Tungsten-carbon bond, triple

Protonation of 12 yields a compound best described as a face-protonated methylidyne complex, the tungsten-carbon bond length lying in the range observed for a triple bond (28). Protonation of the osmium compound 13 yields a true carbene complex, which for R = Ph has been characterized by X-ray crystallography (see Sections IV and VI). 

The tungsten-carbon single, double, and triple bond lengths in this compound are 225.8, 194.2. and 178.5 pm, respectively, and the accompanying W—C—C bond angles are 124°. 150°. and 175 , all of which is quite consistent with tungsten-carbon bond orders of 1,2. and 3. 

A tungsten complex which possesses all three types of metal-carbon bonds, single (alkyl), double (alkylidene), and triple bonds (alkylidyne) has been prepared as shown in eq. (3) and structurally characterized [15]. 

Several stable Group 6 metal-ketene complexes are known [14], and photo-driven insertion of CO into a tungsten-carbyne-carbon triple bond has been demonstrated [15]. In addition, thermal decomposition of the nonheteroatom-stabilized carbene complexes (CO)5M=CPh2 (M=Cr, W) produces diphenylke-tene [16]. Thus, the intermediacy of transient metal-ketene complexes in the photodriven reactions of Group 6 Fischer carbenes seems at least possible. 

It must be pointed out that tungsten [22-26] and molybdenum [26-29] carbonyl precursors also have remarkable catalytic activity in the cycloisomerization of alky-nols to produce dihydropyrans and dihydrofurans via intramolecular nucleophilic addition of the hydroxy group to the terminal carbon of the triple bond, activated... 

Despite Schrock s extensive work on tantalum, molybdenum, and tungsten car-byne complexes (e.g., 47, 49, 50, 51, and 52) [96, 97, 99, 100], it must be recalled, however, that they were not the first compounds with a metal—carbon triple bond. 

E. O. Fischer, G. Kreis, C. G. Kreiter, J. Muller, G. Huttner, and H. Lorenz, trans-Halo[alkyl(aryl)carbyne]tetracarbonyl Complexes of Chromium, Molybdenum and Tungsten. A New Complex Type with Transition Metal-Carbon Triple Bond, Angew. Chem. Int. Ed. Engl. 12, 564-565 (1973). 

Fp C=CC2[Co2(CO)6]-moieties linked by a C-C single bond and is obtained from the reaction of the tetrayndiyl complex Fp i-(C=C)4 and Co2(CO)8.422 The two C2Co2 cores, which again involve the inner C=C triple bonds, induce a transoid conformation (S-shaped) in the carbon chain, analogous to that described above for the tungsten complexes. 

It is commercially available and is used as starting material for the chemical vapor deposition of tungsten (see Sections 5.6.3. and 5.7.5) and for the preparation of metathesis catalysts which form double and triple bonds with carbon (see Chapter 10). 

A few metal complexes of selenothioic and diselenoic acids have been reported. In a study on the reactivity of metal-carbon triple bond compounds toward chalcogens, it was found that molybdenum (52) and tungsten (53) carbyne complexes reacted with elemental selenium to yield the corresponding di-selenoate complexes 54 and 55, respectively (Eqs. 13 and 14) [18]. 

Other metal complexes of titanium, zirconium, vanadium, chromium, molybdenum, tungsten, manganese, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver and gold to synthesize a wide variety of interesting new compounds. It utilizes Hoffmann s [51] isolobal relationship between the C=C bond and the metal-carbon triple bond. 

Congtkxes with other One-carbon-donor Ligands. The dimeric molecule [Mos(CH2SiMe3),] is isostructural with the analogous tungsten compound. It consists of two tetrahedral MofCHjSiMes), units held toother by a Mo-Mo triple bond of 2.167 A. The dimer exhibits approximate 2) symmetry. The average Mo-C(CH ) distance is 2.131 A. 

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