10.1021/acs.inorgchem.7b01868.s001
Luis M. Martínez-Prieto
Luis M.
Martínez-Prieto
Pilar Palma
Pilar
Palma
Eleuterio Álvarez
Eleuterio
Álvarez
Juan Cámpora
Juan
Cámpora
Nickel Pincer Complexes with Frequent Aliphatic Alkoxo
Ligands [(<sup>iPr</sup>PCP)Ni-OR] (R = Et, <i>n</i>Bu, <i>i</i>Pr, 2‑hydroxyethyl). An Assessment of the Hydrolytic
Stability of Nickel and Palladium Alkoxides
American Chemical Society
2017
parent alcohol ROH
ligand
i Pr
CH 2 CH 2 OH
equilibrium
acidic
hydroxide
series
PCP
Pd
Et
covalent Ni-OR bonds
Nickel Pincer Complexes
nickel pincer complexes
NMR
hydrolysis
constant
X-ray diffraction data
iPr
heteroatom-free R groups
2- methoxyethoxide complexes
Ni alkoxide complexes
n Bu
2017-10-06 15:49:26
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Nickel_Pincer_Complexes_with_Frequent_Aliphatic_Alkoxo_Ligands_sup_iPr_sup_PCP_Ni-OR_R_Et_i_n_i_Bu_i_i_i_Pr_2_hydroxyethyl_An_Assessment_of_the_Hydrolytic_Stability_of_Nickel_and_Palladium_Alkoxides/5478622
A series of nickel
pincer complexes with terminal alkoxo ligands [(<sup>iPr</sup>PCP)Ni-OR]
(R = Et, <i>n</i>Bu, <i>i</i>Pr, CH<sub>2</sub>CH<sub>2</sub>OH; <sup>iPr</sup>PCP is the 2,6-bis(diisopropylphosphinomethyl)phenyl
pincer ligand) was synthesized and fully characterized. Together with
the previously reported methoxo analogues of Ni and Pd, these complexes
constitute a unique series of isostructural late transition-metal
alkoxides. Spectroscopic and X-ray diffraction data provide direct
indications of the strong polarization of their covalent Ni-OR bonds.
One of the most salient features of this class of compounds is their
facile hydrolysis with traces of moisture, leading to equilibrium
mixtures with the corresponding hydroxides [(<sup>iPr</sup>PCP)M–OH]
(M = Ni or Pd) and alcohols, ROH. To compare the hydrolytic stability
of nickel and palladium alkoxides, we performed NMR titrations of
both hydroxides with several alcohols and determined the corresponding
equilibrium constants. In general, these constants are ca. 1 order
of magnitude smaller for M = Ni than Pd, indicating that Ni alkoxide
complexes are more readily hydrolyzed than their Pd counterparts.
For alkoxide complexes containing heteroatom-free R groups, the tendency
to hydrolyze decreases as the parent alcohol ROH becomes more acidic,
that is, R = Me > Et > <i>i</i>Pr. This intuitive
trend is broken for 2-methoxyethanol, the most acidic alcohol investigated.
The hydroxo/2-methoxyethanol exchange equilibrium constants are comparable
to those of ethanol (M = Ni) or methanol (M = Pd), showing that the
corresponding 2-methoxyethoxide complexes are more prone to hydrolysis
than anticipated. These experimental observations were rationalized
in the light of density functional theory calculations.