Insertion of tetrafluoroethylene into the iron-iron bond of (.mu.(SCH3)Fe(CO)3)2, its thermal rearrangement to a bridging carbene ligand, and the transformation of the carbene to a perfluoromethylcarbyne ligand. Structures of .mu.(SCH3)2.mu.(C2F4)Fe2(CO)6 and .mu.(SCH3)2.mu.(FCCF3)Fe2(CO)6 at - 162.degree.C

Abstract

The insertion of tetrafluoroethylene into the Fe-Fe bond of the dinuclear complex (g(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 ^(SCFÍ3)2^(C2F4)Fe2(C0)6 (1), where C2F4 bridges the Fe atoms with two ff(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 ^(SCH3)2M(FCCF3)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 [g(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) Á, the dihedral angle around theS atoms is 135.0°, and the average Fe-S-Fe angle is 91.6°. Compound 1 crystallizes in the orthorhombic space group D\\-Pbca in a cell of a = 15.029 (8), b = 13.561 (5), c = 15.437 (8) Á. Compound 2 crystallizes with eight formula units in space group C\h-P2\/c of the monoclinic system in a cell of dimensions a = 11.545 (3), b = 16.681 (5), c = 16.830 (6) Á with ß = 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 Á, 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 (/x(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.The study of the reactivity of the metal-metal bond in dinuclear complexes toward alkynes, alkenes, or more generally small unsaturated molecules is an increasing field of interest. This is particularly true for dinuclear complexes with metal to metal multiple bonds.2•3 However, insertion reactions of alkynes and alkenes into metal-metal single bonds in dinuclear

Carbon–Fluorine Bond Activation in Fluoroolefins: Clear Documentation of Cooperative CF Bond Activation by Adjacent Metal Centers

“…Fluoroolefins bound in the bridging site between a pair of metal centers can be viewed as resulting from the addition of the dimetal unit across the olefinic bond to generate a 1,2‐dimetalated fluoroalkane with concomitant rehybridization of the olefinic carbon atoms to sp 3 , as confirmed in the structures of C 2 F 4 ‐bridged diiron5 and diiridium7 compounds. In such a geometry the bridging fluoroolefin can be viewed as analogous to two fluoroalkyl groups, for which the lability of the α‐fluorine atoms towards abstraction of a fluoride ion has been demonstrated 8.…”

“…A wide variety of transition‐metal complexes have been used to activate CF bonds,2 but in almost all cases these approaches have been limited to the activation at a single metal center. We are aware of only two studies in which activation of CF bonds has been observed for bridging fluorocarbyl ligands 5. 6…”

Facile Carbon–Fluorine Bond Activation and Subsequent Functionalisation of 1,1‐Difluoroethylene and Tetrafluoroethylene Promoted by Adjacent Metal Centres

“…Tetrafluoroethylene, one of the most studied fluoroolefins, has been shown to undergo CF activation by a number of routes, including [1,2]‐fluoride shifts8 and F − ion abstraction induced by either Lewis or Bronsted acids,8b, 9 in which coordination of the fluoroolefin to the metal results in labilisation of the CF bonds. This labilisation is possibly a result of back donation into the CF σ * orbitals, rendering the coordinated olefin susceptible to fluoride abstraction by strong electrophiles 2.…”

Preparation and Protonation of Fe2(pdt)(CNR)6, Electron-Rich Analogues of Fe2(pdt)(CO)6

“…Isolated as its BF 4 − salt, this species arises via a multistep pathway from the tetrafluoroethylene complex Fe 2 (SMe) 2 (CO) 4 (PMe 3 ) 2 (C 2 F 4 ), culminating in fluoride abstraction with BF 3 . 42 This cation was described as a terminal carbyne complex, but our DFT calculations suggest otherwise (Figure 13). Since crystallographic studies of the related Fe 2 (SMe) 2 (CO) 6 ( μ - η 1 , η 1 -C 2 F 4 ) and Fe 2 (SMe) 2 (CO) 6 ( μ -C(F)CF 3 ) complexes 42 show that the S Me groups adopt the anti disposition, this conformation was adopted in our calculations.…”