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Calcium-Catalyzed Arene C-H Bond Activation by Low-Valent Al I

Calcium-Catalyzed Arene C-H Bond Activation by Low-Valent Al I

Steffen Brand, Holger Elsen, Jens Langer, Samuel Grams, Sjoerd Harder

Angew Chem Int Ed Engl. 2019 Oct 21;58(43):15496-15503.

PMID: 31465144

Abstract:

The low-valent ß-diketiminate complex (DIPP BDI)Al is stable in benzene but addition of catalytic quantities of [(DIPP BDI)CaH]2 at 20 °C led to (DIPP BDI)Al(Ph)H (DIPP BDI=CH[C(CH3 )N-DIPP]2 , DIPP=2,6-diisopropylphenyl). Similar Ca-catalyzed C-H bond activation is demonstrated for toluene or p-xylene. For toluene a remarkable selectivity for meta-functionalization has been observed. Reaction of (DIPP BDI)Al(m-tolyl)H with I2 gave m-tolyl iodide, H2 and (DIPP BDI)AlI2 which was recycled to (DIPP BDI)Al. Attempts to catalyze this reaction with Mg or Zn hydride catalysts failed. Instead, the highly stable complexes (DIPP BDI)Al(H)M(DIPP BDI) (M=Mg, Zn) were formed. DFT calculations on the Ca hydride catalyzed arene alumination suggest that a similar but more loosely bound complex is formed: (DIPP BDI)Al(H)Ca(DIPP BDI). This is in equilibrium with the hydride bridged complex (DIPP BDI)Al(μ-H)Ca(DIPP BDI) which shows strongly increased electron density at Al. The combination of Ca-arene bonding and a highly nucleophilic Al center are key to facile C-H bond activation.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP7784238	Aluminum iodide		7784-23-8	Price

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