Reactivity of Cycloplatinated Amine Complexes: Intramolecular C–C Bond Formation, C–H Activation, and PPh₂ Migration in Coordinated Alkynylphosphines

The monomeric ortho-platinated complexes [Pt­{R1CH­(1-C6H4)­NMe2-C,N}­{Ph2PCCR2}­Cl] (R1 = Me, Et; R2 = Me, Ph) with trans-N,P geometries were obtained regiospecifically from the reaction between the dimeric [Pt2(μ-Cl)2{R1CH­(1-C6H4)­NMe2-C,N}2] and the corresponding alkynylphosphines in high yields. The phosphine complexes are highly stable in the solid state and in solution. However, in the presence of additional Pt­(II) ions, an intramolecular coupling reaction occurred in which a new carbon–carbon bond was formed between the aromatic γ-carbon of the ortho-platinated chiral phenylamine and the α-carbon of the (Ph2P)–CαCβ–(R2) ligand. The (Ph2P) moiety migrated to the neighboring β-carbon during the coupling reaction. By the judicious selection of the substituents on the alkynylphoshine along with deliberate introduction of selected chirality on the ortho-platinated phenylamine, the coupling reaction and the (Ph2P) migration were found to proceed via an associative intramolecular mechanism that involves a Pt-vinylidene intermediate.