Conformation-Reactivity Relationships for the Organotransition-Metal Complexes (η5-C5H5)Fe(CO)(PPh3)R and (η5-C5H5)Re(NO)(PPh3)R (R = Alkyl and Aryl)

A conformational analysis is described for pseudooctahedral complexes of the type (η5-C5H5)Fe(CO)(PPh,)R (1) and (η5-C5H5)Re(NO)(PPh3)R (2) (R = alkyl and aryl). The analysis is based upon extended Hiickel calculations performed on the model iron complexes (η5-C5H5)Fe(CO)(PPhH2)R [R = CH3, C2H5, CH(CH3)2, C(CH3)3, Sn(CH3)3, and Ph] and rhenium complexes (η5-C5H5)Re(NO)(PPhH2)R [R = C2H5, CH2Ph, and CH2(2,6-C6H3Me2)]. For R groups in 1 and 2 with a single Ca substituent (e.g., C2H5 and CH2Ph), the most preferred conformation places the Ca substituent between the cyclopentadienyl and the CO(NO) ligands. For R groups in 1 and 2 with two Cα substituents [e.g., CH(CH3)2], the most stable conformation has the two substituents straddling the cyclopentadienyl ligand. These most stable conformations correlate well with known X-ray crystal structures for 1 and 2. The conformational analysis elaborated herein is used to explain the high stereospecificities that have been observed in the reactions of 1 and 2. © 1985, American Chemical Society. All rights reserved.