Reaction of 1-aryl-2-methylenecyclopropanes with rhodium(I) complexes leading to ring opening isomerization and pi co-ordination of the C = C double bond

1-Aryl-2-methylenecyclopropanes reacted with [RhCl(PPh3)(3)] at 50 degrees C to give [RhCl(eta(4)-CH2=CArCH=CH2) (PPh3)(2)] (Ar = C6H5 1a, C6H4F-p 1b, C6H4Me-p 1c or C6H4OMe-p 1d) via ring opening isomerization of the substra te and its subsequent co-ordination to Rh. The diene-co-ordinated rhodium c omplexes have been characterized by X-ray crystallography and NMR spectrosc opy. Similar reaction at 0 degrees C afforded the rhodium(I) complexes with x-coordinated 1-aryl-2-methylenecyclopropane, [RhCl(eta(2)-CH2=CCH2CHAr)(P Ph3)(2)] (Ar = C6H5 2a, C6H4F-p 2b, C6H4Me-p 2c or C6H4OMe-p 2d). Exchange of the ligand of 2a with added 1-aryl-2-methylenecyclopropanes occurs rever sibly at 30-45 degrees C with the thermodynamic parameters of the reactions 2a + CH2=CCH2CHC6H4X-p reversible arrow 2b (or 2c) + CH2=CCH2CHC6H5 being Delta H degrees = -10.3 kJ mol(-1) and Delta S degrees = -32 J K-1 mol(-1) for X = F and Delta H degrees = 2.2 kJ mol(-1) and Delta S degrees = -2.6 J K-1 mol(-1) for X = Me, respectively, at 298 K. The structure of a PEt3 co -ordinated analog, [RhCl(eta(2)-CH2=CCH2CHC6H4Me-p) (PEt3)(2)] 3c, has been determined by X-ray crystallography. The reaction of 1-methylene-2-phenylc yclopropane with [RhCl(PPh3)(3)] at 25 degrees C gave a mixture of 1a and 2 a. Heating of a benzene solution of 2a at 50 degrees C turned it into 1a in low yield (<7%), while the reactions of 1-methylene-2-phenylcyclopropane w ith 2a at the same temperature gave 1a (10%) and 2-phenylbuta-1,3-diene (14 %). The amounts of the products formed via ring opening isomerization in th ese reactions are much smaller than those in the reaction of 1-methylene2-p henylcyclopropane with [RhCl(PPh3)(3)] at 50 degrees C.