Dinuclear palladium(ii) complexes with bridging amidate ligands

Abstract

New homonuclear dimeric Pd(ii) complexes have been synthesized by the reaction of Pd(en)(2+) or Pd(bipy)(2+) (where en = ethylenediamine and bipy = 2,2'-bipyridine) units with acetamide or by the Pd(ii) mediated hydrolysis of CH(3)CN. In these dimers the two metal centers are bridged by either two amidates or by the combination of one hydroxo group and one amidate ligand. The crystal structures of complexes {[Pd(bipy)](2)(micro-1,3-CH(3)CONH)(2)}(NO(3))(2).H(2)O.1/2(CH(3))(2)CO.1/2CH(3)CN () and {[Pd(bipy)](2)(micro-1,3-CH(3)CONH)(2)}(OTf)(2) () showed intrametallic Pd-Pd distances of 2.8480(8) A () and 2.8384(7) A (), respectively, in accordance with the accepted values for a strong Pd-Pd interaction. The presence of pi[dot dot dot]pi interactions between the bipyridine ligands on the di-micro-amidate complexes of Pd(bipy)(2+) shortens the distance between the two Pd centers and allows the formation of the metal-metal interaction. By contrast, the crystal structure of complex {[Pd(en)](2)(micro-1,3-CH(3)CONH)(2)}(OTf)(2).H(2)O (), (where OTf = triflate) where there is no pi[dot dot dot]pi interaction between the ligands on the metal centers, is also reported, and no Pd-Pd interaction is observed. Additionally, one of the complexes, {[Pd(en)](2)(micro-OH)(micro-CH(3)CONH)}(NO(3))(2) (), presents an interesting hydrogen bonded 3-D network formed by nitrate ions and water molecules. All complexes have been characterized by infrared and (1)H NMR spectroscopy.

1H NMR spectroscopic identification of binding modes of 2,2′-bipyridine ligands in complexes of square-planar d8 metal ions

“…16 In DMSO-d 6 solution, the two H5 sets in 12 are still superimposed, yet can be clearly differentiated. The chemical shift of the H5 resonances in D 2 O at ca.…”

“Directed” Assembly of Metallacalix[n]arenes with Pyrimidine Nucleobase Ligands of Low Symmetry: Interchanging Metals in Mixed‐Metal Metallacalix[4]arenes and Incorporating Additional Metals at the Exocyclic Groups

“…These Pd-Pd distances are virtually identical to those found in the corresponding Pd 8 complex. [7] Of the known dinuclear Pd II complexes, with [19] or without bpy ligands, [20] these Pd-Pd distances are amongst the shortest. In particular, they are also significantly shorter than, for example, those in the closely related head-to-tail dimer…”

Nickel, palladium and platinum

“…76 The two metal centres in [{Pd(2,2 0 -bipy)} 2 (m-1,3-CH 3 CONH) 2 }](NO 3 ) 2 are bridged by two amidates showing a remarkably short intrametallic Pd-Pd distance of 2.84 A ˚. 77 Rare examples of tetrapalladated derivatives in which two flat tetradentate bridging ligands are perfectly face-to-face as a result of a remarkable ancillary ligand effect are reported in the complex [{Pd 2 (m-OAc) 2 } 2 (m-L 26 )] [H 2 L 26 = 2,5-diamino-1,4-benzoquinonediimine]. 78 The unique combination of the labile square-planar geometry of Pd(II) continues to make it attractive to the area of supramolecular chemistry, leading to its inclusion in rotaxanes, 79 catenanes, 80 dynamic combinatorial libraries of metallacalix[n]arenes, 81 self-assembled rectangular metallomacrocycles, 82 and triangles and squares.…”