Cis-Trans Ring Substituent Isomerism in Cyano-Substituted Metallathietane-3,3-dioxide Complexes of Platinum(II) and Palladium(II)

Reactions of the platinum complexes cis-[PtCl2(PPh3)(2)], [PtCl2(dppf)], or [PtCl2(dppe)], and the palladium complexes, [PdCl2(PPh3)(2)] or [PdCl2(dppe)], with bis(cyanomethyl)sulfone NCCH2SO2CH2CN in methanol with added trimethylamine base gave the new cyano-substituted metallathietane-3,3-dioxide complexes [M{CH(CN)SO2CH(CN))L-2] (M = Pd, Pt) in good yields and purities. H-1 and P-31{H-1} NMR spectroscopy indicates that (in the majority of cases) the products are formed as a mixture of cis and trans isomers, with regard to the disposition of the cyano groups across the four-membered ring. An X-ray structure determination on a crystal of [Pd(CH(CN)SO2CH(CN)}(PPh3)(2)] showed it to be of the cis isomer, the first structurally characterized cis isomer of this type of complex. The four-membered palladacyclic ring is highly planar, in contrast to other metallathietane-3,3-dioxide complexes that have puckered rings. Factors influencing the relative abundances of the two isomers of [Pd{CH(CN)SO2CH(CN)}(PR3)(2)] have been investigated by means of NMR spectroscopy and DFT calculations.