- Efficient synthesis of aluminium-terminated polyethylene by means of irreversible coordinative chain-transfer polymerisation using a guanidinatotitanium catalyst
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A series of guanidinato-ligand-stabilised titanium complexes has been synthesised and characterised. These compounds can be prepared by carbodiimide insertion into titanium-amide bonds. Reaction of carbodiimides N,N′-bis(2,6-diisopropylphenyl)carbodiimide, N,N′-bis(2,6-dimethylphenyl)carbodiimide and N-tert-butyl-N′-(2,6-diisopropylphenyl)carbodiimide (2a-2c, respectively) with [(Et2N)TiCl3] led to mono(guanidinato)trichloridotitanium(IV) complexes (3a-3c). Subsequent conversion with methylmagnesium chloride gave the corresponding trimethyl complexes (4a and 4b). Single-crystal X-ray diffraction analyses were carried out for all complexes. Compound 4a showed very high activities in the polymerisation of ethylene in the presence of very high amounts of triethylaluminium and undergoes polymeryl chain transfer to aluminium. Irreversible coordinative chain-transfer polymerisation and a unique combination of catalyst economy and high activity were observed. In the presence of 1000 equivalents of aluminium, a chain elongation of 83.3 % could be achieved with an activity of 9900 kgPE molcat-1 h-1 bar-1. The influence of the steric demand of the ligand on the polymerisation capability is significant and was investigated too. A series of novel mono(guanidinato)titanium(IV) complexes has been synthesised and characterised. Single-crystal analyses were performed for all complexes. Compound 4a showed very high activities in the polymerisation of ethylene in the presence of very high amounts of aluminium after activation with fluorinated borates. Irreversible coordinative chain transfer to aluminium was observed.
- Obenauf, Johannes,Kretschmer, Winfried P.,Kempe, Rhett
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p. 1446 - 1453
(2015/04/27)
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- Efficient synthesis of aluminium-terminated polyethylene by means of irreversible coordinative chain-transfer polymerisation using a guanidinatotitanium catalyst
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A series of guanidinato-ligand-stabilised titanium complexes has been synthesised and characterised. These compounds can be prepared by carbodiimide insertion into titanium-amide bonds. Reaction of carbodiimides N,N′-bis(2,6-diisopropylphenyl)carbodiimide, N,N′-bis(2,6- dimethylphenyl)carbodiimide and N-tert-butyl-N′-(2,6-diisopropylphenyl) carbodiimide (2a-2c, respectively) with [(Et2N)TiCl3] led to mono(guanidinato)trichloridotitanium(IV) complexes (3a-3c). Subsequent conversion with methylmagnesium chloride gave the corresponding trimethyl complexes (4a and 4b). Single-crystal X-ray diffraction analyses were carried out for all complexes. Compound 4a showed very high activities in the polymerisation of ethylene in the presence of very high amounts of triethylaluminium and undergoes polymeryl chain transfer to aluminium. Irreversible coordinative chain-transfer polymerisation and a unique combination of catalyst economy and high activity were observed. In the presence of 1000 equivalents of aluminium, a chain elongation of 83.3 % could be achieved with an activity of 9900 kgPE molcat-1 h-1 bar-1. The influence of the steric demand of the ligand on the polymerisation capability is significant and was investigated too. A series of novel mono(guanidinato)titanium(IV) complexes has been synthesised and characterised. Single-crystal analyses were performed for all complexes. Compound 4a showed very high activities in the polymerisation of ethylene in the presence of very high amounts of aluminium after activation with fluorinated borates. Irreversible coordinative chain transfer to aluminium was observed. Copyright
- Obenauf, Johannes,Kretschmer, Winfried P.,Kempe, Rhett
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p. 1446 - 1453
(2014/04/03)
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- Syntheses and15N NMR Spectra of Iminodiaziridines - Ring-Expansions of 1-Aryl-3-iminodiaziridines to 1H- and 3aH-Benzimidazoles, 2H-Indazoles, and 5H-Dibenzo[d,f] [1,3]diazepines
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Iminodiaziridines are synthesized, by (i) 1,3-dehydrochlorination with potassium, teri-butoxide of N-chloroguanidines, generated in situ from. N,N′,N″-substituted guanidines with tert-butyl hypochlorite, and (ii) base-mediated 1,3-elimination of sulfuric acid from N,N',N″- substituted hydroxyguanidine O-sulfonic acids. At elevated temperatures, (alkylimino)diaziridines undergo valence isomerization by 1,3shift, [2+1] cycloelimination to afford isocyanides and diazenes, and ring-opening elimination to yield alkylideneguanidines. N′-Aryl-N-hydroxyguanidine O-sulfonic acids furnish (N-arylimino)diaziridines, but no 1-aryl-3- iminodiaziridines, instead giving rearranged isomere. Precursors containing perdeuterated feri-butyl groups give rearranged products that show complete scrambling. This indicates that l-aryl-3iminodiaziridines are intermediates that undergo very rapid I degenerate valence isomerization. Provided that the ortho aryl positions are substituted, high yields of (arylimino)diaziridines are obtained, along with 2-imino-2,3-dihydro-3aHbenzimidazoles, Otherwise, 2-amino-lH-benzimidazoles and strongly fluorescent 3-amino-2H-indazoles, originating from rearrangements of the elusive l-aryl-3-iminodiaziridines, predominate. N',N″-Diaryl-N-hydroxyguanidine O-sulfonic acids give only rearranged products: a 2-amino-1H-benzimidazole and a 6-amino-5H-dibenzo[d,f][1. 3]diazepine if aryl = phenyl, or a 2-imino-2,3-dihydro-3aH-benzimidazole if aryl = mesityl. 3aH-Benzimidazoles slowly dimerize through Diels-Alder reactions. 15N NMR signals were assigned, to the syn and anti ring nitrogen atoms of iminodiaziridines with the help of a combination of homonuclear NOE and HNHMBC or HN-gHMBC experiments.
- Quast, Helmut,Ross, Karl-Heinz,Philipp, Gottfried,Hagedorn, Manfred,Hahn, Harald,Banert, Klaus
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supporting information; experimental part
p. 3940 - 3952
(2010/03/01)
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- Oxo and imido/imido exchange and C-H activation reactions based on pentamethylcylopentadienyl imido tantalum complexes
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Reactions of [TaCp*Cl4] with two, three and four equivalents of LiNHtBu give the halo- and amido-imido complexes [TaCp*Cl2(NtBu)] (1a), [TaCp*Cl(NtBu)(NHtBu)] (2) and [TaCp*(NtBu)(NHtBu)2] (3), respectively. The related complex [TaCp*Cl2{N(2,6-Me2C6H3)}] (1b) is prepared by a similar reaction using two equivalents of Li[NH(2,6-Me2C6H3)]. Complex 3 can be transformed into 2 and further into 1a by reaction with SiClMe3. Complex 1a reacts with CNtBu to give the 18-electron adduct [TaCp*Cl2(NtBu)(CNtBu)] (4) whereas addition of excess CN(2,6-Me2C6H3) results in reductive elimination of the carbodiimide tBuN=C=N(2,6-Me2C6H3) (5) to give [TaCp*Cl2{CN(2,6-Me2C6H 3)}3]. However complex 1b does not react with any of the isocyanide ligands. Both complexes 1a and 1b react with PhCHO undergoing imido/oxo exchange to give the imines PhCH=NR (R=tBu, 2,6-Me2C6H3 (6)) and dimeric [TaCp*Cl2(O)]2 or trimeric [(TaCp*Cl)3(μ2-Cl)(μ2-O) 3(μ3-O)] oxo-complexes, whereas only 1a reacts with CO2, PhCH=NR′ (R′=Ph, Me) and (2,6-Me2C6H3)N=C=NtBu producing tBuN=CO, PhCH=NtBu and tBuN=C=NtBu, respectively and the corresponding oxo or imido tantalum derivative. None of the complexes reacts with CO or NCR (R=Me, Ph). The complex [TaCp*Me(NtBu)(NHtBu)] activates C-H bonds when heated in benzene and toluene affording [TaCp*Ph(NtBu)(NHtBu)] (7) and a mixture of [TaCp*(m-MeC6H4)(NtBu)(NHtBu)] 8a and [TaCp*(p-MeC6H4)(NtBu)(NHtBu)] (8b). All of the reported organic compounds and tantalum complexes were characterized by 1H- and 13C-NMR spectroscopy.
- Royo, Pascual,Sánchez-Nieves, Javier
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- Cycloaddition of N-Aryl-tert-butylketenimines to Both Nitrosobenzene and 2-Methyl-2-nitrosopropane
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Reactions of the ketenimines 1a, b with nitrosobenzene (2a) do not give the appropriate 1,2-oxazetidines such as 3Aa,b, but produce small amounts of the benzoxazoles 4a, b and the 1,4-benzoxazines 5Aa, b.However, from 1a-c and the nitrosoalkane 2b the analogous compounds 5Ba-c and/or 3Ba-c are formed (depending on conditions); mixtures of 1d-f and 2b afford 3Bd-f only.The heterocycles 4 and 5 are believed to arise through the intermediary cycloadduct 14/14'.
- Moderhack, Dietrich,Stolz, Karsten
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p. 3411 - 3421
(2007/10/02)
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