2-(Diphenylphosphino)-pyridine as an ambidentate ligand in homo- and hetero-binuclear complexes of copper, silver, and gold

The reaction of 2-diphenylphosphino-pyridine (1) with AgBF₄ in an equimolar ratio affords the cyclic, dinuclear complex 2 with mixed P,N-coordination of the metal atoms. With two equivalents of 1 the 2:1 complexes 4a,b are formed which have the metal atoms solely P-coordinated. The previously reported gold complex (3), an analogue of 2, or [Au(tht)₂]ClO₄ (tht = tetrahydrothiophen) also give the 2:1 complexes (5a,b) when treated with an excess of ligand 1. Addition of AgClO₄ to a solution of 5a in acetone, or treatment of 4a with [Au(tht)₂]ClO₄ in dichloromethane, give the same mixed-metal complex 6, where the Au atoms are exclusively P-coordinated, while the Ag atoms are coordinated by the two pyridine nitrogen atoms. In the crystal there are also weak interactions of the perchlorate counterions with the silver atom. Addition of [Cu(MeCN)₄]BF₄ to compound 5b gives the Cu/Au-complex with P,P-coordinated gold and N,N-bonded copper centers. All products were characterized by standard analytical and spectroscopic techniques; the crystal structure of complex 6 was determined in a single crystal X-ray diffraction study.