Synlett 2004(10): 1789-1793  
DOI: 10.1055/s-2004-829548
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis and Application of Complexes of a Novel Chiral Diphenylphosphino-Functionalized N-Heterocyclic Carbene

Erhard Bappert, Günter Helmchen*
Organisch-Chemisches Institut der Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49(6221)544205; e-Mail: g.helmchen@urz.uni-heidelberg.de.;
Further Information

Publication History

Received 14 April 2004
Publication Date:
15 July 2004 (online)

Abstract

Complexes of the ligand (S,S)-1-(2-diphenylphosphanyl-naphtalen-1-yl)-3-(2-isopropyl-phenyl)-4,5-diphenyl-imidazolin-2-ylidene, a representative of a new class of chiral ligands, were obtained via a short route starting from (S,S)-1,2-diphenyl-ethylen-1,2-diamine; a Rh-complex was found to promote catalytic hydrogenation of α,β unsaturated esters with up to 99% ee.

15

Physical data of (S,S)-4: mp 195-197 °C; [α]D 24 -297 (c 1.13, CHCl3). 1H NMR (300 MHz, CDCl3) for the major isomer of (S,S)-4: δ = 0.93 (d, J = 6.6 Hz, 3 H, CH3), 1.02 (d, J = 6.6 Hz, 3 H, CH3), 3.45 [sept, J = 7.0 Hz, 1 H, CH(CH3)2], (dd, J = 13.6 Hz, J PH = 5.2 Hz, 1 H, CHN), 6.57 (d, J = 13.6 Hz, 1 H, CHN), 6.92-7.79 (m, 27 H, CHAr), 7.82 (d, J = 8.5 Hz, 1 H, CHNaph), 7.99 (d, J = 7.7 Hz 1 H, CHNaph), 8.11 (br s, 1 H, NCHN), 8.54 (d, J = 8.8 Hz, 1 H, CHNaph). 13C NMR (125.8 MHz, CDCl3) for the major isomer of (S,S)-4: δ = 23.60, 24.96, 27.70, 74.97, 79.00 (d, J = 14.1 Hz), 124.36, 126.18, 126.88, 127.26, 127.54, 128.54, 128.87, 128.94, 129.11, 129.13, 129.24 (d, J = 6.6 Hz), 129.39 (d, J = 7.5 Hz), 129.56, 129.72, 129.77, 129.98, 130.08, 130.15, 130.26, 130.66 (d, J = 4.7 Hz), 130.96, 131.42, 132.23, 132.38 (d, J = 14.1 Hz), 132.68 (d, J = 18.8 Hz), 133.30 (d, J = 19.8 Hz), 133.76 (d, J = 18.8 Hz), 134.05 (d, J = 6.6 Hz), 134.30, 134.73 (d, J = 5.7 Hz), 136.41 (d, J = 25.4 Hz), 144.35, 157.38. 31P NMR (121.5 MHz, CDCl3): δ = -19.52 (s, minor isomer, 13%), -21.80 (s, major isomer, 87%). HRMS (FAB+, direct insert): m/z calcd for C46H40N2P [M - BF4]+: 651.2929. Found: 651.2936.

18

X-ray single crystal structure determination of compound 5: colorless crystal (polyhedron), dimensions 0.12 × 0.17 × 0.2 mm3, crystal system orthorhombic, space group P21212, Z = 2, a = 16.730 (2) Å, b = 22.902 (3) Å, c = 11.2472 (15) Å, V = 4309.3 (10) Å3, ρ = 1.303 g/cm3, T = 200(2) K, θ max = 23.91 deg, radiation MoKα, λ = 0.71073 Å, 0.3 deg ω-scans with CCD area detector, covering a whole sphere in reciprocal space, 30565 reflections measured, 6649 unique [R(int) = 0.0893], 5558 observed [I>2σ(I)], intensities were corrected for Lorentz and polarization effects, an empirical absorption correction was applied using SADABS (program SADABS V2.03 for absorption correction; G. M. Sheldrick, Bruker Analytical X-ray-Division, Madison, Wisconsin 2001) based on the Laue symmetry of the reciprocal space, µ = 0.56mm-1, structure solved by direct methods and refined against F 2 with a Full-matrix least-squares algorithm using the SHELXTL-PLUS (5.10) software package (software package SHELXTL V5.10 for structure solution and refinement, G. M. Sheldrick, Bruker Analytical X-ray-Division, Madison, Wisconsin 1997), 525 parameters refined, hydrogen atoms were treated using appropriate riding models, Flack absolute structure parameter 0.07 (6), goodness of fit 1.21 for observed reflections, final residual values R1 (F) = 0.077, wR2 (F2) = 0.167 for observed reflections, residual electron density -1.14 to 1.10 eÅ-3. CCDC 236937 contains the supplementary crystallographic data for this structure. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html [or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 (1223)336033; e-mail: deposit@ccdc.cam.ac.uk].

22

With PhCF3, n-hexane, MeOH, and THF enantioselectivities were lower.

23

Representative Procedure for Catalytic Hydrogenation: Preparation of (R)-8: An autoclave was charged with dimethyl itaconate (158 mg, 1.00 mmol), (S,S)-6 (0.9 mg, 1.0 µmol) and CH2Cl2 (15 mL). The autoclave was then sealed and pressurized to 30 bar of H2. The reaction mixture was stirred for 20 h at r.t. The solution was passed over a short plug of silica gel with CH2Cl2 as eluent. After evaporation of the solvent, 2-methyl-succinic acid dimethyl ester was obtained in quantitative yield. The ee value was determined to be 98.2% ee by GC on a chiral phase (analytical data cf. Table [1] ).