From Olefin Metathesis Catalyst to Alcohol Racemization Catalyst in One Step

Abstract

Die ungewöhnliche Umlagerung eines Ruthenium‐Katalysators von der Indenyliden‐ in die η5‐Indenyl‐Form wurde beobachtet. Der resultierende Komplex ist das formale Zersetzungsprodukt eines Olefinmetathese‐Präkatalysators und ein schon in sehr geringen Mengen außergewöhnlich aktiver Katalysator der Racemisierung von chiralen Alkoholen.

Insights into the Decomposition of Olefin Metathesis Precatalysts

“…Recently, our efforts have been focused on understanding the stability of metathesis complexes, especially the versatile synthon [RuCl 2 ((3‐phenyl)indenylidene)(PPh 3 ) 2 ] ( M10 ), which is used for the synthesis of first‐, second‐, and third‐generation metathesis precatalysts 4. When M10 was heated in alcohol solution, the new species [RuCl(η 5 ‐(3‐phenyl)indenyl)(PPh 3 ) 2 ] ( 3 ) was formed, wherein the indenylidene ligand coordinated in an η 5 ‐fashion (Scheme ) 5. This complex, and its cationic derivative,6 have since been shown to be highly active in a number of transformations 5–7.…”

A Cationic Ruthenium Complex for the Dynamic Kinetic Resolution of Secondary Alcohols

“…In 2012, we described the use of a neutral phenylindenyl ruthenium complex (1) in the racemization of sec-alcohols. [10] This process required the presence of an alkoxide base (KOtBu). In the racemization of secondary alcohols catalyzed by ruthenium(II) species, an initiation step [6b, c, 8a, 9] based on an alkoxide-activation of the precatalyst is always required (Scheme 1).…”

Insights into the Decomposition of Olefin Metathesis Precatalysts

“…[4] When M10 was heated in alcohol solution, the new species [RuCl(h 5 -(3-phenyl)indenyl)(PPh 3 ) 2 ] (3) was formed, wherein the indenylidene ligand coordinated in an h 5 -fashion (Scheme 1). [5] This complex, and its cationic derivative, [6] have since been shown to be highly active in a number of transformations. [5][6][7] More recently, we have shown that this indenylidene-to-h 5 -indenyl rearrangement is not limited to M10, but that it also occurs for the related complex [RuCl 2 (3-phenylindenylidene)(iBu-Phoban) 2 ] (M11), thus yielding the hydride species [Ru(H)-(h 5 -(3-phenyl)indenyl)(iBu-Phoban) 2 ] (4; Scheme 1; iBu-Phoban = 9-isobutyl-9-phosphabicyclo[3.3.1]nonane).…”

“…[5] This complex, and its cationic derivative, [6] have since been shown to be highly active in a number of transformations. [5][6][7] More recently, we have shown that this indenylidene-to-h 5 -indenyl rearrangement is not limited to M10, but that it also occurs for the related complex [RuCl 2 (3-phenylindenylidene)(iBu-Phoban) 2 ] (M11), thus yielding the hydride species [Ru(H)-(h 5 -(3-phenyl)indenyl)(iBu-Phoban) 2 ] (4; Scheme 1; iBu-Phoban = 9-isobutyl-9-phosphabicyclo[3.3.1]nonane). [8] Notably, in the latter case, a much cleaner reaction occurred when a secondary alcohol was used.…”

“…[19] The full pathway for M10 to 3 (PPh 3 ) has been modeled previously. [5] This pathway was therefore modeled for M1 (PCy 3 ) and M11 (iBu-Phoban; Figure 2). The potential-energy surfaces (PESs) for the rearrangement of precatalysts M10, M1, and M11, generically indicated as A in the following calculations, to yield complexes of the form [RuCl-(h 5 -(3-phenyl)indenyl)(PR 3 ) 2 ], generically indicated as H in the following calculations, are presented in Figure 2 (energies are normalized to A plus NEt 3 and methanol).…”