The Determination of Maximum Common Substructures by a Genetic Algorithm: Application in Synthesis Design and for the Structural Analysis of Biological Activity
✍ Scribed by Dr. Markus Wagener; Prof. Dr. Johann Gasteiger
- Publisher
- John Wiley and Sons
- Year
- 1994
- Tongue
- English
- Weight
- 483 KB
- Volume
- 33
- Category
- Article
- ISSN
- 0044-8249
No coin nor oath required. For personal study only.
✦ Synopsis
COMMUNICATIONS
stability of the p2-bridged ketenylidene ligand characterized by a strong IR stretching band in the same region as that of terminal metal-coordinated carbonyl groups suggest that metal surfaces or reduced metal oxides may lead more frequently than originally thought to surface-coordinated ketenylidene groups as intermediates or end products of the CO chemisorption process." 61 Thus the earlier suggestions[5, *, ''] that ketenylidene might be a surface-bonded species are considerably strengthened by these novel findings. IR-active =C=C=O sequences absorbing around 2100 cm-' were postulated for carefully dehydrated MgO exposed to carbon monoxide.[17J In agreement with the nucleophilic character of the x carbon atom in organic ketenes,['8J the zirconium(1v) complex 1 b reacts with substrates containing the >C=O group. With carbon dioxide, after appropriate workup, the p-0x0 derivative 2 was isolated and characterized by elemental analysis, 13C NMR spectroscopy, and mass spectrometry (protonated molecular ion: V I ; : = 1297). X-ray diffraction data on 2 show the compound to have a substantially similar structure to 1 b in which the p,-CCO group of 1 b is replaced by the p2-oxo ligand. The reaction of the 3C-labeled 1 b, [Zr,Cp,(02CNiPr2),(p3-O)(p2- 13C13CO)]. with acetone led, inter alia, to the same (p3-O)(p2-0) derivative as in the reaction with CO,, and to the compounds Me,C='3CH'3C(0)NiPr,, iPr,N'3C(0)'3CH3, and iPr2N'3C-(0)'3CH,C(OH)Me, detected by GC-MS, which clearly contain the ketenylidene fragment. Mesityloxide was found among the volatile products.
Experimental Procedure
All experiments were performed under an inert atmosphere of argon, unless otherwise stated. IR. 'H and 13C NMR spectra, and mass spectra (desorption chemical ionization with isobutane as the reagent gas) were measured with Perkin Elmer F T 1725X. Varian Gemini 200, Bruker AM 200, and Finnigan MAT 8400 double-focusing reverse-geometry instruments, respectively. Satisfactory elemental analyses were obtained for all compounds reported in this paper.
1 : Only the preparation of the compound with R = iPr is described in detail. The ethyl derivative was prepared analogously. A solution of [ZrCp,(CO),] (8.08 g, 29.1 mmol) and [Zr(O,CNiPr,),] (19.3 g. 28.9 mmol) in toluene (250 mL) was heated at reflux for 1.5 h. After cooling to room temperature, an 1R spectrum of the solution revealed a strong absorption band at 2013 cm-I . After filtration of some dark insoluble material and evaporation of about 150 mL of toluene under reduced pressure. a colorless crystalline solid precipitated, which was filtered off, washed with toluene (5 x 10 mL), and dried In vacuo at room temperature (8.67 8). The diamagnctic solid was identified as 1 b.