Reactivity of [Ru₃(CO)₁₂] with a Phosphine-Functionalized Imidazol-2-ylidene and Its Imidazolium Salt

The trinuclear cluster [Ru3(CO)12] reacts at room temperature with the phosphine-functionalized N-heterocyclic carbene (NHC) ligand 1-[2-(diphenylphophino)ethyl]-3-methylimidazol-2-ylidene (dppeImMe), in 1:1 mol ratio, to give the edge-bridged trinuclear derivative [Ru3(μ-κ2C,P-dppeImMe)(CO)10] (1). The use of a 1:3 [Ru3(CO)12] to dppeImMe mol ratio leads to the mononuclear derivative [Ru(κ2C,P-dppeImMe)(CO)3] (2), which has a trigonal-bipyramidal ligand arrangement with the NHC and phosphine fragments of the dppeImMe ligand in axial and equatorial positions, respectively. Upon gentle heating (refluxing THF), compound 1 is transformed into the face-capped dihydrido derivative [Ru3(μ-H)2(μ3-κ3C2,P-dppeImCH)(CO)8] (3), which arises from the oxidative addition of two C−H bonds of the N-methyl group of the dppeImMe ligand. The trinuclear salt [Ru3(κP-dppeHImMe)3(CO)9][BF4]3 (4[BF4]3), which contains a P-coordinated 1-[2-(diphenylphophino)ethyl]-3-methylimidazolium ligand ([dppeHImMe]+) on each Ru atom, has been prepared by treating [Ru3(CO)12] with the salt [dppeHImMe][BF4]. The deprotonation of 4[BF4]3 with three equivalents of K[N(SiMe3)2] is an alternative way to prepare the mononuclear complex 2.