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

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

We report a spatially resolved kinetic finite element model of parahydrogen-induced polarisation (PHIP) in a microfluidic chip that was calibrated using on-chip and off-chip NMR data. NMR spectroscopy has great potential as a read-out technique for lab-on-a-chip (LoC) devices, but is often limited by sensitivity. By integrating PHIP with a LoC device, a continuous stream of hyperpolarised material can be produced, and mass sensitivities of pmol s have been achieved. However, the yield and polarisation levels have so far been quite low, and can still be optimised. To facilitate this, a kinetic model of the reaction has been developed, and its rate constants have been calibrated using macroscopic kinetic measurements. The kinetic model was then coupled with a finite element model of the microfluidic chip. The model predicts the concentration of species involved in the reaction as a function of flow rate and position in the device. The results are in quantitative agreement with published experimental data.

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

Stepwise interaction of first row transition metal atoms with 1,5-cyclooctadiene to give (C₈H₁₂)₂M complexes is studied using the M06-L/DZP density functional method. The experimentally known (C₈H₁₂)₂Ni is the thermodynamically most favorable complex, with a predicted geometry consistent with its experimental structure as determined by X-ray crystallography. The other transition metal atoms from scandium to zinc also interact exothermically with 1,5-cyclooctadiene to give (C₈H₁₂)₂M derivatives, but these exhibit lower symmetry than the S₄ symmetry exhibited by (C₈H₁₂)₂Ni. Carbon-hydrogen activation of CH₂ groups in a C₈H₁₂ ligand is predicted for most systems. Thus, conversion of (η^2,2-C₈H₁₂)₂M to (η^3,2-C₈H₁₁)(η^2,1-C₈H₁₃)M, through a hydride intermediate (η^3,2-C₈H₁₁)(η^2,2-C₈H₁₂)MH, is predicted for scandium, vanadium, chromium, manganese, and cobalt. For titanium with a low-lying empty orbital, further C-H activation through a hydride intermediate (η⁶-C₈H₁₀)(η^2,1-C₈H₁₃)TiH is predicted, leading ultimately to (η⁶-C₈H₁₀)(η^1,1-C₈H₁₄)Ti, in which the hexahapto η⁶-C₈H₁₀ ligand is shown by NICS to be aromatic. These two C-H activation processes on a titanium center represent the dehydrogenation of 1,5-cyclooctadiene to 1,3,5-cyclooctatriene with the second 1,5-cyclooctadiene ligand as the hydrogen acceptor. For zinc C-H activation terminates at (η¹-C₈H₁₁)(C₈H₁₂)ZnH, which has a C-Zn-H three-center bond. No energetically favorable C-H activation processes are predicted for the iron, nickel, and copper (η^2,2-C₈H₁₂)₂M derivatives.