Stabilization and Activation: New Alkyl Complexes of Zinc, Magnesium and Cationic Aluminium Featuring Chelating Bisguanidine Ligands

Inter- and Intramolecular Electron Transfer in Copper Complexes: Electronic Entatic State with Redox-Active Guanidine Ligands

Fast and efficient electron transfer in blue copper proteins is realized by a structural harmonization between the Cu^I and Cu^II complex pair ("entatic state" model). Herein, we present now a Cu^I /Cu^II complex pair with redox-active guanidine ligands showing almost perfect match between both redox states. By modifying the ligand electron donor strength, the redox chemistry of the copper complex can be controlled to be either metal-centered or to cross the borderline to ligand-centered. This work is the first systematic study of complexes with redox-active ligands within the concept of the entatic state.

1,8-Bis(silylamido)naphthalene complexes of magnesium and zinc synthesised through alkane elimination reactions

The reactions between magnesium or zinc alkyls and 1,8-bis(triorganosilyl)diaminonaphthalenes afford the 1,8-bis(triorganosilyl)diamidonaphthalene complexes with elimination of alkanes. The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and one or two equivalents of MgⁿBu₂ affords two complexes with differing coordination environments for the magnesium; the reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and MgⁿBu₂ in a 1 : 1 ratio affords 1,8-C₁₀H₆(NSiMePh₂)₂{Mg(THF)₂} (1), which features a single magnesium centre bridging both ligand nitrogen donors, whilst treatment of 1,8-C₁₀H₆(NSiR₃H)₂ (R₃ = MePh₂, ⁱPr₃) with two equivalents of MgⁿBu₂ affords the bimetallic complexes 1,8-C₁₀H₆(NSiR₃)₂{ⁿBuMg(THF)}₂ (R₃ = MePh₂2, R₃ = ⁱPr₃3), which feature four-membered Mg₂N₂ rings. Similarly, 1,8-C₁₀H₆(NSiⁱPr₃)₂{MeMg(THF)}₂ (4) and 1,8-C₁₀H₆(NSiMePh₂)₂{ZnMe}₂ (5) are formed through reactions with the proligands and two equivalents of MMe₂ (M = Mg, Zn). The reaction between 1,8-C₁₀H₆(NSiMePh₂H)₂ and two equivalents of MeMgX affords the bimetallic complexes 1,8-C₁₀H₆(NSiMePh₂)₂(XMgOEt₂)₂ (X = Br 6; X = I 7). Very small amounts of [1,8-C₁₀H₆(NSiMePh₂)₂{IMg(OEt₂)}]₂ (8), formed through the coupling of two diamidonaphthalene ligands at the 4-position with concomitant dearomatisation of one of the naphthyl arene rings, were also isolated from a solution of 7.

Synthesis and structures of mononuclear and dinuclear gallium complexes with α-diimine ligands: reduction of the metal or ligand?

Reduction of the dichloro gallium(III) α-diimine complex [(L(ipr))˙(-)GaCl2] (1, L(ipr) = [(2,6-iPr2C6H3)NC(Me)]2) by different equivalents of sodium metal afforded the gallium complexes [(L(ipr))(2-)Ga(III)(μ2-Cl)2Na(THF)4] (2) and [(Na(THF)6)(+)·((L(ipr))(2-)Ga-Ga(L(ipr))(2-))˙(-)] (3). Interestingly, in complex 2 a Na(+)Cl(-) ion pair is incorporated, while compound 3 is an anionic digallium complex. Moreover, a cationic gallium complex with a tetrachlorogallium(III) counter anion, [(LGaCl2)(+)·(GaCl4)(-)] (4), was accessed from the reaction of GaCl3 with 0.5 equiv. of ligand L(ipr). In contrast, the reaction of GaCl3 with the doubly reduced anion (Na2L(2-)) of the smaller α-diimine ligands L(Me) ([(2,6-Me2C6H3)NC(Me)]2) or L(Et) ([(2,6-Et2C6H3)NC(Me)]2) yielded the Ga-Ga-bonded complexes [(L(Et))˙(-)ClGa(II)-Ga(II)Cl(L(Et))˙(-)] (5) and [(L(Me))˙(-)ClGa(II)-Ga(II)Cl(L(Me))˙(-)] (6). Here L is the neutral α-diimine ligand, L˙(-) represents the monoanion, and L(2-) is the dianionic form of the ligand. The complexes were characterized by X-ray diffraction and their electronic structures were studied by DFT computations.

Synthesis, structure and reactivity study of magnesium amidinato complexes derived from carbodiimides and N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-butadiene ligands

We report an amidinato ligand-supported series of magnesium complexes obtained from the insertion of a magnesium-carbon bond into a carbon-nitrogen double bond of different carbodiimides and α-diimine ligands. The magnesium complexes [Mg(CH2Ph){CyN[double bond, length as m-dash]C(CH2Ph)NCy}]2 (), [Mg(CH2Ph){(i)PrN[double bond, length as m-dash]C(CH2Ph)N(i)Pr}]2 () and the homoleptic [Mg{(t)BuN[double bond, length as m-dash]C(CH2Ph)N(t)Bu}2] () (Cy = cyclohexyl, (i)Pr = isopropyl, (t)Bu = tert-butyl) were prepared by the reaction of dibenzyl magnesium [Mg(CH2Ph)2(Et2O)2] with the respective carbodiimides either in 1 : 1 or 1 : 2 molar ratio in toluene. The analogous reaction of [Mg(CH2Ph)2(Et2O)2] with the N,N'-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (Dipp2DAD) ligand afforded the corresponding homoleptic magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}2] () (Dipp = 2,6 diisopropylphenyl) in good yield. The solid-state structures of magnesium complexes were confirmed by single-crystal X-ray diffraction analysis. It was observed that in each case, a magnesium-carbon bond was inserted into the carbon-nitrogen double bond of either carbodiimides or Dipp2DAD resulting in a monoanionic amido-imino ligand. In a further reaction between and N-aryliminopyrrolyl ligand 2-(2,6-(i)Pr2C6H3N[double bond, length as m-dash]CH)C4H3NH (ImpDipp-H) in 1 : 2 molar ratio, a new magnesium complex [Mg(ImpDipp)2{CyN[double bond, length as m-dash]C(CH2Ph)NHCy}] (), with one amidinato and two aryliminopyrrolyl ligands in the coordination sphere, was obtained in good yield. In contrast, the homoleptic magnesium complex reacted with one equivalent of N-aryliminopyrrolyl ligand (ImpDipp-H) to produce another mixed ligated magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}(ImpDipp)] (), with a benzylated DAD ligand and aryliminopyrrolyl ligands in the coordination sphere. Further reaction of complex with benzyl alcohol (PhCH2OH) afforded the third mixed ligated magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}(OCH2Ph)2] () in very good yield. The magnesium complexes were characterised using standard analytical/spectroscopic techniques and their solid-state structures were established by single-crystal X-ray diffraction analysis.

Stabilization of Complexes of Redox-Active Guanidino-Functionalized Aromatic Compounds (GFAs) by Hydrogen-Bonding

The guanidino-functionalized 1,2,4,5-tetrakis(N,N′-diisopropylguanidino)benzene could act as a redox-active switch, and reversibly forms hydrogen-bond aggregates upon two-electron oxidation. Herein the influence of hydrogen bonding on the structure and electronic properties of the first transition metal complexes of the neutral and oxidized compound are studied. Reaction with CuCl2 leads by coupled redox- and coordination processes to a dinuclear CuII complex of the dicationic guanidine, in which CuCl2– counterions are locked through strong hydrogen-bonds in positions above and below the C6 ring plane. The electronic situation in the electronic ground and excited states of this complex were analysed by quantum chemical calculations.