Efficient Z-Selective Semihydrogenation of Internal Alkynes Catalyzed by Cationic Iron(II) Hydride Complexes.

The bench-stable cationic bis(σ-B-H) aminoborane complex [Fe(PNPNMe-iPr)(H)(η2-H2B = NMe2)]+ (2) efficiently catalyzes the semihydrogenation of internal alkynes, 1,3-diynes and 1,3-enynes. Moreover, selective incorporation of deuterium was achieved in the case of 1,3-diynes and 1,3-enynes. The catalytic reaction takes place under mild conditions (25 °C, 4-5 bar H2 or D2) in 1 h, and alkenes were obtained with high Z-selectivity for a broad scope of substrates. Mechanistic insight into the catalytic reaction, explaining also the stereo- and chemoselectivity, is provided by means of DFT calculations. Intermediates featuring a bisdihydrogen moiety [Fe(PNPNMe-iPr)(η2-H2)2]+ are found to play a key role. Experimental support for such species was unequivocally provided by the fact that [Fe(PNPNMe-iPr)(H)(η2-H2)2]+ (3) exhibited the same catalytic activity as 2. The novel cationic bisdihydrogen complex 3 was obtained by protonolysis of [Fe(PNPNMe-iPr)(H)(η2-AlH4)]2 (1) with an excess of nonafluoro-tert-butyl alcohol.

Influence of the Ionic Liquid on the Activity of a Supported Ionic Liquid Phase FeII Pincer Catalyst for the Hydrogenation of Aldehydes.

The catalytic hydrogenation of different aldehydes to the corresponding alcohols was investigated using an FeII hydride pincer complex as catalyst in the supported ionic liquid phase (SILP) reaction mode. Two different ionic liquids of the type [X4441][NTf2] with X=N or P were applied with mesoporous silica gel as support, which was coated first with a chemisorbed monolayer of the corresponding modified IL to remove acidic surface OH-groups and to prevent IL leaching. Quantitative conversion with turn-over frequencies in the order of 1000 h- 1 were obtained for various aromatic and heteroaromatic aldehydes and highly selective aldehyde reduction was observed also for substrates containing reducible C=C bonds. Aldehydes with longer aliphatic chains or cycloalkyl substituents, however, showed no conversion here, in contrast to a previous study with an imidazolium-based ionic liquid. These differences were ascribed primarily to differences in substrate/ionic liquid interactions. Whereas [N4441][NTf2] and [P4441][NTf2] gave essentially identical results for different substrates in single-batch reactions, prolonged use of the catalyst in repeated reaction cycles lead to a quick drop-off in catalyst activity in [P4441][NTf2], but a continuous, quantitative conversion in [N4441][NTf2].

Manganese-Catalyzed Hydrogenation of Ketones under Mild and Base-free Conditions.

In this paper, several Mn(I) complexes were applied as catalysts for the homogeneous hydrogenation of ketones. The most active precatalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe) (CO)3(CH2CH2CH3)]. The reaction proceeds at room temperature under base-free conditions with a catalyst loading of 3 mol % and a hydrogen pressure of 10 bar. A temperature-dependent selectivity for the reduction of α,ß-unsaturated carbonyls was observed. At room temperature, the carbonyl group was selectively hydrogenated, while the C=C bond stayed intact. At 60 °C, fully saturated systems were obtained. A plausible mechanism based on DFT calculations which involves an inner-sphere hydride transfer is proposed.

Transition metal complexes of antimony centered ligands based upon acenaphthyl scaffolds. Coordination non-innocent or not?

The synthesis and structures of the di- and triorgano antimony compounds (6-Ph2P-Ace-5-)2SbCl (1) and (6-Ph2P-Ace-5-)3Sb (2) are presented along with their use as coordination non-innocent ligands for transition metals, leading to the complexes Cl(6-Ph2P-Ace-5-)2SbCuCl (3), Cl2(6-Ph2P-Ace-5-)2SbPdCl (4), Cl2(6-Ph2P-Ace-5-)2SbPtCl (5) and Cl(6-Ph2P-Ace-5-)3SbRhCl (6). The electronic structures of 1-6 were investigated by DFT computations using a set of topological and surface-based real-space bonding indicators derived from the Atoms-In-Molecules (AIM), Non-Covalent interactions Index (NCI), and Electron Localizability Indicator (ELI-D) methods, unravelling a dative Sb-Cu bond character in 3 and polar-covalent Sb-Pd/Pt/Rh interactions in 4-6.

Selective Hydrogenation of Aldehydes Using a Well-Defined Fe(II) PNP Pincer Complex in Biphasic Medium.

A biphasic process for the hydrogenation of aldehydes was developed using a well-defined iron (II) PNP pincer complex as model system to investigate the performance of various ionic liquids. A number of suitable hydrophobic ionic liquids based on the N(Tf)2 - anion were identified, allowing to immobilize the iron (II) catalyst in the ionic liquid layer and to facilitate the separation of the desired alcohols. Further studies showed that targeted Brønsted basic ionic liquids can eliminate the need of an external base to activate the catalyst.

A tetranuclear arylstibonic acid with an adamantane type structure.

Oxidative chlorination of ArSbCl2 (1) with SO2Cl2 provided ArSbCl4 (2), the base hydrolysis of which gave rise to the arylstibonic acid (ArSb)4O6(OH)4 (3) having an adamantane type structure. The intramolecularly coordinating substituent Ar = 6-diphenylphosphinoacenaphth-5-yl- modulates the Lewis acidity of 1-3 and prevents extensive aggregation.