This post is from last year, I know, but I just recently discovered this webpage!

I found a third solution in addition to the two mentioned here. It has number 2 in the center and the numbers in the corners are (in clockwise order) 1,3,5,7,4,12.
After limiting down the center number to either 2 or 4 and thereafter checking different possibilities I found the three solutions now mentioned, and I do believe that these are the only possible ones.