Alkene-alkyl interconversion: an experimental and computational study of the olefin insertion and beta-hydride elimination processes

摘要

The preparation and characterization of various alkyl, allyl or alkene Rh(III) and Ir(III) complexes as well as studies on the intramolecular reactions leading to transformation of one into another are reported. The silyl-hydrido-Rh(III) complex {Rh(H)[SiMe(o-C6H4SMe)(2)](PPh3)}[BAr4F], with a vacant coordination site, reacts with 1,5-cyclooctadiene (cod) leading to olefin insertion into the Rh-H bond and rearrangement to yield the 16e cyclooctenyl-Rh(iii) complex {Rh(eta(3)-cyclooctenyl)[SiMe(o-C6H4SMe)(2)]}[BAr4F] (1). This compound can be also synthesized by reaction of the 18e chloride precursor {Rh(eta(3)-cyclooctenyl)[SiMe(o-C6H4SMe)(2)]Cl} with NaBAr4F. The reaction of the thioether-silane SiMeH(o-C6H4SMe)(2) with [Rh(nbd)Cl](2) (nbd = norbornadiene) leads to {Rh(sigma-ntyl)[SiMe(o-C6H4SMe)(2)]Cl} (ntyl = nortricyclyl) (2). The abstraction of chloride from this neutral 16e ntyl-Rh(iii) complex with NaBAr4F results in the unusual isomerization of sigma-nortricyclyl into sigma,pi-norbornenyl forming the 16e and cationic {Rh(sigma,pi-nbyl)[SiMe(o-C6H4SMe)(2)][BAr4F] (nbyl = norbornenyl)} compound 3. Coordinatively saturated {Ir((3)-cyclooctenyl)[SiMe(o-C6H4SMe)(2)]Cl} (4) has been synthesized by the reaction of [Ir(cod)Cl](2) with SiMeH(o-C6H4SMe)(2). The reaction of 4 with NaBAr4F led to the formation of the unsaturated and cationic Ir(iii) compound {Ir(eta(3)-cyclooctenyl)[SiMe(o-C6H4SMe)(2)]}[BAr4F] (5). Compound 5 shows low stability in solution and undergoes successive beta-hydride elimination and olefin insertion steps, which were elucidated by DFT calculations, to form 18e {Ir(H)[SiMe(o-C6H4SMe)(2)](eta(4)-cod)}[BAr4F] (6).