A New Cyclometalation Motif: Synthesis, Characterization, Structures, and Reactivity of Pallada- and Platinacycles with a Bidentate {C(sp2,cyrhetrene),N}− Ligand

The synthesis, characterization, X-ray crystal structure, and study of the reactivity of the novel cyretrenyl ligand [{(η5-C5H4-2-C5H4N)}Re(CO)3 (1) with Pd(OAc)2 or [MCl2(DMSO)2] (M = Pd, Pt) are reported. These studies have allowed us to obtain the bis-μ-ligand cyclopalladated complexes [Pd{[κ2-C,N-(η5-C5H3)-2(C5H4N)]Re(CO)3)}(μ-X)]2 (X = OAc (2a), Cl (4a)) and monomeric pallada- and platinacycles of the general formula [M{[κ2-C,N-(η5-C5H3)-2(C5H4N)]Re(CO)3}(X)(L)] (M = Pd, L = PPh3, X = OAc (3a), Cl (5a); M = Pd, L = DMSO, X = Cl (6a); M = Pt, X = Cl, L = PPh3 (5b), DMSO (6b)), where compound 1 acts as a {C(sp2,cyrhetrene),N}− bidentate ligand. All complexes were characterized by elemental analyses, infrared spectroscopy, and one- and two-dimensional NMR. The X-ray crystal structures of 5a·1/2CH2Cl2, 5b, 6a·CH2Cl2, and 6b confirm (a) the existence of the five-membered metallacycle, (b) the {C(sp2,cyrhetrene),N}− mode of binding of the metallo ligand 1, and (c) the cis arrangement between the metalated carbon and the neutral L ligands (PPh3 or DMSO) in these products. A comparative study of the structures, spectroscopic properties, and reactivities of the new cyclometalated compounds and those of their analogues with a bidentate {C(sp2,ferrocene),N}− ligand is also reported.