NDLI: Effect of ligand modification on the reactivity of phosphinoamide-bridged heterobimetallic Zr/Co complexes

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Krogman, Jeremy P. Thomas, Christine M. Saper, Noam I. Foxman, Bruce M. Zhou, Wen
Description	Author Affiliation: Zhou W ( Department of Chemistry, Brandeis University, 415 South Street MS 015, Waltham, MA, USA. thomasc@brandeis.edu.)
Abstract	The effect of modifying the N-aryl substituent (aryl = mesityl vs. m-xylyl) of the phosphinoamide ligands linking Zr and Co in tris(phosphinoamide)-linked heterobimetallic complexes has been investigated. Treatment of the metalloligand $(^{i}Pr_{2}PNXyl)_{3}ZrCl$ (2) (Xyl = m-xylyl) with $CoI_{2}$ affords the iodide-bridged product $ICo(^{i}Pr_{2}PNXyl)_{2}(μ-I)Zr(η^{2-i}Pr_{2}PNXyl)$ (3) rather than the $C_{3}-symmetric$ isomer observed using the N-mesityl derivative, $ICo(^{i}Pr_{2}PNMes)_{3}ZrCl.$ Upon two-electron reduction of complex 3, ligand rearrangement occurs to generate the three-fold symmetric reduced complex $N_{2}Co(^{i}Pr_{2}PNXyl)_{3}Zr(THF)$ (4). Comparison of 4 with the previously reported mesityl-substituted complex $N_{2}Co(^{i}Pr_{2}PNMes)_{3}Zr(THF)$ (1) reveals similar structural features but with a less sterically hindered Zr apical site in complex 4. An obvious electronic difference between these two complexes is also present based on the drastically different infrared $N_{2}$ stretching frequencies of 1 and 4. These notable differences lend themselves to different reactivity in both stoichiometric and catalytic reactions. Alkyl halide addition to complex 4 results in homo-coupling products resulting from alkyl radicals rather than the alkyl-bridged or intramolecular C–H activation products formed upon addition of RX to 1. This difference in reactivity with alkyl halides renders complex 3 a less effective catalyst for the Kumada cross-coupling of alkyl halides with n-octylMgBr than $ICo(^{i}Pr_{2}PNMes)_{3}ZrCl,$ as a greater proportion of homocoupling products are formed under catalytic conditions.
ISSN	14779226
Issue Number	5
Journal	Dalton Trans.
Volume Number	43
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2014-02-07
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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