Synthesis of Self-Stabilized and Donor-Free Silyl(silylene)tungsten Complexes

Abstract

Considerable attention has been focused on the synthesis and chemical behavior of silylene-transition metal complexes. 1,2 Silyl(silylene) complexes L n M(dSiR 2 )-SiR 3 are one of the attractive synthetic targets since such complexes have been assumed to be key intermediates in many transition metal-catalyzed scrambling of substituents and skeletal redistribution of organosilicon and organosilicon-transition metal compounds. 2,3 Silyl-(silylene) complexes have been isolated as internal or external donor-stabilized complexes in which the electrondeficient silylene ligands are stabilized by coordination of two-electron donors. 4-7 Lappert et al. very recently reported the synthesis of the first donor-free silyl-(silylene) complex by the reaction of an isolable silylene and a platinum complex. 8 The silylene ligand in this complex is stabilized electronically by delocalization of lone pair electrons of two amino substituents attached to the silicon atom. There has been no base-free silyl-(silylene) complexes with only alkyl or aryl groups on the silicon atoms.In our previous work on donor-stabilized silyl(silylene) 6,7 and donor-free germyl(germylene)tungsten complexes, 9 we found that the tungsten fragment Cp′W(CO) 2 (Cp′ ) η-C 5 Me 5 , η-C 5 H 5 ) stabilizes the R 3 E-MdER 2 framework efficiently (E ) Si, Ge; M ) metal fragment). This prompted us to synthesize basefree silyl(silylene)tungsten complexes. Here we report the photolysis of a methyltungsten complex in the presence of hydrodisilanes. This reaction afforded either a monomeric base-free silyl(silylene)tungsten complex or a self-stabilized dimer of a silyl(silylene)tungsten complex depending on the sustituents on the silicon atoms.Photolysis of Cp′W(CO) 3 Me (1a, Cp′ ) Cp*, Cp* ) η-C 5 Me 5 ; 1b, Cp′ ) η-C 5 Me 4 Et) in the presence of excess HSiMe 2 SiMe 3 in hexane afforded yellow crystals of a self-stabilized silyl(silylene)tungsten complex with a dimeric structure, [Cp′W(CO) 2 (dSiMe 2 )(SiMe 3 )] 2 (2a, Cp′ ) Cp*; 2b, Cp′ ) η-C 5 Me 4 Et) in 87 and 54% yield, respectively (eq 1). Crystal structure analysis confirmed that complex 2b is the first silylene complex stabilized by coordination of an isocarbonyl ligand, which is coordinated to a tungsten fragment and a silylene ligand via its carbon and oxygen atom, respectively (Figure 1). The tungsten-silylene bond (W-Si(2) 2.489(2) Å) is significantly shorter than the tungsten-silyl bond (WSi(1) 2.609(2) Å), indicating partial double bond character for the W-Si (2) bonding. The silylene ligand is † Present address: Tobita, H.; Shimoi, M.; Ogino, H. J. Am. Chem. Soc. 1988, 110, 4092. (b) Tobita, H.; Ueno, K.; Shimoi, M.; Ogino, H.

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.…”

Silver‐Catalyzed Silylene Transfer

“…Light-induced silicon-silicon bond cleavage was also used for the synthesis of tungsten silylene complexes; [31][32][33] the exposure of tungsten complex 5 to ultraviolet radiation leads to the loss of CO and formation of tungsten silylene complex 7. 33 When the starting tungsten complex bore a cyclopentadiene ligand or when pentamethyldisilane was used, a base-stabilized (THF) tungsten complex was formed. 32 Late transition metal silylenoid complexes were first synthesized by exploiting the lability of silicon-triflate bonds (Scheme 7.2).…”

Hydrido(hydrosilylene)tungsten Complexes with Strong Interactions between the Silylene and Hydrido Ligands

“…The W À Si(1) bond length (2.3703 (11) ) is shorter than those of known silyltungsten complexes (2.469-2.653 ). [16] This length is even shorter than that of the donorfree silyl(silylene)tungsten complex [Cp*W(CO) 2 ( = SiMes 2 )(SiMe 3 )] (2.3850 (12) ), [7] but somewhat longer than that of cationic [Cp*(Me 2 PCH 2 CH 2 PMe 2 )(H) 2 W=SiMe 2 ]B(C 6 F 5 ) 4 (2.358(2) and 2.354(3) ). [4] The WÀH bond is oriented toward the empty p orbital on the silicon atom of the silylene ligand.…”