Ni^II, Cu^IIand Zn^IIcomplexes with a sterically hindered scorpionate ligand (Tpms^Ph) and catalytic application in the diasteroselective nitroaldol (Henry) reaction

Abstract

The Ni(II) and Zn(II) complexes [MCl(Tpms(Ph))] (Tpms(Ph) = SO3C(pz(Ph))3, pz = pyrazolyl; M = Ni 2 or Zn 3) and the Cu(II) complex [CuCl(Tpms(Ph))(H2O)] (4) have been prepared by treatment of the lithium salt of the sterically demanding and coordination flexible tris(3-phenyl-1-pyrazolyl)methanesulfonate (Tpms(Ph))(-) (1) with the respective metal chlorides. The (Tpms(Ph))(-) ligand shows the N3 or N2O coordination modes in 2 and 3 or in 4, respectively. Upon reaction of 2 and 3 with Ag(CF3SO3) in acetonitrile the complexes [M(Tpms(Ph))(MeCN)](CF3SO3) (M = Ni 5 or Zn 6, respectively) were formed. The compounds were obtained in good yields and characterized by analytic and spectral (IR, (1)H and (13)C{(1)H} NMR, ESI-MS) data, density functional theory (DFT) methods and {for 4 and [(n)Bu4N](Tpms(Ph)) (7), the latter obtained upon Li(+) replacement by [(n)Bu4N](+) in Li(Tpms(Ph))} by single crystal X-ray diffraction analysis. The Zn(II) and Cu(II) complexes (3 and 4, respectively) act as efficient catalyst precursors for the diastereoselective nitroaldol reaction of benzaldehydes and nitroethane to the corresponding β-nitroalkanols (up to 99% yield, at room temperature) with diastereoselectivity towards the formation of the anti isomer, whereas the Ni(II) complex 2 only shows a modest catalytic activity.

Water‐Soluble C‐Scorpionate Complexes – Catalytic and Biological Applications

“…The sulfonate group of a Tpms R [e.g., R = H (Tpms) or Ph (Tpms Ph )] ligand can be involved in the coordination to the metal center, and this converts the corresponding N 3 ‐type Tpm R ligand into a more versatile one that can coordinate as a tripodal or bipodal ligand with N 3 ‐, N 2 O‐, N 2 ‐, or NO‐coordination modes (see Figure ) , …”

“…Compounds 9 and 10 can readily undergo the V V → V IV reduction [at I E p red ≈ –0.5 V vs. saturated calomel electrode (SCE)], as detected by cyclic voltammetry and controlled potential electrolysis at platinum electrodes, and this reduction is important for their catalytic performance (see Section 4).…”

“…[NiCl(Tpms Ph )] ( 36 ) was obtained in a good yield through the treatment of the lithium salt of the sterically demanding and coordinatively flexible Tpms Ph– with nickel(II) chloride in methanol under air at room temperature (Scheme ) . Complex 36 exhibits a modest catalytic activity for the diastereoselective nitroaldol (Henry) reaction, which is based on the carbon–carbon coupling of an aldehyde with a nitroalkane to give a β‐nitroalkanol ( anti and syn , see Section 4) …”

Ni(II)-Aroylhydrazone Complexes as Catalyst Precursors Towards Efficient Solvent-Free Nitroaldol Condensation Reaction

“…The use of solvent-free condition is also applied in the nitroaldol reaction [30,31]. Some nickel complexes showed good catalytic activity towards nitroaldol reactions under various conditions such as in homogeneous reaction states [32,33], under solvent-free microwave irradiation [25], in ionic liquids [34,35], or under heterogeneous [36][37][38] conditions. Aroylhydrazone Schiff bases form highly stable complexes with transition metals in various oxidation states, coordination numbers, and nuclearities, and can be tuned easily by changing different carbonyl derivatives [39][40][41][42][43][44][45][46].…”

C-Homoscorpionate Oxidation Catalysts—Electrochemical and Catalytic Activity

“…A systematic investigation of the coordination behavior of new C-scorpionates, as well as some of the known ones, toward a variety of transition metals (e.g., V [44,[46][47][48][49], Mo [17,19,50], Re [51,52], Fe [44,46,49,53], Ru [54], Co [12,13], Ni [44,49,55], Pd [44], Cu [43,45,46,56,57], Ag [14], Au [58] or Zn [44,56]) followed, leading to new classes of complexes exhibiting different types of coordination modes (Figures 4 and 5). Like the pincer of a scorpion, these versatile tripodal ligands bind metal centers with nitrogen atoms from two pyrazolyl rings attached to the central carbon atom; the third pyrazolyl attached to carbon rotates forward like a scorpion's tail to "sting" the metal; hence the name of "scorpionates" (Figure 4).…”