Pentamethylcyclopentadienyl-rhodium and -iridium complexes. Part X. The kinetics of the reactions of some cyclic and acyclic dienes with µ-hydrido-compounds

Abstract

The µ-hydrido-complexes [{M(C₅Me₅)}₂HCl₃](2a; M = Rh) and (2b; M = Ir) react readily with cyclo-octa-1,3- and -1,5-diene, cyclohexa-1,3- and -1,4-diene, to give the cyclic η-allylic complexes which reductively decompose to give [M^I(C₅Me₅)diene]. The rate of the reaction of the hydride with a variety of cyclic and acylic dienes was shown to be first order in hydride and zero order in diene and to be independent of the nature of the diene. The rate-determining step is proposed to be opening of the metal-halide and not the metal-hydride bridge of (2). Cyclopentadiene gives a cyclopentenyl complex with (2), but this loses 2 H to give [M^III(C₅Me₅)(C₅H₅)]⁺; norbornadiene gives a σ,η-norbornenyl complex that reductively eliminates to [M^I(C₅Me₅)(norbornadiene)]. The reactions of the hydrido-complexes (2) with dienes are compared with those of [(MC₅Me₅Cl₂)₂] in alcohol–base.