91 research outputs found
Highly Active Water-Soluble Olefin Metathesis Catalyst
A novel water-soluble ruthenium olefin metathesis catalyst supported by a poly(ethylene glycol) conjugated saturated 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligand is reported. The catalyst displays improved activity in ring-opening metathesis polymerization, ring-closing metathesis, and cross-metathesis reactions in aqueous media
Decomposition of a Key Intermediate in Ruthenium-Catalyzed Olefin Metathesis Reactions
Dinuclear ruthenium complex, with a bridging carbide and a hydride ligand, and methyltricyclohexylphosphonium chloride result from thermal decomposition of olefin metathesis catalyst, (ImesH_2)(PCy)_3)(Cl)_2Ru CH_2. Involvement of dissociated phosphine in the decomposition is proposed. The dinuclear complex has catalytic olefin isomerization activity, which can be responsible for competing isomerization processes in certain olefin metathesis reactions
Decomposition of A Key Intermediate in Ruthenium-Catalyzed Olefin Metathesis Reactions
Prevention of Undesirable Isomerization during Olefin Metathesis
1,4-Benzoquinones have been found to prevent olefin isomerization of a number of allylic ethers and long-chain aliphatic alkenes during ruthenium-catalyzed olefin metathesis reactions. Electron-deficient benzoquinones are the most effective additives for the prevention of olefin migration. This mild, inexpensive, and effective method to block olefin isomerization increases the synthetic utility of olefin metathesis via improvement of overall product yield and purity
Decomposition of Ruthenium Olefin Metathesis Catalysts
The decomposition of a series of ruthenium metathesis catalysts has been examined using methylidene species as model complexes. All of the phosphine-containing methylidene complexes decomposed to generate methylphosphonium salts, and their decomposition routes followed first-order kinetics. The formation of these salts in high conversion, coupled with the observed kinetic behavior for this reaction, suggests that the major decomposition pathway involves nucleophilic attack of a dissociated phosphine on the methylidene carbon. This mechanism also is consistent with decomposition observed in the presence of ethylene as a model olefin substrate. The decomposition of phosphine-free catalyst (H_2IMes)(Cl)_2Ru CH(2-C_6H_4-O-i-Pr) (H_2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) with ethylene was found to generate unidentified ruthenium hydride species. The novel ruthenium complex (H_2IMes)(pyridine)_3(Cl)_2Ru, which was generated during the synthetic attempts to prepare the highly unstable pyridine-based methylidene complex (H_2IMes)(pyridine)_2(Cl)_2Ru CH_2, is also reported
Low Catalyst Loadings in Olefin Metathesis: Synthesis of Nitrogen Heterocycles by Ring-Closing Metathesis
A series of ruthenium catalysts have been screened under ring-closing metathesis (RCM) conditions to produce five-, six-, and seven-membered carbamate-protected cyclic amines. Many of these catalysts demonstrated excellent RCM activity and yields with as low as 500 ppm catalyst loadings. RCM of the five-membered carbamate series could be run neat, the six-membered carbamate series could be run at 1.0 M, and the seven-membered carbamate series worked best at 0.2−0.05 M
Development of a standardized in-hospital cardiopulmonary resuscitation set-up
Objective. This study evaluated whether
chest compression in a standardized inhospital
cardiopulmonary resuscitation
(CPR) set-up can be performed as effectively
as when the rescuer is kneeling beside
the patient lying on the floor. Specifically,
the in-hospital test was standardized
according to the rescuers’ average knee
height.
Methods. Experimental intervention (test
1) was a standardized, in-hospital CPR
set-up: first, the bed height was fixed at 70
cm. Second, the height difference between
the bed and a step stool was set to the average
knee height of the CPR team members
(45 cm). Control intervention (test 2) was
kneeling on floor. Thirty-eight medical
doctors on the CPR team each performed
2 minutes of chest compressions in test 1
and 2 in random order (cross-over trial). A
Little Anne was used as a simulated patient
who had experienced cardiac arrest. Chest
compression parameters, such as average
depth and rate, were measured using an accelerometer
device.
Results. In all tests, the average depths were
those recommended in the most recent
CPR guidelines (50–60 mm); there were no
significant differences between Tests 1 and
2 (53.1 ± 4.3 mm vs. 52.6 ± 4.8 mm, respectively;
p = 0.398). The average rate in Test
2 (119.1 ± 12.4 numbers/min) was slightly
faster than that in Test 1 (116.4 ± 10.2 numbers/
min; p = 0.028). No differences were
observed in any other parameters.
Conclusions. Chest compression quality in
our standardized in-hospital CPR set-up
was similar with that performed in a kneeling
position on the floor.
Trial Registration: Clinical Research Information
Service: KCT000159
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