The First 1,3-Disilabicyclo[1.1.0]butane with Long-Bridge Silicon−Silicon Bond

Abstract

The unique structures and reactivities of metallabicyclo[1.1.0]-butanes containing heavy main group elements have been the focus of experimental and theoretical studies. 1-3 As revealed by the theoretical calculations, one of the most interesting features of metallabicyclo[1.1.0]butanes 3 as well as bicyclo[1.1.0]butanes 4 should be the existence of the bond-stretch isomers, which differ primarily in the distance between the bridge head atoms. As shown in Chart 1, the short-bond (SB) isomers are characterized by not only the short-bridge bond distance (r), but also the small interflap angle (φ) and the large R-M-M angle (θ), while the long-bond (LB) isomers have long r, large φ, and small θ. The bridge bond in an SB isomer is a normal bent σ bond, while the bond in an LB isomer should be ascribed to an inverted σ bond with significant singlet biradical character.Although theoretical calculations have predicted that the LB isomers are more stable than the SB isomers in 1,3-disilabicyclo-[1.1.0]butane as well as tetrasilabicyclo[1.1.0]butane, 3 no experimental evidence for the LB isomers with the bridge Si-Si bond has been reported so far. We wish herein to report the first synthesis of a 1,3-disilabicyclo[1.1.0]butane derivative, which has characteristics of the LB isomer.Disilabicyclo[1.1.0]butane 1 was obtained by using a formal double sila-Peterson reaction 5 of tetrakis(tert-butyldimethylsilyl)-dilithiodisilane 2 6 (eq 1). Adamantanone (64 mg, 0.43 mmol) and 2‚6THF (200 mg, 0.20 mmol), which was prepared by the reaction of the corresponding tetrasilyldisilene 7 with lithium metal, was placed in a Schlenk tube under vacuum, and dry benzene (10 mL) was introduced by distillation to the mixture. The mixture was stirred overnight at room temperature to give a bright-yellow solution; the complete conversion was confirmed by 1 H NMR. After quenching the mixture by excess Me 3 SiCl, the solvent and the resulting t-BuMe 2 SiOSiMe 3 and lithium chloride were removed. Pure 1 was obtained by crystallization from hexane in 70.1% yield. 8 The structure of 1 was determined by 1 H, 13 C, and 29 Si NMR, MS, and X-ray crystallography. 10,11 Compound 1 is oxygen-and moisture-sensitive, but thermally very stable; 1 melts at 175.2-177.3°C without decomposition.X-ray single-crystal analysis of 1 has shown that 1 has the crystallographical mirror plane which includes eight carbon atoms of adamantane moieties and bisects the bridge Si-Si bond ( Figure 1). Two three-membered Si 2 C rings are isosceles. The following four important characteristics were found in the structure of 1: (i) The distance of the bridge Si1-Si1* bond (r) is 2.412(1) Å, (1) For reviews on small ring compounds including group 14 elements, see: (a) Weidenbruch, M. Comments Inorg. A number of metallabicyclo[1.1.0]butanes have been reported. Tetrasilabicyclo[1.1.0]butanes: (a) Masamune, S.; Kabe, Y.; Collins, S.; Williams, D. -disilabicyclo[1.1.0]-butanes: (l) Driess, M.; Fanta, A. D.; Powell, D. R.; West, R. Angew. Chem., Int. Ed. Engl. 1989, 28, 1038. (m) Driess...

Heavy Group 14 1,(n+2)‐Dimetallabicyclo[n.n.n]alkanes and 1,(n+2)‐Dimetalla[n.n.n]propellanes: Are They All Realistic Synthetic Targets?

“…Recently, Kira et al prepared the first 1,3-disilabicyclo-[1.1.0]butane, [1] a compound with a partially inverted SiÀSi bond. [2] A fully inverted SiÀSi bond is found in 1,3-disila-[1.1.1]propellane, a species that hitherto has not been made, even though the parent all-carbon [1.1.1]propellane and a pentastanna[1.1.1]propellane derivative, that is, ligand-stabilized cluster compounds with "naked" Group 14 atoms, [3] were prepared by Wiberg and Walker [4] and Sita et al [5] Of the larger synthesized [n.n.n]propellanes, only 3,7,10-trichalcogenaoctasila [3.3.3]propellanes [6] and a 1,6-disila- [4.4.4]propellane [7] have heavy Group 14 bridgehead atoms.…”

A quest for triplet silylenes XHSi3 at ab initio and DFT levels (X=H, F, Cl and Br)

“…However, in the cases of 3 s-F and 3 s-Br , where the halogens can directly stabilize the silylenic center, this interaction is less pronounced (Scheme 1). Delocalization of Si"Si p electrons, through the divalent center, causes the observed disordered trend of the divalent angles \Si 2 Si 1 X [8,24]. Upon optimization, no rearrangement or ruptures are observed in silylenic species with structures 3 s-X and/or 3 tÀX (Fig.…”

“…Consequently, attention has expanded to silicon-silicon double bonds and triple bonds containing silicon [16][17][18], as well as the small siliconcontaining rings [19]. More recently, Kira et al reported interesting examples of cyclic disilenes [20], spiropentasiladiene [21], 4-silatriafulvene [22], a silicon-containing fused bicyclic compound with a highly strained bridgehead double bond [23], and a disilane with a long Si-Si bridge [24]. Also, a stable silicon analogue of an allene, with a core of Si@Si@Si unit, with sp-hybridized silicon atoms, was synthesized [25].…”

In search of 1,3-disila/germa/stannabicyclo[1.1.1]pentanes with short bridgehead-bridgehead distances and low ring strain energies

“…Very recently, Wiberg and co-workers generated a 5,6-dioxa-1,4-disilabicyclo[2.1.1]hexane having a Si,Si phantom bond of 2.309Å [14], and this is the record in short non-bonded Si,Si distances. The smallest disilabicyclic compound generated is the 1,3-disilabicyclo[1.1.0]butane of Kira and co-workers [15]. Interestingly, both of the last two compounds were stable until their melting points of 185 and 175-177 • C, respectively.…”