Trimethylphosphine-tris(pentafluorophenyl)borane

The title simple Lewis acid-base adduct, C21H9BF15P or (H3C)(3)P-B(C6F5)(3), is essentially insoluble in most noncoordinating organic solvents. The P-B bond lies along a threefold rotation axis. It crystallizes in the trigonal space group R (3) over bar. Weak intramolecular C-H center dot center dot center dot F contacts are present between the methylphosphine and the ortho-F atoms of the fluoroarylborane, resulting in an eclipsed geometry in the reaction partners. The observed insolubility is likely to be due, in part, to an additional intermolecular network of weak contacts involving the para-F atoms of the B-C6F5 groups and the P(CH3)(3) group.