Carbon–fluorine bond cleavage as a route to hybrid ligands

Intramolecular CF bond cleavage provides a convenient, high yield route to metal complexes of hybrid cyclopentadienyl-phosphine ligands. On treatment with proton sponge the complexes [Cp∗RhCl{(C6F5)2PCH2CH2P(C6F5)2}]BF4 and [Cp∗RhCl{(C6F5)2PC6H4SMe-2}]BF4 undergo dehydrofluorinative CC coupling to give the complexes [{η5,η1,η1-C5Me3[CH2C6F4P(C6F5)CH2]2-1,3}RhCl]BF4 and [{η5,η1,η1-C5Me4CH2C6F4P(C6F5)C6H4SMe-2}RhCl]BF4 rapidly and in quantitative yield. The reaction between [Cp∗RhCl{PPh2(C6F5)}(CNR)]BF4 (R=phenyl or cyclohexyl) and proton sponge produces [(η5,η1-C5Me4CH2C6F4PPh2)RhCl(CNR)]BF4, but is far slower and much less clean than for the complexes of the chelating ligands. The neutral complex [Cp∗RhCl2{PPh2(C6F5)}] undergoes no reaction with proton sponge. The proposed mechanism involves initial formation of an η4-fulvene complex, and subsequent nucleophilic attack (SNAr) at an ortho-CF bond.