Pyridazine Based Scorpionate Ligand in a Copper Boratrane Compound

Reaction of potassium tris­(mercapto-tert-butylpyridazinyl)­borate K­[TntBu] with copper­(II) chloride in dichloromethane at room temperature led to the diamagnetic copper boratrane compound [Cu­{B­(PntBu)3}­Cl] (Pn = pyridazine-3-thionyl) (1) under activation of the B–H bond and formation of a Cu–B dative bond. In contrast to this, stirring of the same ligand with copper­(I) chloride in tetrahydrofuran (THF) gave the dimeric compound [Cu­{TntBu}]2 (2) where one copper atom is coordinated by two sulfur atoms and one hydrogen atom of one ligand and one sulfur of the other ligand. Hereby, no activation of the B–H bond occurred but a 3-center-2-electron B–H···Cu bond is formed. The reaction of copper­(II) chloride with K­[TntBu] in water gave the same product 2, but a formal reduction of the metal center from Cu­(II) to Cu­(I) occurred. When adding tricyclohexyl phosphine to the reaction mixture of K­[TnR] (R = tBu, Me) and copper­(I) chloride in MeOH, the distorted tetrahedral Cu complexes [Cu­{TnR}­(PCy3)] (R = tBu 3, Me 4) were formed. Compound 4 is exhibiting an “inverted” κ3-H,S,S, coordination mode. The copper boratrane 1 was further investigated by density functional theory (DFT) calculations for a better understanding of the M→B interaction involving the d8 electron configuration of Cu.