title: New isolable dialkylsilylene and its isolable dimer that equilibrate in solution.
abstract: 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 Å between dicoordinate silicon atoms, while disilene 4 has a remarkably long Si═Si double bond distance of 2.252 Å. An equilibrium between 3 and 4 in solution was observed by NMR and UV-vis spectroscopies, and the thermodynamic parameters of the equilibrium were estimated to be ΔH = -36 ± 3 kJ mol(-1) and ΔS = -170 ± 15 J mol(-1) K(-1). 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.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Abe
authors.forename: Ryoji
authors.initials: R
authors.lastname: Tanaka
authors.forename: Shintaro
authors.initials: S
authors.lastname: Ishida
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Kira
authors.forename: Takeaki
authors.initials: T
authors.lastname: Iwamoto
mesh_terms: D019281:Dimerization; D008958:Models, Molecular; D017646:Organosilicon Compounds / Q000737:chemistry / Q000302:isolation & purification*; D012996:Solutions; D013816:Thermodynamics
chemical_list: D017646:Organosilicon Compounds; D012996:Solutions