O-bound sulfinate

The insertion of SOj can lead to two different products. In most cases, the kinetic product of SOj insertion is an 0-bound sulfinate, whereas the ttiermodynamic product is an S-boimd sulfinate (Equation 12.23). O-bound sulfinates have been observed spectroscopically as intermediates in the reactions of SO with CpFe(CO)jR, CpMo(CO)jR, Mn(CO)jR, and Re(CO)5R. - In other cases of the insertion of SOj into related middle-to-late transition metal-carbon bonds (Equations 12.24 and 12.25 ), only the S-bound sulfinate was observed. In contrast, reactions of SO with hard, early transition metal-alkyl complexes, which are more oxophilic than the softer late transition metal-alkyl complexes, tend to... 

Sulfur dioxide is a much stronger electrophile than CO2 and also needs no vacant site. If SO2 electrophilically attacks the a carbon of an 18e alkyl from the side opposite the metal, an alkyl sulfinate ion is formed with inversion at carbon. Since the anion has much of its negative charge on the oxygens, it is not surprising that the kinetic product of ion recombination is the O-bound sulfinato complex. On the other hand, the thermodynamic product is usually the S-bound sulfinate, as is appropriate for a soft metal binding. This sequence constitutes a 1,2 (O bound sulfinate) or a 1,1 insertion of SO2 (S bound). 

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