STRUCTURAL-CHANGES ACCOMPANYING OXIDATIVE ADDITIONS OF TETRACHLORO-1,2-BENZOQUINONE TO PHOSPHINE-BRIDGED BINUCLEAR AND TRINUCLEAR RHODIUM COMPLEXES

Addition of tetrachloro-1,2-benzoquinone to bi- and trinuclear rhodium complexes results in conversion of terminal carbon monoxide ligands to bridging ones and the formation of new Rh-Rh bonds. These structural changes are not seen in analogous reactions of mononuclear complexes. Reaction of tetrachloro-1,2-benzoquinone with Rh2(CO)2(μ-S)(μ-dpm)2(1) (dpm = bis(diphenyl-phosphino)methane) yields brown Rh2(1,2O2C6Cl4)(μ-CO)(CO)(μ-S)(μ-dpm)2(2), which crystallizes in the monoclinic space group P21/c as a mono(diethyl ether) solvate with a = 15.956 (3) Å, b=21.101 (5)Å, c=18.743 (4) Å, β=112.14 (2)°, and Z=4 at 130 K. Refinement of 7435 reflections with 360 parameters yielded R = 0.0560 and Rw=0.0690. The o-quinone has added to one rhodium to form a chelating catecholato ligand. One of the terminal carbon monoxide ligands in 1 has been converted into a bridging ligand in 2, and the Rh•••Rh distance has shortened from 3.154 (2) Å in 1 to 2.966 (1) Å in 2. Tetrachloro-1,2-benzoquinone also adds to the A-frame [Rh2(CO)2(μ-Cl)(μ-dpm)2][BPh4] in a similar fashion to yield green [Rh2(1,2-O2C6Cl4)(μ-CO)(CO)(μ-dpm)2][BPh4]. With [Rh3(CO)3(μ-Cl)(Cl){μ-(Ph2PCH2)2EPh}2[BPh4] (E=P or As), the adducts [Rh3(1,2-O2C6Cl4)(μ-CO)2(CO)(μ-Cl)Cl{μ-(Ph2PCH2)2EPh}2][BPh4] are formed, in which two terminal carbonyl groups have been converted to bridging groups. These adducts can lose the dioxolene ligand, and its transfer to Ir(CO)Cl(PH3)2has been observed. © 1990, American Chemical Society. All rights reserved.