Stereogenic Lock in 1-Naphthylethanamine Complexes for Catalyst and Auxiliary Design: Structural and Reactivity Analysis for Cycloiridated Pseudotetrahedral Complexes

Abstract

A series of optically-active pseudo-tetrahedral five-membered cyclometalated 1-naphthylethanamine iridium(III) complexes were prepared and characterized to analyze the efficacy of the stereogenic conformational lock in both solid and solution phases. The synthesis of the iridacycles was diastereoselective and the compounds were found to be conformationally rigid. When compared to its phenyl derivative, the structural lock prevented oxidation of the amine moiety within the five-membered organometallic ring during its synthesis. With up to three stereogenic centers in one of the naphthalene complexes, the stereochemistry of the metallacycle remained stable to both thermal and chemical changes. In terms of catalytic performance, the complexes displayed excellent activity for the asymmetric hydrogen transfer reaction, albeit modest enantioselectivities.

Ruthenacycles and Iridacycles as Transfer Hydrogenation Catalysts

“…Leung and coworkers examined the cyclometalation of ( S )- N -methyl- N -naphthy-1-yl-ethylamine using [Ir(Cp*)Cl 2 ] 2 and NaOAc in CH 2 Cl 2 at RT. Surprisingly, they found a mixture of the expected iridacycle 70 and a small amount of the analogous demethylated iridacycle 71 ( Scheme 41 ) [ 62 ]. They managed to isolate both compounds in pure form.…”

Design, synthesis and applications of chiral functionalized phosphapalladacycles

“…In the last several decades, a number of reports have been published about the cyclopalladation of amines, via the carbon-hydrogen bond activation. In most products, the nitrogen atom is coordinated to the palladium metal, producing the so-called azapalladacycle compounds [1][2][3][4][5][6] .…”

“…The list of the pincer complexes in our lab In the presence of sodium acetate as the base, a range of chiral pseudotetrahedral five-membered cyclometalated 1-naphthylethanamine Iridium(III) complexes 61a-d were synthesized through the treatment of the specified amine with the iridium source [IrCp * Cl2]2. The authors also examined the catalytic properties of them for asymmetric hydrogen transfer reaction(Figure 7) 6. …”

Synthetic protocols for designing chiral P,N-chelate complexes

“…A few examples of five-membered chiral metallacycles reported by Leung and his co-workers can be seen in Figure 22.). [52][53][54][55] Figure 22. Examples of metallacycles reported by Leung and co-workers.…”

“…proved to be effective in catalyzing asymmetric transfer hydrogenation with good selectivity (69% ee). 55 1.2.5. Chiral P,N bidentate ligands…”