Mechanistic variety in zirconium-catalyzed bond-forming reaction of arsines

Abstract

Triamidoamine-supported zirconium complexes have been demonstrated to catalyze a range of bond-forming events utilizing arsines. Three different mechanisms have been observed in these reactions. In the first mechanism, triamidoamine-supported zirconium complexes of the general type (N₃N)ZrX (N₃N = N(CH₂CH₂NSiMe₃)₃³⁻; X = monoanionic ligand) catalyzed the dehydrogenative dimerization of diphenylarsine. Mechanistic analysis revealed that As–As bond formation proceeds via σ-bond metathesis steps similar to the previously reported dehydrocoupling of phosphines by the same catalysts. In the second mechanism, sterically encumbered primary arsines appear to be dehydrocoupled via α elimination of an arsinidene fragment. Dehydrocoupling of dmpAsH₂ (dmp = 2,6-dimesitylphenyl) to form (dmp)As = As(dmp) by (N₃N)Zr-complexes appeared to proceed via elimination of dmpAs: from the arsenido intermediate, (N₃N)ZrAsH(dmp). Further support for α-arsinidene elimination came from the thermal decomposition of (N₃N)ZrAsHMes (9) to (MesAs)₄ (10), which obeyed first-order kinetics. In the third mechanism, the observation of stoichiometric insertion reactivity of the Zr–As bond with polar substrates, PhCH₂NC, PhCN, (1-napthyl)NCS, and CS₂, led to the development of intermolecular hydroarsination catalysis of terminal alkynes. Here, (N₃N)ZrAsPh₂ (2) catalyzed the addition of diphenylarsine to phenylacetylene and 1-hexyne to give the respective vinylarsine products. Arsenido complexes 2 and 9 and tetraarsine 10 have been structurally characterized.