Carbene complex formation versus cyclometallation from a phosphoryl-tethered methanide ruthenium complex

Abstract

An oxophosphoryl-substituted methanide ligand system for transition metal complexes has been synthesized and isolated as the sodium salt Na[Ph2P(O)–C(H)–SO2Ph]. This ligand features structural components known to enable the isolation of nucleophilic late transition metal carbene complexes. The corresponding ruthenium(cymene) chlorido complex was readily available by simple salt metathesis reaction. However, in contrast to previously reported thio- and iminophosphoryl-tethered ligand systems, dehydrohalogenation of the chlorido complex led to the formation of a cyclometallated ruthenium complex instead of the carbene complex. All compounds have been characterized in solution and solid state. Additional density functional theory (DFT) studies have been performed to elucidate the mechanism of the observed cyclometallation and to shed light on the effects of different P(V) groups in the ligand system on the stability and reactivity of the corresponding carbene complexes. The calculations show that the weaker coordination of the PO compared to the PS or PN moiety is responsible for the more facile C–H activation.