| The osmium compounds of general formula OsHClL′ L2 (L′ = H2, HCl, PPh 3; L = PiPr3, PtBu2Me) are the reagents of our choice in this work to study new synthetic methodologies for osmium carbene and carbyne compounds. Fischer carbenes OsHCl(=C(OR)CH 3)L2 are accessible from OsH3ClL2 and vinyl ethers H2C=CH(OR) (R Et, Ph, (CH2)3), whereas Schrock carbenes OsCl(O2CX)(=CHCH3)L2 are obtained when reacting OsH3Cl(PiPr3) 2 and OsHCl(PPh3)3 with vinyl acetates H 2C=CHO(CO)X (X = CF3, Cl). The Fischer carbenes are metastable for R = Et, Ph, and the decomposition pathways are dependent on R and their rate on L. For R = Et, EtOH elimination occurs affording the vinylidene complex OsHCl(=C=CH2)L2, a process that is slower for bulkier phosphines. For R = Ph, migration of OPh occurs through an acid-catalyzed process, and the final product is OsHCl(OPh)(CCH3)(PiPr 3)2. Unselective decomposition occurs upon heating when L = PtBu2Me. The Schrock carbenes are also metastable and decompose through two different processes: proton migration to afford carbynes OsHCl(O2CX)(CCH3)L2 and halide redistribution to afford OsCl2(=CHCH3)L2. These dichlorocarbenes, then, experience H-migration to afford the analogous carbynes. When X = Cl, decarboxylation occurs producing the dichlorocarbene.; When the olefin of our study contains C-F bonds, H2C=CXF (X = H, F), the final product OsHCl(F)(CCH3)L2 that we obtain is independent of the degree of fluorination of the starting olefin. Our low temperature experiments suggest an HF catalyzed mechanism dependent on X: via the carbene OsFCl(=CHCH3)L2 when X = H, but via the carbene OsHCl(=CFCH3)L2 when X = F.; We are also interested in the mechanism for C-H activation of cyclic ethers and amines. The mechanism is elucidated by detection of all the intermediates involved through low temperature experiments. The cyclic carbenes OsH xCl(=CECnHn+2)(PiPr3) 2 (E = O, n = 1, x = 1; E = NH, n = 3, 4, x = 3) are synthesized and the dependence of x on E rationalized.; Finally, the synthesis of new osmium complexes Os(H)2(EC(R)C 5H3E′)(PiPr3) 2 (R = H E,E′ = O,O; O,NH; NH,NH; NH,NMe and R = Me, E,E′ = O,O; NH,NH) is achieved when reacting OsH 3Cl(PiPr3)2 and the chelating ligand (E E′ = nitrogen-based ligand) or the monolithium salt of the ligand (E or E′ = O-based ligand). Their structure, reactivity and fluxionality are systematically studied. |
