METAL PI-COMPLEXES OF BENZENE-DERIVATIVES .48. DIMETHYLPHOSPHANO DERIVATIVES OF BIS(BENZENE) CHROMIUM AS MONODENTATE AND CHELATING LIGANDS AT MU-ETHYLIDYNE-NONA(CARBONYL)-TRI(COBALT) - SYNTHESIS VIA ETC-AUTOCATALYSIS, CRYSTAL-STRUCTURE DETERMINATION AND REDOX BEHAVIOR OF -ETA(6)-C6H5)(ETA(6)-C6H6)CR[(MU-MEC)CO-3(CO)(8)], (ME(2)P-ETA(6)-C6H5)(2)CR][(MU-MEC)CO-3(CO)(8)](2) AND [(ME(2)P-ETA(6)-C6H5)(2)CR][(MU-MEC)CO-3(CO)(7)]

Reaction of mu-ethylidyne-nona(carbonyl)-tri(cobalt) (3) with (Me(2)P- eta(6)-C6H5)(eta(6)-C6H6)Cr (1) and (Me(2)P-eta(6)-C6H5)(2)Cr (2), res pectively, at ambient temperature affords the substitution products et a(6)-C6H6)(eta(6)-C6H6)Cr[(mu-CL-MeC)CO3(CO)(8)] (5), [Me(2)P-eta(6)-C 6H5]Cr-2][(mu-MeC)Co-3(CO)(8)](2) (6) and [Me(2)P-eta(6)-C6H5Cr][(mu-M eC)Co-3(CO)(7)] (7). The surprisingly mild conditions under which thes e reactions proceed are a consequence of an electron-transfer chain (E TC) autocatalysis which operates due to the close proximity of the red ox potentials 1(+/0), 2(+/0) and 3(0/-) as determined by cyclic voltam metry. In the case of 6, reduction of the two CCo3 carbonyl cluster un its does not feature redox splitting, i.e. delta E(1/2) < 100 mV. EPR evidence for the ETC mechanism, which is initiated by the formation of the radical ions 1(+), 2(+) and 3(-), is also presented. Compounds 6 and 7 were subjected to X-ray diffraction analysis. 6: triclinic, P ($ ) over bar 1, a = 862.5(4) pm, b = 1005.7(5) pm, c = 1282.7(3) pm, alp ha = 106.54(3)degrees, beta = 94.86(3)degrees, gamma = 93.52(4)degrees , Z = 1, wR = 0.073 for 2419 reflections with F > 4 sigma(F). 7: tricl inic; P ($) over bar 1 a = 1047.4(2) pm, b = 1068.0(1) pm, c = 1442.4( 2) pm, alpha = 90.36(1)degrees, beta = 110.34(1)degrees, gamma = 113.3 2(1)degrees, Z = 2, R = 0.0435 for 2241 reflections with F > 4 sigma(F ).