Structures, physicochemical properties, and reactivities of cobalt(II) complexes supported by a homoscorpionate (Tris(pyrazolyl)borate) ligand Tp ^Ph,Me

The coordination chemistry of a mononuclear cobalt complex supported by the monoanionic hydrotris-(pyrazolyl)borate tridentate ligand [Tp ^Ph,Me] containing substituted phenyl groups at the 3-position of the pyrazole rings and methyl groups at the 5-position of the pyrazole rings is examined. The Co(II) halide complex [Tp ^Ph,Me]CoCl (1) serves as a precursor to the organometallic species [Tp ^Ph,Me]CoMe (2), [Tp ^Ph,Me] CoCH ₂SiMe ₃ (3), [Tp ^Ph,Me]CoCH ₂CH(Me) ₂ (4), [Tp ^Ph,Me]Co(CH ₂) ₂Me (5), [Tp ^Ph,Me]CoEt (6), [Tp ^Ph,Me]Co(CH ₂) ₅Me (7), and [Tp ^Ph,Me]Co(CH ₂) ₃Me (8). All of the cobalt(II) organometallic complexes have been characterized by X-ray crystallography, NMR spectroscopy, FT-IR, and elemental analysis. The X-ray crystallographic analyses reveal that complexes 2-6 and 8 have slightly distorted tetrahedral structures. Solution-state magnetic susceptibility measurements of all complexes in C ₆D ₆ indicate that they all have 3/2 ground states. The reaction of 1 with ^tBuLi and iPrMgCl in hexane under N ₂ results in the production of the i-butyl and n-propyl complexes 4 and 5, respectively, in ∼56% yield. These isomerizations and exchange reactions of the alkyl group proceed via formation of a Co-H species, as determined by trapping experiments.