3 research outputs found
Difference in the Reactivities of H- and Me-Substituted Dinucleating Bis(iminopyridine) Ligands with Nickel(0)
No full textThe reactivity of dinucleating bis(iminopyridine) ligands
bearing
H (L<sup>1</sup>, (<i>N</i>,<i>N</i>′)-1,1′-(1,4-phenylene)bis(<i>N</i>-(pyridin-2-ylmethylene)methanamine)) or Me substituents
(L<sup>2</sup>, (<i>N</i>,<i>N</i>′)-1,1′-(1,4-phenylene)bis(<i>N</i>-(1-(pyridin-2-yl)ethylidene)methanamine)) on the imine
carbon atom with Ni(COD)<sub>2</sub> (COD = 1,5-cyclooctadiene) has
been investigated. Treatment of L<sup>1</sup> with 2 equiv of Ni(COD)<sub>2</sub> forms dinuclear Ni<sub>2</sub>(L<sup>1</sup>)(COD)<sub>2</sub>, whereas the reaction of L<sup>2</sup> with 2 equiv of Ni(COD)<sub>2</sub> leads to Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub>, along
with 1 equiv of Ni(COD)<sub>2</sub>. The compounds were characterized
by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy, mass spectrometry,
and elemental analysis; the structure of Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub> was determined by XRD. Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub> exists as syn and anti stereoisomers in the solid state
and in solution. DFT calculations suggest Ni(I) for both Ni<sub>2</sub>(L<sup>1</sup>)(COD)<sub>2</sub> and Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub>, with the radical anion localized on one iminopyridine
fragment in Ni<sub>2</sub>(L<sup>1</sup>)(COD)<sub>2</sub> and delocalized
over two iminopyridine fragments in Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub>. Both Ni<sub>2</sub>(L<sup>1</sup>)(COD)<sub>2</sub> and
Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub> undergo a reaction with
excess diphenylacetylene, forming diphenylacetylene complexes. However,
whereas Ni<sub>2</sub>(L<sup>1</sup>)(diphenylacetylene)<sub>2</sub> decomposes upon removal of the excess diphenylacetylene, Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub> demonstrates a reversible disassembly/reassembly
sequence upon the addition/removal of diphenylacetylene
Difference in the Reactivities of H- and Me-Substituted Dinucleating Bis(iminopyridine) Ligands with Nickel(0)
No full textThe reactivity of dinucleating bis(iminopyridine) ligands
bearing
H (L<sup>1</sup>, (<i>N</i>,<i>N</i>′)-1,1′-(1,4-phenylene)bis(<i>N</i>-(pyridin-2-ylmethylene)methanamine)) or Me substituents
(L<sup>2</sup>, (<i>N</i>,<i>N</i>′)-1,1′-(1,4-phenylene)bis(<i>N</i>-(1-(pyridin-2-yl)ethylidene)methanamine)) on the imine
carbon atom with Ni(COD)<sub>2</sub> (COD = 1,5-cyclooctadiene) has
been investigated. Treatment of L<sup>1</sup> with 2 equiv of Ni(COD)<sub>2</sub> forms dinuclear Ni<sub>2</sub>(L<sup>1</sup>)(COD)<sub>2</sub>, whereas the reaction of L<sup>2</sup> with 2 equiv of Ni(COD)<sub>2</sub> leads to Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub>, along
with 1 equiv of Ni(COD)<sub>2</sub>. The compounds were characterized
by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy, mass spectrometry,
and elemental analysis; the structure of Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub> was determined by XRD. Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub> exists as syn and anti stereoisomers in the solid state
and in solution. DFT calculations suggest Ni(I) for both Ni<sub>2</sub>(L<sup>1</sup>)(COD)<sub>2</sub> and Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub>, with the radical anion localized on one iminopyridine
fragment in Ni<sub>2</sub>(L<sup>1</sup>)(COD)<sub>2</sub> and delocalized
over two iminopyridine fragments in Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub>. Both Ni<sub>2</sub>(L<sup>1</sup>)(COD)<sub>2</sub> and
Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub> undergo a reaction with
excess diphenylacetylene, forming diphenylacetylene complexes. However,
whereas Ni<sub>2</sub>(L<sup>1</sup>)(diphenylacetylene)<sub>2</sub> decomposes upon removal of the excess diphenylacetylene, Ni<sub>2</sub>(L<sup>2</sup>)<sub>2</sub> demonstrates a reversible disassembly/reassembly
sequence upon the addition/removal of diphenylacetylene
Steric and Electronic Effects in the Formation and Carbon Disulfide Reactivity of Dinuclear Nickel Complexes Supported by Bis(iminopyridine) Ligands
No full textWe
are developing bimetallic platforms for the cooperative activation
of heteroallenes. Toward this goal, we designed a new family of bis(iminopyridine)
((<i>N</i>,<i>N</i>′-1,1′-(1,4-phenylene)bis(<i>N</i>-(pyridin-2-ylmethylene)methanamine) and <i>N</i>,<i>N</i>′-1,1′-(1,4-phenylene)bis(<i>N</i>-(1-(pyridin-2-yl)ethylidene)methanamine)) dinickel complexes,
synthesized their CS<sub>2</sub> compounds, and studied their reactivity.
Bis(iminopyridine) ligands L react with Ni(COD)<sub>2</sub> to form
Ni<sub>2</sub>(L)<sub>2</sub> complexes or Ni<sub>2</sub>(L)(COD)<sub>2</sub> complexes as a function of the steric and electronic properties
of the ligand precursor. Product structures disclosed an <i>anti</i> geometry in the Ni<sub>2</sub>(L)(COD)<sub>2</sub> species and helical
(<i>anti</i>) structures for Ni<sub>2</sub>(L)<sub>2</sub> complexes. Carbon disulfide adducts Ni<sub>2</sub>(L)(CS<sub>2</sub>)<sub>2</sub> were obtained in good yields upon addition of CS<sub>2</sub> to Ni<sub>2</sub>(L)(COD)<sub>2</sub> or in a one-pot reaction
of L with 2 equiv of both Ni(COD)<sub>2</sub> and CS<sub>2</sub>.
Ni<sub>2</sub>(L)(CS<sub>2</sub>)<sub>2</sub> complexes are highly
flexible, displaying both <i>syn</i> and <i>anti</i> conformations (shortest S- - -S separations of 5.0
and 9.5 Å, respectively) in the solid state. DFT calculations
demonstrate virtually no energy difference between the two conformations.
Electrochemical studies of the Ni<sub>2</sub>(L)(CS<sub>2</sub>)<sub>2</sub> complexes displayed two ligand-based reductions and a broad
CS<sub>2</sub>-based oxidation. Chemical oxidation with [FeCp<sub>2</sub>]<sup>+</sup> liberated free CS<sub>2</sub>. The addition
of NHC (NHC = 1,3-di-<i>tert</i>-butylimidazolin-2-ylidene)
to Ni<sub>2</sub>(L)(CS<sub>2</sub>)<sub>2</sub> yielded Ni<sub>2</sub>(NHC)<sub>2</sub>(CS<sub>2</sub>)<sub>2</sub>, in which both carbon
disulfide ligands are bridging two Ni centers
