The synthesis, properties, and structure of bis(amidino)-complexes of palladium. The crystal structure of bis(N,N′-di-p-tolylacetamidino)palladium(II)

Abstract

Bis(amidino)palladium complexes [{Pd[R′NC(R)NR′]₂}_n] have been prepared from the reactions of lithioamidines with [PdCl₂(PhCN)₂]. Mass spectral studies show acetamidino-complexes (R = Me) to be monomeric, but benzamidino-complexes (R = Ph) to be dimeric. In solution the latter complexes are also monomeric (by cryoscopy in C₆H₆),¹³C n.m.r. indicating chelate amidinogroups, but at low temperatures (–80 °C) a second species having bridging amidino-groups is detected. ¹⁹F N.m.r. studies of [Pd{p-FC₆H₄NC(Ph)NC₆H₄F-p}₂] suggest the presence of a species having both bridging and chelate groups. The crystal structure of [Pd{p-MeC₆H₄NC(Me) NC₆H₄-Me-p}₂] has been determined: space group Cmca, a= 32.089(13), b= 7.049(2), c= 12.282(3)Å; there are four molecules in the unit cell, each with symmetry C_2h(2/m). The structure was refined to a discrepancy index, R, of 0.039. The amidino-groups are attached to the square-planar palladium in a symmetrical bidentate σ,σ mode with C–N skeletal distances of 1.322(4)Å, Pd–N distances of 2.038(3)Å, and N–C–N angles of 108.4(3)°.