Synthesis of chelate stabilised alcohol– and alkoxo–platinum(II) complexes. X-Ray crystal structure of [Pt(PPh2CH2CMe2O)2]·3.5H2O
Abstract
Reaction of the new phosphine PPh2CH2CMe2OH with platinum(II) chloro complexes gives complexes of formula [PtCl2(PPh2CH2CMe2OH)2]. The cis isomer in CDCl3 or CD3OD solution is in the ionic, chelate form cis-[[graphic omitted]H)(PPh2CH2CMe2OH)]Cl. At +25 °C, rapid intramolecular –OH exchange takes place. Addition of AgClO4 gives the bis-chelate cis-[[graphic omitted]H)2][ClO4]2. Both of these cis species can be readily deprotonated to give the very stable bis(alkoxo) complex [[graphic omitted])2]. The X-ray structure of this bis(alkoxo) complex as its 3.5H2O solvate has been determined {R= 0.029 for 3 914 observed [I/σ(I) 3.0] diffractometer-collected reflections}. The Pt atom has square-planar co-ordination, with Pt–O bonds of normal length [average 2.024(3)Å]. Thus the general instability of alkoxoplatinum complexes is attributed to facile β-hydride elimination and not to abnormally long and weak Pt–O bonds. The trans isomer forms the fluxional chelate complex trans-[[graphic omitted]H)(PPh2CH2CMe2OH)]Cl in CD3OD, but in CDCl3 it gives a neutral non-chelated species. It is also deprotonated by NEt3 but only to the non-fluxional mono-alkoxo complex [[graphic omitted])(PPh2CH2CMe2OH)]. The 31P-{1H} and 1H n.m.r. data for the complexes are discussed.