Base-Free Molybdenum and Tungsten Bicyclic Silylene Complexes Stabilized by a Homoaromatic Contribution

Abstract

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.

Reductive Cleavage of Carbon Monoxide by a Disilenide

“…The lithium cation is coordinated by two [12]crown‐4 equivalents to form a solvent‐separated ion pair. The divalent Si1 is coordinated to the W center at a Si1–W1 distance of 2.4356(13) Å, which is in the typical range for tungsten–silylene complexes 31d,e. The sum of angles at Si1 (∑Si1=360.0°) further confirms significant SiW bond character, also in line with the large 1 J SiW coupling constant of 6 c ( 1 J SiW =138 Hz).…”

Synthesis and reactivity of N-aryl substituted N-heterocyclic silylenes

“…Synthesis of the NHSi tungsten carbonyl complex 29. [36,39] the size of the 1 J Si,W coupling constant can not be securely correlated to the degree of bonding between the silicon and tungsten atoms in complex 29.…”

Pentasilatricyclo[2.1.0.02,5]pentane and Its Anion

“…Synthesis of 3-chloro-3-phenyl-1,2,4,5-tetrakis(di-tert-butylmethylsilyl)pentasilatricyclo[2.1.0.0 2,5 ]pentane (2) was accomplished by the reaction of the calcium salt of 1,2,3,4-tetrakis(di-tert-butylmethylsilyl)tetrasilabicycloA C H T U N G T R E N N U N G [1.1.0]butan-2,4diide 1 2À ·Ca 2 + [6] with an excess of PhSiCl 3 in THF (Scheme 1). [7] After purification by silica gel/toluene column chromatography carried out in a glove box, 2 was isolated as yellow crystals in 32 % yield.…”

“…[12] The importance of such a K + -arene p-interaction, which outbalanced the obvious disadvantage of geometrical constraints resulting in the overall stabilization of the anionic derivative, was supported by DFT computations on the [3 À ·K + ] model , which well reproduced the real structure of [3 À ·K + ] with the diagnostic umbrella configuration of the anionic Si1 center and K + -arene p-interaction ( Figure 2). [13] On the other hand, skeletal Si À Si bonds to the anionic Si1 center (Si1 À Si3 2.4160 (6) and Si1 À Si4 2.4025(6) ) are markedly stretched compared with other skeletal bonds involving the neutral Si2 atom (Si2 À Si3 2.3182 (6) and Si2 À Si4 2.3321(6) , see Table 1). Calculated values of the skeletal SiÀSi bonds follow the same trend: long bonds to anionic Si1 (Si1ÀSi3 = Si1ÀSi4 2.499 ) and short bonds to neutral Si2 (Si2 À Si3 = Si2 À Si4 2.313 ).…”