Organometallic complexes of platinum-group metals incorporating substituted guanidine dianion (triazatrimethylenemethane) ligands

Article abstract of DOI:10.1016/S0022-328X(97)00654-2

Reactions of the platinum-group metal halide complexes [PtCl₂(COD)] (COD=1,5-cyclo-octadiene), [Cp*RhCl₂(PPh₃)] (Cp=η⁵-C₅Me₅), [Cp*IrCl₂(PPh₃)], [(p-cymene)RuCl₂(PPh₃)] and [(p-cymene)OsCl₂(PPh₃)] with symmetrically trisubstituted (acetyl or phenyl) guanidines, mediated by silver(I) oxide, give complexes formally containing the triazatrimethylenemethane ligand. A full X-ray crystal structure determination is reported for the N,N′,N″-triphenylguanidine dianion complex [Pt{NPhC(=NPh)NPh}(COD)] 4a which shows the presence of a planar Pt-NR-C(=NR)-NR four-membered platinacycle. At room temperature (r.t.), the ¹H- and ¹³C{¹H}-NMR spectra of 4a yield a single set of COD CH and CH₂ resonances. At 240 K however, two sets of resonances are observed, interpreted in terms of fluxionality of the C=N-Ph moiety. Attempted synthesis of the analogous platinum triacetylguanidine complex yields the new ureylene complex [Pt{NAcC(=O)NAc}(COD)], via a hydrolysis reaction. Starting with the osmium compound, both the guanidine complex [(p-cymene)Os{NAcC(=NAc)NAc}(PPh₃)] 9 and the ureylene complex [(p-cymene)Os{NAcC(=O)NAc}(PPh₃)] 10 were formed; similar results were obtained for the iridium system.