Are there any examples of activating meta directors?

I have heard about activating ortho-para directors. For example: methoxy group, hydroxy group, alkyl group, et cetera.

I have heard about deactivating ortho-para directors. For example: halogen substituents

I have heard about deactivating meta directors. For example: nitro, trifluromethyl group, carboxylic acid group, et cetera.

So, naturally, I have embarked on a quest to find Activating Meta directors.

I have found one potential candidate, which is dimethylphenylborane:

Boron possesses a vacant $\mathrm{p}_z$ orbital, which can interact with the $\pi$-cloud of the benzene ring.

Considering the fact that boron is treated as a metalloid, it will definitely be less electronegative than carbon, so the dimethylborane group should offer a good +I effect, which could possibly outweigh the -M effects.

Can anyone shed some light on this issue? Are there any other examples of activating meta directors?

• – jerepierre Jun 30 '17 at 7:11
• You're talking about for EAS? – Zhe Aug 14 '17 at 14:48
• OK. Got it. So what makes you think this is a +I effect? For example. how is having a borane on the ring any different from having a carbonyl attached to the ring? – Zhe Aug 14 '17 at 18:06
• Screwed up the first response I was trying to write... I think this is an interesting idea. You might even consider other substituents instead of methyl on the borane. – Zhe Aug 15 '17 at 2:09
• This is very theoretical, but what if you added a subtituent such as orthonitrate so that the formula is Na2O3NPh, basically a nitrogen attached to a phenyl with 3 oxygens single bonded to it. The meta directing would be done similar to the nitro group, due to recent evidence pointing towards the pentavalent nitrogen structure being a part of resonance, and then the carbon gains electron density because of the pentavalent structure being in resonance with the traditional structure (following octet rule). – AS_1000 Aug 17 '17 at 13:50