Nickel-Catalyzed Isomerization of 2-Methyl-3-butenenitrile

Abstract

Summary: The isomerization of the branched 2M3BN to the linear 3PN by a DPEphosNi species has been investigated by means of variable-temperature NMR spectroscopy, and activation parameters have been determined. An intermediate in this reaction, which is formed via C-C bond activation, could be trapped by addition of ZnCl 2 , and the molecular structure of the corresponding Ni(II) complex has been determined by X-ray crystallography.Among C-C bond formation reactions, the hydrocyanation of alkenes is an attractive, yet challenging, route for the functionalization of carbon-carbon double bonds. 1,2 The isomerization of 2-methyl-3-butenenitrile (2M3BN) to 3-pentenenitrile (3PN), for example, is closely related to hydrocyanation and is at the same time an important step in the industrial adiponitrile process. 3 In combination with Ni(cod) 2 , all classes of bidentate phosphorus ligands (phosphines, 4,5 phosphinites, 6 phosphonites, 4,7 and phosphites 8 ) catalyze the isomerization, without the addition of Lewis acids. However, the influence of ligand parameters on this conversion still remains unknown. The isomerization is, in fact, a suitable reaction to study reductive elimination to the final product 3PN without the deactivation of the catalyst usually caused by HCN during hydrocyanations. 9,10 We started a spectroscopic investigation of the isomerization of 2M3BN to 3PN catalyzed by DPEphos/ Ni(cod) 2 to study the reductive elimination of nitriles, which is the crucial step in catalytic hydrocyanation reactions. In fact, we were moved to report on our results because of recent contributions in this field by Santini et al. 11 and Chaudret et al. 5 Upon addition of 1 equiv of DPEphos to Ni(cod) 2 in toluene-d 8 the 31 P NMR spectrum displays a singlet at δ 33.1 ppm for the species (DPEphos)Ni 0 (cod) (1) (Scheme 1). This signal disappears on addition of approximately 3 equiv of 2M3BN at -35°C, and two doublets appear at δ 21.3 and 24.2 ppm, with 2 J PP ) 38 Hz. These resonances correspond to (DPEphos)Ni 0 -(2M3BN) (2), with 2M3BN coordinating most likely through its alkene bond; the η 2 -alkene complex (DPEphos)Ni 0 (styrene) gives a very similar 31 P NMR spectrum, which shows two doublets at δ 20.2 and 22.9 ppm with 2 J PP ) 44 Hz. When the temperature is raised to +25°C, the two doublets of 2 disappear and a signal could no longer be detected in the 31 P NMR spectrum.The 1 H NMR spectrum shows broad signals at δ 4.5 (CHCH 2 ), 3.4 (CHCH 3 ), 2.4 (1H, CH syn H anti ), 1.6 (CH 3 ), and 1.2 (1H, CH syn H anti ) ppm. Increasing the temperature to +35°C causes slow isomerization of 2M3BN to 3PN, indicated by the methyl signals in the 1 H NMR spectrum. The 3PN analogue (DPEphos)Ni 0 (3PN) (5) could not be detected with VT NMR spectroscopy when approximately 5 equiv of 3PN was added to 1. However, 1 disappears and the same broad signals in the 1 H NMR spectrum occur which were detected upon warming of 2. We ascribe this spectrum to (DPEphos)Ni II (C 4 H 7 )(CN) (3), which is formed by oxidative addition of 2M3BN or

Isomerization of 2-methyl-3-butenenitrile with (bis-diphenylphosphinoferrocene)nickel compounds: Catalytic and structural studies

“…This result is slightly better than the one reported by Sabo-Etienne's group using PPh 3 under similar reaction conditions (96% conversion, 3 h, 81% 3PN), [8] which in our hands and reaction apparatus, systematically gave 58% yield. The system reported herein also outperformed in terms of activity and selectivity the bis(2-diphenylphosphinophenyl)ether (DPEphos) catalytic system reported by Vogt and co-workers [10]. The reaction was followed up to a 75% conversion, but the precise yield of 3PN was not reported, and the formation of additional by products was not mentioned.…”

“…Alternatively, the unchanged doublets can also be associated with a 4-coordinate Zn species, in different coordination environments, as represented in Scheme 4. Closely related species have been structurally characterized by Vogt and co-workers [10].…”

“…More recently, the use of [Ni(COD) 2 ] as catalytic precursor, in combination with P-donor-bidentate ligands such as phosphines, [8][9][10][11] phosphonites [9] and phosphites, [12] has been reported to achieve the transformation of the branched nitrile (2M3BN) to the linear nitrile (3PN). Additionally, this reaction has been studied in aqueous media [13] and ionic liquids [14].…”

Binaphthol‐Based Diphosphite Ligands in Asymmetric Nickel‐Catalyzed Hydrocyanation of Styrene and 1,3‐Cyclohexadiene: Influence of Steric Properties

“…We therefore decided to test ligands L2, L3 and L5 in a closely related reaction, the isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile with 1 and 3 equivalents of ligand. [16] Ligands L2 and L3 showed comparable rates (TOF = 78 and 74 h À1 , respectively) with 1 equiv. of ligand, whereas L5 gave no activity.…”

Enantioselective Nickel‐Catalyzed Hydrocyanation using Chiral Phosphine‐Phosphite Ligands: Recent Improvements and Insights

“…[2e, 5,11] Part of our investigations was also to prove the assumed catalyst structure( I). By slow diffusion of n-pentane into as olution of the isolated complexi nT HF under an inert atmosphere we were able to grow crystals of the complex Ni(3)(cod) suitable for X-ray single crystal analysis.…”