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 ^XpyMeTpK 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 [^XpyMeTpCu]₂(𝜇–OH)₂(6a–6e) complexes were synthesized from the corresponding ^XpyMeTpCu–OAc (5a–5e) complexes. Single crystal X-ray structures of three new dinuclear [^XpyMeTpCu]₂(𝜇–OH)₂complexes reveal H-bonding between the pendant heterocycle and bridging hydroxide ligands while the donor arm engages the copper center in an unusual monomeric ^DMAPMeTpCu–OH complex. Vibrational studies (IR) of each bridging hydroxide complex reveal reduced 𝜈_OH frequencies that tracks with the H-bond accepting ability of the pendant arm.