Multinuclear N.M.R. study of some di- and tri-methylplatinum(IV) complexes

Abstract

The 13C n.m.r. spectrum of the dimer [PtMe2Br(MeOH)(p-OH)]2, formed by dissolving the complex [PtMe2Br(OH)]n in methanol, has been analysed, to give 2JPt-O-Pt 103.6 HZ. 1H and 1H-decoupled 195Pt spectra show complex patterns owing to superposition of spectra from different isotopomers. By contrast, solutions of [PtMe2Br2]n in methanol, which contain monomeric PtMe2Br2(MeOH)2, give simple spectra. [PtMe2Br(OH)]n dissolves in dilute aqueous KOH solution at pH 9 to give a solution containing the 'inert' dimer [PtMe2Br(OH)(μ-OH)]22-. Other species are present at higher pH, but the solution never contains simple PtMe2Br(OH)32- alone. Dissolution of [PtMe2(OH)2(H2O)1.5]. in alkali at pH 12 gives a dimer [PtMe2Br(OH)(μ-OH)]22- whose 13C n.m.r, spectrum has been analysed to give 2JPt-O-Pt 123 .5 HZ. Progressive substitution of water in fac-PtMe3(H2O)3+ by pyridine causes regular 195Pt shifts to lower frequency. 195Pt, 13C and 1H data indicate that fac-PtMe3X32- exist as simple anions for X = NO2, CN, but not for X = NCS. 195Pt chemical shifts of di- and tri-methylplatinum(IV) complexes are discussed. The hydroxobridged dimers resonate at higher frequencies than monomeric complexes, owing to strain in the four-membered Pt(OH)2Pt rings. is much more sensitive to the cis influence than 2JPt-CH3.