Potassium and Lithium Complexes with Monodeprotonated, Dearomatized PNP and PNCNHC Pincer-Type Ligands

Abstract

The reaction of 2,6-bis(di-tert-butylphosphinomethyl)pyridine (tBuPNtBuP) with 1 molar equiv of KCH2C6H5 or LiCH2SiMe3 gave M(tBuP*NatBuP) (M = K, Li; P* = vinylic P donor, tBuP = PtBu2, Na = anionic amido N donor) after monodeprotonation of the α-lutidinyl-CH2 and concomitant dearomatization of the heterocycle. Evidence is provided that the anion tBuP*NatBuP may exist as Z- and E-isomers, interconvertible by rotation about the Cα-N–Cα-P exocyclic formal double bond. Thus, the two isomers of K(tBuP*NatBuP), i.e., [K{(Z)-(tBuP*NatBuP-κP*,κNa,κP)}(THF)], 1-Z·(THF), and [K{(E)-(tBuP*NatBuP-κNa,κP)}(THF)], 1-E·(THF), cocrystallized from THF in a 4:1 ratio. However, in the presence of DME, the isomerically pure [K{(E)-(tBuP*NatBuP-κNa,κP)}(DME)2], 1-E·2(DME), was crystallized. The α-picolinyl-CH2 moiety in RPNCNHC (N = substituted 2-picoline, RP = PCy2, R = Cy; RP = PtBu2, R = tBu; CNHC = N-heterocyclic carbene) was similarly deprotonated with concomitant dearomatization using LiN(SiMe3)2. This afforded the co...