Striking Reactivity of a Stable, Zwitterionic Silylene Towards Substituted Diazomethanes, Azides, and Isocyanides

Abstract

The reactivity of the zwitterionic N-heterocyclic silylene (NHS) LSi: 1 (L = Ar-N-C(Me)=CH-C(=CH(2))-N-Ar, Ar = 2,6-iPr(2)C(6)H(3)), towards diphenyldiazomethane (Ph(2)CN(2)), trimethylsilyl azide (Me(3)SiN(3)), and cyclohexyl isocyanide (C(6)H(11)-NC) is reported. The addition of Ph(2)CN(2) to 1 leads to the diiminylsilane LSi(N=CPh(2))(2) 2 (80% yield), whereas the treatment of 1 with Me(3)SiN(3) gives the spirobicyclic silatetrazoline LSi(NNSiMe(3))(2) 3 (67% yield), and addition of C(6)H(11)-NC gives the silyl cyanide LSi(R)CN (R = cyclohexyl) 4 (32% yield) along with the unexpected azasilacyclobutane 5 (41% yield). The novel compounds were fully characterized by (1)H, (13)C, and (29)Si NMR spectroscopy, ESIMS, elemental analysis, and single-crystal X-ray diffraction.

Computational Analysis of n→π* Back-Bonding in Metallylene–Isocyanide Complexes R2MCNR′ (M = Si, Ge, Sn; R =tBu, Ph; R′ = Me,tBu, Ph)

“…This applies even more so for the CN bond than for the CO bond because electrostatic and -type effects are significantly greater for the former than for the latter. It is interesting to note that Purcell has discussed these bonding effects in the context of CO and CN  as early as 1969, 34 but this work [9] appears to be largely forgotten as judged by the limited number of citations it has attracted. One of the important discoveries in his theoretical work was that, while -type bonding effects play a role when CN  ligand coordinates, an even more important source of increased stabilization comes from the direct decrease in C-N bond repulsion as a result of charge withdrawal from the carbon atom.…”

“…For example, compound 5 undergoes facile C-H bond activation to form isobutene and cyanogermane, 7a whereas 6, if allowed to stand or treated with excess methyl isocyanide, undergoes a three-fold insertion of the isocyanide into the Ge-C bond; 7b C-H bond activation resulting from the reaction of a transient silylene with tert-butyl isocyanide has also been reported, 8 as are coupling reactions of isocyanides with silylenes stabilized by β-diketiminate ligands. 9 In general, metal-mediated coupling and polymerization of unsaturated organic molecules are important industrial processes, 10 and the synthesis of heterocycles resulting from coupling and cycloaddition reactions of isocyanides with other heteroelement unsaturated species is a widely used technique. 11 [4] During our investigations of the chemistry of the adduct 5, it was realized that its ν(CN) stretching band is shifted to slightly lower wave number relative to the analogous stretching frequency of the free isocyanide.…”

Synthesis and Rearrangement of Stable NHC→Silylene Adducts and Their Unique Reactivity towards Cyclohexylisocyanide

“…We have been engaged in exploring the chemistry of the thermally stable, partially zwitterionic, N‐heterocyclic silylene LSi: 1 [L=Ar‐ N ‐C(=CH 2 )CHC(Me)‐ N ‐Ar, Ar=2,6‐ i Pr 2 C 6 H 3 ]9 which shows also a striking reactivity toward isocyanides and reacts with an excess of cyclohexylisocyanide, affording an unusual cycloaddition and CH activation product along with a silacyanide 10. More recently, we communicated the synthesis and structure of the 1:1 adduct 2 , starting from 1 and a NHC (Scheme ) 11.…”

Unexpected Silaazetidine Formation in the Thermolysis of thf‐Supported Silanimine Et2Si=N–SitBu3·thf

“…It is worth to mention that in the thermolysis of homologous silanimines R 2 Si=N-SitBu 3 ·thf (R = Me, Et, tBu) the silanimine dimer (Me 2 SiNSitBu 3 ) 2 [29] for R = Me, the sila- Only a number of crystal structures of 2-silaazetidines are described in the literature. [35,[40][41][42][43] As already mentioned, the most characteristic features in the crystal structures of 2-silaazetidines are the four-membered C 2 NSi rings. X-ray quality crystals of 3 were grown from a benzene solution at ambient temperature.…”