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Tungsten complexes, photolysis

While the germanium-containing tungsten complex 166 rearranged to 167 on photolysis, the isomeric species 168 directly eliminated the silene Me2Si=CH2 yielding 169 (Scheme 26)80. [Pg.1262]

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>. [Pg.888]

The remarkable xenon complex Cr(CO)5(Xe) was also obtained by UV photolysis of Cr(CO)6 in liquefied xenon and found to have a lifetime of ca. 2 s at -98°C [117]. Later, the corresponding molybdenum and tungsten complexes Mo(CO)5(Xe) and W(CO)5(Xe) were generated in a similar way and characterized by time-resolved IR spectroscopy [118]. The bond energies Cr-Xe, Mo-Xe, and W-Xe were not as low as previously anticipated and determined to be 8-9 kcal/mol, independent of the group VI metal. [Pg.103]

Molybdenum and Tungsten.—Flash photolysis and e.s.r. studies40 have been carried out on [Mo(CN)8]3- in solutions of varying pH, concentration, and solvent. The results are consistent with (11) as the primary reaction following excitation of the complex to an LMCT state. [Pg.157]

Tin(II) bis(jS-ketonolates), Sn[0CRCHCR (=0)]2 (R, R = Me, CFj, Ph), are also excellent donor molecules to transition metal carbonyl residues, readily forming the type D structure chromium, molybdemun and tungsten complexes (8) under photolysis in tetrahydrofuran, as well as the manganese complexes (9). The cobalt complexes (10) and (11) prepared by the same method are somewhat different, and in these the stannylene functions as a bridging group. The two platinum(0) complexes (12) and (13) have been obtained from the reaction of tin(II) bis(pentane-2,4-dionate) and Pt(C2H4)(PPhj)2 under different conditions. ... [Pg.664]

I.r. laser techniques have been used to study [Fe(CO)4] in a nitrogen matrix at 20 K. Surprisingly, the quantum yield for intramolecular isomerization is greato-than the quantum yield for formation of [Fe(CO)4(N2)]. Photolysis of matrix isolated [Mo(CO)s] in the presence of Na at 20 K affords [Mo(CO)5Na)]. Under similar conditions, the analogous chromium and tungsten complexes have been detected by i.r. and Raman techniques. The photochemistry of [O(C0)5] and related species in matrices has been studied via polarized light spectroscopy. A mechanism has been proposed which accounts for almost all the experimental data on matrix-isolated [M(CO)s] (M=Cr, Mo, or W), [M(CO)5(Na)], and [M(CO)4(CS)]. Reactions occur via the following steps ... [Pg.183]

In another study the kinetics and mechanism of an unprecedented T/2-vinyl isomerization of a highly fluorinated tungsten(II) metalla-cyclopropene complex was studied (92). Photolysis of a tungsten(II) tetrafluoroaryl metallacycle 1 and perfluoro-2-butyne results in the formation of the kinetic rf -vinyl complex 2 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. Upon heating 2 is converted to the thermodynamic rf -vinyl complex 3 in which the fluoride ligand is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand as shown in Scheme 1. [Pg.20]

Furthermore, Fischer rendered this chemistry more practical by generating vinylidene complexes of pentacarbonylchromium and tungsten directly in situ from terminal alkynes [9]. For example, treatment ofterminal alkynes with WCO)5(CH2Cl2), generated by photolysis of W(CO)6 in CH2CI2, gave thermo-labile tt-alkyne W(CO)5... [Pg.161]

Reduction of [Mo(CO)(Bu C=CH)2Cp] + BF4 with KBHBu3(s) at — 78°C in an atmosphere of carbon monoxide yields a complex of a vinyl substituted y-lactone linked tj3 t]2 (220). The allylidene ruthenium complex 64, obtained by photochemical addition of one alkyne molecule to a /x-carbene derivative, is transformed into pentadienylidene complexes 65 and 66 on photolysis with more alkyne substrate. These reactions show clearly the stepwise growth of chains in alkyne oligomerizations at dimetal centers [Eq. (31)] (221). Similar reactions are also known for dinuclear iron (222), molybdenum (223), and tungsten (224) complexes. [Pg.154]

Base-free alkyl-substituted germyl(germylene)tungsten carbonyl complexes 37 and 38 were synthesized by the photolysis of digermyl complexes of tungsten 39 and 40 in benzene (equation 38). These complexes are formed by the 1,2-germyl migrations after the initial photodissociation of CO from 39 and 40146. [Pg.1255]

Intramolecularly alkoxy base-stabilized bis(germylene)-, 54, or (germylene)(silylene)-, 55, iron complexes, of type IV, were obtained from the photolysis of digermyl or germylsilyl iron complexes (equation 43)14. These are the same type of complexes noted above for base-free tungsten analogs146 involving a-elimination subsequent to photochemical elimination of CO as noted below. [Pg.1258]

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). [Pg.10]


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Complex photolysis

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