Platinum and palladium complexes of thienylpyridine. I. Compounds containing metal-carbon bonds

Article abstract of DOI:10.1021/ic50149a040

Complexes of divalent platinum and palladium with 2-(2′-thienyl)pyridine (TP) have been investigated. In this paper we describe the syntheses and structures of those derivatives which form a metal-carbon σ bond by the spontaneous loss of a hydrogen from an aromatic group (TP-H). The reaction of TP with PtX₄^2- (X = Br^-, I^-) yields orange crystalline Pt(TP)(TP-H)X. In these complexes, one TP acts as a monodentate N donor and the other as an N-C chelate, through the thienyl ring. A yellow, crystalline palladium analog Pd(TP)(TP-H)NO₃ can be prepared by the reaction of TP with AgNO₃ and PdI₄^2-. All of these complexes are monomers and nonelectrolytes in nonpolar solvents. The crystal structure of iodo[2-(2′-thienyl)pyridine][2-(2′-thienyl)pyridyl]platinum(II) was determined from three-dimensional single-crystal X-ray diffraction data collected by counter methods. The complex Pt(C₉H₇NS)(C₉H₆NS)I was found to crystallize in the monoclinic space group P2₁/n with a = 17.360 (3) A?, b = 8.418 (1) A?, c = 13.556 (2) A?, β = 110.53 (2)° Z = 4 molecules/cell. The structure was refined by block diagonal and full matrix methods to a final R factor of 4.6% for 2220 nonzero reflections. The platinum atom is coordinated by two pyridyl nitrogens trans to one another, a thienyl carbon, and an iodide which lies slightly below the plane formed by the platinum and the other three coordinating atoms. The Pt-N distances are 2.04 (1) and 2.02 (1) A? for the nitrogens in the monodentate and the chelated ligands, respectively; the Pt-I and Pt-C distances are 2.68 (1) and 1.97 (2) A?, respectively. The free thiophene ring (not coordinated to the metal by a metal-carbon σ bond) is in an axial position. This ring was found to be disordered by 180° rotation about the pyridine-thiophene bond. The Pt-S distance (2.99 (3) A?) was nevertheless determined with reasonable accuracy and was found to be less than the sum of the van der Waals radii. The line between the platinum and the sulfur makes an angle of ca. 15° with the normal to the equatorial plane at the platinum site. The visible-ultraviolet spectra of these complexes resemble the spectra of five-coordinate d⁸ complexes and the ir spectra show a shifted thiophene band assigned to the thiophene ring in the axial position. These spectral results are interpreted with respect to metal-thiophene axial interaction. The metal to carbon σ bond forms with unusual ease under wet, aerobic conditions due to the thiophene ring reactivity and the chelate stability.