Mathias Glatz

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. Although in the case of Mn selectively imines were obtained, with Fe-exclusively monoalkylated amines were formed. These reactions proceed under base-free conditions and required the addition of molecular sieves.

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-iPr)(CO)2(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 0.1 and 0.05 mol% and a hydrogen pressure of 50 bar (reaching TONs of up to 2000). A mechanism which involves an outer-sphere hydride transfer and reversible PNP ligand deprotonation/protonation is proposed. Analogous isoelectronic and isostructural Re(I) complexes were only poorly active.

Crystal structure of hexa­kis­(dimethyl sulfoxide-κO)manganese(II) diiodide

The title salt consists of isolated octahedrally shaped [Mn(DMSO)6]2+ cations (DMSO is dimethyl sulfoxide) and two I− anions, held together through weak C—H⋯I interactions.

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

A series of neutral bis- and cationic tris-carbonyl complexes of the types cis-[M(κ3P,N,P-PNP)(CO)2Y] and [M(κ3P,N,P-PNP)(CO)3]+ was prepared by reacting [M(CO)5Y] (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 PNPNH-tBu, the cationic square-pyramidal 16e bis-carbonyl complex [Mn(PNPNH-tBu)(CO)2]+ was obtained. In contrast, in the case of rhenium, the 18e complex [Re(PNPNH-tBu)(CO)3]+ was formed. The dissociation of CO was studied by means of DFT calculation revealing in agreement with experimental findings that CO release from [M(κ3P,N,P-PNP)(CO)3]+ is in general endergonic, while for [Mn(κ3P,N,P-PNPNH-tBu)(CO)3]+, this process is thermodynamically favored. X-ray structures of representative complexes are provided.Graphical abstract

Crystal structure of the tetra­hydro­furan disolvate of a 94:6 solid solution of [N2,N6-bis­(di-tert-butyl­phosphan­yl)pyridine-2,6-di­amine]­dibromido­manganese(II) and its monophosphine oxide analogue

The MnBr2 complex of N 2,N 6-bis(di-tert-butylphosphanyl)pyridine-2,6-diamine (1·MnBr2) co-crystallizes with 5.69% of the monophosphine oxide analogue (1O·MnBr2) and two tetrahydrofuran (THF) molecules, namely {N 2,N 6-bis(di-tert-butylphosphanyl)pyridine-2,6-diamine}dibromidomanganese(II)–[bis(di-tert-butylphosphanyl)({6-[(di-tert-butylphosphanyl)amino]pyridin-2-yl}amino)phosphine oxide]dibromidomanganese(II)–tetrahydrofuran (0.94/0.06/2), [MnBr2(C21H41N3P2)]0.94[MnBr2(C21H41N3OP2)]0.06·2C4H8O. The 1·MnBr2 and 1O·MnBr2 complexes are connected by weak N—H⋯Br hydrogen bonding into chains extending along [001] with the THF molecules located between the layers formed by these chains.

Non-order–disorder allotwinning of the rhenium pincer complex cis-Re[(PNPCH2-iPr)(CO)2Cl]

Crystals of cis-Re[(PNPCH2-iPr)(CO)2Cl] are made up of two distinct non-order–disorder polytypes.

Crystal structure of bis­[μ-2-(diiso­propyl­phosphor­yl)propan-2-olato-κ3O1,O2:O1]bis­[chlorido­oxidovanadium(IV)]

The dinuclear title molecular complex is centrosymmetric, with the VIV atom in a distorted square-pyramidal coordination environment.