Activation of ketones by electrophilic metal complexes: Synthesis of some ketonyl platinum(II) complexes and X-ray crystal structure of [PtCl{CH2C(O)CH3}(1,10-phenanthroline)]·1/2Y (Y = H2O or CH2Cl2)

Abstract

Cationic olefin complexes of platinum(II), [PtCl(η2-olefin)(N–N)]+, when the chelate ligand is an aromatic di-imine smoothly react with α-methyl ketones (CH3C(O)R) in acidic conditions to quantitatively form the ketonyl species [PtCl{CH2C(O)R}(N–N)] with elimination of the olefin and of a proton. In contrast, when N–N is an aliphatic diamine the reaction does not occur. The obtained ketonyl complexes (N–N=1,10-phenanthroline, R=CH3, 1, or CH2CH3, 1′; N–N=2,2′-bipyridyl, R=CH3, 2, or CH2CH3, 2′) have been fully characterized via elemental analysis, ESI-MS, and 1H NMR. Crystals of 1, grown from un-dried acetone or dichloromethane, were yellow and dark orange, respectively; both contained a molecule of solvent (water in the yellow form) per two molecules of complex. The dark orange crystals are luminescent at room temperature and, upon heating (above 384K), they lose the solvent molecule and change into an amorphous yellow powder. In both crystals the molecules form stacked columnar arrays. In the yellow form the column axis is tilted from the normal to the phenanthroline planes by 27.38°; the interplanar distances are alternately 3.434 and 3.488Å, while the Pt···Pt distances are 4.4787(7) and 6.4132(8)Å, respectively. In the dark orange form the column axis is nearly perpendicular to the planes of the complexes; the interplanar distances are alternatively ∼3.40 and 3.52Å, while the Pt···Pt distances are 3.4022(2) and 7.6533(2)Å, respectively.