Tungsten pentacarbonyl complexes

A diarsacyclobutadiene is the ligand in the tungsten pentacarbonyl complex 1 which was characterized by X-ray crystallography. 

OM802>. In some cases the tungsten pentacarbonyl complexes 52 and 53 were prepared as more stable products, to aid characterization. Key NMR data are presented. 

The chemistry of the diphosphirenes is an almost completely unexplored field to date only one stable member of this compound class is known [46]. However, tungsten pentacarbonyl complexes of the type 47 at least show a tendency for ring opening (Scheme 6-10). The phosphinidine or carbene intermediates thus formed serve as starting materials for the construction of further novel phosphorus-carbon cage compounds. 

Here, the alkynyl side groups are polymerized to form a three-dimensional netv ork when the copolymer is exposed to UV light (320-390 nm) in the presence of 5 mol% tungsten hexacarbonyl, W(CO)g (see also Subsection 10.2.2.4.1). The polymerization is presumed to be initiated by the formation of a // -alkyne tungsten pentacarbonyl complex, // -RC = CR W(CO)5. 

The above shown polymer photocrosslinks when irradiated in the presence of small amounts of W(CO)6 using a light beam at 320-390 nm. UV photolysis of W(CO)6 in the presence of an alkyne results in the formation of a ri -alkyne tungsten pentacarbonyl complex, [(r -RC=CR )W(CO)5], that rearranges to a vinylidene derivative [R(H)C=C=W(CO)5] and is an intermediate in the initiation step in the polymerization of alkynes. 

Cyclisation of l-aryl-6-hydroxyhex-2-ynyl carbonates to the 2-arylidene-5,6-dihydropyran catalysed by Pd(0) is steieospeciBc, giving only the (Z)-isomer <96SL553>, whilst alk-l-yn-5-ols form dihydtopyranylidene carbenes under the influence of the tungsten pentacarbonyl-THF complex. The carbenes are a source of 2-stannyldihydropyrans <96TL4675>. 

Reactions of Cjq with metal carbene complexes also yield the [6,6] methano-fullerenes [392]. These adducts are probably not formed via a carbene addition, but via a formal [2-1-2] cycloaddition under formation of a metalla cyclobutane intermediate. The Fischer carbene complex [mefhyl(methoxymethylene)]pentacarbonyl chromium can be utilized to prepare l,2-mefhyl(methoxymethano)-fullerene in 20% yield [392]. A tungsten carbene complex was primarily used to initiate the formation of a polyacetylene polymer, but it was discovered that addition of to the complex-polymer-mixture improves the polymerization and dramatically increases the catalytic activity of the carbene complex [393]. can be integrated into the polymer via carbene addition. 

With a tungsten pentacarbonyl catalyst, the calculated mechanisms are summarized in Scheme 4.15 [26]. Coordination of the 4-pentyn-l-ol substrate to the pentacarbonyl tungsten leads to the formation of the 7i-alkyne-W(CO)5 adduct Wl. This coordination process was calculated to be exothermic by 24.3 kcal mol. The cydoisomerization leading to a five-membered-ring exo product starts with the 7i-complex Wl via a one-step process with a barrier of 46.5 kcal mol (path a of Scheme 4.15). The barrier calculated here is comparable with that calculated for the catalyst-free process. From Wl to W3, the tungsten metal center does not play a significant role in the isomerization process. 

X-ray structural analysis of 2,2-dimethyl-3-phenyl-l-methylenecyclopropane tungsten pentacarbonyl reveals an octahedral complex with characteristic W—C bond distance of 238 pm. The typical bond distances within the organic ligand are 138 (complexed C=C), 148 (proximal C—C), 154 (distal C—C) pm, compared e.g. with 140, 148 and 154 pm, respectively, for the Feist s ester iron complex analogue (see above). 

The complex of 19 with tungsten pentacarbonyl has been prepared in 12% yield by reaction of 2,3-dimethylbutadiene with benzotellurophenone coordinated to tungsten pentacarbonyl [86JOM(299)C7]. 

Synthesis of Complexes of Diphenylditelluride with Chromium and Tungsten Pentacarbonyls (3.98) [268]... 

It was also of interest to us how changes in the organic residue of the carbyne ligand influence the stability and the behavior of carbyne complexes. Hence, we treated with boron tribromide a series of pentacarbonyl-[methoxy (aryl) carbene tungsten (0) complexes which were substituted at... 

This particular thiocarbenoid complex and the analogous tungsten derivative are more conveniently synthesized by an initial reaction of [Cr(CO)5 C(CH3)(OCH3) ] or [W(CO)5 C(CH3)(OCH3) ] with benzene-thiolate ion at room temperature followed by acidification with hydrochloric acid. This synthetic route has also been used to prepare a series of pentacarbonyl[(l-phenylthio)ethylidene]tungsten(0) complexes substituted in the 4-position of the phenyl rings.4... 

Data on the redox potentials of germylenes, stannylenes, plumbylenes and their complexes are scarce. In fact, only the electrochemistry of dihalogermylenes, dihalostan-nylenes and their complexes with Lewis bases as well as with chromium, molybdenum and tungsten pentacarbonyles has been studied. 

Silver-NHC complexes have been shown as excellent NHC delivery agents. Few examples of transmetallation using distinct late TMs have been reported. Tungsten pentacarbonyl NFIC complex (203) was found efficient to transfer easily its NHC ligand to palladium (equation 35) and platinum (equation 36) yielding, respectively, palladium dimer (204) and platinum complex (205) with carbonyl ligand transfer. This is to be noted, as chromium and molybdenum analogs of (203) exhibited similar reactivity. 

Li et al °° examined the properties of two organometallic tungsten-carbon complexes, tungsten pentacarbonyl pyridine (TPCP) and tungsten pentacarbonyl fraw -l,2-bis(4-pyridyl)-thylene (TPCB), that also had been studied experimentally. They considered the isolated monomers as well as dimers and studied the systems in solutions. They used density-functional methods in order to calculate the linear and nonlinear responses to electric fields, and the solvents were treated with a... 

An unstable adduct between triphenylphosphine and a photochemically-generated dimethylgermylene has been characterised spectrophotometrically.The first 2,3-dihydro-l,3,2-X -benzodiazaphospholes (73) have been formed in the reactions of triphenylphosphine with g-benzoquinone di-imines stabilised by coordination.A complex of phenylnitrene with a tungsten pentacarbonyl acceptor has been trapped using triphenylphosphine. A kinetic study of the reactions of diazoalkanes with triphenylphosphine, leading to the phosphazenes (74), indicates a biphilic mechanism, the dominant interaction in the transition state involving the diazoalkane as a net electron donor,... 

The transformation has been extended even further to p)ran derivatives by using a tungsten pentacarbonyl-tetrahydrofuran complex. Primary, secondary, and tertiary l-alkyn-5-ols 136 undergo cyclization to dihydropyranylidene carbenes, which can then be converted into the corresponding stannyl dihydrop)Tanes 138 upon treatment with tributyltin triflate and triethy-lamine (O Scheme 46) [236],... 

Similarly, benzylidene(pentacarbonyl) complexes of chromium and tungsten react with cyclo-pentadiene, by stereoselective transfer of the benzylidene moiety to one of the C-C double bonds of the diene, to form coordinated e do-6-phenylbicyclo[3.1.0]hex-2-ene 9 with the metal-ligand unit complexing from the exo side. This method was applied to several other dienes. Reaction with cyclohexa-1,3-diene gave the corresponding cndo-7-phenylbicyclo[4.1.0]hept-2-ene complex. The cyclopropane-containing ligands obtained in this way were liberated from the complex to form the free hydrocarbon system. 

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