Synthesis of normal and mesoionic N-heterocyclic carbene Pd(ii) complexes in near quantitative yields from the corresponding NHC precursor salts under base free and ambient conditions is reported. A plausible mechanism involving charge-assisted hydrogen bonded intermediates is proposed. © 2014 the Partner Organisations.

Sethuraman Sankararaman

Department Of Chemistry

Bemineni Sureshbabu

Venkatachalam Ramkumar

Hydrogen bonds

Palladium compounds

Ambient conditions

N-heterocyclic carbenes

PALLADATION

PD COMPLEX

Plausible mechanisms

PRECURSOR SALTS

Quantitative yields

SITU GENERATION

Organic compounds

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Dalton Transactions

Synthesis of mononuclear and PEPPSI type palladium diiodo complexes of 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene without the use of strong bases and silver salts and at ambient conditions using Pd(OAc)2 is reported. Using stoichiometric amounts of bidendate ligands such as pyrazine, 4,4′-bipyridine and DABCO bridged binuclear palladium diiodo complexes were obtained in excellent yields. By simple variation of reagents and their stoichiometry, one can control the reactions towards the selective formation of mononuclear [(Tz)2Pd(I)2] complexes, iodo bridged binuclear complexes [(Tz)Pd(I)(μ-I)2Pd(I)(Tz)], mononuclear PEPPSI type complexes [(Tz)Pd(I)2(Py)], bridged binuclear PEPPSI type complexes [(Tz)Pd(I)2-(bridge biPy)-(I)2Pd(Tz)]. The catalytic activities of these three structurally different types of complexes are compared for Suzuki-Miyaura coupling reaction. © 2015 Elsevier B.V.

Journal of Organometallic Chemistry

A mild and efficient method for the synthesis of structurally diverse 1,2,3-triazolylidene palladium(II) diiodo complexes. Comparison of catalytic activities for Suzuki-Miyaura coupling

(-) Menthol was converted to 1-menthyl-3-methyl-4-phenyltriazolium iodide and 1-neomethyl-3-methyl-4-phenyltriazolium iodide in four steps. These triazolium salts that are enantio pure but diastereo isomers, served as precursors for the synthesis of the corresponding enantio pure bis(1,2,3-triazol-5-ylidene)PdI2 complexes with menthyl and neomenthyl wing tip groups. The palladium complexes were synthesized in high yields using a recently developed mild method under base free and silver free conditions at ambient temperature. These triazolium salts also served as precursors for the synthesis of the corresponding enantio pure PEPPSI type (1,2,3-triazol-5-ylidene) (pyridine)PdI2 complexes. All the complexes were thoroughly characterized by spectroscopic and single crystal XRD data. The relative catalytic activities of these complexes were compared for Suzuki-Miyaura C-C coupling. © 2015 Elsevier B.V. All rights reserved.

Synthesis and structures of (-) menthyl and (+) neomenthyl substituted enantio pure bis(1,2,3-triazol-5-ylidene)PdI2 complexes and PEPPSI type (1,2,3-triazol-5-ylidene) (pyridine)PdI2complexes. Comparison of catalytic activities for C-C coupling

C2-Symmetric normal and mesoionic bis-N-heterocyclic carbenes (NHCs) derived from 1,1′-((1,1′-biphenyl)-2,2′- diylbis(methylene))bis(3-methyl-4-phenyl-1H-1,2,3-triazol-3-ium) diiodide (5) and 3,3′-((1,1′-biphenyl)-2,2′-diylbis(methylene))bis(1- phenyl-1H-imidazol-3-ium) dibromide (6) were used as ligands for the synthesis of the corresponding Pd(II) complexes. 2,2′-Disubstituted 1,1′-biphenyl moiety was used as the C2-symmetric backbone for the synthesis. 2,2′-Bis(bromomethyl)-1,1′-biphenyl was used as a common precursor for the synthesis of both 5 and 6. These salts were treated with Ag2O for the in-situ generation of the corresponding NHC-Ag(I) complexes which were transmetallated to the corresponding Pd(II) chloro and acetate complexes. The bis(1,2,3-triazol-5-ylidene) derivative gave structurally well-defined mono nuclear chelate complexes that were characterized by spectroscopic and single crystal XRD data. The bis(imidazol-3-ylidene) derivative gave polymeric complex and not the expected mono nuclear chelate complex. These complexes were compared for their reactivity in Suzuki-Miyaura coupling reaction. © 2014 Elsevier B.V. All rights reserved.

C2-Symmetric normal and mesoionic bis-N-heterocyclic carbenes with biphenyl backbone. A comparison of bis(1,2,3-triazol-5-ylidene) and bis(imidazol-2-ylidene) ligands

A palladium complex (3) of abnormal N-heterocyclic carbene (NHC) namely, 4-(hydroxymethyl)-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene was prepared via silver carbene transmetalation method and characterized by spectroscopic and single crystal XRD data. Single crystal analysis revealed the structure of the complex 3 to be a cis isomer. The synthesis of palladium complex 6 via silver carbene transmetalation method led to a mixture of cis-trans isomers. In this case trans isomer was formed as major product. We have reported earlier the synthesis and structural characterization of trans isomer (trans-6). However, the presence of cis isomer was not recognized until the crude reaction mixture was recrystallized from acetonitrile. Pure cis isomer (cis-6) was obtained by washing the cis-trans mixture with acetonitrile followed by slow evaporation of acetonitrile solution at 35 C. Structure of cis (cis-6) isomer was unambiguously established by single crystal XRD data.© 2013 Elsevier B.V. All rights reserved.

Synthesis and structural characterization of cis isomer of 1,2,3-triazol-5-ylidene based palladium complexes

An abnormal or mesoionic N-heterocyclic carbene (NHC), namely 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene (Tz), formed from 1,4-diphenyl-3-methyl-1,2,3-triazolium iodide and silver oxide, gave the corresponding silver carbene complex. The transmetalation reaction of the silver carbene complex with PdCl2(CH3CN)2 gave a trans mononuclear complex, [(Tz)2PdCl2]. Reaction of the silver carbene complex with Pd(OAc)2 gave an acetate-bridged binuclear complex in which the palladium had undergone a C-H insertion at the ortho position of the phenyl group attached to the triazole nitrogen (1-position). The structures of these two complexes were established by single-crystal XRD data and spectroscopic data. The acetate complex was used as a catalyst for the stereoselective hydroarylation of alkynes. © 2011 American Chemical Society.

Organometallics

Synthesis and structure of 1,4-diphenyl-3-methyl-1,2,3-triazol-5-ylidene palladium complexes and application in catalytic hydroarylation of alkynes

Organometallics in Synthesis

Palladium in Organic Synthesis

Chem. Commun.

Application of 1,2,3-triazolylidenes as versatile NHC-type ligands: synthesis, properties, and application in catalysis and beyond

Applications of Transition Metal Catalysis in Drug Discovery and Development

Facile base-free in situ generation and palladation of mesoionic and normal N-heterocyclic carbenes at ambient conditions

Journal	Data powered by TypesetDalton Transactions
Publisher	Data powered by TypesetRoyal Society of Chemistry
ISSN	14779226
Open Access	No