STERIC MEASUREMENT OF SUBSTITUTED CYCLOPENTADIENE LIGANDS AND THE SYNTHESIS AND H-1-NMR SPECTRAL-ANALYSIS OF [(ETA-5-C5H4R)FE(CO)(L)I] COMPLEXES WITH VARIABLE-R

The synthesis of a range of complexes, [(eta(5)-C5H4R)Fe(CO)(L)I] (R = COOMe, I, CHPh2, iPr, SiMe3, Ph, CPh3; L = P(OMe)3, P(OCH2CMe3)3, P(O-omicron-Tol)3, P(OiPr)3, PPh3, P(CH2Ph)3, PPh2Me, P(NMe2)3) is reported. Complexes were characterized by NMR and IR spectroscopy, mass spectrometry, and elemental analysis. Four separate cyclopentadienyl ring proton resonances are observed in the NMR spectra of the iron complexes, and their assignments were determined by NOE experiments. NOE data obtained on [(eta(5)-C5H4R)Fe(CO)(L)I] in which the ortho phenyl ring protons (L = PPh3) or OMe protons (L = P(OMe)3) were irradiated revealed preferred solution conformations of the ligand set relative to the ring substituent. For instance, for R = iPr, CPh3, tBu, and SiMe3, the PPh3 oriented itself close to the ring C atoms meta to the cyclopentadienyl ring substituent. For R = Me and I, near equal probability of all possible solution conformers was observed. The steric size of the substituted cyclopentadienyl ring was determined using the cone angle concept with either the metal (theta(1)) or the ring centroid (theta(2)) as the apex of the cone. Cone angles for a range of substituted C5H4R ligands were determined. A correlation between the cone angles (theta(2), ring centroid as apex) and DELTA(H2 - H5) (H2, H5 ortho cyclopentadienyl ring protons resonances) of the [(eta(5)-C5H4R)Fe(CO)(L)I] complexes was observed (R2 = 0.96, adjusted for degrees of freedom). This correlation was improved upon inclusion of an electronic paramter (i.e. DELTA(H2 - H5) = a-theta(2) + bE; E = Hammett function, a, b = constants), e.g. E = sigma(R)-: R2 = 0.99.