Racemic and chiral expanded salen-type complexes derived from biphenol and binaphthol: Salbip and salbin Joseph M. Grill, Joseph H. Reibenspies, Stephen A. Miller * Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, United States Received 3 March 2005; revised 18 March 2005; accepted 18 March 2005 Available online 12 May 2005 Abstract The reaction of 2-fluoronitrobenzene with 2,2 0 -biphenol or (R)-binaphthol, followed by reduction and subsequent reaction of the resulting diamine with two equivalents of a salicylaldehyde, affords expanded salen-type ligands having backbones based on biphe- nol or binaphthol: salbipH 2 ,(R)-salbinH 2 and (R)-salbin(t-Bu) 4 H 2 . Deprotonation of these ligands with sodium methoxide or potas- sium hydride, followed by metallation with M(OAc) 2 (M = Mn, Co, Ni, or Cu), affords the corresponding metal complexes in good yield (61–85%). The species containing Mn, Co, and Ni all have distorted octahedral geometry, as determined by X-ray crystallog- raphy. The ethereal oxygen atoms occupy two coordination sites with metal–oxygen distances ranging from 2.19 to 2.36 A ˚ . The imine nitrogen atoms are trans to each other in the solid state, an impossible geometry in traditional salen-type complexes. The spe- cies containing Cu are distorted square planar and show much longer metal–ethereal oxygen distances ranging from 2.79 to 3.22 A ˚ . The manganese complexes are competent catalysts for the epoxidation of olefins. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Salen; Catalytic epoxidation; R-binaphthol; 2,2 0 -Biphenol; Chiral 1. Introduction The salen ligand is a versatile, widely used ligand for homogeneous transition metal mediated catalysis [1–11]. The simple salen ligand is synthesized by the condensa- tion of two equivalents of salicylaldehyde with one equivalent of ethylene diamine (Scheme 1) [12]. Transi- tion metal complexes of salen have been known since at least 1931 [12–15], but the most intense investigations have occurred since chiral variants were first applied to asymmetric catalysis in the early 1990s [16,17]. Modified salen complexes have served as catalysts in varied reac- tions such as asymmetric epoxidation [2], copolymeriza- tion of carbon dioxide with epoxides [5,6], and hydrolytic kinetic resolution of racemic epoxides [18,19], depending on the metal employed. Jacobsen and coworkers [17,20,21] reported the syn- thesis of a very successful chiral variant of the salen ligand (Scheme 1). The corresponding manganese (III)- based catalyst is useful for the epoxidation of cis-disub- stituted olefins in the presence of commercial bleach [2]. Overall the asymmetric epoxidation of cis-olefins with JacobsenÕs catalyst is effective but the optimized condi- tions rely on a large catalyst loading (6 mol%) and the use of 4-phenylpyridine-N-oxide as an additive in order to obtain high enantiomeric excesses (eeÕs). Gilheany and coworkers [22–25] reported the synthesis of a series of chiral chromium–salen complexes capable of epoxi- dizing trans-disubstituted olefins with poor to good eeÕs, but the system suffers from limited substrate toler- ance and requires high catalyst loading (10 mol%). Fur- thermore, it requires an expensive additive and an expensive oxidant (PhIO). The eeÕs obtained by Gilhe- any range from 10% to 92% depending on the catalyst, the conditions, and the substrate, and the isolated yields 0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2005.03.034 * Corresponding author. Tel.: +979 8452543; fax: +979 8459452. E-mail address: samiller@mail.chem.tamu.edu (S.A. Miller). Journal of Organometallic Chemistry 690 (2005) 3009–3017 www.elsevier.com/locate/jorganchem