Synthesis, Properties, and Reaction Behavior of Cobalt and Copper Organometallic Complexes with Chelating Ligands

Several cobalt complexes with tripodal chelating ligands Tp and Tp* (Tp = tris(pyrazolyl)borate; Tp* = tris(3,5-dimethyl-pyrazolyl)borate) were synthesized by treating the homoscorpionates of the first generation with CoBr2 under different conditions. These complexes were characterized with X-ray crystallographic determination as well as IR, NMR, MS, and UV-vis spectroscopies. Reaction of KTp with CoBr2 in THF afforded an unprecedented trinuclear Co(II) complex [TpCo(Hpz)Br]2(CoBr2) (1) with Tp as terminal ligands, as well as an oxidized side-product (Tp2Co)(Co2Br6) (2). The terminal Co(II) centers of (1) are octahedrally coordinated while the Co(II) in the bridging unit has a distorted tetrahedral geometry, holding a neighboring Co···Co distance of 3.472 Å. Reaction of KTp* with CoBr2 afforded half-sandwich Tp*CoBr (4) with pseudotetrahedrally coordinated Co(II) center, which is accessible to other donors. Mononuclear Tp*CoSPh (7) and dinuclear (Tp*Co)2O2(pz)2 (8) were prepared through ligand exchange reactions of LiSPh and Li(pz) with (4), respectively. (8) contains two octahedral Co(III) centers bridged by two pyrazolyl and a peroxide groups, in which the Co···Co distance is 3.591 Å.

Reaction of (dppf)Cu(NCMe) (dppf = 1,1’-bis(diphenylphosphino)ferrocene) with chloranilate dianion (CA2-) afforded tetranuclear complex (dppf)2Cu2(CA) (9). Single crystal X-ray diffraction revealed that the Cu(I) centers are coordinated by dppf and CA2- in a distorted-tetrahedral manner. The two Cu(I) centers are located almost in the same plane of the bridging ligand with the Cu···Cu separation of 7.940 Å. In its UV-Vis spectrum, the π−π∗ and n−π∗ absorptions of CA2- bridge are shown at 297.1 nm and 480.4 nm, respectively. Irreversible reduction waves were illustrated in the cyclic voltammogram of (9), which were attributed to an ECE process during the measurement.