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Ruthenium PNP pincer complexes bearing supplementary cyclometalated C,N-bound ligands have been prepared and fully characterized for the first time. By replacing CO and H��� as ancillary ligands in such complexes, additional electronic and steric modifications of this topical class of catalysts are possible. The advantages of the new catalysts are demonstrated in the general ��-alkylation of ketones with alcohols following a hydrogen autotransfer protocol. Herein, various aliphatic and benzylic alcohols were applied as green alkylating agents for ketones bearing aromatic, heteroaromatic or aliphatic substituents as well as cyclic ones. Mechanistic investigations revealed that during catalysis, Ru carboxylate complexes are predominantly formed whereas neither the PNP nor the CN ligand are released from the catalyst in significant amounts. �� 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Novel manganese NNP and PNP pincer complexes have been synthesized. The active catalyst allows the efficient hydrogenation of a wide range of amides under relatively mild conditions to afford alcohols and amines in high yields., Novel well-defined NNP and PNP manganese pincer complexes have been synthetized and fully characterized. The catalyst Mn-2 containing an imidazolyaminolphosphino ligand shows high activity and selectivity in the hydrogenation of a wide range of secondary and tertiary amides to the corresponding alcohols and amines, under relatively mild conditions. For the first time, more challenging substrates like primary aromatic amides including an actual herbicide can also be hydrogenated using this earth-abundant metal-based pincer catalyst.

Five Ru(II) neutral complexes C of the type [RuCl2(eta(6)-arene)(P)] (P = monodentate phosphorus ligand) have been prepared: Cl (arene = p-cymene, P = PPh3); C2 (arene = p-cymene, P = (R)-Monophos); C3 (arene = p-cymene, P = (S)-Ph-Binepine): C4 (arene = benzene, P= PPh3): and C5 (arene = benzene, P= (S)-Ph-Binepine). These complexes have been screened as catalytic precursors in the transfer hydrogenation of acetophenone with 2-propanol. Under optimised conditions at 82 degrees C complexes Cl and C4 provide full conversion in less than 20 min at a [Ru]:substrate ratio of 1:200. With the chiral complexes C2 and C3 good TOF values have been reached but with low enantioselectivities. The activation of the catalytic precursor has been studied. Based on NMR evidence, a mechanism in which the catalytically active species is a Ru monohydride complex arising from the reaction of the catalyst precursor C with 2-propanol in the presence of a base is suggested. The reaction shows different sensitivity towards excess of phosphine: whereas excess of PPh3 slows down the reaction severely, excess of (S)-Ph-Binepine does not cause such a sharp effect. An excess of chloride ion affects the activation of the precursor C. (C) 2012 Elsevier B.V. All rights reserved.

Cationic complexes of rhodium with binaphthophosphepine 1 (Ph-BINEPINE), an axially chiral binaphtalene-core monodentate P-donor ligand (Figure 1), [Rh(nbd)((S)- (Ph-BINEPINE))2]+X-, where X- = BF4 -, CF3SO3 - and BarF-, have been prepared. These complexes have been tested as catalyst precursors in the asymmetric reduction of α,β- unsaturated acid derivatives by both molecular hydrogen and formic acid as a hydrogen donor source.

Nel corso di recenti studi si è dimostrato che la fenilbinaftofosfepina (Ph-BINEPINE), un legante monodentato a chiralità assiale, è l’induttore chirale di gran lunga migliore in una gruppo di due-tre dozzine di altri leganti chirali fosforati mono- e bidentati in alcune reazioni enantioselettive catalizzate da complessi di Pd(II),1 Pt (II)2 e Rh(I).

Chiral diphosphines have become an important class of ligands for asymmetric catalysis. It is the success itself of enantioselective catalysis that has enhanced the demand for new chiral ligands for essentially two reasons. The first one is that no class of ligands can be considered universal anymore, as it is linked to a finite however broad scope of substrates and reactions. The second reason is the proprietary protection of established ligands. Based on these considerations, the range of chelating diphosphines based on [(h6-benzene)Cr(CO)3] complexes which has recently become accessible through the implementation of a stereocontrolled synthetic strategy has been extended. These ligands, which are endowed with central and planar chirality, offer a range of possibilities for their steric, electronic and conformational properties to be modulated. The new ligands have been prepared starting from [(h6-arene)Cr(CO)3] complexes derived from commercially available optically active benzylamines bearing a para-substituent other than hydrogen, in order to asses the influence of such a substituent on the electronic properties of the final diphosphines. The synthetic challenges posed by such a substituent are reviewed. Diphosphines supported by a more rigid scaffold have been prepared as well starting from optically pure (S)-N,N-dimethylaminoindane. By proper choice of reaction conditions, complexation of this amine to the Cr(CO)3 moiety turns out to be highly diastereoselective. The efficiency of the new ligands has been tested in the rhodium promoted asymmetric homogeneous hydrogenation of (Z)-N-acetylaminocinnamic acid methylester and dimethyl itaconate. All the new diphosphines provide rhodium catalyst precursors which promote complete conversion of the substrates. Catalytic performances are dependent on the electron richness and steric demands of the phosphorous substituents and enantioselectivities between 87 and 91% ee are obtained with the more electron rich ligands. No dramatic changes in chiral induction are observed by changing the substituent on the Cr-coordinated arene: likely, the electron-withdrawing nature of the Cr(CO)3 group levels out any contribution these substituents bring about on the electron dowry of the [(h6-arene)Cr(CO)3] moiety as a whole. Nor does the presence of a more rigid scaffold significantly change the catalytic performances of diphosphines derived from [(h6-N,N-dimethyl-1-aminoindane)Cr(CO)3].