Samarium-Promoted Coupling of 1,10-Phenanthroline with Carbonyl Compounds for Synthesis of New Ligands

Abstract

1,10-Phenanthroline reacts with aldehydes and ketones in the presence of samarium diiodide to produce 2-(1-hydroxyalkyl)-1,10-phenanthrolines. The hydroxyalkyl substituent can be functionalized in numerous ways or removed to permit further ligand variation. The carbonyl coupling reaction can also be repeated to provide 2,9-disubstituted phenanthrolines. Taken together, these operations provide ready access to a large number of phenanthroline derivatives to serve as ligand libraries for catalyst exploration.

Atom economical coupling of benzophenone and N-heterocyclic aromatics with SmI2

“…Additionally, the seminal work by Helquist and co-workers focalized on the coupling of various ketones and several N-aromatic heterocycles, notably phenanthroline and bipyridine, using a simple divalent halide, SmI 2 . 18,19 In this article, we propose insights in the mechanism of such a reaction that we were able to extend to neat pyridine with benzophenone, yielding the corresponding bisphenylpyridyl alcohol (Scheme 2). Divalent samarium halides are well-known single electron transfer reagents in organic chemistry.…”

“…The crystallization at cold of both solutions (-40 °C) produced pale yellow X-ray suitable crystals of 2 (bipyridine) and 3 (phenanthroline, Figure 2, Table 1), in which the benzophenone has been reduced to an alcoholate and is linked to the bipyridine and phenanthroline in the a-position to the nitrogen (Scheme 2, Figure 2), similar to what Helquist reported. 18,19 In 2, one residual neutral bipyridine coordinates while in 3 three solvent molecules are coordinated to the samarium ion, which is then octa-coordinated by two iodide atoms and the novel tridentate ligand. The Sm-I distances are 3.288(1) and 3.23(5) Å in 2 and 3, respectively, in good agreement with the presence of a trivalent samarium.…”

“…The reactivity clearly resembles the preparation of carbinols from pyridine and ketones but without the use of mercuric chloride 17 or any coupling additives other than SmI 2 , a much cleaner and atom economical pathway, as reported by Helquist. 18,19 However, the useful reaction was not reported with neat pyridine and although this reactivity does not happen at room temperature with neat pyridine, a solution of II was heated at 110 °C for 16 h and turned yellow. The yellow solution was crystallized and X-ray suitable colourless crystals of 4 were obtained ( Figure 2, Table 1).…”

Development of a Q2MM Force Field for the Silver(I)‐Catalyzed Hydroamination of Alkynes

“…[13,14] Previous studies showed that phenanthroline can be a useful scaffold for chiral substituted derivatives that can easily be synthesized through the SmI 2 -promoted coupling of phenanthroline with chiral ketones, aldehydes and epoxides. [15] Given the generality of the reaction, the question arises which of the chiral moieties chosen from any number of commercially available ketones, aldehydes or epoxides would give the most suitable ligand for enantioselective hydroamination. A library of these ligands could be prepared, but the task would be expensive both in cost of chiral materials and in the time needed to synthesize, purify, characterize, and screen all possible ligands.…”

Samarium-Promoted Coupling of Pyridine-Based Heteroaryl Analogues of Benzylic Acetates with Carbonyl Compounds

“…In the simplest cases, we began with conversion of commercially available pyridine-2-carbinol directly to the acetate derivative 4 , or by conversion of commercially available quinoline-2-carboxylic acid and isoquinoline-1-carboxylic acid into the corresponding ethyl esters followed by reduction with NaBH 4 and reaction of the resulting alcohols with acetic anhydride to give the acetates 5 and 6 . In other cases, we extended our previously developed SmI 2 -promoted coupling of 1,10-phenanthroline with aldehydes and ketones to the analogous use of 2,2‘-bipyridine. The resulting alcohol was then converted into acetate 7 .…”