Borotropic shifting of the hydrotris[3-(2-furyl)pyrazol-1-yl]borate ligand in high-coordinate lanthanide complexes

Abstract

The coordination of hydrotris[3-(2′-furyl)pyrazol-1-yl]borate (Tp2-Fu, C21H16BN6O3) to lanthanide(III) ions is achieved for the first time with the complex [Ln(Tp2-Fu)2](BPh4)·xCH2Cl2 (1-Ln has Ln = Ce and x = 2; 1-Dy has Ln = Dy and x = 1). This was accomplished via both hydrous (Ln = Ce) and anhydrous methods (Ln = Dy). When isolating the dysprosium analogue, the filtrate produced a second crop of crystals which were revealed to be the 1,2-borotropic-shifted product [Dy(κ4-Tp2-Fu)(κ5-Tp2-Fu*)](BPh4) (2) {Tp2-Fu* = hydrobis[3-(2′-furyl)pyrazol-1-yl][5-(2′-furyl)pyrazol-1-yl]borate}. We conclude that the presence of a strong Lewis acid and a sterically crowded coordination environment are contributing factors for the 1,2-borotropic shifting of scorpionate ligands in conjunction with the size of the conical angle with the scorpionate ligand.