Parity-Controlled Self-Assembly of Supramolecular Helices in a Gold(I)–Copper(II) Coordination System with Penicillamine and Bis(diphenylphosphino)alkane

Abstract

A unique gold(I)copper(II) 1D polymeric system, [Cu{Au 2 (L Cn )(pen) 2 }] (L Cn = Ph 2 P(CH 2 ) n PPh 2 (n = 3, 4, and 5); H 2 pen: penicillamine), which involves three types of helices (single-stranded homochiral helix, single-stranded meso helix, and triple-stranded homochiral helix), is reported. This system was created from linear digold(I) metalloligands, which possess a bis (diphenylphosphino) The design and creation of helix structures have long been a subject of considerable attention in a wide range of research fields, not only because of their relevance to biologically important structures such as DNA and α-helices of proteins, 1 but also because of being an effective way of introducing chirality into molecules.2 Self-assembly of metal ions and bridging ligands through coordination bonds is the most common approach to produce infinite, uniform helices.3 To date, several 1D helix coordination polymers have been synthesized using this approach, and their unique functionalities such as luminescence, 4 magnetic, 5 and catalytic properties, 6 as well as their chemical sensing 7 and chiral recognition abilities, 8 have been reported. Most of these helix coordination polymers possess single-stranded structures with either left-handedness or right-handedness. On the other hand, other types of coordination polymers with more unique structures®such as multiplestranded helices, which contain two or more intertwined helical chains; 9 tubular helices, which have a large 1D channel inside the helix; 4c,9a,9e,10 and meso helices, which consist of alternate right-and left-handed helical loops 11,12 ®are highly limited in number. In addition, the controlled construction of different types of helix structures in a rational manner has rarely been achieved, although helix handedness has often been controlled by asymmetric center(s) contained in bridging ligands. 3,13Therefore, the finding of general factors that govern helix topologies is of great demand in this research field.As part of our continuing studies on the stepwise construction of metallosupramolecular architectures by using multifunctional metalloligands with chiral sulfur-containing amino acids such as cysteine (H 2 cys) and penicillamine (H 2 pen), 10a,1417 we recently designed and synthesized linear digold(I) metallo-¹ coordination arms that are linked by bis(diphenylphosphino)alkane (L Cn = Ph 2 P(CH 2 ) n PPh 2 ; n = 1 and 2) through AuP bonds. (Figure 1a) and closed-bridging (Figure 1b) coordination modes, respectively, to form discrete metallocyclic structures. 16,17 We expected that the employment of analogous metalloligands having a longer alkyl chain; n > 2) will lead to the creation of infinite polymeric structures by adopting the extended bridging mode (Figure 1c

The Coordination and Supramolecular Chemistry of Gold Metalloligands

“…Konno'sg roup has extensively investigated the coordination chemistry of the Au I -thiolato complexes H [79], H 2 [80], and H 2 [81], containing one or two d-penicillaminatol igands, toward transition-metal cations (Figure 23). [70] Owing to the presenceo ft he S, NH 2 ,a nd COO À binding sites, these metalloligandsa re very versatile and their coordination behavior is markedly influenced by the pH of the reaction medium.…”

“…[71] MetalloligandH 2 [80]i sp articularly suitable to act as a bridgeb etween two metal cations. Thus, two of thesem etalloligandsc oordinate to two Ag + ions through the Sa toms to give metallocycle 83 (Figure 24).…”

“…The reactiono f83 with CuCl 2 followed by crystallization gave rise to as alt containing the three coinage metal atoms, which is composed of large monocationic and monoanionic cages containing 20 and 21 metal atoms, respectively.T hese cages are arranged in as upramolecular ionic structure resembling that of the rock salt. [72] Te tranuclear complexes containing two square-planar centers have been isolated by reactiono fH 2 [80]w ith Ni II , [73] Pd II [74] or Pt II [74] salts (Figure 25). The cis,cis or trans,trans forms of these complexes (84 and 85)h ave been isolated as potassium salts.…”

“…Depending on the pH, these polymers adopt a3 Df ramework or a1 Dh elical structure. [75] Ni II complexes of the types 84, 86, 87,a nd 88 (Figures 25 and 26) have been isolated by reactiono fH 2 [80]w ith Ni(NO 3 ) 2 . Reversible interconversion between these complexes was observed as responset oc hanges in the H 2 [80]:Ni molar ratio, pH, solvent, or temperature of the solution.T he alterations in the Ni II coordination environment produced in these equilibria are accompanied by marked changes in the color and magnetism of the complexes.…”

“…[75] Ni II complexes of the types 84, 86, 87,a nd 88 (Figures 25 and 26) have been isolated by reactiono fH 2 [80]w ith Ni(NO 3 ) 2 . Reversible interconversion between these complexes was observed as responset oc hanges in the H 2 [80]:Ni molar ratio, pH, solvent, or temperature of the solution.T he alterations in the Ni II coordination environment produced in these equilibria are accompanied by marked changes in the color and magnetism of the complexes. [73] The reactiono fH 2 [80]w ith CoCl 2 ·6 H 2 Of ollowed by oxidation with O 2 gave am ixture of aC o III complex of the type 86 and the metallomacrocyclic complex 89 (Figure 26), which were separated by chromatography and characterized by single-crystal X-ray diffraction.…”