[P(MeNCH₂CH₂)₃N] as a Superior Catalyst for the Conversion of Isocyanates to Isocyanurates

Abstract

The unusually strong Lewis basicity of the P atom and the ability to form transannular PN interactions of various strengths account for the high catalytic activity of [P(MeNCH2CH2)3N] in the title reaction, a key step of which is shown on the right. Thus a 97% yield of triphenyl isocyanurate (Ar = C6H5) was obtained in 3 min, and a 99% yield of tri‐para‐methoxyphenyl isocyanurate (Ar = 4‐MeOC6H4) in 8 min.

Accessing Frustrated Lewis Pair Chemistry from a Spectroscopically Stable and Classical Lewis Acid‐Base Adduct

“…NMR and crystallographic characterization of 3 revealed it to be the product of 1,2-addition of 1 and B(C 6 F 5 ) 3 across the C À Odouble bond of PhNCO ( Figure 2). [11,12] In the presence of the borane,h owever, ap utative intermediate in this process is trapped, thus providing an example of agrowing application of FLPs as tools to trap reactive intermediates. [1b] In the absence of B(C 6 F 5 ) 3 , 1 is known to readily cyclotrimerize isocyanates into isocyanurates.…”

Mechanistic Analysis and Characterization of Intermediates in the Phosphane‐Catalyzed Oligomerization of Isocyanates

“…The 31 P NMR signal at −54.0 ppm assigned by Horvath et al. to the acyclic, tetracoordinated phosphane intermediate 7L neither fits the chemical shift (>0 ppm) usually associated with tetracoordinated phosphorus, nor the one published for monoadduct 6 of azaphosphatrane 14 and phenyl isocyanate (+29.46 ppm) by Verkade . This prompted us to reinvestigate the mechanism proposed for the phosphane‐catalyzed oligomerization of alkyl isocyanates 1 , using a combination of computational NMR shift predictions and experimental NMR measurements employing 15 N‐labeled isocyanate.…”

“…[5] The 31 PNMR signala tÀ54.0 ppm assignedb yH orvath et al to the acyclic, tetracoordinated phosphane intermediate 7L neither fits the chemical shift (> 0ppm) usually associated with tetracoordinated phosphorus, [2a, 6] nor the one published for monoadduct 6 of azaphosphatrane 14 and phenyli socyanate (+ 29.46 ppm) by Verkade. [7] This prompted us to reinvestigatet he mechanismp roposed for the phosphane-catalyzed oligomerization of alkyl isocyanates 1,u sing ac ombination of computational NMR shift predictionsa nd experimental NMR measurements employing 15 N-labeled isocyanate. Herein, we show aq uantitative assignment for the signals reported previously andi nc onsequence, proposeanew mechanism includ-ing key intermediate 7N for the phosphane-catalyzed oligomerization of aliphatic isocyanates (Scheme 1B).…”

Chemistry of pentacoordinated anti-apicophilic phosphorus compounds

“…Triaryl isocyanurate 28 is a trimer of aryl isocyanate and useful as an activator for the continuous anionic polymerization and postpolymerization of e-caprolactam to nylon-6. Tang and Verkade have reported that proazaphosphatrane 25 worked as an efficient catalyst for the trimerization of aryl isocyanate and they found the formation of azaphosphatranes 26 and 27 bearing an anti-apicophilic arrangement during the reaction [25] (Scheme 24).…”