An X-ray crystallographic and high field NMR study of [7-dehydrocholesteryl acetate]Fe(CO)3: Synthesis of a B-ring cyclohexadienyl cationic complex

(7-Dehydrocholesteryl acetate)Fe(CO)3 crystallizes in the triclinic space group P1 with a = 11.238(3), b = 14.718(3), c = 10.899(2) Å, α = 104.83(2), β = 113.77(2), γ = 96.75(2)°, V = 1544.2(6) Å3, for Z = 2, and R1 = 0.0572, R2 = 0.0668 for 3135 reflections with I > 3σ(I). The B ring of the complex adopts an envelope conformation quite different from that of uncomplexed steroidal B-ring dienes which have half-chair structures. The organometallic fragment renders the α-hydrogen attached to C(9) inaccessible to an approaching triphenyimethyl cation and so prevents hydride abstraction and formation of metal complexed B-ring steroidal cyclohexadienyl cations. However, the corresponding 9,11-dehydroergosteryl complex can be protonated at the 11 position to yield a B-ring cationic complex. The complexes are characterized by their high field 1H and 13C NMR spectra.