Oxidative addition B2pin2 activation

Scheme 5 Activation modes for B2pin2- (A) Activation by oxidative addition, (B) activation by o-bond metathesis, and (C) activation by Lewis bases.

The direct borylation of arenes was catalyzed by iridium complexes [61-63]. Iridium complex generated from [lrCl(cod)]2 and 2,2 -bipyridine (bpy) showed the high catalytic activity of the reaction of bis (pinaco la to) diboron (B2Pin2) 138 with benzene 139 to afford phenylborane 140 (Equation 10.36) [61]. Various arenes and heteroarenes are allowed to react with B2Pin2 and pinacolborane (HBpin) in the presence of [lrCl(cod)]2/bipyridne or [lr(OMe)(cod)]2/bipyridine to produce corresponding aryl- and heteroarylboron compounds [62]. The reaction is considered to proceed via the formation of a tris(boryl)iridium(lll) species and its oxidative addition to an aromahc C—H bond. 

ReCp(CO)2(H)(MR3) and ReCp(CO)2H2 are the products of photoinduced oxidative addition of (89) to H MR3 bonds (M = Si, Ge, Sn) (see Section 8.1.5). Photochemical activation of (89) or (90) in the presence of B2pin2 gave cis and /ran5 -ReCp (CO)2(Bpin)2, that is, oxidative addition to the B-B bond. Most remarkable, however, is the fact that further irradiation of this compound or of a mixture of (90) and B2pin2 in pentane led to regiospecific terminal C-H activation of the pentane with formation of CsHnBpin and HBpin. The mechanism of this elegant C H activation process does not seem to take place via C H activation on intermediate ReCp (CO)2.i ... 

Bis(pinacolato)diboron and bis(neopentyl glycolato)diboron have been added to a,P-unsaturated ketones, esters, nitriles, and aldehydes through [RhCl(PPh3)3] activation, presumably via oxidative addition. However, Nishiyama has suggested a bond metathesis step to form Rh(III)-boryl species, from B2pin2 and [Rh(III)(OAc)2(OH)(Phebox)] complex, which... 

Commercially available and inexpensive y-Fe203 magnetic nanoparticles (particle size 58 nm) also efficiently activate B2pin2 and promote a direct borylation of alkenes. " The mechanism of this unusual nano-Fc203-catalyzed aromatic borylation reaction is not clear. The kinetic isotope effect was measured to be 1.3, indicating that a C—H bond activation by oxidative addition to the iron catalyst is not likely. An electrophUic metalation by Fe—B species, followed by reductive ehmination, seems conceivable. 

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