Chiral effects on a fluxional ligand: chiral diphosphine platinum(II) complexes with thiacrowns

We report the syntheses, crystal structures, and spectroscopic properties for two new Pt(II) heteroleptic complexes containing the chiral diphosphine ligands R-BINAP and R,R-Chiraphos along with crown trithioether [9]aneS3(1,4,7-trithiacyclononane). The complexes have the general formula [Pt([9]aneS3)(P2)](PF6)2 (P2= R-BINAP or R,R-Chiraphos) and form similar structures in which the Pt(II) center is surrounded by a cis arrangement of the two P donors from the diphosphine chelate and two sulfur atoms from the trithioether macrocycle. The third sulfur in each complex shows a long distance interaction with the metal, resulting in an elongated square pyramidal structure with platinum-axial sulfur distances ranging from 2.695(3) to 2.802(2) (angstrom) with the Chiraphos complex showing the shorter distance. The X-ray crystal structure of the Chiraphos complex exhibits an unusual example of co-crystallization of solid state conformational diastereoisomers within the same unit cell. The unit cell consists of two crystallographically independent complex cations which are related by a conformational change around one carbon-carbon bond in the [9]aneS3 ligand. The 195Pt NMR chemical shifts for both complexes fall in the range of -4167 to -4452 ppm, consistent with a cis-PtS2P2 coordination sphere. The effects of chirality of the diphosphine are most notably seen in the 13C NMR spectrum of the fluxional [9]aneS3 ligand, resulting in two separate resonances as opposed to the single one which has always been observed in Pt complexes containing achiral diphosphines.