Direct synthesis of doubly deprotonated, dearomatised lutidine PNP Cr and Zr pincer complexes based on isolated K and Li ligand transfer reagents

Abstract

Double deprotonation of 2,6-bis-(di-tert-butylphosphinomethyl)-pyridine (^tBuPN^tBuP), with KCH₂C₆H₅ afforded K₂(^tBuP*N_a^tBuP*), N_a = anionic amido N, ^tBuP* = di-tert-butyl vinylic P donor. The analogous [Li₂(^tBuP*N_a^tBuP*)]₂ (1) was reacted with [CrCl₂(THF)₂] and [ZrCl₄(THT)₂] to give the helical [Cr{Cr(^tBuP*N_a^tBuP*)Cl}₂] (2) and [Zr(^tBuP*N_a^tBuP*)Cl₂] (3), respectively. DFT calculations support dearomatisation of P*N_aP* and its high donor ability.