Synthesis, Structure, Spectroscopy, and Reactivity of Half-Open Rhodocenium and Iridocenium with Oxodienyl Ligands

Abstract

The syntheses of the oxopentadienyl complex [Cp*Rh(η5-CH2C(Me)CHC(Me)O)][BF4] (6) and the iridaoxabenzene [Cp*IrAg2(μ2-OPF2O)2(1,5-η-CHC(CMe3)CHC(CMe3)O)] (9) are reported. Compound 9 is an organometallic polymer, formed in competition with complex [(Cp*Ir)2(μ2-OPF2O)3][PF6] (8). Treatment of [Cp*MCl2]2 (M = Rh, Ir) with lithium 2-methyl-4-oxopentadienide produces Cp*M(Cl)[η3-CH2C(Me)CHC(Me)(O)] (M = Ir, 7; Rh, 10). 1H and 13C NMR, as well as IR spectra, indicate that the ligand acts as an η3-oxodienyl group with an exo-syn conformation. The addition of phosphines, PR3 (R = Ph, Me or PR3 = PHPh2), in acetone to compound [Cp*Ir(η5-CH2C(Me)CHC(Me)O)][PF6] (1) led to the formation of isomers [Cp*Ir(1,5-η-CH2C(Me)CHC(Me)O)(L)][PF6] [L = PMe3, 11; PPh3, 15] and [Cp*Ir(η3-CH2C(Me)CHC(Me)O)(L)][PF6] [L = PMe3, 12; PHPh2, 14; PPh3, 16]. The 1,5-η and the η3 isomers are the kinetic and thermodynamic products, respectively. The addition of phosphines PR3 (R = Me, Ph) in methylene chloride to compound 6 led to the formation of compounds [Cp*Rh(η3-CH2C(Me)CHC(Me)O)(L)][BF4] [L = PMe3, 18; PPh3, 20]. Compounds 18, 20, and [Cp*Rh(η3-CH2C(Me)CHC(Me)O)(PHPh2)][OTf] (21) can also be obtained by adding the corresponding phosphine to compound 10, followed by the addition of AgOTf. The addition at room temperature of acetonitrile to compound 1 led to the formation of [Cp*Ir(η3-CH2C(Me)CHC(Me)O)(NCMe)][PF6] (22), with an exo-anti conformation of the oxodienyl ligand. Facile dissociation of MeCN became evident. The exo-anti isomer structure of 22 has unequivocally been established by an X-ray diffraction study. The analogous rhodium exo-syn isomer [Cp*Rh(η3-CH2C(Me)CHC(Me)O)(NCMe)][BF4] (23) has been established by 1H and 13C NMR spectroscopy. Exo-anti and exo-syn preferences have been established for all synthesized rhodium and iridium compounds. Compounds 1 and 6 did not suffer oxidative addition with SnCl4 and I2. With I2 the bridged iodine compounds [(Cp*M)2(μ2-I)3][X] (M = Ir, X = PF6, 25; M = Rh, X = BF4, 26) were obtained. Crystal structures for iridium compounds 1, 9, 22, and 25 and rhodium compounds 6, 10, 18, and [Cp*Rh(η3-CH2C(Me)CHC(Me)O)(H2O)][BF4] (24) are described.