NL2+ Systems as New-Generation Phase-Transfer Catalysts.

Phase-transfer catalysts (PTCs), currently, are one of the most important tools of chemists for performing organic reactions. PTCs accelerate several types of reactions in biphasic systems, giving excellent yields of the desired product. Most of the PTCs belong to the general formula NR4+X-. In the recent past, several compounds possessing a novel scaffold with the general formula NL2+X- have been reported as PTCs. In the NL2+ species, a nitrogen atom with a formal positive charge accepts electron density from electron-donating ligands. Electronic structure studies reported in the literature confirmed the possibility of L → N coordination (donor-acceptor) interactions in these species, and thus, this class of compounds are known as divalent NI compounds. These species are reported to exhibit better catalytic potential in comparison to the traditional NR4+ systems. Some of the NL2+ systems are found to be useful in asymmetric phase-transfer catalysis. Thus, these systems offer extensive opportunities for exploring the catalytic properties and novel mechanistic aspects associated with their unique electronic structure. In this paper, the synthesis, electronic, and structural properties and the applications in catalysis of the NL2+-based PTCs are reviewed with their bright future scope in catalytic organic chemistry.