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Atypical and Asymmetric 1,3-P,N Ligands: Synthesis,Coordination and Catalytic Performance of Cycloiminophosphanes |
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| Authors: | Mark K Rong Flip Holtrop Eduard O Bobylev Dr Martin Nieger Dr Andreas W Ehlers Dr J Chris Slootweg Prof Dr Koop Lammertsma |
| Institution: | 1. Department of Chemistry and Pharmaceutical Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands;2. Department of Chemistry, University of Helsinki, A. I. Virtasen aukio 1, P.O. Box 55, FIN-00014 Helsinki, Finland;3. Department of Chemistry and Pharmaceutical Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
Department of Chemistry, University of Johannesburg, Oakland Park, 2006 Johannesburg, South Africa Present address: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam, The Netherlands;4. Department of Chemistry and Pharmaceutical Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands Present address: Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam, The Netherlands |
| Abstract: | Novel seven-membered cyclic imine-based 1,3-P,N ligands were obtained by capturing a Beckmann nitrilium ion intermediate generated in situ from cyclohexanone with benzotriazole, and then displacing it by a secondary phosphane under triflic acid promotion. These “cycloiminophosphanes” possess flexible non-isomerizable tetrahydroazepine rings with a high basicity; this sets them apart from previously reported iminophophanes. The donor strength of the ligands was investigated by using their P-κ1- and P,N-κ2-tungsten(0) carbonyl complexes, by determining the IR frequency of the trans-CO ligands. Complexes with RhCp*Cl2]2 demonstrated the hemilability of the ligands, giving a dynamic equilibrium of κ1 and κ2 species; treatment with AgOTf gives full conversion to the κ2 complex. The potential for catalysis was shown in the RuII-catalyzed, solvent-free hydration of benzonitrile and the RuII- and IrI-catalyzed transfer hydrogenation of cyclohexanone in isopropanol. Finally, to enable access to asymmetric catalysts, chiral cycloiminophosphanes were prepared from l -menthone, as well as their P,N-κ2-RhIII and a P-κ1-RuII complexes. |
| Keywords: | cooperative effects coordination modes homogeneous catalysis ligand design N P ligands |