Synthesis of rhodium complexes of an asymmetric η5,η1,η1-cyclo-pentadienyl-bis(phosphine) ligand by regioselective intramolecular dehydrofluorinative C-C coupling

The reaction between [{(eta (5)-C5Me4H)RhX2}(2)] and (C6F5)(2)PCH2CH2P(C(6)F7(5))(2) (dfppe) proceeds in refluxing benzene via cleavage of two C-F bonds and C-H bonds of adjacent methyl groups and formation of two C-C bonds to yield selectively the asymmetric cation [{eta (5),eta (1),eta (1)-C5HMe2-3,4-[CH2-2-C6F4P(C6F5)CH2](2)-1,2}RhX](+). The selectivity for X=Cl was determined to be > 90%. Treatment of [(eta (5)-C5Me4H)RhCl(dfppe)]BF4 With proton sponge afforded [{eta (5),eta (1),eta (1)-C5HMe2-3,4-[CH2-2-C6F4P(C6F5)CH2](2)- 1,2}RhCl]BF4 exclusively. The regioselectivity displayed by these reactions is in stark contrast to that in the reaction between [(Cp*RhX2)(2)] and dfppe, and that between [Cp*RhCl(dfppe)](+) and proton sponge, in which C-H bonds of methyl groups in a 1,3 disposition are cleaved to yield the cation [{eta (5),eta (1),eta (1)-C5Me3[CH2-2-C6F4P(C6F5)CH2](2)-1,3}RhX](+) exclusively. The structure of [{(eta (5)-C5Me4H)RhCl2}(2)] has been determined by single-crystal X-ray diffraction. (C) 2001 Elsevier Science B.V. All rights reserved.