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2. (10 points) Phosphines (PR) act as Lewis bases in a way analogous to ammonia. An MO diagram for the simplest phosphine, PH3, is shown below. H3 P a' e 1 е $ Ca, a. Sketch the HOMO and LUMO of PH, based on the diagram. Which frontier orbital is involved in the Lewis base behavior of phosphine? b. Bulky phosphines such as P(t-Bu), combined with bulky Lewis acids such as B(C6Fs) cannot form normal Lewis adducts due to steric hindrance. These systems are called "frustrated Lewis pairs" (FLPs) and can do some interesting chemistry with small molecules, such as CO2 (Mömming et al. Angew. Chem. Int. Ed., 2009, 48, 6643-6646.) When CO2 interacts with a FLP, which atom in CO2 binds to the phosphine Lewis base? Which atom binds to the borane Lewis acid? Explain.