Lithiated 1,3-Disilabicyclo[1.1.0]butanes Synthesized via Selective Cleavage of Exocyclic Si–Si Bonds on Bridgehead Silicon Atoms

Abstract

Treatment of 1,3-di­(t-butyldimethylsilyl)-1,3-disilabicyclo­[1.1.0]­butane 1a with excess lithium in THF provided 1,3-dilithio-1,3-disilabicyclo[1.1.0]­butane 2 via reductive cleavage of the exocyclic Si–Si bonds at the bridgehead silicon atoms. In the single crystals obtained by recrystallization in the presence of 1,2-dimethoxyethane (DME), 2 exists as a solvent-separated ion pair, and its anionic part forms an aggregate that contains three lithium atoms sandwiched by two 1,3-disilabicyclo[1.1.0]­butan-1,3-diide units. Treatment of 2 with chlorotri­isopropylsilane provided triisopropylsilyl-substituted 1,3-disilabicyclo[1.1.0]­butane 1b. The structural characteristics of 1b are close to that of the short-bond isomer, which is consistent with previous theoretical predictions concerning the steric effects of the bridgehead substituents on the structure of silabicyclo[1.1.0]­butane.

Heavy Tetrel Clusters Based on the Bicyclobutane Framework: Bicyclo[1.1.0]butanes, [1.1.1]Propellanes, and Tricyclo[2.1.0.02,5]pentanes

“…To date, the four heteronuclear Si‐containing bicyclo[1.1.0]butanes are classified as the SB‐isomers. The neutral 1,3‐disilabicyclo[1.1.0]butane 27 with very bulky i Pr 3 Si‐substituents at the bridgehead Si atoms was recently reported by Iwamoto and co‐workers [49] . 27 was synthesized by the coupling of 1,3‐dilithio‐1,3‐disilabicyclo[1.1.0]butane 28 (prepared by the reduction of the previously reported 1,3‐disilabicyclo[1.1.0]butane 29 [50] with excess of lithium powder) with i Pr 3 SiCl (Scheme 20).…”

“…[50,53] In both 29 and 34, the bridgehead bonds are notably long measuring 2.412(1) Å (SiÀ Si in 29) and 2.5827(3) Å (GeÀ Ge in 34). [50,53] The interplanar angle is wide in both 29 [141.1(1)°] and 34 [142.26(9)°], and the bridgehead Si (in 29) and Ge (in 34) atoms feature diagnostic inverted tetrahedral configuration (in their subsequent study, [49] the same authors re-examined crystallographic measurement of 29, getting a slightly different set of metric parameters for 29 which crystallized in a different orthorhombic space group (average data for two crystallographically independent molecules in the unit cell): 2.3861( 12) Å (bridgehead SiÀ Si bond length), 140.0(2)°(interplanar angle), 339.73(14)/339.45(15)°[Σ(Si)]). Based on these structural characteristics, both 29 and 34 were assigned as the LB-isomers of 1,3disila-and 1,3-digermabicyclo[1.1.0]butane derivatives 29 and 34, respectively.…”

“…The neutral 1,3-disilabicyclo[1.1.0]butane 27 with very bulky i Pr 3 Sisubstituents at the bridgehead Si atoms was recently reported by Iwamoto and co-workers. [49] 27 was synthesized by the coupling of 1,3-dilithio-1,3-disilabicyclo[1.1.0]butane 28 (prepared by the reduction of the previously reported 1,3disilabicyclo[1.1.0]butane 29 [50] with excess of lithium powder) with 51 The next representatives of heteronuclear bicyclo[1.1.0]butane SB-isomers, namely, alkaline-earth metal salts of 1,3-disila-2,4-digermabicyclo[1.1.0]butane-2,4-diide 31-33, were synthesized by Lee, Sekiguchi and co-workers by transmetalation of the dipotassium salt of the 1,2-disila-3,4digermacyclobutadiene dianion derivative with an excess of MX 2 (M = Mg, X = Br; M = Ca, X = I; M = Sr, X = I) (Scheme 21). [52] In 31-33, the bridgehead Si atoms are very diagnostically and strongly shielded, being observed at À 231.9 ppm (in 31), À 220.2 ppm (in 32), and À 225.2 ppm (in 33).…”

“…Based on these structural characteristics, both 29 and 34 were assigned as the LB-isomers of 1,3disila-and 1,3-digermabicyclo[1.1.0]butane derivatives 29 and 34, respectively. [50,53] The distinction in the structural parameters of the SB-isomer 27 [49] and the LB-isomer 29, [50] differing only in the size of their bridgehead substituents ( i Pr 3 Si vs. t BuMe 2 Si), is striking: short SiÀ Si bridgehead bond/acute interplanar angle/planar geometry around bridgehead Si atoms in 27 vs. long SiÀ Si bridgehead bond/wide interplanar angle/inverted tetrahedral geometry around bridgehead Si atoms in 29, demonstrating a decisive role of the bulkiness of bridgehead substituents on the structure of 1,3-disilabicyclo[1.1.0]butanes (preference for either SB-or LB-isomer).…”

“…The distinction in the structural parameters of the SB‐isomer 27 [49] and the LB‐isomer 29 , [50] differing only in the size of their bridgehead substituents ( i Pr 3 Si vs . t BuMe 2 Si), is striking: short Si−Si bridgehead bond/acute interplanar angle/planar geometry around bridgehead Si atoms in 27 vs .…”