Transition metal-catalyzed reaction of sulfur dioxide

2 Transition metal-catalyzed reaction of sulfur dioxide 

Although a potentially close similarity between CO and SO2 toward insertion reaction has been recognized, the synthetic applications of catalyst system involving SO2 insertion as a key step are hmited. The reasons may be due to lower reactivity of SO2 than CO and instability of sulfinic acids as representative products of SO2 hxation. 

The first catalytic transformation of SO2 into organic sulfur compounds was reported in 1968 [114], The reaction of ethylene and SO2 in the presence of PdCl2 provides a mixture of sulfones (Eq. 7.21). The result of a loss of the catalyst activity under dehydrative conditions is suggestive of the participation of a hydridopalladium species. A mixture of Pd(acac)2, PPhs, and AlEts is an active catalyst for synthesis of cyclic sulfones (2,5-dialkenylsulfolane) which can be obtained from 1,3-dienes up to 75% yield (Eq. 7.22) [115]. 

Pd(II) species countered by BF4 anion, which may enable liberation of HBF4 without base regenerating catalytically active Pd(0) species. 

Palladium catalysts also promote copolymerization of SO2 with alkenes analogously to copolymerization of CO and alkenes (Eq. 7.24) [119]. The catalyst activities for the polysulfone synthesis are lower by an order of magnitude than those for the polyketone synthesis. Perfectly alternating copolymers can be obtained by use of cationic methylpalladium(II) complexes, [PdMe(CH3CN)L2]BF4 (L2 = l,3-bis(diphenylphosphino)propane and 1,2-bis(2,5-dimethylphosphinolato)benzene), in contrast to a lower degree of alternation provided by a radical polymerization [120]. 

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