Pd(II)‐NNN Pincer Complexes for Catalyzing Transfer Hydrogenation of Ketones

Abstract

Chiral and achiral Pd(II)-NNN pincer complexes (1-3) containing acetonitrile as an ancillary ligand were synthesized and characterized by spectroscopic (UV-visible, FT-IR, NMR and mass) techniques. Polarimetric experiments were employed to measure the specific rotation values of the chiral complexes {[α] D 27 = + 135°(2) and À 136°(3)}. The structures resolved through single crystal X-ray diffraction technique disclosed the distorted square planar geometry of the complexes. Transfer hydrogenation (TH) reactions of ketones were carried out in order to appraise the catalytic efficiency of the complexes. Remarkably, the TH results were promising for all the complexes, however, the chiral complexes (2 and 3) failed to induce chirality. Further probe led us to believe that the pincer complexes turned into Pd particles in situ and the later acted as an active catalyst. The scope of TH was extended to various substituted aromatic and heterocyclic ketones (Conversions = 75-99%).

Greener Synthesis of Pristane by Flow Dehydrative Hydrogenation of Allylic Alcohol Using a Packed-Bed Reactor Charged by Pd/C as a Single Catalyst

“…These results suggest that the reaction had an induction period and the addition of i-PrOH and initially formed secondary alcohol 7 contributed to generate H-Pd species prior to the reaction of molecular hydrogen with Pd. Since ketone 8 was formed after alcohol 7 was formed, the transfer hydrogenation from the secondary alcohol 7 to 8 [26][27][28] was more likely than olefin-isomerization of the allylic alcohol 5 [29][30][31][32]. It seems quite difficult to speculate the mechanism of Pd-catalysis; however, one possible mechanism is shown in Scheme 4.…”

Convenient hydrogenation of furfural to furfuryl alcohol in metal-catalyzed and organo-catalyzed environments

“…Similarly, the selected bond angle for C3 N(3)-Pd(1)-N(2) 161.5 (15) is similar to that of N(1)-Pd(1)-N(3), 160.68 (12) from the Pd(II)-NNN pincer complex. 63…”

“…al. 63 for the Pd(II)-NNN pincer complex reporting Pd(1)-N(1) 2.028(3), Pd(1)-N(2) 1.920(3), and Pd(1)-N(3) 2.035(3). Similarly, the selected bond angle for C3 N(3)-Pd(1)-N(2) 161.5 (15) is similar to that of N(1)-Pd(1)-N(3), 160.68 (12) from the Pd(II)-NNN pincer complex.…”