cis-Protected palladium(ii) based binuclear complexes as tectons in crystal engineering and the imperative role of the cis-protecting agent

The shape and molecular packing of cis-protected Pd(ii) based binuclear complexes depends upon the ligand and cis-protecting agents.

Structurally Diverse Diazafluorene-Ligated Palladium(II) Complexes and Their Implications for Aerobic Oxidation Reactions

4,5-Diazafluoren-9-one (DAF) has been identified as a highly effective ligand in a number of Pd-catalyzed oxidation reactions, but the mechanistic basis for its utility has not been elucidated. Here, we present the complex coordination chemistry of DAF and palladium(II) carboxylate salts. Multiple complexes among an equilibrating mixture of species have been characterized by (1)H and (15)N NMR spectroscopy and X-ray crystallography. These complexes include monomeric and dimeric Pd(II) species, with monodentate (κ(1)), bidentate (κ(2)), and bridging (μ:κ(1):κ(1)) DAF coordination modes. Titration studies of DAF and Pd(OAc)2 reveal the formation of two dimeric DAF/Pd(OAc)2 complexes at low [DAF] and four monomeric species at higher [DAF]. The dimeric complexes feature two bridging acetate ligands together with either a bridging or nonbridging (κ(1)) DAF ligand coordinated to each Pd(II) center. The monomeric structures consist of three isomeric Pd(κ(1)-DAF)2(OAc)2 complexes, together with Pd(κ(2)-DAF)(OAc)2 in which the DAF exhibits a traditional bidentate coordination mode. Replacing DAF with the structurally related, but more-electron-rich derivative 9,9-dimethyl-4,5-diazafluorene (Me2DAF) simplifies the equilibrium mixture to two complexes: a dimeric species in which the Me2DAF bridges the two Pd centers and a monomeric species with a traditional κ(2)-Me2DAF coordination mode. The use of DAF in combination with other carboxylate ligands (CF3CO2(-) or tBuCO2(-)) also results in a simplified collection of equilibrating Pd(II)-DAF complexes. Collectively, the results highlight the ability of DAF to equilibrate rapidly among multiple coordination modes, and provide valuable insights into the utility of DAF as a ligand in Pd-catalyzed oxidation reactions.

Molecular Architectures Derived from Metal Ions and the Flexible 3,3'-Bipyridine Ligand: Unexpected Dimer with Hg(II)

The flexible ditopic ligand 3,3'-bipyridine (3,3'-bpy) has been reacted with a series of transition metal species (Ag(+), Hg(2+), cis-a(2)M(2+) (a = NH(3) or a(2) = en; M = Pt, Pd), trans-a(2)Pt(2+) (a = NH(3))) in an attempt to produce discrete cyclic constructs. While Ag(+) gave a polymeric structure {[Ag(3,3'-bpy)](ClO(4)) . H(2)O}(n) (1), with all other metal entities cyclic structures were formed. Interestingly, Hg(CH(3)COO)(2) produced a dinuclear complex [Hg(3,3'-bpy)(CH(3)COO)(2)](2) . 3H(2)O (2), in which the two 3,3'-bpy ligands adopt a cis-orientation of the coordinating pyridyl entities. With cis-(NH(3))(2)Pt(2+), a cyclic complex 4 was isolated in crystalline form which, according to HRMS, is a trimer. With trans-(NH(3))(2)Pt(2+), different species are formed according to (1)H NMR spectroscopy, the nature of which was not established.