A binuclear aluminium complex as a single competent catalyst for efficient synthesis of urea, biuret, isourea, isothiourea, phosphorylguanidine, and quinazolinones

Abstract

The synthesis and characterisation of two mononuclear aluminium alkyl complexes with the general composition [Al(Me)₂{Ph₂P(E)N(CH₂)₂N(CH₂CH₂)₂O}] (E = Se (2a); S (2b)), and two binuclear aluminium complexes, [Al(Me)₂{Ph₂P-(E)N(CH₂)₂N(CH₂CH₂)₂O}(AlMe₃)] (E = Se (3a) and S (3b)), are described. The binuclear aluminium alkyl complex 3a proved to be a proficient catalyst for the addition of simple nucleophiles to heterocumulenes, leading to the synthesis of a variety of products such as urea, biuret, isourea, isothiourea, phosphorylguanidine, and quinazolinone derivatives, in contrast to its mononuclear analogues. Complex 3a is the first example of a single competent catalyst, which is also low-cost and eco-friendly and derived from a main-group metal, under solvent-free conditions either at room temperature or mild temperatures. Complex 3a possessed a wide functional group tolerance including heteroatoms, yielding the corresponding insertion products in good quantities and with high selectivity.