Bulky N-Substituted 1,3-Benzazaphospholes: Access via Pd-Catalyzed C−N and C−P Cross Coupling, Lithiation, and Conversion to Novel PC−PtBu2 Hybrid Li

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• 作者：Bhaskar Reddy Aluri ; Markus K. Kindermann ; Peter G. Jones ; Ina Dix ; Joachim Heinicke
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：August 4, 2008
• 年：2008
• 卷：47
• 期：15
• 页码：6900-6912
• 全文大小：305K
• 年卷期：v.47,no.15(August 4, 2008)
• ISSN：1520-510X

文摘

The syntheses of novel bulky N-substituted 1,3-benzazaphospholes are presented, together with their reactions with tert-butyllithium and coupling with tBu₂PCl to novel P,P′-hybrid ligands that combine the highly basic and bulky di-tert-butylphosphanyl group with π-acidic low-coordinated phosphorus. The syntheses start with the preparation of new N-secondary 2-bromoanilines 1 by reduction of N-acyl 2-bromoanilides or more generally by Pd-catalyzed selective monoamination of o-dibromobenzene, followed by Pd-catalyzed C−P coupling with P(OEt)₃ to the respective 2-anilino-phosphonates 2. The next steps are reduction to 2-phosphanylanilines 3 and condensation with Me₂NCH(OMe)₂, which leads via phosphaalkenes 4 to the corresponding N-substituted benzazaphospholes 5. The reaction with tBuLi depends on the steric demand of the N substituent. Methyl, neopentyl-, and mesityl-derivatives were converted to PC Li species 6 and coupled with tBu₂PCl to novel PC−PtBu₂ ligands 7, whereas N-adamantyl and N-2,6-diisopropylphenyl-derivatives prefer addition of tBuLi at the PC bond to form dihydroderivatives. The chemical shifts of the low-coordinated phosphorus of 5 and 7 were found to reflect electronic and steric effects of the N substituents. The comparison of the crystal structures of N-neopentyl-1,3-benzazaphospholes 5 and 7 gives evidence of steric repulsion between the adjacent di-tert-butyl and neopentyl groups by the preferred anti orientation of the P-tert-butyl groups and moderate deviations of C2 and P3 of 7b from the ring plane.