A Facile Synthesis of Thioalkyl- and Di(thioalkyl)-Substituted Bipyridines

Abstract

A convenient three-step synthesis has been developed to prepare a series of homologous 4,4¢-di(w-thioalkyl)-2,2¢-bipyridines from 4,4¢-dimethylbipyridine. The smallest member of the series, 4,4¢-di(thiomethyl)-2,2¢-bipyridine, has been synthesized by a slightly different route from 4,4¢-bis(trimethylsilylmethyl)-2,2¢-bipyridine; the monothiomethyl analogue has been obtained from the corresponding mono(trimethylsilylmethyl)bipyridine. Additionally, the chlororheniumtricarbonyl complex of each of the new thiol-substituted ligands has been prepared.There is widespread interest in modifying the surfaces of electrodes and nanoscale materials with metal complexes for use as potential components in catalyst systems, 1 molecular devices, 2 sensors, 2,3 and solar energy conversion. 4 One substance, gold, has been widely employed as the basis for these structures because of the facility with which it can be functionalized by alkanethiols. 5 However, considering the prevalence of modified gold surfaces and the ubiquitous use of bipyridines as ligands for metal atoms and ions, there are surprisingly few reports of thiol-substituted bipyridines, 6 which can be employed to anchor a number of common metal complexes on gold surfaces. Therefore, we now report the preparation of dithiol-and thiol-substituted 2,2¢-bipyridines 4a-d and 11, respectively, as well as their chlororheniumtricarbonyl complexes. The symmetrical disubstituted bipyridines are particularly useful in metal complexes incorporating two or more of these ligands, because the possibility of obtaining multiple stereoisomers is avoided.The disubstituted ligands with three, four, or five methylene units were readily prepared through straightforward reactions that can be accomplished easily on a large scale (Scheme 1). The dialkylation of 4,4¢-dimethyl-2,2¢-bipyridine (1) was achieved by deprotonating both methyl groups with 2.2 equivalents of lithium diisopropylamide, 7 followed by treatment of the dianion with the appropriate 1-bromo-w-chloroalkane to give the di-w-chloroalkylbipyridines 2a-c 8 in yields ranging from 67% to 87%. A Finkelstein reaction (NaI in acetone) converted the chlorine moieties in these compounds into iodines, which were subsequently transformed into thiols 4a-c by nucleophilic substitution reactions with tetrabutylammonium trimethylsilylthiolate generated in situ from tetrabutylammonium fluoride (TBAF) and hexamethyldisilathiane. 9 The halide exchange proceeded in good yields and, although the final reaction gave yields ranging from 21% to 64%, we could nevertheless obtain reasonable amounts of the final dithiols.For the smallest member of the dithiol series, 4,4¢-dithiomethyl-2,2¢-bipyridine (4d), we originally planned to use a similar strategy involving the substitution of each bromine leaving group by a sulfur nucleophile. Unfortunately, the radical bromination 10 of the methyl groups in 1 by N-bromosuccinimide (NBS) in carbon tetrachloride failed to yield the desired product, which is in line with some reports that this reaction works poorl...

Organometallic Iridium(III) Complex Sensitized Ternary Hybrid Photocatalyst for CO2 to CO Conversion

“…The cationic IrPS ( IrP + PF 6 − ) series, [(bpy) 2 Ru(4,4′‐Y 2 ‐bpy)] (Y=CH 2 PO(OH) 2 ; RuP), fac ‐[Re(4,4′‐Y 2 ‐bpy)(CO) 3 Cl] (Y=CH 2 PO(OH) 2 ; ReP, CO 2 reduction catalyst), and BIH (sacrificial ED) were prepared by modifying synthetic protocols described previously, details of which are described below (see Scheme and the Experimental Section).…”