MA Zhi-HongHAN Y-XueWANG HongHAN Zhn-GngZHENG Xue-ZhongLIN Jin②(The College of Chemistry & Mteril Siene, Heei Norml University, Shijizhung 050024, Chin)(College of Bsi Mediine, Heei Medil University, Shijizhung 050017, Chin)(Heei Institute of Food Qulity Supervision Inspetion nd Reserh, Shijizhung 050091, Chin)

Syntheses and Crystal Structures of Three Metal Carbonyl Complexes Based on Pyridyl Side Chain Functionalized Tetramethylcyclopentadienyl Ligand①

MA Zhi-Honga,bHAN Ya-XueaWANG HongcHAN Zhan-GangaZHENG Xue-ZhongaLIN Jina②a(The College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050024, China)b(College of Basic Medicine, Hebei Medical University, Shijiazhuang 050017, China)c(Hebei Institute of Food Quality Supervision Inspection and Research, Shijiazhuang 050091, China)

Thermal treatment of the pyridyl side chain functionalized tetramethyl cyclopentadiene C5Me4CH2(C5H4N) with Fe(CO)5, Ru3(CO)12and Mo(CO)6in refluxing xylene respectively gave the corresponding dinuclear metal carbonyl complexes 1～3.These complexes have been characterized by elemental analysis, IR and1H NMR spectra.The molecular structures of 1～3 were determined by X-ray diffraction analysis.

cyclopentadienyl, metal carbonyl, X-ray diffraction

1 INTRODUCTION

Substituted cyclopentadienyl occupies a prominent role in organometallic chemistry, serving as versatile ligands for transition metals.Subtle changes in either cyclopentadienyl substitution can have profound consequences on chemical reactivity.The cyclopentadienyl complexes have received increasing attention due to their diverse and flexible hapticities and the enhanced reactivities both in stoichiometric and catalytic reactions[1-4].Much attention has been focused on the cyclopentadienyl containing a donor-functionalized side chain[5-7].For the nitrogen atom can act as a good two-electron donor site and can coordinate to a variety of metals, the side chain containing nitrogen cyclopentadienyl ligands has usually been used to form intramolecular coordination to a Lewis acidic metal center or to construct oligonuclear metal complexes, which usually show different structures and reactivities[8-10].In our previous work, we have studied the reactions of heterocyclic substituted cyclopentadienes with Ru3(CO)12and obtained a series of ruthenium carbonyl complexes involving novel intramolecular C–H activation, allyl isomerization, normal and including different bonding modes of cyclopenstadienyl ligands[11,12].To develop a deeper undertanding of the reactions of cyclopentadiene derivatives containing nitrogen with metal carbonyl, in this paper we designed the side chain containing N-heterocyclic ligand precursor and explored its reactions with Fe(CO)5, Mo(CO)6and Ru3(CO)12, which resulted in a series of metal carbonyl complexes.

2 EXPERIMENTAL

2.1 General considerations

All manipulations of air- and moisture-sensitive complexes were performed at an argon/vacuum manifold using standard Schlenk techniques.Solvents were distilled from appropriate drying agents under an atmosphere of nitrogen prior to use.1H NMR spectra were recorded on a Bruker AV 500 instrument, while IR spectra were recorded as KBr disks on a FT IR 8900 spectrometer.X-ray measurements were made on a Bruker Smart APEX diffractometer with graphite monochromated MoKa(l = 0.71073 ?) radiation.Elemental analyses were performed on a Vario EL Ⅲ analyzer.The ligand precursor C5Me4CH2(C5H4N) was synthesized according to the literature methods[13-15].

2.2 Reaction of ligand precursor with Fe(CO)5in xylene

A solution of ligand precursor C5Me4CH2(C5H4N) (0.42 g, 2.0 mmol) and Fe(CO)5(0.7 mL, 5 mmol) in 25 mL of xylene was refluxed for 12 h.After the removal of solvent under reduced pressure, the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2as eluent.The brickred band was eluted and collected.After vacuum removal of the solvents from the above eluate, the residue was recrystallized from n-hexane/CH2Cl2at room temperature to give complex 1 as reddishbrown crystals (yield: 0.343 g, 37.2%).M.p.193 ℃(dec.).Anal.Calcd.for C36H36N2O4Fe2: C, 64.31; H, 5.40; N, 4.17%.Found: C, 63.02; H, 5.67; N, 4.31%.1H NMR (500 MHz, CDCl3): 1.58 (s, 12H, Me), 1.72 (s, 12H, Me), 3.77 (s, 4H,CH2), 7.10 (d, J = 7.50 Hz, 4H, C5H4N), 7.58 (t, J = 7.59 Hz, 2H, C5H4N), 8.54 (d, J = 8.00 Hz, 2H, C5H4N).IR(vCO, cm-1): 1734 (s), 1927 (s).

2.3 Reaction of ligand precursor with Ru3(CO)12in xylene

By using a similar procedure to that described above, ligand precursor C5Me4CH2(C5H4N) (0.42 g, 2.0 mmol) reacted with Ru3(CO)12(0.30 g, 0.47 mmol) in refluxing xylene for 10 h.After removal of solvent under reduced pressure, the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2as eluent.The orange-red band was eluted and collected.After vacuum removal of the solvents from the above eluate, the residue was recrystallized from n-hexane/CH2Cl2at room temperature to give complex 2 as reddishbrown crystals (yield: 0.343 g, 37.2%).M.p.193～194 ℃.Anal.Calcd.for C36H36N2O4Ru2: C, 56.68; H, 4.76; N, 3.67%.Found: C, 55.31; H, 4.97; N, 3.46%.1H NMR (500 MHz, CDCl3): 1.87～1.95 (m, 24H, Me), 3.78 (s, 4H, CH2), 7.10 (m, 2H, C5H4N), 7.18～7.20 (m, 4H, C5H4N), 8.54 (d, J = 8.00 Hz, 2H, C5H4N).IR(vCO, cm-1): 1739(s), 1930 (s).

2.4 Reaction of ligand precursor with Mo(CO)6in xylene

By using a similar procedure to that described above, ligand precursor C5Me4CH2(C5H4N) (0.42 g, 2.0 mmol) reacted with Mo(CO)6(0.528 g, 2.0 mmol) in refluxing xylene for 10 h.After removal of solvent under reduced pressure, the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2as eluent.The brick-red band was eluted and collected.After vacuum removal of the solvents from the above eluate, the residue was recrystallized from n-hexane/CH2Cl2at room temperature to give complex 3 as reddishbrown crystals (yield: 0.343 g, 19.3%).M.p.151～152 ℃.Anal.Calcd.for C36H36N2O6Mo2: C, 55.11; H, 4.62; N, 3.57%.Found: C, 55.38; H, 4.31; N, 3.78%.1H NMR (500 MHz, CDCl3): 1.92～2.06 (m, 24H, Me), 3.80 (s, 4H, CH2), 7.33 (t, J = 7.79 Hz, 4H, C5H4N), 7.80 (s, 2H, C5H4N), 8.55 (d, J = 8.12 Hz, 2H, C5H4N).IR (vCO, cm-1): 1871 (s), 1890 (s), 1927 (s).

2.5 Crystal structure determination

Crystals of complexes 1～3 suitable for X-ray diffraction were isolated from the slow evaporation of hexane-dichloromethane solution.Data collection was performed on a Bruker SMART APEX()Ⅱ-CCD detector with graphite-monochromated MoKa(l = 0.71073 ?) radiation using the φ/ω scan technique.The structures were solved by directmethods and refined by full-matrix least-squares procedures based on F2using the SHELX-97 program system.All non-H atoms were refined with anisotropic displacement parameters.Hydrogen atoms were included in calculated positions riding on the parent atoms and refined with fixed thermal parameters.Crystallographic data and experimental details of the structure determinations are given in Table 1.Selected bond lengths and bond angles are listed in Table 2.

Table 1.Crystal Data and Structure Refinement Parameters for Complexes 1～3

Table 2.Selected Bond Distances (?) and Bond Angles (o) for Complexes 1～3

3 RESULTS AND DISCUSSION

3.1 Reactions of ligand precursor

C5Me4CH2(C5H4N) with Fe(CO)5and Ru3(CO)12

Reactions of ligand precursor C5Me4CH2(C5H4N) with Fe(CO)5and Ru3(CO)12in refluxing xylene afforded the corresponding products 1 (37.2%) and 2 (37.2%), respectively (Schemes 1 and 2).

Scheme 1.Synthesis of complex 1

Scheme 2.Synthesis of complex 2

Based on their1H NMR and IR spectra, 1 and 2 were assigned as the normal M-M single-bonded dinuclear complexes.IR spectra of complexes 1 and 2 showed similar patterns and display characteristic absorption peaks for strong CO in the terminal v(CO) region and bridged v(CO) region, indicating that there are two terminal CO ligands which have the same chemical environment and two bridging CO ligands which have the same chemical environment, too.In their1H NMR spectra, 1 and 2 displayed one or two groups of peaks for the four methyl protons, one singlet for the methylene protons and three groups of peaks for the pyridyl protons.

Slow evaporation of the solvent from the complexes in hexane-CH2Cl2solution gave single crystals 1 and 2 suitable for X-ray diffraction.For the pyridyl side-chain-functionalized cyclopentadienyl ligand, the nitrogen atom can act as a good two-electron donor site and can coordinate to a variety of metals, for example, thermal treatment of the pyridyl side-chain-functionalized cyclopentadiene with Ru3(CO)12and Fe(CO)5could give different intramolecular C–H activated products besides the normal dinuclear metal complexes[16].Although we used heptane or toluene as the solvent, the pyridyl group only acted as substituent and did not coordinate with the Ru and Fe atoms, and the preconceived C–H activated products were not obtained yet.

The crystal structures of complexes 1 and 2 are shown in Figs.1 and 2.Complexes 1 and 2 are normal dinuclear metal carbonyl complexes.

The structures of complexes 1 and 2 are similar; both have two types of carbonyl ligands, namely, terminal and bridging, in their molecular structures.Both structures are the symmetrical (trans) isomers.The two cyclopentadienyl ring planes and pyridyl ring planes are parallel, respectively.For complex 1,the Fe–Fe bond distance is 2.5551(10) ?, which is slightly longer than those in analogous complexes trans-[CpFe(CO)(μ-CO)]2(2.490 ?)[17]and [(η5-C5Me4H)Fe(CO)(μ-CO)]2(2.5480(9) ?)[18], due to the steric effect of the substituent of cyclopentadienyl ring.But the Fe–Fe bond distance is slightly shorter than that reported for trans-[(η5-C5Me4Ph)Fe(CO)(μ-CO)]2(2.5632(6) ?) and trans-[(η5-C5Me4PhOMe)Fe(CO)(μ-CO)]2(2.5630(8) ?)[19], indicating that the steric effect of the ring substituent is smaller than that of the phenyl.For complex 2, the Ru–Ru bond distance (2.7481(12) ?) is slightly longer than that in trans-[η5-CpRu(CO)(μ-CO)]2(2.735(2) ?)[20], which may be attributed to the steric effect of pyridyl and four methyl groups.The Ru–Ru bond distance is slightly shorter than that for trans-{[η5-C5Me4Ph]Ru(CO)(μ-CO)}2(2.7769(4) ?) and trans-{[η5-C5Me4C6H4-4-OCH3]Ru(CO)(μ-CO)}2(2.7701(6) ?)[19], which indicates smaller steric hindrance of pyridyl than those of methyl and methoxy groups at the 4-position of phenyl.The distance is comparable to those found in other substituted cyclopentadienyl ruthenium carbonyl dimers.

Fig.1.Molecular structure of complex 1.Ellipsoids correspond to 30% probability.Hydrogen atoms are omitted for clarity

Fig.2.Molecular structure of complex 2.Ellipsoids correspond to 30% probability.Hydrogen atoms are omitted for clarity

3.2 Reactions of ligand precursors C5Me4CH2(C5H4N) with Mo(CO)6

To develop a wider generality of the reactions of type, we further introduced Mo(CO)6, carried out by similar reaction conditions in the refluxing xylene, to afford product 3 (Scheme 3).

Reactions of ligand precursor C5Me4CH2(C5H4N) (1) with Mo(CO)6in refluxing xylene afforded the corresponding product 3 (19.3%).Based on its1H NMR and IR spectra, 3 was assigned as the normal Mo-Mo single bonded dinuclear complex.The IR spectra of complex 3 exhibited only terminal carbonyl bands (1871, 1890, 1927 cm-1).The1H NMR spectra of 3 displayed one group multiple for the four methyl protons.In addition, complex 3 exhibited one group singlet for the methylene protons and three groups of peaks for pyridyl protons, indicating the symmetrical structures in solution.

Scheme 3.Synthesis of complex 3

Slow evaporation of the solvent from the complexes in hexane-CH2Cl2solution gave singlecrystal 3 suitable for X-ray diffraction.The singlecrystal X-ray determination of complex 3 is presented in Fig.3.It consists of two [C5Me4CH2(C5H4N))Mo(CO)3] units, and each of the molybdenum atoms is coordinated with a Cp ligand in an h5mode and three terminal carbonyl ligands.It has a trans conformation linked by a Mo–Mo bond, lying on a crystallographic inversion.Two independent but chemically equivalent molecules appear in the unit cell.The fifth coordination position is occupied by a cyclopentadienyl ring that is essentially planar.The structural parameters of complex 3 are similar to those in [η5- C5Me4RMo(CO)3]2, and Mo–Mo bond distance for 3 is 3.3045(9) ?, which is comparable to other metalmetal bond distances found for analogous derivatives of the type [η5-C5Me4RMo(CO)3]2(R = Ph-Me, 3.283 ?; R = Ph-OMe, 3.307 ?)[19].However, the Mo–Mo bond distance of 3 is longer than that of trans-[η5- C5H5Mo(CO)3]2(3.235(1) ?)[21]and [(η5-C5H4iPr)Mo(CO)3]2(3.222(5) ?)[22], due to the bulky steric effect of the pyridyl and four methyl groups.

Fig.3.Molecular structure of complex 3.Ellipsoids correspond to 30% probability.Hydrogen atoms are omitted for clarity

4 CONCLUSION

In summary, three dinuclear metal carbonyl complexes were synthesized by the reactions of pyridyl substituted tetramethylcyclopentadiene with Fe(CO)5, Ru3(CO)12and Mo(CO)6in refluxing xylene, respectively.The results clearly revealed the coordination modes of these cyclopentadienyl metal complexes are η5and the N atom of pyridine did not coordinate to the metal atoms.The pyridylsubstituted cyclopentadienyl ligand is trans in the dimeric structures in the solid state.Substituent group variation displays some influence on the M–M bond length of dinuclear tetramethylcyclopentadienyl metal carbonyl complexes.

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10.14102/j.cnki.0254-5861.2011-0639

14 January 2015; accepted 9 April 2015 (CCDC 921932, 921931 and 921933 for complexes 1～3, respectively)

① This work was financially supported by the National Natural Science Foundation of China (No.21372061), Natural Science Foundation of Hebei Province (Nos.B2013205025 and B2014205018), and the Key Research Fund of Hebei Normal University (No.L2012Z02)

② Corresponding author.Doctor, majoring in organometallic chemistry.E-mail: linjin64@126.com