Tungsten complexes alkenes

Bis-nitrogen donor ligand-substituted alkylidyne complexes such as 78 were found to be good alternatives as starting materials to the thermally labile tetracarbonyl complexes 44). Substitution of one pyridine ligand in the bispyridine-substituted complexes 78 occurs in the presence of excess chloride [Eq. (64)] 103). The anionic complexes 79 are stable in the presence of excess chloride but are too labile to be isolated in pure form. These complexes were used in the synthesis of stable alkylidyne alkene tungsten complexes [Eq. (180), Section IV,G]. With phosphines both pyridine ligands in 78 are substituted [Eq. (65)] 44). For PMej the reaction of the tetracarbonyl complex W(CPh)Br(CO)4 had previously been shown to... 

Several alkylidyne alkene tungsten complexes were synthesized in our laboratory. The neutral complex 233 and the anionic complexes 235 were found to react with maleic anhydride and fumaronitrile to afford the products 234 and 236 [Eqs. (179) and (180)] (103). The tmeda-substituted... 

If the creation of vacant sites occurs in this way, it would be erroneous to conclude that the tungsten complex in its active form is not reduced, because reduction can also be accomplished by the reacting alkene molecules. 

Prior to the first examples of the cross-metathesis of functionalised alkenes using these catalysts, however, was a report on the use of a lesser known tungsten complex 5 [18,19]. 

The chemistry of pyrrol-1-ylbenzylidene pentacarbonyl chromium, molybdenum and tungsten complexes was investigated. Reaction with electrophilic alkenes gives l-(phenylcyclo-propyl)pyrroles Under photolytic decarbonylation conditions 2 + 2 cycloaddition products were obtained with nucleophilic alkenes, cyclic dienes and imines. <950M2522>... 

Photolysis of diazophosphane 72 leads to isolable phosphinocarbene 73. Mild thermolysis of 73 furnishes 1,2-dihydro-1 A3,3 A3-diphosphete 74 <2003JA124>. The cyclization of P-alkene 75 can be initiated by W(CO>5-carbene complexes 76 to yield tungsten-complexed lA3,3A3-diphosphetanes 77 (Scheme 23) <20030M5063>. 

A number of allylic chlorides have been reported to yield photoproducts characteristic of the alkene moiety and not of the C—X bond123. Allyl and crotyl halides undergo photochemical reactions with chromium, molybdenum and tungsten complexes, which involve C—X bond cleavage133. 

ALKYNE AND ALKENE HALOCARBONYL COMPLEXES OF MOLYBDENUM(II) AND TUNGSTEN(II)... 

The anti addition of amines to the double bond of cationic (alkene)(cyclopentadienyl)di-carbonyliron complexes and to the analogous molybdenum and tungsten complexes has been reported31 33. The adducts underwent carbonyl insertion-cyclization to give chelate complexes, which were then oxidized to /8-lactams. For example, from the Fp complexes of ( )- and (Z)-2-butene the corresponding /8-lactams were obtained diastereoselectively in 10-15% yield by the direct oxidation of the benzylamine adducts with chlorine at low temperature33. The stereochemistry was determined by H-NMR spectroscopy. 

First, the sulfur atom from a thiirane is added to one of the carbon atoms of the thiirane ligand of the complex, with formation of a zwitterionic intermediate. The zwitterionic intermediate undergoes elimination of ethylene to yield a reactive alkene disulfide tungsten complex. The dithietane ligands from two or more molecules, then combine to form the cyclic polysulfides. If the macrocyclization of thiirane catalyzed by W(CO)s(SC2H4) is performed in the presence of DMAD, small quantities of polythioether macrocycles 156 and 157 are formed <1997OM1430>. 

Alkyne and Alkene Halocarbonyl Complexes of Molybdenum(II) and Tungsten(II). 77... 

A methodology that constructs the ISQ core directly from pyridines using a 7t-basic tungsten complex to disrupt the aromatic stabilization of these inert heterocycles was recently reported [70]. For example, common pyridine derivatives, e.g., 2-dimethylaminopyridine, will undergo stereoselective Diels-Alder reactions with electron-deficient alkenes, e.g., acrylonitrile. 

The phenylcyclopropanes are formed consistently as stereoisomeric mixtures, but the configuration of the predominant isomer depends on the alkene. For monosubstituted alkenes there is a progressive change of the cisjtrans ratio to lower values as the substituent becomes sterically larger. Thus, when the tungsten complex is allowed to react with propene, but-l-ene, 3-methyl-but-l-ene and 3,3-dimethylbut-l-ene, the ratio for the cyclopropane 3 drops from 1.8 to 0.01. ... 

An intramolecular cyclopropanation has been observed for an aminocarbene-tungsten complex 16. In this case, the alkene employed as trapping reagent is bound coordinatively to the transition metal and possible allylic alkene isomerizations are prevented by the geminal methyl... 

Pyrrol-1-ylcarbene complexes 18 effect the cyclopropanation of electron-deficient alkenes in good to very good yield. The C-H insertion products usually observed with aminocarbene complexes are only formed in low yields. Molybdenum and tungsten complexes are more favorable for cyelopropanation reactions than the analogous chromium complexes. The diaste-reoelectivity of the cycloaddition, however, was only moderate cisjtrans ratio of 1 1.6 to 3.4). 

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