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Synthesis 2006(6): 1040-1044  
DOI: 10.1055/s-2006-926361
PAPER
© Georg Thieme Verlag Stuttgart · New York

Steric Variations between the Synthesis of a Stable Chiral C 2-Symmetric Diimidazolidinylidene and an Electron-Rich Tetraazafulvalene

Colin Marshall*, Mark F. Ward, Janet M. S. Skakle
Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen, AB24 3UE, Scotland, United Kingdom
Fax: +44(1224)272921; e-Mail: c.marshall@abdn.ac.uk;
Further Information

Publication History

Received 14 October 2005
Publication Date:
27 February 2006 (online)

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Abstract

C 2-Symmetric electron-rich olefin dimers and imidazolidinylidene ligands with a 2,2-dimethyl-1,3-dioxolane backbone were synthesised and characterised. The steric protection of the carbene dictates which product is obtained.

Key words

electron-rich olefin dimer - imidazolidinylidene - chiral - C 2-symmetric

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Crystallographic data (excluding structure factors) for the structure in this paper were deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 273128, 273129 and 273130. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif or on application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK. Crystal Data for 6a (CCDC 273128 and 273129): Empirical formula C31H42N4O2S2, formula weight 566.81, temperature 296 (2) K, wavelength 0.71073 Å, monoclinic, space group P21. Unit cell dimensions a = 7.7147 (4) Å, b = 18.6723 (8) Å, c = 11.1002 (5) Å, β = 104.461 (2)°, V = 1548.34 (13) Å3, Z = 2, Dc = 1.216 Mg m-3, absorption coefficient 0.205 mm-1, F(000) = 608, crystal size 0.30 × 0.08 × 0.05 mm. Theta range for data collection 1.89-24.99°, index ranges -9 ≤ h ≤ 8, -18 ≤ k ≤ 22, -13 ≤ l ≤ 13, reflections collected 10775, unique reflections 2812 [R int = 0.0940], completeness to θ max (32.63°) = 99.9%, max. and min. transmission 0.9280 and 0.8000, refinement method full-matrix least-squares on F2. Ordered Model: Data/restraints/parameters 2812/1/360, goodness-of-fit on F2 = 0.811, final R indices [I > 2σ(I)], R1 = 0.0412, wR2 = 0.0624, R indices (all data), R1 = 0.0993, wR2 = 0.0727, absolute structure parameter 0.00(9), largest diff. peak and hole 0.207 and -0.169 e Å-3. Disordered Model: Data/restraints/parameters 2812/1/381, goodness-of-fit on F2 = 0.791, final R indices [I > 2σ(I)], R1 = 0.0372, wR2 = 0.0464, R indices (all data), R1 = 0.0956, wR2 = 0.0547, absolute structure parameter -0.02 (7), largest diff. peak and hole 0.132 and -0.137 e Å-3. Two of the methyl groups (numbered C-16, C-17) were found to have very high Ueq values. These could be split to give disorder over the two sites. Whilst this significantly improved wR2, one of the methyl groups (C-16) still had high Ueq values and the data/parameter ratio was worsened. Both models, therefore, have their merits and data for both were deposited.

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Crystal data of compound 6b (CCDC 273130): Empirical formula C37H54N4O2S2, formula weight 650.96, temperature 295 (2) K, wavelength 0.71073 Å, monoclinic, space group P21. Unit cell dimensions a = 13.5162 (13) Å, b = 6.9703 (6) Å, c = 21.051 (2) Å, β = 102.897 (2)°, V = 1933.2 (3) Å3, Z = 2, Dc = 1.118 Mg m-3, absorption coefficient 0.172 mm-1, F(000) = 704, crystal size 0.80 × 0.10 × 0.10 mm. Theta range for data collection 1.98-32.63°, index ranges -10 ≤ h ≤ 20, -10 ≤ k ≤ 10, -31 ≤ l ≤ 29, reflections collected 18951, unique reflections 7507 [R int = 0.1700], completeness to θ max (32.63°) = 99.1%, max. and min. transmission 0.9830 and 0.8721, refinement method full-matrix least-squares on F2, data/restraints/parameters 7507/1/416, goodness-of-fit on F2 = 0.653, final R indices [I > 2σ(I)], R1 = 0.0487, wR2 = 0.0758, R indices (all data), R1 = 0.3135, wR2 = 0.1151, absolute structure parameter 0.12 (9), largest diff. peak and hole 0.155 and -0.163 e Å-3.