Tungsten complexes with alkylidynes

Further developments are likely as the chemistry of the compounds described above is explored. Moreover, entirely new dimensions may be added. For example, the synthesis of tungsten-alkylidyne complexes with carba-borane ligands with cage structures smaller than the icosahedral C2B9 fragment should result in the isolation of new electronically unsaturated metal cluster and electron-deficient molecules of types as yet unknown. 

Alkylidyne complex [W(=CC6H4Me-4)(CO)2(bpy)Br] reacts with [Au(C6F5) (THT)] or [AuCl(THT)] to yield the heterodinuclear complexes with a tungsten -gold bond, 66 (X = C6F5, Cl) (88JCS(D)1957). 

Bis-nitrogen donor ligand-substituted alkylidyne complexes such as 78 were found to be good alternatives as starting materials to the thermally labile tetracarbonyl complexes 44). Substitution of one pyridine ligand in the bispyridine-substituted complexes 78 occurs in the presence of excess chloride [Eq. (64)] 103). The anionic complexes 79 are stable in the presence of excess chloride but are too labile to be isolated in pure form. These complexes were used in the synthesis of stable alkylidyne alkene tungsten complexes [Eq. (180), Section IV,G]. With phosphines both pyridine ligands in 78 are substituted [Eq. (65)] 44). For PMej the reaction of the tetracarbonyl complex W(CPh)Br(CO)4 had previously been shown to... 

Several alkylidyne alkene tungsten complexes were synthesized in our laboratory. The neutral complex 233 and the anionic complexes 235 were found to react with maleic anhydride and fumaronitrile to afford the products 234 and 236 [Eqs. (179) and (180)] (103). The tmeda-substituted... 

The tungsten alkylidynes Tp W( = CH)(CO)2 and Tp W(=CPh)(CO)2 also arise from side reactions of phosphonium alkylidyne complexes with aryloxide nucleophiles from reaction of the quaternary phosphonium salts with adventitious hydroxide to give a dissociated alkyl anion or a product resulting from a 1,2-phenyl migration. At low temperature, phenyl migration is inhibited and only the terminal dissociation product is observed. At room temperature, both phenyl and C-H alkylidyne products form in an approximate 1 1 ratio. 

Scheme 76. Synthesis of bimetallic tungsten-rhodium complexes with bridging alkylidyne groups (R = C6H4Me-4, Me L = PPh3, X = Pp6 L = 2 cod, X = Bp4).

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