Group IV Organometallic Compounds Based on Dianionic “Pincer” Ligands: Synthesis, Characterization, and Catalytic Activity in Intramolecular Hydroamination Reactions

Abstract

Neutral Zr(IV) and Hf(IV) diamido complexes stabilized by unsymmetrical dianionic N,C,N' pincer ligands have been prepared through the simplest and convenient direct metal-induced Caryl-H bond activation. Simple ligand modification has contributed to highlight the non-innocent role played by the donor atom set in the control of the cyclometallation kinetics. The as-prepared bis-amido catalysts were found to be good candidates for the intramolecular hydroamination/cyclization of primary aminoalkenes. The ability of these compounds to promote such a catalytic transformation efficiently (by providing, in some cases, fast and complete substrate conversion at room temperature) constitutes a remarkable step forward toward catalytic systems that can operate at relatively low catalyst loading and under milder reaction conditions. Kinetic studies and substrate-scope investigations, in conjunction with preliminary DFT calculations on the real systems, were used to elucidate the effects of the substrate substitution on the catalyst performance and to support the most reliable mechanistic path operative in the hydroamination reaction.

Metal‐to‐Ligand Alkyl Migration Inducing Carbon–Sulfur Bond Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole‐Containing Amidopyridinate Ligands: Synthesis, Characterization, and Catalytic Activity in the Intramolecular Hydroamination Reaction

“…Scheme illustrates the stepwise procedure developed to prepare 5‐methylthiazole‐ and benzothiazole‐substituted aminopyridine ligands 6 a , b and 7 in moderate yields. Bromo intermediates 3 a , b , 2‐(trimethylstannyl)benzothiazole ( 4 ), and 5‐methyl‐2‐(trimethylstannyl)thiazole ( 5 ) were prepared according to literature procedures,14, 15 in some cases with slight modifications 16. 6‐Bromo‐2‐pyridinecarboxaldehyde ( 1 a ) and 2‐acetyl‐6‐bromopyridine ( 1 b ) were converted to imine derivatives 2 a , b under classical condensation conditions in the presence of a catalytic amount of formic acid 17.…”

Imidazole‐Bridged Tetrameric Group(IV) Heteroleptic Complexes from the Spontaneous Metal‐Ligand Assembly of a Potentially N4‐Tetradentate Ligand

“…To the best of our knowledge, this is the first example of a structurally characterized hafnium(IV) imidazole complex to date. The main structural metrics [ d (Hf‐N im ) = 2.37 Å; d (Hf–N anilido ) = 2.12 Å; d (Hf–NMe 2 ) = 2.08 Å; α(N im –Hf–N anilido ) = 79.8°] fall in the typical range observed for similar complexes in the CSD containing anilido ligands bound to hafnium(IV) [ d (Hf–N anilido ) = 2.11 Å] . Intramolecular C‐H ··· N interactions are present in the molecule between C‐H bonds from methylene or dimethylamido groups and N‐atoms from the same ‐NMe 2 ligands or from the uncoordinated pyridine [d(C ··· NMe 2 ) = 3.662(7) Å; d(C ··· N py ) = 3.483(12) Å].…”

“…In recent years, our group has been extensively working on the preparation of multidentate heteroleptic N‐ligands and their related κ 3 {N,N,N}M 3+/4+ coordination compounds (or κ 3 {N,C,N}M 3+/4+ /κ 3 {N,N,C}M 3+/4+ organometallics) based on highly electrophilic metal ions (from group IV elements of the periodic table or from lanthanides, ) for applications in homogeneous catalysis. In a recent report, we have described the synthesis, characterization and catalytic application of a series of Zr IV /Hf IV alkyl/amido complexes stabilized by a tridentate N‐ligand containing a benzoimidazole fragment .…”

“…Due to the ability of its deprotonated form (imidazolate) to act as a bridging ligand with a wide variety of metal ions, it has already provided a number of polymetallic materials and original complex architectures . Starting from our interest in the synthesis and characterization of group IV pyridylamido complexes containing pyrazole, and imidazolate units, we report herein on the synthesis and coordination chemistry of a new imidazolate‐based polydentate N‐ligand. Our aim was to redistribute the spatial assembly of the donor atom set in L1 to create a new molecular architecture L2 to be employed as tridentate mono‐ or di‐anionic κ 3 {N,N,N} system for group IV metal ions coordination (Scheme ).…”

Effect of the Bridging Unit in Bis-( Benzoxazolyl ) Titanium , Zirconium and Vanadium Complexes on Catalytic Ethylene Polymerization Reactions

“…[23,24] Such complexes are attractive candidates as homogeneous catalysts in the polyolefin chemistry. [25][26][27][28][29][30][31] For the catalytic polymerization of ethylene, 1,2-bis- (benzimidazolyl) benzene copper(II) complexes were reported [32] as well as vanadium complexes with bis-(benzimidazole)amine tridentate ligands [N, N, N]. [33] 2,6-Bis-(2-benzimidazolyl)- Corresponding author: e-mail: helmut.alt@uni-bayreuth.de pyridine zirconiumdichloride/MAO was also reported to polymerize methylacrylate.…”