations have been carried out to examine the structural and energetic aspects of β-hydrogen elimination in several metallacyclic complexes of ruthenium and platinum. Factors affecting barriers of the elimination reactions have been examined. It was found that favorable structural arrangements, in which the transferring β-hydrogen is in close proximity to the metal center, for β-hydrogen elimination exist in certain ring conformations of metallacyclic complexes.
The η2-dihydrogen complex [TpRu(L2)(H2)]+ (L2 = dppm, dppp, or (PPh3)2) prepared in situ by protonation of the hydride precursor reacts with O2 to yield the paramagnetic RuIII-superoxo complex [TpRuIII(L2)(O2)]+, in which antiferromagnetic coupling between the RuIII ion (d5, S = 1/2) and the coordinated superoxide radical (S = 1/2) does not seem to be present.