Abstract
The reaction of Na-2[Fe(CO)(4)] with Br2CF2 in n-pentane generates a mixture of the compounds (CO)(3)Fe(mu -CO)(3-n)(mu -CF2)(n)Fe(CO)(3) (2, n = 2; 3, n = 1) in low yields with 3 as the main product. 3 is obtained free from 2 by reacting Br2CF2 with Na-2[Fe-2(CO)(8)]. The non-isolable monomeric complex (CO)(4)Fe=CF2 (1) can probably considered as the precursor for 2. 3 reacts with PPh3 with replacement of two CO ligands to form Fe-2(CO)(6)(mu -CF2)(PPh3)(2) (4). The complexes 2-4 were characterized by single crystal X-ray diffraction. While the structure of 2 is strictly similar to that of Fe-2(CO)(9), the structure of 3 can better be described as a resulting from superposition of the two enantiomers 3a and 3b with two semibridging CO groups. Quantum chemical DFT calculations for the series (CO)(3)Fe(mu -CO)(3-n)(mu -CF2)(n)Fe(CO)(3) (n = 0, 1, 2, 3) as well as for the corresponding (mu -CH2) derivatives indicate that the progressively larger sigma donor and pi acceptor properties for the bridging ligands, in the order CO < CF2 < CH2, favor a stronger Fe-Fe bond.