The relationship between π-cyclopentadienyl proton N.M.R. chemical shifts and metal carbonyl infrared ν(CO) frequencies in first-row transition-metal π-cyclopentadienylmetal carbonyl derivatives

Abstract

A least squares linear regression of the πcyclopentadienyl proton n.m.r. chemical shifts versus the metal carbonyl force constants k co 78 cyclopentadienylmetal carbonyl derivatives of the types C 5H 5Fe(CO) 2X, C 5H 5Fe(CO)XL, C 5H 5Co(CO)X 2, C 5H 5Mn(CO) 2L, and C 5H 5Mn(CO)(NO)X was performed. The following linear relationship was found: τ(C 5H 5) = 13.203&–0.499 k co. The correlation coefficient (r) was −0.902. Many of the compounds which deviated the most from this straight line had the metal atom in a four or five-membered ring also containing a nitrogen, phosphorus, or sulfur atom. The bonding in π-cyclopentadienyl derivatives is discussed.