Synthesis and Reactivity of Group 4 Metal Benzyl Complexes Supported by Carbazolide-Based PNP Pincer Ligands

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• 作者：Gudrun T. Plundrich ; Hubert Wadepohl ; Lutz H. Gade
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：January 4, 2016
• 年：2016
• 卷：55
• 期：1
• 页码：353-365
• 全文大小：846K
• ISSN：1520-510X

文摘

This study focuses on the viability of the carbazole-based Cbzdiphos PNP pincer ligand as a stabilizing element for group 4 metal complexes, and both the diphenylphosphino- and di-isopropylphosphino-substituted Cbzdiphos protioligands 1^PhH and 1^iPrH were used. Treatment of the lithiated protioligands with the corresponding chlorido precursor compounds of the metals (titanium, zirconium, and hafnium) afforded the trichlorido complexes [(Cbzdiphos^iPr)MCl₃] 2^iPrM and [(Cbzdiphos^Ph)MCl₃] 2^PhM (M = Ti, Zr, Hf), which were converted to the corresponding iodido complexes [(Cbzdiphos^iPr)MI₃] 3^iPrM and [(Cbzdiphos^Ph)MI₃] 3^PhM (M = Ti, Zr, Hf) by reaction with an excess of trimethylsilyl iodide. Reaction of 2^iPrTi and 3^PhTi with 1 equiv of dibenzyl magnesium tetrahydrofuran adduct led to the formation of the alkylidene complexes 4^iPrTi and 5^PhTi, respectively, while the zirconium and hafnium complexes 2^iPrZr and 3^PhZr/Hf formed the cyclometalated monoalkyl compounds [(Cbzdiphos^iPr-CH)ZrBnCl] 6^iPrZr as well as [(Cbzdiphos^Ph-CH)MBnX] 6^PhHf (X = Cl) and 7^PhZr/Hf (X = I) under analogous reaction conditions. On the other hand, stirring 2^PhZr with 0.25 equiv of tetrabenzyl zirconium afforded [(Cbzdiphos^Ph)ZrBnCl₂] (8^PhZr), which contained the PNP ligand intact, while its alkylation with benzyl potassium led to the formation of the cyclometalated monobenzyl complex [(Cbzdiphos^Ph-CH)ZrBnCl] (6^PhZr). The remaining coordination site occupied by the halogenido ligand in the cyclometalated monobenzyl complexes [(Cbzdiphos-CH)MBnX] 6^iPrZr, 6^PhZr/Hf, and 7^PhZr/Hf was readily benzylated by treatment with benzyl potassium to afford the cyclometalated dibenzyl complexes [(Cbzdiphos-CH)MBn₂] 9^iPrZr and 9^PhZr/Hf. Further reaction of 9^PhZr with an excess of benzyl potassium led to the formation of the anionic tribenzyl zirconium ate complex [(Cbzdiphos-CH)MBn₃]K (10^PhZr). Upon heating a solution of 8^PhZr in the presence of 1 mol equiv of trimethyl phosphine, one of the ligand methylene groups was deprotonated, yielding the cyclometalated complex [(Cbzdiphos^Ph-CH)ZrCl₂(PMe₃)] 11^PhZr. Finally, reaction of 7^PhZr with methylene triphenylphosphorane produced the ortho-metalated product [(Cbzdiphos^Ph-CH)Zr(o-C₆H₄PPh₂CH₂)I] (12^PhZr), which is characterized by a slightly puckered five-membered Zr–C(48)–P(3)–C(49)–C(50) metallacycle.