Synthesis of Ti Complexes Supported by an ortho-Terphenoxide Ligand and Their Applications in Alkyne Hydroamination Catalysis

Abstract

The synthesis of a series of Ti complexes of an aryllinked bis-phenoxide ligand, 3,3″-di-tert-butyl-5,5″-dimethyl-[1,1′:2′,1″-terphenyl]-2,2″-bis(olate), (TPO)H 2 , is reported. This ortho-linked terphenyl ligand builds on previously reported metaand para-linked terphenyl-based ligands, completing the isomeric series of terphenoxide ligands. The 4-coordinate (TPO)Ti-(NMe 2 ) 2 is an active catalyst for alkyne hydroamination with a variety of arylamines, revealing good regioselectivity in reactions with unsymmetric alkynes. Terminal alkynes such as phenylacetylene undergo additional insertion reactions with the key azatitanacyclobutene intermediates, providing further evidence that Ti aryloxide complexes are susceptible to this further reactivity.

Yttrium‐Catalyzed Intermolecular Anti‐Markovnikov Hydroamination and Sequential Intermolecular Hydroamination/Endocyclization of Vinylsilanes

“…The ortho ‐terphenoxide ligands 1 a – e (Scheme 2) with silyl substituents of varying steric bulk were synthesized via a four‐step procedure in 34–62% overall yield (see SI for details). Similar to the related t ‐butyl‐substituted ortho‐ terphenoxide ligand, [16] hindered rotation leads to atropisomerism as indicated by broadening of the signals in the 1 H and 13 C NMR spectra at room temperature.…”

“…In all cases, the reaction scope was limited to a narrow range of either primary or secondary amines, respectively, whereas a catalyst system compatible with a wider range of substrates has not been developed. Herein, we report a new class of rare‐earth metal catalysts bearing silyl‐substituted ortho‐ terphenoxide ligands [16] for the anti‐Markovnikov hydroamination of vinylsilanes with both primary and secondary amines [17]…”

Silyl‐Substituted ortho‐Terphenoxide Group 3–5 Complexes: Synthesis, Structure and Applications in Catalysis

“…Figure 1. Titanium and yttrium ortho-terphenoxide complexes [14,15] Scheme 1. Formation of yttrium complexes 2 a, 2 b and 2 d. angle being more acute.…”

“…The analogous bis-ligated ortho-terphenoxide complex II (Figure 1), reported by Tonks and coworkers recently, exhibits similar bond lengths and angles (Table 2). [14] Tantalum and Niobium Complexes II [14] TiÀ O1…”

“…[13a] However, only recently, while our research was ongoing, Tonks and coworkers reported the first transition metal complex in the form of the tert-butyl substituted ortho-terphenoxide titanium complex I for the hydroamination of alkynes, as well as the bisligand complex II (Figure 1). [14] Herein, we explore the complexation behavior of a series of silyl-substituted ortho-terphenoxide ligands with various yttrium, titanium, niobium and tantalum amide precursors and their applications in catalysis. In a separate study, related orthoterphenoxide yttrium aryl complexes IIIa-d have been investigated with respect to their catalytic activity in the intermolecular hydroamination of vinylsilanes.…”