Cobalt-catalysed acyl silane directed ortho C–H functionalisation of benzoyl silanes

Abstract

Despite their synthetic utility, practical and reliable methods to prepare diversely functionalized aromatic acyl silanes (benzoyl silanes) remain scarce. We herein report that cobalt complexes are able to successfully engage...

The Indenyl Effect: Accelerated C−H Amidation of Arenes via Ind*RhIII Nitrene Transfer Catalysis**

“…During related studies we observed that C−H functionalization reactions involving benzoyl silanes containing electron donating groups (e.g. methoxy substituents) were significantly faster and higher yielding than reactions employing neutral or electron deficient benzoyl silanes [12c,d] . This trend was also apparent during the early stages of this investigation for the [Cp*RhCl 2 ] 2 catalysed C−H amidation of 4‐methoxybenzoyl triethylsilane ( 3 e , 99 % yield), 4‐chlorobenzoyl triethylsilane ( 3 p , 36 % yield) and 4‐(trifluoromethoxy)benzoyl triethylsilane ( no reaction ) under identical conditions using 3‐(4‐fluorophenyl)‐1,4,2‐dioxazol‐5‐one.…”

“…Our investigations commenced with the optimisation of the reaction conditions for the Co III catalysed ortho C−H amidation using acyl silane ( 1 a ) and 3‐phenyl‐1,4,2‐dioxazol‐5‐one ( 2 a ) (see Table S1 in the Supporting Information for details) [15] . Despite extensive optimization, yields above 55 % were not achieved for these substrates under Cp*Co III catalysis [12d] . Other catalysts previously employed in inner sphere C−H amidation reactions with 1,4,2‐dioxazol‐5‐ones were explored, however no reaction occurred using either [Cp*IrCl 2 ] 2 or [( p ‐cym)RuCl 2 ] 2 .…”

“…As part of our ongoing interest in the application of acyl silane directing groups in C−H functionalization, [12a,c,d] we conducted a comprehensive study comparing the ability of Cp*CoI 2 (CO), [Cp*RhCl 2 ] 2 , [Cp Ar(CF3)2 RhCl 2 ] 2 and [Ind*RhCl 2 ] 2 to catalyse the acyl silane directed C−H amidation of benzoyl silanes. To achieve this, we subjected a variety of benzoyl silane and 1,4,2‐dioxazol‐5‐one derivatives to the optimised reaction conditions (Scheme 1).…”

“…[11] Acyl silanes can also be engaged as weakly‐coordinating directing groups in the presence of pentamethylcyclopentadienyl (Cp*) derived d 6 half‐sandwich complexes of Co III , Rh III , and Ir III to generate cyclometalated intermediates that react with various reagents to access functionalised benzoyl silanes (Figure 1). [12] Across many of these acyl silane directed C−H functionalization reactions it has been observed that transformations involving neutral or electron deficient benzoyl silanes are often slower and lower yielding than the corresponding reactions of benzoyl silanes containing electron donating groups [12c,d] …”