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.

Metallaaromatic Chemistry: History and Development

“…The C1–C2, C2–C3, and C3–C4 distances are 1.417(5), 1.412(5), and 1.389(5) Å, respectively, and there is very little alternation. These structural parameters strongly indicate the aromaticity of the six-membered ring, which is further supported by its 1 H NMR spectrum (9.61 and 6.83 ppm for H1 and H3, respectively) …”

“…To the best of our knowledge, the polymeric complex 7 is the only iridapyrylium whose structure has been confirmed by X-ray single-crystal diffraction . The sum of internal angles in 7 is ∼719.15°, and there is no atom deviating by more than 0.079 Å from the best mean plane, confirming the planarity of the iridapyrylium ring.…”

“…Another example of a metallapyrylium is complex 7 shown in Figure , which was reported by Paz-Sandoval and co-workers in 2002 . It was generated by dropwise addition of 2,2,5,6,6-pentamethylhept-4-en-3-one to a solution of [Cp*Ir­(OCMe 2 ) 3 ]­(PF 6 ) 2 , which was prepared by the reaction of [Cp*IrCl 2 ] 2 with AgPF 6 in acetone in situ (Scheme ).…”

Synthesis of Planar Chiral Iridacycles by Cationic Metal π‐Coordination: Facial Selectivity, and Conformational and Stereochemical Consequences

“…Under these conditions, compound 2 a remained unreacted, whereas compounds 2 b and 2 d were converted into unique products, i.e., compounds 3 b [PF 6 ] 2 and 3 d [PF 6 ] 2 , in 78 and 20 % yield, respectively (reaction (1)). The time required for complete conversion could be shortened to 15 min when the reaction of compound 2 b with [Cp*Ir(acetone) 3 ](PF 6 ) 2 15 was carried out at low concentrations in acetone. The reactions of ligands 2 a – 2 c with [Cp*Ru(MeCN) 3 ]PF 6 16 in THF at room temperature for over 24 h also led to unique products, i.e., compounds 4 a – 4 c [PF 6 ] in 30, 75, and 75 % yield, respectively (reaction (2)).…”

“…IR spectra were acquired with a FTIR Bruker alpha spectrometer by using an ATR solid‐state sample cell. [Cp*Ir(CH 3 COCH 3 ) 3 ][PF 6 ] 2 15 and [Cp*Ru(NCCH 3 ) 3 ] [PF 6 ]16 were prepared according to literature procedures. The former was dissolved in acetone shortly after its preparation from a reaction of [(Cp*IrCl 2 ) 2 ]13 with AgPF 6 and used as a solution.…”