INTERMETALLIC SIGMA-COMMUNICATION AND PI-COMMUNICATION IN HETERODINUCLEAR MU-CYCLOOCTATETRAENE COMPLEXES

The reaction of [(C5R5)Cr(eta(6)-Cot)](R = H, Me; Cot = cyclooctatetra ene) with [(CO)(2)Fe(eta-cis-cyclooctene)(2)] affords the heterodinucl ear complexes [(C5R5)Cr{mu-eta(5)(Cr):eta(3)(Fe)-Cot}Fe(CO)(3)] (R = H : 1, R = Me: 2) in quite good yields. One of the CO ligands in 1 and 2 can be easily substituted by a phosphane ligand, PR3' (R' = Me, Ph, O Et, F) to obtain 5R5)Cr{mu-eta(5)(Cr):eta(3)(Fe)-Cot}Fe(CO)(2)PR3'] (R = H, R' = Me: 3a; R = H, R' = Ph: 3b; R = Me, R' = Me: 4a; R = Me, R' = Ph: 4b; R = Me, R' = OEt: 4c; R = Me, R' = F: 4d). The X-ray struct ure determinations of 2, 3a, and 4c showed exclusively synfacial coord ination of the two metal ligand moieties, despite the bulky C5Me5 (Cp ) ligand in 2 and 4c. However, the steric demand of Cp gives rise to structural distortions in 2 and 4c, compared to the Cp-containing prod ucts 1 and 3a, and an elongation of the Cr-Fe distance from 293 pm to 303 and 304 pm, respectively The heterodinuclear complexes were invest igated by cyclic voltammetry and ESR spectroscopy in order to elucidat e the role of the permethylation of the cyclopentadienyl ligand and th e influence of phosphane ligands with different pi-accepting abilities . The ESR spectroscopic results reveal surprisingly large P-31 hyperfi ne coupling constants (hfcc). These can be explained by a superpositio n of two different electron spin transfer mechanisms, which include a sigma- and a pi-bonding mode between the Cr and Fe centers.