New concepts for designing d10 -M(L)n catalysts: d regime, s regime and intrinsic bite-angle flexibility.

ABSTRACT

Our aim is to understand the electronic and steric factors that determine the activity and selectivity of transition-metal catalysts for cross-coupling reactions. To this end, we have used the activation strain model to quantum-chemically analyze the activity of catalyst complexes d(10) -M(L)n toward methane C-H oxidative addition. We studied the effect of varying the metal center M along the nine d(10) metal centers of Groups 9, 10, and 11 (M=Co(-), Rh(-), Ir(-), Ni, Pd, Pt, Cu(+), Ag(+), Au(+)), and, for completeness, included variation from uncoordinated to mono- to bisligated systems (n=0, 1, 2), for the ligands L=NH(3), PH(3), and CO. Three concepts emerge from our activation strain analyses 1) bite-angle flexibility, 2) d-regime catalysts, and 3) s-regime catalysts. These concepts reveal new ways of tuning a catalyst's activity. Interestingly, the flexibility of a catalyst complex, that is, its ability to adopt a bent L-M-L geometry, is shown to be decisive for its activity, not the bite angle as such. Furthermore, the effect of ligands on the catalyst's activity is totally different, sometimes even opposite, depending on the electronic regime (d or s) of the d(10) -M(L)n complex. Our findings therefore constitute new tools for a more rational design of catalysts.