Synthesis, Structures, and Solution Dynamics of Titanium and Zirconium Complexes Carrying a Bis(indolyl) and Two Diethylamido Ligands

Indolyl is the anionic species obtained from the deprotonation of the N-H group of indole. Group 4 transition-metal complexes that carry indolyl-based polydentate ligands represent promising homogeneous catalysts for, e.g., olefin polymerization, hydroamination, and nitrogen-fixation reactions due to the weak π-donation and electron-withdrawing properties, as well as the low basicity of indolyl. In this study, we systematically investigated the synthesis and structures of titanium and zirconium complexes that carry deprotonated 2,2'-bis(indolyl)methane ligands (henceforth: bis(indolyl) ligands) and two diethylamido ligands. We found that the coordination geometry of the indolyl nitrogen atom in such bis(indolyl) ligands is affected by the steric impact of the substituents attached to the central aromatic ring. Moreover, we examined the dynamics of such bis(indolyl) ligands in solution for the corresponding zirconium complexes, and the mechanism was discussed in conjunction with DFT calculations. The results of this study suggest that bis(indolyl) ligands may also serve as coordinatively flexible ancillary ligands, and indicate the feasibility of an expansion from bis(indolyl) to bis(indolyl)-donor ligands.

Group 4 metal complexes with new chiral pincer NHC-ligands: synthesis, structure and catalytic activity

Chiral group 4 NHC–metal complexes have been prepared and shown to be active catalysts for the polymerization of rac-lactide.

Group IV organometallic compounds based on dianionic "pincer" ligands: synthesis, characterization, and catalytic activity in intramolecular hydroamination reactions

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.

Asymmetric hydroamination catalyzed by in situ generated chiral amidate and ureate complexes of zirconium — Probing the role of the tether in ligand design

Simple chiral proligands have been synthesized from inexpensive chiral starting materials. These amidate and ureate ligands support zirconium complexes that successfully catalyze intramolecular hydroamination with up to 26% ee. Several elements necessary for successful ligand design are highlighted and discussed. In particular, the strict control of metal geometry through multidentate tethered ligands is determined to be an essential aspect of future ligand development.

rac-(OC-6-33)-bis-[2-(N-Benzyl-methyl-imino-meth-yl-κN)-1H-imidazol-1-ido-κN]bis(ethyl-amido)-titanium(IV)

The title compound, [[Ti(C₂H₁₀N)₂(C₁₁H₁₀N₃)₂] or Ti(C₁₁H₁₀N₃)₂(NEt₂)₂], was prepared by direct reaction of 2-(N-phenyl­methyl­imino­meth­yl)-1H-imidazole and [Ti(NEt₂)₄]. The Ti^IV atom is in a pseudo-octa­hedral coordination environ­ment with the imidazolido-group N-atoms occupying apical positions and amido- and imino-N-atoms cis-located in the equatorial plane. The presence of two bidentate chelating ligands determines the chirality of the Ti^IV atom. The crystallographically independent unit, except for its phenyl rings, adopts nearly pseudo-C₂ symmetry (rotation around a twofold axis passing through the Ti atom and the centre of the imino-N⋯imino-N segment). The Ti—N_amido, Ti—N_imidazolido, and Ti—N_imino bond lengths essentially differ, increasing by approximately 0.2 Å in the series. All ligating N atoms are in a nearly planar environment, which is indicative of additional pπ–dπ donations towards the metal atom. The two diaza­metallacyclic units are planar within 0.03 and 0.05 Å.