Journal of the Korean Chemical Society (대한화학회지)

Korean Chemical Society (대한화학회)
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Synthesis and Characterizations of a Novel Tri-Osmium Carbonyl Boride Cluster (μ-H)2Os3(CO)9(μ-BH2CHC6H5))

새로운 트리오스뮴 붕소 클러스터 (μ-H)2Os3(CO)9(μ-BH2CHC6H5))의 합성 및 그 특성 연구

  • 류택형 (명지대학교 이과대학 화학과) ;
  • 정장훈 (명지대학교 이과대학 화학과)
  • Published : 2005.02.20
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Abstract

Keywords

EXPERIMENTAL SECTION

General Data

All reactions were performed under inert-atmosphere conditions. Standard vacuum line and inertatmosphere techniques were employed.6 Toluene was dried with P2O5, distilled, and stored in a sealed flask. (μ-H)2Os3(CO)10 was prepared according to published procedure.7 13CO (Isotec, 99.99%) was used without further purification. Thin layer chromatography plates (J.T. Baker, 250 μm, plasticbacked) were heated in a 45 ℃ oven for 24 h before use. IR spectrum was obtained with a Mattson Polaris FT-IR spectrometer. 1H, 11B, and 13C NMR spectra were obtained using a bruker AM-250 and WH-500 spectrometers. NMR chemical shifts are referenced to Si(CH3)4 (1H, d=0.00 ppm) and BF3OEt2 (11B, d=0.00 ppm). FAB mass spectrum was obtained on VG 70-250s mass spectrometer.

Preparation of (μ-H)2Os3(CO)9(μ-BH2CHC6H5)

(μ-H)3Os3(CO)9(μ3-BCO) (310 mg, 0.34 mmole) was added to a 100 mL flask equipped with a Kontes vacuum adaptor and then toluene (30 mL) was condensed into the flask at -78 ℃. The solution was stirred at 110 ℃ for 12 hours. Then solvent was removed by means of dynamic high vacuum leaving a brown solid in the flask. The product was separated by preparative TLC on 2 mm silica using a mixed solvent toluene/hexane as an eluent. A pale yellow band (Rf=0.50) in the preparative TLC on silica above was identified and characterized as (μ-H)2Os3(CO)9(μ-BH2CHC6H5) (15mg, 0.0011 mmole, 5% yield based on (μ-H)3Os3(CO)9(μ3-BCO). 1H NMR (CDCl3, 30 ℃) 7.35 (s), 7.23 (s), 7.14 (s), 2.35 (s), -12.1 (br), -12.2 (br), -19.7 (s) ppm. 1H{11B} NMR (CDCl3, 30 ℃) 7.35 (s), 7.23 (s), 7.14 (s), 2.35 (s), -12.1 (s), -12.2 (s), -19.7 (s) ppm. 11B NMR (CDCl3, 30 ℃) 36.1 (br) ppm. 11B{1H} NMR (CDCl3, 30 ℃) 36.1(s) ppm. 13C NMR (CDCl3, -40 and 30 ℃) 174.5 (d of d, JHC=16Hz), 172.4 (s), 168.0 (d, JHC=10Hz), 167.6 (s), 163.5 (s) 146.0 (br), 137.5 (s), 133.6 (d, JHC= 85Hz), 129.7 (d, JHC=191Hz), 127.8 (d, JHC=63Hz), 21.35 (d, JHC=50Hz) ppm. 13C{1H} NMR (CDCl3, -40 and 30 ℃) 174.5 (s), 172.4 (s), 168.0 (s), 167.6 (s), 163.5 (s) 146.0 (br), 137.5 (s), 133.6 (s), 129.7 (s) 127.8 (s), 21.35 (s) ppm. IR(νCO) 2101(m), 2077(s), 2070(s), 2022(s), 2015(s) cm−1. FAB mass spectrum calculated m/e 940, obs. m/e 942.

Preparation of 13CO enriched (μ-H)2Os3(CO)9-(μ-BH2CHC6H5)

Os3(CO)12 (41% 13CO) prepared by a published procedure8 was the starting point in the preparation of 13CO enriched (μ-H)2Os3(CO)9(μ-BH2CHC6H5). The enriched Os3(CO)12 was converted to H2Os3(CO)10 by hydrogenation of the Os3(CO)12. The H2Os3(CO)10 was converted to 13CO labeled (μ-H)3Os3(CO)9(μ3-BCO) by reacting it with B2H6. Thermolysis of the (μ-H)3Os3-(CO)9(μ3-BCO) by the procedure described above yielded 13CO labeled (μ-H)2Os3(CO)9(μ-BH2CHC6H5).

 

RESULTS AND DISCUSSIONS

Reaction of (μ-H)3Os3(CO)9(μ3-BCO) with toluene at 110 ℃ for 12 hours yielded a novel tri-osmium carbonyl boride cluster (μ-H)2Os3(CO)9(μ-BH2CHC6H5) in 5% yield based upon (μ-H)3Os3(CO)9(μ3-BCO) (reaction 1). The osmium cluster is an

Fig. 1.1H and 1H{11B} NMR spectra of (μ-H)2Os3(CO)9(μ-BH2CHC6H5).

air-stable solid at room temperature. However, it decomposes at 110 ℃. The cluster was characterized by 1H, 11B & 13C NMR spectroscopies at various temperatures from -40 to 30 ℃. 1H NMR spectrum at 30 ℃ shows a sharp singlet at -19.7 ppm and two broad signals at -12.1 and -12.2 ppm which are partially overlapped. The boron decoupled 1H{11B} NMR spectrum at 30 ℃ shows the reduction of the broad signals to two sharp singlets at the same chemical shifts as shown in Fig. 1. Generally, the signal of hydrogen bridging between boron and transition metal atom in 1H NMR spectrum is broad at room temperature due to coupling with boron atom and the signal in the boron decoupled 1H{11B} NMR spectrum is sharpened to be a singlet. Therefore these two signals can be assigned to two nonequivalent hydrogens which bridge between osmium and boron atoms and thus couple with a boron atom. This is consistent with the signal in 1H NMR spectrum of bridge hydrogens B-H-Os of tri-osmium carbonyl boride cluster H2Os3(CO)9BH3 previously reported. The slight difference between two chemical shift values shows that this molecule has asymmetric structure but two hydrogens have very close etectronic environments. 1H NMR spectrum at -40 ℃ consists of two distinct sharp signals at -12.1 and -12.2 ppm which show two different non-equivalent hydrogens. The sharp singlet at -19.7 ppm can be assigned to Os-H-Os bridge hydrogens. This chemical shift is a typical value for bridge hydrogen between osmium and osmium atoms. The integration of 1H NMR spectrum shows that the ratio of the intensity of the signals at -12.1, -12.2, and -19.7 ppm is 1:1:2. Therefore, the signal at -19.7 ppm can be assigned to two bridge hydrogens. 1H NMR spectrum at 30 ℃ does not show any broad signal at downfield which may be assigned to terminal hydrogen bonded to boron atom. However, it shows a singlet at 2.35 ppm assigned to aliphatic hydrogen bonded to carbon and three signals at 7.35, 7.23, and 7.14 ppm which are attributed to aromatic hydrogens. 11B NMR spectrum at 30 ℃ shows a broad signal at 36.10 ppm. This chemical shift, which is at a lower field than the resonance of typical trigonal boron compounds,9 as the manner of that seen for carbides in 13C NMR spectroscopy,10 suggests that this cluster has boridic character.11 The chemical shift in 11B NMR spectrum of transition metal boride is usually shown at the far downfield. For example, penta-osmium carbonyl boride cluster HOs5(CO)16B with an interstitial boron atom bonded to five osmium atoms has typical boridic nature. The value of the chemical shift of the cluster is 184.4 ppm. However, the chemical shift of this new cluster is not that far downfield. Therefore, 11B NMR spectrum suggests that the cluster should have a boron atom bonded to three osmium atoms. The proton decoupled 11B{1H} NMR spectrum at 30 ℃ shows a sharp signal. This means the cluster has a boron atom bonded to hydrogen atoms. Therefore, the signal can be assigned to boron which is bonded to hydrogen atoms which bridge osmium and boron atoms.

13C NMR spectrum of the tri-osmium borane cluster at room temperature is shown in Fig. 2. It consists of a quartet at 174.5, a doublet at 168.0, three singlets at 172.4, 167.6, and 163.5, a broad signal at 146.0, a singlet at 137.5, three doublets at 133.6, 129.7, 127.8, and 21.35 ppm. The five signals from 174.5 to 163.5 ppm are due to terminal carbonyls bonded to osmium atoms. The 13C NMR spectrum of the cluster at -40 ℃ shows no change of the chemical shifts, indicative of no rapid exchange of the terminal carbonyls. The proton decoupled 13C{1H} NMR spectrum of the cluster shows five singlets at the same chemical shifts. That is, it shows the reductions of the quartet to a singlet and the doublet to a singlet at the same chemical shifts, 174.5 and 168.2 ppm respectively. It suggests that the carbonyls couple with Os-H-Os bridge hydrogens. The ratio of five singlets at 174.5, 172.4, 168.0, 167.6, and 163.5 ppm in the proton decoupled 13C NMR spectrum is approximately 2 : 1 : 2 : 2 : 2. This cluster may have pseudo Cs symmetry with a tetrahedral Os3B core based on the spectra. The nine terminal carbonyls can be assigned based on the intensity and the characterization of the spectra as shown in Fig. 2. The quartet at 174.5 ppm reflecting coupling with two non-equivalent hydrogens can be assigned to two terminal carbonyls CO(5) which are trans to two hydrogens bridging osmium atoms. The singlet at 172.3 ppm can be assigned to carbonyl CO(2). The doublet at 168.0 ppm coupled with a hydrogen can be assigned to two carbonyls CO(3) which are trans to one hydrogen. The two singlets at 167.6 and 163.5 ppm can be assigned to two carbonyls CO(4) and two carbonyls CO(1), respectively, which do not have trans hydrogen. The broad signal at 146.0 ppm shows that the carbon couples with a boron atom and thus the signal can be assigned to an vinylidene carbon which is bonded to a boron, aliphatic carbon and osmium atoms. This chemical shift value is similar to that of the carbon atom bonded to boron and osmium atoms in (μ-H)3Os3(CO)9[(μ3-η2-C(OBC8H14)B(Cl)].12 Four signals from 137.5 to 127.8 ppm are due to aromatic carbons and a signal at 21.35 ppm to an aliphatic carbon. The singlet at 137.5 ppm can be assigned to a aromatic cabon which has no hydrogen. and three doublets at 133.6, 129.7, and 127.8 ppm, to aromatic cabons coupling with a hydrogen. The doublet at 21.35 ppm can be assigned to an aliphatic carbon coupling with a hydrogen.

Fig. 2.13C{1H} and 13C NMR spectra of (μ-H)2Os3(CO)9-(μ-BH2CHC6H5).

Fig. 3.FAB mass spectrum of (μ-H)2Os3(CO)9(μ-BH2CHC6H5).

The FAB mass spectrum of the cluster is shown in Fig. 3. The highest intensity peak in the parent envelope calculated for H10BC17O9Os3 is m/e=940 and the value found m/e=942. The sequential loss of the carbonyl ligands was observed in the mass spectrum. The parent envelope and the distribution of peak intensities in the envelope in general are in accord with those predicted for natural abundance isotope distribution. IR spectrum shows typical vibration absorbance for terminal carbonyls and aliphatic and aromatic carbon-hydrogen and carboncarbon bonds. The solid state structure of was not characterized by the single crystal X-ray diffraction analysis. However, the molecular structure of (μ-H)2Os3(CO)9(μ-BH2CHC6H5) may be proposed as shown in Fig. 4 based on 1H, 11B, and 13C NMR, infrared and FAB mass spectra. The molecule has pseudo Cs symmetry with a tetrahedral Os3B core where the boron atom is bonded to three osmium atoms. It has nine terminal CO’s of which three terminal CO’s are bonded to each osmium atom. A vinylidene carbon bonded by benzyl group is bonded to a boron and osmium atoms and the cluster has two B-H-Os bridge hydrogens and two Os-H-Os bridge hydrogens.

Fig. 4.Proposed molecular structure of (μ-H)2Os3(CO)9(μ-BH2CHC6H5).

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