Pentacarbonyl tungsten

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>. 

I.3.4.2.6. Compounds with Unusual Double Bonds 1,3-Dipolar cycloaddition of l-chloro-2-phenyl-2-trimetkylsilyl-l-phosphaethene with nitrile oxides, followed by elimination of Me SiCl, results in 3,5-diphenyl-l,4,2-oxaphosphazole 190 (356). Chromium, molybdenum, and tungsten pentacarbonyls of 3,5-diphenyl-).3-phosphinins react with nitrile oxides to give the corresponding 1,3-dipolar cycloadducts, at the P = C bond, see 191 (Ar = Ph, Mes) (357). 

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

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]... 

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. 

Metal-catalyzed cycloisomerization reactions of w-alkynols (4-pentyn-l-ol derivatives) provide a rapid and efficient access to tetrahydrofurans. In general, these reactions may proceed through two different reaction pathways, formally leading to endo- or r-vo-cycloisomerization products. The formation of the rwn-tetrahydrofuran product can be achieved with catalytic amounts of tungsten pentacarbonyl (Equation 85) <2005CEJ5735>. 

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],... 

In conformity with the calculations the yicrz-fused heterocycles with a phosphorus atom proved to be quite stable. For instance, treating 1,8-dilithionaphthalene (18) with (A, A -diisopropylamino)dichlorophosphine afforded in a 75% yield a P-substituted naphtho[l,8-Z)c]phosphete (19) that took up tungsten pentacarbonyl to form a complex compound 20 (02AG(E)3897). The latter on further reaction with platinum tetratriphenylphosphinate and carbon monoxide suffers a recyclization of the four-membered ring into a five-membered one (20—>21). The reaction of... 

Cycloaddition reactions of derivatives of chromium and tungsten pentacarbonyl compounds... 

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