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DC Field | Value | Language |
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dc.contributor.advisor | Emslie, David | - |
dc.contributor.author | Motolko, Kelly | - |
dc.date.accessioned | 2017-10-05T12:56:20Z | - |
dc.date.available | 2017-10-05T12:56:20Z | - |
dc.date.issued | 2017-11 | - |
dc.identifier.uri | http://hdl.handle.net/11375/22085 | - |
dc.description.abstract | The synthesis and electropositive metal (Y, Lu, La, Zr, Hf) chemistry of two rigid dianionic xanthene-based ligands, 4,5-bis(2,4,6-triisopropylanilido)- -2,7-di-tert-butyl-9,9-dimethylxanthene (XN2) and 4,5-bis(2,4,6-triisopropylphenylphosphido)- 2,7-di-tert-butyl-9,9-dimethylxanthene (XP2) have been explored. The reaction of the pro-ligand H2XN2 with [Y(CH2SiMe2R)3(THF)2] (R = Me or Ph) produced the monoalkyl yttrium complexes [(XN2)Y(CH2SiMe3)- (THF)].(O(SiMe3)2)x (3, x = 1-1.5) and [(XN2)Y(CH2SiMe2Ph)(THF)].(O- (SiMe3)2) (4). Neutral 3 reacted with excess AlMe3 to yield [(XN2)Y{(m- Me)2AlMe2}(THF)].O(SiMe3)2 (5.O(SiMe3)2), which is thermally robust, and transfer of the XN2 ligand to aluminum was not observed. However, [(XN2)- AlMe].(O(SiMe3)2)0.5 (6.(O(SiMe3)2)0.5) was synthesized via the reaction of H2XN2 with AlMe3. Compounds 3, 5 and 6 were characterized by X-ray crystallography, and neutral 3, while being poorly active for ethylene polymerization, was highly active for both intra- and inter-molecular hydroamination with a variety of substrates. The synthesis of the pro-ligand H2XP2 was achieved via reduction of 4,5-bis(2,4,6-triisopropylphenylchlorophosphino)-2,7-di-tert-butyl-9,9-dimethylxanthene (XP2Cl2; 7). Double deprotonation of H2XP2 (8) with excess KH yielded the potassium salt, [K2XP2(DME)2.5] (9), which when stirred in THF followed by recrystallization from hexanes, produced the tetrametallic complex, [K4(XP2)2(THF)4] (10) featuring a central K4P4 cage. The reaction of [K2XP2(DME)2.5] (9) with [YI3(THF)3.5] yielded a mixture of products including [(XP2)YI(THF)2] (11) and tris(2,4,6-triisopropylphenylphosphinidene) (P3Tripp3); pure 11 could be isolated in low yield by extraction with a minimum volume of hexanes or O(SiMe3)2. In the solid state, complex 11 reveals a face-capped trigonal bipyramidal geometry at yttrium, in which the xanthene backbone is planar and adopts a large angle (85 degrees) between the P(1)/C(4)/C(5)/P(2) and P(1)/Y/P(2) planes. Due to the successful synthesis and hydroamination catalysis achieved with the XN2 ligand in combination with yttrium, the chemistry of XN2 was further explored using both smaller (Lu) and larger (La) rare earth elements. The alkane elimination reaction of H2XN2 with [Lu(CH2SiMe3)3(THF)2], followed by crystallization from O(SiMe3)2, yielded [(XN2)Lu(CH2SiMe3)(THF)].(O- (SiMe3)2)1.5 (12.(O(SiMe3)2)1.5). By contrast, lanthanum complexes of the XN2 dianion were prepared by salt metathesis; treatment of H2XN2 with excess KH in DME produced the dipotassium salt, [K2(XN2)(DME)x] (2; x = 2-2.5), and subsequent reaction with [LaCl3(THF)3] afforded [{(XN2)LaCl- (THF)}x].(O(SiMe3)2)0.25x (13.(O(SiMe3)2)0.25x; x = 1 or 2) after crystallization from O(SiMe3)2. Compound 13.(O(SiMe3)2)0.25x reacted with two equivalents of LiCH2SiMe3, to form the dialkyl-`ate' complex, [Li(THF)x][(XN2)- La(CH2SiMe3)2].Toluene.LiCl (14.Toluene.LiCl; x = 3). Both 12 and 14 (x = 4) were structurally characterized by X-ray crystallography, and were evaluated as catalysts for intramolecular hydroamination. While compound 14 showed poor activity, the neutral lutetium alkyl complex, 12, is highly active for both intramolecular hydroamination and more challenging intermolecular hydroamination. Like the yttrium analogue, 3, reactions with unsymmetrical alkenes yielded Markovnikov products. Additionally, it is noteworthy that the activity of 12 surpassed that of 3 in the reaction of diphenylacetylene with 4-tert-butylbenzylamine. The reaction of H2XN2 with [Zr(NMe2)4], followed by crystallization from O(SiMe3)2, yielded [(XN2)Zr(NMe2)2].(O(SiMe3)2)0.5 (15.(O(SiMe3)2)0.5). The zirconium dimethyl complex [(XN2)ZrMe2] (16) was accessed via two routes; either by treatment of 15.(O(SiMe3)2)0.5 with excess AlMe3, or by reaction of 15.(O(SiMe3)2)0.5 with excess Me3SiCl, affording [(XN2)ZrCl2] (17), followed by the subsequent reaction of 17 with 2 equivalents of MeLi. The reaction of 16 with one equivalent of B(C6F5)3 or [CPh3][B(C6F5)4] yielded cationic [(XN2)- ZrMe][MeB(C6F5)3] (18) and [(XN2)ZrMe(arene)][B(C6F5)4] (19; arene = n6-benzene, n6-toluene or bromobenzene), respectively. Both 18 and 19 are active for ethylene polymerization under 1 atm of ethylene at 24 and 80 degree Celcius in toluene, with activities ranging from 23.5{883 kg/(mol.atm.h), yielding polymers with weight average molecular weights (Mw) of 71{88 kg/mol and polydispersities (Mw/Mn) of 3.94-4.67. | en_US |
dc.language.iso | en | en_US |
dc.subject | organometallic, rigid ligands, rare earth, group 4 transition metal, hydroamination, ethylene polymerization | en_US |
dc.title | Rare Earth and Group 4 Transition Metal Complexes of Rigid Dianionic Pincer Ligands | en_US |
dc.title.alternative | Early Metal Complexes of Rigid Dianionic Ligands | en_US |
dc.type | Thesis | en_US |
dc.contributor.department | Chemistry | en_US |
dc.description.degreetype | Thesis | en_US |
dc.description.degree | Doctor of Philosophy (PhD) | en_US |
dc.description.layabstract | Pincer ligands are defined as meridionally-coordinating tridentate ligands, and are typically mono-, di- or tri-anionic. This thesis is focused on the synthesis and reactivity of rigid dianionic pincer ligands with an NON- or POP-donor array, with particular emphasis on rare earth and group 4 transition metal complexes. This work explores the effect that these rigid ligands have on the reactivity of the resulting metal complexes and the thermal stability of the solid state structures. Both neutral and cationic mono alkyl complexes have been isolated, and several are highly active catalysts for intra- and intermolecular hydroamination or ethylene polymerization. | en_US |
Appears in Collections: | Open Access Dissertations and Theses |
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Motolko_Kelly_SA_2017August_PhD.pdf | 15.37 MB | Adobe PDF | View/Open |
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