New Cu(I)-Ethylene Complexes Based on Tridentate Imine Ligands: Synthesis and Structure

A new bulky facially coordinating <i>N</i>₃-donor tach-based ligand (tach: <i>cis,cis</i>-1,3,5-triaminocyclohexane) [<b>1</b>: <i>cis,cis</i>-1,3,5-tris­(2-fluoro-6-(trifluoromethyl)­benzylideneamino)­cyclohexane] has been obtained from the condensation of tach with 3 equiv of the appropriate benzaldehyde. Reaction of <b>1</b> with [Cu­(NCMe)₄]­[PF₆] gave the complex [(<b>1</b>)­Cu­(NCMe)]­[PF₆]. Displacement of the acetonitrile ligand is possible with CO and C₂H₄ (3–5 bar). Cu­(I)-ethylene complexes of ligands <b>1</b> and <b>2</b> [<b>2</b>: <i>cis,cis</i>-1,3,5-(mesitylideneamino)­cyclohexane] were prepared successfully by treatment of the ligands with CuBr and AgSbF₆ in the presence of ethylene. These complexes display reversible complexation of the ethylene molecule under mild changes to pressure, suggesting possible application in olefin separation and extraction

New Cu(I)-Ethylene Complexes Based on Tridentate Imine Ligands: Synthesis and Structure

A new bulky facially coordinating <i>N</i>₃-donor tach-based ligand (tach: <i>cis,cis</i>-1,3,5-triaminocyclohexane) [<b>1</b>: <i>cis,cis</i>-1,3,5-tris­(2-fluoro-6-(trifluoromethyl)­benzylideneamino)­cyclohexane] has been obtained from the condensation of tach with 3 equiv of the appropriate benzaldehyde. Reaction of <b>1</b> with [Cu­(NCMe)₄]­[PF₆] gave the complex [(<b>1</b>)­Cu­(NCMe)]­[PF₆]. Displacement of the acetonitrile ligand is possible with CO and C₂H₄ (3–5 bar). Cu­(I)-ethylene complexes of ligands <b>1</b> and <b>2</b> [<b>2</b>: <i>cis,cis</i>-1,3,5-(mesitylideneamino)­cyclohexane] were prepared successfully by treatment of the ligands with CuBr and AgSbF₆ in the presence of ethylene. These complexes display reversible complexation of the ethylene molecule under mild changes to pressure, suggesting possible application in olefin separation and extraction

Zirconium-Catalyzed Imine Hydrogenation via a Frustrated Lewis Pair Mechanism

Zirconium-based frustrated Lewis pairs (FLPs) are active imine hydrogenation catalysts under mild conditions. Complexes of the type [Cp^R₂ZrOMes]­[B­(C₆F₅)₄] utilize the imine substrate itself as the Lewis base component of the FLP. Catalyst performance is a function of ligand structure; in general more bulky, more electron rich cyclopentadienyl derivatives give the best results. However, Cp* derivatives are not catalytically active, being stable after initial heterolytic cleavage of H₂; this allows experimental verification of the competence of the zirconocene–imine pair in FLP-type heterolytic H₂ cleavage. Enamines and protected nitriles are also hydrogenated if an additional internal phosphine base is used

Catalytic Conversion of Ethanol to <i>n</i>‑Butanol Using Ruthenium P–N Ligand Complexes

We report several ruthenium catalysts incorporating mixed donor phosphine-amine ligands for the upgrade of ethanol to the advanced biofuel <i>n</i>-butanol, which show high selectivity (≥90%) at good (up to 31%) conversion. In situ formation of catalysts from mixtures of [RuCl₂(η⁶-<i>p</i>-cymene)]₂ and 2-(diphenylphosphino)­ethylamine (<b>1</b>) shows enhanced activity at initial water concentrations higher than those of our previously reported diphosphine systems. Preliminary mechanistic studies (electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy) suggest the possibility of ligand-assisted proton transfer in some derivatives

Small Molecule Activation by Intermolecular Zr(IV)-Phosphine Frustrated Lewis Pairs

We report intermolecular transition metal frustrated Lewis pairs (FLPs) based on zirconocene aryloxide and phosphine moieties that exhibit a broad range of small molecule activation chemistry that has previously been the preserve of only intramolecular pairs. Reactions with D₂, CO₂, THF, and PhCCH are reported. By contrast with previous intramolecular examples, these systems allow facile access to a variety of steric and electronic characteristics at the Lewis acidic and Lewis basic components, with the three-step syntheses of 10 new intermolecular transition metal FLPs being reported. Systematic variation to the phosphine Lewis base is used to unravel steric considerations, with the surprising conclusion that phosphines with relatively small Tolman steric parameters not only give highly reactive FLPs but are often seen to have the highest selectivity for the desired product. DOSY NMR spectroscopic studies on these systems reveal for the first time the nature of the Lewis acid/Lewis base interactions in transition metal FLPs of this type

Cobalt PCP Pincer Complexes via an Unexpected Sequence of Ortho Metalations

The cobalt PCP pincer complexes [Co­{2,6-(CH₂PPh₂-κ<i>P</i>)₂C₆H₃-κ<i>C</i>¹}­(L)₂], where L = PMe₃ (<b>1</b>), CO (<b>2</b>), have been prepared. Complex <b>1</b> is obtained by a transmetalation reaction between 1-lithio-2,6-bis­((diphenylphosphino)­methyl)­benzene and [CoCl­(PMe₃)₃]. Subsequent exposure of <b>1</b> to CO gave complex <b>2</b>. Complexes <b>1</b> and <b>2</b> can also be obtained from 1,3-bis­((diphenylphosphino)­methyl)­benzene and [CoMe­(PMe₃)₄]. Instead of ortho metalation occurring directly at the C2 (pincer) position of the diphosphine, ortho metalation first occurs at the C4 position to form [Co­{2-(CH₂PPh₂-κ<i>P</i>)-4-(CH₂PPh₂)-C₆H₃-κ<i>C</i>¹}­(PMe₃)₃] (<b>4</b>). After reflux of the reaction mixture for 24 h, a rearrangement of <b>4</b> occurs to give pincer complex <b>1</b> with loss of PMe₃ in ca. 50% yield; this rearrangement was accompanied by some decomposition. The mechanism for the conversion of <b>4</b> to <b>1</b> has been probed using 1-deuterio-2,6-bis­((diphenylphosphino)­methyl)­benzene. Unexpectedly, the labeled ligand led to 15% deuterium enrichment of an ortho CH of the terminal PPh₂ group in the product complex <b>1</b>, and the proposed mechanism for this rearrangement involves a four-membered cobaltacyclic intermediate

Cobalt PCP Pincer Complexes via an Unexpected Sequence of Ortho Metalations

The cobalt PCP pincer complexes [Co­{2,6-(CH₂PPh₂-κ<i>P</i>)₂C₆H₃-κ<i>C</i>¹}­(L)₂], where L = PMe₃ (<b>1</b>), CO (<b>2</b>), have been prepared. Complex <b>1</b> is obtained by a transmetalation reaction between 1-lithio-2,6-bis­((diphenylphosphino)­methyl)­benzene and [CoCl­(PMe₃)₃]. Subsequent exposure of <b>1</b> to CO gave complex <b>2</b>. Complexes <b>1</b> and <b>2</b> can also be obtained from 1,3-bis­((diphenylphosphino)­methyl)­benzene and [CoMe­(PMe₃)₄]. Instead of ortho metalation occurring directly at the C2 (pincer) position of the diphosphine, ortho metalation first occurs at the C4 position to form [Co­{2-(CH₂PPh₂-κ<i>P</i>)-4-(CH₂PPh₂)-C₆H₃-κ<i>C</i>¹}­(PMe₃)₃] (<b>4</b>). After reflux of the reaction mixture for 24 h, a rearrangement of <b>4</b> occurs to give pincer complex <b>1</b> with loss of PMe₃ in ca. 50% yield; this rearrangement was accompanied by some decomposition. The mechanism for the conversion of <b>4</b> to <b>1</b> has been probed using 1-deuterio-2,6-bis­((diphenylphosphino)­methyl)­benzene. Unexpectedly, the labeled ligand led to 15% deuterium enrichment of an ortho CH of the terminal PPh₂ group in the product complex <b>1</b>, and the proposed mechanism for this rearrangement involves a four-membered cobaltacyclic intermediate