A Heterobimetallic Superoxide Complex formed through O₂ Activation between Chromium(II) and a Lithium Cation

Abstract

The reaction of 1,1,3,3-tetraphenyl-1,3-disiloxandiol (LH2) with n-butyllithium and CrCl2 results in a mononuclear chromium(II) complex (1) that further reacts with O2 at low temperatures to yield a mononuclear chromium(III) superoxide complex [L2CrO2(THF)][Li2(THF)3] (2). The crystal structure revealed that the chromium superoxido entity is stabilized by the coordination to an adjacent lithium cation. Complex 2 thus contains an unprecedented heterobimetallic [Cr(III)(μ-O2)Li(+)] core; beyond this it is the first chromium superoxide for which a temperature-dependent magnetic characterization could be achieved, and the first structurally characterized representative with chromium in an exclusive O-donor environment.

The Influence of Alkali Metal Ions on the Stability and Reactivity of Chromium(III) Superoxide Moieties Spanned by Siloxide Ligands

“…For 1,H R-ESI-MS, crystal structure, IR, UV/Vis data (THF) and elemental analysis are in accordance with ref. [9].F or 3,c rystal structure and UV/Vis data are in accordance with ref. [11]…”

“…In 2 , one Li + ion is displaced out of the CrO 4 plane, so that an electrostatic interaction between the distal O atom of the superoxide ligand and the Lewis acidic Li + occurs (Scheme ). Evidently, the interaction leads to a stabilization of the chromium(III) superoxide unit and has therefore allowed us to stop the reaction of 1 with O 2 directly after the primary O 2 activation step . Although complex 2 is intrinsically quite unstable in THF, it only reacts slowly with organic substrates such as 2,6‐di‐ tert ‐butyl‐4‐methoxyphenol.…”

“…[8] We have recently investigated the mononuclearc omplex [L 2 Cr]Li 2 (THF) 4 (1)( Scheme 1) formed through the reaction of the disilanol 1,1,3,3-tetraphenylsilan-1,3-diol (LH 2 )w ith nBuLi and CrCl 2 .C omplex 1 was found to reactr eadily with dioxygen forming the chromium(III) superoxide complex [L 2 Cr]Li 2 O 2 (THF) 5 (2), which was crystallized at low temperatures. [9] In 2,o ne Li + ion is displaced out of the CrO 4 plane, so that an electrostatic interaction between the distal Oa tom of the superoxide ligand and the Lewis acidic Li + occurs (Scheme 1). Evidently, the interaction leads to as tabilization of the chromium(III) superoxideu nit and has therefore allowed us to stop the reaction of 1 with O 2 directlya fter the primary O 2 activations tep.…”

“…Molecular structure of 7.For clarity hydrogen atoms are omitted. Selectedbondlengths []a nd angles [8]: Cr1ÀO3 1.9550(13), Cr1ÀO6 1.9680(13), Cr1ÀO4 1.9711(13), Cr1ÀO1 1.9858(13), Cr1ÀCl1 2.3655(6),C r1À Li1 2.605(3), Cr1ÀLi2 2.850(3), Na1ÀCl1 2.564(4);O3-Cr1-Cl1 95.02(4),O6-Cr1-Cl1 87.84(4),O4-Cr1-Cl1 95.41(4), O1-Cr1-Cl1 86.10(4), O6-Cr1-Li1 47.30(9), O1-Cr1-Li1 47.80(9), Cl1-Cr1-Li161.89(8), O3-Cr1-Li2 42.08(8), Cl1-Cr1-Li2 93.76(7),Li1-Cr1-Li2 155.61(10),Cr1-Cl1-Li1 63.64(8).…”

Heptanuclear Cage CuII‐Silsesquioxanes: Synthesis, Structure and Catalytic Activity

“…Cage metallasilsesquioxanes were found to be active in alkene polymerization, epoxidation or epoxide ring opening, metathesis, hydroformylation, Ullmann–Goldberg condensation and amidation . Recently, significant attention was drawn to the potential of CLMS application in the homogeneous oxidation of C–H compounds with activity confirmed for Fe‐,, Cr‐, Ni‐, and Co‐based compounds. In turn, the best potential for this type of catalytic activity was found for Cu II ‐based cage silsesquioxanes.…”