Synthesis of Cyclic Diamino-Substituted Metal Carbene Complexes

Abstract

A series of heterocyclic metal carbene complexes were prepared by the deoxygenation reaction of M(CO)6 (M = Cr, Mo, W) with RNH(CH2)nNPPh3 (R = H, Et, Ph; n = 2, 3, 4) to form the corresponding isocyanide complex, which subsequently underwent intramolecular cyclization to give (CO)5MCN(R)(CH2)nNH in good yields. None of the carbene complex reacted further with amine−phosphinimine RNH(CH2)nNPPh3 to give the bis(carbene) complex. Deprotonation of the N−H of the carbene complex followed by the reaction of alkyl iodides provided the N-alkylated product. In the case of N-allyl-substituted complexes (CO)5MCNR(CH2)2N(CH2CHCH2) (M = Cr, Mo, W), the carbon−carbon double bond underwent intramolecular ligand displacement of carbonyl ligand to yield the corresponding π-coordinated complex. Unlike the group VI metal carbonyl complexes, treatment of ReBr(CO)5 with 2 molar equiv of Ph3PN(CH2)2NH2 provided a bis(carbene) complex fac-(CO)3BrRe(CNHCH2CH2NH)2. All complexes are characterized by both spectral and elemental analyses. Complexes (CO)5MoCNHCH2CH2CH2NH (18) and fac-(CO)3BrRe(CNHCH2CH2NH)2 (42) were further characterized by X-ray single-crystal analysis.