A catalytic cycle for oxidation of tert-butyl methyl ether by a double C−H activation-group transfer process

A square-planar, iridium(I) carbene complex is shown to effect atom and group transfer from nitrous oxide and organic azides, releasing the corresponding formate or formimidate and an iridium(I)−dinitrogen adduct. The dinitrogen complex performs C−H activation upon photolysis or thermolysis, regenerating the carbene from tert-butyl methyl ether with loss of H_2. Taken together, these reactions represent a net catalytic cycle for C−H functionalization by double C−H activation to generate metal−carbon multiple bonds. Additionally, the unusual group transfer from diazo reagents underscores the unique nature of the reactivity observed for nucleophilic-at-metal carbene complexes

Synthetic and Mechanistic Studies of Small-Molecule Activation at Low-Valent Iron, Cobalt, and Iridium Centers

The preparation of transition-metal systems for catalytic multielectron transformations of small molecules remains a significant challenge for synthetic chemists. The realization of new transformations often depends critically on the design of frameworks capable of stabilizing unusual oxidation states and molecular geometries, providing a frontier molecular-orbital landscape that is well suited to interact with the molecules of interest. This thesis has sought to address two particularly noteworthy challenges in the field of small-molecule activation, dinitrogen reduction and C–H bond functionalization, through judicious ligand choice and design. Chapters 2 and 3 describe the syntheses of new tri- and tetradentate hybrid ligands incorporating a single X-type donor (amido or silyl) and multiple phosphine donors designed to stabilize low oxidation states at iron and cobalt and support dinitrogen reduction and other multielectron redox transformations. While the amidophosphine ligands do allow access to unusual monovalent iron and cobalt complexes, the isolation of dinitrogen adducts supported by these ligands remains elusive and the weakness of the silicon–nitrogen bond makes the complexes prone to decomposition. In contrast, the tris(phosphino)silyl ligands presented in Chapter 3 afford straightforward access to the first terminally bonded dinitrogen complexes of monovalent iron, and the structure of these and related complexes are described along with preliminary experiments showing that protonolysis of the iron(I)–dinitrogen complexes produces hydrazine in reasonable stoichiometric yields. Chapters 4 through 7 address the functionalization of ether and amine C–H bonds by a double C–H activation route. Chapter 4 describes the investigation of reactivity of low-valent, pincer-supported iridium species with a variety of ethers, leading to a number of selective C–H, C–C, and C–O bond cleavage events, affording in several cases iridium carbene complexes by double C–H activation and loss of dihydrogen. Chapter 5 presents an exploration of the electronic structure of the unusual square-planar iridium(I) alkoxycarbenes and their nucleophilic activation of several heterocumulene substrates, leading to multiple-bond metathesis events promoted by metal- rather than ligand-initiated reactivity. Chapter 6 describes the discovery of new atom and group transfer reactions from diazo reagents to the alkoxycarbenes and the implementation of these reactions in an unprecedented catalytic cycle for C=E bond formation by multiple C–H activations. Chapter 7 explores the related reactivity of a low-valent pincer iridium complex with methyl amines and the reactivity of the resulting iridium(III) dihydrido aminocarbenes, which is shown to diverge substantially from that observed for the iridium(I) carbene species.</p

The influence of forgiveness and apology on cardiovascular reactivity to mental stress

This study sought to investigate the relation between forgiveness and cardiovascular reactivity and recovery in the laboratory as influenced by apology. Men (n = 29) and women (n = 50) were chosen for participation based on scoring in the top or bottom third of the Forgiving Personality Inventory. Participants were exposed to an interpersonal transgression (i.e., harassment by the experimenter) while performing a serial subtraction task. Cardiovascular activity was measured before, during, and following the task. Also following the task, approximately half of the participants received an apology from the experimenter for his/her scripted rude behavior. No reactivity differences during the serial subtraction task were observed across groups (all ps \u3e .05). During the recovery period, however, persons high in forgiveness displayed more rapid diastolic and mean arterial blood pressure recovery (ps \u3c .05). This effect was most prominent directly following the apology, where women high in forgiveness who received an apology benefitted the most in diastolic and mean arterial blood pressure recovery (ps .05). Regarding the overall effects of the apology, women who received an apology recovered from the transgression more quickly than women who did not receive an apology (ps \u3c .05). Surprisingly, the effect was in the opposite direction for men who displayed higher diastolic and mean arterial blood pressure upon recovery from the transgression if they received an apology (ps \u3c .05).These results indicate that that the potentially healthful benefits associated with forgiveness and apology may be moderated by sex

Complexes of iron and cobalt with new tripodal amido-polyphosphine hybrid ligands

Divalent complexes of iron and cobalt with new, monoanionic tripodal amido-polyphosphine ligands have been thoroughly characterized, and XRD analysis reveals geometries that are distinct for this class of ligand

Factors Dictating Carbene Formation at (PNP)Ir

The mechanistic subtleties involved with the interaction of an amido/bis(phosphine)-supported (PNP)Ir fragment with a series of linear and cyclic ethers have been investigated using density functional theory. Our analysis has revealed the factors dictating reaction direction toward either an iridium-supported carbene or a vinyl ether adduct. The (PNP)Ir structure will allow carbene formation only from accessible carbons α to the ethereal oxygen, such that d electron back-donation from the metal to the carbene ligand is possible. Should these conditions be unavailable, the main competing pathway to form vinyl ether can occur, but only if the (PNP)Ir framework does not sterically interfere with the reacting ether. In situations where steric hindrance prevents unimpeded access to both pathways, the reaction may progress to the initial C−H activation but no further. Our mechanistic analysis is density functional independent and whenever possible confirmed experimentally by trapping intermediate species experimentally. We have also highlighted an interesting systematic error present in the DFT analysis of reactions where steric environment alters considerably within a reaction

Probing the C-H Activation of Linear and Cyclic Ethers at (PNP)Ir

Interaction of the amido/bis(phosphine)-supported (PNP)Ir fragment with a series of linear and cyclic ethers is shown to afford, depending on substrate, products of α,α-dehydrogenation (carbenes), α,β-dehydrogenation (vinyl ethers), or decarbonylation. While carbenes are exclusively obtained from tert-amyl methyl ether, sec-butyl methyl ether (SBME), n-butyl methyl ether (NBME), and tetrahydrofuran (THF), vinyl ethers or their adducts are observed upon reaction with diethyl ether and 1,4-dioxane. Decarbonylation occurs upon interaction of (PNP)Ir with benzyl methyl ether, and a mechanism is proposed for this unusual transformation, which occurs via a series of C−H, C−O, and C−C bond cleavage events. The intermediates characterized for several of these reactions as well as the α,α-dehydrogenation of tert-butyl methyl ether (MTBE) are used to outline a reaction pathway for the generation of PNP-supported iridium(I) carbene complexes, and it is shown that the long-lived, observable intermediates are substrate-dependent and differ for the related cases of MTBE and THF. Taken together, these findings highlight the variety of pathways utilized by the electron-rich, unsaturated (PNP)Ir fragment to stabilize itself by transferring electron density to ethereal substrates through oxidative addition and/or the formation of π-acidic ligands

Prevalence, Determinants, and Clinical Significance of Masked Hypertension in a Population-Based Sample of African Americans: The Jackson Heart Study

Background: The disproportionate rates of cardiovascular disease in African Americans may, in part, be due to suboptimal assessment of blood pressure (BP) with clinic BP measurements alone. To date, however, the prevalence of masked hypertension in African Americans has not been fully delineated. The purpose of this study was to evaluate masked hypertension prevalence in a large population-based sample of African Americans and examine its determinants and association with indices of target organ damage (TOD). Methods: Clinic and 24-hour ambulatory BP monitoring were conducted in 972 African Americans enrolled in the Jackson Heart Study. Common carotid artery intima-media thickness, left ventricular mass index, and the urinary albumin:creatinine excretion ratio were evaluated as indices of TOD. Results: Masked hypertension prevalence was 25.9% in the overall sample and 34.4% in participants with normal clinic BP. All indices of TOD were significantly higher in masked hypertensives compared to sustained normotensives and were similar between masked hypertensives and sustained hypertensives. Male gender, smoking, diabetes, and antihypertensive medication use were independent determinants of masked hypertension in multivariate analyses. Conclusions: In this population-based cohort of African Americans, approximately one-third of participants with presumably normal clinic BP had masked hypertension when BP was assessed in their daily environment. Masked hypertension was accompanied by a greater degree of TOD in this cohort