Unusual NHC–Iridium(I) Complexes and Their Use in the Intramolecular Hydroamination of Unactivated Aminoalkenes

Abstract

N-heterocyclic carbene (NHC) ligands with naphthyl side chains were employed for the synthesis of unsaturated, yet isolable [(NHC)Ir(cod)](+) (cod=1,5-cyclooctadiene) complexes. These compounds are stabilised by an interaction of the aromatic wingtip that leads to a sideways tilt of the NHC-Ir bond. Detailed studies show how the tilting of such N-heterocyclic carbenes affects the electronic shielding properties of the carbene carbon atom and how this is reflected by significant upfield shifts in the (13) C NMR signals. When employed in the intramolecular hydroamination, these [(NHC)Ir(cod)](+) species show very high catalytic activity under mild reaction conditions. An enantiopure version of the catalyst system produces pyrrolidines with excellent enantioselectivities.

Synthesis and chiroptical properties of organometallic complexes of helicenic N‐heterocyclic carbenes

“…Complex 1a displays a typical C 3 –Ir bond length of 2.011 Å. These metric data are similar to corresponding values for other reported carbenic cycloiridiated complexes . The [4]helicenic part shows a helicity of 27.36° in the solid state, but it is not configurationally stable in solution.…”

Phosphine‐NHC Manganese Hydrogenation Catalyst Exhibiting a Non‐Classical Metal‐Ligand Cooperative H2 Activation Mode

“…Very significantly,the relatively constrained coordination of the NHC-phosphinomethanide ligand in 6a results in astrong distortion of yaw angle q [20] for the NHC ligation (6a: 29.58 8 vs. 2-4, 6b:6 .2-7.28 8). Considering that the shielding of the 13 CNMR chemical shift of carbenic carbon atoms in metal complexes increases as the value of q, [21] the signal recorded at d C 178.0 ppm for 6 in solution (see above) appears to be totally consistent with the most stable structure 6a.I n addition, computed 13 CNMR chemical shift for the carbenic atom in complex 6a (d C 181.5 ppm) matches well with the experimental value (d C 178.0 ppm), av alue significantly different from that computed for complex fac-6b (d C 215.1 ppm) (see Table S5 in the Supporting Information for details), thus the deprotonation product of 2 was be assigned to complex 6a.…”

“…Aliphatic 2decanone was hydrogenated in the efficient manner albeit at 100 8 8C( entry 19). Theh eterocyclic substrates bearing potentially coordinating groups can also be reduced (entries [20][21][22] but with lower efficiency.…”

Phosphine‐NHC Manganese Hydrogenation Catalyst Exhibiting a Non‐Classical Metal‐Ligand Cooperative H2 Activation Mode

“…Am aximum TONo f6 200 was achieved with 0.01 mol %i nt-AmOH, showing that this catalyst is competitive with the best Mnbased systems for this reaction reported to date [23b-c] No reaction took place in the presence of the sole hydride complex 3,w hile catalytic activity could be restored in the presence of base,s howing its critical role in the catalytic cycle. Theh eterocyclic substrates bearing potentially coordinating groups can also be reduced (entries [20][21][22] but with lower efficiency. [10c] Interestingly,t he reaction is tolerant to aryl groups substituted with halogen atoms (F,Cl, Br,I)and CF 3 moiety (entries 9-14).…”