Hydrophilic Pd⁰ Complexes Based on Sugars for Efficient Suzuki–Miyaura Coupling in Aqueous Systems

Abstract

Two classes of hydrophilic Pd 0 complexes containing P,N and N,N sugar-based ligands were prepared and tested in the Suzuki-Miyaura cross-coupling reaction under environmentally friendly aqueous conditions. The best catalyst was toler-4199 ant towards different substrates, and its activity is comparable with the highest values reported so far for reactions in aqueous media [loading 0.0010 %, turnover frequency (TOF) 3.5 ϫ 104 h -1 ].ligands with the desired coordinating motifs. Moreover, as the chemistry of carbohydrates is well developed, it is easy to fine tune the chemical-physical properties to make the ligands selectively soluble in desired green solvents, such as water or ionic liquids. [2] Although sugar-derived ligands have been applied in several catalytic C-C and C-X bond formations (X = O, N, S, P), [1] their scope has not been extended comprehensively to other powerful couplings such as the Suzuki-Miyaura reaction, for which only some sporadic examples have been reported. [3] Nevertheless, in this field, sugar candidates are really attractive building blocks owing to their solubility in www.eurjic.org FULL PAPERwater, [4] which allows the green and sustainable synthesis of biaryls. [5] On this basis, we report the preparation of diphenylphosphino-imino (PN) and pyridino-imino (NN) sugar-based ligands, along with the syntheses of the corresponding hydrophilic Pd 0 complexes (Figure 1, fdn = fumarodinitrile). Some imino ligands have recently been employed in Suzuki-Miyaura couplings, [6] but in all cases the activities ranged from low to moderate.The design of both PN and NN ligands was aimed at ensuring their easy, high-yield synthesis.Four imino sugar residues were employed: three of them are derived from glucose functionalized at the 1-, 2-and 6positions, and the fourth is instead a mannoside derivatized at the 6-position. Scheme 1. Synthesis of the complexes.Scheme 2. Synthesis of the ligands. 4200As expected, all of the complexes were soluble in aqueous media and could be fruitfully employed in the Suzuki-Miyaura coupling reaction.

New “one‐pot” Pd(II) and Zn(II) complexes of Schiff bases, derivatives of 1‐amino‐1‐deoxy‐d‐sorbitol: Spectroscopic studies and biological and catalytic activities

“…The values of δOH and the position of the 15 N signals of DMSO-d 6 solution were similar to those observed for other amino sugar Schiff bases, which indicated the presence of mediumstrength intramolecular hydrogen bond and proton transfer equilibrium. [23][24][25] Large differences in CP MAS NMR values between 15 N and the solution of DMSO-d 6 (up to ca. 90 ppm) indicated the shift of the equilibrium strongly toward the proton-transferred form in the solid state.…”

“…Complexes of Schiff bases play an important role in the detection of various ions, exhibit biological properties, and are widely used as catalysts . Recently, several studies focused on Schiff bases and their complexes, derivatives of natural products, for example, amino sugars, amino acids, and chitosan . Identifying new enantiomerically pure systems is one of the major goals of organic chemistry.…”

“…Such reports were the starting point to our studies. To the best of our knowledge, most studies on complexes of amino sugar Schiff bases deal sugars deal with compounds containing moiety other than d ‐glucamine and rather in ring form . Only a few studies deal with compounds containing sugar chain moiety, and therefore d ‐glucamine as a reactant in the synthesis of Schiff bases is an unexplored chiral raw material.…”

“…[4,11,12] Recently, several studies focused on Schiff bases and their complexes, derivatives of natural products, for example, amino sugars, amino acids, and chitosan. [7,[13][14][15][16][17][18][19][20] Identifying new enantiomerically pure systems is one of the major goals of organic chemistry. Although the number of papers published on Schiff bases is increasing every year, they still have a huge potential and are promising ligands of metal complexes.…”

“…To the best of our knowledge, most studies on complexes of amino sugar Schiff bases deal sugars deal with compounds containing moiety other than D-glucamine and rather in ring form. [13,15] Only a few studies deal with compounds containing sugar chain moiety, [14,[18][19][20][21][22][23] and therefore Dglucamine as a reactant in the synthesis of Schiff bases is an unexplored chiral raw material. Our primary aim was a convenient "one-pot" synthesis of new optically active zinc(II) and palladium(II) complexes, derivatives of natural products such as D-glucamine; their spectroscopic characterization; and preliminary tests for biological and catalytic activities.…”