王 娜 馬志宏 韓占剛 林 進＊, 鄭學忠＊,

(1河北師范大學化學與材料科學學院,石家莊 050024)

(2河北醫(yī)科大學基礎(chǔ)醫(yī)學院,石家莊 050017)

0 Introduction

Cyclopentadienyl metal complexes have been extensively investigated since ferrocene has been discovered.Replacement of the hydrogen atoms by other substituents alters both the steric and electronic influences of the η5-cyclopentadienyl ring,resulting in differing reactivity and stability of the substituted cyclopentadienyl metal complexes[1-3].Especially for metallocene polymerization catalysts,the steric and electronic effects of cyclopentadienyl ring substituents have great influence on catalytic activity[4].Our team has been focusing on the synthesis of a series of cyclopentad-ienyl metal carbonyl complexes[5-8].The goal of the research described in this and subsequent papers is to investigate the reactivity of substituted cyclopenta-dienyl with molybdenum carbonyl and to obtain sufficient structural data by single-crystal X-ray diffraction in order to understand and hopefully to predictthe steric and electronic influences of cyclopentadienyl substituents on the molecular structures and reactions of the corresponding biscyclopentadienyl dinuclear metal carbonyl complexes.

1 Experimental

1.1 General procedures

Argon atmosphere protects all operations involving air-or moisture-sensitive compounds,using standard Schlenk techniques.

Diethyl ether,xylene,and n-hexane were freshly distilled from sodium/benzophenone ketyl under nitrogen prior to use.Methylene chloride was distilled over P2O5under nitrogen.The ligands(C5H5R)(R=nbutyl(1),benzyl(2),n-propyl(3),allyl(4))were synthesized according to the literature[9].Column chromatography was carried out on alumina column using dichloromethane and petroleum ether as eluent.

1H NMR spectrum was recorded on a Bruker AV 500 instrument,while IR spectrum was recorded as KBr pellets on a FT IR-8900 spectrometer.Elemental analysis was performed on a Vario EL Ⅲ analyzer.The structures of crystals were determined by Bruker Smart APEX diffractometer with graphite monochromated Mo Kα (λ=0.071 073 nm)radiation.The TGDTG measurements were carried out on a SDT Q600 V20.9 Build 20 thermogravimetric analyzer.

1.2 Synthesis of complexes 5～8

1.2.1 Synthesis of complex[(η5-C5H4nBu)Mo(CO)3]2(5)

A solution of ligand 1 (0.244 g,2.0 mmol)and Mo(CO)6(0.528 g,2.0 mmol)in 30 mL of xylene was refluxed for 12 h.After removal of solvent xylene,the residue was chromatographed on an alumina column using petroleum ether/CH2Cl2as eluent.The red band afforded complex 5 as red crystals (0.249 g,81.1%yield),m.p.103～105 ℃.Anal.Calcd.for C24H26Mo2O6(%):C,47.86;H,4.35.Found(%):C,47.83;H,4.31.1H NMR (500 MHz,CDCl3): δ:5.26～5.28 (m,4H,C5H4),5.47～5.61 (m,4H,C5H4),2.31 (t,J=8.0 Hz,4H,C5H4CH2),1.42～1.58(m,8H,(CH2)2),0.97(t,J=7.5 Hz,6H,CH3),IR(KBr,νCO,cm-1):1 939(s),1 913(s),1 888(s).

1.2.2 Synthesis of complexes 6,7,8

Using a procedure similar to that described above,the reactions of ligands 2～4 with Mo(CO)6in xylene refluxing 12 h afforded complexes 6～8 as red crystals in 72.6%,74.6%,69.2%yields,respectively.The complex 6:m.p.164 ～166 ℃ .Anal.Calcd.for C30H22Mo2O6(%):C,53.75;H,3.31.Found(%):C,53.71;H,3.29.1H NMR (500 MHz,CDCl3):δ:5.15～5.26(m,4H,C5H4),5.41～5.56(m,4H,C5H4),3.72(s,4H,C6H5CH2),7.37～7.45(m,10H,C6H5),IR(KBr,νCO,cm-1):1 944(s),1 908(s),1 888(s).The complex 7:m.p.113～114 ℃.Anal.Calcd.for C22H22Mo2O6(%):C,46.01;H,3.86.Found(%):C,45.98;H,3.85.1H NMR(500 MHz,CDCl3):δ:5.27～5.33(m,4H,C5H4),5.60～5.69(m,4H,C5H4),2.31(t,J=7.5 Hz,4H,CH2),1.57～1.63(m,4H,CH2),1.03(t,J=7.5 Hz,6H,CH3),IR(KBr,νCO,cm-1):1 951(s),1 915(s),1 892(s).The complex 8:m.p.149～150 ℃.Anal.Calcd.for C22H18Mo2O6(%):C,46.34;H,3.18;Found(%):C,46.31;H,3.17.1H NMR (500 MHz,CDCl3): δ:5.28～5.37(m,4H,C5H4),5.60～5.71 (m,4H,C5H4),2.31 (d,J=8.0 Hz,4H,CH2),2.02(d,J=6.0 Hz,4H,CH2),5.56～5.59(m,2H,CH),IR(KBr,νCO,cm-1):1 952(s),1 910(s),1 888(s).

1.3 Crystal structure determinations for complexes 5 and 6

Crystals suitable for X-ray analysis of complexes 5 (crystal size:0.45 mm×0.15 mm×0.11 mm)and 6(crystal size:0.48 mm ×0.42 mm ×0.05 mm)were grown from a CHCl2/hexane (2 ∶1,V ∶V)solution at room temperature.The Bruker Smart APEX diffractometer equipped with a Mo Kα (λ=0.071 073 nm)collect the data of the crystals.The structure was solved by direct method and refined by full-matrix least squares.All calculations were performed using the SHELX-97 program system.The crystal data and summary of X-ray data collection are presented in Table 1.

CCDC:883603,5;881472,6.

Table 1 Crystal structure parameters of complexes 5 and 6

2 Results and discussion

2.1 Synthesis of complexes 5～8

The reactions of the ligands (C5H5nBu,C5H5CH2C6H5,C5H5nPropyl,C5H5Allyl)with Mo(CO)6,refluxing in xylene for 12 h produced the corresponding Mo-Mo bonded dinuclear complexes(complex 5:81.1%,complex 6:72.6%,complex 7:74.6%,complex 8:69.2%)(Scheme 1).The solvent hexane/CH2Cl2(1 ∶2,V ∶V)evaporated slowly and produced the suitable single crystal.

Scheme 1 Synthesis of complexes 5～8

The IR spectra of dimolybdenum complexes all showed strong CO absorption peaks (complex 5 at 1 939(s),1 913(s),1 888(s)cm-1;complex 6 at 1 944(s),1 908(s),1 888(s)cm-1;complex 7 at 1 951(s),1 915(s),1 892(s)cm-1,complex 8 at 1 952(s),1 910(s),1 888(s)cm-1)in the terminal νCOregion,which consist with the facts that the complexes are similar structures.The1H NMR spectra of complexes 5～8 all showed two groups of peaks for the cyclopentadienyl(complex 5 at 5.26 ～5.28,5.47 ～5.61;complex 6 at 5.15～5.26,5.41～5.56;complex 7 at 5.27～5.33,5.60～5.69;complex 8 at 5.28～5.37,5.60～5.71).Meanwhile,the1H NMR spectrum of complex 5 showed four groups of peaks for n-butyl(CH3at 0.97,(CH2)2at 1.42～1.58,C5H4CH2at 2.31),the1H NMR spectrum of complex 6 showed two groups of peaks for benzyl(phenyl at 7.37 ～7.45 and PhCH2at 3.72),the1H NMR spectrum of complex 7 showed three groups of peaks for n-propyl (CH3at 1.03,CH2at 1.57～1.63,C5H4CH2at 2.31)and the1H NMR spectrum of complex 8 showed three groups of peaks for allyl(CH at 5.56～5.59,C5H4CH2at 2.31,CH22.02).

The results above agree with the single crystal X-ray diffraction analysis results.

2.2 Crystal structures of the complexes 5 and 6

The structures of complexes5 and 6 were presented in Fig.1 and 2,respectively.The selected bond lengths and angles are listed in Table 2.

Fig.1 Structure of complex 5 with the atomic numbering scheme

Fig.2 Structure of complex 6 with the atomic numbering scheme

Table 2 Selected bond distances(nm)and angles(°)for complexes 5 and 6

The crystal structures(Fig.1 and Fig.2)indicate that the complex 5 is monoclinic crystal system and the complex 6 is triclinic crystal system.Besides,the crystals have trans conformation with six terminal carbonyl ligands and Cp ring planes are parallel,respectively.Similar to the cyclopentadienyl analogue trans-[CpMo(CO)3]2,the complex 6 is Cisymmetry,while the complex 5 is C2h5symmetry.And the X-ray diffraction analyses also show that in complexes 5 and 6,every molybdenum atom is coordinated with a η5-cyclopentadienyl and three carbony ligands,respectively.The Mo-Mo single bond distance(complex 5:0.322 9 nm;complex 6:0.323 1 nm)is comparable to that in trans-[(η5-C5H4)CH(CH3)(C2H5)Mo(CO)3]2(0.322 3 nm)[8]and trans-[(η5-C5H4)CH(C2H5)(C2H5)Mo(CO)3]2(0.322 8 nm)[8],and is slightly shorter than trans-[(η5-C5Me4)benzylMo(CO)3]2(0.326 6 nm)[10]andtrans-[(η5-C5Me4)(CH2)3CH3Mo(CO)3]2(0.3286nm)[11].The distances between Mo and Cp ring are 0.2012 nm(complex 5)and 0.2011 nm(complex 6),respectively.The two distances are both shorter than that in[(η5-C5Me4)(CH2)3CH3Mo(CO)3]2(0.2027 nm)[11].The comparisons made above indicate that the number of cyclopentadienyl substituent have some effect on the metalmetal bond length.

2.3 Thermal property

Thermal stability studies were performed for the title complexes.The TG-DTG curves of complex 5 at heating rate of 1 ℃·min-1.The thermal decomposition process of complex 5 completes in four steps as is shown by the DTG curve.The TG curve indicates that the mass loss are 1.81%(0.316 3 mg),11.39%(1.996 mg),45.46% (7.965 mg),13.43% (2.353 mg),respectively.The first and second steps are considered to be the removal of 3 mmol of CO (theoretical loss is 13.946%).The third step is considered to be the removal of 1 mmol of C18H26O2(theoretical loss is 45.49%).And the fourth step is considered to be the removal of 3 mmol of CO(theoretical loss is 13.95%).It can also be seen from the IR spectrum of the intermediate for the last stage that the absorption valence band of the C=O group disappear.

The DSC curve clearly illustrates that there are four exothermic peaks with an enthalpy value of 53.43 J·g-1between 98.39～107.87 ℃,65.75 J·g-1between 170.60 ～202.51 ℃ ,11.17 J·g-1between 276.64 ～288.55 ℃ and 41.82 J·g-1between 590.26～643.81 ℃and two endothermic peaks with an enthalpy value of 65.75 J·g-1between 107.87～170.60 ℃,11.17 J·g-1between 202.51～276.64 ℃.

The TG-DTG curves of complex 6 at heating rate of 1 ℃·min-1.And the thermal decomposition process of complex 6 also completes in four steps as is shown by the DTG curve.The TG curve indicates that the mass loss are 9.601%(1.012 mg),20.36%(2.146 mg),11.74% (1.238 mg), 8.303% (0.8753 mg),respectively.The first step is considered to be the removal of 1 mmol of C5H4(theoretical loss is 9.547%).The second and third steps are considered to be the removal of 2 mmol of C7H7O(theoretical loss is 31.92%).And the fourth step is considered to be the removal of 2 mmol of CO (theoretical loss is 8.354%).According to the theory,there are four C=O groups in the intermediate for the last stage.But the IR spectrum of the intermediate for the last stage that the absorption valence band of the C=O group disappear,indicating that the complex 6 has been completely decomposed.

The DSC curve clearly illustrates that there are three exothermic peaks with an enthalpy value of 256.9 J·g-1between 162.21～176.11 ℃,111.8 J·g-1between 282.27 ～309.17 ℃ ,6.488 Jg-1between 382.28～391.10 ℃ and two endothermic peaks with an enthalpy value of 111.8 J·g-1between 176.11～282.27℃,6.488 J·g-1between 309.17～382.28 ℃.

3 Conclusions

In summary,four new dinuclear molybdenum carbonyl complexes have been synthesized by the reactions of cyclopentadiene derivatives with Mo(CO)6in refluxing xylene.The structures of complexes 5 and 6 have been characterized by the X-ray single crystal diffractometer.Comparing the structure of the type Cp*2Mo2(CO)6(where Cp*=substituted cyclopentadienyl ligand),we see that the ligands coordinate to the Mo center by η5mode and changing the substituents has someeffecton thecyclopentadienylcoordination ability and the Mo-Mo bond length.Thermal decomposition of complexes 5 and 6 occurs in four steps, performing endothermic and exothermic processes.The complexes 5 and 6 can be completely decomposed in the last stage.

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