10.1021/ja063282x.s003 Liam P. Spencer Liam P. Spencer Chad Beddie Chad Beddie Michael B. Hall Michael B. Hall Michael D. Fryzuk Michael D. Fryzuk Synthesis, Reactivity, and DFT Studies of Tantalum Complexes Incorporating Diamido-<i>N</i>-heterocyclic Carbene Ligands. Facile Endocyclic C−H Bond Activation American Chemical Society 2006 tantalum alkylidene ligand metallaaziridine moiety tantalum derivatives DFT Studies Metathesis reactions alkane elimination reactions Cl 2Ta pendent amine donor deuterium atoms Attempts trialkyl tantalum complexes energy pathway metallaaziridine ring forms model complexes show ArNHCH 2CH Ar DFT calculations 2006-09-27 00:00:00 Dataset https://acs.figshare.com/articles/dataset/Synthesis_Reactivity_and_DFT_Studies_of_Tantalum_Complexes_Incorporating_Diamido_i_N_i_heterocyclic_Carbene_Ligands_Facile_Endocyclic_C_H_Bond_Activation/3057370 The syntheses of tantalum derivatives with the potentially tridentate diamido-<i>N</i>-heterocyclic carbene (NHC) ligand are described. Aminolysis and alkane elimination reactions with the diamine−NHC ligands, <sup>Ar</sup>[NCN]H<sub>2</sub> (where <sup>Ar</sup>[NCN]H<sub>2</sub> = (ArNHCH<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>(C<sub>3</sub>N<sub>2</sub>); Ar = Mes, <i>p</i>-Tol), provided complexes with a bidentate amide−amine donor configuration. Attempts to promote coordination of the remaining pendent amine donor were unsuccessful. Metathesis reactions with the dilithiated diamido−NHC ligand (<sup>Ar</sup>[NCN]Li<sub>2</sub>) and various Cl<i><sub>x</sub></i>Ta(NR‘<sub>2</sub>)<sub>5-</sub><i><sub>x</sub></i> precursors were successful and generated the desired octahedral <sup>Ar</sup>[NCN]TaCl<i><sub>x</sub></i>(NR‘<sub>2</sub>)<sub>3-</sub><i><sub>x</sub></i> complexes. Attempts to prepare trialkyl tantalum complexes by this methodology resulted in the formation of an unusual metallaaziridine derivative. DFT calculations on model complexes show that the strained metallaaziridine ring forms because it allows the remaining substituents to adopt preferable bonding positions. The calculations predict that the lowest energy pathway involves a tantalum alkylidene intermediate, which undergoes C−H bond activation α to the amido to form the metallaaziridine moiety. This mechanism was confirmed by examining the distribution of deuterium atoms in an experiment between <sup>Mes</sup>[NCN]Li<sub>2</sub> and Cl<sub>2</sub>Ta(CD<sub>2</sub>Ph)<sub>3</sub>. The single-crystal X-ray structures of <i><sup>p</sup></i><sup>-Tol</sup>[NCNH]Ta(NMe<sub>2</sub>)<sub>4</sub> (<b>3</b>), <sup>Mes</sup>[NCNH]TaCHPh(CH<sub>2</sub>Ph)<sub>2</sub> (<b>4</b>), <i><sup>p</sup></i><sup>-Tol</sup>[NCN]Ta(NMe<sub>2</sub>)<sub>3</sub> (<b>7</b>), <sup>Mes</sup>[NCCN]Ta(CH<sub>2</sub><i><sup>t</sup></i><sup></sup>Bu)<sub>2</sub> (<b>11</b>), and <sup>Mes</sup>[NCCN]TaCl(CH<sub>2</sub><i><sup>t</sup></i><sup></sup>Bu) (<b>14</b>) are included.