Synthesis and Applications of (ONO Pincer)Ruthenium‐Complex‐Bound Norvalines

Abstract

Two (ONO pincer)ruthenium‐complex‐bound norvalines, Boc−[Ru(pydc)(terpy)]Nva−OMe (1; Boc=tert‐butyloxycarbonyl, terpy=terpyridyl, Nva=norvaline) and Boc−[Ru(pydc)(tBu‐terpy)]Nva−OMe (5), were successfully synthesized and their molecular structures and absolute configurations were unequivocally determined by single‐crystal X‐ray diffraction. The robustness of the pincer Ru complexes and norvaline scaffolds against acidic/basic, oxidizing, and high‐temperature conditions enabled us to perform selective transformations of the N‐Boc and C−OMe termini into various functional groups, such as alkyl amide, alkyl urea, and polyether groups, without the loss of the Ru center or enantiomeric purity. The resulting dialkylated Ru‐bound norvaline, n‐C11H23CO−l‐[Ru(pydc)(terpy)]Nva−NH‐n‐C11H23 (l‐4) was found to have excellent self‐assembly properties in organic solvents, thereby affording the corresponding supramolecular gels. Ru‐bound norvaline l‐1 exhibited a higher catalytic activity for the oxidation of alcohols by H2O2 than parent complex [Ru(pydc)(terpy)] (11 a).

ONO-pincer ruthenium complex-bound norvaline for efficient catalytic oxidation of methoxybenzenes with hydrogen peroxide

“…43 In the 2-catalyzed reaction, the color of the aqueous phase of the reaction mixture turned pale red, indicating the formation of high oxidation state ionic Ru species derived from ligand dissociation followed by over oxidation as described in our previous paper. 25 These results indicate that the amino acid moiety of 1 influences positively to suppress the undesired deactivation of the catalyst by an excess amount of H 2 O 2 .…”

“…1 The ruthenium complex-bound norvaline 1 and its single crystal structure. 25 Table 1 The ruthenium complex-bound norvaline 1-catalyzed oxidation of 1,3-dimethoxybenzene under various conditions observed under the condition of one-portion addition of H 2 O 2 , where the reaction almost stopped after 3 h, affording 3a in 29% yield. 43 In the 2-catalyzed reaction, the color of the aqueous phase of the reaction mixture turned pale red, indicating the formation of high oxidation state ionic Ru species derived from ligand dissociation followed by over oxidation as described in our previous paper.…”

“…We have recently succeeded in synthesizing an ONO-pincer ruthenium complex 24 -bound norvaline, Boc-L-[Ru]Nva-OMe 1 25 (Fig. 1, [Ru] = Ru( pydc)(terpy) 26 2, developed by Nishiyama 27 ).…”

“…28 We demonstrated that metalated amino acid 1 catalyzed the oxidation of alcohols with H 2 O 2 , and the catalytic activity of 1 was much higher than that of the parent ruthenium complex 2. 25 By further focusing on the catalytic activity of 1, we have found that it shows excellent catalytic activity toward the oxidation of methoxybenzenes to p-benzoquinones with a wide substrate scope and unique chemoselectivity (eqn ( 1)). This type of reaction is well-known as an important class of enzymatic metabolism of phenol derivatives.…”

Synthesis of an oligomer ruthenium complex and its catalysis in the oxidation of alcohols

“…[55][56][57][58] Compared with that of the ligand, the spectrum of oligomer-Ru(terpy)(pydic) exhibits additional bands at 622 cm À1 and 468 cm À1 respectively, attributed to the Ru-O and Ru-N vibration. 59,60 Besides, all the characteristic peaks in the IR spectrum of Ru(terpy)(pydic) based complexes 61 can be found in that of oligomer-Ru(terpy)(pydic). To further conrm the formation of oligomer-Ru(terpy)(pydic), the Raman spectra of oligomer-Ru(terpy)(pydic) and its model complex Ru(terpy)(pydic) were taken and compared.…”