Platinum(IV)-mediated nitrile-sulfimide coupling: a route to heterodiazadienes

Pt(IV)-mediated addition of the sulfimide Ph2S = NH and the mixed sulfide/sulfimides o- and p-PhS(=NH)](PhS)-C6H4 by the S=NH group to the metal-bound nitriles in the platinum(IV) complexes PtCl4(RCN)2] proceeds smoothly at room temperature in CH2Cl2 and results in the formation of the heterodiazadiene compounds PtCl4NH=C(R)N=SR'Ph]2] (R' = Ph, R = Me, Et, CH2Ph, Ph; R' = o- and p-(PhS)C6H4; R = Et). While trans-PtCl4(RCN)2] (R = Et, CH2Ph, Ph) reacting with Ph2S=NH leads exclusively to trans-PtCl4NH=C(R)N=SPh2]2], cis/trans-PtCl4(MeCN)2] leads to cis/trans mixtures of PtCl4NH=C(Me)N=SPh2]2] and the latter have been separated by column chromatography. Theoretical calculations at both HF/HF and MP2//HF levels for the cis and trans isomers of PtCl4NH=C(Me)N=SMe2]2] indicate a higher stability for the latter. Compounds trans-PtCl4E-NH=C(R)N=SPh2]2] (R = Me, Et) and cis-PtCl4E-NH=C(Me)N=SPh2]Z-NH=C(Me)N=SPh2]] have been characterized by X-ray crystallography. The complexes PtCl4NH=C(R)N=SPh2]2] undergo hydrolysis when treated with HCl in nondried CH2Cl2 to achieve the amidines PtCl4NH=C(NH2)R]2] the compound with R = Et has been structurally characterized) and Ph2SO. The heterodiazadiene ligands, formed upon Pt(IV)-mediated RCN/sulfimide coupling, can be liberated from their platinum(IV) complexes PtCl4NH=C(R)N=SR'Ph]2] by reaction with Ph2PCH2CH2PPh2 (dppe) giving free NH=C(R)=SR'Ph and the dppe oxides, which constitutes a novel route for such rare types of heterodiazadienes whose number has also been extended. The hybrid sulfide/sulfimide species o- and p-PhS(=NH)](PhS)C6H4 also react with the Pt(II) nitrile complex PtCl2(MeCN)2] but the coupling--in contrast to the Pt(IV) species--gives the chelates PtCl2M-I=C(Me)N=S(Ph)C6H4SPh]]. The X-ray crystal structure of PtCl2M-I=C(Me)N=S(Ph)C6H4SPh-o]] reveals the bond parameters within the metallacycle and shows an unusual close interaction of the sulfide sulfur atom with the platinum.