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Issue 9, 2013
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Exploring the limits of redox non-innocence: pseudo square planar [{κ4-Me2C(CH2N[double bond, length as m-dash]CHpy)2}Ni]n (n = 2+, 1+, 0, −1, −2) favor Ni(II)

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Abstract

Treatment of Ni(COD)2 with Me2C(CH2N[double bond, length as m-dash]CHpy)2 (dmp(PI)2) afforded pseudo-square planar, diamagnetic {dmp(PI)22−}NiII (Ni[0]), which contains radical anion pyridine-imine (PI) units bound to Ni(II). Ag+ oxidation of Ni[0] provided [{dmp(PI)2}Ni]+ (Ni[+]) whose assignment as Ni(I) or Ni(II) was made on the basis of ab initio calculations, and EPR spectroscopy. Upon crystallization, Ni[+] formed an asymmetric dimer, [{dmp(PI)2}2NiIINi0]2+ (Ni[2+]Ni[0]), consisting of pseudo-octahedral Ni(II) and pseudo-tetrahedral Ni(0). Ferrocenium oxidation (2 equiv.) of Ni[0] provided [{dmp(PI)2}(MeCN)2NiII]2+ (Ni[2+]), while KC8 reduction provided [{dmp(PI)23−}NiII](K(THF)2)+ (Ni[−]) in polymeric form (K+ counterion) or as ion-pairs (with K+(crypt-2.2.2)). Excess K0 or 2 equiv. Cs0 and Ni[0] provided highly sensitive [{dmp(PI)24−}NiII]2− (Ni[2−]), which disproportionates with C[double bond, length as m-dash]C bond formation and dehydrogenation to afford [{2-py,3-PI,4-Me2-azacyclopent-2-ene2−}2Ni]2− [K+(crypt-2.2.2)]2 (Ni[AcPP]) upon addition of crypt-2.2.2. All redox events may be construed as shuttling electrons in and out of the ligand scaffold. While radical character is implicated in the calculations of Ni[+], Ni[0], and Ni[−], the pseudo-square planar species are remarkably resilient to further reactivity, thereby highlighting the stability provided by this geometry.

Graphical abstract: Exploring the limits of redox non-innocence: pseudo square planar [{κ4-Me2C(CH2N [[double bond, length as m-dash]] CHpy)2}Ni]n (n = 2+, 1+, 0, −1, −2) favor Ni(ii)

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Publication details

The article was received on 18 Mar 2013, accepted on 25 Jun 2013 and first published on 26 Jun 2013


Article type: Edge Article
DOI: 10.1039/C3SC50743B
Citation: Chem. Sci., 2013,4, 3636-3648
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    Exploring the limits of redox non-innocence: pseudo square planar [{κ4-Me2C(CH2N[double bond, length as m-dash]CHpy)2}Ni]n (n = 2+, 1+, 0, −1, −2) favor Ni(II)

    V. A. Williams, E. B. Hulley, P. T. Wolczanski, K. M. Lancaster and E. B. Lobkovsky, Chem. Sci., 2013, 4, 3636
    DOI: 10.1039/C3SC50743B

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