Freeport-McMoRan Copper & Gold Inc took a big step on Monday in its plan to expand into energy, when Plains Exploration & Production Co shareholders approved the miner's $6 billion takeover deal, sweetened by two special dividends. The world's largest listed copper producer's bid to buy Plains, unveiled in December, ran into strong headwinds in recent weeks when prominent investors and proxy advisory firms said Freeport's offer was too low. But the companies shored up support by announcing the dividends on Monday morning, hours before shareholders were set to vote. The payouts will provide Plains shareholders with about $470 million in cash and stock on top of the $6 billion deal already on the table. The dividends effectively increase the amount Plains shareholders would receive by $3.65 in cash and stock, bringing their haul in line with Freeport's original $50-a-share bid. A decline in Freeport shares since December lowered the payoff and fanned o