Preparation, Spectroscopic Properties, and Crystal Structures of Fe2(CO)6(μ-CO)(μ-CF2)2, Fe2(CO)6(μ-CO)2(μ-CF2), and Fe2(CO)6(μ-CF2)(PPh3)2 – Theoretical Studies of Methylenic vs. Carbonyl Bridges in Diiron Complexes

✍ Scribed by W. Petz; F. Weller; A. Barthel; C. Mealli; J. Reinhold

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: German
• Weight: 253 KB
• Volume: 627
• Category: Article
• ISSN: 0372-7874
• DOI: 10.1002/1521-3749(200108)627:8<1859::aid-zaac1859>3.0.co;2-p

✦ Synopsis

The reaction of Na 2 [Fe(CO) 4 ] with Br 2 CF 2 in npentane generates a mixture of the compounds (CO) 3 Fe(l-CO) 3±n (l-CF 2 ) 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 Br 2 CF 2 with Na 2 [Fe 2 (CO) 8 ]. The non-isolable monomeric complex (CO) 4 Fe=CF 2 (1) can probably considered as the precursor for 2. 3 reacts with PPh 3 with replacement of two CO ligands to form Fe 2 (CO) 6 (l-CF 2 )(PPh 3 ) 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 re-sulting from superposition of the two enantiomers 3 a and 3 b with two semibridging CO groups. Quantum chemical DFT calculations for the series (CO) 3 Fe(l-CO) 3±n (l-CF 2 ) n Fe(CO) 3 (n = 0, 1, 2, 3) as well as for the corresponding (l-CH 2 ) derivatives indicate that the progressively larger r donor and p acceptor properties for the bridging ligands, in the order CO < CF 2 < CH 2 , favor a stronger Fe±Fe bond.