The insertion of tetrafluoroethylene into the Fe-Fe bond of the dinuclear complex (µ(SCH3)Fe(CO)3)2 is photochemically induced. When the temperature of the reaction is stabilized at 20 °C, the major product is the yellow dinuclear species µ(SCH3)2µ(C2F4)Fe2(CO)6 (1), where C2F4 bridges the Fe atoms with two σ(C-Fe) bonds, the C-C bond being parallel to the Fe-Fe axis. When the temperature is higher, i.e., 35 °C, the product is the red dinuclear species µ(SCH3)2µ(C2F4)Fe2(CO)6 (2), which contains a >CF-CF3 carbene bridge. It is possible by heating 1 to obtain 2 and a mechanism for this reaction is proposed, based in part on a study of the action of BF3 on 1. The action of BF3 on 2, followed by the addition of trimethylphosphine, affords [µ(SCH3)2Fe2(CO)3(PCH3)3)2(CCF3)][BF4] (7), which may be a perfluoromethylcarbyne complex. A proof for the two different kinds of insertion of C2F4 is presented in the form of crystal structure determinations of 1 and 2. In 1 each iron atom is octahedrally coordinated to three carbonyl groups, two bridging S atoms, and one C atom of C2F4. The Fe-Fe separation is 3.311 (1) Å, the dihedral angle around the S atoms is 135.0°, and the average FeS-Fe angle is 91.6°. Compound 1 crystallizes in the orthorhombic space group D2h15-Pbca in a cell of a = 15.029 (8), b = 13.561 (5), c = 15.437 (8) Å. Compound 2 crystallizes with eight formula units in space group C2h5-P21/c of the monoclinic system in a cell of dimensions a = 11.545 (3), b = 16.681 (5), c = 16.830 (6) Å withβ = 97.86 (2)°. Based on 2471 and 4416 unique reflections for 1 and 2, respectively, the structures were refined by full-matrix least-squares techniques to conventional agreement indices (on F) of R = 0.044 and Rw = 0.049 for 1 and R = 0.039 and Rw = 0.048 for 2. In 2, each iron atom is also octahedrally coordinated, being bound as in 1 to three carbonyl groups, two bridging S atoms, but here to the same bridging C atom of the >CF-CF3 carbene group. The Fe-Fe separation averages 2.963 A, the dihedral angle around the sulfur atoms is 107.2°, and the average Fe-S-Fe angle is 79.39°. The Fe2S2 unit is more compact in 2 than in 1 but less compact than in the starting material (µ(SCH3)Fe(CO)3)2. The flexibility of such molecules around the S-S axis, together with the reactivity of the Fe-Fe bond, is discussed.
ASJC Scopus subject areas
- Colloid and Surface Chemistry