Metathesis incomplete

Other Ionic Impurities from Incomplete Metathesis Reactions... 

Using an equimolar quantity of allyl methyl sulphide and ds-pent-2-ene resulted in incomplete reaction of the allyl sulphide and some self-metathesis of the sulphide substrate. When an excess (4 equiv) of but-2-ene was used, however, the desired but-2-enyl sulphide was formed in a good yield at ambient temperature. In this case, the large quantities of unwanted hydrocarbon starting material and self-metathesis products were gaseous alkenes and therefore easily removed. Using a large excess of one alkene to improve the yield of the desired cross-metathesis product in this way is obviously only viable if this alkene is inexpensive and both it and its self-metathesis product are easily removed. 

The properties of siloxide as ancillary ligand in the system TM-O-SiRs can be effectively utilized in molecular catalysis, but predominantly by early transition metal complexes. Mono- and di-substituted branched siloxy ligands (e.g., incompletely condensed silsesquioxanes) have been employed as more advanced models of the silanol sites on silica surface for catalytically active centers of early TM (Ti, W, V) that could be effectively used in polymerization [5], metathesis [6] and epoxidation [7] of alkenes as well as dehydrogenative coupling of silanes [8]. 

This volume provides the reader with the most important and exiting results pertaining the use of NHC complexes in transition-metal catalysis. Following an introductory chapter, which deals with the properties of NHC compounds and discusses some insightful examples, routes to NHC complexes will be described, a prerequisite for doing catalysis. Chapters on NHC complexes in oxidation chemistry and in metathesis reactions are accompanied by a chapter on palladium-catalyzed reactions and another on catalysis by other metals. Finally, this book would be incomplete without treating applications in asymmetric catalysis, which rounds out this volume. 

Organometallic oxide clusters containing cubic or incomplete cubic frameworks are very useful for homogeneous or heterogeneous catalysts in the oxidation and metathesis of unsaturated hydrocarbons. Theoretical studies modeling catalytic hydrocarbon transformations on integrated cubic metal oxide clusters show that coordinatively unsaturated metal sites and valley sites play an important role in the activation. We recently reported a novel organometallic oxide cluster with multiple valley sites, [n-... 

Mixed imido-oxo complexes are relatively rare, but could be obtained by incomplete reaction of some amines and anilines with molybdate, MesSiCl, and NFt3 in dme or pyridine, by reaction of [Mo02Cl2(NCMe)2] with one equivalent of RNCO followed by derivatization, or oxo/imido ligand metathesis of [Mo(NMes)2Cl2(dme)] and [Mo02Cl2(dme)]. These complexes generally adopted distorted octahedral structures with cis imido and 0x0 ligands, with ZMo=N-C >154° (mostly >168°). 

All of these complexes were characterized by multinuclear NMR ( H, C, "B, Hg) and fast atom bombardment mass spectrometry (FAB/MS). Monoanion complexes (8) and (9) form dianion complexes (11) and (12), respectively, on further treatment with the respective halides <92JA380>. Both monoanion and dianion complexes can undergo metathesis with [As(QH4)4]Cl to form products (13) and (14), respectively <91AG(E)1507,92JA380>. Uncomplexed cyclotetramer (1) was extracted from its iodide ion complexes (8) and (11) by Ag(OAc) in ethanol. The same reaction from bromide and iodide complexes resulted in incomplete extraction of host tetramer <92AG(E)893>. Uncomplexed host macrocycles (1) and (3) were characterized by H, C, and B NMR <92AG(E)893,93JAI93). 

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