LEWIS ACID MEDIATED REACTIONS OF ORGANOTRANSITION METAL-COMPLEXES - MARKED PROMOTION OF THE SULFUR-DIOXIDE INSERTION IN ALKYL(ETA-5-CYCLOPENTADIENYL)TRICARBONYLTUNGSTEN(II) BY BORON(III) AND ANTIMONY(V) FLUORIDES

The insertion of SO2into the W-R bond of η5-C5H5W(CO)3R (R = CH3, 1a; R = CH2C6H5, 1b) in liquid SO2is markedly promoted by the Lewis acids BF3and SbF5. Thus, at -26 °C the reaction of 1a with SO2-BF3appears to be at least 20 000 times faster than the reaction of 1a with S02alone. The promoted reaction proceeds to the corresponding Lewis acid stabilized O-sulfinato complexes, η5-C5H5W(CO)3[OS(OBF3or OSbF5)R] (BF3: R = CH3, 3a; R = CH2C6H5, 3b.SbF5: R = CH3, 4a; R = CFHCSHS, 4b), which were isolated and characterized by a combination of elemental analysis and infrared and 1H NMR spectroscopy; by contrast, the insertion of SO2alone continues to the S-sulfinato complexes, η5-C5H5W-(CO)3S(O)2R (R = CH3, 2a; R = CH2C6H5, 2b). Treatment of 3a with NH3, C6H5NH2, or other Lewis bases affords 2a in good yield, whereas storage of 3a in benzene-pentane furnishes some isomeric η5-C5H5W(CO)3[S(O)(OBF3)CH3] (5a). Complex 5a also results upon treatment of 2a with BF3in toluene at 2.5 °C or in SO2at —16 °C; this.reaction may be reversed by the application of vacuum. Other similar 1: 1 adducts of 2a or 2b and BF3or SbFs (or F5SbOSO) were prepared by direct reaction of the appropriate components in SO2solution. The promotion of the reaction of the tungsten-alkyl complexes with SO2by BF3or SbFs is thought to derive from a stronger electrophilic character of the Lewis acid-SO2adduct than of the SO2alone. Mechanistic aspects of the promoted and unpromoted insertion of SO2are discussed, and possible extensions of this approach to other reactions at transition metal-carbon a bonds are considered. © 1979, American Chemical Society. All rights reserved.