A series of κ 2 -(N,N)-coordinated bis(2-pyridylimino)isoindolato (BPI) complexes [Cp*Ir(BPI)Cl], which possess "three-legged piano-stool" structures, with the iridium atom being coordinated by the Cp* ligand 2 × N and Cl, were prepared via deprotonation of the BPIH ligands with either potassium hydride or LDA and subsequent reaction with [Cp*IrCl 2 ] 2 in THF. Cationic complexes [Cp*Ir(BPI)] + containing κ 3 -(N,N,N)-coordinated BPI ligands were prepared as well as complexes with bidentate-coordinated BPI ligands, where the chloride ligand was substituted by either neutral or anionic ligands. Substitution in the orthoposition of the PBI ligands led to the formation of cycloiridated κ 3 -(N,N,C) species. Upon substitution of the anionic ligand by triphenylphosphine, a product was obtained with a hitherto unobserved κ 2 -(N,N) coordination of oMe-BPI to the metal center via the deprotonated nitrogen atom of the isoindole unit and one of the imine nitrogen atoms of the BPI ligand. A series of (para-cymene) osmium half-sandwich complexes with analogous structures and reactivities to their isoelectronic Cp*Ir(BPI) congeners were also prepared. Finally, it has been demonstrated that both Ir and Os complexes are catalytically active in the transfer hydrogenation of various ketones and imines.
Lysobacter enzymogenes lysyl endoproteinase (LysC) is a trypsin-type serine protease with a high pH optimum that hydrolyses all Lys-Xaa peptide bonds. The high specificity of LysC renders it useful for biotechnological purposes. The K30R variant of a related lysyl endoproteinase from Achromobacter lyticus has favourable enzymatic properties that might be transferrable to LysC. To visualize structural differences in the substrate-binding sites, the crystal structures of wild-type and the K30R variant of LysC were determined. The mutation is located at a distance of 12 Å from the catalytic triad and subtly changes the surface properties of the substrate-binding site. The high pH optimum of LysC can be attributed to electrostatic effects of an aromatic Tyr/His stack on the catalytic aspartate and is a general feature of this enzyme subfamily. LysC crystals in complex with the covalent inhibitor N(α)-p-tosyl-lysyl chloromethylketone yielded data to 1.1 and 0.9 Å resolution, resulting in unprecedented precision of the active and substrate-binding sites for this enzyme subfamily. Error estimates on bond lengths and difference electron density indicate that instead of the expected oxyanion a hydroxyl group binds to the partially solvent-exposed oxyanion hole. Protonation of the alkoxide catalytic intermediate might be a recurring feature during serine protease catalysis.
A series of osmium complexes with monoanionic, meridionally coordinating 1,3-bis(2-pyridylimino)isoindolates (BPI) as spectator ligands has been synthesized. Reaction of the dichlorido metal precursor [OsCl 2 (PPh 3 ) 3 ] with the lithiated BPI ligand transfer reagent gave the chlorido complex [(tBu-BPI Me )Os(PPh 3 ) 2 Cl] (2) which, in turn, was reacted with lithium triethylborohydride to yield the hydrido complex [(tBu-BPI Me )Os(PPh 3 ) 2 H] (3). Treatment of complex 2 with thallium hexafluorophosphate under a nitrogen pressure afforded the cationic dinitrogen complex [(tBu-BPI Me )Os(PPh 3 ) 2 (N 2 )]PF 6 (4), which contains an end-on coordinated dinitrogen molecule trans to the isoindolato nitrogen atom. To synthesize the alkynyl complex [(tBu-BPI Me )Os(PPh 3 ) 2 (CCPh)] (5), the chlorido complex 2 was treated with lithium phenylacetylide. Complex 5 was subsequently converted quantitatively by addition of one or two equivalents of HBF 4 to the vinylidene complex [(tBu-BPI Me )Os(PPh 3 ) 2 (C CHPh)]BF 4 (6), and the cationic species [(H-tBu-BPI Me )Os(PPh 3 ) 2 (CCHPh)](BF 4 ) 2 (7), respectively; the latter being formed via protonation of one imine nitrogen atom of the BPI ligand. Upon stirring, a toluene solution of the chlorido complex 2 with benzyl potassium, the four-membered metallacycle [(tBu-BPI Me )Os(PPh 3 )(o-C 6 H 4 PPh 2 )] (8) was obtained, which reacted with molecular hydrogen and phenyl acetylene to give the hydrido complex 3 and the acetylide complex 5, respectively. Stirring of 8 with methyl acetylenedicarboxylate (DMAD) yielded [(tBu-BPI Me )Os(DMAD)(o-C 6 H 4 PPh 2 )] (9), while treatment with carbon monoxide gave the acyl complex [(tBu-BPI Me )Os(o−C(O)-C 6 H 4 PPh 2 )(CO)] (10) by an insertion of CO into the osmium carbon bond.
One-pot syntheses of three new enantiopure heteroscorpionate ligands derived from (+)-camphor or (-)-menthone are described. The ligands are obtained by reacting pyrazoles derived from (+)-camphor or (-)-menthone with sodium hydride and thionyl chloride. Subsequent reactions with pyridine and various aldehydes afford the tripod ligands in multi-gram amounts. Especially the menthopyrazole based ligand 6 showed encouraging ee values up to 69% in the Cu(I) catalysed enantioselective cyclopropanation of styrene with ethyl diazoacetate.
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