Reduction of Ta(DIPP)₂Cl·OEt₂(DIPP= 2,6-OC₆H₃ⁱPr₂) with 2 equiv. of NaHg in the presence of 3,5-lutidine results in cyclometalation of DIPP to give TaCl(DIPP)-(OC₆H₃ⁱPr-η²(C,C)-CMe =CH₂)(3,5-lutidine)₂ (10) in moderate yield. Metallacycle 10 was also isolated from the reaction of (η⁶-C₆Me₆)Ta(DIPP)₂Cl with 3,5-lutidine. Examination of both crude reaction mixtures by ¹H NMR revealed 10 to be the major product without any indication of the formation of η²-lutidine species. These observations suggest that η²(N,C)-coordination of 3,5-lutidine is kinetically incompetitive with respect to the cyclometalation of DIPP by d² tantalum. Such undesired reactivity of DIPP can be potentially inhibited by the use of linked aryloxide ligands to prevent close approach of metalatable C-H bonds of DIPP to the metal center. An efficient route to a family of silane-linked aryloxides was developed. Tris(2-hydroxy-3-isopropylphenyl)methylsilane (H₃TIPSI, 59), bis(2-hydroxy-3-isopropyl-phenyl)diphenylsilane (H₂BIPSI, 61), and bis(2-hydroxy-3-isopropylphenyl)dimethyl-silane (H₂BIPSI, 60) were obtained via deprotection of the parent silane-linked anisoles. The anisoles were prepared in high yields by treating 2-methoxy-3-isopropyl-phenyllithium·0.5TMEDA (27·0.5TMEDA) with an appropriate amount of chloroalkylsilanes. The deprotection was carried out employing BBr₃ in CH₂Cl₂ followed by hydrolysis of the intermediate boron ethers in the presence of a non-nucleophilic base to avoid protiodesilylation. Additionally, a significantly improved synthesis of 1,2-bis(3-isopropyl-2-hydroxyphenyl)ethane (H₂BIPP, 40) employing 27·0.5TMEDA as a starting reagent is reported. 2-Methoxyphenyllithium 27·0.5TMEDA was prepared via catalytic ortho-directed metalation of 2-isopropylanisole, and the mechanistic aspects of such metalations are presented. Trinuclear complex (AlBr₂)₃TIPSI (55) was isolated from the reaction of Me₃TISPI with 3 equiv. of AlBr₃ in benzene at 60°C. Preliminary reactivity studies show that Me₃TIPSI (49) and Me₂BIPSI (51) can be reacted with TaBr₅ under similar conditions to give Br₃Ta(MeTIPSI)(THF)₂ (62) and Br₃Ta(BIPP)OEt₂ (63), respectively, after appropriate reaction work ups.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/282749 |
| Date | January 1998 |
| Creators | Filippov, Igor, 1971- |
| Contributors | Wigley, David E. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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