Dynamic titanium phosphinoamides as unique bidentate phosphorus ligands for platinum

Treatment of lithium phosphinoamides, Ph2PN(Li)R [R = Bu-1, Pr-i], with TiCl4 results in formation of titanium phosphinoamides, (Ph2PNR)(2)TiCl2 [R = Bu-t (1a), Pr-i (1b)]. Crystallographic studies show that there are covalent bonds between the titanium and two nitrogen atoms, whereas two phosphorus atoms are coordinated to the metal center intramolecularly. Variable-temperature NMR studies suggest reversible dissociation of the phosphorus moieties from the titanium in solution. The dissociated phosphorus moieties are effectively captured by Pt(11) species; reactions of la with either (eta(4)-COD)PtCl2, (eta(4)-COD)Pt(R)(Cl) (R = Me, p-Tol), or [Me2Pt(mu-SMe2)](2) afford the corresponding Ti-Pt heterobi metallic complexes. The molecular structures of these complexes reveal that they have a six-membered dimetallacycle, in which a titanium and a platinum are connected by two bridging phosphinoamide ligands; the Pt-Ti distances indicate the existence of a Pt -> Ti dative bond. The conformation of the dimetallacycle is a boat form, with two metals at the bow and the stem in the crystal; however, dynamic conformational change involving cleavage and re-formation of the Pt-Ti dative bond is indicated from variable-temperature NMR studies.