Hydroamination of isocyanates and isothiocyanates by alkaline earth metal initiators supported by a bulky iminopyrrolyl ligand

Abstract

A series of new heteroleptic alkaline earth (Ae) metal complexes of general formula [{(Ph₂CHNCH)₂C₄H₂N}AeI(THF)₃] {Ae = Ca (2), Sr (3), and Ba (4)} were synthesized via salt metathesis by reacting potassium salt of ligand 1-K [{(Ph₂CHNCH)₂C₄H₂N}K(THF)₂] with anhydrous alkaline earth metal diiodides (AeI₂). The homoleptic calcium and barium complexes [{(Ph₂CHNCH)₂C₄H₂N}₂Ae] [Ae = Ca (5), Ba (6)] were prepared by treating metal bis-hexamethyldisilazide [Ae{N(SiMe₃)₂}₂(THF)₂] with the protic ligand 1-H [(Ph₂CH–NCH)₂C₄H₂NH] in a 1 : 2 molar ratio. Calcium complex 5 was used as an active pre-catalyst for the addition of N–H bond of arylamines across the heterocumulenes such as phenylisocyanate (PhNCO) and phenylisothiocyanate (PhNCS) under neat conditions, and up to 99% yields of the corresponding urea and thiourea derivatives were obtained.