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
N1 - Funding Information:
This study was funded by the Lebanese National Council for Scientific Research and by the University Research Board at AUB. We thank the National Science Foundation for support of this work through Grant CHE No. 1465203. The HPC teams at AUB and Rutgers are thanked for providing computational resources and administrative support.
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
C2 - 29894175
AN - SCOPUS:85049367400
VL - 57
SP - 7516
EP - 7523
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 13
ER -