Structural and Electronic Properties of Iron(0) PNP Pincer Complexes.

In the present work we have prepared and fully characterized several Fe(0) complexes of the type [Fe(PNP)(CO)] treating Fe(II) complexes [Fe(PNP)(Cl)] with KC in the presence of carbon monoxide. While complexes [Fe(PNP-Pr)(CO)], [Fe(PNP-Pr)(CO)] adopt a trigonal bipyramidal geometry, the bulkier and more electron rich [Fe(PNP-Bu)(CO)] is closer to a square pyramidal geometry. Mössbauer spectra showed isomer shifts very close to 0 and similar to those reported for Fe(I) systems.

Rhenium-Catalyzed Dehydrogenative Coupling of Alcohols and Amines to Afford Nitrogen-Containing Aromatics and More.

An efficient synthesis of quinolines, pyrimidines, quinoxalines, pyrroles, and aminomethylated aromatic compounds catalyzed by a well-defined Re(I) PNP pincer complex is described. All reactions proceed with liberation of dihydrogen and elimination of water. Under optimized reaction conditions a wide range of organic functional groups are tolerated.

Synthesis and characterization of bis- and tris-carbonyl Mn(I) and Re(I) PNP pincer complexes.

Abstract: A series of neutral bis- and cationic tris-carbonyl complexes of the types -[M(κ -PNP)(CO)Y] and [M(κ -PNP)(CO)] was prepared by reacting [M(CO)Y] (M = Mn, Re; Y = Cl or Br) with PNP pincer ligands derived from the 2,6-diaminopyridine, 2,6-dihydroxypyridine, and 2,6-lutidine scaffolds. With the most bulky ligand PNP-Bu, the cationic square-pyramidal 16e bis-carbonyl complex [Mn(PNP-Bu)(CO)] was obtained. In contrast, in the case of rhenium, the 18e complex [Re(PNP-Bu)(CO)] was formed.

Chemoselective Hydrogenation of Aldehydes under Mild, Base-Free Conditions: Manganese Outperforms Rhenium.

Several hydride Mn(I) and Re(I) PNP pincer complexes were applied as catalysts for the homogeneous chemoselective hydrogenation of aldehydes. Among these, [Mn(PNP-Pr)(CO)(H)] was found to be one of the most efficient base metal catalysts for this process and represents a rare example which permits the selective hydrogenation of aldehydes in the presence of ketones and other reducible functionalities, such as C=C double bonds, esters, or nitriles. The reaction proceeds at room temperature under base-free conditions with catalyst loadings between 0.

Non-order-disorder allotwinning of the rhenium pincer complex cis-Re[(PNP-iPr)(CO)Cl].

Crystals of cis-Re[(PNP-iPr)(CO)Cl] (1) are made up of two geometrically non-equivalent polytypes with respective symmetries of P2/c and I2/a. The structures were determined in a concurrent refinement, taking into account overlap of diffraction spots. The polytypes are composed of layers with p12/c1 symmetry and are of the non-order-disorder (OD) type (the layer interfaces are non-equivalent).

Carbon dioxide hydrogenation catalysed by well-defined Mn(i) PNP pincer hydride complexes.

The catalytic reduction of carbon dioxide is of great interest for its potential as a hydrogen storage method and to use carbon dioxide as C-1 feedstock. In an effort to replace expensive noble metal-based catalysts with efficient and cheap earth-abundant counterparts, we report the first example of Mn(i)-catalysed hydrogenation of CO to HCOOH. The hydride Mn(i) catalyst [Mn(PNP-Pr)(H)(CO)] showed higher stability and activity than its Fe(ii) analogue.

Crystal structure of the tetra-hydro-furan disolvate of a 94:6 solid solution of [,-bis-(di--butyl-phosphan-yl)pyridine-2,6-di-amine]-dibromido-manganese(II) and its monophosphine oxide analogue.

The MnBr complex of ,-bis-(di--butyl-phosphan-yl)pyridine-2,6-di-amine (·MnBr) co-crystallizes with 5.69% of the monophosphine oxide analogue (O·MnBr) and two tetra-hydro-furan (THF) mol-ecules, namely [,-bis-(di--butyl-phosphan-yl)pyridine-2,6-di-amine]-dibromido-manganese(II)-[bis-(di--butyl-phosphan-yl)({6-[(di--butyl-phosphan-yl)amino]-pyridin-2-yl}amino)-phosphine oxide]di-bromido-manganese(II)-tetra-hydro-furan (0.94/0.

Sustainable Synthesis of Quinolines and Pyrimidines Catalyzed by Manganese PNP Pincer Complexes.

This study represents the first example an environmentally benign, sustainable, and practical synthesis of substituted quinolines and pyrimidines using combinations of 2-aminobenzyl alcohols and alcohols as well as benzamidine and two different alcohols, respectively. These reactions proceed with high atom efficiency via a sequence of dehydrogenation and condensation steps that give rise to selective C-C and C-N bond formations, thereby releasing 2 equiv of hydrogen and water. A hydride Mn(I) PNP pincer complex recently developed in our laboratory catalyzes this process in a very efficient way.

Synthesis and characterization of cationic dicarbonyl Fe(II) PNP pincer complexes.

Abstract: In the present work, we have prepared a series of octahedral Fe(II) complexes of the type -[Fe(PNP)(CO)Cl]-PNP are tridentate pincer-type ligands based on 2,6-diaminopyridine. These complexes are formed irrespective of the size of the substituents at the phosphorus sites and whether -[Fe(PNP)(Cl)(CO)] or -[Fe(PNP)(Cl)(CO)] are reacted with CO in the presence of 1 equiv of silver salts. X-ray structures of representative complexes are presented.

Crystal structure of hexa-kis-(dimethyl sulfoxide-κO)manganese(II) diiodide.

The asymmetric unit of the title salt, [Mn(C2H6OS)6]I2, consists of one Mn(II) ion, six O-bound dimethyl sulfoxide (DMSO) ligands and two I(-) counter-anions. The isolated complex cations have an octa-hedral configuration and are grouped in hexa-gonally arranged rows extending parallel to [100]. The two I(-) anions are located between the rows and are linked to the cations through two weak C-H⋯I inter-actions.

Divergent Coupling of Alcohols and Amines Catalyzed by Isoelectronic Hydride Mn(I) and Fe(II) PNP Pincer Complexes.

Herein, we describe an efficient coupling of alcohols and amines catalyzed by well-defined isoelectronic hydride Mn(I) and Fe(II) complexes, which are stabilized by a PNP ligand based on the 2,6-diaminopyridine scaffold. This reaction is an environmentally benign process implementing inexpensive, earth-abundant non-precious metal catalysts, and is based on the acceptorless alcohol dehydrogenation concept. A range of alcohols and amines including both aromatic and aliphatic substrates were efficiently converted in good to excellent isolated yields.

Crystal structure of bis-[μ-2-(diiso-propyl-phosphor-yl)propan-2-olato-κ(3) O (1),O (2):O (1)]bis-[chlorido-oxidovanadium(IV)].

The dinuclear mol-ecule of the title complex, [VOCl{μ-OC(Me)2P(iPr)2-κ(2) O}]2 or [V2(C9H20O2P)2Cl2O2], which was obtained due to an unexpected oxidation reaction, is centrosymmetric, with the inversion centre located in the middle of the central V2O2 core. These core O atoms arise from the symmetry-related 2-(diiso-propyl-phosphor-yl)propan-2-olate dianions. The V(IV) atom is additionally bonded to one terminal Cl ligand, the second O atom of the dianion and double bonded to a vanadyl O atom, leading to an overall distorted square-pyramidal VO4Cl coordination polyhedron with the vanadyl O atom as the apex.

Twinning of three Fe-PNP pincer complexes interpreted according to order-disorder (OD) theory.

The systematic twinning of three 2,6-diaminopyridine-based Fe-PNP complexes is interpreted using order-disorder (OD) theory. The monoclinic [Fe(0)(PNP(Et)-(i)Pr)(CO)2] [P112(1)/b, Z' = 4] possesses pseudo-orthorhombic metrics and crystallizes as a reflection twin by pseudo-merohedry with the twin plane (100). The structure is made up of layers with idealized p2(1)a(b) symmetry.

Iron(II) complexes featuring κ3- and κ2-bound PNP pincer ligands--the significance of sterics.

Treatment of anhydrous FeX2 (X = Cl, Br) with 2 equiv. of the sterically little demanding N,N'-bisphosphino-2,6-diaminopyridine based PNP ligands--featuring Ph, biphenol (BIPOL), Me, Et, nPr, and nBu substituents at the phosphorus sites and H, Me, and Ph substituents at the N-linkers--afforded diamagnetic cationic octahedral complexes of the general formula [Fe(κ(3)-P,N,P-PNP)(κ(2)-P,N-PNP)X](+) featuring a κ(2)-P,N bound PNP ligand. With the sterically more encumbered N-methylated ligand PNP(Me)-Ph the related complex [Fe(κ(3)-P,N,P-PNP(Me)-Ph)(κ(2)-P,N-PN(HMe)-Ph)Cl](+) rather than [Fe(κ(3)-P,N,P-PNP(Me)-Ph)Cl2] was formed.

An iron(II) complex featuring κ(3) and labile κ(2)-bound PNP pincer ligands - striking differences between CH2 and NH spacers.

Treatment of anhydrous FeCl2 with 2 equiv. of the pincer ligand PNP-Ph afforded the diamagnetic cationic octahedral complex [Fe(κ(3)-P,N,P-PNP)(κ(2)-P,N-PNP)Cl](+) featuring a κ(2)-P,N-bound PNP ligand. Preliminary reactivity studies revealed that the κ(2)-P,N-bound PNP ligand is labile reacting with CO to afford trans-[Fe(PNP-Ph)(CO)2Cl](+).