Reactions of halofluorocarbons with group 6 complexes M(C5H5)(2)L (M = Mo,W; L = C2H4, CO). Fluoroalkylation at molybdenum and tungsten, and at cyclopentadienyl or ethylene ligands

The molybdenum(II) and tungsten(II) complexes [MCp2L] (Cp = eta (5)-cyclope ntadienyl; L = C2H4, CO) react with perfluoroalkyl iodides to give a variet y of products. The Mo(II) complex [MoCp2(C2H4)] reacts with perfluoro-n-but yl iodide or perfluorobenzyl iodide with loss of ethylene to give the first examples of fluoroalkyl complexes of Mo(IV), MoCp2(CF2CF2CF2CF3)I (8) and MoCp2(CF2C6F5)I (9), one of which (8) has been crystallographically charact erized. In contrast, the CO analogue [MoCp2(CO)I reacts with perfluorobenzy l, iodide without loss of CO to give the crystallographically characterized salt, [MoCp2(CF2C6F5)(CO)I+I- (10), and the W(II) ethylene precursor [WCP2 (C2H4)] reacts with perfluorobenzyl iodide without loss of ethylene to affo rd the salt [WCp2(CF2C6F5)(C2H4)1(+)I(-) (11). These observations demonstra te that the metal-carbon bond is formed first. In further contrast the tung sten precursor [WCP2(C2H4)] reacts With perfluoro-n-butyl iodide, perfluoro -iso-propyl iodide, and pentafluorophenyl iodide to give fluoroalkyl- and f luorophenyl-substituted cyclopentadienyl complexes WCp(eta (5)-C5H4RF)(H)I (12, R-F = CF2CF2CF2CF3; 15, R-F = CF(CF3)(2); 16, R-F = C6F5); the Mo anal ogue MoCp(eta (5)-C5H4RF)(H)I (14, R-F = CF(CF3)(2)) is obtained in similar fashion. The tungsten(IV) hydride compounds react with iodoform to afford the corresponding diiodides WCp(eta (C5H4RF)-C-5)I-2 (13, R-F = CF2CF2CF2CF 3; 18, R-F = CF(CF3)(2); 19, R-F = C6F5), two of which (13 and 19) have bee n crystallographically characterized. The carbonyl precursors [MCp2(CO)] ea ch react with perfluoro-iso-propyl iodide without loss of CO, to afford the exo-fluoroalkylated cyclopentadiene M(II) complexes MCp(eta (4)-C5H5RF)(CO )I (21, M = Mo; 22, M = W); the exo-stereochemistry for the fluoroalkyl gro up is confirmed by an X-ray structural study of 22. The ethylene analogues [MCP2(C2H4)] react with perfluoro-tert-butyl iodide to yield the products M Cp2[(CH2CH2C(CF3)(3)]I (25, M = Mo; 26, M = W) resulting from fluoroalkylat ion at the ethylene ligand. Attempts to provide positive evidence for fluor oalkyl radicals as intermediates in reactions of primary and benzylic subst rates were unsuccessful, but trapping experiments with CH3OD (to give RFD, not RFH) indicate that fluoroalkyl anions are the intermediates responsible for ring and ethylene fluoroalkylation in the reactions of secondary and t ertiary fluoroalkyl substrates.