Attaching di­(1R)-menthylphosphino fragments (menthyl = Men = 1R,2S,5R-2-isopropyl-5-methylcyclohex-1-yl) to molecular scaffolds turns them into homochiral, bulky, electron-rich phosphine ligands with proven and potential applications in coordination chemistry and transition-metal catalysis. Dimenthylphosphine P-oxide (Men2POH; 1) is established as a platform chemical toward dimenthylphosphino-containing targets via transformation to the known ligand precursors dimenthylchlorophosphine (4) and dimenthylphosphine (6). Transformations of 1 to dimenthylphosphinyl chloride (5) and dimenthylphosphinic acid (8) are elaborated. A phospha-Michael type 1,4-addition of 1 to p-benzo- or 1,4-naphthoquinone gives the corresponding o-hydroxyaryl­(dimenthyl)­phosphine oxides. Deprotonation of 1 with n-BuLi provides a phosphinyl nucleophile, whose reactions with alkyl halides or 1,n-dihaloalkanes provide tertiary alkyl dimenthylphosphine oxides or 1,n-bis­(dimenthylphosphino)­alkane bis­(P-oxides) 10a–c, respectively. As an example, oxide 10b was deoxygenated to the diphosphine Men2P­(CH2)3PMen2 (11) and characterized via the square-planar complex [(Men2P­(CH2)3PMen2)­PdCl2] (12). A selection of P-aryl dimenthylphosphines, including PhP­(Men)2 (19) and 2-ClC6H4P­(Men)2 (22), as well as the menthyl analogues Men-JohnPhos (21) and Men-SPhos (24), of the respective Buchwald ligands have been prepared. The combination of the secondary phosphine oxide (SPO) 1 with PdCl2 produces halide-bridged [(Men2POH)2Pd2Cl2] (25), mononuclear [(Men2POH)2PdCl2] (26), or the halide-bridged pseudochelate complex [(Men2PO···H···OPMen2)2Pd2Cl2] (27), depending on the reaction stoichiometry and conditions, all of which have been crystallographically characterized. The new ligands 1, 19, 21, 22, and 24 and complexes 25 and 26 have been evaluated in model palladium-catalyzed C–C- and C–N-fragment coupling reactions and found to display specific reactivity profiles due to the presence of the menthyl groups. Ligand 22 in particular catalyzed an asymmetric biaryl-forming coupling to give 2-methoxy-1,1′-binaphthalene with an er of up to 93:7.

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A group of transition-metal catalyzed hydrogen moving reactions, encompassing hydrogen autotransfer (HAT; also called borrowing hydrogen, BH), dehydrogenative condensation (DHC) and alkene isomerization, displays high atom economy and relies on widely available starting materials. Such reactions have considerable potential for clean reaction design and application in sustainable synthesis. With the aim to develop and study synthetic applications of the title reactions, we have set up synthetic access routes to a toolbox of structurally varied ligands for and pincer complexes of some transition metals (cobalt, ruthenium, iridium) that are well established for the title reactions. Ligand target structures, for which often improved syntheses have been found, encompass 6,6'-dihydroxy-2,2'-bipyridine, 2(3-hydroxyphenyl)pyridines (as backbones for PCN pincers), 2(6-methylpyridine-2yl)pyridines (as backbones for PNN pincers) and 2(3-tolyl)pyridines (as backbones for PCN pincers). To support research towards asymmetric versions of the title reactions, we have prepared asymmetrically modified versions of well-established catalysts, including chiral, enantiopure versions of Milstein's PNN-ruthenium pincer, Kempe's triazinyl-diaminophosphanyl PNP-iridium-or -cobalt pincers, Huang's PCN-iridium pincers, and Grotjahn's alkene zipper complex. The strategy applied to 'chiral switching' relied on replacing symmetric dialkylphosphine donorgroups by dimenthylphosphine or aryl(menthyl)phosphine donor units. The resulting ligands or complexes have been structurally characterized, and the catalytic potential of the catalysts has been established in exploratory model reactions (transfer hydrogenation; diol to lactone dehydrogenative condensation; alkene isomerization). Several model reactions have been designed which will allow to study asymmetric catalytic hydrogen moving reactions.

Es wird eine experimentelle Anordnung zur direkten Untersuchung von Reaktionen zwischen Atomen und Radikalen beschrieben. Hierbei werden Radikale durch Blitzlichtphotolyse in einem Strömungssystem bei einem hohen Überschuß von Atomen erzeugt. Die absolute Geschwindigkeit von Atom‐Radikal‐Reaktionen wird anschließend durch kinetische Spektroskopie direkt bestimmt. Für die Geschwindigkeit der Reaktionergab sich