The synthesis of a rigid 4,5-bis(triphenylphosphinimino)-2,7-di-tert-butyl-9,9-dimethylxanthene (Ph3PN)2XT (1) ligand is outlined, along with a modified synthesis for previously reported 1,8-bis(triphenylphosphinimino)naphthalene (Ph3PN)2NAP (3). Reaction of neutral (Ph3PN)2XT with [Y(CH2SiMe3)3(THF)2] resulted in double cyclometallation, yielding the base-free monoalkyl complex, [({Ph2(C6H4)PN}2XT)Y(CH2SiMe3)] (2). Layering a concentrated THF solution of 2 with hexanes at −28 °C afforded THF-coordinated [({Ph2(C6H4)PN}2XT) Y(CH2SiMe3)(THF)]·2THF (2-THF·2THF), with a distorted pentagonal bipyramidal geometry and approximately meridional coordination of the pentadentate {Ph2(C6H4)PN}2XT dianion. Similarly, (Ph3PN)2NAP reacted with [Y(CH2SiMe3)3(THF)2] to afford a THF-coordinated monoalkyl complex, [{(Ph2(C6H4)PN)2NAP}Y(CH2SiMe3)(THF)] (4-THF). Layering a DME solution of 4-THF with hexanes at −28 °C afforded X-ray quality crystals of [{(Ph2(C6H4)PN)2NAP}Y(CH2SiMe3)(κ2-DME)]·hexane (4-DME·hexane), with a highly distorted pentagonal bipyramidal geometry and a facial coordination mode of the tetradentate {Ph2(C6H4)PN}2NAP dianion
The synthesis of a rigid 4,5-bis(1,3-diisopropylimidazol-2-imine)-2,7,9,9-tetramethylacridan H(AII2) ligand (5) was achieved via a Buchwald-Hartwig cross-coupling reaction. Reaction of the proligand H(AII2) with [M(CH2SiMe3)3(THF)2] (M = Y(6), Sc(8)) yielded the base free dialkyl complexes [(AII2)Y(CH2SiMe3)2] (6) and [(AII2)Sc(CH2SiMe3)2] (8). The reaction of 6 with one equivalent of [CPh3][B(C6F5)4] yielded [(AII2)Y(CH2SiMe3)][B(C6F5)4] (7) in-situ. Complex 7 proved to be a potent intramolecular hydroamination catalyst for a variety of aminoalkane substrates.
The attempted synthesis of 4,5-bis(1,3-diisopropylimidazol-2-imine)-2,7-di-tert-butyl-9,9-dimethylxanthene (XII2) via the Staudinger reaction resulted in the isolation of the triazene intermediate 4,5-bis(1,3-diisopropylimidazol-2-yliedene{triazene})-2,7-di-tert-butyl-9,9-dimethylxanthene XIA2 (9). Reaction of XIA2 with one equivalent of [Y(CH2SiMe3)3(THF)2] led to the isolation of [(XIA2)Y(CH2SiMe3)3] (10). Synthesis of XII2 (11) was achieved via a Buchwald-Hartwig cross-coupling reaction. Reaction of XII2 with one equivalent of YCl3(THF)3.5 resulted in the isolation of [(XII2)YCl3] (12). In contrast, the reaction of XII2 with one equivalent of [Y(CH2SiMe3)3(THF)2] led to several unidentified products. Reaction of XII2 with 1 equivalent of [H(Et2O)2][B(C6F5)4] led to the isolation of the precursor [H(XII)2][B(C6F5)4] (13). The reaction of 13 with 1.1 equivalents of [M(CH2SiMe3)3(THF)2] (M = {Y(14), Sc(15)} led to the isolation of the monocationic [(XII)2M(CH2SiMe3)2][B(C6F5)4] complexes. The reaction of [(XII)2Sc(CH2SiMe3)2][B(C6F5)4] with 1.1 equivalents of B(C6F5)3 led to the abstraction of a methyl anion from the silicon center, with concomitant migration of the remaining alkyl group to the positively charged silicon, forming a new CH2SiMe2CH2SiMe3 alkyl group. This process is accompanied by MeB(C6F5)3 anion formation, forming a contact ion pair to afford the dicationic species [(XII)2Sc(CH2SiMe3)][MeB(C6F5)3][B(C6F5)4] 16. In contrast, the reaction of 15 with 1.3 equivalents of [CPh3][B(C6F5)4] in the presence of 5 equivalents of toluene resulted in the synthesis of [(XII)2Sc(CH2SiMe3)(ɳx-toluene)][B(C6F5)4]2 17 in-situ. Complex 17 is a highly potent ethylene polymerization catalyst with an activity of 868 kg/mol·atm·h. The reaction of 15 with [HNMe2Ph][B(C6F5)4] led to the cyclometallation of the resulting NMe2Ph byproduct to yield [(XII2)Sc(C6H4NMe2)][B(C6F5)4]2 (18) in-situ.
The synthesis of a rigid, asymmetric 4-(1,3-diisopropylimidazol-2-imine)-5-(2,6-diisopropylanilido)- 2,7-di-tert-butyl-9,9-dimethylxanthene XAI (19) ligand was achieved by a two step Buchwald-Hartwig cross-coupling reaction with initial cross coupling of 1,3-diisopropylimidazol-2-imine followed by the cross-coupling of 2,6-diisoproylaniline. The reaction of XAI with 1.1 equivalents of [Y(CH2SiMe3)3(THF)2] yielded [(XAI)Y(CH2SiMe3)2] (20). Subsequent reaction of [(XAI)Y(CH2SiMe3)2] with 1 equivalent of [CPh3][B(C6F5)4] in the presence of 10 equivalents of toluene resulted in the synthesis of the toluene coordinated [(XAI)Y(CH2SiMe3)(ɳx-toluene)][B(C6F5)4] (21) complex. Similar to 7, complex 21 was highly active for intramolecular hydroamination of various substrates. / Dissertation / Doctor of Philosophy (PhD) / Cationic group 3 alkyl complexes are underreported in comparison to analogous group 4 complexes. The scarcity of these complexes can be attributed to their propensity to engage in undesirable reactions such as ligand redistribution and cyclometallation. To increase the thermal stability of such complexes, design features, such as carefully positioned steric bulk and ligand rigidity are beneficial. Additionally, such ligands must also have considerable donor ability, in order to stabilize inherently electron deficient cationic metal centers. This work details the synthesis of a variety of neutral and monoanionic ligands that incorporate the aforementioned design features, which were utilized in the successful synthesis of a variety of neutral, monocationic and extremely rare dicationic group 3 alkyl complexes. The cationic monoalkyl complex in this work proved to be a highly potent intramolecular hydroamination catalyst. Furthermore, a rare dicationic scandium complex was highly active for ethylene polymerization
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/26032 |
| Date | January 2020 |
| Creators | Vasanthakumar, Aathith |
| Contributors | Emslie, David, Chemistry |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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