Activation and cleavage of alkynes by the dinuclear tantalum complexes ([NPN]Ta)2(µ-H)4 and ([NPN]Ta)2(µ-η1:η2-N2)(µ-H)2 (where NPN = PhP(CH2SiMe2NPh)2)

Reaction of phenylacetylene with the dinuclear tetrahydride complex ([NPN]Ta)2(µ-H)4 gives the product ([NPN]Ta)2(µ-PhCCH)(µ-H)2 (where NPN is PhP(CH2SiMe2NPh)2). Activation of other terminal alkynes by ([NPN]Ta)2(µ-H)4 accesses ([NPN]Ta)2(µ-RCCH)(µ-H)2 (R = n-Pr, t-Bu). Crystallographic analysis of the R = Ph derivative showed it to be a bis(µ-alkylidene) bound asymmetrically to the two tantalum centres. Storage of solutions of ([NPN]Ta)2(µ-PhCCH)(µ-H)2 under vacuum promotes the loss of H2 and cleavage of the C—C bond to give a bis(µ-alkylidyne) complex, ([NPN]Ta)2(µ-CPh)(µ-CH). Addition of diphenylacetylene did not give the desired ([NPN]Ta)2(µ-CPh)2, but rather promotes a complex decomposition of the supporting [NPN] ligands. Reaction of phenylacetylene with the dinitrogen complex ([NPN]Ta)2(µ-η1:η2-N2)(µ-H)2 results in the dissociation of the bound dinitrogen and the formation of ([NPN]Ta)2(µ-PhCCH)(µ-H)2, which is identical to that derived from the reaction with the dinuclear tetrahydride. Key words: tantalum, alkyne, alkylidene, alkylidyne, amidodiphosphine, dinuclear hydride dinitrogen, activation of small molecules.