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Synthesis and Characterizations of a Novel Tri-Osmium Carbonyl Boride Cluster (μ-H)<sub>2</sub>Os<sub>3</sub>(CO)<sub>9</sub>(μ-BH<sub>2</sub>CHC<sub>6</sub>H<sub>5)</sub>)
Synthesis and Characterizations of a Novel Tri-Osmium Carbonyl Boride Cluster (μ-H)2Os3(CO)9(μ-BH2CHC6H5))
Journal of the Korean Chemical Society. 2005. Feb, 49(1): 121-124
Copyright © 2005, The Korean Chemical Society
  • Received : November 23, 2004
  • Published : February 20, 2005
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Taek-Hyoung Ryu
Jang-Hoon Chung

Abstract
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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 P 2 O 5 , distilled, and stored in a sealed flask. (μ-H) 2 Os 3 (CO) 10 was prepared according to published procedure. 7 13 CO (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. 1 H, 11 B, and 13 C NMR spectra were obtained using a bruker AM-250 and WH-500 spectrometers. NMR chemical shifts are referenced to Si(CH 3 ) 4 ( 1 H, d=0.00 ppm) and BF 3 OEt 2 ( 11 B, 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) 3 Os 3 (CO) 9 3 -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 (R f =0.50) in the preparative TLC on silica above was identified and characterized as (μ-H) 2 Os 3 (CO) 9 (μ-BH 2 CHC 6 H 5 ) (15mg, 0.0011 mmole, 5% yield based on (μ-H) 3 Os 3 (CO) 9 3 -BCO). 1 H NMR (CDCl 3 , 30 ℃) 7.35 (s), 7.23 (s), 7.14 (s), 2.35 (s), -12.1 (br), -12.2 (br), -19.7 (s) ppm. 1 H{ 11 B} NMR (CDCl 3 , 30 ℃) 7.35 (s), 7.23 (s), 7.14 (s), 2.35 (s), -12.1 (s), -12.2 (s), -19.7 (s) ppm. 11 B NMR (CDCl 3 , 30 ℃) 36.1 (br) ppm. 11 B{ 1 H} NMR (CDCl 3 , 30 ℃) 36.1(s) ppm. 13 C NMR (CDCl 3 , -40 and 30 ℃) 174.5 (d of d, J HC =16Hz), 172.4 (s), 168.0 (d, J HC =10Hz), 167.6 (s), 163.5 (s) 146.0 (br), 137.5 (s), 133.6 (d, J HC = 85Hz), 129.7 (d, J HC =191Hz), 127.8 (d, J HC =63Hz), 21.35 (d, J HC =50Hz) ppm. 13 C{ 1 H} NMR (CDCl 3 , -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(ν CO ) 2101(m), 2077(s), 2070(s), 2022(s), 2015(s) cm −1 . FAB mass spectrum calculated m/e 940, obs. m/e 942.
- Preparation of13CO enriched (μ-H)2Os3(CO)9-(μ-BH2CHC6H5)
Os 3 (CO) 12 (41% 13 CO) prepared by a published procedure 8 was the starting point in the preparation of 13 CO enriched (μ-H) 2 Os 3 (CO) 9 (μ-BH 2 CHC 6 H 5 ). The enriched Os 3 (CO) 12 was converted to H 2 Os 3 (CO) 10 by hydrogenation of the Os 3 (CO) 12 . The H 2 Os 3 (CO) 10 was converted to 13 CO labeled (μ-H) 3 Os 3 (CO) 9 3 -BCO) by reacting it with B 2 H 6 . Thermolysis of the (μ-H) 3 Os 3 -(CO) 9 3 -BCO) by the procedure described above yielded 13 CO labeled (μ-H) 2 Os 3 (CO) 9 (μ-BH 2 CHC 6 H 5 ).
RESULTS AND DISCUSSIONS
Reaction of (μ-H) 3 Os 3 (CO) 9 3 -BCO) with toluene at 110 ℃ for 12 hours yielded a novel tri-osmium carbonyl boride cluster (μ-H) 2 Os 3 (CO) 9 (μ-BH 2 CHC 6 H 5 ) in 5% yield based upon (μ-H) 3 Os 3 (CO) 9 3 -BCO) (reaction 1). The osmium cluster is an
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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 1 H, 11 B & 13 C NMR spectroscopies at various temperatures from -40 to 30 ℃. 1 H 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 1 H{ 11 B} NMR spectrum at 30 ℃ shows the reduction of the broad signals to two sharp singlets at the same chemical shifts as shown in . 1 . Generally, the signal of hydrogen bridging between boron and transition metal atom in 1 H NMR spectrum is broad at room temperature due to coupling with boron atom and the signal in the boron decoupled 1 H{ 11 B} 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 1 H NMR spectrum of bridge hydrogens B-H-Os of tri-osmium carbonyl boride cluster H 2 Os 3 (CO) 9 BH 3 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. 1 H 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 1 H 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. 1 H 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. 11 B 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 13 C NMR spectroscopy, 10 suggests that this cluster has boridic character. 11 The chemical shift in 11 B NMR spectrum of transition metal boride is usually shown at the far downfield. For example, penta-osmium carbonyl boride cluster HOs 5 (CO) 16 B 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, 11 B NMR spectrum suggests that the cluster should have a boron atom bonded to three osmium atoms. The proton decoupled 11 B{ 1 H} 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.
13 C NMR spectrum of the tri-osmium borane cluster at room temperature is shown in . 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 13 C 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 13 C{ 1 H} 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 13 C NMR spectrum is approximately 2 : 1 : 2 : 2 : 2. This cluster may have pseudo C s symmetry with a tetrahedral Os 3 B 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 . 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) 3 Os 3 (CO) 9 [(μ 3 2 -C(OBC 8 H 14 )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.
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13C{1H} and 13C NMR spectra of (μ-H)2Os3(CO)9-(μ-BH2CHC6H5).
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FAB mass spectrum of (μ-H)2Os3(CO)9(μ-BH2CHC6H5).
The FAB mass spectrum of the cluster is shown in . 3 . The highest intensity peak in the parent envelope calculated for H 10 BC 17 O 9 Os 3 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) 2 Os 3 (CO) 9 (μ-BH 2 CHC 6 H 5 ) may be proposed as shown in . 4 based on 1 H, 11 B, and 13 C NMR, infrared and FAB mass spectra. The molecule has pseudo C s symmetry with a tetrahedral Os 3 B 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.
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Proposed molecular structure of (μ-H)2Os3(CO)9(μ-BH2CHC6H5).
Acknowledgements
This work was supported by grant No. 2001-2-12200-001-2 from the Basic Research Program of the Korea Science & Engineering Foundation.
References
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