Several reactions of tantalum-imine complexes with isocyanates, a hydrazone, and imides

Haruka Shimizu,Shu Kobayashi,Miho Ohsumi,Paul Krapcho

doi:10.3998/ark.5550190.0006.642

Abstract

We have revealed that tantalum-imine complexes reacted regioselectively with phenyl or benzyl isocyanate to afford α-amino amides in high yields. The reaction provides a general method of α- amino amides from various imines and isocyanates using a low-valent tantalum prepared from TaCl5 and Zn in situ. In addition, we have found a novel reaction of a tantalum-imine complex with a hydrazone and imides to afford heterocyclic compounds in good yields.

Highlights

Metal-imine complexes have attracted much attention in the area of organometallic chemistry, and their formation and chemical properties have been well investigated.[1,2,3,4] In many cases, they were formed in situ via ligand-metal exchange followed by a loss of β-hydrogen of an amide moiety,[5] migration of an alkyl group to anmetal,[6] and reduction of a low-valent complex with phosphaazaallene.[7]
Reactions with isocyanates We thought that a tantalum-imine complex could be a general precursor for α-amino amides
The reaction of a Ta-imine complex with cyclohexyl isocyanate. It was known in the reaction of a zirconium-imine complex with isocyanate that steric hindrance on the imine nitrogen or on the isocyanate discouraged insertion into the ZrN bond and gave clean Zr-C insertion.5c Since it was expected that the same phenomena could be observed in the case of a tantalum-imine complex, we used phenyl isocyanate instead of cyclohexyl isocyanate

Summary

Introduction

Metal-imine complexes have attracted much attention in the area of organometallic chemistry, and their formation and chemical properties have been well investigated.[1,2,3,4] In many cases, they were formed in situ via ligand-metal exchange followed by a loss of β-hydrogen of an amide moiety,[5] migration of an alkyl group to an (iminoacyl)metal,[6] and reduction of a low-valent complex with phosphaazaallene.[7]. Reactions with isocyanates We thought that a tantalum-imine complex could be a general precursor for α-amino amides.

Results

Conclusion