Impact of Group 10 Metals on the Solvent‐Induced Disproportionation of o‐Semiquinonato Complexes

Abstract

The oxidationo f[ M II (3,5-DTBCat)(DTBbpy)]( M= Ni ([Ni]), Pd ([Pd]), and Pt ([Pt]); 3,5-DTBCat = 3,5-di-tert-butylcatecholato;D TBbpy = 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 ))a nd Pt ([Pt](PF 6 ))). The negative solvatochromic properties of the SQ complexes allowed us to estimate the relativeo rder of their dipole moments: [Pd](PF 6 ) > [Pt](PF 6 ) > {[Ni](PF 6 )} 2 .T he complexes [Pd](PF 6 ) and [Pt](PF 6 ) adopt monomeric structures and are stable in CH 2 Cl 2 and toluene, whereast hey gradually disproportionate at room temperature to [M] and 3,5-di-tert-butylbenzoquinone( 3,5-DTBBQ)i np olar solvents such as THF, MeOH,E tOH, DMF,o r DMSO. Ther esults of spectroscopics tudies suggestedt hat the oxidized nickel complex adopts am onomeric structure ([Ni](PF 6 ))i nC H 2 Cl 2 ,b ut ad imeric structure ({[Ni](PF 6 )} 2 )i n the other investigateds olvents. In polar solvents, {[Ni](PF 6 )} 2 may disproportionate to [Ni] and 3,5-DTBBQ at 323 K, thereby demonstrating as ignificant solvent-and metal-dependence in temperature. The relative activities of {[Ni](PF 6 )} 2 and [M](PF 6 ) toward disproportionation are relatedt ot he electrochemically estimated K dis values in CH 2 Cl 2 and DMF.T he present work demonstrates that solvent polarity and the dipolem oments of the SQ complexesp romote disproportionation, which can be controlled by aj udicious choiceo ft he metali on, solvent, and temperature.[a] S. Scheme1.Disproportionation of semiquinonato complexes. Scheme2.Synthetic scheme for [M]and {[M](PF 6 )} n .

Tuning PtII‐Based Donor–Acceptor Systems through Ligand Design: Effects on Frontier Orbitals, Redox Potentials, UV/Vis/NIR Absorptions, Electrochromism, and Photocatalysis

“…Such rearrangements have been proposed for rhodium complexes employing the same ligands by Perutz and co‐workers . Also, a possible dimerization cannot be ruled out, as discussed recently by Chang and co‐workers . Upon oxidation of compound 3 to 3 + , the electron density on the already electron‐poor bis(amidosulfonyl) ligand is further reduced, resulting in a weaker platinum–nitrogen bond.…”

“…[20,21] Also, ap ossible dimerizationc annot be ruled out, as discussed recently by Chang and co-workers. [29] Upon oxidation of compound 3 to 3 + ,t he electron density on the already electron-poor bis(amidosulfonyl) ligand is further reduced, resulting in aw eaker platinum-nitrogen bond. This possibly resultsi nalinkagei somerization at the platinum center with one of the oxygen atoms of the sulfonyl group coordinating to it instead of the nitrogen atom (Scheme 3).…”

Square-Planar Heteroleptic Complexes of α-Diimine-NiII-Catecholate Type: Intramolecular Ligand-to-Ligand Charge Transfer

“…The synergistic existence of donor and acceptor organic parts in the coordination sphere of the metal center is a distinctive feature for a wide range of LL'CT chromophores. The acceptor moiety is usually represented by a neutral redox form of α-diimines (Scheme 1) with significant steric hindrances [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] and/or a rigid carbon skeleton [13,15,[25][26][27]. Thus, it provides the required planarity of the complex's structure.…”

“…Despite such variability of the LL'CT process towards α-diimine-M II -catecholate compounds, there are sporadic works devoted to a targeted molecular design of LL'CT dyes with the primary goal to influence the position and/or intensity of the electronic absorption bands [10,15,[21][22][23][36][37][38], and solvatochromic properties [17,19,22,23,39]. On the other hand, the related square-planar Pd II derivatives are the research objects due to a cytotoxic activity [40][41][42][43].…”

Nanoarchitectonics for Coordination Asymmetry and Related Chemistry

“…Chang and co-workers investigated oxidation and solvent-induced disproportionation of semiquinonato complexes. 138 Ohba and co-workers analyzed conversion between ortho-isomer and para-isomerr of molecular hydrogen with nuclear-spin conversion catalysts of Prussian blue analogs. 139 Nanoscopic effect of the phase transition of Ti4O7 was investigated by Tokoro et al 140 Anomalous behaviors of phase transition between charge-delocalized phase and chargelocalized phase can be explained surface energy driven perturbations to free energy.…”