Synthetic Approaches to (smif)₂Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) Reveal Redox Non-Innocence and C–C Bond-Formation

Abstract

Attempted syntheses of (smif)2Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) based on metatheses of TiClnLm (n = 2–4) with M(smif) (M = Li, Na), in the presence of a reducing agent (Na/Hg) when necessary, failed, but several apparent Ti(II) species were identified by X-ray crystallography and multidimensional NMR spectroscopy: (smif){Li(smif-smif)}Ti (1, X-ray), [(smif)Ti]2(μ-κ3,κ3-N,N(py)2-smif,smif) (2), (smif)Ti(κ3-N,N(py)2-smif,(smif)H) (3), and (smif)Ti(dpma) (4). NMR spectroscopy and K-edge XAS showed that each compound possesses ligands that are redox non-innnocent, such that d1 Ti(III) centers AF-couple to ligand radicals: (smif){Li(smif-smif)2−}TiIII (1), [(smif2−)TiIII]2(μ-κ3,κ3-N,N(py)2-smif,smif) (2), [(smif2−)TiIII](κ3-N,N(py)2-smif,(smif)H) (3), and (smif2−)TiIII(dpma) (4). The instability of the (smif)2Ti relative to its C-C coupled dimer, 2, is rationalized via the complementary nature of the amide and smif radical anion ligands, which are also common to 3 and 4. Calculations support this contention.

Non-innocent ligands in copper complexes catalyzed oxidation of thiols

“…To verify this assumption, the evolution of the thiol-metal complex was studied by the MAS NMR technique. As we have previously shown, [34,35] this technique can only be used when only univalent copper compounds are present, that is, copper-containing intermediates can thus be studied.…”

Disparate reactivity from isomeric {Me 2 C(CH 2 N CHpy) 2 } and {Me 2 C(CH NCH 2 py) 2 } chelates in iron complexation

“…The generation of 2-N(TMS) 2 , and the ensuing thermolysis, suggested the potential for carbon-carbon bond formation in the system [3][4][5]7], hence a hydrazine derivative, 1,2-diphenyl-1,2-dimethylhydrazine, was added to oxidatively release organic product from the metal. For example, 1 equiv dmp(PM) 2 and 1 equiv hydrazine were placed in C 6 D 6 with 10% Fe{N(TMS) 2 } 2 (THF), and a new organic product formed after 2 d at 23°C.…”

“…Treatment of (Me 3 P) 3 Fe(j-CH 2 PMe 2 )H with dmp(PI) 2 2.2.1. Synthesis of {dmp(PI) 2 }FePMe 3 The failure to use Fe{N(TMS) 2 } 2 (THF) to deprotonate and chelate the dimine precursor dmp(PI) 2 prompted an attempt analogous to the previous use of Ni(COD) [33] as extolled in the explanation of Fig. 1.…”

“…As part of an investigation involving 1,3-di-(2-pyridyl)-2-azaallyls [1][2][3][4][5][6][7][8] and related species as chelating agents, imines that can serve as azaallyl precursors were incorporated into tetradentate platforms. In Fig.…”

Generation of TiII Alkyne Trimerization Catalysts in the Absence of Strong Metal Reductants

“…Given that they are highly reducing, Ti II reagents have typically been formed from the reaction of Ti IV halide precursors with powerful reductants: KC 8 , 2,7b LiAlH 4 ,11 Na/Hg, 15 and Mg. 16 Recently, we have reported several catalytic oxidative C–N bond forming reactions that proceed through a formal Ti II /Ti IV redox couple (Scheme 1). These reactions presumably generate a Ti II intermediate in the absence of a strong metal reductant by coupling a Ti IV imido unit with two alkynes (or an alkyne and an alkene).…”