The Progression of Synthetic Strategies to Assemble Titanium Complexes Bearing the Terminal Imide Group

Abstract

The synthesis of terminal titanium imides is described in this account. The incorporation of this functional group has evolved from more simplistic approaches to more complex or unusual methods. Past and current synthetic strategies to incorporate the terminal imide functionality are explained with particular emphasis on low-coordinate titanium environments bearing this ubiquitous but vital type of motif. More recently, the imide functionality has demonstrated to be a key intermediate for modeling important industrial processes such as the hydrodenitrogenation of crude oil.

Understanding the role of an easy-to-prepare aldimine–alkyne carboamination catalyst, [Ti(NMe2)3(NHMe2)][B(C6F5)4]

“…It was determined that the absence of aniline, which was presumed to be the source of imido, had no effect in the catalytic formation of the a,b-unsaturated imine [9]. This was puzzling since it is generally accepted that a terminal imido ligand is being transferred in the catalytic cycle (Scheme 1, vide supra) [4,13,14]. The fact that a catalytic carboamination process could occur in the absence of aniline suggested that the imide group is derived from the aldimine as opposed to the aniline.…”

“…The fact that a catalytic carboamination process could occur in the absence of aniline suggested that the imide group is derived from the aldimine as opposed to the aniline. Therefore, we investigated another mechanism to formation of the imide which did not involve the more common route, such as transimination (imide formation derived from aniline deprotonation) [4].…”

“…In this contribution we report some investigations toward understanding the role of an easy-to-prepare carboamination pre-catalyst, [Ti(NMe 2 ) 3 (NHMe 2 )][B(C 6 F 5 ) 4 ] [9], by examining the source and role of the imide, variance of the dimethylamide ancillary ligand, and anion or activator being used in the catalytic process. We reported previously that mixing of the commercially available reagents Ti(NMe 2 ) 4 with [NHMe 2 Ph][B(C 6 F 5 ) 4 ] gives rise to the salt, [Ti(NMe 2 ) 3 (NHMe 2 )][B(C 6 F 5 ) 4 ], which has been demonstrated to be a very reactive pre-catalyst for the carboamination of alkynes with aldimines [9]. It was found that neither the anilinium proton source nor the neutral titanium complex, alone, were active catalysts for this transformation, which was surprising given that Ti (NMe 2 ) 4 has been shown by Odom and Schafer to be a highly active hydroamination catalyst [10e12].…”

“…In an attempt to circumvent some of these limitations, and given our interest in the reactivity and the catalytic ability of 3d earlytransition metal complexes having metal-ligand multiple bonds [4,5], we explored the role of various titanium imidos [6e9] in this interesting reaction given the fact that NeC and CeC bonds are catalytically formed and broken. In this contribution we report some investigations toward understanding the role of an easy-to-prepare carboamination pre-catalyst, [Ti(NMe 2 ) 3 (NHMe 2 )][B(C 6 F 5 ) 4 ] [9], by examining the source and role of the imide, variance of the dimethylamide ancillary ligand, and anion or activator being used in the catalytic process.…”

Reactivity of a Dititanium Bis(pentalene) Complex toward Heteroallenes and Main-Group Element–Element Bonds

“…Metal-driven reductive transformations of organic azides to imido complexes are well known for titanium, 65,[71][72][73] and other early transition metals. [74][75][76][77] However with Ti mononuclear terminal-imido complexes are typically formed.…”