Abstract
The square-planar monohydride complex RhH{xant(PiPr2)2} (1; xant(PiPr2)2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) activates C–H bonds of arenes. Heating of benzene solutions of 1 at 80 °C affords RhPh{xant(PiPr2)2} (2). Under the same conditions, toluene gives Rh(m-tolyl){xant(PiPr2)2} (3a) and Rh(p-tolyl){xant(PiPr2)2} (3b) in a 78:22 molar ratio, whereas m-xylene leads to Rh(C6H3-3,5-Me2){xant(PiPr2)2} (4). At room temperature, fluorobenzene and 1,3-difluorobenzene generate Rh(C6H4-2-F){xant(PiPr2)2} (5) and Rh(C6H3-2,6-F2){xant(PiPr2)2} (6), respectively. Complex 1 also promotes the B–H bond activation of pinacolborane (HBpin) and catecholborane (HBcat). The reactions initially give the trans-dihydride derivatives RhH2(BR2){xant(PiPr2)2} (BR2 = Bpin (7), Bcat (8)), which lose H2 to afford the square-planar Rh(BR2){xant(PiPr2)2} (BR2 = Bpin (9), Bcat (10)). Complex 2 reacts with HBpin to regenerate 1 and to give Ph-Bpin. Similarly, complex 9 regenerates 1 and gives Ph-Bpin by reaction with ...
Highlights
C−H bond functionalization reduces the production of toxic byproducts thereby contributing to the growing field of reactions with decreased environmental impact.[1]
This paper reports the C−H bond activation of arenes, the B−H bond activation of boranes, and the stoichiometric and catalytic formation of aryl boronate esters promoted by the square-planar rhodium monohydride
The reactions lead to aryl−rhodium(I) complexes and release molecular hydrogen
Summary
C−H bond functionalization reduces the production of toxic byproducts thereby contributing to the growing field of reactions with decreased environmental impact.[1] One of the most efficient reactions is the direct borylation of hydrocarbons, which represents a powerful tool for the functionalization of feedstocks,[2] in combination with cross-coupling methodologies or specific transformations developed for organoboranes.[3]. The borylation of arenes without the need for directing groups is a challenge in the field of C−H bond functionalization because it provides products with complementary regioselectivity, which appears to be determined by steric factors.[4] In this context, significant progress is being made by using iron,[5] cobalt,[6] rhodium,[7] and iridium[8] catalysts with bispinacolborane (B2pin2) and pinacolborane (HBpin). The study of these elemental steps is of great interest
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