Photoelectron spectroscopy and rates of CO substitution of (. eta. sup 5 -C sub 5 H sub 4 X)Rh(CO) sub 2 compounds. Separation of. sigma. and. pi. ring substituent effects

Journal Article · Tue Jan 01 00:00:00 EST 1991 · Organometallics; (United States)

DOI:https://doi.org/10.1021/om00047a042· OSTI ID:6107062

Lichtenberger, D L; Renshaw, S K ^[1]; Basolo, F; Cheong, Minsek ^[2]

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1. Univ. of Arizona, Tucson (United States)
2. Northwestern Univ., Evanston, IL (United States)

The He I photoelectron spectra for a series of monosubstituted ({eta}{sup 5}-C{sub 5}H{sub 4}X)Rh(CO){sub 2} compounds are reported (where X = NO{sub 2}, CF{sub 3}, Cl, H, CH{sub 3}, NMe{sub 2}) and compared to the rates of carbonyl substitution reactions. The carbonyl substitution by phosphine follows an associative mechanism, and the rates are generally inhibited by greater electron richness at the metal center in these compounds. However, the rates for certain substitutions, particularly when X is Cl or NMe{sub 2}, are faster than indicated by the inductive characteristics of these groups. The photoelectron spectra of the ({eta}{sup 5}-C{sub 5}H{sub 4}X)Rh(CO){sub 2} compounds illustrate the effects of X on the electronic structure and rates of substitution. Pronounced shifts are seen in the cyclopentadienyl {pi} and metal d valence ionizations as the X group is varied. The shifts of most of the valence ionizations closely follow the inductive capabilities of the X substituents, as also indicated by correlations with Hammett {sigma} values and the carbonyl stretching frequencies of the compounds. Certain ionizations are also affected by orbitals of the X group that have {pi} symmetry with respect to the cyclopentadienyl ring. Thus, the ionization energy shifts provide a relative measure of the inductive and resonance ({pi}) interaction between X and the compound. The rates of CO substitution correlate with the ionizations when the shifts due to both the inductive and resonance ({pi}) effects are taken into account. These results suggest that the slipped ring' intermediate ({eta}{sup 5}-C{sub 5}H{sub 4}X)Rh(CO){sub 2}PPh{sub 3} is stabilized through {pi} delocalization on the cyclopentadienyl ring, thus enhancing the rates of substitution.

• DOE Contract Number: FG02-86ER13501
• OSTI ID: 6107062
• Journal Information: Organometallics; (United States), Vol. 10:1; ISSN 0276-7333
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
RHODIUM COMPLEXES
PHOTOELECTRON SPECTROSCOPY
CARBONYLS
CHEMICAL REACTION KINETICS
CYCLOALKENES
CYCLOPENTADIENE
ELECTRONIC STRUCTURE
IONIZATION POTENTIAL
LIGANDS
PHOSPHINES
ALKENES
COMPLEXES
DIENES
ELECTRON SPECTROSCOPY
HYDROCARBONS
KINETICS
ORGANIC COMPOUNDS
PHOSPHORUS COMPOUNDS
POLYENES
REACTION KINETICS
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES
400102* - Chemical & Spectral Procedures