Synthesis and reactivity of cationic iridium(III) complexes

Chapter 1. Synthesis and characterization of a set of iridium(III) compounds utilizing the sterically encumbering hydridotris(3,5-dimethylpyrazolyl)borate ligand (TpMe2) has been performed and a comparison with the corresponding Cp* complexes is presented. TpMe2(PMe₃)Ir(Me)OTf (7, OTf = O₃SCF₃) was synthesized and found to be unreactive toward a variety of C-H bonds in contrast to the behavior of Cp*(PMe₃)IrMeOTf (1). We have rationalized this lack of reactivity in terms of an electronic effect rather than a steric effect imposed by the TpMe2 ligand.; Chapter 2. A comparison of the electron-donating abilities of the hydridotris(pyrazolyl)borate ligand and cyclopentadienyl ligand toward several transition metals is presented. These data demonstrate that there is no definitive trend in donor ability across the periodic table and that broad generalizations about the relative donating abilities of the two ligands should be discouraged.; Chapter 3. Synthesis of the cationic hydridotris(pyrazolyl)borate iridium(III) complex, [Tp(PMe₃)IrMe(CH₂Cl₂)][BAr _f] (2-CH₂Cl₂, Tp = hydridotris(pyrazolyl)borate, BAr_f = B[3,5-C₆H₃(CF₃)₂] ₄) is reported. Spectroscopic characterization of 2-CH₂Cl ₂ in CH₂Cl₂ solution indicates that exchange of bound CH₂Cl₂ with free CH₂Cl₂ is slow on the NMR time scale. A steric rationale for these binding preferences is presented. A kinetic study on the substitution of CH₂Cl ₂ in 2-CH₂Cl₂ by CD₃CN is described. The data are most consistent with dissociative loss of CH ₂Cl₂ to generate the unsaturated species [Tp(PMe₃)IrMe][BAr _f] which then reacts with CD₃CN to generate [Tp(PMe ₃)IrMe(NCCD₃)][BAr_f]. The relevance of these substitution experiments to C-H activation by cationic iridium(III) complexes is discussed.; Chapter 4. Reaction of Cp*(PMe₃)IrPh(OH) (1) with nitriles is undetectably slow in benzene solution at room temperature. However, in the presence of Cp*(PMe₃)IrPh(OTf) (2) (OTf = O₃SCF₃) the reaction is strongly catalyzed, leading to iridium(III) carboxamides Cp*(PMe₃)IrPh[NHC(O)R] (6a–d) [R = C₆H₄CH₃ ( 6a), C₆H₅ (6b), C₆H ₄CF₃ (6c), CH₃ (6d)]. We propose that these transformations occur by initial displacement of the trifluoromethanesulfonate (“triflate”) anion of 2 by a molecule of nitrile, leading to a nitrile-substituted iridium cation [Cp*(PMe₃)IrPh(NCR)]+ (10). Following this, the nucleophilic hydroxide group of 1 attacks the (activated) nitrile molecule bound in 10, leading (after proton transfer) to the iridium carboxamide complex. (Abstract shortened by UMI.)...