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 sigma-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 alpha 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 -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.

Dehydrogenative Bond-Forming Catalysis Involving Phosphines

“…For these complexes, two mechanism have been identified [107]. In the dehydrocoupling of Ph 2 AsH to (Ph 2 As) 2 , kinetic data supported As-As bond formation via -bond metathesis similar to the dehydrocoupling of phosphines by related catalysts [62].…”

Dehydrogenative Bond-Forming Catalysis Involving Phosphines: Updated Through 2010

“…For these complexes, two mechanism have been identified [55]. In the dehydrocoupling of Ph 2 AsH to (Ph 2 As) 2 , kinetic data supported As-As bond formation via -bond metathesis similar to the dehydrocoupling of phosphines by related catalysts [28].…”

“…However, no (CyPH) 2 or (CyP) 4 was observed until all PhPH 2 was consumed. It was found that the methyl complex reacts selectively with an equivalent excess of CyPH 2 and PhPH 2 to exclusively form (N 3 N)ZrPHPh (9), which was structurally characterized [55]. The cyclohexyl derivative, (N 3 N)ZrPHCy [28], is known but was not observed within the limits of detection.…”

“…However, in the presence of a small quantity of 19, the equilibrium favors complex (N 3 N)ZrAsHMes (26) and the decomposition of 26 to (AsMes) 4 and 19 obeys first-order kinetics, consistent with elimination (eq. 12) [55].…”

Rare Earth Pincer Complexes: Synthesis, Reaction Chemistry, and Catalysis

“…The intrinsic reactivity of rare earth complexes can sometimes promote facile reaction at sp 2 and sp 3 C-H groups that are often considered to be quite inert. The intramolecular activation of C-H bonds generally leads to cyclometalated species that can be relevant to various catalytic transformations [32,33]. These complexes also serve as excellent platforms from which unique bonding and reactivity patterns can be studied [20].…”