Abnormal Reactivity of an N‐Heterocyclic Carbene (NHC) with a Phosphaalkene: A Route to a 4‐Phosphino‐Substituted NHC

A Facile Route to Functionalized N-Heterocyclic Carbenes (NHCs) with NHC Base-Stabilized Dichlorosilylene

“…16 For example, the C1-N1 and C1-N2 bond distances are close to those in IPr. The N1-C1-N2 angle of 101.40 (12)°is identical to that in IPr. 16 Triazine 3 crystallizes in the triclinic space group P1 j with two toluene molecules in the asymmetric unit ( Figure 2).…”

“…Selected bond lengths (Å) and angles (deg): C1-N2, 1.3654(19); C2-C3, 1.356(2); C2-N2, 1.4124(19); C2-Si1, 1.8417(16); Si1-Cl1, 2.0553(6); N3-Si1, 1.6726(14); N2-C1-N1, 101.40(12); N3-Si1-C2, 109.63(7); C2-Si1-Cl1, 107.50(5); Cl1-Si1-Cl2, 101.93(3).…”

Synthesis of 4- and 4,5-Functionalized Imidazol-2-ylidenes from a Single 4,5-Unsubstituted Imidazol-2-ylidene

“…3 Because of the commonly practiced synthetic routes, most unsaturated NHCs feature an unsubstituted carbon-carbon double bond or alternatively alkyl or aryl groups are placed at the 4 and 5 positions. 4 The rare exceptions are imidazol-2-ylidenes annulated to a quinone derivative ( A ) 5 or a heterocycle (such as B and C ), 6 the oxazoline-derivatives ( D , E ), 7 and NHCs featuring one ( F , G ) 8 or two ( H ) 9 heavier main group elements.…”

Carbenes and Nitrenes

“…76 Results of DFT calculations support a proton shift yielding (35) followed by addition to the phosphaalkene and two subsequent proton shifts. …”

“…The formation of a Breslow intermediate (76) obtained by nucleophilic addition of NHC (75) to an aldehyde is now a well-established process for carrying out umpolung reactions from aldehydes. There have been many reports where the carbon bearing the highest electron density is involved in nucleophilic reactions, classically followed by elimination of the azolium leaving group in a tetrahedral intermediate (similar to the addition-elimination reaction of carboxylic acid derivatives).…”