Reactivity of 2-methyl-3-butenenitrile in the presence of catalytic amounts of various cobalt complexes in ionic liquid

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Abstract

The behavior of 2-methyl-3-butenenitrile (2M3BN) in the presence of catalytic amount of several cobalt complexes was evaluated. Irrespective of the nature of cobalt complexes and the experimental conditions (presence of ligand [such as P(OPh)3 or pyridine], or/and of Lewis acid [ZnCl2, AlCl3], organic solvent or ionic liquid), the product of isomerization 2-methyl-2-butenenitrile was obtained instead of the expected rearranged product 3-pentenenitrile (3PN). This result was explained by the activation of Csingle bondH bond instead of Csingle bondCN bond. With 3PN, the first example of a reversible cleavage of the Csingle bondCN with complex derived from Co+ was evidenced.

Graphical abstract

2M3BN in the presence of catalytic amount of several cobalt complexes was mainly isomerized into 2M2BN due to a easier activation of C–H bond instead of Csingle bondCN bond.

With 3PN, the first example of a reversible cleavage of the Csingle bondCN with complex derived from Co+ was evidenced.

Introduction

The rearrangement of 2-methyl-3-butenenitrile (2M3BN) into 3-pentenenitrile (3PN), the second step in the preparation of the adiponitrile, is often chosen as a model reaction in order to determine the catalytic performance of new ligands [1], [2] or new media, such as ionic liquid [3], [4]. Besides, this conversion occurring through a Csingle bondCN bond cleavage (Fig. 1a), there is a possible isomerization of 2M3BN into the side product, 2-methyl-2-butenenitrile (2M2BN) which forms via Csingle bondH activation (Fig. 1a).

The nickel(0) complexes clearly give the best results and the mechanism of the reaction of rearrangement of 2M3BN into 3PN with Ni0 catalyst (Fig. 1a) has been studied extensively [5], [6], [7], [8]. This mechanism is based on a Ni0  Ni2+ equilibrium. However, some authors claimed that cobalt complexes such as Co2(CO)8, Hg[Co(CO)4]2 and HCo[(P(OAr)3]4 {Ar = C6H5, o-CH3C6H4} present, for this reaction, analogous results to those of Ni0 [9], [10], [11], [12], [13].

Recently, we reported this catalytic rearrangement in the presence of phosphine complexes Ni0, in biphasic ionic liquid/organic solvent. Several neutral and ionic phosphines and ionic liquids have been tested. The best results in the conversion of 2M3BN (96%) and selectivity to 3PN (93%) were obtained for the catalytic system associating Ni(cod)2, (m-sulfophenyl)-diphenylphosphine sodium salt, [TPPMSNa] as the ligand and 1-butyl-2,3-dimethylimidazolium-bis(trifluoromethylsulfonyl)imide [BMMIm][NTf2] as the ionic liquid, in a biphasic ionic liquid/heptane solvent system. Partition experiments proved that the catalyst was immobilized in the ionic phase. TON (1020) and TOF (103 h−1) of the catalyst were measured [3], [4]. Recycling of the catalyst is possible but leads to an important deactivation which is related to the evolution of the nature of the ligand by ion exchange between the cation (Na+) of the ligand and the cation [BMMIm+] of the ionic liquid. This exchange induces a change in the nature of the ligand, thereby altering the nature of the catalyst and of the catalytic activity [14].

To immobilize a catalyst into ionic liquid, the catalyst ought to be ionic. Another approach is to use the ionic catalytic precursor in which the charge is on the metal center and with neutral ligand [15], [16], [17], [18], [19], [20].

In this paper, we report our attempts to realize the rearrangement 2M3BN into 3PN with a series of ionic cobalt complexes in the oxidation state Co1−, Co1+ and even Co0. The Co1− complex is isoelectronic with Ni0. On the other hand, the cationic complex Co1+ such as [(Ph2CHdouble bondCHPPh2)2Co]+[ClO4], seems to be a possible candidate for this reaction due to the fact it reacts with HCN to give the cationic complex Co3+ [21]:

Section snippets

Synthesis of cobalt complexes

Several cobalt complexes (PPh3)3CoCl [22], 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridinecobaltmethyl, (BIP)CoMe [23], 1,1,1-tris(diphenyl-phosphinomethyl)ethane cobalt chloride, P3CoCl [24], HCo(P(OPh)3)4, NaCo(CO)4 [25], [Co(pyridine)6][Co(CO)4]2 [26], (η3allyl)Co(CO)2PPh3 [27] and H[Co{P(OPh)3}4] [28], [29] have been synthesized according to the procedure available in the literature.

The reaction of (PPh3)3CoCl with Li(N(SO2CF3)2, (LiNTf2), in the presence of bidentate phosphines, using

Conclusion

Several cobalt complexes in the oxidation states −1, 0, +1, synthesized (PPh3)3CoCl, [(Ph2PCH2CH2PPh2)2Co]+[NTf2], [(Ph2PCHdouble bondCHPPh2)2Co]+[NTf2], P3CoCl, (BIP)CoMe, (η3allyl)Co(CO)3, (η3allyl)Co(CO)2PPh3, [P3Co]+[Co(CO)4], HCo(P(OPh)3)4, NaCo(CO)4, commercial Co2(CO)8 and CpCo(CO)2 were tested in the catalytic reaction of rearrangement of 2M3BN. Irrespective of the nature of cobalt complexes and the experimental conditions (presence of ligand [P(OPh)3 or pyridine], or/and of Lewis acid [ZnCl2,

Experimental

CoCl2·6H2O, zinc powder, 3-pentenenitrile, triphenylphosphine, CoBr2 and MeMgBr were purchased from Aldrich and used without further purification. Li(N(CF3SO2)2) was purchased from Solvionic and used as received.

Solvents were distilled using the appropriate drying agents: CaH2 for acetonitrile and dichloromethane, K2CO3 for chloroform and acetone, sodium for toluene and sodium/benzophenone for diethylether and tetrahydrofuran. 2-Methyl-3-butenenitrile was purchased from Rhodia Research Center,

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