Ruthenium/C₅Me₅/Bisphosphine‐ or Bisphosphite‐Based Catalysts for normal‐Selective Hydroformylation

Abstract

Hydroformylation of alkenes is the most widely industrially applied homogeneous transition-metal-catalyzed reaction. [1] Since the discovery by Roelen that [HCo(CO) 4 ] can promote this transformation, [2] cobalt complexes have been used extensively as hydroformylation catalysts. However, more recently developed rhodium/phosphine complexes generally afford higher selectivity compared to cobalt catalysts for the production of normal aldehydes (n-aldehydes), which are utilized as intermediates for the synthesis of plasticizers, solvents, and detergents. Additionally, rhodium complexes typically produce negligible quantities of alkanes from competing alkene hydrogenation unlike cobalt-based hydroformylation catalysts. Thus, rhodium catalysts have come to play a major role in industry.Intensive studies have been devoted both in industry and in academia to the development of bisphosphine or bisphosphite ligands that promote highly normal-selective (n-selective) rhodium-catalyzed hydroformylation of 1-alkenes. [3] However, recent global increases in demand for rhodium, particularly in the automotive industry, is increasing the price of this already expensive precious metal. [4] In contrast, more cost-effective cobalt-based systems suffer from concomitant formation of alkane by-products. Considering these factors, the development of hydroformylation catalysts using other transition metals is desirable. In contrast to the extensive studies on cobalt and rhodium systems, other transition metals such as palladium, [5] iridium [6] , and ruthenium [7] have received less attention as potential hydroformylation catalysts. We have targeted ruthenium, which is less expensive compared to rhodium. Only two examples of rutheniumcatalyzed hydroformylation with high n-selectivity (normal/ iso (n/i) > 30) have been reported. [7d,h] Our design for ruthenium hydroformylation catalysts is illustrated in Figure 1. In conventional rhodium catalysts for hydroformylation, the hydridorhodium(I) A is a key species to which alkenes insert to generate the corresponding alkylrhodium species. In contrast, the dihydrido ruthenium(II) B is known as a catalytically active species for hydrogenation of alkenes, which is a problematic side reaction in hydroformylation. By comparing the species A and B, we envisioned replacing one hydride in B with a cyclopentadienyl anion. Through this strategic change, the [CpRu II ] complex C was expected to be inactive as an alkene hydrogenation catalyst because the ruthenium center lacks one of the requisite hydride ligands present in the active hydrogenation intermediate B. Herein, we report a new catalyst system that consists of a [Cp*Ru II ] (Cp* = C 5 Me 5 ) complex ligated by chelating bisphosphines. These complexes effect the hydroformylation of 1-alkenes with the highest level of activity and n to i selectivity to date for any ruthenium-based catalyst, [7d,h] even though the activity remains well below that of the best rhodium-based catalysts. Additionally, these ruthenium catalysts successfully supp...

Ruthenium-catalysed alkoxycarbonylation of alkenes with carbon dioxide

“…In addition to traditional carbonylation catalysts, recently ruthenium complexes demonstrated their potential in hydroformylation 25,26 and hydroaminomethylation reactions using CO 27 . On the basis of our expertise in this area, we became interested to use carbon dioxide as CO surrogate for such reactions.…”

Phosphine‐ and Hydrogen‐Free: Highly Regioselective Ruthenium‐Catalyzed Hydroaminomethylation of Olefins

“…Hence, it is of interest that recent examples of rutheniumcatalyzed CÀC bond-formation reactions [11] were reported and showed their potential in hydroformylation reactions. [12] Nevertheless, powerful alternatives to rhodium-catalyzed HAMs have been rarely reported. [13] Last year our group presented a general protocol for a highly n-selective ruthenium-catalyzed HAM using syngas.…”

“…The use of various P ligands did not additionally improve the n-selectivity. A moderate product yield was obtained with NMP (NMP = Nmethyl-2-pyrrolidone) as the solvent and 0.5 mol % [Ru 3 (CO) 12 ] in the presence of 20 mol % K 2 CO 3 as the base (entry 1). Other solvents and solvent mixtures led to lower yields (entries 2 and 3).…”

Towards the Development of a Selective Ruthenium‐Catalyzed Hydroformylation of Olefins

“…[9] Notably, Takahashi, Yamashita, Tanaka, and Nozaki reported in 2012 a [Ru II Cp*] complex with bidentate ligands for highly regioselective hydroformylation of propene and 1-decene. [10] The observed chemo-and regioselectivity is comparable to standard rhodium catalyst system, however, the catalytic activity was still significantly lower. More recently, a modified catalyst for domino hydroformylation/reduction was reported.…”