具有金屬-金屬作用單核自組裝體的合成及其對Suzuki偶聯反應的高效催化

胡志勇 鄧 威 路紅琳 黃海平 于澍燕＊，

（1北京工業大學環境與能源工程學院，綠色催化與分離北京市重點實驗室，自組裝化學實驗室，北京 100124）

（2天津民祥生物醫藥股份有限公司，天津 300350）

Spontaneous and precise assembly of compounds into giant，well-defined，functional superstructures are attractive for their novel structures[1-4]and promising applications in molecular recognition，catalysis，guest inclusion，luminescence，anion complexation and so on[5-9].Over the last decade，numerous novel metalorganic molecules have been constructed by metaldirected self-assembly[10-14].The Fujita group has established a seriesofcomplexesthatcan be selfassembled by simply mixing ligands and bare squareplanar Pdギ ions[15-16].And in our previous research，we have reported an array of well-defined metallic supramolecular structures formed by quantitatively assembling[17-18].More recently，transition metals with specific coordination geometries have been employed for the rational design and construction of highly ordered supramolecular structures[19].

Owing to the fact that the aryl-aryl structure motif is an important building block in organic chemistry，the Suzuki reaction is widely applied in academic research as well as in industrial synthesis of fine chemicals and highly complex pharmaceuticals[20].A representative Suzuki-Miyaura cross-coupling reaction is shown in Scheme 1.In the Suzuki reaction，Pdbased catalysts coordinated with organophosphorus ligands are frequently used in Suzuki-crossing reactions.Since the organophosphorus ligands are poisonous，from the environmental point of view，making the Suzuki reaction green is a continuous process pursued by organic chemists.In the past few years，considerable attention has been paid to functional metal-organic assemblies that show promise in catalysis with environment-friendly[21].Especially，palladium and platinum were employed in the Suzuki coupling reactions for their high stability and remarkable efficiency[22].

Scheme 1 Representative Suzuki-Miyaura cross-coupling reaction

In this work，we designed and synthesized three mononuclear complexes using the self-assembly approach，namely[（bpy）Pd（L）]NO3（1·NO3·H2O），[（bpy）Pt（L）]NO3（2·NO3·H2O），and[（phen）Pd（L）]NO3（3·NO3·H2O），respectively.All of these three complexes have been intensively studied by NMR and ESI-MS，and X-ray single-crystal diffraction analysis have been employed for complex 1·PF6·CH3CN.In addition，considering the structural characteristics and the palladium and platinum （Ⅱ，Ⅱ）properties，these three welldefined complexes have been developed and applied into Suzuki-coupling reactions，as expected，all of these three complexes show excellent catalysis properties.

Scheme 2 Self-assembly of complexes 1·NO3·H2O，2·NO3·H2O and 3·NO3·H2O

1 Experimental

1.1 Materials and instruments

All chemicals for synthesis and analysis were obtained commercially with analytical grade and used without further purification.All solvents were of reagent pure grade and were purified according to conventional methods.

The ESI-MS were performed on a JEOL Accu-TOF mass spectrometer.1H and13C NMR spectra were performed on a Bruker AV 400 MHz spectrometer.

1.2 Syntheses and characterization of mononuclear complexes[23]

The self-assembly of mononuclear Pd complex 1·NO3·H2O was shown in Scheme 2.Ligand L （11.2 mg，0.05 mmol）was treated with[（bpy）2Pd2（NO3）2]（NO3）2（19.3 mg，0.025 mmol）in a mixture of water and acetone with 2∶1 molar ratio.The mixture was stirred at 60 ℃ for 7 h to give 1·NO3·H2O.1H NMR of 1·NO3·H2O （400 MHz，DMSO-d6，298 K，TMS）：δ 8.27（m，J=7.9 Hz，4H），8.11 （t，J=7.7 Hz，2H），7.83 （d，J=7.5 Hz，4H），7.61 （m，J=7.4 Hz，4H），7.39 （t，J=7.8 Hz，4H），6.76 （s，1H）.13C NMR for 1·NO3·H2O （400 MHz，DMSO-d6，298 K，TMS）：δ 181.32，155.96，147.28，142.56，135.15，133.30，129.30，128.48，124.62，96.84，49.07.ESI-MS （CH3CN，m/z）：Calcd.for[（bpy）Pd（L）]+485.05，Found 485.01.Elemental analysis calculated for 1·NO3·H2O （C25H21N3O6Pd，%）：C：53.06，H：3.74，N：7.43.Found（%）：C：53.03，H：3.76，N：7.42.A tenfold excess of KPF6was added to the solution，the yellow precipitation were collected by centrifugation，washed with minimum amount of water and dried in vacuum to give 1·PF6·H2O as pale yellow solid （32.1 mg，0.049 mmol，97%yield）.Single crystals of 1·PF6·CH3CN were obtained by the slow vapor diffusion of diethyl ether into their acetonitrile solutions over two weeks.The needle-shaped pale yellow crystals were collected by filtration，washed with water several times and dried in vacuum.1H NMR of 1·PF6·H2O （400 MHz，DMSO-d6，298 K，TMS）：δ 8.38 （d，J=7.8 Hz，2H），8.35（d，J=7.8 Hz，2H），8.19 （t，J=7.8 Hz，2H），7.93 （d，J=7.4 Hz，4H），7.70 （t，J=6.6 Hz，2H），7.62 （t，J=7.3 Hz，2H），7.43 （t，J=7.8 Hz，4H），6.86 （s，1H）.13C NMR for 1·PF6（400 MHz，DMSO-d6，298 K，TMS）：δ 181.14，155.83，147.13，142.48，134.98，133.28，129.24，128.41，124.57，96.70，31.15.ESI-MS （CH3CN，m/z）：Calcd.for[（bpy）Pd（L）]+485.05，Found 485.03.Elemental analysis calculated for 1·PF6·H2O （C25H21F6N2O3PPd，%）：C：46.28，H：3.26，N：4.32.Found（%）：C：46.30，H：3.30，N：4.29.Elemental analysis calculated for 1·PF6·CH3CN （C27H22F6N3O2PPd，%）：C：48.27，H：3.30，N：6.25.Found（%）：C：48.25，H：3.32，N：6.23.

Ligand L （11.2 mg，0.05 mmol）was treated with[（bpy）2Pt2（NO3）2]（NO3）2（23.7 mg，0.025 mmol）in a mixture of water and acetone with 2∶1 molar ratio at 60 ℃ for 7 h to give 2·NO3·H2O.1H NMR of 2·NO3·H2O （400 MHz，DMSO-d6，298 K，TMS）：δ 8.64 （d，J=5.5 Hz，2H），8.42 （d，J=8.0，2H），8.24 （t，J=7.8 Hz，2H），8.03 （d，J=7.8 Hz，4H），7.73 （m，J=7.4 Hz，4H），7.49（t，J=7.8 Hz，4H），6.94 （s，1H）.13C NMR （400 MHz，DMSO-d6，298 K，TMS）：δ 178.37，156.39，146.50，141.87，134.79，133.25，129.39，128.11，124.78，97.32，49.07.ESI-MS （CH3CN，m/z）：Calcd.for[[（bpy）Pt（L）]]+574.11，Found 574.07.Elemental analysis calculated for 2·NO3·H2O （C25H21N3O6Pt，%）：C：45.87，H：3.23，N：6.42.Found（%）：C：45.85，H：3.26，N：6.40.A tenfold excess of KPF6was added to the above solution，the yellow precipitation were collected by centrifugation，washed with minimum amount of water and dried in vacuum to give 2·PF6·H2O as yellow solid （35.6 mg，0.048 mmol，95%yield）.1H NMR confirmed the quantitative formation of 2·PF6·H2O.1H NMR （400 MHz，DMSO-d6，298 K，TMS）：δ 8.63 （d，J=5 Hz，2H），8.41 （d，J=7.8 Hz，2H），8.23 （t，J=7.8 Hz，2H），8.02 （d，J=7.4 Hz，4H），7.72 （m，4H），7.48 （t，J=7.9 Hz，4H），6.93 （s，1H）.13C NMR （400 MHz，DMSO-d6，298 K，TMS）：δ178.80，156.66，146.77，142.06，135.10，133.29，129.47，128.32，128.21，124.87，97.67.ESI-MS （CH3CN，m/z）：Calcd.for[（bpy）Pt（L）]+574.11，Found 574.09.Elemental analysis calculated for 2·PF6·H2O （C25H21F6N2O3PPt，%）：C：40.71，H：2.87，N：3.80.Found：C：40.69，H：2.88，N：3.78.

Ligand L （11.2 mg，0.05 mmol）was treated with[（phen）2Pd2（NO3）2]（NO3）2（20.5 mg，0.025 mmol）in a mixture of water and acetone with 2∶1 molar ratio at 60 ℃ for 7 h to give 3·NO3·H2O.1H NMR of 3·NO3·H2O：（400 MHz，DMSO-d6，298 K，TMS）：δ 8.93 （d，J=8.2 Hz，2H），8.87 （d，J=5.2 Hz，2H），8.23 （s，2H），8.15（m，J=4.7 Hz，6H），7.69 （t，J=7.3 Hz，2H），7.55 （t，J=7.6 Hz，4H），7.02 （s，4H）.13C NMR （400 MHz，DMSO-d6，298 K，TMS）：δ 180.27，147.95，145.69，140.94，134.31，133.23，130.46，129.09，128.33，126.65，49.07.ESI-MS （CH3CN，m/z）：Calcd.for[（phen）Pd（L）]+509.05，Found 509.01.Elemental analysis calculated for 3·NO3·H2O （C27H21N3O6Pt，%）：C：54.97，H：3.59，N：7.12.Found（%）：C：55.00，H：3.56，N：7.11.A ten-fold excess of KPF6was added to the solution，the yellow precipitation were collected by centrifugation，washed with minimum amount of water and dried in vacuum to give pale yellow solid of 3·PF6·H2O. （33.2 mg，0.049 mmol，97%yield）.1H NMR confirmed the quantitative formation of 3·PF6·H2O.1H NMR of 3·PF6·H2O：（400 MHz，DMSO-d6，298 K，TMS）：δ 8.56 （d，J=8.1 Hz，2H），8.48 （d，J=4.4 Hz，2H），7.98 （s，2H），7.86 （m，2H），7.80 （d，J=7.4 Hz，4H），7.59 （t，J=7.3 Hz，2H），7.37 （t，J=7.8 Hz，4H），6.61 （s，1H）.13C NMR（400 MHz，DMSO-d6，298 K，TMS）：δ 180.46，148.01，145.86，141.00，134.46，133.26，130.52，129.13，128.36，126.66，96.02.ESI-MS （CH3CN，m/z）：Calcd.for[（phen）Pd（L）]+509.05，Found 509.04.Elemental analysis calculated for 3·PF6·H2O （C27H21F6N2O3PPd，%）：C：48.20，H：3.15，N：4.16.Found：C：48.18，H：3.15，N：4.17.

1.3 X-ray crystallography of complex 1·PF6·CH3CN

X-ray diffraction data of the crystals of complex 1·PF6·CH3CN was collected at 150（2）K by using Bruker Smart Apex CCD area detector equipped with a graphite monochromated Mo Kα radiation （λ=0.071 073 nm）.The structure of 1·PF6·CH3CN was solved by direct method and refined by employing full matrix least-square on F2by using SHELXTL （Bruker，2000）program and expanded using Fourier techniques[24-25].All non-H atoms of the complex 1·PF6·CH3CN were refined with anisotropic thermalparameters.The hydrogen atoms were included in idealized positions with isotropic displacement parameters constrained to 1.5 times the Uequivof their attached carbon atoms for methylene hydrogens，and 1.2 times the Uequivof their attached carbon atoms for all others.SQUEEZE option was employed to treat the disordered counter anions.The crystallographic data of complex 1·PF6·CH3CN were listed in Table 1 and the selected hydrogen bond lengths and bond angles of complex 1·PF6·CH3CN were listed in Table S1 and S2.

CCDC：1566337，1·PF6·CH3CN.

Table 1 Crystallographic data for complex 1·PF6·CH3CN

2 Results and discussion

2.1 Characterization of 1·PF6·H2O,2·PF6·H2O and 3·PF6·H2O

NMR were fully carried out to characterize the complexes of 1·PF6·H2O，2·PF6·H2O and 3·PF6·H2O.Analysis by1H NMR spectroscopy of 1·NO3·H2O in DMSO-d6solutions clearly showed an array of welldefined resonance and suggested the self-assembly of[（bpy）2Pd2（NO3）2]（NO3）2and L to form a single product（Fig.S1～S2）.Upon replaced by，a series of peaks shifted downfield as shown in Fig.1.The results of1H NMR spectroscopy indicated that the formation of a 1∶1 complex of 1·PF6·H2O.Detailed analysis of1H NMR spectra belonged to the complex 1·PF6·H2O was discussed as below：for complex 1·PF6·H2O，the featured single peak at 6.86 corresponded to methylene-H，the triplet at 7.43 were assigned to aromatic-H2，aromatic-H2′，aromatic-H4 and aromatic-H4′，the triplet at 7.62 with integral of 2 H assigned to pyridine-H7 and pyridine-H7′，and the triplet at 7.70 with integral of 2 H assigned to pyridine-H8 and pyridine-H8′，the doublet at 7.93 with integral of 4 H assigned to aromatic-H1，aromatic-H1′，aromatic-H5 and aromatic-H5′，the triplet at 8.19 with integral of 2 H assigned to aromatic-H3 and aromatic-H3′，the downfield 4 H assigned to pyridine-H6，pyridine-H6′，pyridine-H9 and pyridine-H9′，respectively.And the results of13C NMR spectroscopy as shown in Fig.S8 agreed well with the analysis results of1H NMR spectroscopy.These resultswere consistentwith those ofthe complexes 2·NO3·H2O，2·PF6·H2O，3·NO3·H2O and 3·PF6·H2O （Fig.S3～S6 and Fig.S9～S12）.

Fig.1 1H NMR spectrum of complex 1·NO3·H2O and 1·PF6·H2O in DMSO-d6

ESI-MS studies also confirmed the structure of 1·NO3·H2O，1·PF6·H2O，2·NO3·H2O，2·PF6·H2O，3·NO3·H2O and 3·PF6·H2O in solution （Fig.2，S13～S17）.Isotope patterns matched those simulated and peak separations consistent with the charges.When an acetonitrile solution of 1·PF6·H2O was subjected to the ESI-MS，prominent peaks for[（bpy）Pd （L）]+were clearly observed at 485.03，indicating the complete formation of metal-organic complexes.Additionally，the striking peak at485.03 also confirmed the spontaneousdeprotonation of1，3-diphenylpropane-1，3-dione （L）in solution driven by coordination effect.Similarly，the ESI-MS study of 2·PF6·H2O and 3·PF6·H2O afforded a series of peaks at m/z 574.09 and 509.04 were similar to that of complex 1·PF6·H2O.

Fig.2 ESI-MS spectrum of complex 1·PF6·H2O in acetonitrile

2.2 Crystal structure of 1·PF6·CH3CN

The molecular structure of complex 1·PF6·CH3CN was unambiguously determined by reliable methods of X-ray diffraction analysis.As shown in Fig.3，complex 1·PF6·CH3CN crystallizes in monoclinic space group P21/n.The crystal structure of 1·PF6·CH3CN displays a mononuclear palladiumギ complex with planar conformation，and a parallel pattern is formed between planes.A dimeric crystal structure is formed by the efficient π-π stacking interactions and the metalmetal interactions，which make the complex of 1·PF6·CH3CN be an efficient catalyst.The central palladiumギ is coordinated by two N atoms （the two N atoms of bpy）and two O atoms（the two O atoms of L）in a square coordination mode.The distances of Pd（1）-O（1）and Pd（1）-O（2）are 0.200 7 and 0.197 8 nm，respectively.And the distances between Pd（1）and the two N atoms are 0.201 6 and 0.198 5 nm，respectively.While the intermolecular Pdギ…Pdギ distance is about 0.322 4 nm，which indicates that the interactions exist between them，and the interaction may be suitable for the catalysis applications of the complex 1·PF6·CH3CN.The angles of O（1）-Pd （1）-O（2）and N （1）-Pd （1）-N （2）were 93.06°and 82.10°，respectively.The dihedral angle，defined by planes O（1）-Pd（1）-O（2）and N（1）-Pd（1）-N（2），is 5.48°.Extending a，b and c axes withanions and acetonitrile molecules frozen inside as shown in Fig.3 and S18.The structure determined by X-ray crystallographic analysis agreed well with the NMR and ESI-MS analysis.We had tried many times to obtain the crystals of 2·PF6·CH3CN and 3·PF6·CH3CN，but failed.

Fig.3 Molecular structure （left）and the dimeric crystal structure （right）of 1·PF6·CH3CN

2.3 Catalytic activity

For the importance of the Suzuki cross-coupling reaction and the structural characteristics of palladium and platinum （Ⅱ，Ⅱ）complexes，1·PF6·H2O，2·PF6·H2O and 3·PF6·H2O were devoted to explore the catalyst activity.In our previous work，we have discussed the catalyst activity of pyrazolate-based dipalladiumギ complexes[26].In this work，different solvents，temperature，reaction time and reagents were examined to optimize the process conditions.

Firstly，effects of different solvents were investigated，and the optimum conditions were shown in Table 2.According to previous experiments records[27]，1，4-dioxane and ethanol were prepared for the catalyst activity，and it was observed that different solvents are suited for different reactions.Meanwhile，the temperature and the reaction time were adjusted to achieve the optimal strategy.

Next，the influence of reagents was explored in the controlled experiments.Differentyields butsatisfactory results were obtained for the aryl-aryl reactions （Table 3）.But for the heterocyclic-based reactions，since the previous set of experiments have consistently use unprotected starting pyrazol-based，the palladium or platinum ions in 1·PF6·H2O，2·PF6·H2O and 3·PF6·H2O complexes could coordinate with the unprotected starting pyrazole，leading to sideproducts and yield decreasing.Then a series of protected starting pyrazol-based were employed for the cross-coupling reactions，as expected，the yields of adducts were higher.With the optimized reaction conditions in hand，a broad substrate listed in Table 3 is observed.The results of control experiment and blank experiment show that good catalytic effect would be found only when main catalysts and subcatalysts coexist simultaneously.It seems that the electronic effect of metal-metal interaction and the steric effectofthe catalystsmake the reaction efficiency.

Table 2 Catalytic activity of complexes 1·PF6·H2O,2·PF6·H2O and 3·PF6·H2O

Table 3 Catalytic activity of complexes 1·PF6·H2O,2·PF6·H2O and 3·PF6·H2O

Continued Table 3

Continued Table 3

3 Conclusions

In summary，we have synthesized three monometallic complexes in quantitative yields by a directed self-assembly of diketone-based ligands with[（bpy）Pd（NO3）]NO3，[（bpy）Pt（NO3）]NO3and[（phen）Pd（NO3）]NO3in a 2∶1 molar ratio.The assemblies have been characterized by NMR and ESI-MS，and the complex of 1·PF6·CH3CN was fully defined by single-crystal X-ray diffraction method.These characterizations show the structural similarity of these assemblies.The singlecrystal structures show that weak intramolecular Pd…Pd interactions exist in 1·PF6·CH3CN.More significantly，these metal-organic species with metal-metal interaction have potential application in the field of Suzuki cross-coupling reaction.

Supporting information is available at http：//www.wjhxxb.cn

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