(i) Complexes of the form LNi(CO)3 are commonly used to measure on a scale the electron-donating ability of ligands (L), particularly phosphines. Briefly describe how this assessment is carried out, including details of the type of spectroscopy used, how the measurement is influenced by the ligand, and how electronic and steric factors are separated.

(ii) You are carrying out a hydrogenation using [Rh(COD)2][BF4] (COD = cyclo-octa-1,5-diene) and have a range of monodentate phosphines available. Kinetic data suggests that the reductive elimination step is rate-limiting. What type of electronic adjustment in the choice of phosphine ligand is likely to enhance the reaction rate? Where will such ligands fall in the scale in part

(i)? Give two example ligand structures with contrasting donor abilities but similar steric demands, and specify which is likely to be preferable here.