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 tert-butylethylene) 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 > SBun2 > SPhMe > dibenzothiophene > SPh2 > benzothiophene > SPri2
> thiophene ≈ SButMe > SBus2 ≈ H2CCHCMe3 ≫ SBut2. Dinitrogen reacted with 1 to yield a mixture
of terminal and bridging N2 complexes and was found to bind more strongly than SPri2. Reaction of
(PNP)Rh(SPri2) (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 SPri2, followed by irreversible addition
of PhBr. Evidence for a similar dissociative mechanism for the conversion of 10 to (PNP)Rh(S(O)Ph2)
in a ligand exchange reaction was also discovered. Solid-state structures of [(PNP)Rh]2(N2) (19a) and
(PNP)Rh(H2CCHCMe3) (21) were determined using X-ray crystallography. Approximately square-planar geometry about Rh was registered.