Chiral Rodlike Platinum Complexes, Double Helical Chains, and Potential Asymmetric Hydrogenation Ligand Based on “Linear” Building Blocks:  1,8,9,16-Tetrahydroxytetraphenylene and 1,8,9,16-Tetrakis(diphenylphosphino)tetraphenylene

Abstract

This paper is concerned with the synthesis of 1,8,9,16-tetrahydroxytetraphenylene (3a) via copper(II)-mediated oxidative coupling, its resolution to optical antipodes, and its conversion to 1,8,9,16-tetrakis(diphenylphosphino)tetraphenylene (3b). On the basis of these chiral "linear" building blocks, three rodlike chiral complexes, triblock (R,R,R,R)-17 and (S,S,S,S)-20 and pentablock (R,R,R,R,R,R,R,R)-22, were constructed. As a hydrogen bond donor, racemic and optically active 3a was allowed to assemble with linear acceptors to afford highly ordered structures. A 1:1 adduct of 4,4'-bipyridyl and (+/-)-3a exists in a dimeric form of 3a linked by 4,4'-bipyridyl through hydrogen bonds. Pyrazine serves as a short linker between achiral parallel chains each formed by (+/-)-3a, while self-assembly of homochiral 3a into alternate parallel chains occurs in the adduct of 5,5'-dipyrimidine with (+/-)-3a. Self-assembly of (S,S)-3a or (R,R)-3a with 4,4'-dipyridyl yielded a packing of chiral double helical chains formed by chiral tetrol 3a molecules. A novel chiral ligand, (S,S)-23, derived from 3a was used in the asymmetric catalytic hydrogenation of alpha-acetamidocinnamate, yielding up to 99.0% ee and 100% conversion.

Synthesis of tetraphenylene derivatives and their recent advances

“…Thus, conversion of racemic tetrahydroxytetraphenylene 58 into its tetra-(S)-camphorsulfonate esters after esterification with (S)-camphorsulfonyl chloride resulted in two diastereomers (132a and 132b). Chromatographic separation and subsequent deprotection afforded enantiopure 1,8,9,16-tetrahydroxyltetraphenylene (58) [79,80]. The presence of hydroxyl groups in the tetraphenylene skeleton has provided openings for further chemistry through late functional group transformations.…”

Chiral tetrathienylene: synthesis and X-ray structure

“…Because of the out-of-plane twisting between the adjacent thiophene rings, these linkages correspond to the chiral axes; both α, α-linkages adopt identical axial chirality but opposite to that of the β, β-linkages, analogously to the linkages in tetraphenylenes (18)(19)(20)(21).…”

Asymmetric Synthesis of Chiral Tetraphenylenes

“…Meanwhile the biaryl moieties in tetraphenylenes provide intriguing possibilities for the design of novel ligands for asymmetric synthesis. Examples of tetraphenylenes include the chiral rod 4, [9] planarized tetraphenylene 5 (a fragment of a two-dimensional graphene-like carbon sheet and building block for helical stacks of carbotetranions), [10] the conjugated double helix 6 (a fragment of a Rileys "threedimensional graphite"), [11,12] and ligand 7 which is used for enantioselective hydrogenation (Figure 3). [9] However, applications of tetraphenylenes are rather limited, primarily because of the difficulty in obtaining the chiral tetraphenylene core, especially by asymmetric synthesis or by resolution.…”

“…Tanaka and co-workers employed analogous cationic-Rh I -catalyzed intermolecular double [2+2+2] cycloadditions in the asymmetric synthesis of [9]helicene-like molecules, such as 11 with moderate enantioselectivities (Scheme 3).…”

“…[23] For example, the reaction of [CpCo(CO) 2 ] with the nonayne precursor results in the formation of nine rings to produce [9]heliphene 13. Of those nine rings, six are cyclobutadienes, and therefore the estimated ring strain introduced in the triple [2+2+2] cycloaddition step is about 300 kcal mol À1 .…”