Organic Synthesis with Elemental Lanthanides – Going Beyond Samarium and Ytterbium

Abstract

Dedicated to our friend and colleague Prof. Peter Junk on the occasion of his 60th birthday Lanthanide (Ln) metals are strong reducing agents (E 0 (Ln 3 + / Ln 0 ) � À 2.3 V vs. NHE) which can be applied in various manners in organic synthesis. While samarium and ytterbium have been employed for more than 50 years, the last 20 years have seen the emergence of synthetic applications using other metals, such as lanthanum, cerium, praseodymium, neodymium or dysprosium. The large electron reservoir of lanthanide metals, the Lewis acidic character of the Ln 3 + ions and their intermediate electronegativity compared to lithium or magnesium can provide unique reactivity patterns. This review provides an overview on the potential of these metals for synthetic organic chemistry in the following areas: 1) for Grignard type reactivity and radical generation, 2) in reduction chemistry involving carbonyl compounds and dehalogenation reactions and 3) in combination with transition metals.

Gas‐phase formation of Grignard‐type organolanthanide (III) ions RLnCl3−: The influences of lanthanide center and hydrocarbyl group

“…Organolanthanide halide compounds have been widely used in organic synthesis as an important class of intermediates that can undergo Grignard-type reactions and Barbier-type reactions to form new C-C bonds yielding a diverse range of valuable products such as alcohols, ketones, and aldehydes. [1][2][3] The fact that Grignard-type organolanthanides exhibit several utilizable differences in reactivity in comparison with organomagnesium compounds (Grignard reagents) has gained much attention in the past several decades. Since the first discovery of ytterbium (II) Grignard-type analogue in 1970, 4 the syntheses, structures, and reactivities of the Grignard-type organolanthanides have been intensively investigated, and the focus has been significantly on the divalent lanthanides, especially Yb (II), Sm (II), and Eu (II).…”

“…Organolanthanide halide compounds have been widely used in organic synthesis as an important class of intermediates that can undergo Grignard‐type reactions and Barbier‐type reactions to form new C–C bonds yielding a diverse range of valuable products such as alcohols, ketones, and aldehydes 1–3 . The fact that Grignard‐type organolanthanides exhibit several utilizable differences in reactivity in comparison with organomagnesium compounds (Grignard reagents) has gained much attention in the past several decades.…”

Samarium and Ytterbium in Organic Electrosynthesis

“…32 In the context of lanthanides, it is well-established that divalent reagents based on, for example, samarium can furnish hydrodehalogenated products from a variety of alkyl and aryl halides. 3 Mellah and Sun studied the properties of electrochemically formed SmCl 2 , SmBr 2 and Sm(OTf) 2 . 33 While the redox potential of the Ln(II) complexes were found to become more negative in the order OTf < I < Br < Cl, with SmCl 2 having the most negative reduction potential, all electrochemically formed complexes were competent in mediating the reductive dechlorination of 1-chlorododecane to give the corresponding alkane in yields of around 80% in the absence of current.…”

“…Elemental lanthanide metal reagents have successfully been used as single-electron reductants and as starting materials to generate divalent organometallic reagents for nucleophilic additions. 3 Further-more, divalent lanthanide complexes are versatile reagents and catalysts in a wide range of radical transformations, including asymmetric reactions and total synthesis applications, [4][5][6] with samarium(II) iodide (Kagan's reagent) as the benchmark complex. Finally, trivalent lanthanide complexes are excellent Lewis acids, with trifluoromethanesulfonate (triflate) complexes being a particularly useful class of water-tolerant catalysts.…”

Samarium(III) Triflate in Organic Synthesis: a Mild and Efficient Catalyst

“…[1][2][3][4] Besides, lanthanides have a remarkable contribution to the synthesis of organic synthetic products as well as in the manufacture of petroleum. [5] Among lanthanides, samarium (Sm 62 , electronic configuration [Xe] 4f 6 6 s 2 ) has emerged as an interesting element in organic synthesis as it is a cheap metal, and it is stable in the air as well as it comprises a potent reducing power (Sm 3 + /Sm = À 2.41 V). [6] The derivative of samarium namely samarium(II) iodide (Kagan's reagent) is extremely popular in organic synthesis, especially in crosscoupling reactions and total synthesis of bioactive natural products as a single-electron reducing agent.…”