2,6-diisopropylphenyl imidazolium

Nolan reported the use of the 2,6-diisopropylphenyl imidazolium carbene precursor, which contains an unsaturated backbone, for the reaction of aryl chlorides with a variety of amines at 100 °C [165, 166]. This temperature is lower than those conventionally used for reactions of aryl chlorides, but is higher than those used with P(tBu)3 or the 2-biphenylyl di-tert-butylphosphines. Reaction yields were high when 2 mol % palladium was used. Reactions of primary amines occurred in good yield, even when unhindered aryl halides were used. The monoarylamine was obtained in 86 % yield, and only a 5 % yield of the diaryl-amine by-product was isolated. Notably, reactions of both aryl bromides and iodides proceeded at room temperature. 

It is reported recently that unactivated aryl chlorides can be used as a substrate in the Kumada coupling. For example, when 4-chlorotoluene (5.34) is reacted with phenyl-magnesium bromide (5.35) in the presence of Pd2(dba)3 and IPr-HCl [l,3-bis(2,6-diisopropylphenyl)imidazolium chloride] in dioxane-THF (tetrahydrofuran), the product 4-phenyltoluene (5.36) is isolated in 99% yield °. 

Benzyl alcohols. After transmetaUation arylboiDnic acids are converted into aryl-rhodium species that are nucleophilic toward various aldehydes. A very active catalyst (1) is that derived from Rh2(OAc)4, l,3-bis(2,6-diisopropylphenyl)imidazolium chloride and r-BuOK. ... 

Aryl hydrazides such as ArN(Boc)NH2 are available by this method (from ArBr and B0CNHNH2)." A phosphine-free catalyst system for for N-arylation specifies addition of l,3-bis(2,6-diisopropylphenyl)imidazolium chloride. Apparently, carbene derived from this additive becomes ligated to the Pd atoms. 

N-Heterocyclic carbenes (NHC) are examples of ligands that possess the desired attributes [19]. In 2004, Caddick and Cloke reported that a Pd/NHC-based catalyst cross-couples primary alkyl bromides with alkyl- and vinyl-9-BBN reagents (Eq. 6) [20]. A system composed of Pd(dba)2/IPr HCl/AgOTf (IPr HCl=l,3-bis(2,6-diisopropylphenyl)imidazolium chloride) in the presence of KOt-Bu provides the most efficient catalyst. The yields of the cross-coupling products are modest (Table 3). 

In a 250-mL Schlenk flask were added copperfi) chloride (1.0 g, 10.10 mmol), l,3-Z>w(2,6-diisopropylphenyl)-imidazolium chloride (4.29 g, 10.10 mmol), and sodium t-butoxide (0.97 g, 10.10 mmol). To this flask was added dry THF (100 mL) under Ar, and the mixture was magnetically stirred for 20 h at RT. The mixture was then filtered through a plug of Celite and the solvent evaporated in vacuo to give a white solid (4.59 g, 9.40 mmol, 93%). ... 

Silver ( Ag) (f=l/2, 1/2). Silver-containing layered networks [Ag(L)] (L = 4-pyridinesulfonate or p-toluenesulfonate) were treated with primary amines in different ratios. Solid-state ° Ag, and CP/ MAS NMR experiments were used to study the interactions between the primary amines and the parent materials. Ag chemical shift tensor parameters are extremely sensitive to changes in silver environments. Reaction of Ag20 with the A-heterocyclic carbene precursors 3,5-bis[3-(2,4,6-tri-methylphenyl)imidazolium-l-ylmethyl]-lH-pyrazole bishexafluorophosphate and 3,5-bis[3-(2,6-diisopropylphenyl)imidazolium-l-ylmethyl]-lH-pyrazole bishexafluorophosphate yielded silver(I) complexes 2 and 3, respectively The identity of those species could be elucidated by detailed NMR spectroscopic studies ( H, C, N, Ag and DOSY experiments). 

Spin-spin couplings between nitrogen and silver nuclei, /nAg, and Ag chemical shifts provided useful structural information on silver complexes obtained by Scheele et in the reaction of 3,5-bis[3-(2,4,6-trimethyl-phenyl)imidazolium-1 -ylmethyl] -1 Ff-pyrazole bishexafluorophosphate and 3,5-bis[3-(2,6-diisopropylphenyl)imidazolium-l-ylmethyl]-l.ff-pyrazole bishexafluorophosphate with Ag20. The latter complex is not stable in solution but exists in equilibrium with tetra- and hexanuclear complexes. 

To a mixture of l,3-bis 2,6-diisopropylphenyl)imidazolium chloride (15 g, 35.29 mmol, 1 equiv) and potassium tert-butoxide (4.20 g, 37.76 mmol, 1.07 equiv) was added dry THF (200 mL) and the mixture was stirred for 4 h at room temperature. Then the solvent was evaporated in vacuo. The residue was dissolved in 200 mL of hot toluene (70°C) and poured into a filter frit containing a thin layer of Celite in open air. The filtrate was evaporated in vacuo to dryness to give ylidene 7 as an off-white solid (11.65 g, 85%). 

To a mixture of l,3-bis(2,6-diisopropylphenyl)imidazolium chloride (2 g, 4.71 mmol, 1 equiv) and potassium hydroxide (0.53 g, 9.42 mmol, 2 equiv) was added toluene (100 mL) HPLC-grade. The mixture was stirred at 70°C for 12 h until the solution turned clear. The mixture with excess of KOH was filtered through the Celite in air, the solvent was evaporated in vacuum to dryness to give ylidene as a light yellowish NMR pure solid (1.74 g, 95%). Mp 217°C. 

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