A zirconocene triazenido hydride complex activates CO.

Starting from the alkyne complex CpZr(py)(η-MeSiCSiMe) (Cp = η-cyclopentadienyl, py = pyridine), the synthesis and complete characterisation of a zirconocene(IV) triazenido hydride complex and its use in the activation of small molecules is reported. The reaction with CO led to the formation of a zirconocene(IV) triazenido-formate complex, which was further investigated for its stability towards different bases with respect to the formation of formic acid. The experimentally observed reaction pathway was investigated computationally using DFT methods, revealing the favourable role of pyridine coordination in the hydrogen transfer from the triazene to the alkyne unit of the zirconocene reagent.

Highly (regio)selective hydroformylation of olefins using self-assembling phosphines.

New phosphines with self-assembling 6-pyridinone moities were prepared, characterized, and examined in the hydroformylation of diverse olefins. Testing various known and novel ligands in the presence of [Rh(acac)(CO)] under industrially relevant conditions, the hydroformylation of 1-octene proceeds best with 6,6'-(phenylphosphanediyl)bis(pyridin-2(1)-one) (DPONP). Control experiments and modelling studies indicate dimerization of this ligand at higher temperatures (>100 °C).

A General Concept for the Electronic and Steric Modification of 1-Metallacyclobuta-2,3-dienes: A Case Study of Group 4 Metallocene Complexes.

The synthesis of group 4 metal 1-metallacyclobuta-2,3-dienes as organometallic analogues of elusive 1,2-cyclobutadiene has so far been limited to SiMe substituted examples. We present the synthesis of two Ph substituted dilithiated ligand precursors for the preparation of four new 1-metallacyclobuta-2,3-dienes [rac-(ebthi)M] (M=Ti, Zr; ebthi=1,2-ethylene-1,10-bis(η-tetrahydroindenyl)). The organolithium compounds [Li(RCPh)] (1 b: R=Ph, 1 c: R=SiMe) as well as the metallacycles of the general formula [rac-(ebthi)M(RCR)] (2 b: M=Ti, R=R=Ph, 2 c: M=Ti, R=Ph, R=SiMe; 3 b: M=Zr, R=R=Ph; 3 c: M=Zr, R=Ph, R=SiMe) were fully characterised.

Atroposelective Ir-Catalyzed C-H Borylation of Phthalazine Heterobiaryls.

The atroposelective iridium-catalyzed borylation of menthyloxy-substituted phthalazine heterobiaryls with diborons is reported. Utilizing [Ir(OMe)(COD)]/2-aminopyridine as a rarely used efficient catalyst system, the heterobiaryls were selectively borylated in the 2-position of the carbocycle, exclusively yielding only one of the atropisomers, depending on the substitution of the phthalazine with (+)-menthyl or (-)-menthyl moieties. Exemplary further functionalization of a borylated atropisomer demonstrated that nickel-catalyzed Suzuki-Miyaura cross-coupling with an aryl halide was able to provide stereoretention to a certain degree (up to 75% ).

Bis(N-Heterocyclic Carbene) Manganese(I) Complexes: Efficient and Simple Hydrogenation Catalysts.

The use of bis(NHC) manganese(I) complexes 3 as catalysts for the hydrogenation of esters was investigated. For that purpose, a series of complexes has been synthesized via an improved two step procedure utilizing bis(NHC)-BEt adducts. By applying complexes 3 with KHBEt as additive, various aromatic and aliphatic esters were hydrogenated successfully at mild temperatures and low catalyst loadings, highlighting the efficiency of the novel catalytic system.

Unusual selectivity in the ring-opening of γ-valerolactone oxide by amines.

Primary and secondary amines selectively react with the lactone moiety of γ-valerolactone oxide (GVLO). Several primary amines afforded the resulting epoxyamides with an intact epoxy group. In some cases addition of two equivalents of amine resulted in additional epoxide opening to give α,γ-dihydroxy-β-amino-amides.

{μ-2,2'-(Ethane-1,2-di-yl)bis-[4,6-bis-(tri-methyl-sil-yl)-1,3-di-hydro-cyclo-penta-[]pyrrol-5-one]}bis-[tri-carbonyl-iron(0)].

The binuclear title compound, [Fe(CHNOSi)(CO)], consists of two central iron(0) atoms, each of them surrounded by a cyclo-penta-dienone moiety and three carbonyl ligands in a three-legged piano-stool shape. Furthermore, the bis-(cyclo-penta-dienone) ligand acts as a bridge between the two metal atoms.

Carbonyl-bis-{6,6'-[(3,3'-di--butyl-5,5'-dimeth-oxy-1,1'-biphenyl-2,2'-di-yl)bis(oxy)]bis-(dibenzo[,][1,3,2]-dioxaphosphepine)}hydridorhodium(I) toluene- 2.25-solvate.

The crystal-structure determination of the title compound, [RhH(CHOP)(CO)]·2.25CD, is reported. The bis-phosphite ligand, CHOP, is well known as Biphephos.

1-[(Methyl-sulfon-yl)-oxy]pyridin-1-ium methane-sulfonate.

The title mol-ecular salt, CHNOS·CHOS, consists of a cationic sulfonated pyridine -oxide moiety and a methane-sulfonate anion. An N-O bond length of 1.4004 (15) Å is observed in the cation.

1,3-Thia-zole-4-carbo-nitrile.

The title compound, CHNS, is a 1,3-thia-zole substituted in the 4-position by a nitrile group. In the crystal, C-H⋯N hydrogen bonds and aromatic π-π stacking inter-actions are observed.

Mono- and dinuclear zirconocene(iv) amide complexes for the catalytic dehydropolymerisation of phenylsilane.

The dehydropolymerisation of phenylsilane is investigated using group 4 metallocene amide complexes as catalysts. The dinuclear zirconocene amide complex CpZr(NMe)(μ-MeSiCSiMe)Zr(NMe)Cp (2) (Cp = η-cyclopentadienyl) shows high activity in dehydrocoupling reactions, producing polyphenylsilanes with molecular weights ranging from 200 to 3000 g mol and linear-to-cyclic product ratios of up to 80 : 20. Likewise, different ratios of oligomers and polymers with different tacticities could be described.

Efficient Hydrogenation of N-Heterocycles Catalyzed by NNP-Manganese(I) Pincer Complexes at Ambient Temperature.

Manganese-catalyzed hydrogenation reactions have aroused widespread interest in recent years. Among the catalytic systems described, especially PNP- and NNP-Mn pincer catalysts have been reported for the hydrogenation of aldehydes, ketones, nitriles, aldimines and esters. Furthermore, NNP-Mn pincer compounds are efficient catalysts for the hydrogenolysis of less reactive amides, ureas, carbonates, and carbamates.

Revisiting Reduction of CO to Oxalate with First-Row Transition Metals: Irreproducibility, Ambiguous Analysis, and Conflicting Reactivity.

Construction of higher C compounds from CO constitutes an attractive transformation inspired by nature's strategy to build carbohydrates. However, controlled C-C bond formation from carbon dioxide using environmentally benign reductants remains a major challenge. In this respect, reductive dimerization of CO to oxalate represents an important model reaction enabling investigations on the mechanism of this simplest CO coupling reaction.

Synthesis of α-keto aldehydes selective Cu(I)-catalyzed oxidation of α-hydroxy ketones.

An efficient approach to synthesize α-keto aldehydes was established through selective oxidation of α-hydroxy ketones catalyzed by Cu(I) using oxygen as oxidant. A wide array of α-keto aldehydes was prepared with isolated yields of up to 87%. The potential utilization of this reaction was evaluated by gram-scale reactions and synthetic applications.

1-Zirconacyclobuta-2,3-dienes: synthesis of organometallic analogs of elusive 1,2-cyclobutadiene, unprecedented intramolecular C-H activation, and reactivity studies.

The structure, bonding, and reactivity of small, highly unsaturated ring systems is of fundamental interest for inorganic and organic chemistry. Four-membered metallacyclobuta-2,3-dienes, also referred to as metallacycloallenes, are among the most exotic examples for ring systems as these represent organometallic analogs of 1,2-cyclobutadiene, the smallest cyclic allene. Herein, the synthesis of the first examples of 1-zirconacyclobuta-2,3-dienes of the type [Cp'Zr(MeSiCSiMe)] (Cp' = -(ebthi), (ebthi = 1,2-ethylene-1,1'-bis(η-tetrahydroindenyl)) (2a); -MeSi(thi), thi = (η-tetrahydroindenyl), (2b)) is presented.

HCOOH disproportionation to MeOH promoted by molybdenum PNP complexes.

Molybdenum(0) complexes with aliphatic aminophosphine pincer ligands have been prepared which are competent for the disproportionation of formic acid, thus representing the first example so far reported of non-noble metal species to catalytically promote such transformation. In general, formic acid disproportionation allows for an alternative access to methyl formate and methanol from renewable resources. MeOH selectivity up to 30% with a TON of 57 could be achieved while operating at atmospheric pressure.

A Selective and General Cobalt-Catalyzed Hydroaminomethylation of Olefins to Amines.

A new cobalt catalyst is presented for the domino hydroformylation-reductive amination reaction of olefins. The optimal Co-tert-BuPy-Xantphos catalyst shows good to excellent linear-to-branched (n/iso) regioselectivity for the reactions of aliphatic alkenes with aromatic amines under mild conditions. This system is far more selective than traditional cobalt(I) catalysts and even better than most known rhodium catalysts.

Palladium-Catalyzed Domino Aminocarbonylation of Alkynols: Direct and Selective Synthesis of Itaconimides.

The first direct and selective synthesis of substituted itaconimdes by palladium-catalyzed aminocarbonylation of alkynols is reported. Key to the success of this transformation is the use of a novel catalyst system involving ligand and appropriate reaction conditions. In the protocol here presented, easily available propargylic alcohols react with -nucleophiles including aryl- and alkylamines as well as aryl hydrazines to provide a broad variety of interesting heterocycles with high catalyst activity and excellent selectivity.

Palladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds.

A direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon-carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions.

3,3-Difluoroallyl ammonium salts: highly versatile, stable and selective gem-difluoroallylation reagents.

The selective synthesis of fluorinated organic molecules continues to be of major importance for the development of bioactive compounds (agrochemicals and pharmaceuticals) as well as unique materials. Among the established synthetic toolbox for incorporation of fluorine-containing units, efficient and general reagents for introducing -CF- groups have been largely neglected. Here, we present the synthesis of 3,3-difluoropropen-1-yl ammonium salts (DFPAs) as stable, and scalable gem-difluoromethylation reagents, which allow for the direct reaction with a wide range of fascinating nucleophiles.

Bis(benzo[]quinolin-10-olato-κ ,)bromidomanganese(III).

The title compound, [MnBr(CHNO)], consists of a manganese(III) atom, which is coordinated by one bromido and two benzo[]quinolin-10-olato ligands. The Mn complex exhibits a distorted square-pyramidal coordination geometry with the Br ligand in the apical position. Neighbouring complexes are held together by π-π inter-actions and weak C-H⋯Br hydrogen bonds.

The role of allyl ammonium salts in palladium-catalyzed cascade reactions towards the synthesis of spiro-fused heterocycles.

There is a continuous need for designing new and improved synthetic methods aiming at minimizing reaction steps while increasing molecular complexity. In this respect, catalytic, one-pot cascade methodologies constitute an ideal tool for the construction of complex molecules with high chemo-, regio-, and stereoselectivity. Herein, we describe two general and efficient cascade procedures for the synthesis of spiro-fused heterocylces.

Catalytic, Kinetic, and Mechanistic Insights into the Fixation of CO with Epoxides Catalyzed by Phenol-Functionalized Phosphonium Salts.

A series of hydroxy-functionalized phosphonium salts were studied as bifunctional catalysts for the conversion of CO with epoxides under mild and solvent-free conditions. The reaction in the presence of a phenol-based phosphonium iodide proceeded via a first order rection kinetic with respect to the substrate. Notably, in contrast to the aliphatic analogue, the phenol-based catalyst showed no product inhibition.