Pyridazine based scorpionate ligand in a copper boratrane compound.

Reaction of potassium tris(mercapto-tert-butylpyridazinyl)borate K[Tn(tBu)] with copper(II) chloride in dichloromethane at room temperature led to the diamagnetic copper boratrane compound [Cu{B(Pn(tBu))(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{Tn(tBu)}](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[Tn(tBu)] 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[Tn(R)] (R = tBu, Me) and copper(I) chloride in MeOH, the distorted tetrahedral Cu complexes [Cu{Tn(R)}(PCy(3))] (R = tBu 3, Me 4) were formed. Compound 4 is exhibiting an "inverted" κ(3)-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 d(8) electron configuration of Cu.

Novel pyridazine based scorpionate ligands in cobalt and nickel boratrane compounds.

Heating of 6-methylpyridazine-3-thione (HPn(Me)) and 6-tert-butylpyridazine-3-thione (HPn(tBu)) with potassium borohydride in diphenylmethane in a 3:1 ratio gave two new scorpionate ligands K[HB(Pn(Me))(3)] and K[HB(Pn(tBu))(3)]. Single crystal X-ray diffraction analysis of the methyl derivative K[HB(Pn(Me))(3)] revealed a dimeric species with one potassium atom coordinated by six sulfur atoms of two scorpionate ligands and a second potassium atom coordinated by three nitrogen atoms of one of the two ligands as well as by three water molecules. The reaction of K[HB(Pn(tBu))(3)] with nickel(II) chloride or cobalt(II) chloride in CH(2)Cl(2) led to the new boratrane compounds [M{B(Pn(tBu))(3)}Cl] (M = Ni 1, Co 3) where a formal reduction of the metal ions to Ni(I) and Co(I), respectively, and activation of the B-H bond occurred. Similar reactivity was observed by employing K[HB(Pn(R))(3)] (R = Me, tBu) and nickel(II) chloride in water. Reaction with cobalt(II) chloride in water also gave boratrane compounds [Co{B(Pn(R))(3)}(Pn(R))] (R = tBu 4, Ph 5), but instead of a chloride a bidentate pyridazinethionate ligand from a defragmentated scorpionate is found in the molecules. The molecular structures of all nickel and cobalt compounds were determined by single crystal X-ray diffraction analyses confirming the formation of boratranes in compounds 1-5. Magnetic measurements confirm the reduced oxidation states and the paramagnetic character of the Ni(I) and Co(I) complexes. Supportive DFT studies were carried out for a better understanding of the electronic nature of the metal-boron bond of the boratrane complexes.