I ntermetallic c a nd n Communication in Heterodinuclear ¿i-Cyclooctatetraene Complexes**

The reaction of ((C5R 5)Cr(/?6- Cot)) (R = H, Me; Cot = cyclooctatetra- ene) with ((CO)3FeO/-m-cyclooctene)2) affords the heterodinuclear complexes ((C5R 5) C r { ^ 5(Cr):i/3(F^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, PR'3 (R# = Me, Ph, OEt, F) to ob­ tain ((C5R 5)Cr{/t->75(Cr):J/3(#?)-Cot}Fe- (CO)2PR'3) (R = H, R' = Me: 3a; R = H, R' = Ph: 3b; R = Me, R' = Me: 4a; R = Me, R' -Ph: 4b; R = Me, R' = and 304 pm, respectively. The heterodinu­ clear complexes were investigated by cyclic voltammetry and ESR spec­ troscopy in order to elucidate the role of the permethylation of the cyclopentadi- enyl ligand and the influence of phos­ phane ligands with different rc-accepting abilities. The ESR spectroscopic results reveal surprisingly large 31P hyperfine coupling constants (hfee). These can be explained by a superposition of two dif­ ferent electron spin transfer mechanisms, which include a a- and a 7t-bonding mode between the Cr and Fe centers,