SYNTHESIS AND PROPERTIES OF RHODIUM(I) CHLORANILATE AND 2,5-DIHYDROXY-1,4-BENZOQUINONATE COMPLEXES - CRYSTAL-STRUCTURES OF THE BINUCLEAR [RH2(MU-CA)(COD)2] AND TETRANUCLEAR [RH4(MU-CA)2(COD)4] COMPLEXES (CA = CHLORANILATE ANION)

If one treats [Rh2(mu-OMe)2(diolefin)2] [diolefin = cycloocta-1,5-diene (cod),norborna-1,5-diene(nbd)or tetrafluoro[5,6]bicyclo[2.2.2]octa-2,5,7-triene (tfb)} with chloranilic acid (H2CA) or 2,5-dihydroxy-1,4-benzoquinone (H-2-DHBQ) in a 1:1 ratio, the binuclear complexes [Rh2(mu-L)(diolefin)2] (L = CA2-, DHBQ2-) can be obtained. The complex [Rh(acac)(cod)] (acac = acetylacetonate) reacts with H2CA to give the tetranuclear complex [Rh4(mu-CA)2(cod)4]. The complex [Rh2(mu-DHBQ)(cod)2] undergoes two sequential reversible one-electron reductions at a platinum electrode in dichloromethane. The crystal structures of the complexes Rh4(mu-CA)2(cod)4] (1) and [Rh2(mu-CA)(cod)2](2) have been determined by X-ray diffraction methods. Crystal data for 1: space group P2(1)/n, a = 15.284 (6) angstrom, b = 8.976 (4) angstrom, c = 16.553 (7) angstrom, beta = 112.40 (2)-degrees, Z = 2,2086 reflections, R = 0.0253. Crystal data for 2: space group C2/c, a = 19.310 (7) angstrom, b = 6.608 (3) angstrom, c = 19.283 (8) angstrom, beta = 117.06 (2)-degrees, Z = 4, 1526 reflections, R = 0.0624. In the centrosymmetric tetranuclear complex 1 each CA2- dianion, in the o-quinone form, displays a novel coordination mode interacting with three rhodium atoms via three a-bonds through oxygens and two pi-bonds through two adjacent double bonds. The coordination around each Rh atom is completed by a cod molecule interacting in the usual manner through the two double bonds. If the midpoints of the double bonds interacting with the metals of the CA2- and cod ligands are taken into account, two Rh atoms are in a square planar and two are in a square pyramidal arrangement. The CA2- ligand, involved in a very complicate bonding with three metals, has lost the planarity, the six-membered ring showing a ''boat'' conformation with the two planar moieties tilted by 31.6 (3)-degrees. In the centrosymmetric binuclear complex 2, the strictly planar CA2- ligand, in the more common p-quinone form, chelates to two Rh centers through the oxygen atoms as a tetradentate ligand. The coordination around each Rh atom is completed by a cod ligand.