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.