ARTICLE DOI: 10.1002/zaac.200900485 Quinine-Derived Imidazolidin-2-imine Ligands: Synthesis, Coordination Chemistry, and Application in Catalytic Transfer Hydrogenation Sabina-Alexandra Filimon, [a] Cristian G. Hrib, [a] Sören Randoll, [a] Ion Neda, [b] Peter G. Jones, [a] and Matthias Tamm* [a] Keywords: Chirality; Ruthenium; Palladium; Nickel; Hydrogen transfer catalysis Abstract. Two new optically active bidentate N,N-ligands, DMIQCI (3a) and DMIQCD (3b), containing a quinuclidine core and an imida- zolidin-2-imine unit, were synthesized. The reaction of these ligands with [(η 5 -C 5 Me 5 )RuCl] 4 afforded the brick-red ruthenium(II) com- plexes [(η 5 -C 5 Me 5 )Ru(DMIQCI)Cl] (4) and [(η 5 -C 5 Me 5 )Ru- (DMIQCD)Cl] (5), which were used as catalysts in the transfer hydro- genation of acetophenone in boiling 2-propanol. The reactions of 3a Introduction During the past decades, intensive research into developing syntheses of chiral metal complexes for asymmetric catalysis has been carried out, which has induced an increased interest in the synthesis of new optically active ligands [1, 2]. In partic- ular, cinchona alkaloids and their derivatives, such as quinco- rine and quincoridine, which are relatively cheap and readily available in both pseudo-enantiomeric forms, were used [3]. These two pseudo-enantiomeric 1,2-amino alcohols, quinco- rine [QCI = (2S,4S,5R)-2-hydroxymethyl-5-vinyl-2-quinucli- dine] and quincoridine [QCD = (2R,4S,5R)-2-hydroxymethyl- 5-vinyl-2-quinuclidine] have four stereogenic centers, includ- ing the (1S)-configured bridgehead nitrogen atom [4]. The 1,2- diamines (1S,2S,4S,5R)-2-(aminomethyl)-5-vinyl-1-azabicy- clo[2.2.2]octane (1a) and (1S,2R,4S,5R)-2-(aminomethyl)-5- vinyl-1-azabi-cyclo[2.2.2]octane (1b) (Scheme 1), derived from QCI and QCD [5], respectively, are of special interest, because they seem to be promising building blocks, bearing three potential donor sites: the NH 2 group, a tertiary nitrogen atom and an olefinic C=C bond, which can be utilized for the synthesis of a variety of new ligands. These 1,2-diamines were previously used as ligands in iridium- and ruthenium-catalyzed asymmetric transfer hydrogenation of ketones [6, 7]. Other P,N- [8] and O,N-ligands [9] based on the quincorine and quin- * Prof. Dr. M. Tamm Fax: +49-531-391-5387 E-Mail: m.tamm@tu-bs.de [a] Institut für Anorganische und Analytische Chemie Technische Universität Carolo-Wilhelmina Hagenring 30 38106 Braunschweig, Germany [b] InnoChemTech GmbH Hagenring 30 38106 Braunschweig, Germany Z. Anorg. Allg. Chem. 2010, 636, 691–699 © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 691 and 3b with [(COD)PdCl 2 ] (COD = 1,5-cycloocta-diene) and with [(DME)NiBr 2 ] (DME = 1,2-dimethoxyethane) afforded the square-pla- nar palladium(II) complexes [(DMIQCI)PdCl 2 ] (7) and [(DMIQCD)PdCl 2 ] (8) or the tetrahedral nickel(II) complexes [(DMIQCI)NiBr 2 ](9) and [(DMIQCD)NiBr 2 ](10), respectively. The X-ray crystal structures of 4, 7, 9·THF, and 10 are reported. coridine framework and their coordination chemistry and ap- plications in homogeneous catalysis have been described. Scheme 1. Synthesis of the 1,2-diamines 1a and 1b together with the atom numbering scheme and stereocenters (*) in QCI and QCD. Poly(guanidine) ligands [10] have found exceptional applica- tions as superbasic proton scavengers [11] and as ligands for transition metal complexation [12], in particular in copper chemistry and dioxygen activation [13, 14]. Moreover, mono- and bis(guanidine) chelate ligands were used for the prepara- tion of homogeneous catalysts, e.g. for the ring-opening po- lymerization of lactides and for the atom transfer radical po- lymerization of styrene [15, 16]. Furthermore, it was shown that bis(imidazolin-2-imine) ligands (BL R ), which exhibit pro- nounced electron-donor properties, are able to stabilize coordi- native unsaturated 16-electron molybdenum and ruthenium half-sandwich complexes of the type [(η 7 -C 7 H 7 )Mo(BL R )] + ,