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Meyer C, Scherer M, Schonberg H, Ruegger H, Loss S, Gramlich V, Grutzmacher H: Coordination chemistry of phosphanyl amino acids: solid state and solution structures of neutral and cationic rhodium complexes. Dalton Trans. 2006 Jan 7;(1):137-48. Epub 2005 Nov 29.
Copper phosphide or arsenide complexes, [Cu (EPh (2))(neo)] (E = P, As, neo = 2,9-dimethyl-1,10-phenanthroline; trivial name: neocuprine) react selectively with the N-protected brominated serine derivatives, 2-(S)-(alkoxycarbonylamino)-3-bromomethylpropionates ((ROCO) SerBr, : R = PhCH (2), : tBu, : Me) to give the corresponding phosphanylated or arsanylated amino acids, (ROCO) SerPhos (: Phos = PPh (2)) and (Z) SerArs (Ars = AsPh (2), Z = PhCH (2) OCO). The dipeptide (Z) AlaSerPhos was likewise prepared. The phosphanes , and the arsane reacted cleanly with [Rh (2)(micro-Cl)(2)(cod)(2)] to give the rhodium (I) complexes [RhCl (cod)((Z) SerPhos)] , [RhCl (cod)((Boc) SerPhos)] (Boc = tBuOCO), [RhCl (cod)((Z) AlaSerPhos)] , and [RhCl (cod)((Z) SerArs)] which were characterized by X-ray diffraction studies. A common structural feature is an intramolecular (N) H [dot dot dot] Cl (Rh)-hydrogen bridge which according to NMR investigations remains intact in solution. The abstraction of chloride from the coordination sphere of Rh (I) in or has a profound structural impact. While in and , the ligands bind in a monodentate fashion, via the phosphorus atom only, they serve as bidentate ligands via the phosphorus centre and the peptidic C=O group in [Rh (cod)(kappa (2)-(Z) SerPhos)] PF (6) and [Rh (cod)(kappa (2)-(Z) AlaSerPhos)] PF (6). This causes also the amino acid residue structures to change from alpha-helix type in and to a beta-sheet type in both. Addition of chloride to and fully re-establishes the structures of both. The complexes [RhCl (cod)((Z) SerPhos)] and [RhCl (cod)((Boc) SerPhos)] show good activities in homogeneously catalyzed hydrogenations of olefins while the dipeptide complex is less active. Phosphane addition to greatly diminishes the catalytic activity. The cationic complex [Rh (cod)(kappa (2)-(Z) AlaSerPhos)] PF (6) shows low activity which, however, is greatly increased by addition of one equivalent of phosphane. |
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