A Neutral Tetraphosphacyclobutadiene Ligand in Cobalt(I) Complexes

摘要

The unusual reactivity of the newly synthesized -diketiminato cobalt(I) complexes, [((LCo)-Co-Dep)(2)] (2a, L-Dep=CH[C(Me)N(2,6-Et2C6H3)](2)) and [L(Dipp)Cotoluene] (2b, L-Dipp=CH[CHN(2,6-(Pr2C6H3)-Pr-i)](2)), toward white phosphorus was investigated, affording the first cobalt(I) complexes [((LCo)-Co-Dep)(2)((2):(4),(4)-P-4)] (3a) and [((LCo)-Co-Dipp)(2)((2):(4),(4)-P-4)] (3b) bearing the neutral cyclo-P-4 ligand with a rectangular-planar structure. The redox chemistry of 3a and 3b was studied by cyclic voltammetry and their chemical reduction with one molar equivalent of potassium graphite led to the isolation of [((LCo)-Co-Dep)(2)((2):(4),(4)-P-4)][K(dme)(4)] (4a) and [((LCo)-Co-Dipp)(2)((2):(4),(4)-P-4)][K(dme)(4)] (4b). Unexpectedly, the monoanionic Co2P4 core in 4a and 4b, respectively, contains the two-electron-reduced cyclo-P-4(2-) ligand with a square-planar structure and mixed-valent cobalt(I,II) sites. The electronic structures of 3a, 3b, 4a, and 4b were elucidated by NMR and EPR spectroscopy as well as magnetic measurements and are in agreement with results of broken-symmetry DFT calculations.