Scorpionato Halide Complexes [(TpPh,Me)Ni–X] [X = Cl, Br, I; TpPh,Me = Hydrotris(3‐phenyl‐5‐methyl‐1‐pyrazolyl)borate]: Structures, Spectroscopy, and Pyrazole Adducts

Pseudotetrahedral scorpionato halide complexes [(TpPh,Me)Ni–X] [TpPh,Me = hydrotris(3‐phenyl‐5‐methyl‐1‐pyrazolyl)borate] were synthesized by metathesis of Tl(TpPh,Me) and NiX2 (X = Cl, Br, I). Pyrazole adducts [(TpPh,Me)Ni(HpzPh,Me)(X)] (X = Cl, I) were also obtained. [(TpPh,Me)Ni–X] (X = Br, I) are isomorphous with previously reported [(TpPh,Me)Ni–Cl], and a new solvated pseudo‐polymorph [(TpPh,Me)Ni–Cl]·2CH2Cl2 was found in this work. Ni–X bond lengths correspond to ionic radii of the halide ions, but some variations in Ni–Cl and Ni–N bond lengths are respectively attributed to bending of the chloride from the ideal threefold HB···Ni axis and to the size of the 3‐pyrazole substituents. Electronic spectra were rationalized by means of time‐dependent (TD) DFT calculations on simplified C3v‐symmetric [(Tp)Ni–X] models. Exogenous pyrazole binds to give the pentacoordinate adducts [(TpPh,Me)Ni(HpzPh,Me)(X)] (X = Cl, I). We obtained a crystal structure of the iodide adduct, as well as that of [(TpPh,Me)Ni(HpzPh,Me)(Cl)]·0.5MeCN, isomorphous with a previously reported aquo monosolvate. A hallmark of adduct formation is an intramolecular N–H···X hydrogen bond between the added pyrazole and the adjacent halide ligand, thus giving rise to a strong IR absorption band. The stretching frequency correlates to the N(H)···X separation for the range of known adducts.