Rhodium Acetylacetonate and Iron Tricarbonyl Complexes of Tetracyclone and 3-Ferrocenyl-2,4,5-triphenylcyclopentadienone: An X-ray Crystallographic and NMR Study

Tetracyclone reacts with Fe2(CO)9 and with (acac)Rh(C2H4)2 to give (C4Ph4CO)Fe(CO)3 (3) and (C4Ph4CO)Rh(acac) (11), respectively. Likewise, 3-ferrocenyl-2,3,4-triphenylcyclopentadienone (2) yields (C4Ph3FcCO)Fe(CO)3 (7) and (C4Ph3FcCO)Rh(acac) (14). In 3, the peripheral phenyl substituents adopt a propeller conformation in the solid state, and the barrier to fluxionality of the Fe(CO)3 fragment is so low as to preclude the observation of slowed tripodal rotation at low temperature. In contrast, the ferrocenyl analogue 7 shows restricted tripodal rotation, but this may be the result of steric interference by the bulky ferrocenyl substituent. In the crystal, (tetracyclone)Rh(acac) (11) exists as a head-to-tail dimer in which the rhodium center is bonded to the γ-carbon of the acetylacetonate ligand in the other half of the molecule. The ferrocenyl analogue 14 is monomeric both in the solid state and in solution, and the rotation barrier of the Rh(acac) fragment has been evaluated as 12 kcal mol-1. The mass spectra of the rhodium complexes are discussed in terms of doubly charged ions containing Rh(III). The potential use of these metal-complexed cyclopentadienones as precursors to pentaarylcyclopentadienyl systems is discussed.