Bis [beta]-aminoketone complexes of zirconium and titanium and their catalytic applications
Creators: name: Roberts, Andrew Scott
Publisher: name: University Of Tasmania
Year: 2023

description: This thesis describes the synthesis and catalytic testing of new group(IV) transition metal complexes of zirconium and titanium with bidentate, chelate ˜í‚â§-aminoketone ligands (I). These complexes were prepared in order to develop catalysts active in the production of low molecular weight linear a-olefins containing greater than 95% oligomers in the range C4 to CIO. This goal was largely achieved by two catalyst systems with EASC as cocatalyst: (1) The disubstituted aminoketone adducts ZrC14.2R2Nacac, R = alkyl, aryl, gave product distributions with �-C10 approaching 98% and yields of up to 0.3 kg oligomers.g-1(ZrC14).hour-1 (TOF 2,500) and, (2) The aminostyrene substituted complex Zr(a-(CH2=CH)Ph-Nacac)2Cl2.(DCM) gave products with �-C10 greater than 93% and activities of up to 4.5 kg oligomers.g-1(ZrC14).hour-1 (TOF 38,000). The success of the adduct catalyst systems was attributed to the combination of electronegative chloride ligands, generating a highly Lewis acidic metal centre, with the sterically controlling aminoketone ligands. In contrast, complicated three way olefin-cocatalyst-metal interactions in the aminostyrene complex (generating an unusual or perhaps several, active species) were postulated as the cause for the outstanding performance of this catalyst. The catalytically important olefin substituted zirconium complexes (II) Zr(olefinNbzac)2Cl2, olefin= allyl, butenyl and Zr(a-(CH2=CH)PhNacac)2Cl2.(DCM) and the related phenyl substituted complex Zr(PhNbzac )2Cl2.1/2(DCM) were prepared by sodium salt elimination from the metal chloride and sodium ˜í‚â§-aminoketonate. The less thermally stable titanium complexes Ti(R-Nacac)2Cl2, R = Ph, p-MeOPh and allyl (II), were synthesised in the same manner, but could also be prepared from the bis ligand adducts and triethylamine, eliminating the hydrochloride salt HCLNE~. Crystal structures of Ti(p-MeOPhNacac)2Cl2 and TiC14.2R-NHacac, R = i-Pr, allyl, show these complexes to be isostructural with the analogous zirconium complexes. The titanium adducts and complexes were found to polymerise ethylene in low yields with a maximum activity of 0.65 kg product g-1(TiC14).hour-1 (TOF 4,400). The bis olefin-˜í‚â§-aminoketone alkyl complexes, Zr(olefinNacac)2BZ22, olefin = allyl, butenyl and pentenyl were prepared and characterised via in situ NMR experiments. Mono ligand alkyl complexes Zr(olefinNacac)Bz3 (Ill), olefin = allyl, butenyl, pentenyl, were also prepared in situ and characterised at 233K by NMR. Above this temperature the allyl and butenyl complexes underwent further reaction, best described as intramolecular olefin insertion, to give metallocyclic products (IV). In contrast, the mono ligand pentenyl complex disproportionated upon wanning to give the bis ligand complex and tetrabenzylzirconium. Both these processes occurred at ea 253K indicating very facile systems likely arising from the coordinative unsaturation of the mono ligand complexes and the !ability of the pendant olefin-amino functionalities. Tridentate ligand complexes 'Zr(Me2N(CH:J3N‚Äöv†¬©O)Bz3', N‚Äöv†¬©O = Nacac, Ndpvm, were prepared, isolating the Nacac complex as an unstable solid at room temperature, whilst observing the Ndpvm complex in an in situ NMR experiment up to 233K. At this temperature 'Zr(Me2N(CH2) 3Ndpvm)Bz3' displayed observable tridentate coordination, as evidenced by split dimethylamino methyl signals in the 1H-NMR spectrum. With warming of this complex past 233K further reaction occurred, eliminating toluene to give a complex with empirical formula determined by NMR as 'Zr(CH2N(Me)(CH2) 3Ndpvm)Bz2' (IV). This reaction was discussed in terms of previously described CH activation reactions. Subsequent preparation of this highly unstable complex verified these results, though its unstable nature did not permit full characterisation.