Gold(I) N-heterocyclic carbene based initiators for bulk ring-opening polymerization of l-lactide

Ray, Lipika; Katiyar, Vimal; Barman, Samir; Raihan, Mustafa J.; Nanavati, Hemant; Shaikh, Mobin M.; Ghosh, Prasenjit

doi:10.1016/j.jorganchem.2007.06.033

Cited by 86 publications

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“…[22] Herein, we describe the synthesis, structures and catalytic studies of copper complexes of a chiral NHC precursor based on an imidazol-phenoxyimine motif (Scheme 1) that we envisaged could have potential application to enantioselective catalysis. Palladium, rhodium and dimetallic iron/ silver complexes of 1a have been reported previously [23] showing tridentate NHC (C), imine (N), phenoxide (O) (CNO), NHC only (RhC), or bridging (AgC, FeNO) coordination, respectively.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Copper(I) Complexes of N‐Heterocyclic Carbene–Phenoxyimine/amine Ligands: Structures of Mononuclear Copper(II), Mixed‐Valence Copper(I)/(II), and Copper(II) Cluster Complexes

et al. 2009

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Copper(I) bromide complexes (2a and 2b) of NHC–phenolimine ligand precursors {3‐[(1R,2R)‐2‐{[1‐(3,5‐di‐tert‐butyl‐2‐hydroxyphenyl)meth‐(E)‐ylidene]amino}cyclohexyl]‐1‐isopropyl‐4‐phenyl‐3H‐imidazol‐1‐ium bromide (1a) and 3‐[(1R,2R)‐2‐{[1‐(2‐hydroxyphenyl)meth‐(E)‐ylidene]amino}cyclohexyl]‐1‐isopropyl‐4‐phenyl‐3H‐imidazol‐1‐ium bromide (1b), respectively} have been prepared. Complexes 2a and 2b exhibit copper coordination only through the carbene carbon atom (C) and do not spontaneously eliminate HBr to give additional phenoxyimine (NO) bonds, which is attributed to intramolecular hydrogen bonding. Crystallisation of 2a and 2b gives 2a′ and 2b′, respectively, that contain (C) copper(I) bromide and (NO)2 copper(II) coordination. Complex 2b′ also exhibits intermolecular CuIBr interactions giving a Cu2Br2 bridge that links two molecules of 2b′ resulting in an ellipse motif. Reduction of the ligand precursor imine group of 1a allows synthesis of silver(I) and copper(I) NHC–phenolamine complexes 6 and 7, respectively, that also retain the phenol hydrogen atom. Attempts to selectively prepare 2a′ gave a copper(II) complex 9 that exhibits an (NO)2CuII structure with pendant imidazolium salt groups. Reaction between the silver(I) bromide derivative of 1a and CuCl2·2H2O gives a complex derived from a Cu6(O)(OH)4Cl3 core and two (NO) and one (CNO) ligands, respectively. The use of 2a and 7 as precatalysts for 1,4‐conjugate addition to enones and aziridination of alkenes was studied, showing that, whilst both catalysts are active, enantioselectivities are low, which is attributed to the lack of Cu‐(NO) coordination. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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Section: Introductionmentioning

confidence: 99%

Synthesis of Copper(I) Complexes of N‐Heterocyclic Carbene–Phenoxyimine/amine Ligands: Structures of Mononuclear Copper(II), Mixed‐Valence Copper(I)/(II), and Copper(II) Cluster Complexes

et al. 2009

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“…Our interest lies in developing the chemistry of N/O-functionalized N-heterocyclic carbenes [21][22][23][24] particularly with regard to their utility in biomedical applications [25,26] and in chemical catalysis [27][28][29][30][31][32], with special focus on the palladium mediated C-C cross-coupling reactions namely the Suzuki-Miyaura coupling [33,34], the Sonogashira and the Hiyama couplings [35,36]. In particular, we aim at designing efficient, robust and stable precatalysts of N/O-functionalized N-heterocyclic carbenes that would carry out the cross-coupling reactions under more amenable conditions.…”

Section: Introductionmentioning

confidence: 99%

Copper-free and amine-free Sonogashira coupling in air in a mixed aqueous medium by palladium complexes of N/O-functionalized N-heterocyclic carbenes

Samantaray

Shaikh

Ghosh

2009

Journal of Organometallic Chemistry

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“…Apart from the methyl group [ 28 ] and keto group [ 14 ] discussed already, Ray et al . Apart from the methyl group [ 28 ] and keto group [ 14 ] discussed already, Ray et al .…”

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“…It seems that the racemic mixture of N-hydroxycyclohexyl imidazole is used in further reactions, normally even without mention of chirality [14,15]. Double functionalisation is facile, as the two wingtip groups need to be introduced stepwise.…”

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“…The interest in functionalised carbene complexes of gold(I) derives not only from the longer known biological applications [21][22][23], but also from a recent interest in their performance in catalysis [14,15,24,25]. Ray et al tested a series of nonfunctionalised, hydroxy functionalised and hydroxy/keto difunctionalised NHC ligands in the ROP of L-lactide [14].…”

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N‐Heterocyclic Carbenes with Anionic Functional Groups

Kühl

2010

Functionalised N‐Heterocyclic Carbene Complexes

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We have already seen that many functionalised NHC ligands are modelled on previously known functionalised phosphanes. In the case of an oxygen -containing functional group where the oxygen atom can carry a (formal) negative charge, we can expect functionalised NHC ligands that resemble phosphinophenols [ 1 , 2 ], phosphinoalcohols [ 3 -5 ] or phosphino carboxylic acids [ 6 ]. All these functionalised phosphane groups were employed as ligands in catalytic reactions.The rationale behind the concept of NHC ligands carrying anionic oxygen functional groups goes beyond the application in catalysis. NHC ligands do not bond strongly to the early transition metals [ 7 ] or alkaline earth metals [ 8 ]. However, both these groups of metals bind strongly to alkoxides or aryloxides. It is therefore reasonable to design functionalised NHC ligands with a view to an oxygen (nitrogen) based anchor group in addition to the somewhat loosely binding carbene unit. This results in the formation of a hemilabile chelate ligand [ 9 ].Conversely, NHC bind strongly to the late transition metals (group 9 and group 10), metals that have only a low affi nity to oxygen. Here, the oxygen -containing functional group serves as the hemilabile ligand [ 10 ]. We will therefore see a great versatility in the anionic tether and in the range of (transition) metal employed.Thiel and coworkers reacted imidazole with epoxycyclohexane to form the racemic hydroxycyclohexyl imidazole. Attempts to separate the enantiomers by kinetic resolution with lipase B of Candida antarctica and isopropenyl acetate as acylating agent [ 11 , 12 ] failed, but gave the racemic ester in high yields (see Figure 4.1 ). Alkylation was then Functionalised N-Heterocyclic Carbene ComplexesOlaf Kühl

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Gold(I) N-heterocyclic carbene based initiators for bulk ring-opening polymerization of l-lactide

Cited by 86 publications

References 100 publications

Synthesis of Copper(I) Complexes of N‐Heterocyclic Carbene–Phenoxyimine/amine Ligands: Structures of Mononuclear Copper(II), Mixed‐Valence Copper(I)/(II), and Copper(II) Cluster Complexes

Synthesis of Copper(I) Complexes of N‐Heterocyclic Carbene–Phenoxyimine/amine Ligands: Structures of Mononuclear Copper(II), Mixed‐Valence Copper(I)/(II), and Copper(II) Cluster Complexes

Copper-free and amine-free Sonogashira coupling in air in a mixed aqueous medium by palladium complexes of N/O-functionalized N-heterocyclic carbenes

N‐Heterocyclic Carbenes with Anionic Functional Groups

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