文摘
The new isolable dialkylsilylene 3 bearing a bidentate alkyl substituent was synthesized. Recrystallization of silylene 3 gave yellow crystals of 3 and orange-red crystals of tetraalkyldisilene 4, a dimer of 3. In the solid state, 3 exists as a monomer with a closest distance of 6.745 脜 between dicoordinate silicon atoms, while disilene 4 has a remarkably long Si鈺怱i double bond distance of 2.252 脜. An equilibrium between 3 and 4 in solution was observed by NMR and UV鈥搗is spectroscopies, and the thermodynamic parameters of the equilibrium were estimated to be 螖H = 鈭?6 卤 3 kJ mol鈥? and 螖S = 鈭?70 卤 15 J mol鈥? K鈥?. Analysis of the percent buried volume, a measure of the steric demand around the divalent silicon, showed that the flexible steric bulkiness of the alkyl substituent of 3 and 4 allows the reversible dimerization of silylene 3 to disilene 4 and the isolation of both species.