In Situ Electrochemical-NMR Spectroscopy. Reduction of Aromatic Halides

A three-electrode, two-compartment cylindrical electrochemical cell has been constructed for in situ operation in a 500 MHz ¹H NMR spectrometer. The cell was designed around a standard 10-mm sample tube holder and is lowered into position within the magnet by height-adjustable aluminum rods that support the wires connecting the potentiostat to the working, auxiliary and reference electrodes. The electrochemical cell functions under diffusion-controlled conditions in nonspinning mode and is able to operate under variable temperature and oxygen-free regimes. The working electrode consists of a 10-nm-thick gold film deposited onto the surface of a 7.49-mm-o.d. glass NMR tube that is located directly within the radio frequency coils of the NMR probe. The NMR spectra were collected simultaneously to the current flowing during the electrolysis with typical NMR line widths being approximately 2 Hz. The highly symmetrical nature of the cell design meant that probe tuning and gradient shimming changed minimally between experiments, which allowed standard shim sets to be saved and recalled for later use, thereby greatly reducing the time taken for tuning processes. Insertion and removal of the cell from within the magnet is achieved within a few seconds, which combined with the rapid shimming process makes the cell suitable for routine operation. The cell was used to study the in situ reduction of 9-bromoanthracene, 9-chloroanthracene, and 4-bromobenzophenone in deuterated acetonitrile with tetrabutylammonium hexafluorophosphate as the supporting electrolyte.