UPDATE 1-Brazil's Itaú buys BTG Pactual's debt collector stake, trumps rival bid

SAO PAULO, Dec 31 (Reuters) - Itaú Unibanco Holding SA, Brazil's No. 1 bank by market value, has agreed to pay Grupo BTG Pactual SA about 1.21 billion reais ($305 million) for a stake in a debt collection company and a pool of non-performing loans, in a last-minute bid that trumped a rival bid.