ACIDOLYSIS OF [MEC(CH2PPH2)3]RH(CH3)N COMPOUNDS - CONTROLLED CREATION OF UNSATURATION

Reaction of (triphos)RhMe3 (triphos = MeC(CH2PPh2)3) with HBF4.OEt2 in CH2Cl2 gives (triphos)RhMe2BF4, which readily adds MeCN and reacts with CO to give acetone and (triphos)Rh(CO)2+. When the protonation product is treated with 100 psi of C2H4, (triphos)Rh(C2H4)2+ is produced. This cation is intramolecularly fluxional and exchanges readily with (C2H4)-C-13. The ethylene is weakly bound and is readily replaced by water to give [(triphos)Rh(C2H4)(H2O)]BF4, whose structure was established by X-ray diffraction. Crystallographic data (-172-degrees-C): a = 10.502 (2) angstrom, b = 16.518 (4) angstrom, c = 24.210 (5) angstrom, and beta = 97.81 (1)-degrees with Z = 4 in space group P2(1)/c. The trigonal-bipyramidal rhodium has C2H4 equatorial and H2O axial. The water hydrogen bonds to BF4 (O...F = 2.665 angstrom). Added ethylene will, in turn, displace coordinated water. This same compound is formed on protonation of (triphos)RhMe(C2H4) in the presence of ethylene and water. Protonation of (triphos)RhMe(C2H4) in the presence of acetonitrile yields (triphos)Rh(NCCH3)(C2H4)+, which has acetonitrile in an axial position. Analysis of variable-temperature H-1, C-13, and P-31 NMR data for these 18-electron cations suggests that they react by preliminary ''arm-off'' dissociation of one of the three phosphorus donor groups.