2-Picolylamino(diphenylphosphinoselenoic)amide supported zinc complexes: Efficient catalyst for insertion of N–H bond into carbodiimides, isocyanates, and isothiocyanate

GRAPHICAL ABSTRACT

ABSTRACT

We report here the hydroamination of heterocumulenes such as carbodiimides, isocyanates, and isothiocyanates by zinc complexes supported by the ligand 2-picolylamino-(diphenylphosphinoselenoic)amide [{(Ph₂P-(˭Se)}₂NCH₂(C₅H₄N)] (1). A series of zinc complexes [κ²-{(Ph₂P-(˭Se)}₂NCH₂(C₅H₄N)ZnX₂] [(X˭Cl (2), Br (3a), I (4)] were prepared from ligand 1 and the corresponding zinc dihalide in a 1:1 molar ratio at 60°C in a chloroform solvent. The reaction of ligand 1 and ZnBr₂ in methanol yielded another zinc complex [κ²-{(Ph₂P-(˭Se)}₂NCH₂(C₅H₄N)ZnBr₂(CH₃OH)] (3b). The molecular structures of compounds 3a, 3b, and 4 were established through single-crystal X-ray diffraction analyses. The solid-state structures of all the complexes revealed a κ²- chelation through pyridine nitrogen and selenium atoms of ligand 1 to the zinc ion. Complex 2 proved to be a competent pre-catalyst for the addition of the amine N–H bond to carbodiimides, isocyanates, and isothiocyanates. The reaction scope was expanded to reactions of aliphatic and aromatic amines with phenylisocyanate and phenylisothiocyanate in toluene solvents, which proceeded rapidly at room temperature with 5 mol% catalyst loading to yield (up to 99%) the corresponding derivatives of urea and thio-urea. However, a temperature of 90°C was needed for the hydroamination of N,N′ dicyclohexylcarbodiimide. We also report the most plausible mechanism of the hydroamination reaction.

KEYWORDS:

• P-N Ligands
• Selenium
• Sulfur
• Carbodiimides
• Isocyanate
• Isothiocyanate
• Zinc

Acknowledgments

This work was supported by the Science and Engineering Research Board (SERB), Department of Science and Technology (DST), Government of India, under project no. (SB/S1/IC/045/2013). A.H. and K.B. thank CSIR, India, for their PhD fellowships.