Cobalt Boryl Complexes: Enabling and Exploiting Migratory Insertion in Base‐Metal‐Mediated Borylation

Abstract

Cobalt boryl complexes, which have only been sporadically reported, can be accessed systematically with remarkable (but controllable) variation in the nature of the M-B bond. Complexes incorporating a very strong trans σ-donor display unparalleled inertness, reflected in retention of the M-B bond even in the presence of extremely strong acid. By contrast, the use of the strong π-acceptor CO in the trans position, results in significant Co-B elongation and to labilization of the boryl ligand via unprecedented CO migratory insertion. Such chemistry provides a pathway for the generation of coordinative unsaturation, thereby enabling ligand substitution and/or substrate assimilation. Alkene functionalization by boryl transfer, a well-known reaction for noble metals such as Rh or Pt, can thus be effected by an 18-electron base-metal complex.

Easy access to nucleophilic boron through diborane to magnesium boryl metathesis

“…Although this latter feature also ensures that the electropositive boron centre retains a significant partial positive charge (for 1 ; calculated natural population analysis charge on B=+0.072), these species behave as boron-centred nucleophiles by dint of a net polarization of the boron–lithium bond (in effect, B δ+ –Li δ++ ) induced by the even lower effective nuclear charge of lithium (for 1 ; calculated natural population analysis charge on Li=+0.755)913. Although a rich and varied chemistry has since arisen from the reactivity of compound 1 and related N- heterocyclic boryl anions with organic914, transition metal15161718 and main group electrophiles1419202122232425, alternative nucleophilic boron reagents remain very rare species262728293031. Notable exceptions are Braunschweig's dimetalloborylene and borolyl anions (for example, 2 and 3 )3233 Bertrand and Kinjo's carbene-stabilised monovalent boron species (for example, 4 )3435363738 and a remarkable tricyanoborandiyl dianion394041.…”

Synthesis of Acylborons by Ozonolysis of Alkenylboronates: Preparation of an Enantioenriched Amino Acid Acylboronate

“…There are only four known approaches for the preparation of acylborons (Scheme A). The first one is the reaction of a boryl metal species and a carbonyl electrophile, such as an acyl chloride (Scheme A a) –. In the second approach, acyl anion equivalents trap boryl electrophiles to afford acylborons (Scheme A b) .…”

“…In each of these three approaches, highly reactive and unstable nucleophiles, such as boryl metal species or organolithium compounds are required, and thus they exhibit low functional‐group tolerance. The only exception is the palladium‐catalyzed borylation reaction of acyl chlorides with a boryl‐zinc reagent as reported by Aldridge and co‐workers in 2015, although access to the boron species is challenging . Yudin and co‐workers developed a conceptually new acylboron synthesis involving Dess–Martin oxidation of α‐hydroxy boronate.…”

1,3,2‐Diazaborolyl Anions – From Laboratory Curiosities to Versatile Reagents in Synthesis

“…As the treatment of Na[Co(CO) 4 ] with organoboron halides R 2 BX invariantly furnished tricobaltmethylidyne clusters [{(CO) 3 Co} 3 C‐O‐BR] an alternative route to cobalt diazaborolyls had to be designed. Here alkoxycarbonyl cobalt complexes such as 126 were chosen as starting materials.…”