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.