Activation of a (cyclooctadiene) rhodium(i) complex supported by a chiral ferrocenyl phosphine thioether ligand for hydrogenation catalysis: a combined parahydrogen NMR and DFT study

Abstract

The reaction of [RhCl(P,S(t)Bu)(COD)] (1) or [Rh(P,S(t)Bu)(COD)]BF4 (2) where (P,S(t)Bu) is CpFe[η(5)-1,2-C5H3(PPh2)(CH2S(t)Bu)] with H2 in MeOH gives rise to COD hydrogenation and formation of a solvent-stabilized product. The formation of hydride species cannot be observed in view of a very rapid H/D exchange between H2 and the solvent. Introduction of pyridine or acetonitrile slows down this exchange process and allows observation of diastereometric dihydride complexes, [Rh(P,S(t)Bu)(H)2(L)2](+), the stereochemistry of which was fully elucidated. The hydride site exchange rates have been derived from EXSY NMR experiments and used, with assistance from DFT calculation, to elucidate the isomerization and site exchange mechanisms.

Ketone Hydrogenation with Iridium Complexes with “non N–H” Ligands: The Key Role of the Strong Base

“…In the absence of base, activation of either [IrCl­(COD)] 2 / 1 Et or [Ir­(OMe)­(COD)] 2 / 1 Et with H 2 in a coordinating solvent such as i PrOH, presumably generates [Ir­(H) 2 ( 1 Et )­( i PrOH) 2 ] + after COD hydrogenation and cyclooctene expulsion. Related species have been observed for the rhodium analogue by 1 H NMR using para- hydrogen induced polarization . Subsequent deprotonation by the external or internal base could lead for instance to [IrH­( 1 Et )­( i PrOH)] or to the related alkoxide derivative [Ir­(O i Pr)­( 1 Et )­( i PrOH)], from which a host of different mechanisms may be imagined.…”

“…Related species have been observed for the rhodium analogue by 1 H NMR using para-hydrogen induced polarization. 84 Subsequent deprotonation by the external or internal base could lead for instance to [IrH(1 Et )(iPrOH)] or to the related alkoxide derivative [Ir(OiPr)(1 Et )(iPrOH)], from which a host of different mechanisms may be imagined. When the reaction is carried out in an aromatic hydrocarbon solvent, η 2 -arene coordination or alkoxide bridge formation can temporarily saturate the iridium coordination sphere, although the vacant position can then be saturated by the ketone substrate or by the alcohol product.…”

Spatially Resolved Kinetic Model of Parahydrogen Induced Polarisation (PHIP) in a Microfluidic Chip

“…A molecule of cyclooctene (COE) and an active catalyst molecule are produced. [23] The catalytic cycle starts with coordination of the unsaturated precursor molecule. [24] The next step is the oxidative addition of hydrogen into the complex followed by a migratory insertion onto the unsaturated molecule, which results in an alkene.…”

“…A set of kinetic equations was derived from the known reaction mechanism. [ 23 , 24 , 25 ] Although kinetic data can be obtained using microfluidic devices, such measurements are much more cumbersome due to limited signal‐to‐noise ratio (SNR) in the microfluidic system with thermal hydrogen. Additionally, the time scale for the formation of propyl acetate is difficult to reach in flow as extremely low flow rates would be required.…”

Carbon–Hydrogen Activation in Zerovalent Bis(1,5-cyclooctadiene) Complexes of the First Row Transition Metals: A Theoretical Study

“…The formation of (C 8 H 10 )­(C 8 H 14 )Ti proceeds by two successive C–H activation processes and effectively represents the dehydrogenation of 1,5-cyclooctadiene to 1,3,5-cyclooctatriene on a titanium center with the second 1,5-cyclooctadiene ligand as the hydrogen acceptor. Such C–H activation studies can provide insight into the functionalization of various hydrocarbons. − …”