Photochemical behavior of (diphosphine)(η2-tolane)Pt0 complexes. Part A: Experimental considerations in solution and in the solid state

Abstract

A series of various (diphosphine)(η²-tolane)Pt⁰ complexes exhibiting manifold substitution pattern of the tolane ligand (5a–g) and different rigid diphosphines defining various bite angles at the Pt center (9a–b) have been synthesized. All compounds were isolated and characterized by means of spectroscopic methods and additionally by X-ray structure determination (5a–e, 9a–b). In view of potential C_aryl–C_ethynyl bond activation, we investigated their photochemical behavior in the solid state as well as in solution by irradiating with sunlight. The reactivity towards C_aryl–C_ethynyl bond activation in the crystalline state and in solution is discussed in relation to substituents attached to the tolane ligand and on the extent of the torsion of its phenyl rings. Complexes 5a–c and 9a either bearing electron withdrawing bromides or possessing a large dihedral angle of the phenyl rings, showed selective oxidative addition of the C_aryl–C_ethynyl bond to the Pt center in the solid state, yielding complexes 6a–c and 10a, respectively. In contrast, 5d–f and 9b proved to be unreactive under similar conditions because of their electron donating methoxy groups as well as the reduced twisting of their phenyl or pyridyl moieties of the tolane ligands. Irradiation of complexes 5a and 5b with sunlight in solution revealed the formation of the appropriate C–Br activated compounds 7a and 7b along with 6a and 6b in a 1 : 1 mixture. The observed photochemical C_aryl–C_ethynyl bond activation is reversible under thermal conditions, regaining the appropriate Pt⁰ complexes by reductive elimination.