Stereoselective formation of a single-stranded helicate: Structure of a bis(palladium-allyl)quaterpyridine complex and its use in catalytic enantioselective allylic substitution

Abstract

Chiral C2-symmetric quaterpyridine L reacts with [Pd(eta3-C3H5)Cl]2 to form a chiral single-stranded helical binuclear palladium complex of formula [Pd2(eta3-C3H5)2(L)]2+; the complex can efficiently catalyze allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate with enantioselectivity up to 85%.

Synthesis and Helical Structure of Spiroborate‐Based Double‐Stranded Helicate with Oligophenol Strands Bearing Bipyridine Units

“…[7] Among them, the helicates have gained popularity due to their applications in many areas, such as synthetic receptors, [9] liquid crystalline materials, [10] catalysis, [11] and DNA recognition. [12] Most of them rely on the coordination of transition metal cations to pyridine-or phenanthroline-containing molecular strands, and their three-dimensional structures are determined by the coordination geometry requirements.…”

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A large number of synthetic double helices have been developed during the past few decades because of their significant aesthetic and biomimetic appeal, and several structural motifs for double helices are now available, [1][2][3][4][5][6][7][8] including the peptide analogues of DNA, [2] transition metal complexes, namely the helicates, [3,4] aromatic oligoamides, [5] amidiniumcarboxylate salt bridges, [6] and oligoresorcinols. [7] Among them, the helicates have gained popularity due to their applications in many areas, such as synthetic receptors, [9] liquid crystalline materials, [10] catalysis, [11] and DNA recognition. [12] Most of them rely on the coordination of transition metal cations to pyridine-or phenanthroline-containing molecular strands, and their three-dimensional structures are determined by the coordination geometry requirements.

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The simple production of nonsymmetric quaterpyridines through Kröhnke pyridine synthesis

“…Potts et al reported a high yield synthesis [15] that requires the cleavage of alkylthio-substituents before the final ligands can be obtained and precludes the preparation of asymmetrical analogues. Various coupling methodologies have also been developed: (i) the Ullmann reaction with copper powder at high temperature [9]; (ii) coupling of 6-halo-2,2’-bipyridines in the presence of nickel reagents [16–17], some of which are chiral [18–19]; and (iii) a Stille-based synthetic pathway [17,20], or a Suzuki–Miyaura cross-coupling reaction [21]. The use of triazine derivatives (which under particular conditions undergo an inverse Diels–Alder reaction) can also produce oligopyridines [22].…”

Triple Helicates with Golden Strands: Self‐Assembly of M2Au6 Complexes from Gold(I) Metallaligands and Iron(II), Cobalt(II) or Zinc(II) Cations

“…[11,16,17] However, when achiral ligands containing long or flexible spacers are used, formation of helicates or mesocates, or mixtures of both, is generally unpredictable. [15,18] Optically pure helicates present interesting applications as chiral molecular cages, [19] asymmetric catalysts, [20,21] and in medicinal chemistry. [16] They have been obtained by resolution of racemic mixtures, [16,22] or, more conveniently, by enantioselective self-assembly of enantiopure chiral ligands and metal cations.…”