Cyclic Tetranuclear and Hexanuclear Palladium(II) Complexes and Their Host−guest Chemistry

Abstract

Cyclic tetrameric complexes have been prepared by the reaction of Pd(en)Cl 2 or Pd(dapol)Cl 2 , or their nitrato analogs, with Na 2 (5′GMP) in aqueous solution, where en = 1,2-diaminoethane, dapol = 1,3-diamino-2-propanol, 5′-GMP = guanosine 5′-monophosphate. Addition of certain small molecules containing hydrophobic groups resulted in the expansion of the tetramer to a cyclic hexamer with strong bonding of one guest per hexameric host. At pH 5-6, the guest molecule can be a cation, anion, or neutral, and those species containing trimetylsilyl and t-butyl groups bonded the most strongly. The size of the central cavity of the [Pd(en)(5′GMP)] 6 host has been estimated to be 5.2 Ǻ. Formation of the host-guest complex caused a large upfield shift (Δδ) of 2.5-2.9 ppm in the 1 H NMR spectrum of the most highly affected guest protons, which were those in closest proximity to the guanine nucleobases. NOESY spectra were used to determine the interaction sites between the host and the guest. Apparent association constants determined at 26 °C and pD 5.4 for the [Pd(en)(5′GMP)] 6 -DSS and [Pd(en)(5′GMP)] 6 -t-butanol systems, where DSS is 3-(trimethylsilyl)-1-propanesulfonate anion, were 1.36 ± 0.11 × 10 4 and 2.74 ± 0.95 × 10 4 M −3/2 , respectively. The Pd(dapol)-5′GMP system forms hexameric host-guest complexes, similar in nature to those of the Pd(en)-5′-GMP system. The molecular and crystal structures of Pd(dapol)Cl 2 are also reported.

Interactions of 1,5-naphthyridine with Pd(en)Cl2 or [Pd(en)(H2O)2](NO3)2 in aqueous solution

“…A similar multiplet has been observed previously in cyclic [Pd(en)(µ- N 1, N 7-5′-GMP)] n (n = 4 or 6) and was the result of rigidity in the en moiety due to the steric crowding around the Pd(II). 30 Since the 1:1 Pd(en)- 1,5-NAP complex is clearly monomeric, the reason for any steric crowding is unknown at this time. However, it is apparent that NO 3 − involvement must be important because it was not present when Pd(en)Cl 2 was used.…”

Synthesis, characterization and cytotoxicity studies of palladium(II)–proflavine complexes

“…Since the N(10) position is protonated in water at neutral pH, it must be deprotonated for the Pd(II) complex to bond at this site, while bonding to the NH 2 groups does not require deprotonation. It is known that Pd(II) is capable of lowering the pK a of a proton by at least several pK units [33]. The data on DMSO solutions of [Pd(proflavineH)Cl 2 ](SO 4 ) 0.5 ·H 2 O showed that in this coordinating solvent the stability of the N(10)-bonded Pd structure, II , was slightly more stable than that of the NH 2 -bonded Pd structure.…”

Palladium(II)‐Based Self‐Assembled Heteroleptic Coordination Architectures: A Growing Family

“…Relative to L21,t he steric disadvantage is minimisedi np yridylethynyl-based ligand L23,a nd hence, it is am uch better donort han that of cyanophenyl derivatives L22 a/b.T hus, the mixture of cis-[Pd(dppp)](OTf) 2 with ligands L22 b and L23 did not necessarily require the formation of ah eteroleptic complex in as pontaneous manner.I nstead,s elf-recognition occurred, leadingt oakinetic mixtureo fh omoleptic complexes [Pd 4 (dppp) 4 (L23) 2 ](OTf) 8 (27)a nd [Pd 4 (dppp) 4 (L22 b) 2 ](OTf) 8 (28). However,u pon heating am ixture of 27 and 28,achange could be observed.…”

“…However,t here are many homoleptic hexanuclear complexes of [(PdL') 6 (L) n ]c omposition. [24][25][26][27][28] Althoughc omplexes of [(PdL') 6 (L) 4 ]a re widely known, [24] other complexes,s uch as [(PdL') 6 (L)]-typet ubes, [25] [(PdL') 6 (L) 2 ]-type discs, [26] [(PdL') 6 (L) 3 ]-type tubes [27] and [(PdL') 6 (L) 6 ]-type hexagons, [28] are also known.H owever,h eteroligated hexanuclear assemblies with similar designs to those mentioned above are 6 (L a )(L b )] 2 -type [2]catenanes [29] and [(PdL') 6 (L a ) 2 (L b ) 4 ]-type [3]catenanes. [30] The complexation of cis-[Pd(en)(NO 3 ) 2 ]w ith am ixture of tripodal tridentate ligand L24 andf lat tridentate ligand L25 in a3 :1:1 stoichiometry under aqueous conditions resulted in catenane [Pd 3 (en) 3 (L26)(L27)] 2 (NO 3 ) 12 (30;F igure 12).…”

“…However, there are many homoleptic hexanuclear complexes of [(PdL′) 6 (L) n ] composition . Although complexes of [(PdL′) 6 (L) 4 ] are widely known, other complexes, such as [(PdL′) 6 (L)]‐type tubes, [(PdL′) 6 (L) 2 ]‐type discs, [(PdL′) 6 (L) 3 ]‐type tubes and [(PdL′) 6 (L) 6 ]‐type hexagons, are also known. However, heteroligated hexanuclear assemblies with similar designs to those mentioned above are not known.…”