organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
recrystallization. Both of these factors are expected to be
highly relevant to possible use of the materials in both
industrial and laboratory settings.
ISSN 0108-2701
The catalyst studied in the current work is a typical example
of the class (Ahrendt et al., 2000), is commercially available,
and has been described as `an inexpensive, bench-stable solid
that is readily handled by experimentalists or automated
systems' (Beeson & MacMillan, 2005). We therefore selected
this compound for a full structural characterization, which is of
interest both to con®rm the reported molecular structure of
this material, and with a view to rationalizing its solid-state
properties, including particle morphology and ¯ow, solubility,
stability, etc. Synchrotron radiation was employed in order to
gain the best quality structural information from these weakly
scattering materials and to ensure that our study was not
biased in favour of solid forms which readily form single
crystals. A simpli®ed reaction scheme is given below.
Structural diversity in imidazolidinone
organocatalysts: a synchrotron and
computational study
Jonathan C. Burley,a* Ryan Gilmour,b Timothy J. Priorc
and Graeme M. Dayd
aSchool of Pharmacy, University of Nottingham, University Park, Nottingham
NG7 2RD, England, bETH Zurich, Swiss Federal Institute of Technology,
È
Laboratorium fur Organische Chemie, ETH Honggerberg, Wolfgang-Pauli-Strasse 10,
È
È
CH-8093 Zurich, Switzerland, cDepartment of Chemistry, University of Hull,
È
Cottingham Road, Kingston-upon-Hull HU6 7RX, England, and dThe University
Chemical Laboratory, Lensfield Road, Cambridge CB2 1EW, England
Correspondence e-mail: jonathan.burley@nottingham.ac.uk
Received 17 August 2007
Accepted 17 October 2007
Online 14 December 2007
(S)-1-(Methylaminocarbonyl)-3-phenylpropanaminium chloride
(S2ÁHCl), C10H15N2O+ÁCl , crystallizes in the orthorhombic
space group P212121 with a single formula unit per asymmetric
unit. (5R/S)-5-Benzyl-2,2,3-trimethyl-4-oxoimidazolidin-1-ium
chloride (R3 and S3), C13H19N2O+ÁCl , crystallize in the same
space group as S2ÁHCl but contain three symmetry-indepen-
dent formula units. (R/S)-5-Benzyl-2,2,3-trimethyl-4-oxoimi-
dazolidin-1-ium chloride monohydrate (R4 and S4),
C13H19N2O+ÁCl ÁH2O, crystallize in the space group P21 with
a single formula unit per asymmetric unit. Calculations at the
B3LYP/6±31G(d,p) and B3LYP/6±311G(d,p) levels of the
conformational energies of the cation in R3, S3, R4 and S4
indicate that the ideal gas-phase global energy minimum
conformation is not observed in the solid state. Rather, the
effects of hydrogen-bonding and van der Waals interactions in
the crystal structure cause the molecules to adopt higher-
energy conformations, which correspond to local minima in
the molecular potential energy surface.
Comment
A number of research groups have reported on the utility of
chiral imidazolidinone catalysts for a range of enantioselective
organic reactions (Ahrendt et al., 2000; Wilson et al., 2005;
Paras & MacMillan, 2001; Jen et al., 2000; Marigo et al., 2005;
Kunz & MacMillan, 2005; Beeson & MacMillan, 2005; Brochu
et al., 2004). Several reviews of the ®eld of organocatalysis
exist (AlmasËi et al., 2007; Bolm et al., 2005; Gaunt et al., 2007;
Tsogoeva, 2007; List, 2006). Enantiomeric excesses greater
than 90% are regularly achieved in relatively high yielding
reactions that are dif®cult to accomplish by other means.
However, there are to date very few structural studies of these
materials, and no reports of their stability to storage or
S2ÁHCl
[(S)-1-(methylaminocarbonyl)-3-phenylpropan-
aminium chloride] adopts the orthorhombic space group
P212121 with a single formula unit per asymmetric unit
(Fig. 1a). All chemically intuitive hydrogen-bonding oppor-
tunities are satis®ed in the solid state (Fig. 2a). Sheets of
hydrogen bonds are formed, which lie parallel to the ab plane.
The chloride ion is hydrogen bonded by three protonated
amine groups [N16Á Á ÁCl1
= 3.094 (2), 3.149 (2) and
Ê
3.166 (2) A], and the carbonyl group of the amide unit is
hydrogen bonded to the amide H atom on an adjacent mol-
Ê
ecule [N11Á Á ÁO10 = 3.018 (3) A]. The hydrophobic (phenyl)
o10 # 2008 International Union of Crystallography
DOI: 10.1107/S0108270107051396
Acta Cryst. (2008). C64, o10±o14