Carbonylation of ethene catalysed by Pd(II)-phosphine complexes.

This review deals with olefin carbonylation catalysed by Pd(II)-phosphine complexes in protic solvents. In particular, the results obtained in the carbonylation with ethene are reviewed. After a short description of the basic concepts relevant to this catalysis, the review treats in greater details the influence of the bite angle, skeletal rigidity, electronic and steric bulk properties of the ligand on the formation of the products, which range from high molecular weight perfectly alternating polyketones to methyl propanoate. It is shown that the steric bulk plays a major role in directing the selectivity. Particular emphasis is given to the factors governing the very active and selective catalysis to methyl propanoate, including the mechanism of the catalytic cycles with diphosphine- and monophosphine-catalysts. A brief note on the synthesis of methyl propanoate using a "Lucite" type catalyst in ionic liquids is also illustrated. A chapter is dedicated to the carbonylation of olefins in aqueous reaction media. The nonalternating CO-ethene copolymerization is also treated.

Catalytic properties of [Pd(COOMe)(n)X(2-n)(PPh(3))(2)] (n = 0, 1, 2; X = Cl, NO(2), ONO(2), OAc and OTs) in the oxidative carbonylation of MeOH.

cis-[Pd(ONO(2))(2)(PPh(3))(2)] (1) reacts under mild conditions with CO in methanol (MeOH) in the presence of pyridine (py), yielding trans-[Pd(COOMe)(ONO(2))(PPh(3))(2)] (1a). The use of NEt(3) instead of py leads to a mixture of 1a, trans-[Pd(COOMe)(2)(PPh(3))(2)] (2), and [Pd(CO)(PPh(3))(3)]. Pure 2 was prepared by reacting cis-[Pd(OTs)(2)(PPh(3))(2)] with CO in MeOH and subsequently adding NEt(3). The nitro complex trans-[Pd(COOMe)(NO(2))(PPh(3))(2)] (3a) was prepared by reacting trans-[Pd(COOMe)Cl(PPh(3))(2)] with AgNO(2) or with AgOTs and NaNO(2). New syntheses for 1 and trans-[Pd(NO(2))(2)(PPh(3))(2)] (3) are also reported. All complexes have been characterized by IR and (1)H and (31)P{(1)H} NMR spectroscopies. Complexes 1 and 2 exchange irreversibly and quantitatively one nitrato with one carbomethoxy ligand, yielding 1a. 2 in CD(2)Cl(2) at 40 degrees C decomposes with the formation of dimethyl carbonate (DMC), whereas under 4 atm of CO, DMC and dimethyl oxalate (DMO) are formed, ca. 12% each; in the presence of PPh(3) and in the absence of CO, decomposition occurs at 60 degrees C with the formation of DMC only, suggesting that decarbonylation involves a five-coordinate intermediate or predissociation of a PPh(3) ligand. The oxidative carbonylation of MeOH does not occur when using NaNO(2) or NaNO(3) as the oxidant and 1, 1a, 3, or 3a as the catalyst precursor. On the contrary, when using benzoquinone (BQ) as the oxidant, these complexes, 2, or [Pd(COOMe)(2-n)X(n)(PPh(3))(2)] (X = Cl, OAc, OTs; n = 1, 2) promote selective catalysis to DMO. After catalysis the precursors are transformed into [Pd(BQ)(PPh(3))(2)](2).H(2)BQ, [Pd(CO)(PPh(3))](3) and [Pd(CO)(PPh(3))(3)]. Also the last with BQ gives selective catalysis to DMO. The solid-state structures of 1.CH(2)Cl(2) and 1a have been determined by means of single-crystal X-ray diffraction.