Combined computational and experimental study of substituent effects on the thermodynamics of H2, CO, arene, and alkane addition to iridium

Karsten Krogh-Jespersen, Margaret Czerw, Keming Zhu, Bharat Singh, Mira Kanzelberger, Nitesh Darji, Patrick D. Achord, Kenton B. Renkema, Alan S Goldman

Research output: Contribution to journalArticle

117 Citations (Scopus)

Abstract

The thermodynamics of small-molecule (H2, arene, alkane, and CO) addition to pincer-ligated iridium complexes of several different configurations (three-coordinate d8, four-coordinate d8, and five-coordinate d6) have been investigated by computational and experimental means. The substituent para to the iridium (Y) has been varied in complexes containing the (Y-PCP)Ir unit (Y-PCP = ν3-1,3,5-C6H2[CH2 PR2]2Y; R = methyl for computations; R = tert-butyl for experiments); substituent effects have been studied for the addition of H2, C-H, and CO to the complexes (Y-PCP)Ir, (Y-PCP)Ir(CO), and (Y-PCP)Ir(H)2. Para substituents on arenes undergoing C-H bond addition to (PCP)Ir or to (PCP)Ir(CO) have also been varied computationally and experimentally. In general, increasing electron donation by the substituent Y in the 16-electron complexes, (Y-PCP)Ir(CO) or (Y-PCP)Ir(H)2, disfavors addition of H-H or C-H bonds, in contradiction to the idea of such additions being oxidative. Addition of CO to the same 16-electron complexes is also disfavored by increased electron donation from Y. By contrast, addition of H-H and C-H bonds or CO to the three-coordinate parent species (Y-PCP)Ir is favored by increased electron donation. In general, the effects of varying Y are markedly similar for H2, C-H, and CO addition. The trends can be fully rationalized in terms of simple molecular orbital interactions but not in terms of concepts related to oxidation, such as charge-transfer or electronegativity differences.

Original languageEnglish
Pages (from-to)10797-10809
Number of pages13
JournalJournal of the American Chemical Society
Volume124
Issue number36
DOIs
Publication statusPublished - Sep 11 2002

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Iridium
Alkanes
Carbon Monoxide
Thermodynamics
Paraffins
Electrons
Electronegativity
Molecular orbitals
Charge transfer
Oxidation
Molecules
Experiments

ASJC Scopus subject areas

  • Chemistry(all)

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Combined computational and experimental study of substituent effects on the thermodynamics of H2, CO, arene, and alkane addition to iridium. / Krogh-Jespersen, Karsten; Czerw, Margaret; Zhu, Keming; Singh, Bharat; Kanzelberger, Mira; Darji, Nitesh; Achord, Patrick D.; Renkema, Kenton B.; Goldman, Alan S.

In: Journal of the American Chemical Society, Vol. 124, No. 36, 11.09.2002, p. 10797-10809.

Research output: Contribution to journalArticle

Krogh-Jespersen, Karsten ; Czerw, Margaret ; Zhu, Keming ; Singh, Bharat ; Kanzelberger, Mira ; Darji, Nitesh ; Achord, Patrick D. ; Renkema, Kenton B. ; Goldman, Alan S. / Combined computational and experimental study of substituent effects on the thermodynamics of H2, CO, arene, and alkane addition to iridium. In: Journal of the American Chemical Society. 2002 ; Vol. 124, No. 36. pp. 10797-10809.
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abstract = "The thermodynamics of small-molecule (H2, arene, alkane, and CO) addition to pincer-ligated iridium complexes of several different configurations (three-coordinate d8, four-coordinate d8, and five-coordinate d6) have been investigated by computational and experimental means. The substituent para to the iridium (Y) has been varied in complexes containing the (Y-PCP)Ir unit (Y-PCP = ν3-1,3,5-C6H2[CH2 PR2]2Y; R = methyl for computations; R = tert-butyl for experiments); substituent effects have been studied for the addition of H2, C-H, and CO to the complexes (Y-PCP)Ir, (Y-PCP)Ir(CO), and (Y-PCP)Ir(H)2. Para substituents on arenes undergoing C-H bond addition to (PCP)Ir or to (PCP)Ir(CO) have also been varied computationally and experimentally. In general, increasing electron donation by the substituent Y in the 16-electron complexes, (Y-PCP)Ir(CO) or (Y-PCP)Ir(H)2, disfavors addition of H-H or C-H bonds, in contradiction to the idea of such additions being oxidative. Addition of CO to the same 16-electron complexes is also disfavored by increased electron donation from Y. By contrast, addition of H-H and C-H bonds or CO to the three-coordinate parent species (Y-PCP)Ir is favored by increased electron donation. In general, the effects of varying Y are markedly similar for H2, C-H, and CO addition. The trends can be fully rationalized in terms of simple molecular orbital interactions but not in terms of concepts related to oxidation, such as charge-transfer or electronegativity differences.",
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AU - Czerw, Margaret

AU - Zhu, Keming

AU - Singh, Bharat

AU - Kanzelberger, Mira

AU - Darji, Nitesh

AU - Achord, Patrick D.

AU - Renkema, Kenton B.

AU - Goldman, Alan S

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AB - The thermodynamics of small-molecule (H2, arene, alkane, and CO) addition to pincer-ligated iridium complexes of several different configurations (three-coordinate d8, four-coordinate d8, and five-coordinate d6) have been investigated by computational and experimental means. The substituent para to the iridium (Y) has been varied in complexes containing the (Y-PCP)Ir unit (Y-PCP = ν3-1,3,5-C6H2[CH2 PR2]2Y; R = methyl for computations; R = tert-butyl for experiments); substituent effects have been studied for the addition of H2, C-H, and CO to the complexes (Y-PCP)Ir, (Y-PCP)Ir(CO), and (Y-PCP)Ir(H)2. Para substituents on arenes undergoing C-H bond addition to (PCP)Ir or to (PCP)Ir(CO) have also been varied computationally and experimentally. In general, increasing electron donation by the substituent Y in the 16-electron complexes, (Y-PCP)Ir(CO) or (Y-PCP)Ir(H)2, disfavors addition of H-H or C-H bonds, in contradiction to the idea of such additions being oxidative. Addition of CO to the same 16-electron complexes is also disfavored by increased electron donation from Y. By contrast, addition of H-H and C-H bonds or CO to the three-coordinate parent species (Y-PCP)Ir is favored by increased electron donation. In general, the effects of varying Y are markedly similar for H2, C-H, and CO addition. The trends can be fully rationalized in terms of simple molecular orbital interactions but not in terms of concepts related to oxidation, such as charge-transfer or electronegativity differences.

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