Synthesis of Ruthenium Complex Based on 2 , 6-Bis ( 1-( phenyl )-1 H-benzo [ d ] imidazol-2-yl ) pyridine and 2-( 1-Phenyl-1 H-benzo [ d ] imidazol-2-yl ) benzoate and Catalytical Oxidation Property of 1-( 1 H-Benzo [ d ] imidazol-2-yl ) ethanol to 1-( 1 H-Benzo [ d ] imidazol-2-yl ) ethanone with H

A new ruthenium complex, Ru(bpbp)(pbb)Cl, based on 2,6-bis(1-(phenyl)-1H-benzo[d]imidazol-2-yl)pyridine (bpbp) and 2-(1phenyl-1H-benzo[d]imidazol-2-yl)benzoate (pbb) was synthesized. The complex Ru(bpbp)(pbb)Cl could catalytically oxidize 1(1H-benzo[d]imidazol-2-yl)ethanol to 1-(1H-benzo[d]imidazol-2-yl)ethanone with H 2 O 2 as oxidant. Influence of temperature and catalyst amount on the oxidation reaction was evaluated. The reaction optimal conditions are as follows: molar ratio of catalyst to substrate to H 2 O 2 is 1 : 1000 : 3000, the proper reaction temperature is 50C and reaction time lasts 5 h, and the isolated yield of 1-(1H-benzo[d]imidazol-2-yl)ethanol to 1-(1H-benzo[d]imidazol-2-yl)ethanone under the optimal reaction conditions is 57%.


Introduction
Benzimidazole is one of the oldest known nitrogen heterocycles and was first synthesized by Hoebrecker.The properties of benzimidazole and its derivatives have been studied over more than one hundred years.Benzimidazole derivatives are useful intermediates/subunits for the development of molecules of pharmaceutical or biological interest [1][2][3][4][5][6][7][8]; acetyl group contains carbonyl group and -H group, which can take part in many reactions; thus 1-(1H-benzo[d]imidazol-2-yl)ethanone is a key intermediate for preparation of complicate benzimidazole-based compounds.Oxidation of 1-(1H-benzo[d]imidazol-2-yl)ethanol to 1-(1H-benzo[d]imidazol-2-yl)ethanone is of great importance for precursors of a variety of valuable fine chemicals.Traditionally, 1-(1H-benzo[d]imidazol-2-yl)ethanone is produced by solid phase oxidation of (1H-benzo[d]imidazol-2-yl)methanol with KMnO 4 /Al 2 O 3 or oxidized by dichromates salt [9][10][11][12].In these traditional oxidation processes, large amounts of toxic, volatile organic solvents and metal oxidants were extensively used and it is difficult to magnify the quantity of product.Hence, developing green selective oxidation process of (1H-benzo[d]imidazol-2-yl)ethanol is still a challenging task in catalysis.Hydrogen peroxide is an environmentally benign oxidant, which theoretically generates only water as a by-product.The discovery of new catalyst employing H 2 O 2 as oxidant is gathering much attention [13][14][15][16].Ruthenium complex constitutes a versatile class of catalysts for important synthetic transformations in organic chemistry [17].Benzimidazole is more easily synthesized than imidazole; we continued to focus on the synthesis and applications of complexes based on benzimidazole compound [18][19][20][21].In recent years, we turned our attention to catalytic oxidation properties of ruthenium complex based on benzimidazole group ligand [22,23].Herein, we synthesized a new benzimidazole-based ligand and its ruthenium complex to investigate its catalytic oxidation properties of (1Hbenzo

Experimental
2.1.Reagents and Methods.Chemicals were of analytical grade and purchased from J&K Company without further purification unless indicated.2-(Chlorocarbonyl)benzoic acid was synthesized according to literature [24].Mass spectra were obtained on a Shimadzu LCMS-2010A.Elemental analyses were carried out with an Elementar vario EL elemental analyzer. 1HNMR was recorded on a Bruker AVANCE 400 spectrometer (400 MHz).Chemical shifts are given in ppm and refer to the residual solvent as the internal standard.IR spectra were recorded on a Bruker 550 FT-IR spectrometer.6-dicarboxamide (5.00 g, 10 mmol) was heated at 250 ∘ C for 3 h under nitrogen.After cooling, water (50 mL) was added to the mixture and extracted with CH 2 Cl 2 (50 × 3 mL).The combined organic layers were washed with water.Solvent of the filtrate was removed in vacuo to obtain a crude solid.White    crude violet solid ruthenium complex could be obtained after evaporation of alcohol.Pure ruthenium complex was obtained from recrystallization from alcohol.IR.The measurements of C, H, and N element analysis are in good agreement with the theory calculated values.The appearance of 1592 and 1450 cm −1 in the ruthenium complex Ru(bpbp)(pbb)Cl shows deprotonation to coordination to Ru 2+ ion.
Only 35% yield of 1-(1H-benzo[d]imidazol-2-yl)ethanone was obtained when the reaction was conducted at 30 ∘ C,  130.57 (18) while the selectivity would become poor as further rising the temperature to 80 ∘ C (entries 1, 2, and 3).Therefore, the optimized temperature was proved to be 50     isolated yield of 57% by removing the solvent.The product was identified by 1 HNMR spectrum (400 MHz, CDCl 3 ) (Figure 5) and IR spectrum (Figure 6), which are all in agreement with the assumed structure.IR is also same with the standard Bio-Rad/Sadtler IR Data.

Table 1 :
Crystal data and structure refinement for 2-(1-phenyl-1Hbenzo[d]imidazol-2-yl)benzoic acid.× 10 −4 mmol, 0.01 mol% based substrate), and 0.2 mmol (inert internal standard) were added into a reaction tube.The reactor containing this mixture was heated to proper temperature in an oil bath under vigorous stirring, and then the aqueous hydroperoxide (30% H 2 O 2 , 10 mol/L) was slowly dropped in.The product samples were drawn at regular time intervals and analyzed by GC and GC-MS.

Table 3 :
Optimization of reaction conditions a .