Syntheses, Structures and Electronic Properties of Zwitterionic Iron(II) and Cobalt(II) Complexes Featuring Ambidentate Tris(pyrazolyl)methanide Ligands

Abstract

By deprotonation of the corresponding tris(pyrazolyl)methane ((Me)Tpm) precursor complexes [M((Me)Tpm)(2)][(OTf)(2)] (1 and 2), the zwitterionic tris(pyrazolyl)methanide iron(II) (3) and cobalt(II) (4) "sandwich" complexes of the general formula [M((Me)Tpmd)(2)] are easily accessible. The structurally characterised complexes 3 and 4 are the first such homoleptic 3d transition metal species to feature two "naked", outward pointing pyramidal carbanions. Density functional theory calculations show metal-centred HOMOs and LUMOs with the destabilised carbanion orbitals in the energy region of the filled transition-metal-centred frontier orbitals. The electronic structures of these complexes have been investigated in detail by various spectroscopic techniques such as NMR, EPR, SQUID, Mössbauer, etc. Both complexes adopt a high-spin (HS) configuration at room temperature in solution and in the solid state. A thermally induced high-spin to low-spin (HS-LS) transition is observed for the iron(II) complex 3. The HS-LS transition temperature of 3 in solution differs from that in the solid state, which in turn strongly depends on the amount of solvent molecules in the crystal lattice. Electrochemical studies on the corresponding cobalt(II) complex 4 provide evidence for a HS-Co(II) <==> LS-Co(III) transition upon oxidation, which was confirmed by preliminary synthetic oxidation reactions. Overall, it can be concluded that the related kappa(3)N-donor ligands tris(pyrazolyl)hydroborates (Tp(R)) and (R)Tpmd ligands have similar bonding properties and that the metal cations experience more or less the same ligand environment.

Heteroscorpionate Rare‐Earth Metal Zwitterionic Complexes: Syntheses, Characterization, and Heteroselective Catalysis on the Ring‐Opening Polymerization of rac‐Lactide

“…Transition-metalbased zwitterionic complexes have been explored widely that exhibited novel structures, electronic, magnetic, and nonlinear optical properties or unique catalysis. [12] To date, the only rare-earth-metal-based zwitterion was mentioned in a previous work as a formula [Sc{C(3,5-Me 2 Pz) 3 }Cl 2 A C H T U N G T R E N N U N G (thf)] without characterization. [25] Thus complexes 5 a-c represented the first well-defined rare-earth metal zwitterions.…”

“…Under the same conditions, only traces of PLAs were isolated unless the polymerization time was prolonged to more than 20 h. The resulting PLAs had narrower molecular-weight distribution (M w /M n = 1.3) but lower heterotacticity (P r = 0.7) than those obtained from 5 a and 5 b systems (runs [11][12][13][14]. This could be explained by the much stronger coordination of methoxy group to the metal center in 6 a and 6 b than that of the solvated thf molecule in 5 a and 5 b.…”

“…The carbanion species can coordinate to the central metal with apical carbanion in k 1 mode or through the heteroatoms of the pyrazole and X group in k 3 mode to form zwitterionic metal complexes that have been reported to possess special properties and unique catalysis. [12] Unfortunately, C À H actiAbstract: Novel neutral phosphinemodified heteroscorpionate ligand (3,5-Me 2 Pz) 2 CHPPh 2 (1) and its derivatives oxophosphine (2) and iminophosphine (3) heteroscorpionates were synthesized for the first time. These neutral heteroscorpionate ligands displayed unique chemistry towards rare-earth metal trisA C 2 ] afforded heteroscorpionate rare-earth metal trialkyl adduct complexes 4 a-c.…”

Trigonal antiprismatic Co(ii) single molecule magnets with large uniaxial anisotropies: importance of Raman and tunneling mechanisms

“…1b), a ligand that has been used in spin crossover compounds. 57–65 Herein, we report two mononuclear SMMs, viz. , [Co II (Tpm) 2 ][ClO 4 ] 2 ( 1 ) and [Co II (Tpm) 2 ][BPh 4 ] 2 ·2MeCN ( 2 ), which have the same magnetic unit, [Co II (Tpm) 2 ] 2+ , but different chemical surroundings.…”

Synthesis, characterization, and MMA polymerization activity of tetrahedral Co (II) complex bearing N, N-bis(1-pyrazolyl)methyl ligand based on aniline moiety

“…To confirm the catalytic inertness for olefin oligomerization, dimerization of 1-octene in toluene was also attempted at 30°C and 80°C with no noticeable result. As the tetrahedral benzo[b]thiophen-2-yl-substituted (imino) pyridine-Co(II) complexes [57] were reported to have catalytic activity for oligomerization of ethylene to linear α-olefins, it would not be appropriate to attribute the lack of catalytic activity of precursor complexes 1a-4a to their structural properties. Additionally, no catalytic activity for olefin polymerization was demonstrated indirectly, by the failure of bis-hydrocarbyl substituted Co derivative synthesis.…”