Alkynes complex hydrides

From the energetically preferred n-alkyne complex there is an alternative pathway involving the hydride ligand (Figure 5). The first step is an easy (AE = 6.6 kcal.mol 1) migratory insertion of the C=C triple bond into the cis Ru-H bond to yield a a-vinyl complex, A, 10.4 kcal.mol 1 below the it-alkyne complex. This 14-electron o-vinyl complex has also a saw-horse... 

Yamamoto has proposed a mechanism for the palladium-catalyzed cyclization/hydrosilylation of enynes that accounts for the selective delivery of the silane to the more substituted C=C bond. Initial conversion of [(77 -C3H5)Pd(GOD)] [PF6] to a cationic palladium hydride species followed by complexation of the diyne could form the cationic diynylpalladium hydride intermediate Ib (Scheme 2). Hydrometallation of the less-substituted alkyne would form the palladium alkenyl alkyne complex Ilb that could undergo intramolecular carbometallation to form the palladium dienyl complex Illb. Silylative cleavage of the Pd-G bond, perhaps via cr-bond metathesis, would then release the silylated diene with regeneration of a palladium hydride species (Scheme 2). 

Hydride abstraction from 225 gives the dibenzannuleted tropyne complex 226 (Scheme 27).85 As in the case of 223, 226 reacts rapidly with HBr to give 227, which, in solution, isomerizes slowly to 228. KBEt3H and bis(dicyclohexylphosphine)ethane attack the 4-position of the tropyne to give alkyne complexes 225 and 229, respectively. 

PhC=CH and PhC=CPh analogs [Eq. (26)] (80). Five coordination is also found in the porphyrin alkyne complex, Mo(TTP)(PhC=CPh) (TTP= mesotetra-p-tolylporphyrin) (81). Reduction of a toluene solution of Mo(TTP)C12 with lithium aluminum hydride in the presence of excess diphenylacetylene produced the violet Mo(TPP)(PhC=CPh) adduct [Eq. (27)]. 

The interaction of aUcynes with iridium hydride complexes can lead to a number of different alkyne complexes. Reaction between two equivalents of 2-butyne and [IrH4(PPhMe2)3] produces one equivalent of butene and the butyne complex [Ir(MeC=CMe)(PPhMe2)3]+ (35) with a structure that differs from the expected square planar. Reaction between the same iridium complex and dimethylacetylenedicarboxylate produces a bis-aUcyne complex (36). ... 

Alkenes and alkynes react with complex hydrides only under special conditions. Reaction products are often intermediates prior to solvolysis to the final hydrocarbons desired in organic syntheses " e.g. ... 

Reactivity studies reveal that the bis(indenyl)zirconium sandwich complexes serve as isolable, modular precursors to the rich chemistry of divalent zirconocene. Addition of 1 atm of carbon monoxide generates the bis(indenyl)-zirconocene dicarbonyl complex, 307, while treatment with N,N-dimethylaminopyridine results in C-H activation to form the zirconocene pyridyl hydride complex 308. Crystallographic characterization of both complexes as well as multinuclear NMR spectroscopy establishes that the more familiar 77s, 77s hapticity for the indenyl ligands has been restored. Alkyne coupling reactions are also observed as addition of 2-butyne to 302 allows observation of the alkyne complex, 208, and ultimately the zirconacyclopentadiene 309 (Scheme 50).104... 

Hydroalumination of alkynes. The hydride reacts with alkynes in a hydrocarbon solvent by cis addition to yield a tran.t-vinylalane (1) from 1-alkynes and a cis-vinylalane from disubstituted alkynes. Treatment of the vinylalane with methyl-lithium in ether in a 1 1 ratio to give an ate complex (2) followed by carbonation... 

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