Self-assembly of 2,4,6-tripyridyl-1,3,5-triazine (tpt) subunits with arene ruthenium building blocks and oxalato bridges affords cationic triangular metallo-prisms of the type [Ru 6 (arene) 6 (tpt) 2 (C 2 O 4 ) 3 ] 6+ (arene = C 6 Me 6 and p-Pr i C 6 -H 4 Me); the unexpected double helical chirality of the metalloprisms observed in the solid state persists in solution giving rise to two different stereodynamic processes as demonstrated by NMR enantiodifferentiation experiments.The self-assembly of transition metal complexes to give discrete supramolecular architectures has been studied by several groups and is the subject of some extensive reviews. 1 Both, two-and threedimensional architectures are known, in which the metal centres or the branched ligands or a combination of both control the shape of the resulting assemblies. The simplest three-dimensional construction which involves the fewest components is the triangular prism: only five building blocks are necessary to obtain a triangular prism; two trigonal subunits, and three linear connecting units. 2 However, metal-based triangular prisms including more components 3 are known as well. If no stereogenic elements are introduced within the components of the prism and the two planar triangular subunits perfectly eclipsed, the triangular prism possesses a D 3h symmetry, and is therefore achiral. However, a slight deviation from the eclipsed conformation reduces the achiral point group D 3h to the chiral D 3 symmetry group and therefore generates ''double-rosette'' type helicity with P or M configuration. 4 Moreover, concerted rotation of some aromatic rings of the tritopic subunits creates three-bladed propeller chirality with D (clockwise) or L (counterclockwise) configuration. Whereas either or both of these stereogenic elements can easily be detected in the solid state, so far, it has been hardly observed in solution, 5 the complexes being too configurationally labile or the system being achiral in solution.Herein we report the synthesis and characterisation of two cationic triangular metallo-prisms incorporating arene ruthenium building blocks, bridged by oxalato ligands, and connected by two 2,4,6-tripyridyl-1,3,5-triazine (tpt) subunits (Scheme 1). (1) and [Ru 6 (C 6 Me 6 ) 6 (tpt) 2 (C 2 O 4 ) 3 ] 6+ (2), which turned out to be quite soluble in (CH 3 ) 2 CO, CH 3 CN and MeOH, and only sparingly soluble in CH 2 Cl 2 and CHCl 3 .The molecular structures of 1 and 2 have been solved by singlecrystal X-ray analysis of the triflate salts, for the IR and NMR data see supporting information.{ From a structural point of view, the two tpt subunits are expected to be around 5.5 Å apart, based on the Ru-Ru separation observed in 3 (mean 5.503(6) Å ). 8 Indeed, the single-crystal X-ray structure analyses of 1 and 2 reveal an average Ru-Ru separation of 5.49 Å . Surprisingly, the two central triazine units in 2 are very close. The centroid … centroid distance between the two triazine moieties is only 3.42 Å as compared to 3.83 Å in 1, where the tpt ligands adopt an...

An enantioselective synthesis of a putative lipiarmycin aglycon was accomplished and features: 1) Brown's enantioselective alkoxyallylboration and allylation of aldehydes, 2) chain elongation by iterative Horner-Wadsworth-Emmons olefination, 3) Evans' aldol reaction and 4) an ene-diene ring-closing metathesis. A neighboring-group-assisted chemoselective reductive desilylation was uncovered in this study and was instrumental to the realization of the present synthesis.

Pd(II) allyl and Pd(0) olefin complexes containing the configurationally labile ligand 1,2-bis-[4,5-dihydro-3H-dibenzo[c-e]azepino]ethane were studied as models for intermediates in Pd-catalyzed allylic alkylations. According to NMR and DFT studies, the ligand prefers C(s) conformation in both eta3-1,3-diphenylpropenyl and eta3-cyclohexenyl Pd(II) complexes, whereas in Pd(0) olefin complexes it adopts different conformations in complexes derived from the two types of allyl systems in both solution and, as verified by X-ray crystallography, in the solid state. These results demonstrate that the Pd complex is capable of adapting its structure to the reacting substrate. The different structural preferences also provide an explanation for the behavior of 1,3-diphenyl-2-propenyl acetate and 2-cyclohexenyl acetate in Pd-catalyzed allylic alkylations using pseudo-C2 and pseudo-C(s) symmetric ligands.

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