Research on “post‐metallocene” polymerization catalysis ranges methodologically from fundamental mechanistic studies of polymerization reactions over catalyst design to material properties of the ...polyolefins prepared. A common goal of these studies is the creation of practically useful new polyolefin materials or polymerization processes. This Review gives a comprehensive overview of post‐metallocene polymerization catalysts that have been put into practice. The decisive properties for this success of a given catalyst structure are delineated.
“Post‐metallocene” polymerization catalysis research ranges from fundamental mechanistic studies by catalyst design to material properties of polyolefins. A common goal of these studies is the creation of practically useful new materials or processes. A comprehensive overview of post‐metallocene polymerization catalysts that have been put into practice is provided. The decisive properties for this success of a given catalyst structure are delineated.
Remote control: Substituents strongly affect the catalytic properties of complexes 1 in ethylene polymerization, despite their remoteness from the active center. An appropriate substitution pattern ...provides very active and robust catalysts.
The mechanism and kinetics of the solvolysis of complexes of the type (L−L)Pd(C(O)CH3)(S)+CF3SO3- (L−L = diphosphine ligand, S = solvent, CO, or donor atom in the ligand backbone) was studied by NMR ...and UV−vis spectroscopy with the use of the ligands a−j: SPANphos (a), dtbpf (b), Xantphos (c), dippf (d), DPEphos (e), dtbpx (f), dppf (g), dppp (h), calix-6-diphosphite (j). Acetyl palladium complexes containing trans-coordinating ligands that resist cis coordination (SPANphos, dtbpf) showed no methanolysis. Trans complexes that can undergo isomerization to the cis analogue (Xantphos, dippf, DPEphos) showed methanolyis of the acyl group at a moderate rate. The reaction of trans-(DPEphos)Pd(C(O)CH3)+CF3SO3- (2e) with methanol shows a large negative entropy of activation. Cis complexes underwent competing decarbonylation and methanolysis with the exception of 2j, cis-(calix-diphosphite)Pd(C(O)CH3)(CD3OD)+CF3SO3-. The calix-6-diphosphite complex showed a large positive entropy of activation. It is concluded that ester elimination from acylpalladium complexes with alcohols requires cis geometry of the acyl group and coordinating alcohol. The reductive elimination of methyl acetate is described as a migratory elimination or a 1,2-shift of the alkoxy group from palladium to the acyl carbon atom. Cis complexes with bulky ligands such as dtbpx undergo an extremely fast methanolysis. An increasing steric bulk of the ligand favors the formation of methyl propanoate relative to the insertion of ethene leading to formation of oligomers or polymers in the catalytic reaction of ethene, carbon monoxide, and methanol.
Reaction of Cp*Ti{NC(Ar(F(2)))N(i)Pr(2)}Me(2) (1, Ar(F(2)) = 2,6-C(6)H(3)F(2)) with Ph(3)CB(C(6)F(5))(4) gave the base-free structurally authenticated dication ...Cp*(2)Ti(2){NC(Ar(F(2)))N(i)Pr(2)}(2)(mu-Me)(2)B(C(6)F(5))(4)(2) (3-BF(20)(2)) containing two doubly alpha-agostic bridging methyl groups. 3-BF(20)(2) is a highly effective ethylene-propylene polymerization catalyst at 90 degrees C, and its performance is identical to the catalyst generated in situ from 1 and Ph(3)CB(C(6)F(5))(4).
Ethylene polymerisation productivities of tris(pyrazolyl)methane-supported catalysts Ti(NR){HC(Me2pz)3}Cl2 show a dramatically different dependence on the imido R-group compared to those of their ...TACN analogues, attributed to differences in fac-N3 donor topology; when treated with AliBu3, the zwitterionic tris(pyrazolyl)methide compound Ti(N-2-C6H4tBu){C(Me2pz)3}Cl(THF) also acts as a highly active, single site catalyst (TACN = 1,4,7-trimethyltriazacyclononane).
One-pot reactions of V(NMe2)4 with a range of primary alkyl- and arylamines RNH2 and Me3SiCl afforded the corresponding five-coordinate vanadium(4+) imido compounds V(NR)Cl2(NHMe2)2 R = ...2,6-C6H3(i)Pr2 (1a, previously reported), 2-C6H4(t)Bu (1b), 2-C6H4CF3 (1c), (t)Bu (1d), Ad (Ad = adamantyl, 1e). The crystal structures of 1b (two diamorphic forms) and 1c featured N-H...Cl hydrogen-bonded chains. Reaction of 1a-e with the neutral face-capping, N3 donor ligands TACN (TACN = 1,4,7-trimethyltriazacyclononane) or TPM TPM = tris(3,5-dimethylpyrazolyl)methane gave the corresponding six-coordinate complexes V(NR)(TACN)Cl2 (2a-e) and V(NR)(TPM)Cl2 (3a-e). The X-ray structures of 2b, 2c, 2d, 3b, 3c, and 3e were determined. When activated with methylaluminoxane, certain of the complexes V(NR)(TPM)Cl2 (3) formed moderately active ethylene polymerization catalysts, whereas none of the compounds V(NR)(TACN)Cl2 (2) were active.
The square-planar bis(aquo) palladium(II) complexes Pd(H2O)2(dppf)(OTs)2 and Pd(H2O)2(dppomf)(OTs)2 are effective catalysts for the methoxycarbonylation of ethene, yet they exhibit quite different ...selectivity: the dppf-modified catalyst produces several low molecular weight oxygenates, spanning from methyl propanoate to alternating oligomers of carbon monoxide and ethene, while the dppomf catalyst yields exclusively methyl propanoate (dppf = 1,1‘-bis(diphenylphosphino)ferrocene; dppomf = 1,1‘-bis(diphenylphosphino)octamethylferrocene; OTs = p-toluenesulfonate). In an attempt to rationalize the different selectivities of the two catalytic systems, the methoxycarbonylation of ethene has been carried out under various experimental conditions in both autoclaves and high-pressure NMR tubes. Also, a number of model compounds have been synthesized with the aim of elucidating the structure of intermediate species observed by NMR during catalysis. Model reactions for the initiation, propagation, and chain-transfer steps in either alternating copolymerization or selective production of methyl propanoate have been performed. On the basis of all of these studies, it can be concluded that the behavior of the dppf precursor is similar to that of any other PdII catalyst modified with a chelating diphosphine. In particular, the formation of β-chelate intermediates from either Pd−H or Pd−OMe and their importance in controlling the perfect alternation of monomers have been experimentally demonstrated. The selective production of methyl propanoate with the use of the dppomf-modified catalyst has been attributed to the greater propensity of dppomf versus dppf to form PdII complexes with a dative Fe−Pd bond, which forces the P atoms to be trans to each other, yielding Pd-acyl species that do not react with ethene in MeOH. β-Chelate species are not formed by the dppomf-modified catalyst.
Alternating copolymerization of carbon monoxide with ethylene or 1-olefins in aqueous emulsion by water-insoluble palladium(II) complexes is reported. Latices of aliphatic polyketones (1-olefin/CO ...copolymers and ethylene/undec-10-enoic acid/CO terpolymers), prepared by catalytic polymerization, are described for the first time. An in situ catalyst system {R2P(CH2)3PR2}Pd(OAc)2/ strong acid (R = Ph or (CH2)13CH3) or well-defined complexes {Ph2P(CH2)3PPh2}PdMe(NCCH3)+Y- (Y- = B{3,5-(F3C)2C6H3}4- or SbF6 -) were used in the form of a solution of the palladium(II) complex in miniemulsion droplets of a hydrocarbon dispersed in the continuous aqueous phase. Catalyst activities of up to 5 × 103 TO h-1 slightly exceed those of nonaqueous polymerizations in methanol with the same catalysts. Polymer molecular weights (GPC vs PMMA standards) are typically M w 2 × 105 (ethylene copolymers) respectively M w 2 × 104 (1-olefin copolymers) with M w/M n 2−4. The 1-olefin copolymers exhibit glass transition temperatures of T g = +10 to −55 °C, which is in the range desirable for latex applications.
Methylpalladium chloride, cationic methyl- and acylpalladium triflate complexes were synthesised containing bis(dialkyl) and bis(diphenyl)phosphine ferrocene ligands.
Trans-coordinated cationic ...methylpalladium complexes containing 1,1′-bis(di-
tert-butylphosphino)ferrocene, form a palladiumiron bond. The less bulky 1,1′-bis(di-
iso-propylphosphino)ferrocene ligand coordinates in a
cis fashion in methylpalladium chloride complexes. A palladiumiron bond was indicated in the cationic acylpalladium complexes of both alkylphosphine ligands. 1,1′-Bis(diphenylphosphino)ferrocene does not form a palladiumiron bond in the monocationic acyl- and methylpalladium complexes. The complexes were characterised by
1H-,
31P-,
13C-NMR spectroscopy, elemental analysis, and UV–vis spectroscopy.
Synthesis and characterisation of (P–P)PdR(X) and (P–P)PdR(s)
+X
− complexes (P–P=bis(alkyl) or bis(diphenyl)phosphine ferrocene, R=CH
3 or C(O)CH
3, s=CH
3CN or Fe, X=Cl or CF
3SO
3). NMR spectroscopy and conductivity measurements provided evidence for the presence or absence of a palladium–iron interaction in these complexes. The structures of these complexes is mainly governed by the size of the alkyl substituents on phosphorus and the electron density at the palladium centre.
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