Reactivity of nickel metal precursors towards amido linked N-heterocyclic carbenes and their catalytic studies for cross coupling reactions

Abstract

The refluxing of chloroacetamide derivatives with n-butyl imidazole resulted in their corresponding salt of composition 1-(n-butyl)-3-N-(2-Ar)acetamido-1, 3-imidazolium chloride (Ar = furylmethyl (1a); phenylmethyl (1b)). The latter salt on treatment with DBU followed by the addition of chalcogen atom resulted into a compoundSimilarly, the reaction of the imidazolium salts with, excess K2CO3 and NiCl2.6H2Ofurylmethyl (3a); phenylmethyl (3b)). The latter complexes have also been isolated by using Ni(II) phosphine precursors [NiCl2(P-P)] (P-P = PPh3, dppf). The molecular structure of [(1-(nbutyl)-3-N-(2-furylmethyl)acetamido-1, 3-imidazol-3-ylidine)]2Ni and [(1-(n-butyl)-3-N-(2-phenylmethyl)acetamido-1, 3-imidazol-3-ylidine)]2Ni were established by single crystal X-ray diffraction analysis. The catalytic property of complex 3a and 3b for cross coupling reactions has been studied.

Synthesis of Palladium complexes derived from Amido linked N‐Heterocyclic Carbenes and their use in Suzuki cross coupling reactions

“…[14,19] The rich charge density is further enhanced with prompt chelation of NHC ligand through carbon as well as nitrogen atoms to the metal center. [5,19] 1 H NMRs of complexes 1 a/1 b displayed resonances at 7.25/ 7.15 and 6.94/6.90 ppm of 4 th and 5 th position of imidazole ring respectively, supporting the complexation of palladium metal to carbene centre. Furthermore, the disappearance of the proton signal for 2 nd position of imidazole ring as well as the amide proton also confirmed the coordination to the metal.…”

“…[19] Secondly, two prominent vibrations were observed at~538 and 693 cm À 1 which support the existence of PdÀ C carbene and PdÀ N bonds respectively. [5,[20][21][22] We have also reported similar reactivity pattern of imidazolium salt with [NiCl 2 (LÀ L)] (L=PPh 3 , dppf), where substitution of phosphine occurs through NHC. [5] We, however have not been able to confirm the phosphine-displacement step.…”

“…The 13 C{ 1 H} NMR displayed all the expected signals in the regioñ 13 to 169 ppm including the de-shielded resonance at 169 ppm which is regarded as the signature peak of a PdÀ C carbene bond. [5,9,15] The IR spectra of complexes 1 a and 1 b displayed all possible vibrations ranging from 2966 to 536 cm À 1 .…”

“…Internally functionalized amido linked N-heterocyclic carbenes (NHC) is an active area of research [1][2][3][4] The strong ϭ donor property of these carbenes [5] results to air stable compounds with strong metal carbon bonds. [6][7][8][9] Especially, NHC complexes of group 10 metals are highly efficient catalysts for CÀ C coupling reactions such as Suzuki-Miyaura, [2,8,10,11] Sonogashira [12,13] and the Hiyama couplings.…”

“…[17,18] We have recently reported the synthesis of 1-(n-butyl)-3-N-(2-Ar)acetamido-1, 3-imidazolium chloride (Ar = furylmethyl,phenylmethyl) and their reactivity towards [NiCl 2 (PÀ P)] (LÀ L=2 PPh 3 , dppf). [5] The interesting outcomes of our previous study prompted us to further explore the chemistry of these imidazolium salts towards palladium metal precursors and study their promising catalytic activities for Suzuki coupling reactions.…”