Olefin Hydroarylation Catalyzed by (Pyridyl-Indolate)Pt(II) Complexes: Catalytic Efficiencies and Mechanistic Aspects

A series of Pt(II) complexes of the type (N–N)PtPh(SR_2) (N–N = 2,2′-pyridyl-indolate) were prepared, and their performance as catalysts for the hydroarylation of olefins was assessed. Evidence that the catalysis is homogeneous and is Pt-mediated is provided by control experiments with added hindered base (2,6-di-tert-butyl-4-methylpyridine) and Hg(0). Two potential catalytic intermediates, (^tBuPyInd)PtPh(C_2H_4) and (^tBuPyInd)Pt(CH_2CH_2Ph)(C_2H_4), were synthesized, and their catalytic efficacy was explored. Additionally, decomposition and deactivation pathways, including styrene formation via β-hydride elimination and ligand reductive demetalation, were identified

Cooperative ligand design for late transition metal coordination compounds

This thesis describes several cyclopentyl linked enamide phosphine ligands. Reactivity and mechanistic studies using coordination compounds featuring these ligands enable exploration of ligand cooperativity. Despite complex behavior in solution due to tautomerization, coordination of (NPN)DMP/DIPPH₂ to Rh generates RhCl{(NPN)DMP/DIPPH₂}(COE). Synthesis of RhCl{(NPN)DMP/DIPPH₂}(CO) and RhHCl₂{(NPN)DMP/DIPPH₂} is possible. NMR spectroscopy and in certain cases X-ray analysis establishes the diimine tautomer of the ligand coordinates to Rh in each case. Enamide phosphine complexes, Ir{(NP)DIPP}(COD) and Ir{(NP)DMP}(COD) are synthesized from simple imine phosphine ligands. Ir{(NP)DIPP}(COD) reacts with H₂ or PriOH to form [IrH₃{(NP)DIPPH}]₂. The imine tautomer of the ligand coordinates to Ir. Treating [IrH₃{(NP)DIPPH}]₂ with CO generates Ir{(NP)DIPP}(CO)₂. A proton from the imine ligand of [IrH₃{(NP)DIPPH}]₂ combines with an Ir hydride to release H₂. Observation of three intermediates, involved in conversion of [IrH₃{(NP)DIPPH}]₂ to Ir{(NP)DIPP}(CO)₂, suggests that tautomerization of the dissociated arm is involved in cooperative H₂ loss. Four imine phosphine ligands (R(NP)R'H), where the N-aryl groups (R) and the groups attached to P(R') are varied, are synthesized. Combining each ligand with RuHCl(PPri₃)₂(CO) and KOBut generates four enamide phosphine complexes: RuH{R(NP)R'}(PPri₃)(CO). Reacting RuH{R(NP)R'}(PPri₃)(CO) with H₂ generates RuH₂{R(NP)R'H}(PPri₃)(CO). The imine tautomeric form of the ligand coordinates to Ru in all four cases. The R' groups influence the rate of reaction and percent conversion to RuH₂{R(NP)R'H}(PPri₃)(CO). The mechanism for H₂ activation is explored using RuH{Pri(NP)Pri}(PPri₃)(CO). An intermediate is identified as RuH₂(H₂){Pri(NP)PriH}(PPri₃)(CO). The T₁,min value of a ¹H NMR resonance at δ -7.2 is 22 ms at 238 K (measured to 400 MHz), consistent with a Ru dihydrogen dihydride complex. The N donor of the enamine tautomeric form of the ligand is protonated by H₂ or D₂ and has dissociated from Ru. Tautomerization of the dissociated arm is involved in formation of the final product. Certain factors inhibit alcohol dehydrogenation catalysis for Ir{(NP)DIPP}(COD) and RuH{Pri(NP)Pri}(PPri₃)(CO). Two tridentate enamide phosphine ligands are developed in an effort to generate a catalyst. These ligands enable synthesis of RuH{(PNN)But}(CO) and RuH{(PNN)Pri}(CO). Exposing RuH{(PNN)But}(CO) to 1000 equivalents of benzyl alcohol yields a TON of 13 and TOF of 0.6 h-¹ after 22 hours. Nearly identical results are obtained for RuH{(PNN)Pri}(CO).Science, Faculty ofChemistry, Department ofGraduat

Ruthenium Complexes Stabilized by Bidentate Enamido-Phosphine Ligands: Aspects of Cooperative H₂ Activation

Four bidentate, hybrid ligands (^R(NP)^R′H) featuring imine-nitrogen and alkyl-phosphine donors linked by a cyclopentyl ring were synthesized. The ortho position of the aryl group attached to nitrogen is varied such that R is Me or Prⁱ; additionally, the groups decorating phosphorus (R′) are varied between Bu^t or Prⁱ. The addition of each ligand to RuHCl­(PPrⁱ₃)₂(CO) in the presence of KOBu^t generates four enamido-phosphine complexes RuH­{^R(NP)^R′}­(PPrⁱ₃)­(CO) that were characterized by NMR spectroscopy, elemental analyses, and, in the case of R = Prⁱ and R′ = Bu^t or Prⁱ, X-ray crystallography. Depending on R′, the reaction of RuH­{^R(NP)^R′}­(PPrⁱ₃)­(CO) with H₂ generates varying amounts of the imine-phosphine complex RuH₂{^R(NP)^R′H}­(PPrⁱ₃)­(CO). Insights into the mechanism of H₂ activation by these enamido derivatives were explored using RuH­{^Pr(NP)^Pri}­(PPrⁱ₃)­(CO), for which an intermediate was identified as the dihydrogen–dihydride complex, RuH₂(H₂)­{^Pri(NP)^PriH}­(PPrⁱ₃)­(CO), on the basis of the <i>T</i>_1,min value of 22 ms for the ¹H NMR resonance at δ −7.2 at 238 K (measured at 400 MHz). The N donor of the enamine tautomeric form of the ligand is protonated by H₂ or D₂ and dissociates from Ru. Tautomerization of the enamine to the imine form of the dissociated arm is involved in formation of the final product

Use of the Imine–Enamine Equilibrium in Cooperative Ligand Design

The imine–phosphine ligands Ph₂PC₅H₇NAr, where Ar = 2,6-Prⁱ₂C₆H₃, 2,6-Me₂C₆H₃, were deprotonated using KH to generate the corresponding potassium salts, which were reacted with [(COD)­IrCl]₂ to generate the enamidophosphine derivatives (COD)­Ir­(Ph₂PC₅H₆NAr) (Ar = 2,6-Prⁱ₂C₆H₃, <b>4a</b>; Ar = 2,6-Me₂C₆H₃, <b>4b</b>). These complexes were exposed to alcohols, H₂, and CO to generate a series of products, some of which involve protonation of the enamido unit to generate the imine tautomer. The reaction of <b>4a</b> with isopropyl alcohol or H₂ generates the dinuclear hexahydride [(Ph₂PC₅H₇N-2,6-Prⁱ₂C₆H₃)­IrH₂]₂(μ-H)₂ (<b>5a</b>), while the reaction with primary alcohols generates the dicarbonyl enamidophosphine complex (CO)₂Ir­(Ph₂PC₅H₆NAr) (<b>6a</b>). The reaction of the hexahydride <b>5a</b> with CO generates <b>6a</b>, for which a mechanism is proposed on the basis of monitoring this reaction as a function of time by NMR spectroscopy. On the basis of these experiments, cooperative ligand effects can be replicated by imine–phosphine ligands by proton transfer to and from the ligand backbone