Which state refused to send anyone to philadelphia for the convention?

Rhode Island

Explanation:

Incidentally, Rhode Island, while now the smallest state geographically in the Nation, was much more important in colonial times. It was coincidentally the last state to ratify the Constitution.

The Constitutional Convention, as it was also known, was held to address the multiple problems that the fledgeling United States government faced under the current Articles of Confederation. Even the delegates who supported the Articles were able to come to a general agreement on the necessity for deeper changes that ultimately led to a new constitution.