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Impact of Group 10 Metals on the Solvent‐Induced Disproportionation of o ‐Semiquinonato Complexes
Author(s) -
Yamada Shota,
Matsumoto Takeshi,
Chang HoChol
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201900172
Subject(s) - disproportionation , chemistry , group (periodic table) , solvent , medicinal chemistry , organic chemistry , catalysis
The oxidation of [M II (3,5‐DTBCat)(DTBbpy)] (M=Ni ( [Ni] ), Pd ( [Pd] ), and Pt ( [Pt] ); 3,5‐DTBCat=3,5‐di‐ tert ‐butylcatecholato; DTBbpy=4,4′‐di‐ tert ‐butyl‐2,2′‐bipyridine) afforded the dimeric {[Ni II (3,5‐DTBSQ)(DTBbpy)](PF 6 )} 2 ( {[Ni](PF 6 )} 2 ; 3,5‐DTBSQ=3,5‐di‐ tert ‐butylsemiquinonato) and monomeric semiquinonato (SQ) complexes [M II (3,5‐DTBSQ)(DTBbpy)](PF 6 ) (M=Pd ( [Pd](PF 6 ) ) and Pt ( [Pt](PF 6 ) )). The negative solvatochromic properties of the SQ complexes allowed us to estimate the relative order of their dipole moments: [Pd](PF 6 ) > [Pt](PF 6 ) > {[Ni](PF 6 )} 2 . The complexes [Pd](PF 6 ) and [Pt](PF 6 ) adopt monomeric structures and are stable in CH 2 Cl 2 and toluene, whereas they gradually disproportionate at room temperature to [M] and 3,5‐di‐ tert ‐butylbenzoquinone (3,5‐DTBBQ) in polar solvents such as THF, MeOH, EtOH, DMF, or DMSO. The results of spectroscopic studies suggested that the oxidized nickel complex adopts a monomeric structure ( [Ni](PF 6 ) ) in CH 2 Cl 2 , but a dimeric structure ( {[Ni](PF 6 )} 2 ) in the other investigated solvents. In polar solvents, {[Ni](PF 6 )} 2 may disproportionate to [Ni] and 3,5‐DTBBQ at 323 K, thereby demonstrating a significant solvent‐ and metal‐dependence in temperature. The relative activities of {[Ni](PF 6 )} 2 and [M](PF 6 ) toward disproportionation are related to the electrochemically estimated K dis values in CH 2 Cl 2 and DMF. The present work demonstrates that solvent polarity and the dipole moments of the SQ complexes promote disproportionation, which can be controlled by a judicious choice of the metal ion, solvent, and temperature.