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

The coordination of hydrotris[3-(2'-furyl)pyrazol-1-yl]borate (Tp2-Fu , C21 H16 BN6 O3 ) to lanthanide(III) ions is achieved for the first time with the complex [Ln(Tp2-Fu )2 ](BPh4 )·xCH2 Cl2 (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.