DOI: 10.1002/adsc.200600315 Binaphthol-Based Diphosphite Ligands in Asymmetric Nickel- Catalyzed Hydrocyanation of Styrene and 1,3-Cyclohexadiene: Influence of Steric Properties JosWilting, a MichleJanssen, a ChristianMüller, a MartinLutz, b AnthonyL.Spek, b and Dieter Vogt a, * a Laboratory of Homogeneous Catalysis, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands Fax:(+ 31)-40-245-5054; e-mail: D.Vogt@tue.nl b Crystal and Structural Chemistry, Utrecht University, 3584 CH Utrecht, The Netherlands Received:June29,2006;Publishedonline:January8,2007 Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/. Abstract: A series of chiral (R)-binaphthol-based di- phosphite ligands with different substituents was pre- pared and applied in the asymmetric nickel-catalyzed hydrocyanation of styrene and 1,3-cyclohexadiene to investigate the influence of their steric properties. The optimum steric properties for the hydrocyana- tion reaction lie within a narrow window. With the optimized ligand, hydrocyanation of styrene gave full conversion (Subs/Ni = 100) with 49% ee, the TON was determined to be 600. Hydrocyanation of 1,3-cy- clohexadiene gave 50% conversion (Subs/Ni = 500) with an excellent ee of 86%. This demonstrates that high ees are not only accessible for vinylarenes but also for conjugated dienes in the asymmetric nickel- catalyzed hydrocyanation. Keywords: conjugated dienes; diphosphite ligands; hydrocyanation; hydrogen cyanide; nickel; vinylar- enes Introduction The production of adiponitrile from butadiene and hydrogen cyanide is an important homogeneous nickel-catalyzed process in industry. [1] Since the first report on asymmetric hydrocyanation of norborn- ACHTUNGTRENNUNG(adi)ene by Elmes and Jackson in 1979, [2] accounts on asymmetric hydrocyanation of carbon-carbon double bonds have occasionally appeared in literature. Table1 shows an overview regarding the asymmetric hydrocyanation of vinylarenes (Scheme 1). [3] RajanBabu and Casalnuovo discussed the impor- tance of the electronic properties of the ligand in the asymmetric hydrocyanation of MVN. [7] It was shown earlier that chelating p-acceptor ligands with a high binding affinity to Ni(0) can lead to very stable nickel bis-chelate complexes, decreasing the catalytic activi- ty. [9] All studies show that finding a suitable ligand system is rather tedious and (fine tuning) is necessary inordertoobtainbothhighconversionandhighenan- tioselectivity. Thus, we investigated a modular ligand suitable for modification on several positions. In this report we focus on chiral (R)-binaphthol-derived di- phosphite ligands with sterically different substituents Table 1. Literature overview of the asymmetric hydrocyana- tion of vinylarenes. Entry Substrate Temp[8C] Yield[%] ee [%] Ref. 1 Styrene 25 nd 65 [4] 2 Styrene 60 22 42 [5] 3 Styrene 100 100 51 [6] 4 Styrene 20 5 65 [6] 5 4-MeStyrene 100 100 41 [6] 6 4-MeStyrene 25 nd 70 [7] 7 4-i-BuStyrene 60 40 63(S) [5] 8 4-i-BuStyrene 25 100 57(S) [7] 9 MVN [a] 60 100 30(S) [5] 10 MVN [a] 0 100 91(S) [7] 11 MVN [a] 0 100 95(R) [8] [a] MVN = 6-methoxy-2-vinylnaphthalene. Scheme 1. Asymmetric hydrocyanation of vinylarenes. 350 #2007Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim Adv. Synth. Catal. 2007, 349,350–356 FULL PAPERS