(Correction: The original article misstated when Charles Prince, the former chief executive of Citigroup, declined an invitation to the Festival of Thinkers in Abu Dhabi. It was in September, not "just days" before the festival began on October 21.) 

 
An investment by Abu Dhabi is being hailed today as a huge boost for Citigroup, but it might nearly have been a missed opportunity.

Charles Prince, then the chairman and chief executive officer of Citigroup, was invited by Abu Dhabi to participate in October's biennial Festival of Thinkers, which brought 18 Nobel laureates and some 175 top business leaders, scholars, media executives, and artists to the oil-rich Persian Gulf state for four days of celebrating and conviviality.

The participants had access to top decisionmakers in Abu Dhabi, whose proven oil reserves are estimated to last for another 300 years.

The invitation to Prince came from Sheik Nahayan Mabarak al-Nahayan, the festival's founder and the minister of higher education and scientific research of the United Arab Emirates.

The 52-year-old Sheik Nahayan also happens to be the chairman of the Abu Dhabi Group, a private investment fund that is one of the largest investors based in the United Arab Emirates.

The market value of Sheik Nahayan's investments—in banks,   telecommunications, real estate, media (he owns a majority stake in CNBC Pakistan, for example), and financial services, among other sectors—is well above $10 billion, and the Oxford-educated sheik is reportedly on the lookout for more opportunities, particularly in the United States.

Prince, however, declined the invitation. After some inquiries, a spokesman replied on September 20 that the chief executive had prior commitments.

The C.E.O., to be sure, was struggling with a bank in crisis. Citigroup took a write-down of $5.9 billion  on investments tied to subprime mortgages in October, and was soon estimating it would need to take billions more. Prince resigned on November 4 after having lost the support of backers like Prince Walid bin Talal of Saudi Arabia.

Still, had the embattled Citigroup C.E.O. been able to travel to Abu Dhabi for the festival, he almost certainly could have obtained assurances of badly needed funds—a lifeline that might have saved his job as well.

Abu Dhabi officials have long been considering such investments as rising prices for crude oil yield unprecedented wealth for their state and other OPEC members. Indeed, the six countries that make up the Gulf Cooperation Council expect their combined budget surplus in 2007 to exceed $700 billion.

And although Sheik Nahayan's invitation to Chuck Prince had not hinted at an investment by Abu Dhabi, the complex web of decisionmaking in the United Arab Emirates is such that Prince most certainly would have found interested investors had he attended the Festival of Thinkers.

This became clear late Monday night, when Citigroup announced that the investment arm of the Abu Dhabi government had agreed to pump $7.5 billion into the bank. This will give the Abu Dhabi Investment Authority—the government's investment arm—a 4.9 percent equity stake, slightly more than that held by Prince Walid.

Abu Dhabi's cash infusion at once strengthens Citigroup's capital base, which has thinned on account of costly acquisitions, the collapse of the subprime mortgage market, and the resulting turmoil in the credit markets.

"This investment reflects our confidence in Citi's potential to build shareholder value," said the Abu Dhabi Investment Authority's managing director, Sheik Ahmed bin Zayed al-Nahyan.