Kazunori Takanashi

Base-free molybdenum and tungsten bicyclic silylene complexes stabilized by a homoaromatic contribution.

Unprecedented base-free bicyclic silylene complexes of molybdenum and tungsten 3a,b (a, M = Mo; b, M = W) were prepared by the reaction of the calcium salt of 1,2,3,4-tetrakis(di-tert-butylmethylsilyl)tetrasilabicyclo[1.1.0]butane-2,4-diide 2(2-) x Ca(2+) with Cp(2)MCl(2) (M = Mo, W). The unusual structural features of 3b (long SiW double bond, short skeletal (sp(2)-Si)-(sp(3)-Si) bonds and extremely long Si-Si bridge) are indicative of a contribution from the zwitterionic resonance form W(delta-)-Si(delta+), in which the electrophilic silicon center is stabilized by the Si(3)-homoaromatic conjugation. This was supported by the theoretical calculations (NBO, NPA) revealing the presence of pi(WSi) and sigma(Si-Si bridge) interactions.

From tetragermacyclobutene to tetragermacyclobutadiene dianion to tetragermacyclobutadiene transition metal complexes.

The reaction of 3,4-dichlorotetragermetene derivative 2 with Na(2)[Fe(CO)(4)] in THF produced a (tetragermacyclobutadiene)tricarbonyliron complex, [{η(4)-((t)Bu(2)MeSi)(4)Ge(4)}]Fe(CO)(3)4, which has a slightly folded Ge(4) ring perhaptocoordinated to the Fe center. Structural and spectral characteristics of 4 show a remarkable π-donating ability of the tetragermacyclobutadiene ligand toward the transition metal, surpassing that of tetrasilacyclobutadiene and cyclobutadiene ligands. Reduction of 2 with KC(8) resulted in exclusive formation of the dipotassium salt of the tetragermacyclobutadiene dianion derivative 3(2-)·[K(+)(thf)(2)](2), representing a rare example of a 6π-electron compound that, on the basis of its structural and magnetic properties, was recognized as a nonaromatic species. Reaction of 3(2-)·[K(+)(thf)(2)](2) with CpCoI(2)(PPh(3)) produced a (cyclopentadienyl)(tetragermacyclobutadiene)cobalt complex, [{η(4)-((t)Bu(2)MeSi)(4)Ge(4)}]CoCp 7, as the first example of a sandwich compound featuring an all-germanium-containing cyclic polyene ligand.

Pentasilatricyclo[2.1.0.02,5]pentane and Its Anion

In their comprehensive review, Michl and co-workers listed bicycloACHTUNGTRENNUNG[1.1.1]pentanes, [1.1.1]propellanes and tricyclo[2.1.0.0]pentanes among the most highly strained polycyclic compounds, otherwise known as cages. The nonclassical nature and unusual hybridization mode of the bridging bonds in [1.1.1]propellanes and tricyclo[2.1.0.0]pentanes, sharply deviating from the normal sp states, as well as the nontrivial interbridgehead nonbonding interaction in bicycloACHTUNGTRENNUNG[1.1.1]pentanes, make them very attractive targets for both experimental and computational pursuits. Even though the field of organic derivatives of such cage compounds is rather well investigated from both synthetic and theoretical sides, the field of their analogues of the heavy Group 14 elements is still largely unknown. Thus, for example, only four stable heavy [1.1.1]propellanes of the type R6E5 (E=heavy Group 14 element) have been reported to date, representing examples of pentastanna-, digermatristannaand pentagerma ACHTUNGTRENNUNG[1.1.1]propellanes.[2] As for the heavy tricyclo[2.1.0.0]pentanes, the only known stable representative featuring an extremely long Ge C bridge bond was reported by us several years ago. The latter compound revealed structural peculiarities that are sharply distinctive from those of its organic counterparts. However, the particularly attractive all heavy Group 14 element-consisting analogues of tricyclo[2.1.0.0]pentane were still unknown prior to our studies, and in this communication we wish to report the synthesis of the first pentasilatricyclo[2.1.0.0]pentane derivative and its subsequent reduction to produce a rather unusual anionic derivative manifesting a number of unprecedented structural features. Synthesis of 3-chloro-3-phenyl-1,2,4,5-tetrakis(di-tert-butylmethylsilyl)pentasilatricyclo[2.1.0.0]pentane (2) was accomplished by the reaction of the calcium salt of 1,2,3,4-tetrakis(di-tert-butylmethylsilyl)tetrasilabicyclo ACHTUNGTRENNUNG[1.1.0]butan-2,4diide 1 ·Ca [6] with an excess of PhSiCl3 in THF (Scheme 1). After purification by silica gel/toluene column chromatography carried out in a glove box, 2 was isolated as yellow crystals in 32 % yield. In accordance with its tricyclic structure, 2 exhibited (in both H and C NMR spectra) a set of three signals for the Me groups and a set of four signals for the tBu groups, along with resonances of the phenyl ring atoms. The resonances of both bridgehead silicon atoms in 2 at 222.4 and 217.1 ppm were observed in the highfield region diagnostic of highly strained polycyclic compounds, whereas the signal of the bridging silicon atoms was observed at 117.0 ppm.

3Δ-1,2,3,4-Disilagermastannetene: the first cyclic germastannene

Abstract3Δ-1,2,3,4-Disilagermastannetene, the first cyclic germastannene, was quantitatively synthesized by the reaction of 1- and 2-disilagermirenes with the dichlorostannylene--dioxane complex in THF. The title germastannene is quite stable in the solution, which was explained by the appreciable π(Ge=Sn)-σ*(Si--Cl) orbitals mixing.