Stability of (chloromethyl)platinum(II) complexes

Abstract

The stabilities of [Pt(CH₂Cl)₂(cod)], [Pt(CH₂Cl)Cl(cod)](cod = cycloocta-1,5-diene) and a range of phosphine-containing mono- and cis-bis-(chloromethyl)platinum(II) complexes have been investigated in deuteriochloroform at room temperature. Some of the bis(chloromethyl) derivatives appear to be indefinitely stable (cod and chelating arylphosphines), others suffer very slow decomposition to the dichlorides (non-chelating arylphosphines), and the remainder decompose relatively rapidly, and cleanly, to the dichlorides plus ethylene (alkylphosphines, non-chelating faster than chelating). Rapid decomposition of the arylphosphine complexes can be induced by adding hexafluoroisopropyl alcohol to the deuteriochloroform solutions. Attempts to generate [Pt(CH₂Cl)₂{P(C₆H₁₁)₃}₂] by addition of P(C₆H₁₁)₃ to [Pt(CH₂Cl)₂(cod)] resulted in the formation of cis-[Pt^–{CH₂CH₂P⁺(C₆H₁₁)₃}Cl₂{P(C₆H₁₁)₃}]; a mechanism is proposed. All cis-mono(chloromethyl) derivatives studied appear to be indefinitely stable. In contrast, the trans-mono(chloromethyl) complexes, although stable in very dry solvent, undergo decomposition in the presence of moisture to the corresponding hydrides plus formaldehyde; a mechanism is proposed. The hydrides undergo subsequent conversion into a mixture of cis and trans dichlorides.