Catalytic Transformations of Alkynes via Ruthenium Vinylidene and Allenylidene Intermediates

NOTICE: This is the peer reviewed version of the following book chapter: Varela J. A., González-Rodríguez C., Saá C. (2014). Catalytic Transformations of Alkynes via Ruthenium Vinylidene and Allenylidene Intermediates. In: Dixneuf P., Bruneau C. (eds) Ruthenium in Catalysis. Topics in Organometallic Chemistry, vol 48, pp. 237-287. Springer, Cham. [doi: 10.1007/3418_2014_81]. This article may be used for non-commercial purposes in accordance with Springer Verlag Terms and Conditions for self-archiving.Vinylidenes are high-energy tautomers of terminal alkynes and they can be stabilized by coordination with transition metals. The resulting metal-vinylidene species have interesting chemical properties that make their reactivity different to that of the free and metal π-coordinated alkynes: the carbon α to the metal is electrophilic whereas the β carbon is nucleophilic. Ruthenium is one of the most commonly used transition metals to stabilize vinylidenes and the resulting species can undergo a range of useful transformations. The most remarkable transformations are the regioselective anti-Markovnikov addition of different nucleophiles to catalytic ruthenium vinylidenes and the participation of the π system of catalytic ruthenium vinylidenes in pericyclic reactions. Ruthenium vinylidenes have also been employed as precatalysts in ring closing metathesis (RCM) or ring opening metathesis polymerization (ROMP). Allenylidenes could be considered as divalent radicals derived from allenes. In a similar way to vinylidenes, allenylidenes can be stabilized by coordination with transition metals and again ruthenium is one of the most widely used metals. Metalallenylidene complexes can be easily obtained from terminal propargylic alcohols by dehydration of the initially formed metal-hydroxyvinylidenes, in which the reactivity of these metal complexes is based on the electrophilic nature of Cα and Cγ, while Cβ is nucleophilic. Catalytic processes based on nucleophilic additions and pericyclic reactions involving the π system of ruthenium allenylidenes afford interesting new structures with high selectivity and atom economy

DFT studies of reductive elimination, C–H activation and β-hydride elimination in alkyl and aryl palladium amine complexes

The factors affecting C-N bond formation via reductive elimination from Pd(I (t) Bu)(neopentyl)(morpholide) (I (t) Bu = 1,3-Di-tert-butyl-imidazol-2-ylidene) are studied computationally. DFT calculations indicate that choosing an alkyl group without beta hydrides, such as neopentyl, has a detrimental effect on the possibility of C-N reductive elimination. In the absence of beta hydride elimination, a pathway of lower energy than reductive elimination is found, namely morpholide-promoted C-H activation of neopentyl (t) Bu has a significantly lower activation energy than reductive elimination. Changing the ancillary ligand from I (t) Bu to tricyclopentylphosphine (P(Cyp)(3)) has little impact. By contrast, replacing neopentyl by phenyl leads to a c. 50% reduction in activation energy. Study of Pd(I (t) Bu)(2-methylpropyl)(morpholide) permits comparison of the potential energy surfaces for three possible processes; (1) reductive elimination (2) morpholide-promoted C-H activation and (3) beta-hydride elimination and reveals that the activation energies for these processes increase in the order of (3) < (2) < (1)

Do knowledge, knowledge sources and reasoning skills affect the accuracy of nursing diagnoses? a randomised study

ABSTRACT: BACKGROUND: This paper reports a study about the effect of knowledge sources, such as handbooks, an assessment format and a predefined record structure for diagnostic documentation, as well as the influence of knowledge, disposition toward critical thinking and reasoning skills, on the accuracy of nursing diagnoses. Knowledge sources can support nurses in deriving diagnoses. A nurse's disposition toward critical thinking and reasoning skills is also thought to influence the accuracy of his or her nursing diagnoses. METHOD: A randomised factorial design was used in 2008-2009 to determine the effect of knowledge sources. We used the following instruments to assess the influence of ready knowledge, disposition, and reasoning skills on the accuracy of diagnoses: (1) a knowledge inventory, (2) the California Critical Thinking Disposition Inventory, and (3) the Health Science Reasoning Test. Nurses (n=249) were randomly assigned to one of four factorial groups, and were instructed to derive diagnoses based on an assessment interview with a simulated patient/actor. RESULTS: The use of a predefined record structure resulted in a significantly higher accuracy of nursing diagnoses. A regression analysis reveals that almost half of the variance in the accuracy of diagnoses is explained by the use of a predefined record structure, a nurse's age and the reasoning skills of `deduction' and `analysis'. CONCLUSIONS: Improving nurses' dispositions toward critical thinking and reasoning skills, and the use of a predefined record structure, improves accuracy of nursing diagnoses. KEYWORDS: Clinical practice; Critical reasoning; Knowledge; Nursing diagnoses; RCT