Synthesis, Structure, and Reactivity of Dinuclear Nickel Amino-Thiophenolate Complexes Bearing Bridging VO2(OH)2– and VO2(OR)2– Coligands
journal contributionposted on 2012-05-07, 00:00 authored by Vasile Lozan, Jochen Lach, Berthold Kersting
A series of novel mixed ligand dinickel complexes of the type [NiII2L(μ-L′)]+, where L′ is a tetrahedral oxo-alkoxo vanadate (L′ = [O2VV(OR)2]−, R = H or alkyl) and L a macrocyclic N6S2 supporting ligand, have been prepared, and their esterification reactivity has been studied. The orthovanadate complex [Ni2L(μ-O2V(OH)2)]+ (2), prepared by reaction between [Ni2L(μ-Cl)]ClO4 with Na3VO4 and a phase transfer reagent in CH3CN, reacts smoothly with MeOH and EtOH forming the vanadate diesters [Ni2L(μ-O2V(OMe)2)]+ (3) and [Ni2L(μ-O2V(OEt)2)]+ (4). The dialkyl orthovanadate esters in 3 and 4 are readily transesterified with mono- and difunctional alcohols. Complex 3 can also be generated from 4 by transesterification with MeOH. Complexes 3 and 4 react with diols (ethylene glycol, propylene glycol and diethylene glycol) as well to afford the complexes [Ni2L(μ-O2V(OH)(OCH2CH2OH))]+ (5), [Ni2L(μ-O2V(OCH2)2CH2)]+ (6), and [Ni2L(μ-O2V(OCH2CH2)2O)] (7). The crystal structures of the tetraphenylborate salts of complexes 3–7 reveal in each case four-coordinate O2VV(OR)2– groups bonded in a μ1,3-bridging mode to generate trinuclear complexes with a central N3Ni(μ-S)2(μ1,3-O2V(OR)2)NiN3 core. The stabilization of the four-coordinate VVO2(OR)2– moieties is a consequence of both the two-point coordinative fixation to and the steric protection of the bowl-shape binding pocket of the [Ni2L]2+ fragment. Cyclic voltammetry experiments reveal that the encapsulated vanadate esters are not reduced in a potential window of −2.0 to +2.5 V vs SCE. The spins of the nickel(II) (Si = 1 ions) in 3 are weakly ferromagnetically coupled (J = +23 cm–1, (H = −2JS1S2)) to produce an S = 2 ground state.
macrocyclic N 6Sdialkyl orthovanadate estersJSComplexes 3Ni 2L fragmentVVOvanadate diestersligand dinickel complexes2 ground statedifunctional alcoholstetraphenylborate salts1 ionsphase transfer reagentNa 3VOSCEComplex 31Sencapsulated vanadate estersO 2VV Resterification reactivityCyclic voltammetry experimentsNiII 2Ldiethylene glycolpropylene glycolN 3Ni corecrystal structuresethylene glycolCH 3CNNi 2Lsteric protectiontrinuclear complexes