First example of the solid-state thermal cyclometalation of ligated benzophenone imine giving novel luminescent platinum(II) species

The (benzophenone imine) platinum(II) compounds trans-[PtCl2(Ph2C=NH)( RR'SO)] [ R, R' = Me, Me (2); n-Pr, n-Pr (3); (CH2) (4) (4); Me, Ph (5); Me, p-MeC6H4 (6)] were prepared by the reaction of Ph2C=NH with K[PtCl3( RR'SO)], obtained in situ from K-2[ PtCl4] and the corresponding sulfoxide, giving 2 - 6 as well as cis- [ PtCl2( Ph2C=NH) 2] ( 1) as a minor product. The complexes were characterized by H-1, C-13, and Pt-195 NMR and IR spectroscopy, electrospray ionization mass spectrometry, and C, H, and N elemental analysis. The X- ray crystallography of 1 enables confirmation of the cis configuration of the complex, while in 2 and 4 center dot(1)/2CHCl3, the imine and sulfoxide ligands are mutually trans. The solid-state structure of 4 center dot(1)/2CHCl3 consists of two dimeric Pt moieties representing a rather weak Pt center dot center dot center dot Pt interaction. The dimeric architecture of 4 center dot(1)/2CHCl3 is enhanced by the hydrogen bonding between imine H atoms and O atoms. The orthometalation of 1 and 2 - 6 proceeds both in the solid phase and in a toluene suspension, leading to the formation of [PtCl {Ph(C6H4) C=NH}(Ph2C=NH)] (7) and [PtCl {Ph(C6H4) C=NH}(RR'SO)] (8 - 12), respectively, isolated in nearly quantitative yields. Complexes 8 - 12 are emissive at room temperature both in solution ( lambda(max)(em) similar to 535 nm) and in the solid state (lambda(max)(em) 560-610 nm), with excited-state lifetimes of ca. 300 - 600 ns, representing a new family of Pt-II- based luminescent complexes. Compounds 8 and 10 have been characterized by X- ray analysis, confirming the square- planar coordination geometry of the metal center with the almost planar platinacycles. In 8, the asymmetric unit contains two independent Pt molecules, while in 10, it includes four Pt molecules linked by the intermolecular hydrogen- bonding network between the NH group and Cl atoms.