10.1021/om950836o.s001 James M. Boncella James M. Boncella Mary L. Cajigal Mary L. Cajigal Khalil A. Abboud Khalil A. Abboud Competition between π Donation and α-C−H Agostic Interactions in Complexes of the Type Tp‘Ta(CH-<i>t</i>-Bu)(X)(Y) (X = Halide; Y = Halide, NR<sub>2</sub>, OR; Tp‘ = Hydrotris(3,5-dimethylpyrazolyl)borate) American Chemical Society 1996 PrC 6 H 3 THF alkylidene carbon proton NR CH π donor properties Cl KN Tp 1996-04-02 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Competition_between_Donation_and_-C_H_Agostic_Interactions_in_Complexes_of_the_Type_Tp_Ta_CH-_i_t_i_-Bu_X_Y_X_Halide_Y_Halide_NR_sub_2_sub_OR_Tp_Hydrotris_3_5-dimethylpyrazolyl_borate_/3776754 The compounds Tp‘Ta(CHC(CH<sub>3</sub>)<sub>3</sub>)X<sub>2</sub> (<b>2</b> (X = Cl), <b>3</b> (X = Br)) (Tp‘ = hydrotris(3,5-dimethylpyrazolyl)borate), have been synthesized by the reaction of KTp‘ with Ta(CHC(CH<sub>3</sub>)<sub>3</sub>)X<sub>3</sub>(thf)<sub>2</sub> in THF. One Cl ligand in <b>2</b> can be substituted with OR<sup>-</sup> (R = <i>i</i>-Pr, Me) or NMe<sub>2</sub><sup>-</sup>. The values of <sup>1</sup><i>J</i><sub>C-H</sub> for the alkylidene carbon are uniformly low due to the α-H agostic interaction between the metal center and the alkylidene proton. The magnitude of <sup>1</sup><i>J</i><sub>C-H</sub> in these compounds depends upon the π donor properties of the remaining ligands. Attempted synthesis of monoarylamide complexes by displacement of Cl<sup>-</sup> from <b>2</b> with N(H)Ar<sup>-</sup> results in proton transfer from N to C and formation of the imido complexes Tp‘Ta(CH<sub>2</sub>C(CH<sub>3</sub>)<sub>3</sub>)(NAr)Cl (Ar = 2,6-<i>i</i>-PrC<sub>6</sub>H<sub>3</sub> (<b>7</b>), Ph (<b>8</b>)). When <b>2</b> reacts with KN(Me)Ph, proton transfer occurs from the Me group to the alkylidene carbon giving the imine complex Tp‘Ta(η<sup>2</sup>-CH<sub>2</sub>NPh)(CH<sub>2</sub>CMe<sub>3</sub>)Cl (<b>9</b>). A single-crystal X-ray diffraction study of <b>9</b> confirmed the structure and suggested that <b>9</b> is best described as an azametallacyclopropane complex.