Ligand-coupling reactions of hypervalent species

Abstract

Abstract. The concept of ligand coupling is explained and the actual examples of many important reactions in which not only sulfur and phosporus centered hypervalent species, but iodine, silicon and copper centered hypervalent ones are presented. It was also mentioned that many other reactions in which the central metal atoms in the nickel, triad elements are considered to behave as the catalytic site for ligand coupling reaction, such as the Waker process and the Heck reaction.Ever since we found the following reaction,(l) we have extended our concept of ligand coupling(2) and have so many examples of these or similar reactions. However, there were prior many reactions to enable us to postulate the concept. A typical example of a three-centered, four electron bond, called a hypervalent bond by Musher,(3) can be found in the substance in the structure of quternary florinated sulfur as demonstrated by X-ray analysis by Rundle et a1. (4) and Pimentel, (5) in the following figure. (Fig. 1 -tcThe central atom in a hypervalent species is valence-shell-expanded and tends to to extrude one pair of electrons to the normal valency of an octet. This is the driving force of the reaction and there are three conceivable ways for hypervalent species to collapse to form stable octet species; self-decomposition as exemplified by the wellstudied Wittig reaction,( 6)ligand exchange, (7,8) and ligand coupling.(9-13) It is well known that the equatorial ligands form sp2 and the axial linkages assume 805

Enantioselective Routes to Sulfoxides Based Upon the Use of Carbanionic Leaving Groups

“…For instance, with a suitable choice of carbanionic leaving groups, it should be possible to extend the same methodology to the synthesis of any type of diaryl sulfoxide. Detailed mechanistic aspects, such as competition between ligand exchange and ligand coupling (observed in other related process [47] ), also deserve attention in future work.…”

α‐Arylation by Rearrangement: On the Reaction of Enolates with Diaryliodonium Salts

“…Alternatively, the ligand could leave before addition of the nucleophile, forming an intermediate iodonium cation (ArIL + ). In either case, ArILNu is formed, and subsequent-ly gives the product Nu À L. This could either take place by reductive elimination (also called ligand coupling), [12] by nucleophilic attack on the carbon bonded to iodine by the released ligand, with reductive loss of ArI, [9,13] or by SET mechanisms. [14] Diaryliodonium salts are generally believed to react by the reductive elimination pathway, delivering the equatorial aryl moiety to the axially installed nucleophile.…”

Hypervalent Iodine and Carbohydrates – A New Liaison

“…In most cases, reactions of 1 with tron-rich enol ether double bond were anticipated to be idenucleophiles are terminated by the reductive elimination ally suited for reactions with iodanes, such as the Koser process, affording final products 3 containing a combireagent 2b [11] . As shown for tri-O-acetyl--galactal 6, oxination of L and Nu [6] . Due to this behaviour, compounds dative regioselective deblocking at C-3 takes place in the like 1 are occasionally termed "nonorganometallic" represence of 2b and powdered molecular sieves (3 Å ) agents.…”