Thioether, dinitrogen, and olefin complexes of (PNP)Rh: Kinetics and thermodynamics of exchange and oxidative addition reactions

A variety of (PNP)Rh-L complexes (where L = organic sulfide or sulfoxide, dinitrogen, or tertbutylethylene) have been synthesized by trapping transient (PNP)Rh (1) in situ. Equilibrium studies established the relative affinity of the (PNP)Rh fragment (1) for various L in the following order (of decreasing affinity): Ph2SO > SBu2n > SPhMe > dibenzothiophene > SPh2 > benzothiophene > SPr2i > thiophene approximate to SBu'Me > SBu2n approximate to H2C=CHCMe3 >> SBu'(2). Dinitrogen reacted with 1 to yield a mixture of terminal and bridging N-2 complexes and was found to bind more strongly than SPr2i. Reaction of (PNP)Rh(SPr2i) (10) with PhHal led to the corresponding oxidative addition products (PNP)Rh(Ph)(Hal) (Hal = Cl, 18a; Hal = Br, 18b; Hal = I, 18c). The relative rates of oxidative addition of PhHal to 10 were found to be in the order PhI > PhBr > PhCl. Kinetic studies of the reaction of 10 with PhBr were consistent with the reaction proceeding via reversible dissociation of SPr2i, followed by irreversible addition of PhBr. Evidence for a similar dissociative mechanism for the conversion of 10 to (PNP)Rh(S(O)Ph-2) in a ligand exchange reaction was also discovered. Solid-state structures of [(PNP)Rh](2)(N-2) (19a) and (PNP)Rh(H2C=CHCMe3) (21) were determined using X-ray crystallography. Approximately square-planar geometry about Rh was registered.