Tungsten carbene/carbyne complexes

Metallacyclopent-l-enes have been obtained by formal [2 + 3] cycloaddition of ethylene to Re(CtBu)(CHtBu)(OR)2 (a carbene/carbyne complex) [612]. Nucleophilic tungsten(II) complexes can react directly with cyclopentanone to yield cyclopentylidene complexes [613]. 

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... 

In connection with carbene and carbyne complexes, an especially interesting tungsten compound is 18-C-XXV, which contains W=C, W=C, and W—C bonds, whose lengths are 1.79, 1.94, and 2.26 A, respectively. 

The tungsten thiocarbyne complex 171 is attacked by PRj (R = Me, Et) at the carbyne carbon atom (164). Templeton and co-workers found that with PEtj the phosphonium carbyne complex 172 is obtained [Eq. (141)] whereas reaction with PMcj gives the bisphosphonium carbene complex 173 [Eq. (142)]. One PMej appears to be able to dissociate from 173, and... 

Reaction of a reduced Philipps catalyst with Fischer-type molybdenum or tungsten carbene or carbyne complexes led to very active bimetallic, heterogeneous olefin metathesis catalysts. Surface metal ions might be involved in bonding interactions with the organometallic complex, possibly leading to heterometallic species on inorganic oxides. ... 

Schrock and Fischer type carbyne tungsten or molybdenum complexes are very interesting catalysts for alkene metathesis or alkyne polymerisation reactions. Within the first reaction steps they form carbene complexes and on these carbene complexes further metathesis or polymerisation occur. 

ABSTRACT. Dicarbonyl(t 5-cyclopentadienyl)carbyne complexes of molybdenum and tungsten prove to be a valuable synthetic tool Reaction with phosphines provides substituted carbyne complexes and leads via an intramolecular CC-coupling to t 1- or Tj -ketenyl complexes respectively. Electrophiles attack the metal carbyne triple bond forming hetero- and acyclic carbene complexes, r 2-acyl compounds, T -ketene complexes and metalla-dithia-bicyclobutane cations. Dithio-carboxylates are formed in reaction of these dicarbonyl(Ti5 cyclo-pentadienyl)carbyne complexes with sulfur or cyclohexene sulfide. 

Fischer first prepared carbyne complexes by the action of boron halides on carbene compounds of chromium, molybdenum, and tungsten. 

Figure 3 Optimized geometries at MP2/11 of tungsten carbene and carbyne complexes values in parentheses are obtained at HF/11.

In the preparative section 3.2 devoted to metal-carbene complexes, it is shown how the a-elimination reaction from high oxidation state early-transition-metal-alkyl complexes is one of the general methods of synthesis of Schrock s Ta and Nb alkylidene complexes. The other direction, formation of an alkylidene from an alkylidyne complex, can also be a valuable route to metal alkylidenes. For instance, Schrock s arylamino-tungsten-carbynes can be isomerized to imido-tungsten-carbene by using a catalytic amount of NEts as a base. These compounds are precursors of olefin metathesis catalysts by substitution of the two Cl ligands by bulky alkoxides (dimethoxyethane then decoordinates for steric reasons), and this route was extended to Mo complexes ... 

TM compounds in high and low oxidation states with metal-carbon double and triple bonds have been the subject of a systematic theoretical study. Table 7 shows the calculated metal-ligand bond lengths of several tungsten carbene and carbyne complexes at the HF and MP2 levels of theory. The HF optimizations were carried out using two different basis sets. Basis set I has DZ quality at tungsten (no additional 6p... 

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. 

Scheme 8.14 Preparation of neutral and cationic tungsten carbynes 53-55 from the carbene complexes 15a,b as the precursor (R = Me, Ph for X- and L see text)...

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