Electron transfer from borohydride and selective reductions of iron cations. Synthesis of tetrathiooxalate iron derivatives

Article abstract of DOI:10.1021/om00091a013

Cations of the type Fe(η²-CS₂R)(CO)₂(L)₂⁺ (L = PPh₃; R = Me (2a), Et (2b), CH₂C(Me)=CH₂ (2c)) react with NaBH₄ to afford, via electron transfer, C-C coupling products (RS)₂C₂S₂Fe₂(CO)₄(L) ₂ (3a-c). Complexes 2 containing an acylalkyl group, R, also give complexes 3d,e, but only on reduction with activated magnesium. Reduction of cations 2a-c with sodium amalgam leads first to 3a-c and then to the (RS)₂C₂S₂Fe(CO)₂(L) complexes (4). Complexes 4a-c are also obtained on treatment of 3a-c with Lewis acids in the presence of air. Cation 2h (L = P(OMe)₃, R = Me) is less easily reduced (E_c = -0.81 V vs SCE) than 2a (L = PPh₃; E_c = -0.74 V vs SCE) and, when treated with NaBH₄, undergoes electron transfer and hydride addition: complex 6, analogous to 3, and Fe(η²-HCS₂Me)(CO)₂L₂ (5) are thus formed. Reaction of 2h with Na/Hg affords by contrast small amounts of FeCS(CO)₂L₂ (8) and (R₂S)₂C₂S₂Fe(CO)L₂ (9). The X-ray diffraction structures of 3a and 4a have been determined. 3a: space group P1, Z = 2, a = 9.669 (2) A?, b = 13.477 (3) A?, c = 17.323 (3) A?, α = 101.1 (2)°, β = 91.5 (2)°, γ = 110.3 (2)°, V = 2048 A?³, R = 0.058 for 3802 reflections having I > σ(I). 4a: space group P2₁/a, Z = 4, a = 24.144 (6) A?, b = 10.017 (2) A?, c = 10.745 (2) A?, α = 97.38 (2)°, V = 2577 A?³, R = 0.084 for 2440 reflections having I > 3σ(I).