Reaction Chemistry of Silver(I) Trifluoromethanesulfonate Complexes of Nitrogen-Confused C-Scorpionates

Abstract

Two new C-scorpionate ligands with a bis(3,5-dimethylpyrazol-1-yl)methyl group bound to the 3 position of either an N-tosyl (L*) or an N-H pyrazole (L*) ring have been prepared. The silver(I) complexes of these new ligands and the two previously reported analogous ligands with unsubstituted bis(pyrazol-1-yl)methyl groups (L and L) in both 1:1 and 2:1 ligand/metal ratios were investigated to explore the effects of ligand sterics on their physical and chemical properties. The structurally characterized derivatives of the type [Ag(L)](OTf) are four-coordinate, where the confused pyrazolyl is not bound to the metal. On the other hand, three 1:1 complexes [Ag(L)](OTf) had all pyrazolyls bound, while the μ-κ,κ-L derivative had an unbound confused pyrazolyl. The molecularity of the latter four ranged from polymeric to dimeric to monomeric in the solid with increasing steric bulk of the ligand. The utility of these complexes in stoichiometric ligand-transfer reactions and in styrene aziridination was demonstrated. Thus, tricarbonylmanganese(I) complexes were prepared as kinetically inert models for comparative solution diffusion NMR studies. Also, [Fe(L)](OTf) was prepared for similar reasons and to compare the effects of anion on spin-crossover properties.

Silver(I) and Copper(I) Complexes of Semi‐Bulky Nitrogen‐Confused C‐Scorpionates

“…It is noted that in solution the triflate ion in [Ag( x L iPr2 )](OTf) is not bound to the metal, rather it is displaced by CD 3 CN. The 19 F NMR spectrum of each of the four silver compounds is identical and shows only a single resonance at –79.3 ppm, a chemical shift that is identical to that in the spectrum of either NBu 4 OTf, [(κ 3 N ‐ x L*)Mn(CO) 3 ](OTf) (x = Ts, H), or [Fe(κ 3 N ‐ H L) 2 ](OTf) 2 ,, species with “free” triflate ions. Ion‐pairing of triflate with cations has minimal effect on the chemical shift of the 19 F resonance because the ion pair contact occurs only with the oxygen atoms.…”

“…Views of the structures of these complexes are found in Figure , while Table collects selected bond lengths and angles. The structure of 1a· acetone is comparable to the related complex Ag( Ts L * )(OTf) reported previously . That is, silver center in 1a· acetone is tetracoordinate via bonding to a κ 3 N ‐ ligand and an oxygen (O3) of the triflate ion.…”

“…Aziridines are important synthetic intermediates in organic synthesis, medicinal chemistry, and polymer chemistry, Catalytic approaches to their syntheses have rapidly expanded in recent years , . Transition metal‐catalyzed reactions involving nitrene transfer to alkenes have gained prominence in this regard , . Of these latter catalysts, copper(I) and silver(I) scorpionate complexes [tris(pyrazolyl)borates, (normal scorpionates, or Tp R , Scheme , top left), tris(pyrazolyl)methanes (Tpm R or C ‐scorpionates, Scheme , top right), certain C‐heteroscorpionates (Scheme , bottom left), and certain nitrogen‐confused C‐scorpionates (Scheme , bottom right)] have proven adept at catalytically affording aziridines from alkenes and various nitrene sources under mild conditions.…”

“…Transition metal‐catalyzed reactions involving nitrene transfer to alkenes have gained prominence in this regard , . Of these latter catalysts, copper(I) and silver(I) scorpionate complexes [tris(pyrazolyl)borates, (normal scorpionates, or Tp R , Scheme , top left), tris(pyrazolyl)methanes (Tpm R or C ‐scorpionates, Scheme , top right), certain C‐heteroscorpionates (Scheme , bottom left), and certain nitrogen‐confused C‐scorpionates (Scheme , bottom right)] have proven adept at catalytically affording aziridines from alkenes and various nitrene sources under mild conditions. Thus, Pérez and co‐workers found that Tp*Cu(C 2 H 4 ), or other CuTp R complexes (prepared in‐situ) catalyze the aziridination of styrene, cyclooctene, or 1‐hexene over the course of a few hours at room temperature in CH 2 Cl 2 using PhI=NTs as a nitrene transfer agent.…”

“…In a previous study, eight complexes of the type [Ag( x L R ) n ](OTf) ( n = 1, 2 and x L R = H L, Ts L, H L*, and Ts L*) were characterized and evaluated for their ability to catalyze aziridination of styrene. Both ESI(+) MS and NMR spectroscopic studies indicated that the analytically pure [Ag( x L R ) n ](OTf) compounds did not retain their structure in CH 3 CN rather were involved in multiple dynamic equilibria in solution.…”