Syntheses and Structures of Five-Coordinate Zirconium Alkyl Complexes Supported by Diketiminate Ligands

Abstract

An alkane elimination reaction generates the diketiminate compound (TTP)Zr(CH2Ph)3 (1) from Zr(CH2Ph)4 and TTPH (TTPH = 2-p-tolylamino-4-p-tolylimino-2-pentene). The molecular structure of 1 was solved, and it shows a five-coordinate zirconium with three η 1-coordinated benzyl groups and an η 2-bound TTP ligand. When 1 is heated to 45 °C in hydrocarbon solvents, toluene is eliminated and the orthometalated product 2 is formed. The molecular structure of 2 indicates η 1 and η 2 benzyl groups. The variable-temperature 1H NMR (−78 to 50 °C) spectra exhibit a single benzyl resonance. The magnitude of 1 J CH for the benzyl methylene resonance is consistent with a rapid exchange between η 1 and η 2 bonding modes in solution. Isotopic labeling experiments employing (PPP-d 10)Zr(CH2Ph)3(3-d 10, PPP = 2-phenylamino-4-phenylimino-2-pentenato) support direct C−H activation through a four-centered transition state. Based on kinetic experiments, C−H activation is unimolecular, and the rate-limiting step exhibits a large kinetic isotope effect: k H/k D = 5.2(5) at 65 °C. The thermal stability of alkyl complexes is improved by replacing the ortho protons with isopropyl groups. (DDP)ZrMe3 (5) can be prepared from (DDP)ZrCl3 via halide metathesis using MeLi (DDP = 2-(2,6-diisopropyl)phenylamino-4-(2,6-diisopropyl)phenylimino-2-pentenato). The thermal stability of 5 is greatly enhanced compared to those of 1 and 3.

Synthesis and Structure of Zirconium and Hafnium Polymerisation Catalysts Stabilised by Very Bulky Aminopyridinato Ligands

“…In the solid state, one of the three benzyls is η 2 -coordinated and rest are η 1 -coordinated to the electron deficient metal centres. Moreover, one of the three benzyls has been partially abstracted using B(C 6 F 5 ) 3 , the phenyl ring of Bbounded benzyl shows an η 6 -coordination fashion. These zwitterionic complexes do not react with a second equiv.…”

“…1 H NMR spectroscopy shows that the zwitterionic structure of 8a found in the solid state is maintained in solution. An NMR tube reaction was carried out for 5b with B(C 6 F 5 ) 3 to form 8b in C 6 D 6 . Noteworthy in the 1 H NMR spectrum are broad signals, especially two broad singlets at δ = 2.10 and 2.21 ppm for the Zr-CH 2 Ph protons, one broad singlet for the protons of the isopropyl group of the ligands and one broad singlet for the B-CH 2 protons.…”

“…The Zr/Hf chemistry of dialkyl cations stabilised by anionic polydentate N-ligands is rather unexplored but might be unique due to the presence of two metal-alkyl functionalities and the tuneable N-ligand environment (Figure 1). The starting materials for generating such N-ligand stabilised dialkyl cations, namely Zr/Hf trialkyls stabilised by anionic N-ligands, are well documented and known for amidinates, [1] guanidinates, [2] diketiminate, [3] macrocyclic amides, [4] tropocoronands [5] and tris(pyrazolyl)borates. [6] Dialkyl cations have been generated from the corresponding tris(pyrazolyl)borates.…”

Synthesis and structural characterization of LiI, ZnII, CdII, and HgII complexes containing a fluorinated β-diketiminate ligand

“…Encouraged by the very rich chemistry already displayed by this valuable ligand, it is attractive to synthesize its analogues and explore the potential applications. Consequently, several research groups have investigated a variety of ligands by varying both the steric and electronic factors based on the β-diketiminate framework [28][29][30][31][32][33][34] . In this context, we describe the synthesis and structural analysis of a series of new lithium, zinc, cadmium, and mercury complexes derived from a fluorinated β-diketiminate ligand.…”

The Template Effect of Palladium(II): Synthesis, Characterization, and Crystal Structures of 2,4‐Substituted 1,3,5‐Triazapentadienatopalladium(II) Complexes

“…[2,3] Similar diimine ligands, namely N-phosphanyl-β-diimine ligands, [4] sterically demanding aromatic diimine ligands, [5] and their complexes have also been developed. Many metal β-diiminate complexes, such as magnesium, [6] aluminum, [7] nickel and palladium, [8] zirconium, [9] rhodium, [10] gallium, [11] and scandium [12] etc. have been reported.…”