Tungsten alkyne complexes

The aminocarbonylation of alkynes has been less explored as compared to that of alkenyl and (hetero)aryl halides. Nevertheless, several noteworthy applications of this reaction have been reported, including the syntheses of 2-ynamides, chiral 2-carbamoyl-7r-allylic tungsten complexes, angular triquinanes, 2-(carbamoylmethylene)tetrahydrofurans, alle-nyl amides, and others. ... 

A number of reactions between M2(OR)6 compounds and alkynes have been found to give alkylidyne compounds by a metathesis of the M=M and C=C bonds (see Sections 15.3.6.4) and evidence has been presented275 for an equilibrium between a ditungstatetrahedrane and a methyl-idyne-tungsten complex supported by BulO ligands (equation 72). 

Related tungsten complexes have been prepared by diverse routes. Phosphine, phosphite, and isonitrile W(CO)2(RC=CR)LI2 complexes form from W(CO)4LI2 and alkyne [Eq. (3)] (44). Parent acetylene (HC2H) complexes were isolated as m-dicarbonyl derivatives for L equal to PMe3 or AsMe3, and both cis- and Pms-dicarbonyl derivatives were characterized with phenylacetylene in the coordination sphere. 

Alt and co-workers have prepared numerous alkyl (67) and acyl (68) tungsten(II) alkyne complexes. A definitive paper detailing these results was published in 1985 (69). The reaction sequence which converts CpW-(CO)3R and free alkyne to CpW(CO)(RC=CR)R and free CO is not simple. Low temperature photolysis (-30°C) of the reagents in pentane first yields acyl alkyne products [Eq. (15)]. These products result from trapping of the initial alkyl alkyne derivative which rapidly reacts with CO to form the observed acyl product [Eq. (16), L = CO] (69). 

Addition of the electron-rich amino alkyne, Et2NC=CMe, to the 172-ketenyl tungsten complex, (T 2-RC=C=0)CpW(PMe3)(C0), results in trimethylphosphine substitution and opening of the Tj2-ketenyl ligand to an V-ketenyl [Eq. (18)] (71). 

Tungsten-cobalt-alkyne complexes can be formed via alkylidyne cou-... 

The photochemical cis-trans isomerization of bisphosphine-substituted carbyne complexes [Eq. (57), Section IV,B], which was studied in our group, was postulated to proceed via pentacoordinate metal ketenyl intermediates (97). Support for this postulate was found in the low-temperature characterization of ketenyl complex 208 on irradiation of complexes 207 in the presence of PMe, [Eq. (164)]. In the presence of phenylacetylene the ketenyl alkyne tungsten complex W(/ -PhCCO)CI(PhC2H)(CO)(PMe3)2 forms at low temperatures. 

However, this work pre-dated the discovery of protonation of dinitrogen in the molybdenum and tungsten complexes and, once this had come to light, we turned our attention to the behaviour of isocyanides and alkynes at those sites that activated dinitrogen to reduction. For isocyanides, the first step was to bind these ligands in place of dinitrogen in the complexes trflns-[M(N2)2(dppe)2], which was done by a displacement reaction [Equation (23)]. ... 

The iminophosphine (134) with 1-alkynes gave various products of 1,1- or 1,2-additions. A new synthesis of diphosphenes (135) from aryldichlorophosphines and a tungsten complex has been described the tungsten complex catalysed an exchange between two diphosphenes to give the unsymmetric diphosphene. A ferrocenyl-substituted diphosphene (136) has been prepared which seems to represent a borderline case with respect to dimerisation thus the dimer (137) readily dissociates to (136) upon heating in xylene. 

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