Binuclear Palladium Complexes Supported by Bridged Pincer Ligands


A series of binucleating ligands each containing two tridentate pincer sites based on a central, monoanionic aryl (C) donor flanked by neutral phosphinito (P) and imino (N) donors, [(PCN)-(CH<sub>2</sub>)<sub><i>n</i></sub>-(PCN)] (<b>1</b>), or a central, monoanionic amido (N) flanked by neutral phosphine (P) and imino donors (N), [(PNN)-(CH<sub>2</sub>)<sub><i>n</i></sub>-(PNN)] (<b>4</b>), are presented. The metalating sites were linked through the condensation of two equivalents of <i>m</i>-hydroxybenzaldehyde or the purposively built asymmetric diarylamine [(H)­N­(2-C­(O)­H-4-Me-C<sub>6</sub>H<sub>3</sub>)­(2-P­(<i>i</i>Pr)<sub>2</sub>-4-Me-C<sub>6</sub>H<sub>3</sub>)] (<b>3</b>) with primary α,ω-diamines (1,2-diaminoethane, <i>n</i> = 2; 1,4-diaminobutane, <i>n</i> = 4), which simultaneously constructed the imino arms and bridged the pincer cores. Ligands <b>1</b> and <b>4</b> were then used in the synthesis of neutral, square-planar palladium­(II) complexes <b>5</b> and <b>6</b>, [(PCN-C<sub><i>n</i></sub>)­Pd<sub>2</sub>X<sub>2</sub>, (PNN-C<sub><i>n</i></sub>)­Pd<sub>2</sub>X<sub>2</sub>; <i>n</i> = 2, 4; X = Cl, OAc, OTf]. The difference in the <i>trans</i> influence of the central donor was demonstrated through X-ray crystal structures of <b>5b-Cl</b>, (PCN-C<sub>4</sub>)­Pd<sub>2</sub>Cl<sub>2</sub>, and <b>6b-Cl</b>, (PNN-C<sub>4</sub>)­Pd<sub>2</sub>Cl<sub>2</sub>. The (PNN-C<sub><i>n</i></sub>)­Pd<sub>2</sub>X<sub>2</sub> complexes (<b>6</b>) proved to be redox-active, presumably via oxidation of the ligand, and cyclic voltammetry illustrated the extent to which electronic communication between the two pincer sites is mediated by the length of the bridge between them. (PCN-C<sub><i>n</i></sub>)­Pd<sub>2</sub>OTf<sub>2</sub> (<b>5-OTf</b>) and (PNN-C<sub><i>n</i></sub>)­Pd<sub>2</sub>OTf<sub>2</sub> (<b>6-OTf</b>) complexes reacted with hydride donors such as Et<sub>3</sub>SiH or β-hydride-containing alkoxides such as NaO<i>i</i>Pr to generate bridging-hydride monocations [(PCN)­Pd-H-Pd­(PCN)-C<sub><i>n</i></sub>]­[OTf] (<b>5-H</b>, <i>n</i> = 2, 4) and [(PNN)­Pd-H-Pd­(PNN)-C<sub>2</sub>]­[OTf] (<b>6a-H</b>), where the supported Pd–Pd separation was also found to be affected by the bridge length. In the case of the (CH<sub>2</sub>)<sub>4</sub>-bridged (PNN-C<sub>4</sub>)­PdOTf (<b>6b-OTf</b>), a bridging-hydride monocation was not observed. Instead, the formation of [(PN­(H)­N)­Pd-Pd­(PNN)-C<sub>4</sub>]­[OTf] (<b>6b-H</b>), protonated at the amido N of the ligand with a direct Pd­(I)–Pd­(I) bond, was recorded

Similar works

Full text

oai:figshare.com:article/2568778Last time updated on 2/12/2018

This paper was published in FigShare.

Having an issue?

Is data on this page outdated, violates copyrights or anything else? Report the problem now and we will take corresponding actions after reviewing your request.