Synthesis of Highly Fluorinated Arene Complexes of [Rh(Chelating Phosphine)]+ Cations, and their use in Synthesis and Catalysis.

Alasdair I Mckay,Andrew S Weller,Michael C Willis,Max Savage,James Barwick‐Silk

doi:10.1002/chem.201904668

Alasdair I Mckay, Andrew S Weller + Show 3 more

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https://doi.org/10.1002/chem.201904668

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Journal: Chemistry	Publication Date: Feb 11, 2020
Citations: 8	License type: CC BY 4.0

Affiliation: University of Oxford, University of York

Abstract

The synthesis of rhodium complexes with weakly binding highly fluorinated benzene ligands is described: 1,2,3‐F3C6H3, 1,2,3,4‐F4C6H2 and 1,2,3,4,5‐F5C6H are shown to bind with cationic [Rh(Cy2P(CH2)xPCy2)]+ fragments (x=1, 2). Their structures and reactivity with alkenes, and use in catalysis for promoting the Tishchenko reaction of a simple aldehyde, are demonstrated. Key to the synthesis of these complexes is the highly concentrated reaction conditions and use of the [Al{OC(CF3)3}4]− anion.

Highlights

Fluorinated benzenes (PFBs), exemplified by fluorobenzene (FC6H5) through to pentafluorobenzene (F5C6H) (Scheme 1 a), have emerged as versatile solvents in contemporary synthetic chemistry and catalysis
We have reported the synthesis of fluorobenzene (FC6H5) and difluorobenzene (1,2-F2C6H4) complexes [Rh(L2)(FnC6H6Àn)] [BArF4] (L2 = monodentate or bidentate phosphine) as drop–in precatalysts for challenging catalytic transformations.[1b,3,11] These are accessed via hydrogenation of a NBD or COD precursor in the arene of choice (e.g., 1 a, Scheme 1 b)
We report an extension to this synthetic methodology to prepare and structurally characterize fluoroarene complexes of 1,2,3-F3C6H3, 1,2,3,4-F4C6H2 and F5C6H with two different [Rh(Cy2P(CH2)xPCy2)]+ fragments (x = 1 and 2), as partnered with the [Al{OC(CF3)3}4]À anion

Summary

Introduction

Fluorinated benzenes (PFBs), exemplified by fluorobenzene (FC6H5) through to pentafluorobenzene (F5C6H) (Scheme 1 a), have emerged as versatile solvents in contemporary synthetic chemistry and catalysis. Others have reported related fluoroarene complexes.[5f,6,12] While the fluoroarene in these complexes can be replaced by relatively stronger ligands (e.g. acetone) there are instances when substitution does not take place as the arene binds too strongly,[11e] especially with smaller biteangle diphosphine ligands. To overcome this we have recently reported the first structurally characterized metal complex with a weakly binding 1,2,3-F3C6H3 ligand, [Rh(Cy2PCH2PCy2)(1,2,3F3C6H3)][Al{OC(CF3)3}4] 3 a (Scheme 2).[13] Displacement of the fluoroarene by H3B·NMe3 generates the corresponding sigma amine-borane complex. The weakly binding properties of these arenes is exploited in the synthesis of an alkene complex only previously accessible using molecular solid-state solid/gas reactivity in the absence of solvent;[15] and in catalysis for the intermolecular Tishchenko reaction of a simple aldehyde

Results and Discussion

Conclusions

Conflict of interest