Rhodium(I) Complexes with Hemilabile N-Heterocyclic Carbenes: Efficient Alkyne Hydrosilylation Catalysts

Abstract

A series of alkylammonium-imidazolium chloride salts [RImH(CH 2) n NMe 2 ]Cl•HCl (R = Me, t-Bu, Mes, n = 2, 3) have been prepared by alkylation of 1-substituted imidazole compounds with the corresponding chloro-alkyl-dimethylamine hydrochloride. These salts are precursors for the synthesis of a library of rhodium (I) complexes containing amino-alkyl functionalized N-heterocyclic carbene (NHC) ligands with hemilabile character by varying the substituent on the heterocyclic ring and the length of the linker with the dimethylamino moiety. The monodeprotonation of alkylammoniumimidazolium salts with NaH in the presence of [{Rh(µ-Cl)(cod)} 2 ] gave the amino-imidazolium salts [RImH(CH 2) n NMe 2 ][RhCl 2 (cod)]. Further deprotonation with NaH under non anhydrous conditions gave the neutral complexes [RhCl(cod)(RIm(CH 2) n NMe 2)] in good yields. The abstraction of the chloro ligand by silver salts rendered the cationic complexes [Rh(cod)(κ 2 C,N-RIm(CH 2) 3 NMe 2)][BF 4 ] (R = Me, Mes) by coordination of the NMe 2 fragment of the sidearm of the functionalized NHC ligands. The catalytic activity of the rhodium complexes in the hydrosilylation of terminal alkynes using HSiMe 2 Ph has been investigated with Ph-C≡CH, t-Bu-C≡CH, n-Bu-C≡CH, and Et 3 Si-C≡CH as substrates. Higher activities were achieved using neutral complexes having small substituents at the heterocyclic ring (R = Me). Excellent selectivities in the β-(Z)-vinylsilane isomer were found in the hydrosilylation of 1hexyne and predominantly the β-(E) and α-bis(silyl)alkene isomers were obtained in the hydrosilylation of triethylsilylacetylene.

Decomposition of Formic Acid Catalyzed by a Phosphine‐Free Ruthenium Complex in a Task‐Specific Ionic Liquid

“…[39] First, IL 1·HCl was prepared from the reaction of 1-methylimidazole (19.1 g; 232.4 mmol) and 2-chloro-N,N-diethylethylamine hydrochloride (40.0 g; 232.4 mmol) in acetonitrile (200 mL) under reflux conditions. After 4-5 days of reaction, a white solid was separated by filtration and washed with a 1:1 v/v mixture of ethyl ether and acetonitrile (3 80 mL).…”

N‐Heterocyclic Carbene Rhodium Complexes and Their Reactions with H2 and with CO

“…For 6, three 13 C{ 1 H} doublets are seen at δ = 186.0 (J Rh-C = 54 Hz), 184.2 (J Rh-C = 72 Hz) and 182.1 ppm (J Rh-C = 45 Hz) for the one carbene-carbon and the two inequivalent carbonyls; signal assignment is not obvious, because J Rh-C values for the carbene carbon atom are typically in the 35-65 Hz range (e.g.ref. [2,[4][5][6][7]9,13,15] [5,30] For 7, the 13 C{ 1 H} spectrum shows only one doublet at δ = 186.0 ppm (J Rh-C = 54 Hz) for the two carbonyl ligands, and one for the carbene-carbon at δ = 179.2 ppm (J Rh-C = 45 Hz), although two ν CO IR bands at 2070 and 1990 cm -1 are consistent with inequivalent carbonyls, at least in the solid-state structure. This phenomenon has been found in other carbenecarbonyl-Rh complexes.…”

[NiX2(NHC)2] Complexes in the Hydrosilylation of Internal Alkynes

“…The selectivity towards any of these products depends upon several factors, such as the substituents on the alkyne and the silane, the catalyst, and the reaction conditions. The hydrosilylation of alkynes may be catalyzed by a number of different metal complexes, including rhodium, [5][6][7] iridium, [6,8] ruthenium [9,10] and platinum. [11][12][13] Complexes of the less precious metals nickel, [14] cobalt, [15] and titanium [16] have also [a] Leiden Institute of Chemistry, Leiden University, P. O.…”