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)

Abstract

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(CH 2 SiMe 2 NPh) 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 H 2 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-η 1 :η 2 -N 2 )(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. Résumé : La réaction du phénylacétylène avec le complexe tétrahydrure dinucléaire ([NPN]Ta) 2 (µ-H) 4 conduit au produit ([NPN]Ta) 2 (µ-PhCCH)(µ-H) 2 dans lesquels NPN = PhP(CH 2 SiMe 2 NPh) 2 . L'activation d'autres alcynes terminaux par du ([NPN]Ta) 2 (µ-H) 4 permet d'accéder aux composés ([NPN]Ta) 2 (µ-RCCH)(µ-H) 2 dans lesquels R = n-propyle et tbutyle. Une analyse cristallographique du dérivé avec R = Ph montre qu'il s'agit d'un bis(µ-alkylidène) lié d'une façon asymétrique aux deux centres de tantale. L'entreposage de solutions de ([NPN]Ta) 2 (µ-PhCCH)(µ-H) 2 sous vide facilite la perte de H 2 et le clivage de la liaison C-C pour conduire à la formation d'un complexe bis(µ-alkylidyne), ([NPN]Ta) 2 (µ-CPh)(µ-CH). L'addition de diphénylacétylène n'a pas conduit au ([NPN]Ta) 2 (µ-CPh) 2 attendu, mais a plutôt favorisé une décomposition complexe des ligands supports [NPN]. La réaction du phéhylacétylène avec le complexe de diazote ([NPN]Ta) 2 (µ-η 1 :η 2 -N 2 )(µ-H) 2 conduit à une dissociation du diazote lié et à la formation de ([NPN]Ta) 2 (µ-PhCCH)(µ-H) 2 identique à celui obtenu par réaction avec le tétrahydrure dinucléaire.

Synthesis, Structure, and Reactivity of Niobium and Tantalum Alkyne Complexes

“…71,72 The combination of 49 with various terminal alkynes led to the displacement of the N 2 ligand and the formation of 50, a dinuclear Ta complex wherein the reduced alkyne unit is bridged between the two metal centers; 50 can also be accessed directly from 48, along with the loss of 1 equiv of H 2 . 73 On the basis of the short Ta−C (∼2.05 Å) and long C−C (1.397(6) Å) bond distances, the …”

Complete disassembly of carbon disulfide by a ditantalum complex

“…Shown in Scheme 1 is a possible mechanism for the disassembly process. Based on prior reactivity studies of 1, we propose that CS 2 displaces 9,11 the N 2 and adds to generate a m-Z 2 -CS 2 moiety (A), which undergoes C-S bond cleavage to produce the thiocarbonyl sulfido species B; 6,12 the next two steps involve migratory insertion of CS into the bridging hydrides to first generate the bridging thioformyl C, 13,14 then to generate D that has a methylene-thiolate bridge. Cleavage of the remaining C-S single bond gives the observed product 2.…”

P047: Look beyond crown rump length

“…For example, with phenyl acetylene and simple alkenes such as propene, we observed displacement of the N 2 unit or migratory insertion reactions into the tantalum hydrides, respectively (Scheme ) 3d. 5 In contrast, a variety of EH hydride reagents (EH=R 2 BH, R 2 AlH, RSiH 3 ) have been shown to add across the side‐on/end‐on N 2 unit of 1 to generate new functionalized nitrogen fragments and the formation of terminal TaH bonds 6. As these EH additions can be considered to be additions across a quasi‐TaN multiple bond,3d, 7 we continued our search for other reagents that could engage in [2+2] chemistry with the side‐on/end‐on η 2 :η 1 ‐N 2 moiety.…”