Novel Pyridazine Based Scorpionate Ligands in Cobalt and Nickel Boratrane Compounds

Heating of 6-methylpyridazine-3-thione (HPnMe) and 6-tert-butylpyridazine-3-thione (HPntBu) with potassium borohydride in diphenylmethane in a 3:1 ratio gave two new scorpionate ligands K[HB(PnMe)3] and K[HB(PntBu)3]. Single crystal X-ray diffraction analysis of the methyl derivative K[HB(PnMe)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(PntBu)3] with nickel(II) chloride or cobalt(II) chloride in CH2Cl2 led to the new boratrane compounds [M{B(PntBu)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(PnR)3] (R = Me, tBu) and nickel(II) chloride in water. Reaction with cobalt(II) chloride in water also gave boratrane compounds [Co{B(PnR)3}(PnR)] (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.