Metall-?-Komplexe von Benzolderivaten. XXXIX. Di6-benzol>chrom: ein Baustein fuer polynukleare Bimetallkomplexe?

Article abstract of DOI:10.1016/0022-328X(92)83043-H

Nucleophilic substitution at bis(1,4-dichloro-η⁶-benzene)chromium by means of lithiumdiphenylphosphide affords di<1,4-bis(diphenylphosphano)η⁶-benzene>chromium (5).Two para-positioned organometallic diphos units and a central metal atom featuring variable charge and magnetism, render the complex 5 a versatile potential bridging ligand in oligomeric materials.Here the bifunctional chelating nature of 5 is exploited for the synthesis of the hetera-metallocyclophane <2,2,11,11-tetracarbonyl-1,1,3,3,10,10,12,12-octaphenyl-2,11-dinickela(0)-1,3,10,12-tetraphospha-η¹²- <3.3>paracyclophane>chromium (6).According to 1h, 13C and 31P NMR spectroscopic evidence the bridges -PPh2-Ni(CO)2-PPh2- in 6 in the range -80 less than T less than +50 deg C are subject to rapid reversion.This also applies to the singly -PPh2-Ni(CO)2-PPh2- bridged complex 2 which was prepared from bis(diphenylphosphano-η⁶-benzene)chromium (1) and Ni(CO)4.Cyclic voltammetry uncovers a rich redox chemistry for the trinuclear complex 6 which, however, is reversible only for the first oxidation step 6^+/0.The anodic peak potentials which follow this first, chromium-centered, oxidation are assigned to the couples Ni^+/0, Cr^2+/1 and Ni^2+/1+.The reduction 6^0/- occurs quasi reversibly; the relative ease, with which the stage 6^- is reached, points to electron delocalization over both Ni(CO)2 units.The radical cations 1⁺, 2⁺, 5⁺ and 6⁺ are also accessible through chemical oxidation, they are subjected to EPR spectroscopic study.The hyperfine interaction a(31P), observed for 2⁺ and 5⁺ testifies to spin delocalization into the ligand periphery.