Tuning Ruthenium Carbene Complexes for Selective P-H Activation through Metal-Ligand Cooperation.

The use of iminophosphoryl-tethered ruthenium carbene complexes to activate secondary phosphine P-H bonds is reported. Complexes of type [(p-cymene)-RuC(SO2 Ph)(PPh2 NR)] (with R = SiMe3 or 4-C6 H4 -NO2 ) were found to exhibit different reactivities depending on the electronics of the applied phosphine and the substituent at the iminophosphoryl moiety. Hence, the electron-rich silyl-substituted complex undergoes cyclometallation or shift of the imine moiety after cooperative activation of the P-H bond across the M=C linkage, depending on the electronics of the applied phosphine. Deuteration experiments and computational studies proved that cyclometallation is initiated by the activation process at the M=C bond and triggered by the high electron density at the metal in the phosphido intermediates. Consistently, replacement of the trimethylsilyl (TMS) group by the electron-withdrawing 4-nitrophenyl substituent allowed the selective cooperative P-H activation to form stable activation products.