Three 18-Electron Tantalum(I) Compounds, TaCl(CO)(2)(dppe)(2), [TaCl(CO)(2)(dppe)(2)](2x), and TaCl(CO)(4)(dppe) (dppe = 1,2-Bis(diphenylphosphino)ethane), Which Exhibit Low Levels of Paramagnetism.

Reductive carbonylation of TaCl5 in the presence of 1,2-bis(diphenylphosphino)ethane (dppe) under the appropriate conditions results in the formation of TaCl(CO)2(dppe)2 (1), as the major product, and the possibly cyclic oligomer [TaCl(CO)2(dppe)2]2x (2, 2x ≥ 4) as a minor product. Carbonylation of 1 (1 atm) results in the rapid but reversible formation of TaCl(CO)4(dppe) (3). Solutions of all three compounds exhibit low levels of paramagnetism, possibly attributable to thermal population of low-lying triplet excited states. Crystal data for the toluene solvate of 1, C68H64ClO2P4Ta:  triclinic, P1 (No. 2), a = 13.937(12) A, b = 14.811(7) A, c = 14.929(9) A, α = 102.30(5)°, β = 95.60(7)°, γ = 98.41(5)°, Z = 2.