Catalytic syntheses of poly cyclic compounds based on norbornadiene-2,5 in the presence of nickel complexes: III. Cyclic
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Catalytic Syntheses of Polycyclic Compounds Based on Norbornadiene-2,5 in the Presence of Nickel Complexes: III. Cyclic Dimerization of Norbornadiene-2,5 in the Presence of Organophosphorus Additives V. R. Flid, V. B. Kuznetsov, A. A. Grigor'ev, and A. P. Belov Lomonosov State Academy of Fine Chemical Technology, Moscow, 117571 Russia ReceivedDecember17, 1999 Abstract--The cyclodimerization of norbornadiene-2,5 (NBD) catalyzed by the systems formed on the basis of bis(rl3-allyl)nickel and organophosphorus compounds and the process kinetics are studied. The formation rate of all products follows the overall second-order rate law: first order with respect to the catalyst and NBD. The addition of phosphines and phosphites substantially decreases the reaction rate compared to that in nickel systems containing no organophosphorus additives. The influence of the phosphine ligand structure and temperature on the ratio of the reaction products is studied. The blocking of one coordination site on the nickel atom changes the process kinetics. The loss of two vacancies results in the loss of the catalytic activity of the system. A mechanism explaining the stoichiometry and composition of the reaction products is proposed. INTRODUCTION In our previous papers [ 1, 2], we described the catalytic cyclodimerization of norbornadiene-2,5 (NBD) catalyzed by Ni(0) complexes. The NBD-nickel systems formed by different methods from the starting nickel complexes are the true catalysts of this reaction. The modifying additives used in NBD cyclodimerization, along with transition metal compounds, are known to stabilize the catalytically active state of the metal and, in some cases, affect the process rate and ratio of the products [3-5]. Organophosphorus compounds are the most efficient. A detailed study of their role in NBD cyclodimerization would make it possible to deliberately affect this reaction. In addition, the use of phosphine ligands that form a strong bond with the metallic center is an important step toward heterogenized catalytic systems. EXPERIMENTAL The synthesis of bis(rl3-allyl)nickel and all procedures concerning its storage and transfer into a reactor were carded out according to the procedures described in [1, 2]. Kinetic experiments were carded out at constant temperature in 25-mi static vacuum reactors with sampler. The reaction mixture was analyzed and the process course was monitored by gas chromatography on a CarloErba model 4200 chromatograph using an SPB-I capillary column (30 m long).
The concentrations of reactants and reaction conditions were varied within the following limits: Concentration of NBD Concentration of Ni(CaHs)2 Temperature Molar ratio organophosphorus ligand : nickel
0.5-5.0 mol/l 0.01--0.10 mol/l 10--100~ 1--4
The following organophosphorus compounds (Fluka) were used: (a) Phosphines: trimethylphosphine, triethylphosphine, triisopropylphosphine, tri-tert-butylphosphine, tricyclohexylphosphine, triphenylphosphine and triortho-tolylphosphine, and bis(1,2-diphenylphosphino)ethane (Diphos); (b) P
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