# Synthesis and Reactivity of Dipalladated Derivatives of Terephthalaldehyde

## TL;DR

This paper reports the synthesis and reactivity of new dipalladated terephthalaldehyde complexes, including the first examples of CO insertion into two aryl–metal bonds.

## Contribution

The first fully characterized dipalladated terephthalaldehyde complexes and CO insertion into two aryl–metal bonds are presented.

## Key findings

- Dipalladated terephthalaldehyde complexes 2a and 2b were synthesized and fully characterized.
- CO insertion into both aryl–Pd bonds of 2a and 2b produced complexes 3a and 3b, the first of their kind.
- Depalladation of complex 4 yielded a new organic compound 5, confirmed by X-ray crystallography.

## Abstract

The polynuclear complex [{μ-C1,C4,N,N″-C6H2{C(H)=N(nBu)}2-2,5}{Pd(μ-OAc)}]2 (I) reacts with tbbpy (4,4′-di-tert-butyl-2,2′-bipyridine) and TlOTf to form the
dinuclear complex [{μ-C1,C4,N,N″-C6H2{C(H)=N(nBu)}2-2,5}{Pd(tbbpy)}2] (1). The hydrolysis of I with
acetic acid in a 5:1 acetone/water mixture, in the presence of two
equivalents of tbbpy and excess NaX (X = Br, I), yields the dipalladated
terephthalaldehyde complexes [C6H2{PdX(tbbpy)}2-1,4-(CHO)2-2,5] [X = Br (2a), X =
I (2b)], which are the first fully characterized complexes
of this type. The reaction of 2a,b with CO results in
the insertion of CO into both aryl–Pd bonds, forming [C6H2{C(O){PdX(tbbpy)}}2-1,4-(CHO)2-2,5] [X = Br (3a), X = I (3b)],
which are the first examples of complexes with CO inserted into two
separate aryl–metal bonds involving the same ligand. The bromo
complex 2a reacts with excess XylNC in acetone, causing
the precipitation of the dinuclear complex 2,3,6,7-tetrahydrobenzo[1,2-c:4,5-c′]dipyrrole-1,5-dione-2,6-dixylyl-3,7-bis{=C(NHXyl)-C(=NXyl)-[PdBr(CNXyl)2]} (4), which is the result of the insertion
of three molecules of the isocyanide into each aryl–Pd bond
and the nucleophilic attack of one of them at each formyl group. When
complex 4 reacts with TlOTf and residual water in 1,2-dichloroethane
at 70 °C, depalladation occurs, and the organic compound 2,3,6,7-tetrahydrobenzo[1,2-c:4,5-c′]dipyrrole-1,5-dione-2,6-dixylyl-3,7-bis{=C(NHXyl)–C(O)NHXyl}
(5) can be isolated. The crystal structures of 1·4CHCl3, 4·2CH2Cl2·3hexane, and 5·2CDCl3 have been determined by X-ray crystallography.