SUBSTITUTED CYCLOPENTADIENYL COMPOUNDS .2. MOLECULAR-ORBITAL STUDY OF RING SLIPPAGE IN SOME RHODIUM(I) DERIVATIVES AND THE X-RAY STRUCTURE OF ETA-5-PHENYLCYCLOPENTADIENYLBIS(ETA-2-ETHENE)RHODIUM(I)

The X-ray structure of (eta-5-C5H4-C6H5)Rh(eta-2C2H4)2 has been determined. The substituent on the cyclopentadienyl ring crosses a double bond of the complexed ethene. i.e. relative to the rhodium atom it is transoid to the second olefinic double bond. The geometry of related systems is such that olefinic functions parallel the bond between the cyclopentadienyl ring and substituent. CNDO/U molecular orbital calculations have been performed on a series of these systems. The former orientation is often associated with a small contribution from an eta-4-diolefin-eta-1-alkyl rotamer while the latter is associated with an eta-3-allyl-eta-2-ene rotamer. The reasons for the preference for one of these structures in substituted cyclopentadienyl-rhodium(I)bis(olefin) compounds are discussed.