Unraveling the Major Differences between the Trinuclear Cyclopentadienylmetal Carbonyl Chemistry of Cobalt and That of Nickel-A Theoretical Study

Yuexia Lin; Hongyan Wang; R Bruce King

doi:10.1021/acsomega.3c02849

Unraveling the Major Differences between the Trinuclear Cyclopentadienylmetal Carbonyl Chemistry of Cobalt and That of Nickel-A Theoretical Study

ACS Omega. 2023 Jul 6;8(28):25392-25400. doi: 10.1021/acsomega.3c02849. eCollection 2023 Jul 18.

Authors

Yuexia Lin¹, Hongyan Wang¹, R Bruce King²

Affiliations

¹ School of Physical Science and Technology, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, China.
² Department of Chemistry and Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, United States.

Abstract

The geometries and energetics of the trinuclear cyclopentadienylmetal carbonyls Cp₃M₃(CO)_n (Cp = η⁵-C₅H₅); M = Co, Ni; n = 3, 2, 1, 0) have been investigated by density functional theory. The cobalt and nickel systems are found to be rather different owing to the different electronic configurations of the metal atoms. For cobalt, the small calculated energy separation of 5.0 kcal/mol between the two lowest-energy singlet Cp₃Co₃(μ₃-CO)(μ-CO)₂ and Cp₃Co₃(μ-CO)₃ tricarbonyl structures accounts for the experimental results of both isomers as stable species that can be isolated and structurally characterized by X-ray crystallography. The corresponding Cp₃Ni₃(CO)₃ species in the nickel system are predicted not to be viable owing to exothermic CO dissociation to give the experimentally observed very stable Cp₃Ni₃(μ-CO)₂, which is found to be the lowest-energy isomer by a substantial margin of ∼25 kcal/mol. In all of the low-energy Cp₃M₃(CO)_n (n = 2, 1) structures, including that of the experimentally known triplet spin state Cp₃Co₃(μ₃-CO)₂, all of the carbonyl groups are face-bridging or face-semi-bridging μ₃-CO groups bonded to all three metal atoms of the M₃ triangle. In the lowest-energy carbonyl-free Cp₃M₃ (M = Co, Ni) structures, agostic C-H-M interactions are found using hydrogens of the Cp rings. In addition, the lowest-energy Cp₃Ni₃ is the only structure among all of the low-energy Cp₃M₃(CO)_n (M = Co, Ni; n = 3, 2, 1, 0) structures in which each Cp ring is a bridging rather than terminal ligand.