Enantiomerically Pure Bis-β-diketones: Valuable Building Blocks for Metallosupramolecular Chemistry

Abstract

A series of enantiomerically pure bis-b-diketone derivatives was prepared by a Claisen-type condensation between protected tartaric acid diesters and several ketones. Hereby the tartaric acid unit is introduced as either a 2,2-dimethyldioxolane or as a 5,6-dimethoxy-5,6-dimethyl-1,4-dioxane derivative. The yields of the Claisen reaction are relatively low, but the starting materials are readily available, so that the one-step procedure leads to the bis-b-diketone derivatives in up to gram quantities.b-Diketonates are a class of compounds that represents one of the most powerful chelating units for the coordination of metal ions. The obtained complexes are applied in different fields, due to their special magnetic, electrochemical, or photophysical properties. Chiral derivatives are used as NMR shift reagents but are also efficient catalysts for stereoselective reactions. Thus the interest in bdiketonates and their derivatives starts with synthetic chemistry, structural coordination chemistry, and finally enters the field of materials science. 1 Working in the field of supramolecular chemistry and being specially interested in the stereochemistry of selfassembly processes, we were searching for an entry to prepare chiral linear bis-b-diketonate ligands in order to obtain enantiomerically pure helicates or other supramolecular structures, like trinuclear coordination compounds and clusters. 2,3 The obtained oligonuclear complexes with transition or f-block metals could be promising candidates for chiral catalysis or novel luminescent materials.Herein we describe a simple synthetic approach towards a series of bis-b-diketonates applying a Claisen-type condensation reaction as a key step of the synthesis. Hereby we use ester-substituted heterocycles as bis-electrophilic chiral building blocks, which are derived from protected tartaric acid derivatives. Scope and Limitations1,3-Dicarbonyl compounds can be prepared by the reaction of an enolate with carboxylic acid derivatives like esters or acid chlorides. In order to prepare the chiral dioxolanes 3a-g or the dioxanes 4c,d, we performed the reaction of the methyl ketones 1a-g with the tartaric acid derivatives 2a and 2b (see Scheme 1, Figure 1), which are easily prepared according to literature procedures. 4,5 Reaction of acetone (1a) with diester 2a gave 3a as an oily product. In order to prepare different bis-b-diketones, the substituent R at the starting methyl ketones 1 was systematically varied. Thus, the reaction of the acetophenone derivatives 1b-f with 2a proceeded similarly. However, now the corresponding b-diketones could be recrystallized from ethanol and the crystalline materials were characterized by elemental analysis as well as standard spectroscopic methods (see Table 1).In order to extend the p-system in the periphery of the bisb-diketones, we introduced the 4-tolanyl methyl ketone (1g) which was prepared in 69% from phenylacetylene and 4-bromoacetophenone in a Sonogashira coupling reaction. 6 In the following reaction step, the tolanyl-substituted b...

Diastereoselective formation of luminescent dinuclear lanthanide(iii) helicates with enantiomerically pure tartaric acid derived bis(β-diketonate) ligands

“…This diester is reacted with acetone, acetophenone, or p-bromoacetophenone in the presence of sodium amide as base. 14 The solid phase structure of 3-H 2 is shown in Fig. 2.…”

“…Under those conditions, the free ligand 3-H 2 leads to a positive Cotton effect at 300 nm and a negative one at 340 nm. 14 In the corresponding lanthanide(III) complexes, the ligand centered transitions are shifted to 325 (À) and 350 nm (+) with reversed Cotton effects. This indicates a different conformation of the free ligand compared to the ligand in the complex.…”

Symmetry Driven Self-Assembly of Metallo-Supramolecular Architectures

“…68 Ligand 8b is incommensurate for the assembly of triplestranded helicates. Due to a different dihedral angle of the chelating units at the bridging ring system (approx.…”

Exciton Coupling Analysis and Enolization Monitoring by Vibrational Circular Dichroism Spectra of Camphor Diketones

“…Chelating β-diketones and related ligands are popular functional building blocks extensively investigated in coordination chemistry for decades. − Their complexes can be used in different areas based on their particular magnetic, electrochemical, or photophysical properties. For chiral species, they can be applied as NMR shift reagents and excellent catalysts for enantioselective reactions.…”