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.

Synthesis of dimethylplatinum(IV) compounds, [{PtMe2X2}n], [{PtMe2XY}n], and, in solution,fac-[PtMe2X(H2O)3]+, where X and Y are anionic ligands

“…The 'H and P3C spectra in CD30D each showed a singlet with satellites from the methyl groups. The Pt-CH3 coupling constant was consistent with methanol as the ligand trans to methyl (26)(27)(28)(29). The 'H-decoupled ' "~t NMR spectrum in methanol showed a single peak, at significantly higher frequency than that for [PtMe,Br,(MeOH),] ( l l ) , as expected with replacement of bromo by chloro ligands (30)(31)(32).…”

“…NMR spectra can also provide useful information, although 'J,,, tends to be influenced more, relatively, by ligands cis to methyl than 2p,-Cn3 (7,29). The shielding of the methyl I3c nucleus also depends on the trans ligand, with higher nuclear shielding trans to water than trans to halide (cf., 'H (28) or ' 5~ (30) bound to platinum).…”

NMR spectroscopic investigations of transition metal complexes in organometallic and bioinorganic chemistry

“…Specifically, Pt 0 and Pt II complexes typically exhibit δ Pt values ranging from À1000 to À6000 ppm, while Pt IV complexes are observed within the range of +8000 to À7000 ppm. [225][226][227][228][229] The integration of 195 Pt NMR spectroscopy with electrospray ionization-mass spectrometry (ESI-MS) presents a valuable approach for investigating the plasma stability of Pt IV -based anticancer drugs. 230 Pt IV complexes with haloacetato axial ligands were shown to undergo hydrolysis under physiological conditions (pH 7 at 37 C) with δ Pt values of +1425 and + 1310 ppm indicating [Pt IV (dach)(TFA)(OH)(ox)] (dach = 1,2-diaminocyclohexane; TFA = trifluoroacetate; ox = oxalato) and [Pt IV (dach)(TFA)(OH) 2 (ox)], respectively.…”

“…Within 195 Pt NMR spectra, Pt complexes with Pt 0 , Pt II , and Pt IV oxidation states are distinguishable (Figure 5b). Specifically, Pt 0 and Pt II complexes typically exhibit δ Pt values ranging from −1000 to −6000 ppm, while Pt IV complexes are observed within the range of +8000 to −7000 ppm 225–229 . The integration of 195 Pt NMR spectroscopy with electrospray ionization–mass spectrometry (ESI–MS) presents a valuable approach for investigating the plasma stability of Pt IV ‐based anticancer drugs 230 .…”