10.1021/acs.organomet.8b00387.s002 Zhihui Zhang Zhihui Zhang Xuejun Feng Xuejun Feng Qun Chen Qun Chen Mingyang He Mingyang He Yaoming Xie Yaoming Xie R. Bruce King R. Bruce King Energetics of Variable Hapticity of Carbocyclic Rings in Cyclopentadienylmetal Carbonyl Systems of the Second Row Transition Metals C<sub>5</sub>H<sub>5</sub>M(CO)<sub><i>n</i></sub>C<sub><i>m</i></sub>H<sub><i>m</i></sub> (M = Ru, Tc, Mo, Nb) Including Mechanistic Studies of Carbonyl Dissociation American Chemical Society 2018 Cyclopentadienylmetal Carbonyl Systems derivative C 8 H 8 ring 16- electron configuration C 8 H 8 uncomplexed CpM energy barrier Carbonyl Dissociation Decarbonylation CpNb decarbonylation step proceeds C n H n ring energy transition state monocarbonyl C n H n 2018-07-23 17:49:41 Dataset https://acs.figshare.com/articles/dataset/Energetics_of_Variable_Hapticity_of_Carbocyclic_Rings_in_Cyclopentadienylmetal_Carbonyl_Systems_of_the_Second_Row_Transition_Metals_C_sub_5_sub_H_sub_5_sub_M_CO_sub_i_n_i_sub_C_sub_i_m_i_sub_H_sub_i_m_i_sub_M_Ru_Tc_Mo_Nb_Including_Mechanistic_Studies_of_C/6852368 Decarbonylation of the experimentally known CpRu­(CO)<sub>2</sub>(η<sup>1</sup>-C<sub>5</sub>H<sub>5</sub>), CpMo­(CO)<sub>2</sub>(η<sup>3</sup>-C<sub>7</sub>H<sub>7</sub>), and CpNb­(CO)<sub>2</sub>(η<sup>4</sup>-C<sub>8</sub>H<sub>8</sub>) (Cp = η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>), each with uncomplexed 1,3-butadiene units in the C<sub><i>n</i></sub>H<sub><i>n</i></sub> ring, as well as the related CpTc­(CO)<sub>2</sub>(η<sup>2</sup>-C<sub>6</sub>H<sub>6</sub>), to give the corresponding carbonyl-free derivatives CpM­(η<sup><i>n</i></sup>-C<sub><i>n</i></sub>H<sub><i>n</i></sub>) derivatives has been studied by density functional theory. For ruthenium, technetium, and molybdenum the coordinated C<sub><i>n</i></sub>H<sub><i>n</i></sub> ring of the intermediate monocarbonyl CpM­(CO)­(η<sup><i>n</i>–2</sup>-C<sub><i>n</i></sub>H<sub><i>n</i></sub>) contains an uncomplexed CC double bond and each decarbonylation step proceeds with a significant energy barrier represented by a higher energy transition state. However, decarbonylation of CpNb­(CO)<sub>2</sub>(η<sup>4</sup>-C<sub>8</sub>H<sub>8</sub>) to the monocarbonyl proceeds without an energy barrier, preserving the tetrahapto coordination of the C<sub>8</sub>H<sub>8</sub> ring to give CpNb­(CO)­(η<sup>4</sup>-C<sub>8</sub>H<sub>8</sub>) in which the niobium atom has only a 16-electron configuration. All of the monocarbonyl derivatives CpM­(CO)­(C<sub><i>n</i></sub>H<sub><i>n</i></sub>) are predicted to be strongly energetically disfavored with respect to disproportionation to give CpM­(CO)<sub>2</sub>(C<sub><i>n</i></sub>H<sub><i>n</i></sub>) + CpM­(C<sub><i>n</i></sub>H<sub><i>n</i></sub>). This allows us to understand the failure to date to synthesize any of the monocarbonyl derivatives.