The crystal and molecular structure of () 436-(η 5-C 5H 5)Fe(CO)(CH 3CO)[Ph 2PNHCH(Me)(Ph)

Abstract

The X-ray crystal structure and absolute configuration of (−) 436-(η 5-C 5H 5)Fe(CO)(CH 3CO)[Ph 2PNHCH(Me)(Ph)] have been determined from single crystal diffraction data. The compound crystallizes in the monoclinic space group P2 1 with two molecules in a unit cell of dimensions a = 10.676(4), b = 8.913(7), c = 13.275(9) Å, and β = 91.36°. The structure was solved by the Patterson method and refined to a final R value of 4.7% using 2299 independent data. The iron atom has distorted octahedral coordination, and the configuration at the iron is found to be ( S) for the (−) 436 diastereoisomer. The FeCp distances average 2.131 Å, with an Fe-(ring centroid)distance of 1.76 Å. The Fe-acetyl distance is virtually identical to that found in another iron/acetyl complex, but shows substantial variation from other compounds where the nature of the C(O)R group is changed. Comparison to the Mo-alkyl/Mo-acetyl series is made, and the argument for back-donation in transition metal acyls is strengthened. The orientation of the acetyl group is determined by a strong NH⋯O intra-molecular hydrogen bond having an N⋯O separation of only 2.86 ». The phosphine ligand has a very short FeP bond which could be in part caused by the role of the adjacent nitrogen in hydrogen bonding. The remaining ligand geometry is the same as that found in a recently reported ruthenium structure, although the absolute configurations at the chiral carbons are reversed, with the current compound being designated ( S) at this site.