1,4,2‐Diazaphospholidine‐3,5‐diones and Related Compounds: A Lecture on Unpredictability in Catalysis

Abstract

Whereas 1-organyl-phospholanes and 1-organyl-2,3-dihydro-1H-phospholes catalyze isocyanate oligomerization, the reaction of isocyanates with 1-organyl-2,5-dihydro-1H-phospholes results in the formation of 1,3-dienes and a novel class of P-heterocycles, 1,4,2-diazaphospholidine-3,5-diones. Isothiocyanates and carbodiimides exhibit analogous behavior. The resultant species readily form P-oxides, P-sulfides (see picture), and quaternary onium salts.

Cyclo-oligomerization of isocyanates with Na(PH2) or Na(OCP) as “P−” anion sources

“…Lewis bases such as anions of simple inorganic and organic salts (e.g. uorides, hydroxides, carboxylates, alkoxides), 2 N-heterocyclic carbenes 3 amine bases 4 as well as acyclic 5 or cyclic [6][7][8] phosphanes are well known to catalyze the cyclo-oligomerization of isocyanates (A) to form uretdiones, B as cyclic dimers and isocyanurates C, or their isomers iminooxadiazinediones D, as trimers (Fig. 1).…”

Structure–Property Relations in Oligomers of Linear Aliphatic Diisocyanates

“…“Trimerizations” (formation of isocyanurates and/or iminooxadiazinediones, the latter often being referred to as asymmetrical trimers, AST for short) and “dimerizations” (uretdione formation) almost invariably lead to mixtures of products containing all three different NCO derivatives mentioned. On the other hand, small deviations in structure of a catalyst may lead to completely different results in isocyanate oligomerization . The situation is even more complex in diisocyanate chemistry as the oligomerization depicted as the example of diisocyanate “trimerization” in Figure may also lead to hybrid oligomers containing two or more different structural types in one oligomer molecule.…”

Nitrogen, phosphorus, arsenic, antimony and bismuth

“…53 The reaction of isocyanates with dihydrophosphole 48 results in the elimination of butadiene and the formation of the heterocycle 49. 54 A similar process occurs when isothiocyanates and carbodiimides were used as substrates.…”