1785-03-1Relevant articles and documents
Fast cyclotrimerization of a wide range of isocyanates to isocyanurates over acid/base conjugates under bulk conditions
Cheng, Ruihua,Liu, Wei,Wu, Li,Ye, Jinxing
, (2020/07/06)
An array of organic bases DMAP (4-dimethylaminopyridine), DBU (1, 8-diazabicyclo [5.4.0] undec-7-ene), TBD (1, 5, 7-triazabicyclo [4.4.0] dec-5-ene), and their base/acid conjugate organocatalyst systems were evaluated in the trimerization of various isocyanates. The performance depended greatly on the combination of the catalyst systems, and the [HTBD][OAc] (acetic acid) catalyst systems were considerably the most active in contrast to the corresponding DMAP and DBU counterparts. The [HTBD][OAc] catalyst system was capable of providing isocyanurates from the cyclotrimerization of various isocyanate substrates in excellent yields in seconds even under bulk conditions. A bifunctional catalytic mechanism over [HTBD][OAc] was proposed.
Potassium complexes containing bidentate pyrrole ligands: Synthesis, structures, and catalytic activity for the cyclotrimerization of isocyanates
Guo, Zhiqiang,Xu, Yuan,Wu, Xiaoqin,Wei, Xuehong,Xi, Chanjuan
supporting information, p. 8116 - 8121 (2019/06/19)
Bidentate pyrrolyl ligands, 2-(t-butyliminomethyl)pyrrole and 2-(t-butylaminomethyl)pyrrole, reacted with KH to give complexes [C4H3N(2-CHNtBu)K(THF)]n (1) and [C4H3N(2-CH2NHsup
Reactivities of zero-valent group 10 complexes toward organic isocyanates: Synthesis of metallacycles containing dimeric isocyanate units, isocyanate cyclotrimerization, and computational chemistry
Han, Young-Sung,Jung, Kang-Yeoun,Kim, Yong-Joo,Baeck, Kyoung Koo,Lee, Gang Min,Lee, Soon W.
, p. 15614 - 15625 (2019/10/19)
The reactions of [Pd(olefin)(PR3)2] (PR3 = PMe3, PMe2Ph) with two equivalents of an aryl or alkyl isocyanate afford cis-[Pd{-N(R)C(O)N(R)C(O)-}(PR3)2] (R = 1-naphthyl, 4-phenoxyphenyl), which are five-membered palladacycles bearing dimeric isocyanate units, or cyclic tetramers as assemblies of four five-membered palladacycles, [Pd{C(O)N(R′)C(O)N(R′)}(PMe3)]4, (R′ = 3-methylbenzyl, 4-methylbenzyl or 4-methoxybenzyl), depending on the alkyl substituent on R-NCO. Interestingly, these reactions afford cyclic trimers as catalytic products when two equivalents or excess amounts of benzyl isocyanate are used. In contrast, reactions of [Pt(olefin)(PR3)2] with two equivalents of an alkyl or aryl isocyanate afford only the five-membered platinacycle, namely cis-[Pt{-N(R)C(O)N(R)C(O)-}(PMe3)2] (R = 3-methylbenzyl, 4-methylbenzyl, 4-fluorobenzyl, 4-methoxybenzyl, (S)-(+)-(1-naphthyl)ethyl, (R)-(-)-(1-naphthyl)ethyl, 4-phenoxyphenyl and 2,6-difluorophenyl). Aided by theoretical calculations, we propose mechanisms for the formation of the five-membered palladacycle or platinacycle, the cyclic tetramer, and the cyclotrimerization of the organic isocyanate. In addition, the ligand-exchange reactions between a five-membered platinacycle bearing a chiral substituent such as (S)-(+)-(1-naphthyl)ethyl or (R)-(-)-(1-naphthyl)ethyl) moieties and 1,2-bis(diethylphosphino)ethane (DEPE), a chelating phosphine, clearly afford the corresponding platinacycle bearing a DEPE ligand with retention of chirality. On the other hand, reactions of [Ni(COD)2] with various organic isocyanates in the presence of tertiary phosphines only afford the corresponding cyclic trimers. In contrast, similar reactions in the presence of N-heterocyclic carbenes (NHC) such as 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidine (SIPr) afford unexpected adducts between R-NCO and the NHC ligand.
