TORONTO, Sept 11 (Reuters) - Canada's main stock index turned negative in afternoon trade on Tuesday, as banking stocks extended losses ahead of a key German court ruling on the legality of the euro zone's bailout fund. At 1:19 p.m. (1719 GMT) the Toronto Stock Exchange's S&P/TSX composite index was down 2.18 points, or 0.02 percent, at 12,213.25. It had risen as high as 12,264.13 in the morning.