Recent Advances in the Chemistry of Transition Metal Complexes of Unsaturated Bidentate Sulfur Donor Ligands (Metal Dithienes)

The transition metal complexes of ligands derived from 1,2-dithiodiketones and/or cis-1,2-ethylenedithiols, known as metal dithienes or dithiolenes, undergo reactions typical of unsaturated organic compounds. This behavior is rationalized by topological considerations. The planar bisdithienes of Ni(II), Pd(II), and Pt(II) of composition M [S 2 C 2 R 2 ] 2, e.g., are closely related topologically to p-benzoquinone. The characteristic π-delocalization in metal dithienes accounts for the high electron affinity and electric conductivity of the neutral complexes. Dithiene resonance is also the essential stabilizing factor of trigonal prismatic geometry in the neutral trisdithienes, M [S 2 C 2 R 2 ] 3 . Alkylation of anionic dithienes or dithiolatocomplexes affords new complexes—e.g., of composition Ni[(CH 3 ) 2 (S 2 C 2 Ph 2 ) 2 ]. The latter reacts with Fe(CO) 5 to form a complex of diphenyl(thioketocarbene), Ph 2 C 2 S[Fe 2 (CO) 6 ]. Synthesis of a number of macrocyclic complexes is described also.