H. Amouri

η4-quinone, η5-semiquinone and η6-hydroquinone complexes of pentamethylcyclopentadienyl iridium. X-ray molecular structure of [Cp*Ir(η4-1,4 benzoquinone)]

Abstract Treatment of hydroquinone with [Cp * Ir(solvent) 3 ][BF 4 ] 2 ( 1 ) in acidic medium afforded the stable π -bonded complex [Cp * Ir( η 6 -hydroquinone)][BF 4 ] 2 ( 2 ) in high yield. Complex 2 can be easily deprotonated by a base to give the related [Cp * Ir( η 5 -semiquinone)][BF 4 ] ( 3 ) and [Cp * Ir( η 4 -quinone)] ( 4 ) compounds identified by spectroscopic methods. Complex 4 reacts with an excess of HBF 4 ·Et 2 O to give the starting material 2 quantitatively. Interestingly, these chemical transformations occur with facile reversible changes of the oxidation state from Ir(III) to Ir(I). Further the X-ray molecular structure of 4 is reported.

The rearrangement pathway in [Cp2Mo2(CO)4(RCCCR2)]+ cations: An extended Hückel molecular orbital and Bürgi-Dunitz trajectory study

Abstract The fluxional behavior of metal cluster cations of the type [Cp2Mo2(CO)4(RCCCR′R″)]+ has been widely studied by variable-temperature NMR techniques, and a mechanism involving migration of the carbocationic center between the organometallic vertices has been proposed. In this report, the suggested mechanism has been investigated by means of extended Huckel molecular orbital calculations (EHMO), and allows the evaluation of the lowest energy pathway by which this process may occur. These computations are supplemented by a Burgi-Dunitz trajectory analysis of 11 X-ray crystal structures of such cations which yields a series of “snapshots” of the migration process. Together the EHMO and trajectory approaches give a remarkably complete picture of the molecular dynamics of such molecules.

Unexpected formation of Cp* IrCl2PPh3 from the reaction of [Cp* Ir(η5-C6H5O)][BF4] with PPh3 in dichloroethane involving C-Cl bond activation

The reaction of [Cp* Ir( η 5 -C 6 H 5 O)][BF 4 ] ( 1 ) with PPh 3 in refluxing C 2 H 4 Cl 2 afforded unexpectedly but reproducibly the known compound Cp* IrCl 2 PPh 3 ( 2 ) which was identified by 1 H-NMR spectroscopy and single crystal X-ray diffraction. This unexpected chemical transformation to give 2 involves ‘C-Cl’ abstraction from dichloroethane mediated by the ‘Cp* Ir’ fragment. A rationale for this surprising transformation is advanced.

Surprisingly facile decomposition of the dication : a metal-mediated Hunsdiecker reaction of a succinimidyl ester?

Abstract A series of dicationic organoiridium complexes [Cp * Ir(arene)] 2+ , ( 4 , 5 and 6 ) have been prepared in which the π-bonded phenyl ring is attached to an alkyl chain terminated by a succinimidyl ester, thus forming Bolton-Hunter reagents for protein labelling. In solution, the benzyl derivative, 4 , underwent facile decomposition. Loss of the succinimidyl moiety followed by decarboxylation led to [Cp * Ir(η-MeO C 6 H 4 Me)][BF 4 ] 2 ( 7 ). This product was characterized spectroscopically and by X-ray crystallography. Compound 7 crystallizes in the space group P2 1 /a with a = 13.567(5)A, b = 17.664(1)A, c = 9.044(5)A, β = 90.15°, V = 2167A 3 and Z = 4. A rationale for this surprisingly facile decomposition invokes stabilization of the intermediate benzyl radical by the iridium.

bis[Dichloro(η-pentamethylcyclopentadienyl)rhodium(III) and -iridium(III)] from bis[Chloro(1, 5-cyclooctadiene)rhodium(I) and -iridium(I)] Oxidation, and Formation of 1, 5-Cyclooctadiene(η-pentamethylcyclopentadienyl)rhodium(I)

Abstract An efficient and rapid alternative route for high yield (>90%) syntheses of [Cp∗MCl2]2 complexes (M = Rh, Ir) is described. This method involves the oxidation of M(I) to M(III) with HCl, from the commercially available [MCl(cod)]2 compounds (cod = 1, 5 cyclooctadiene). Repeating the above experiments for M =Rh but using Na2CO3 instead of HCl, afforded the known compound [Cp∗RhCod].

Electrochemical behavior of some bioorganometallic complexes

Abstract An electrochemical investigation of several complexes of the type Ru(II)Cp∗(Ar) and Rh(III)Cp∗(Ar) ( Cp ∗ = η 5 - pentamethylcyclopentadienyl, Ar = aromatic ring ) has been performed. The electrochemical results, although very complicated from a mechanistic point of view, nonetheless suggest a possible application of RuCp∗ and RhCp∗ fragments as labels of steroids for polarographic assay.

Activation and regioselective ortho-functionalization of phenols promoted by ‘Cp*Ir’ fragment: synthesis, structures and applications to organic synthesis. Cp*=C5Me5

Abstract Several stable oxo-dienyl–iridium complexes of the type [Cp*Ir(oxo- η 5 -dienyl)][BF 4 ] ( 2b – 6 ) have been prepared in high to quantitative yields. Treatment of these oxo-dienyl compounds with NaOMe affords the corresponding novel neutral dienone complexes of the type [Cp*Ir(oxo- η 4 -dienone)] ( 7 – 11 , 17 ). Subsequent mild oxidation of the novel dienone–iridium complexes by I 2 produces the related functionalized free phenols along with the starting organometallic material recycled in the form [Cp*Ir( μ -I)I] 2 . Extension of this chemistry to other type of nucleophiles such as phosphines, allows the isolation of a stable iridium η 4 -phenol tautomer complex [Cp*Ir( η 4 -exo-2-(PMe 3 )–C 6 H 5 O)] + . The latter was identified by X-ray diffraction and represents the key intermediate for the nucleophilic phenol functionalization reaction and the first molecular structure of a monocyclic phenol tautomer complex. Finally the use of the Cp*Ir system in organic synthesis is presented and discussed.

Charge stabilization in cationic anthronyl-substituted alkynes: synthesis, characterization and X-ray molecular structures of M2L6 complexed alkynyl-substituted C10-anthrone [M2L6(μ,η2,η2-R2CCC(OR1)(C13H8O))] (M2L6 Co2(CO)6, MoCoCp(CO)5)

Abstract A series of the novel M 2 L 6 -complexed alkynyl-substituted C10-anthrone derivatives were prepared and fully characterized. Furthermore, the X-ray molecular structures of three complexes belonging to this family were determined with the general formula M 2 L 6 ( μ , η 2 , η 2 -R 3 CCC(OR 1 )(C 13 H 8 O))], M 2 L 6  Co 2 ( CO ) 6 . R 1  CH 3 . R 2  H 5; M 2 L 6  MoCOCp ( CO ) 5 . R 1  CH 3 , R 2  H 7 and M 2 L 6  CO 2 ( CO ) 6 . R 1  CH 3 , R 2  C 6 H 5 8. Addition of HBF 4 to the compounds [MoCoCp(CO) 5 ( μ , η 2 , η 2 -HCCC(OR 1 )(C 13 H 8 O))], R 1 H 6: R 1 CH 1 7, produced the cationic counterpart [MoCOCp(CO) 5 ( μ , η 2 , η 2 -HCCC(C 13 H 8 O))] + BF 4 9 The charge stabilization in this novel carbenium ion possessing an anthrone fragment was investigated and showed that the dinuclear cluster alleviates the positive charge at the C10 carbon center. Further, the reactivity of these carbenium ion towards nucleophiles was also examined.