Rhodium and Iridium Complexes of Bulky Tertiary Phosphine Ligands. Searching for Isolable Cationic M^III Alkylidenes

Cyclometalated chloride complexes of rhodium and iridium based on (η⁵-C₅Me₅)­M^III fragments that result from the metalation of the xylyl substituent of a coordinated PR₂(Xyl) phosphine (Xyl = 2,6-Me₂C₆H₃) have been prepared by reaction of the appropriate metal precursor with the corresponding phosphine. For iridium, the four complexes <b>1a</b>–<b>d</b>, derived from the phosphines PⁱPr₂(Xyl), PCy₂(Xyl), PMe₂(Xyl), and PPh₂(Xyl), respectively, have been prepared, whereas for rhodium only the complexes <b>2a</b>,<b>d</b>, derived from PⁱPr₂(Xyl) and PMe₂(Xyl), respectively, have been studied. Chloride abstraction from compounds <b>1</b> and <b>2</b> by NaBAr_F (BAr_F = B­(3,5-C₆H₃(CF₃)₂)₄) leads to either cationic dichloromethane adducts or to cationic hydride alkylidene structures resulting from α-H elimination. The rhodium complexes investigated yield only dichloromethane adducts. However, in the iridium system the less sterically demanding phosphines PMe₂(Xyl) and PPh₂(Xyl) also provide dichloromethane adducts as the only observable products, whereas for the bulkier PⁱPr₂(Xyl) and PCy₂(Xyl) ligands the hydride alkylidene formulation prevails. Nonetheless, variable-temperature NMR studies reveal that in solution each of these two structures exists in equilibrium with undetectable concentrations of the other by means of facile reversible α-H elimination and migratory insertion reactions. Reactivity studies on the cationic hydride alkylidene complexes of iridium are reported as well

Efektivní aritmetika eliptických křivek nad konečnými tělesy

The thesis deals with arithmetics of elliptic curves over finite fields and methods to improve those calculations. In the first part, algebraic geometry helps to define elliptic curves and derive their basic properties including the group law. The second chapter seeks ways to speed up these calculations by means of time-memory tradeoff, i.e. adding redundancy. At last, the third part introduces a wholly new curve form, which is particularly effective for such purposes

Cationic Ir(III) Alkylidenes Are Key Intermediates in C–H Bond Activation and C–C Bond-Forming Reactions

This work describes the chemical reactivity of a cationic (η⁵-C₅Me₅)­Ir­(III) complex that contains a bis­(aryl) phosphine ligand, whose metalation determines its unusual coordination in a κ⁴-<i>P</i>,<i>C</i>,<i>C′</i>,<i>C″</i> fashion. The complex (<b>1</b>^<b>+</b> in this paper) undergoes very facile intramolecular C–H bond activation of all benzylic sites, in all likelihood through an Ir­(V) hydride intermediate. But most importantly, it transforms into a hydride phosphepine species <b>4</b>^<b>+</b> by means of an also facile, base-catalyzed, intramolecular dehydrogenative C–C coupling reaction. Mechanistic studies demonstrate the participation as a key intermediate of an electrophilic cationic Ir­(III) alkylidene, which has been characterized by low-temperature NMR spectroscopy and by isolation of its trimethylphosphonium ylide. DFT calculations provide theoretical support for these results

Cationic Ir(III) Alkylidenes Are Key Intermediates in C–H Bond Activation and C–C Bond-Forming Reactions

This work describes the chemical reactivity of a cationic (η⁵-C₅Me₅)­Ir­(III) complex that contains a bis­(aryl) phosphine ligand, whose metalation determines its unusual coordination in a κ⁴-<i>P</i>,<i>C</i>,<i>C′</i>,<i>C″</i> fashion. The complex (<b>1</b>^<b>+</b> in this paper) undergoes very facile intramolecular C–H bond activation of all benzylic sites, in all likelihood through an Ir­(V) hydride intermediate. But most importantly, it transforms into a hydride phosphepine species <b>4</b>^<b>+</b> by means of an also facile, base-catalyzed, intramolecular dehydrogenative C–C coupling reaction. Mechanistic studies demonstrate the participation as a key intermediate of an electrophilic cationic Ir­(III) alkylidene, which has been characterized by low-temperature NMR spectroscopy and by isolation of its trimethylphosphonium ylide. DFT calculations provide theoretical support for these results

Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using “Sandwich” Diimine Palladium Catalysts

Cationic Pd­(II) catalysts incorporating bulky 8-<i>p</i>-tolylnaphthyl substituted diimine ligands have been synthesized and investigated for ethylene polymerization and ethylene/methyl acrylate copolymerization. Homopolymerization of ethylene at room temperature resulted in branched polyethylene with narrow <i>M</i>_w/<i>M</i>_n values (ca. 1.1), indicative of a living polymerization. A mechanistic study revealed that the catalyst resting state was an alkyl olefin complex and that the turnover-limiting step was migratory insertion, thus the turnover frequency is independent of ethylene concentration. Copolymerization of ethylene and methyl acrylate (MA) was also achieved. MA incorporation was found to increase linearly with MA concentration, and copolymers with up to 14 mol % MA were prepared. Mechanistic studies revealed that acrylate insertion into a Pd–CH₃ bond occurs at −70 °C to yield a four-membered chelate, which isomerizes first to a five-membered chelate and then to a six-membered chelate. Barriers to migratory insertion of both the (diimine)­PdCH₃(C₂H₄)⁺ (19.2 kcal/mol) and (diimine)­PdCH₃(η²-C₂H₃CO₂Me)⁺ (15.2 kcal/mol) were measured by low-temperature NMR kinetics

Cyclometalated Iridium Complexes of Bis(Aryl) Phosphine Ligands: Catalytic C–H/C–D Exchanges and C–C Coupling Reactions

This work details the synthesis and structural identification of a series of complexes of the (η⁵-C₅Me₅)­Ir­(III) unit coordinated to cyclometalated bis­(aryl)­phosphine ligands, PR′(Ar)₂, for R′ = Me and Ar = 2,4,6-Me₃C₆H₂, <b>1b</b>; 2,6-Me₂-4-OMe-C₆H₂, <b>1c</b>; 2,6-Me₂-4-F-C₆H₂, <b>1d</b>; R′ = Et, Ar = 2,6-Me₂C₆H₃, <b>1e</b>. Both chloride- and hydride-containing compounds, <b>2b</b>–<b>2e</b> and <b>3b</b>–<b>3e</b>, respectively, are described. Reactions of chlorides <b>2</b> with NaBAr_F (BAr_F = B­(3,5-C₆H₃(CF₃)₂)₄) in the presence of CO form cationic carbonyl complexes, <b>4</b>^<b>+</b>, with ν­(CO) values in the narrow interval 2030–2040 cm^–1, indicating similar π-basicity of the Ir­(III) center of these complexes. In the absence of CO, NaBAr_F forces κ⁴-<i>P</i>,<i>C</i>,<i>C</i>′,<i>C</i>″ coordination of the metalated arm (studied for the selected complexes <b>5b</b>, <b>5d</b>, and <b>5e</b>), a binding mode so far encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C–C coupling reaction converts the κ⁴ species <b>5d</b> and <b>5e</b> into the corresponding hydrido phosphepine complexes <b>6d</b> and <b>6e</b>. Using CD₃OD as the source of deuterium, the chlorides <b>2</b> undergo deuteration of their 11 benzylic positions whereas hydrides <b>3</b> experience only D incorporation into the Ir–H and Ir–CH₂ sites. Mechanistic schemes that explain this diversity have come to light thanks to experimental and theoretical DFT studies that are also reported

Cyclometalated Iridium Complexes of Bis(Aryl) Phosphine Ligands: Catalytic C–H/C–D Exchanges and C–C Coupling Reactions

This work details the synthesis and structural identification of a series of complexes of the (η⁵-C₅Me₅)­Ir­(III) unit coordinated to cyclometalated bis­(aryl)­phosphine ligands, PR′(Ar)₂, for R′ = Me and Ar = 2,4,6-Me₃C₆H₂, <b>1b</b>; 2,6-Me₂-4-OMe-C₆H₂, <b>1c</b>; 2,6-Me₂-4-F-C₆H₂, <b>1d</b>; R′ = Et, Ar = 2,6-Me₂C₆H₃, <b>1e</b>. Both chloride- and hydride-containing compounds, <b>2b</b>–<b>2e</b> and <b>3b</b>–<b>3e</b>, respectively, are described. Reactions of chlorides <b>2</b> with NaBAr_F (BAr_F = B­(3,5-C₆H₃(CF₃)₂)₄) in the presence of CO form cationic carbonyl complexes, <b>4</b>^<b>+</b>, with ν­(CO) values in the narrow interval 2030–2040 cm^–1, indicating similar π-basicity of the Ir­(III) center of these complexes. In the absence of CO, NaBAr_F forces κ⁴-<i>P</i>,<i>C</i>,<i>C</i>′,<i>C</i>″ coordination of the metalated arm (studied for the selected complexes <b>5b</b>, <b>5d</b>, and <b>5e</b>), a binding mode so far encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C–C coupling reaction converts the κ⁴ species <b>5d</b> and <b>5e</b> into the corresponding hydrido phosphepine complexes <b>6d</b> and <b>6e</b>. Using CD₃OD as the source of deuterium, the chlorides <b>2</b> undergo deuteration of their 11 benzylic positions whereas hydrides <b>3</b> experience only D incorporation into the Ir–H and Ir–CH₂ sites. Mechanistic schemes that explain this diversity have come to light thanks to experimental and theoretical DFT studies that are also reported

Distortional Effects of Noncovalent Interactions in the Crystal Lattice of a Cp*Ir(III) Acylhydroxamic Acid Complex: A Joint Experimental–Computational Study

[Cp*Ir­(μ-OH)₃IrCp*]­OH reacts with PhCONHOH to give [Cp*Ir­(η²-ONCOPh)], in which the doubly deprotonated −NHOH unit binds side-on via N and O, an otherwise unrecorded binding mode. The X-ray structure shows pyramidalization at Ir together with secondary bonding between the carbonyl oxygen and Ir (<i>d</i>_Ir···O = 2.873(8) Å). The related <i>o</i>-hydroxyphenyl­hydroxamic acid gives a conventional chelate structure in which both sp³ O atoms are bound in deprotonated form. In contrast, PhSO₂NHOH reacts with S–N cleavage to give the nitrosyl, [Cp*Ir­(NO)­(SO₂Ph)]. A detailed computational analysis identifies noncovalent interactions in the crystal lattice (crystal-packing effects) as responsible for the distortion in [Cp*Ir­(η²-ONCOPh)]

Distortional Effects of Noncovalent Interactions in the Crystal Lattice of a Cp*Ir(III) Acylhydroxamic Acid Complex: A Joint Experimental–Computational Study

[Cp*Ir­(μ-OH)₃IrCp*]­OH reacts with PhCONHOH to give [Cp*Ir­(η²-ONCOPh)], in which the doubly deprotonated −NHOH unit binds side-on via N and O, an otherwise unrecorded binding mode. The X-ray structure shows pyramidalization at Ir together with secondary bonding between the carbonyl oxygen and Ir (<i>d</i>_Ir···O = 2.873(8) Å). The related <i>o</i>-hydroxyphenyl­hydroxamic acid gives a conventional chelate structure in which both sp³ O atoms are bound in deprotonated form. In contrast, PhSO₂NHOH reacts with S–N cleavage to give the nitrosyl, [Cp*Ir­(NO)­(SO₂Ph)]. A detailed computational analysis identifies noncovalent interactions in the crystal lattice (crystal-packing effects) as responsible for the distortion in [Cp*Ir­(η²-ONCOPh)]

Catalyst Activation by Loss of Cyclopentadienyl Ligands in Hydrogen Transfer Catalysis with Cp*Ir^III Complexes

The activity of the two related complexes [Cp*Ir­(IMe)₂X]­BF₄ (X = Cl (<b>1</b>), H (<b>2</b>)) in transfer hydrogenation from isopropyl alcohol to acetophenone was investigated. The results suggest that the commonly accepted monohydride mechanism for transfer hydrogenation mediated by cyclopentadienyl iridium species does not apply to chloride <b>1</b>. We have found evidence that, although the two monodentate NHC ligands are retained in the coordination sphere, the Cp* ligand is completely released under mild conditions in a precatalytic activation step. Synthesis of modified versions of the initial precatalyst <b>1</b> with different cyclopentadienyl and NHC ligands demonstrated that increasing the steric pressure around the iridium center facilitates precatalyst activation and thus enhances the catalytic performance. Study of five new iridium­(III) complexes bearing mono- or diphosphines helped us monitor Cp* ligand loss under mild conditions. An unusual P–C bond cleavage was also noted in a 1,2-bis­(dimethylphosphino)­methane (dmpm) ligand. On the basis of these findings, a novel catalyst activation mechanism is proposed for [(η⁵-C₅R₅)­Ir] transfer hydrogenation based on the lability of the cyclopentadienyl ligand