The reaction of platinum(II) chloride with neat benzonitrile gave bis(benzonitrile)dichloroplatinum(II) as a mixture of cis and trans isomers in variable proportions, depending on the temperature. The geometry of the chromatographically separated isomers was identified on the basis of the dipole-moment and IR data. The 13C NMR spectra in CDCl3 also enabled us to discriminate between isomers in both chemical shift and coupling to the 195Pt of the cyanide carbon, the resonance peak of which was utilized to follow the isomerization. The rate constant (kc) for the cis-to-trans isomerization was found to be (3.8±0.3)×10−6 s−1 in CDCl3 at 25 °C, ten times larger than that [kt=(2.9±0.2)×10−7 s−1] of the reverse reaction. The equilibrium between cis and trans strongly favored trans in CDCl3 at 25 °C, whereas in benzonitrile the cis form was the dominant species at room temperature, while the trans form was dominant at higher temperatures.

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Although dichlorobis(benzonitrile)platinum(II) has been thought so far to exist solely as a cis isomer, the reaction of platinum(II) chloride with neat benzonitrile affords a mixture of cis and trans complexes in variable proportions depending on the temperature. The 13C NMR spectra of the trans isomer and 13CN-enriched cis isomer are reported together with the rate and equilibrium data for the cis\ightleftarrows trans isomerization in CDCl3.

trans-Dichlorobis(benzonitrile) platinum(II) reacted with twice the molar amount of thallium(I) acetylacetonate and benzoylacetonate in dichloromethane at room temperature to afford mainly N-acetyl β-ketoamine chelates, trans-[Pt{N(COMe)=C(Ph)CH=COMe(and Ph)}2] (1a and 3a). This N,O-chelate structure of 1a was determined by X-ray analysis. Reactions of cis-[PtCl2(PhCN)2] gave C-acetyl and C-benzoyl β-ketoamine chelates, cis-[Pt{NH=C(Ph)C(COMe(and Ph))=COMe}2], together with other minor products. Formation of these β-ketoamine chelates is explained by the nucleophilic reactions of the β-diketonate carbanions at the coordinated cyanide carbon atom, followed by migration of the acetyl group or the methine proton of the nucleophiles onto the imino nitrogen atom formed during these reactions. In the presence of free β-diketones, migration of the acyl group was generally suppressed; this led to high yields of C-acyl complexes especially in reactions of cis-[PtCl2(PhCN)2]. In each case, the reaction proceeded with retention of the geometrical configuration around the central metal atom. The structures of other products, including a compound obtained by acid hydrolysis of 1a, were explored and discussed, based on IR and 2H NMR data.

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