Isolation of Bis- and Mono-Cyclometallated Ru−IMes Complexes upon Reaction of [Ru(PPh3)3HCl], IMes and ZnMe2

Addition of an excess of ZnMe2 to a mixture of [Ru(PPh3)3HCl] and IMes (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) yields the bis-cyclometallated complex, [Ru(IMes)“(PPh3)2] 2, together with the mono-cyclometallated, Ru−Zn heterobimetallic complex [Ru(IMes)′(PPh3)2(ZnMe)] 3. Treatment of 2 with H2, PhSiH3 or pinacolborane yields the previously reported complex, [Ru(IMes)′(PPh3)2H] 1, the synthesis of which has been reinvestigated. Further studies of small molecule reactivity show that 1 adds H2 to give [Ru(IMes)(PPh3)2H4] 4, whilst 2 reacts with catecholborane to give [Ru(IMes-Bcat)′(PPh3)2H] 5, in which (IMes-Bcat)′ signifies a borylated NHC ligand that is singly-metallated onto Ru. Treatment of 2 with CO gives the 18-electron dicarbonyl product [Ru(IMes)”(PPh3)(CO)2] 6. Compounds 1–3, 5 and 6 have been structurally characterised.