Pt II-mediated imine-nitrile coupling leading to symmetrical (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes containing the incorporated 1,3-diiminoisoindoline moiety

Abstract

Treatment of trans-[PtCl 2(NCR) 2] (1; R = Et (1a), Ph (1b)) with 1,3-diiminoisoindoline (2) gives access to the corresponding symmetrical (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes [PtCl{NH=C(R)N=C(C 6H 4)NC=NC(R)=NH}] (3). The reactions of 1 with one equivalent of 1,1,3,3-tetramethylguanidine (4), 1,3-diphenylguanidine (6), or acetone oxime (8) leads to the formation of mixed asymmetrical Pt(II) complexes trans-[PtCl 2{NH=C(R)N=C(NMe 2) 2}(NCR)] (5), [PtCl{NH=C(R)NC(NHPh)=NPh}(NCR)] (7), or trans-[PtCl 2{NH=C(Ph) ON=CMe 2}(NCPh)] (9), respectively, as a result of nucleophilic addition to one of the nitrile ligands in 1. Treatment of 5, 7, and 9 with one equivalent of 2 leads to complexes 3. The complexes were characterized by IR, 1H, 13C{ 1H}, and 195Pt NMR (for 3) spectroscopies, ESI +-MS, elemental analyses, and X-ray diffraction (for 3). Complex 3a has an asymmetric unit with five independent Pt molecules of the same chemical composition and two molecules of water, resulting in a total of 40 molecules of the complex and sixteen guest water molecules per unit cell. Theoretical calculations revealed that the most plausible mechanism of formation of complexes 3 includes stepwise nucleophilic addition of 2 to one of the nitrile ligands in 1, a first cyclization upon formation of the Pt-N bond and elimination of HCl, and a second nucleophilic addition/cyclization. © 2012 American Chemical Society.