[blaisem]

Under properties of the B-C bond,

https://en.wikipedia.org/wiki/Organoboron_chemistry#Properties_of_the_B-C_bond

Boron is described as being relatively electropositive and thus correspondingly more susceptible to oxidation.

In the next paragraph, it labels Boron as an electrophile. Wouldn't an electrophile wish to keep electrons?

I am trying to understand this in the context of a Suzuki coupling, where I have a pinacol boronic ester attached to a pyridine and want to understand how the Boron activates/deactivates the pyridine (am having trouble with the side reaction where the pyridine adds oxidatively to palladium as the pyridine is mono-substituted with bromine).

Thanks for any advice!

[mjc123]

First, the remarks are made, not about boron itself, but boron compounds or (boron in a compound). For example, alkylboranes are said to be susceptible to oxidation. As B is more electropositive than C, in an oxidation reaction like R₃B  (RO)₃B it is formally C, not B, that undergoes an increase in oxidation number. (The mechanism involves transfer of R^- from B to O, so the electropositivity of B favours this.)
Boron has 3 valence electrons, therefore tends to form compounds with an incomplete octet. This is the reason for B compounds undergoing electrophilic reactions, as the octet can be made up by donation of a lone pair from a Lewis base into the empty orbital on B, e.g. BF₃ + F^-  BF₄^-. But this can be reversed; tetrafluoroborates can often be heated to give the fluoride and BF₃. Whereas you wouldn't get CF₄ giving CF₃⁺ + F^-, because CF₃⁺ isn't a stable compound.
You can also get dative delocalisation, e.g. >N:-B<  >N⁺=B^-<. Note that this puts a negative charge on B, though it is electropositive. This is the reverse of the familiar phenomenon that O or Cl is inductively electron-withdrawing but mesomerically electron-donating. In principle this could happen on pyridine, deactivating it to electrophilic attack, though I'm not sure from your description whether B is directly attached to pyridine, and if so whether as a C substituent or an N adduct.