Iridium(III) Cp* Complexes for the Efficient Hydroamination of Internal Alkynes

Abstract

A series of iridium(III) and rhodium(III) 1,2,3,4,5-pentamethylcyclopentadienyl (Cp*) complexes of the type [M(Cp*)(LL)Cl]BPh 4 were synthesized, where LL is a chelating diimine or mixed pyrazolyl-phosphine or pyrazolyl-N-heterocyclic carbene donor ligand. The majority of these complexes were characterized by X-ray crystallography, allowing for a detailed comparison of their structural properties. These complexes were shown to yield active hydroamination catalysts upon in situ abstraction of the chloride coligand using AgBF 4 . The activity of these catalysts for the intramolecular hydroamination of alkyne-amines to yield indolyl and pyrolyl heterocycles was investigated. It was found that chelating ligand groups containing a strongly coordinating Nheterocyclic carbene donor led to the most effective catalysis and that an increase in the steric bulk of the ligand was detrimental to the catalyst efficiency.

Cationic Rh and Ir complexes containing bidentate imidazolylidene–1,2,3-triazole donor ligands: synthesis and preliminary catalytic studies

“…Rh(I)/Rh(III) and Ir(I)/Ir(III) complexes have been demonstrated by us and others to be efficient catalysts for this transformation. 12,20,32,[40][41][42][43][44][45][46][47][48] We have found that small variations in donor ability of the ligands can lead to significant variations in the catalytic efficiency of the resulting metal complexes. 32,41,49 We tested a number of the Rh(I), Rh(III) and Ir(III) complexes containing the NHC-1,2,3-triazolyl donor ligands described here as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to form 2-methyl-1-pyrroline (Table 3).…”

“…The M-C* (Table 2) are within the range reported in the literature for analogous Rh(III) and Ir(III) complexes with Cp* co-ligands. 12,32,[35][36][37][38][39] The M-C2 bond in complexes 4b, 4d and 5b with the small methyl substituent on the imidazolyl ring is significantly shorter than the equivalent bond in the analogous complexes with the mesityl substituent 4a, 4c and 5a ( Table 2). The longer M-C2 bond in complexes with a mesityl substituent is likely to be due to steric repulsion between the Cp* and the bulky mesityl group.…”

“…We recently demonstrated that similar Ir(III) complexes with bidentate N-N or N( pyrazolyl)-NHC donor ligands in the presence of AgBF 4 could efficiently promote the intramolecular hydroamination of aminoalkynes. 12 This improvement in catalytic reactivity in the presence of Ag + was attributed to the generation of a vacant coordination site on the Ir(III) via Cl − abstraction with Ag + ion. 12 In that paper, the catalytic reactivity was found to be better using an N( pyrazolyl)-NHC donor ligand than when N-N donor ligands were used.…”

Catalytic sugar-assisted transfer hydrogenation with Ru(II), Rh(III) and Ir(III) halfsandwich complexes

“…Such compounds with chelating nitrogen ligands are effectively used in catalysis, e. g. in water oxidation [23], intramolecular hydroamination of alkynes [24], Diels-Alder reactions [25], asymmetric Michael addition reactions [26], asymmetric hydrogenation [27,28], and transfer hydrogenation [29][30][31], reactions of ketones and imines.…”

“…The formerly unknown precursor complexes with methyl 2,3-diamino-4,6-O-benzylidene-2,3-dideoxy-␣-D-hexopyranosides (compounds 1-4, Chart 1), methyl 2-amino-4,6-OChart 1. Diaminomonosaccharides 1-4, methyl 2-amino-4,6-O-benzylidene-2,3-dideoxy-3-tosylamido-␣-D-glucopyranoside (5) and corresponding diamino derivatives (S)-2,2 -diamino-1,1 -binaphthalene (6) and (R,R)-1,2-diphenylethylenediamine (7) and their halfsandwich complexes of iridium(III), -rhodium(III) and ruthenium(II) (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) for transfer hydrogenation ([T-4-R] and [T-4-S] denote the absolute configuration of the metal center in a pseudo-tetrahedral environment following the CIP rules).…”