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

Electronic and Structural Effects of Low-Hapticity Coordination of Arene Rings to Transition Metals

A DFT computational study and a structural analysis of the coordination of arenes to transition metals in low -hapticity (η¹ and η²) modes have been developed, including a pseudosymmetry analysis of the molecular orbitals and the introduction of a hapticity map that makes evident the different degrees of intermediate hapticities. Calculations on [Pt^IIL₃(C₆H₆)] model complexes reveal a preference for the η² mode, while the η¹ coordination is found to be a low-energy transition state for a haptotropic shift. The attachment of the arene to a side group that is coordinated to the metal introduces geometrical constraints, which result in hapticities intermediate between one and two. Comparison of the η¹ arene complexes with benzonium cations shows that in the former case the bonding to the metal involves essentially the π system of the arene, affecting only slightly the delocalized nature of the carbon–carbon bonds. This behavior is in sharp contrast with the frequently found η¹ coordination of Cp that involves σ bonding and full dearomatization of the ring

Reactivity of a Cationic (C₅Me₅)Ir^III-Cyclometalated Phosphine Complex with Alkynes

The electrophilic cationic complex [(η⁵-C₅Me₅)­Ir­(C^∧P)]⁺, which contains a metalated phosphine derived from PMe­(Xyl)₂ (Xyl = 2,6-Me₂C₆H₃), reacts at −60 °C with the alkynes HCCH, PhCCH, and PhCCMe, with formation of the corresponding π adducts [(η⁵-C₅Me₅)­Ir­(C^∧P)­(η²-alkyne)]⁺. Thermal activation of these complexes leads to products that result from the C–C coupling of the alkyne and the σ Ir–C bond of the metalated phosphine, whose nature depends markedly upon the alkyne involved. Thus, for HCCH the carbon–carbon bond -forming reaction leads to an iridium-bound alkene moiety as the thermodynamic product, whereas the analogous complexes derived from the bulkier PhCCH and PhCCMe alkynes undergo further transformation into allylic structures. Mechanistic studies supported by the use of PhCCD demonstrate the implication of an undetected vinylidene structure, IrCC­(H)­Ph, in the key carbon–carbon bond-forming step of the PhCCH reaction system, whereas for the internal alkyne PhCCMe a migratory insertion mechanism is operative. However, no clear distinction between these two routes can be made for the C–C bond-forming reaction for which HCCH is responsible

A Cationic Terminal Methylene Complex of Ir(I) Supported by a Pincer Ligand

A rare example of a cationic methylene complex of Ir­(I), [(PONOP)­Ir­(CH₂)]⁺, <b>2</b> (PONOP = 2,6-bis­(di-<i>tert</i>-butylphosphinito)­pyridine), has been prepared by α-hydride abstraction from the previously described neutral methyl complex [(PONOP)­Ir­(CH₃)]. The intrinsic high reactivity of the compound prevented both the isolation of a pure solid and its full characterization in the solid state. Nevertheless, the proposed molecular structure finds unequivocal support in multinuclear NMR spectroscopy and in reactivity studies that include reactions with Lewis bases, dihydrogen, and ethyl diazoacetate. An ylide compound, <b>3</b>, resulted from the reaction between [(PONOP)­Ir­(CH₂)]⁺ and PMe₃, while the η²-alkene complex <b>5</b> formed in a CC coupling reaction involving the methylene ligand of <b>2</b> and ethyl diazoacetate. Hydrogenolysis of the IrCH₂ linkage of <b>2</b> led to several, previously known, hydride and dihydrogen iridium complexes

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

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

Activation of Small Molecules by the Metal–Amido Bond of Rhodium(III) and Iridium(III) (η⁵‑C₅Me₅)M-Aminopyridinate Complexes

We report the synthesis and structural characterization of five-coordinate complexes of rhodium and iridium of the type [(η⁵-C₅Me₅)­M­(N^N)]⁺ (<b>3-M</b>^<b>+</b>), where N^N represents the aminopyridinate ligand derived from 2-NH­(Ph)-6-(Xyl)­C₅H₃N (Xyl = 2,6-Me₂C₆H₃). The two complexes were isolated as salts of the BAr_F anion (BAr_F = B­[3,5-(CF₃)₂C₆H₃]₄). The M–N_amido bond of complexes <b>3-M</b>^<b>+</b> readily activated CO, C₂H₄, and H₂. Thus, compounds <b>3-M</b>^<b>+</b> reacted with CO under ambient conditions, but whereas for <b>3-Rh</b>^<b>+</b>, CO migratory insertion was fast, yielding a carbamoyl carbonyl species, <b>4-Rh</b>^<b>+</b>, the stronger Ir–N_amido bond of complex <b>3-Ir</b>^<b>+</b> caused the reaction to stop at the CO coordination stage. In contrast, <b>3-Ir</b>^<b>+</b> reacted reversibly with C₂H₄, forming adduct <b>5-Ir</b>^<b>+</b>, which subsequently rearranged irreversibly to [Ir]­(H)­(C­(Me)­N­(Ph)−) complex <b>6-Ir</b>^<b>+</b>, which contains an N-stabilized carbene ligand. Computational studies supported a migratory insertion mechanism, giving first a β-stabilized linear alkyl unit, [Ir]­CH₂CH₂N­(Ph)–, followed by a multistep rearrangement that led to the final product <b>6-Ir</b>^<b>+</b>. Both β- and α-H eliminations, as well as their microscopic reverse migratory insertion reactions, were implicated in the alkyl-to-hydride–carbene reorganization. The analogous reaction of <b>3-Rh</b>^<b>+</b> with C₂H₄ originated a complex mixture of products from which only a branched alkyl [Rh]­C­(H)­(Me)­N­(Ph)– (<b>5-Rh</b>^<b>+</b>) could be isolated, featuring a β-agostic methyl interaction. Reactions of <b>3-M</b>^<b>+</b> with H₂ promoted a catalytic isomerization of the Ap ligand from classical κ²-N,N′ binding to κ-N plus η³-pseudoallyl coordination mode