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 K2[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 1H, 13C, and 195Pt 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 4·1/2CHCl3, the imine and sulfoxide ligands are mutually trans. The solid-state structure of 4·1/2CHCl3 consists of two dimeric Pt moieties
representing a rather weak Pt···Pt interaction. The
dimeric architecture of 4·1/2CHCl3 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 ( ∼535 nm) and in the solid state ( 560−610 nm), with excited-state lifetimes of ca. 300−600
ns, representing a new family of PtII-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.