Laser flash photolysis silene dimerization

Conlin and coworkers studied the silene (Me3Si)2Si=C(OSiMe3) Me using laser flash photolysis, and while much was learned about some details of its reactions, it was not possible to establish unambiguously the mechanism by which dimerization occurred110. 

Head-to-tail dimerization of 1,1-diphenylsilene (19a), produced by laser flash photolysis of 1,1-diphenylsilacyclobutane (17a), yields the 1,3-disilacyclobutane 2761,62 with a rate constant fcdim = (1-3 0.3) x 1010 M 1 s 1 in hexane solution at 25 °C (equation 17)46. This value is within a factor of two of the diffusional rate constant in hexane at this temperature, indicating that dimerization of this silene is faster than reaction with even the most potent of nucleophilic trapping reagents (see Table 3). More recently, the temperature dependence of the rate constant for dimerization of 19a has been studied63. The results of these experiments are shown in Figure 1, and lead to Arrhenius activation parameters of a = -4 2 Id moD1 and log(A/M 1 s"1) = 9.2 0.4. 

ConUn and coworkers have smdied the kinetics of the dimerization of the silene 369 by laser flash photolysis. 369 gives in a clean reaction exclusively the linear dimer 370 (equation 103). Second-order kinetics were observed with a bimolecular rate constant of... 

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