The interaction of vinyl acetate and allyl acetate with chloro-bridged platinum(II) complexes [Pt 2Cl 4(PR 3) 2]: Crystal structure of cis-[PtCl 2(PMe 2Ph2)(CH 2=CHOCOCH 3)

Abstract

Five complexes of type cis-[PtCl 2(PR 3)Q] (PR 3 =PMe 3, PMe 2Ph, PEt 3; Q = CH 2 CHOCOCH 3 or CH 2=CHCH 2OCOCH 3) have been prepared. The crystal structure of cis-[PtCl 2[PME 2Ph)(CH 2=CHOCOCH 3)] is described. Crystals of cis-[PtCl 2(PME 2Ph)(CH 2-CHOCOCH 3)] are triclinic, with a 8.441(4), b 13.660(5), c 7.697(3) Å, a 101.61(3)°, β 111.85(3)° γ 95.22(3)°, p P1, Z = 2. The structure was determined from 2011 reflections I σ 3σ ( I) and refined to R = 0.037. The CH 3COO grouping is syn to the cis-PMe 2Ph ligand, with bond lengths of PtCl (trans to P) 2.367(3), PtCl ( trans to olefin) 2.314(3), PtP 2.264(2), and PtC of 2.147(12) and 2.168(11) Å. The complexes cis-[PtCl 2- (PR 3)Q] were studied by variable temperature 1H and 31P NMR spectroscopy. Spectra of the vinyl acetate complexes were temperature dependent as a result of rotation about the platinum—olefin bond. The rotation was “frozen out” at ca. 240 K; for cis-[PtCl 2(PME 2Ph)(CH 2=CHOCOCH 3] Δ G≠ (rotation) 15.0 ± 0.2 kcal mol -1. NMR parameters for the rotamers are reported. NMR studies of the interaction between chloro-bridged complexes of type [Pt 2Cl 2(PR 3) 2] (PR 3 = P-N-Pr 3 or PMe 2Ph) and vinyl acetate shows that even at low temperatures (213 K) equilibrium favours the bridged complex and the proportion of trans-[PtCl 2(PR 3)CH 2=CHOCOCH 3)] is very small e.g. 2%. The allyl acetate complexes cis-[PtCl 2(PR 3)(CH 2=CHCH 2OCOCH 3)] showed only one rotamer over the range 333–213 K. Reversible dissociation of cis-[PtCl 2(PMe 2Ph)- (CH 2=CHCH 2OCOCH 3)] to [Pt 2Cl 4(PMe 2Ph) 2] + allyl acetate was studied at ambient temperature. At low temperatures e.g. 213–190 K addition of allyl acetate to a CDCl 3 solution of [Pt 2Cl 2(P-n-Pr 3) 2] reversibly gave some olefin complex trans-[PtCl 2(P-n-Pr 3)(CH 2=CHCH 2OCOCH 3)] and some O-bonded complex trans-[PtCl 2(P-n-Pr 3)(CH 2=CHCH 2OCOCH 3)].