What you said
Can he not sit on his own in your classroom? This may limit the extent to which he is able to antagonise others. If he's starting to throw chairs, he should be sent to the headteacher, or to sit in reception and cool off.
You have a duty of care towards him, but if he is throwing things he is endangering the others and yourself. Pass the buck on to the head and if they disagree contact your union.
The expert view
Poor you. You're moving mountains, and being expected to juggle them too. The hard work you're putting in - and it sounds like you're doing exactly the right thing, incidentally - is at grave risk of being undermined here by the actions of one, as it so often is.
This boy needs to be isolated. Every day he acts up, he needs to be removed from the group until the end of the morning or afternoon. Find somewhere he can be removed to: a panic room, a quiet room, the head's study, whatever you can find.
He works alone until he can get through an entire morning in relative peace. If he messes about in lessons, he gets removed from the class and put into solitary for the next half-day. Work out the details yourself, but get this set up.
Make sure you have the support of your headteacher. Ask them if they can help arrange this. Tell them you need it in order to teach this young charmer about the values of the community and what happens to people who abuse their peers and their learning.
It sounds tough, but he needs a tough lesson now. He needs to realise that attention and love aren't gained through being unpleasant but by complying with the needs of others.
Tom Bennett is author of `The Behaviour Guru' and `Not Quite a Teacher'.