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 ²J_Pt-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)]₂^2-. 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)]₂^2- whose ¹³C n.m.r, spectrum has been analysed to give ²J_Pt-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-PtMe₃X₃^2- 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 ²J_Pt-CH3.