Tris(pyrazolyl)borate Copper Hydroxide Complexes Featuring Tunable Intramolecular H-bonding

A modular synthesis provides access to a series of new tris(pyrazolyl)borate ligands <sup>XpyMe</sup>TpK that possess a single functionalized pendant pyridyl (py) or pyrimidyl (pyd) arm designed to engage in tunable intramolecular H-bonding to metal–bound functionalities. To illustrate such H-bonding interactions, a series of [<sup>XpyMe</sup>TpCu]<sub>2</sub>(𝜇–OH)<sub>2</sub>(<b>6a</b><b>–6e</b>) complexes were synthesized from the corresponding <sup>XpyMe</sup>TpCu–OAc (<b>5a–5e</b>) complexes. Single crystal X-ray structures of three new dinuclear [<sup>XpyMe</sup>TpCu]<sub>2</sub>(𝜇–OH)<sub>2</sub>complexes reveal H-bonding between the pendant heterocycle and bridging hydroxide ligands while the donor arm engages the copper center in an unusual monomeric <sup>DMAPMe</sup>TpCu–OH complex. Vibrational studies (IR) of each bridging hydroxide complex reveal reduced 𝜈<sub>OH </sub>frequencies that tracks with the H-bond accepting ability of the pendant arm.