Kinetics and Mechanism of Sulfur Dioxide Insertion

Kinetic studies on the sulfur dioxide insertion have been few and most have utilized liquid SO2 as the reaction medium. The most exhaustive investigation in neat SO2 was conducted on the systems CpFe(CO)2R and various (R Cp)Fe(CO)2R (77, 74, 75) studied cursorily were CpMo(CO)3R, CpRu(CO)2R, RMn(CO)5, and RRe(CO)5 71, 76). Kinetic studies in organic solvents have been confined to a few CpFe(CO)2R complexes 71, 77). Of the many SO2 reactions of the main group metal-carbon systems, only those involving some MesSnR aryl and benzyl compounds were examined kinetically 51, 52, 99). 

Further studies on these systems have shown that the S-sulfinate is probably formed by the pathways depicted in Eq. (13) (73). This has 

From the evidence cited above it has been assumed that the formation of the O-sulfinates is a common feature of the insertion reactions of coordinatively saturated transition metal alkyls and aryls. The kinetic studies discussed in Section III refer to the scission of the M—R bond which yields the appropriate metal sulfinate. 

The nature of R exerts a very profound effect on the reactivity of the alkyls and aryls of a given system MR toward sulfur dioxide. Kinetic 

The data show that in those cases where steric effects are unimportant, e.g., for several CpFe(CO)2R with R = CH2X, the reactivity increases with an increase in the electron-releasing tendency of X. Accordingly, R = CHaCeFs 11) CHaPh CHaCeHiOMe-p, and R = CHaCN CHaOMe Me 71, 75). For such complexes there is a reasonable 

---