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.

The Electronics of CH Activation by Energy Decomposition Analysis: From Transition Metals to Main-Group Metals

“…In one report, insertion transition states were analyzed for model CH activation reactions between methane and zero-valent group 2 (Be, Mg, and Ca) and group 12 (Zn and Cd) metals [61][62][63][64]. One motivation of this study was to provide an understanding based on transition state interactions why the lowest oxidation state of s-block main-group elements compared to Pd(0) have dramatically larger activation barriers for methane CH bond insertion.…”

“…The Bickelhaupt group also examined model CH activation reactions between methane and low-oxidation state group-11 transition-metal cations Cu(I), Ag(I), and Au(I), with a comparison to Pd(0) [61][62][63][64]. This study revealed that at the beginning of the reaction pathway the low-oxidation state group II cations are more effective electrophiles than Pd(0) due to the much lower energy of the 4s, 5s, or 6s LUMOs.…”

“…The Bickelhaupt group has applied the ADF-EDA scheme to a number of model alkane CH activation reactions (for select examples, see [61][62][63][64]). In one report, insertion transition states were analyzed for model CH activation reactions between methane and zero-valent group 2 (Be, Mg, and Ca) and group 12 (Zn and Cd) metals [61][62][63][64].…”

Understanding the Heteroatom Effect on the Ullmann Copper-Catalyzed Cross-Coupling of X-Arylation (X = NH, O, S) Mechanism

“…On the one hand, when X is NH the major contribution to the total strain energy is the deformation associated with the copper(I) complex (ΔEstrain ‡ [(phen)Cu I (NHPh)] = +17.6 kcal/mol vs. ΔEstrain ‡ (PhI) = +12.7 kcal/mol). It is well-known, that such a change in the complex angle is required to achieve the maximum orbital overlap between the interacting orbitals of the fragments [84,85]. In this case, the occupied d orbital should interact with the σ*(C-I) vacant orbital.…”

“…It is well-known, that such a change in the complex angle is required to achieve the maximum orbital overlap between the interacting orbitals of the fragments [84,85]. In this case, the occupied d orbital should interact with the σ*(C-I) vacant orbital.…”