A New, Flexible N,N,N‐Tripodal Facially Capping Ligand System: Synthesis and Structural Characterization of β‐Triketimines and Their M(CO)₃ Complexes (M = Cr, Mo, W)

Abstract

Reaction of imidoyl chlorides Ar*N=CClR (Ar* = 2‐iPrC6H4, 2,6‐iPr2C6H3, 2‐MeOC6H4; R = Me, Ph, tBu) with [Li(nacnac)] [nacnac = (Ar*NCMe)2CH] gives β‐triketimines L, most of which exist in solution in equilibrium with their imine/enamine tautomers. The route is highly modular, allowing independent variation of at least five parameters. The solution equilibria are very sensitive to such substituent pattern variation. Single‐crystal X‐ray diffraction analyses of examples of both tautomers and a geometric isomer in the solid state are presented, alongside solution NMR studies of the tautomerism. All examples revert exclusively to the β‐triimine form on complexation with M(CO)3 fragments (M = Cr, Mo, W). Facial isomers result. The ligands are weak σ‐donors, as adjudged by CO IR stretching frequencies in [LM(CO)3]. Crystal‐structure determination on the isostructural pair [HC(2‐iPrC6H4N=CMe)3M(CO)3] (M = Cr, Mo) revealed a hexagonal packing arrangement composed of aryl–aryl and carbonyl (CO)–H–C interactions which generates pseudocylindrical voids accounting for 6–9 % of the crystal volume. In only one case were these occupied by solvent molecules. This family of facially capping N,N,N‐ligands with finely tunable bulk have wide potential in coordination chemistry.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The behaviour of β-triketimine cobalt complexes in the polymerization of isoprene

“…These ligands exhibited extensive tautomerism in solution, as reported for earlier examples, 37 but as previously found when metal-bound, 36,37 the seven examples all adopted fac-triketimine ligated forms: b-triketimine cobalt complexes were prepared from the reaction of these ligands with cobalt bromide in the presence of NaBArF, Scheme 1. These ligands exhibited extensive tautomerism in solution, as reported for earlier examples, 37 but as previously found when metal-bound, 36,37 the seven examples all adopted fac-triketimine ligated forms: b-triketimine cobalt complexes were prepared from the reaction of these ligands with cobalt bromide in the presence of NaBArF, Scheme 1.…”

“…NaBArF, 42 t BuCONH-2-OCH 3 37 and complexes 1, 2 and 4 (ref. The ligands, CoBr 2 and NaBArF were stored in an argon-lled glovebox before they were transferred into Schlenk tubes.…”

Synthesis and structural characterization of a nickel(II) precatalyst bearing a β‐triketimine ligand and study of its ethylene polymerization performance using response surface methods

“…The β‐triketimine ligand 2 was synthesized by reaction of β‐diketimine 1 with n ‐BuLi giving a lithium diketiminate which was then reacted with acetimidoyl chloride, giving pale yellow crystals of 2 in good yield after recrystallization from methanol and DCM (Scheme ) 24. This reaction appears to proceed with good chemoselectivity for CC bond formation as was previously found for other electrophiles 35.…”

“…Industrial toluene for polymerization was obtained from Arak Petrochemical Co. (Arak, Iran) and was distilled over sodium wire. The starting compounds N ‐(2, 4, 6‐trimethyl phenyl acetimidoyl chloride and NaBAr' 4 ([Na] + [3,5‐(CF 3 ) 4 C 6 H 3 ] 4 B] − ) were prepared according to literature procedures 24, 31…”

“…We recently reported on a new class of ligands, derived from Nacnac 1 , termed the β‐triketimines, 2 (Scheme ), neutral and tridentate, as for the mer ligand in 5 , but fac capping, as shown in the products of their reaction with M(CO) 3 [M = Cr, Mo, W] 24. This family of ligands with finely tunable bulk have wide potential in coordination chemistry; a number of their nickel complexes have been prepared, as neutral complexes and as cations, such as 3a (Scheme ), which when paired with large anions and activated with methylaluminoxane (MAO), show activity as catalysts for polyethylene (PE) polymerization 25…”