Reactions of CO₂ and CS₂ with 1,2-Bis(di-<i>tert</i>-butylphosphino)ethane Complexes of Nickel(0) and Nickel(I)

Reaction of CS2 with [(dtbpe)Ni]2(η2,μ-C6H6) (1; dtbpe =1,2-bis(di-tert-butylphosphino)ethane) in toluene gives the carbon disulfide complex (dtbpe)Ni(η2-CS2) (2), characterized by standard spectroscopic methods and X-ray crystallography. Reaction of CS2 with the Ni(I) complex (dtbpe)Ni(OSO2CF3) gives the diamagnetic, trimetallic cluster [{(dtbpe)Ni(κ1,η2-CS2)}2(dtbpe)Ni][SO3CF3]2 (3-OTf). The solid-state structure of 3-OTf reveals that the two CS2 ligands bind η2 to two (dtbpe)Ni centers and κ1 to the third, unique (dtbpe)Ni in the complex dication, and NMR spectroscopic data indicate that this structure is maintained in solution. Oxidation of 2 by ferrocenium hexafluorophosphate affords the identical trimetallic complex dication as the PF6− salt, [{(dtbpe)Ni(κ1,η2-CS2)}2(dtbpe)Ni][PF6]2 (3-PF6). These results are consistent with the intermediacy of a Ni(I)−CS2 complex, [(dtbpe)Ni(CS2)+], that is unstable with respect to disproportionation. Reaction of 1 with one equivalent of CO2 provides the carbon dioxide adduct (dtbpe)Ni(η2-CO2) (4), that was also crystallographically characterized. Thermolysis of 4 in benzene solution at 80 °C results in reduction of the CO2 ligand to CO, trapped as (dtbpe)Ni(CO)2, and partial oxidation of a dtbpe ligand to give OP(tert-Bu)2CH2CH2P(tert-Bu)2.