Józef J. Ziółkowski

PERSPECTIVES OF RHODIUM ORGANOMETALLIC CATALYSIS. FUNDAMENTAL AND APPLIED ASPECTS OF HYDROFORMYLATION

Abstract Today’s hydroformylation process almost exclusively use rhodium homogeneous catalysts. Some domination of octacarbonyl dicobalt as the catalyst precursor was followed with broad application of rhodium based organometallic catalysts modified with mainly phosphorus ligands of different donor–acceptor properties and/or different cone/bite angles. Although there are many papers dealing with the comparative studies on structure-reactivity correlation, the effects of electronic and steric parameters of P-ligands on the catalytic activity of rhodium catalysts are not always predictable. Phosphines and phosphites as ligands, simple and structurally developed, bulky, mono and bidentate are still of great interest in the modification procedures of rhodium catalysts, especially when high regioselectivity in the hydroformylation is expected. Further development of the synthesis of phosphorus ligands led to the preparation of water soluble ligands and the creation of a new class of two-phase homogeneous catalysts, in this way solving problems of separation and/or catalysts reuse. Some new water soluble phosphines (PNS, PNa, PC) as well as N -pyrrolyl phosphines (PPh x (NC 4 H 4 ) 3− x ) of required electronic parameters applied for synthesis of new rhodium catalyst precursors will be discussed and the results of structural studies will be used in the explanation of the observed catalytic activity in the model hydroformylation reaction of olefins (1-hexene, unsaturated alcohols) as well as related reactions, i.e. isomerization and hydrogenation.

A new, highly selective, water-soluble rhodium catalyst for methyl acrylate hydroformylation

Abstract Hydroformylation of methylacrylate to α-aldehyde can be achieved in a two-phase system in the presence of two new water-soluble phosphines. High yields and selectivities of α-aldehyde (ca. 80% with a α/β ratio of 1:20) were obtained. Spectroscopic studies have been carried out and some new rhodium complexes formed in situ in catalytic systems have been identified.

New insights into the chemistry of oxomolybdenum(VI) complexes with N-salicylidene-2-aminoethanol

Abstract Oxomolybdenum(VI) complexes with tridentate Schiff base, N -salicylidene-2-aminoethanol (H 2 sae), has been synthesised by the reaction of Mo(O) 2 (sal) 2 (where Hsal=salicylic aldehyde) with 2-aminoethanol. This reaction leads to dimeric [MoO(μ-O)(sae)] 2 and new monomeric [Mo(O) 2 (sae){1,2-O (−) C 6 H 4 C(H)N (+) (H)C 2 H 4 OH}] ( 1 ) compounds. Also substitution of acetylacetonate ligand in Mo(O) 2 (acac) 2 by H 2 sae in EtOH leads to the same complexes (vide infra), but in MeOH monomeric compound Mo(O) 2 (sae)(MeOH) ( 2 ) was formed. The molecular structure of complexes 1 and 2 have been determined by X-ray studies, which confirm that one of the H 2 sae co-ordinates as η 3 -tridentate O,N,O′ ligand, while in complex 1 this ligand exists also in zwitterionic form with intramolecular hydrogen bonding, O⋯HN, 2.584(3) A, of phenolic oxygen bonded to the molybdenum atom. The crystals of 1 are triclinic, space group P 1 , a =8.483(2) A, b =10.187(3) A, c =11.034(3) A, α =105.26(2)°, β =95.29(2)°, γ =95.10(2)°, and D calcd =1.666(1) g cm −3 for Z =2. The crystals of 2 are monoclinic, space group P 2 1 / c , a =6.697(2) A, b =7.375(2) A, c =24.100(3) A, β =92.76(5)°, and D calcd =1.805(1) g cm −3 for Z =4.

Palladium(0) nanoparticles encapsulated in diamine-modified glycidyl methacrylate polymer (GMA-CHDA) applied as catalyst of Suzuki–Miyaura cross-coupling reaction

Cyclohexyldiamine-modified glycidyl methacrylate polymer (GMA-CHDA) in the form of gel-type beads was used to encapsulate Pd(0) nanoparticles 4–15 nm in diameter and applied as a new, reusable catalyst for the Suzuki–Miyaura cross-coupling reaction of 2- and 4-bromotoluene with phenylboronic acid. It was found that the precatalyst preparation methodology strongly influenced its catalytic activity. The best results (100% yield of the product) were obtained when GMA-CHDA was first treated with hydrazine (reducing agent for Pd(II)) and next with PdCl2 solution. The new catalyst acts heterogeneously, and the post-reaction solution after catalyst separation is not catalytically active, suggesting that there is no leaching.

New efficient aerobic oxidation of some alcohols with dioxygen catalysed by N-hydroxyphtalimide with vanadium co-catalysts

New efficient vanadium co-catalysts have been developed for the oxidation of some alcohols with O(2) catalysed by N-hydroxyphthalimide (NHPI). Various alcohols (primary and secondary) were selectively oxidized by O(2) under mild conditions in the presence of a catalytic amount of NHPI as a radical-producing agent combined with small amounts of vanadium complexes with or without the addition of a simple salt (e.g. LiCl) or base (e.g. pyridine).

Rh(acac)(CO)(PR 3 ) and Rh(oxinate)(CO)(PR 3 ) complexes—substitution chemistry and structural aspects

The substitution of CO in Rh(acac)(CO) 2 by the phosphorus ligands P(OPh) 3 , P(NC 4 H 4 ) 3 , and PPh 2 (NC 4 H 4 ) has been studied kinetically by stopped-flow spectrophotometry as a function of temperature. With P(OPh) 3 and P(NC 4 H 4 ) 3 , both CO ligands are replaced in a stepwise fashion via the intermediate Rh(acac)(CO)(PR 3 ). However, the disubstituted complexes Rh(acac)(PR 3 ) 2 are thermodynamically unstable. Judged from the activation parameters, the individual steps are associative processes. In the case of PPh 2 (NC 4 H 4 ) only the monosubstituted complex is formed. The differences in the substitution rates as well as the stability of the various products are largely dominated by electronic (e.g. basicity) effects. X-ray structures of some of the mono-substituted complexes are given. In addition, also the reaction of Rh(oxinate)(CO) 2 with P(OPh) 3 has been studied kinetically showing that oxinate has a labilizing effect relative to acetylacetonate

Infrared and NMR, 1H, 19F, 31P studies of Rh(I) complexes of the formula: [Rh(β-diketone)(CO)X(P)Y] (x = 0, 1, 2; y = 0, 1, 2; × + y = 2; P = PPh3 or P(OP)3)

Products of substitution reactions of CO by PPH3 and P(OP)3 in Rh(β-diketone)(CO)2 complexes (where β-diketone: acetylacetone, thenoyltifluoroacetone, trifluoracetone, benzoyltrifluoroacetone, naphthoyltrifluoroacetone) were examined by IR and NMR. Reactions with PPh3 produced the compounds containing one CO group, i.e. Rh(β-diketone(CO)(PPh3). In the case of asymmetric β-diketones, two isomers were observed in solution. The presence of free phosphine caused labilization of the coordination sphere of complexes followed by fast exchange between the free and the coordinated phosphine. Reactions with P(OPh)3 produced Rh(β-diketone)-[P(OPh)3]2 or Rh(β-diketone)[P(OPh)3] complexes, depending on the amount of P(OPh)3 used. The NMR results indicate considerable delocalization of the electron density in these compounds.

Redox potential, ligand and structural effects in rhodium(I) complexes

The electrochemical behaviour of the set of tetracoordinate rhodium(I) complexes [Rh(O∩O)(CO)L] [O∩O=MeC(O)CHC(O)Me (acac), L=CO (1), P(NC4H4)3 (2), PPh(NC4H4)2 (3), PPh2(NC4H4) (4), PPh3 (5), PCy3 (6), P(OPh)3 (7) or PPh2(C6H4OMe-4) (8); O∩O=PhC(O)CHC(O)Me (bac), L=CO (9) or PPh3 (10); O∩O=PhC(O)CHC(O)CF3(bta), L=CO (11) or PPh3 (12)] and of the pentacoordinate [RhH(CO)L3] [L=P(NC4H4)3 (13), PPh3 (14), P(OPh)3 (15) or P(OC6H4Me-4)3 (16)] and [RhHL4] [L=PPh3 (17) or P(OC6H4Me-3)3 (18)] was studied by cyclic voltammetry and controlled potential electrolysis, in aprotic medium, at a Pt electrode. They present a single-electron oxidation wave (I) (irreversible or quasi-reversible) that can be followed, at a higher potential, by a second and irreversible one (II). The values of first oxidation potential for the tetracoordinate complexes fit the additive Levers electrochemical parameterisation, and the ligand electrochemical Lever EL and Pickett PL parameters were estimated for the N-pyrrolyl phosphines PPhn(NC4H4)3−n (n=0, 1 or 2) and for the organophosphines PCy3 and PPh2(C6H4OMe-4), the former behaving as weaker net electron donors (the electron donor ability decreases with the increase of the number of N-pyrrolyl groups) than the latter phosphines. The pentacoordinate hydride complexes 13–18 fit a distinct relationship which enabled the estimate of the EL ligand parameter for the phosphites P(OC6H4Me-3)3 and P(OC6H4Me-4)3. Electrochemical metal site parameters were obtained for the square planar and the pentacoordinate Rh(I)/Rh(II) couples and, for the former, the redox potential is shown to present a much higher sensitivity to a change of a ligand than the octahedral redox couples investigated so far. Linear relationships were also observed between the oxidation potential and the PL ligand parameter (for the series [Rh(acac)(CO)L]) or the infrared ν(CO) frequency, and a generalisation of the former type of correlation is proposed for series of square-planar 16-electron complexes [M′SL] with a common 14-electron T-shaped binding metal centre {M′S}. Oxidation of 5 by Ag[PF6] leads to the dimerisation of the derived Rh(II) species.

PHOTOCHEMICAL SYNTHESIS, SPECTROSCOPIC PROPERTIES AND BARRIERS TO ALKENE ROTATION IN THE NOVEL BIS(ALKENE) TETRACARBONYL COMPLEXES OF TUNGSTEN

Abstract Photolysis of W(CO) 6 in the presence of twentyfold alkene excess (1-pentene, 1-hexene, 2-hexene, 3-hexene, 1-heptene, 1-octene, 1-decene, cyclopentene, cyclohexene cycloheptene and cyclooctene) in n -hexane leads to the formation of the corresponding bis(alkene)tetracarbonyl complexes of tungsten via the less stable [( ν 2 -alkene)W(CO) 5 ] complexes; the products have been isolated and characterized by their IR, UV-visible and NMR spectra. Bis(alkene)tetracarbonyl complexes of tungsten exhibit fluxional behaviour on the NMR time scale due to rotation of the alkene ligands around the axis defined by the metal and the midpoint of the C 2 linkage. The barriers to alkene rotation, which reflects the energy difference between the ortogonal and the parallel arrangement of the two C=C units, of a number of bis(alkene) complexes, have been determined using variable-temperature 13 C NMR spectroscopy.

HYDROFORMYLATION AND ISOMERIZATION OF HEX-1-ENE CATALYZED BY RH(ACAC)(CO)(PPH3) : EFFECT OF MODIFYING LIGANDS

Abstract The application of the [Rh(acac)(CO)(PPh3)], [A], complex as a hex-1-ene hydroformylation catalyst (at 1 MPa and 353 K) produced 68% hex-2-ene and 20% aldehydes. Identified via IR in the post-reaction mixture were [Rh4(CO)12], [D], and [Rh6(CO)16], [E], carbonyls, which, applied as catalysts, produced hex-2-ene with a 70–90% yield. The presence of free triphenylphosphine changed the reaction course completely and increased the yield of aldehydes to 80% in all catalytic systems, independent of the catalyst precursor structure. The presence of amines [TBA (tribenzylamine), TFA (triphenylamine), and PhNH2 (aniline)] in reactions catalyzed by [A] and [A] + PPh3 leads to a decrease in the hex-2-ene yield and an increase in the yield of aldehydes.