A Highly Active Bifunctional Iridium Complex with an Alcohol/Alkoxide‐Tethered N‐Heterocyclic Carbene for Alkylation of Amines with Alcohols

Abstract

A series of new iridium(III) complexes containing bidentate N‐heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHCOR, R=H, Me) were prepared. The complexes catalyzed the alkylation of anilines with alcohols as latent electrophiles. In particular, biscationic IrIII complexes of the type [Cp*(NHC‐OH)Ir(MeCN)]2+2[BF4−] afforded higher‐order amine products with very high efficiency; up to >99 % yield using a 1:1 ratio of reactants and 1–2.5 mol % of Ir, in short reaction times (2–16 h) and under base‐free conditions. Quantitative yields were also obtained at 50 °C, although longer reaction times (48–60 h) were needed. A large variety of aromatic amines have been alkylated with primary and secondary alcohols. The reactivity of structurally related iridium(III) complexes was also compared to obtain insights into the mechanism and into the structure of possible catalytic intermediates. The IrIII complexes were stable towards oxygen and moisture, and were characterized by NMR, HRMS, single‐crystal X‐ray diffraction, and elemental analyses.

Lithium Complexes with Bridging and Terminal NHC Ligands: The Decisive Influence of an Anionic Tether

“…With the anionic donors, a hybrid ligand is realised that features very different bonding from the two donors, with the “soft” NHC donor featuring a large component of covalency in bonding to metals, whereas the anionic donors, particular with “hard” O atoms, feature a substantial ionic component to the bonding. This can lead to interesting hemilability effects of the NHC in early transition metal and lanthanide complexes, or the potential for lability/reactivity of the O donor in late transition metal complexes . With Cp, Ind and Flu donors, the situation is more nuanced with strong donation expected from both donors to late transition metals.…”

Chelating N-heterocyclic carbene–carboranes offer flexible ligand coordination to IrIII, RhIII and RuII: effect of ligand cyclometallation in catalytic transfer hydrogenation

“…The solid-state structures ( Figure 3) show piano stool geometry around the metal centres, with each metal bearing two chloride atoms, an NHC and either Cp* (2b) or p-cymene (6b). The M-Ccarbene bond lengths of 1.92(3) Å (2b) and 2.064(7) Å (6b) are relatively short when compared to other IrCp*(NHC)Cl2 and Ru(pcymene)(NHC)Cl2 complexes in the literature, 37,[41][42][43][44][45] which may be an effect of the carborane substituent causing the carbenic carbon to be more nucleophilic than other NHCs. Similarly to complex 3a, the Ir complex 2b underwent cyclometallation upon reaction with Ag2O in MeCN.…”

Reusable Supported Ruthenium Catalysts for the Alkylation of Amines by using Primary Alcohols

“…Other cyclic amines such as pyrrolidine, morpholine, azepane, tetralin, and 1-methylpiperazine were benzylated to respective tertiary amines 8-12 in good to excellent yields ( Table 2, entries [8][9][10][11][12]. Importantly, alkylated products 13 and 14 were obtained in 94 ( …”

“…Organic halides were traditionally obtained from nonhazardous alcohols and were used as electrophiles for further alkylation of primary and secondary amines. Subsequently, a number of Ru [7] and Ir [8] catalysts have been reported, and they were proven to be effective for the al-kylation of both amines and carbonyl compounds under homogenous reaction conditions. [4] Under this methodology, the alcohols are activated to an active carbonyl compound by dehydrogenation.…”