Ruthenium and osmium porphyrin carbene complexes: Synthesis, structure, and connection to the metal-mediated cyclopropanation of alkenes

Abstract

A series of monocarbene ruthenium/osmium porphyrins [M(Por)(CRR′)] (M = Ru, Os; R=R′ in some cases) and two biscarbene osmium porphyrins [Os(Por)(CR2)2] have been prepared by several research groups from reactions of diazo compounds with ruthenium/osmium porphyrins [M(Por)]2, [M(Por)(CO)] (M = Ru, Os), [Ru(Por)], or [Os(Por)(CR2)], or from reactions of K2[Ru(Por)] with germinal dihalides. The structures of [Os(TTP)(CRR′)(THF)] (CRR′=C(p-C6H4CH3)2, CHSiMe3), [Ru(TPP)(C(CO2Et)2)(MeOH)], [Ru(Por*)(CRR′)] (CRR′=CPh2, C(Ph)CO2CH2CH=CH2), [Os(TPFPP)(CPh2)(MeOH)], and [Os(TPFPP)(CPh2)2] have been determined by X-ray crystallography, which feature M=C(carbene) bond lengths of 1.79(2)-1.870(2) Å for the monocarbene complexes and 2.035(2), 2.027(3) Å for the biscarbene complex. Reactions of [Os(TTP)(CHR)] (R = C02Et, SiMe3) with para-substituted pyridines 4-X-C5H4N afford osmium porphyrin ylide complexes [Os(TTP)(CH(R)(4-X-C5H4N)) (4-X-C5H4N)]. The complexes [Os(TTP)(CHCO2Et)], [Ru(TPP)(C(CO2Et)2)], and [Os(TPFPP)(CPh2)2] all undergo cyclopropanation reactions with styrene. The biscarbene complex [Os(TPFPP)(CPh2)2] also reacts with unfunctionalized alkenes such as cyclohexene to yield C-H insertion products. A few ruthenium/osmium porphyrin carbene complexes, including [Os(TTP)(CHCO2Et)], [Ru(TPP)(CHCO2Et)], [Ru(Por*)(CHX)(L)] (X = CO2R, CO2CH2CH=CRCRt; L = a ligand with considerable trans effect such as CHX), and [Os(TPFPP)(CPh2)2], are proposed to be the active intermediates in the corresponding ruthenium/osmium porphyrin-catalyzed alkene cyclopropanations. © 2002 Elsevier Science B.V. All rights reserved.