Half-sandwich ruthenium(II) complexes of aminophosphines: synthesis, structures and catalytic applications in C–C coupling reactions between styrenes and diphenyldiazomethane

The half-sandwich Ru(II) complexes of the type [CpRu(PPh2N(H)R)(PPh3)Cl], [CpRu(PPh2N(H)R)2Cl] (R=Ph, C6H11) and [CpRu(PPh2N(R′)PPh2-κP,κP)(PPh3)]Cl (R′=Et, nPr, iPr, nBu), were synthesized and the structures of complexes [CpRu(PPh2N(H)Ph)(PPh3)Cl] and [CpRu(PPh2N(H)Ph)2Cl] were confirmed by single crystal X-ray diffraction studies. All ruthenium complexes were employed in the cyclopropanation reaction of styrene derivatives in the presence of diphenyldiazomethane. All complexes afford 1,1,3,3-tetraphenyl cyclobutane along with cyclopropane derivatives; complex, [CpRu(PPh2N(nBu)PPh2-κP,κP)(PPh3)]Cl shows better selectivity in the formation of 1,1,2-triphenylcyclopropane. In all reactions appreciable amounts of cyclopropanation products and metathesis products, 1,2-diphenylcyclopropane and 1,1-diphenylethene were obtained along with 1,1,3-triphenylpropene derivatives. The variable temperature NMR studies have suggested that the cyclopropanation reactions in the presence of ionic complex, [CpRu(PPh2N(R′)PPh2-κP,κP)(PPh3)]Cl proceeds via carbene intermediate, [CpRu(CPh2)(PPh2N(R′)PPh2-κP)(PPh3)]Cl.