A novel reactivity mode for metal-activated dialkylcyanamide species: addition of N,N'-diphenylguanidine to a cis-(R2NCN)2Pt(II) center giving an eight-membered chelated platinaguanidine

Abstract

The nucleophilic addition of N,N'-diphenylguanidine, HN=C(NHPh)(2) (DPG), to two adjacent dialkylcyanamide ligands in cis-[PtCl(2)(NCNR(2))(2)] (R = Me; R(2) = C(5)H(10), C(4)H(8)O) gives unusual eight-membered chelates [PtCl(2){NH=C(NR(2))N(Ph)C(=NH)N(Ph)C(NR(2))=NH}] (1-3) with trisguanidine as the cyclic ligand, in which the central guanidine =NH group remains uncoordinated. Treatment of trans-[PtCl(2)(NCNR(2))(2)] (R = R = Me; R(2) = C(5)H(10), C(4)H(8)O) with 1 equiv of HN=C(NHPh)(2) in a solution (R = R = Me; R(2) = C(5)H(10)) or in a suspension (R(2) = C(4)H(8)O) of CHCl(3) or MeNO(2) at 20-25 degrees C for 20 h results in the generation of the 1,3,5-triazapentadiene monochelates [PtCl{NH=C(NR(2))N(Ph)C(NH(2))=NPh}(NCNR(2))](Cl) (4-6). When any of trans-[PtCl(2)(NCNR(2))(2)] reacts with 2 equiv of DPG at 20-25 degrees C for 1-2 days or 4-6 are treated with 1 equiv more of HN=C(NHPh)(2) at the same temperature, the complexes bearing two chelate rings [Pt{NH=C(NR(2))N(Ph)C(NH(2))=NPh}(2)](Cl)(2) (7-9) are formed. The formulation of the obtained complexes was supported by satisfactory C, H, and N elemental analyses, agreeable ESI(+)-MS, IR and (1)H and (13)C{(1)H} NMR spectroscopies; the structures of 1 and 2 were determined by the single-crystal X-ray diffraction. Theoretical studies (at the B3LYP level of theory) revealed that the alkylnitrile eight-membered product is significantly less stable than the corresponding cyanamide species 1-3, and this fact, at least partially, explains why the former was not detected in the reaction between cis-dinitrileplatinum(II) complexes and DPG.