Metal-acetylide bonding in (η5-C5H5)Fe(CO)2C≡CR compounds. Measures of metal-dπ-acetylide-π interactions from photoelectron spectroscopy

Dennis L. Lichtenberger, Sharon K. Renshaw, R Morris Bullock

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Abstract

Gas-phase He I and He II photoelectron spectroscopy is used to experimentally determine the bonding interactions of η1-acetylide ligands in (η5-C5H5)Fe(CO)2C≡CR compounds (R = H, tBu, or phenyl). The spectra show a large amount of interaction between the metal dπ orbitals and the acetylide π orbitals. Evidence for this is obtained from the splitting of metal-based ionization bands, from the shifts in Cp-based and acetylide-based ionizations, from the changes in ionization cross sections between the He I and He II spectra, and from vibrational fine structure in the metal-based ionizations. The data indicate that the predominant π interactions between the acetylide ligands and the metal are filled/filled interactions between the occupied acetylide π bonds and the occupied metal dπ orbitals. The electronic interactions of the C≡CR ligands with the metal are compared with those of CH3 (a primiarly σ donor ligand), halides (π donor ligands), and C≡N (a weak π* acceptor ligand), and are very similar to the interactions of the chloro ligand. Metal-to-acetylide-π* back-bonding is extremely small in the acetylide compounds. Varying the acetylide substituent causes significant changes in the σ and π donor properties of the C≡CR ligand. Compared to C≡CH, the C≡CtBu ligand is a stronger ódonor ligand and also has a stronger filled/filled interaction between the metal dπ and acetylide π orbitals. The electronic mixing with the C≡CPh ligand is even more extensive, since the metal dπ orbitals and the C≡C π bonds are further mixed with the phenyl ring π orbitals. The nature of these π interactions helps to explain the observed reactivity of electrophiles with MLnC≡CR compounds and the observed electronic communication along the metal-carbon-carbon atom chain in transition metal-acetylide compounds.

Original languageEnglish
Pages (from-to)3276-3285
Number of pages10
JournalJournal of the American Chemical Society
Volume115
Issue number8
Publication statusPublished - Apr 21 1993

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Photoelectron Spectroscopy
Carbon Monoxide
Photoelectron spectroscopy
Metals
Ligands
Ionization
Carbon
iron pentacarbonyl
Transition metal compounds
Gases

ASJC Scopus subject areas

  • Chemistry(all)

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Metal-acetylide bonding in (η5-C5H5)Fe(CO)2C≡CR compounds. Measures of metal-dπ-acetylide-π interactions from photoelectron spectroscopy. / Lichtenberger, Dennis L.; Renshaw, Sharon K.; Bullock, R Morris.

In: Journal of the American Chemical Society, Vol. 115, No. 8, 21.04.1993, p. 3276-3285.

Research output: Contribution to journalArticle

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title = "Metal-acetylide bonding in (η5-C5H5)Fe(CO)2C≡CR compounds. Measures of metal-dπ-acetylide-π interactions from photoelectron spectroscopy",
abstract = "Gas-phase He I and He II photoelectron spectroscopy is used to experimentally determine the bonding interactions of η1-acetylide ligands in (η5-C5H5)Fe(CO)2C≡CR compounds (R = H, tBu, or phenyl). The spectra show a large amount of interaction between the metal dπ orbitals and the acetylide π orbitals. Evidence for this is obtained from the splitting of metal-based ionization bands, from the shifts in Cp-based and acetylide-based ionizations, from the changes in ionization cross sections between the He I and He II spectra, and from vibrational fine structure in the metal-based ionizations. The data indicate that the predominant π interactions between the acetylide ligands and the metal are filled/filled interactions between the occupied acetylide π bonds and the occupied metal dπ orbitals. The electronic interactions of the C≡CR ligands with the metal are compared with those of CH3 (a primiarly σ donor ligand), halides (π donor ligands), and C≡N (a weak π* acceptor ligand), and are very similar to the interactions of the chloro ligand. Metal-to-acetylide-π* back-bonding is extremely small in the acetylide compounds. Varying the acetylide substituent causes significant changes in the σ and π donor properties of the C≡CR ligand. Compared to C≡CH, the C≡CtBu ligand is a stronger {\'o}donor ligand and also has a stronger filled/filled interaction between the metal dπ and acetylide π orbitals. The electronic mixing with the C≡CPh ligand is even more extensive, since the metal dπ orbitals and the C≡C π bonds are further mixed with the phenyl ring π orbitals. The nature of these π interactions helps to explain the observed reactivity of electrophiles with MLnC≡CR compounds and the observed electronic communication along the metal-carbon-carbon atom chain in transition metal-acetylide compounds.",
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AB - Gas-phase He I and He II photoelectron spectroscopy is used to experimentally determine the bonding interactions of η1-acetylide ligands in (η5-C5H5)Fe(CO)2C≡CR compounds (R = H, tBu, or phenyl). The spectra show a large amount of interaction between the metal dπ orbitals and the acetylide π orbitals. Evidence for this is obtained from the splitting of metal-based ionization bands, from the shifts in Cp-based and acetylide-based ionizations, from the changes in ionization cross sections between the He I and He II spectra, and from vibrational fine structure in the metal-based ionizations. The data indicate that the predominant π interactions between the acetylide ligands and the metal are filled/filled interactions between the occupied acetylide π bonds and the occupied metal dπ orbitals. The electronic interactions of the C≡CR ligands with the metal are compared with those of CH3 (a primiarly σ donor ligand), halides (π donor ligands), and C≡N (a weak π* acceptor ligand), and are very similar to the interactions of the chloro ligand. Metal-to-acetylide-π* back-bonding is extremely small in the acetylide compounds. Varying the acetylide substituent causes significant changes in the σ and π donor properties of the C≡CR ligand. Compared to C≡CH, the C≡CtBu ligand is a stronger ódonor ligand and also has a stronger filled/filled interaction between the metal dπ and acetylide π orbitals. The electronic mixing with the C≡CPh ligand is even more extensive, since the metal dπ orbitals and the C≡C π bonds are further mixed with the phenyl ring π orbitals. The nature of these π interactions helps to explain the observed reactivity of electrophiles with MLnC≡CR compounds and the observed electronic communication along the metal-carbon-carbon atom chain in transition metal-acetylide compounds.

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