Stock futures mixed but Aetna's $5 billion deal shows confidence

Stock index futures were little changed on Monday after posting six weeks of gains, but insurer Aetna's purchase of rival Coventry Health Care for $5.7 billion showed companies are still seeing value in the market.

But futures lost some ground after the European Central Bank sought to quash speculation about the shape its planned bond-buying program would take, saying it was misleading to talk about decisions that had not yet been taken.

Coventry shares jumped 18 percent to $41.30 after Aetna said it will pay a total value of $42.08 per share for the company, putting the deal at a 20.4 percent premium to the stock's Friday closing price. The deal is the latest in a string of multibillion-dollar acquisitions in the U.S. healthcare sector.

The S&P 500 closed its sixth week of gains on Friday, closing in on four-year highs, as investors anticipate the European Central Bank will take steps to control the euro crisis in September. Last week the index broke away from the 1,400 level where it had stalled for much of August.

"There is a better feeling out there that there is a sense of more unity growing within the EU, and it is being backed by the ECB," said Peter Cardillo, chief market economist at Rockwell Global Capital in New York. "Over the next week or so we are looking at 1,435 to 1,450 on the S&P."

The latest edition of Der Spiegel said the ECB is discussing interest rate thresholds for individual euro zone countries with a view to intervening if the premium over German bonds is exceeded. In its latest comments the ECB stopped short of ruling out the report outright.

S&P 500 futures fell 0.5 point but were slightly above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures fell 18 points, and Nasdaq 100 futures added 3 points.

CME Group Inc , the biggest U.S. futures exchange operator, said on Monday it was applying to the British Financial Services Authority for approval to open in the middle of next year a London-based market trading currency futures.

Federal Reserve Bank of Chicago releases its Chicago Fed National Activity Index for July at 8:30 a.m. (1230 GMT). The index read -0.15 in the prior month.

Struggling retailer Best Buy Co Inc said its founder Richard Schulze has turned down an offer from the board to conduct due diligence in connection with his proposal to take the company private at a valuation of more than $8 billion. The shares fell 4.7 percent.

The global economic outlook is more uncertain now than at the start of the financial crisis in late 2008, Doug Oberhelman, chief executive of Caterpillar , the world's largest maker of construction equipment, said on Monday.

European stocks <.FTEU3>, which have rallied sharply since late July, fell 0.1 percent on Monday although the losses were limited by growing expectation of bold action from the European Central Bank to lower the borrowing costs of Spain and Italy.

(Editing by Kenneth Barry)