Abstract
R4PONOP-Ir-Me (R1) and R4POCOP-Ir-CO (R2), R = tBu or iPr, are known to undergo acid-catalyzed oxidative addition of H2 that yields octahedral products with two hydrides in a trans-configuration. We use density functional theory to study the free energies (?Gtrans) and equilibrium isotope effects (EIEtrans) for H2/D2 addition to R1, R2, and related complexes for R = tBu, iPr, and Me. For a given R, reaction of R1 is ∼5 kcal/mol more exergonic than R2. For a given subclass of complexes, ?Gtrans is more exergonic for the smaller R. The computed values of ?Gtrans vary between +5.1 and -17.4 kcal/mol. EIEtrans varies between 0.78 and 1.22. Counterintuitively, it is the less-exergonic reactions that afford products with shorter Ir-H bonds, greater symmetric and asymmetric trans-Ir-(H)2 stretching vibrational frequencies, and more inverse EIEtrans. This disparity is amplified in Me4PONOP-Os-CO, where ?Gtrans is -35.2 kcal/mol, yet the Os-H bonds are long, and the Os-H vibrational frequencies are low as compared with the Ir-H bonds, and EIEtrans is high (1.20). Attempts are made to account for the inverted bond strength-bond length correlation based on the hydricity of the products and the total negative charge on the trans-Ir(H)2 unit as computed using the Quantum Theory of Atoms in Molecules.
| Original language | English |
|---|---|
| Pages (from-to) | 7516-7523 |
| Number of pages | 8 |
| Journal | Inorganic Chemistry |
| Volume | 57 |
| Issue number | 13 |
| DOIs | |
| Publication status | Published - Jul 2 2018 |
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ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
Cite this
H2 Addition to Pincer Iridium Complexes Yielding trans-Dihydride Products : Unexpected Correlations of Bond Strength with Bond Length and Vibrational Frequencies. / Omar, Boushra S.; Mallah, Josephina; Ataya, Mohamad; Li, Bo; Zhou, Xiaoguang; Malakar, Santanu; Goldman, Alan S; Hasanayn, Faraj.
In: Inorganic Chemistry, Vol. 57, No. 13, 02.07.2018, p. 7516-7523.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - H2 Addition to Pincer Iridium Complexes Yielding trans-Dihydride Products
T2 - Unexpected Correlations of Bond Strength with Bond Length and Vibrational Frequencies
AU - Omar, Boushra S.
AU - Mallah, Josephina
AU - Ataya, Mohamad
AU - Li, Bo
AU - Zhou, Xiaoguang
AU - Malakar, Santanu
AU - Goldman, Alan S
AU - Hasanayn, Faraj
PY - 2018/7/2
Y1 - 2018/7/2
N2 - R4PONOP-Ir-Me (R1) and R4POCOP-Ir-CO (R2), R = tBu or iPr, are known to undergo acid-catalyzed oxidative addition of H2 that yields octahedral products with two hydrides in a trans-configuration. We use density functional theory to study the free energies (?Gtrans) and equilibrium isotope effects (EIEtrans) for H2/D2 addition to R1, R2, and related complexes for R = tBu, iPr, and Me. For a given R, reaction of R1 is ∼5 kcal/mol more exergonic than R2. For a given subclass of complexes, ?Gtrans is more exergonic for the smaller R. The computed values of ?Gtrans vary between +5.1 and -17.4 kcal/mol. EIEtrans varies between 0.78 and 1.22. Counterintuitively, it is the less-exergonic reactions that afford products with shorter Ir-H bonds, greater symmetric and asymmetric trans-Ir-(H)2 stretching vibrational frequencies, and more inverse EIEtrans. This disparity is amplified in Me4PONOP-Os-CO, where ?Gtrans is -35.2 kcal/mol, yet the Os-H bonds are long, and the Os-H vibrational frequencies are low as compared with the Ir-H bonds, and EIEtrans is high (1.20). Attempts are made to account for the inverted bond strength-bond length correlation based on the hydricity of the products and the total negative charge on the trans-Ir(H)2 unit as computed using the Quantum Theory of Atoms in Molecules.
AB - R4PONOP-Ir-Me (R1) and R4POCOP-Ir-CO (R2), R = tBu or iPr, are known to undergo acid-catalyzed oxidative addition of H2 that yields octahedral products with two hydrides in a trans-configuration. We use density functional theory to study the free energies (?Gtrans) and equilibrium isotope effects (EIEtrans) for H2/D2 addition to R1, R2, and related complexes for R = tBu, iPr, and Me. For a given R, reaction of R1 is ∼5 kcal/mol more exergonic than R2. For a given subclass of complexes, ?Gtrans is more exergonic for the smaller R. The computed values of ?Gtrans vary between +5.1 and -17.4 kcal/mol. EIEtrans varies between 0.78 and 1.22. Counterintuitively, it is the less-exergonic reactions that afford products with shorter Ir-H bonds, greater symmetric and asymmetric trans-Ir-(H)2 stretching vibrational frequencies, and more inverse EIEtrans. This disparity is amplified in Me4PONOP-Os-CO, where ?Gtrans is -35.2 kcal/mol, yet the Os-H bonds are long, and the Os-H vibrational frequencies are low as compared with the Ir-H bonds, and EIEtrans is high (1.20). Attempts are made to account for the inverted bond strength-bond length correlation based on the hydricity of the products and the total negative charge on the trans-Ir(H)2 unit as computed using the Quantum Theory of Atoms in Molecules.
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U2 - 10.1021/acs.inorgchem.7b03086
DO - 10.1021/acs.inorgchem.7b03086
M3 - Article
AN - SCOPUS:85049367400
VL - 57
SP - 7516
EP - 7523
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 13
ER -