Self-Assembly in Palladium(II) and Platinum(II) Chemistry: The Biomimetic Approach

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Abstract
The self-assembly of complex cationic structures by combination of cis-blocked square planar palladium(II) or platinum(II) units with bis(pyridyl) ligands having bridging amide units has been investigated. The reactions have yielded dimers, molecular triangles, and polymers depending primarily on the geometry of the bis(pyridyl) ligand. In many cases, the molecular units are further organized in the solid state through hydrogen bonding between amide units or between amide units and anions. The molecular triangle [Pt3(bu2bipy)3(μ-1)3]6+, M = Pd or Pt, bu2bipy = 4,4‘-di-tert-butyl-2,2‘-bipyridine, and 1 = N-(4-pyridinyl)isonicotinamide, stacks to give dimers by intertriangle NH··OC hydrogen bonding. The binuclear ring complexes [{Pd(LL)(μ-2)}2](CF3SO3)4, LL = dppm = Ph2PCH2PPh2 or dppp = Ph2P(CH2)3PPh2 and 2 = NC5H4-3-CH2NHCOCONHCH2-3-C5H4N, form transannular hydrogen bonds between the bridging ligands. The complexes [{Pd(LL)(μ-3)}2](CF3SO3)4, LL = dppm or dppp, L = PPh3, and 3 = N,N‘-bis(pyridin-3-yl)-pyridine-2,6-dicarboxamide, and [{Pd(LL)(μ-4)}2](CF3SO3)4, LL = dppm, dppp, or bu2bipy, L = PPh3, and 4 = N,N‘-bis(pyridin-4-yl)-pyridine-2,6-dicarboxamide, are suggested to exist as U-shaped or square dimers, respectively. The ligands N,N‘-bis(pyridin-3-yl)isophthalamide, 5, or N,N‘-bis(pyridin-4-yl)isophthalamide, 6, give the complexes [{Pd(LL)(μ-5)}2](CF3SO3)4 or [{Pd(LL)(μ-6)}2](CF3SO3)4, but when LL = dppm or dppp, the zigzag polymers [{Pd(LL)(μ-6)}x](CF3SO3)2x are formed. When LL = dppp, a structure determination shows formation of a laminated sheet structure by hydrogen bonding between amide NH groups and triflate anions of the type NH··OSO··HN.

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