1.3.4.5- Tetramethylimidazol-2-ylidene

Figure 23 Solid-state structure, partial labeling scheme and selected bond lengths of [(Cp )2Zn(1,3,4,5-tetramethylimidazol-2-ylidene)] 49. 

In this experiment, the synthesis of the first donor-stabilized hydrosilanimine by the reaction of RSiHCl2 (R = Ar(SiMe3)N, Ar = 2,6-tPr2C6H3) with N-heterocyclic carbenes 1,3,4,5-tetramethylimidazol-2-ylidene (IMe4) was described. 

Like the parent Cp2Be, the beryllocenes 10, 11, and 12 are sublimable, air- and oxygen-sensitive solids. They do not react with pyridine, CO, or l,3,4,5-tetramethylimidazol-2-ylidene, but do react with CNC6H3Me2-2,6 to give half-sandwich iminoacyl products via insertion into the Be-C cr-bond, described in Section 2.02.2.3.2. 

By treating the soft iV-heterocyclic carbenel,3,4,5-tetramethylimidazol-2-ylidene 278 with an electron-rich di(isopro-pyl)amino-phosphaalkyne 279, the bicyclic azaphospholene 281 was formed in almost quantative yield via a P-Ccarbene bond formation 280 and C-H insertion (Equation 123) <2001AGE3144>. 

Cyclic thiourea derivatives like l,3,4,5-tetramethylimidazole-2(3H)-thione— prepared by condensation of substituted thioureas with a-hydroxyketones—can be converted into the corresponding imidazolin-2-ylidene by desulfurization with sodium or potassium [Eq. (23)]. This method was used to prepare and isolate l,3-bis-neo-pentylbenzimidazolin-2-ylidene with Na/K. With LDA as the base it is also possible to generate free benzimidazolin-2-ylidenes in solution. ... 

Examples of well-defined, highly active Ni/carbene complexes catalyzing the Suzuki reaction have also been reported. McGuinness and coworkers have shown that using as little as 0.03 mol % of Ni(tmiy)2l2 or Ni(tmiy)2(o-tolyl)Br (tmiy = l,3,4,5-tetramethylimidazol-2-ylidene) in the coupling of 4-bromoacetophenone with phenylboronic acid led to 19% (TON = 630) and 58% (TON = 1930) conversion of the aryl halide, respectively [55]. 

Reaction between Ru3(CO)12 and three equivalents of the NHCs ImMes2 and ImDipp2 give quantitative yields of mononuclear Ru(CO)4(NHC), whereas sulfido clusters 39 and 40 are isolated from the reaction with the NHC precursor S=ImMes2. A similar reaction with the smaller ImMe4 (l,3,4,5-tetramethylimidazol-2-ylidene) affords the trinuclear cluster 41, a result that most likely stems from the difference in steric bulk around the nitrogen.32... 

Organolanthanide carbene complexes have been elusive for a long time. With the use of Arduengo-type heterocyclic carbenes this interesting class of compounds has become readily available. The (imidazol-2-ylidene) samarium complexes shown in Scheme 105 were obtained from l,3,4,5-tetramethylimidazol-2-ylidene and Cp 2Sm(THF) in different molar ratios.519... 

Of interest is the imidazol-2-ylidene adduct of structure 1 from the lithium salt of dimethylamino-3,4-dimethylboratabenzene and l,3,4,5-tetramethylimidazol-2-ylidene (OOOM3751). The B-C bond between the two heterocycles is purely single, and conjugation between the two heterorings is absent. 

After the successful preparation of the first stable compounds containing silicon-silicon triple bonds [200], their reactivity with NHCs was investigated. NHCs have been shown to bind to one silicon center, generating a lone pair of electrons on the second, which can participate in reactions as a Lewis base. As a result, these silylynes can be considered ambiphilic, much like the SiX2 fi agment. In fact, NHC-Si(R)=Si(R)=ZnCl2 (NHC= l,3,4,5-tetramethylimidazol-2-ylidene, R = isoprop)dbis(bis(trimethylsilyl)methyl)silyl) was prepared in this fashion by Yamaguchi ef /. (Scheme 15.16) [201]. 

Vsip couplings of 186.4, 131.8 and 116.4 Hz have been observed by Hansen et al ° for the labile, zwitterionic halfparent phosphasilene L Si=PH (L =CH[(C=CH2)CMe(N-2,6-i-Pr2C6H3)2] and its two stable 4-dimethylaminopyridine and l,3,4,5-tetramethylimidazol-2-ylidene adducts, respectively. Interestingly, the Vhp couplings determined for these compounds are almost identical, 143.0,144.1 and 144.1 Hz, respectively. 

N-Heterocyclic Carbene-Stabilized Silylene Monohydride RSi ( NHC)H (R = rBuaSi, NHC = U,4, 5-tetramethylimidazol-2-ylidene)... 

YBu3Si)SiH2Cl, l,3,4,5-tetramethylimidazol-2-ylidene " NHC), toluene, hexane. 

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