Goldman Sachs is not giving its multimillionaire clients a lot of time or information to think about investing in a $1.5 billion Facebook private offering.

According to a customer who received a letter from Goldman, clients were given just until the end of this week to decide whether they want a piece of the social networking giant.

The world's largest investment bank this week agreed to invest $475 million into Facebook and initiated plans to raise as much as $1.5 billion through a special purpose investment vehicle marketed to its private wealth management customers. The private sales would value Facebook at $50 billion,

Holding the keys to one of the hottest investment opportunities around, Goldman gave ultra-wealthy clients little time to decide. Customers who received the Goldman email on Sunday were required to sign a nondisclosure agreement.

The private placement memorandum, which would contain detailed financial information about the company and terms of the investment, had not yet been circulated as of Tuesday afternoon, two clients told Reuters. The minimum investment is expected to be $2 million.

Both the minimum investment and the investment deadline may be subject to change, the investors said. Goldman declined to comment.

A follow-up letter from Goldman ,that most clients got on Monday, contained very little information about Facebook, other than metrics about visitors that compare favorably to Google, another Internet giant, that went public in 2004.

Goldman's offering of Facebook shares, through an as-yet unnamed special vehicle, is being closely watched on Wall Street because it could set the stage for other private companies that want to raise money but do not want the hassle and expense of publicly traded shares.

A second Goldman customer said he was surprised that the firm still has not sent out a private placement memorandum, concluding Goldman seems to expect customers to invest on blind faith.

The aggressive valuation attached to Facebook could give some savvy investors pause, making it difficult for them to double their money in five years. That may not matter for a household name that recently eclipsed Google as the most visited site on the Internet and is the subject of a popular 2010 movie that may contend for best-picture honors.

A third Goldman client pitched on the deal said he believes Facebook has $2 billion in revenues, though the person does not know if the fast-growing company is cash flow positive or profitable. The Goldman fund values Facebook at about 25 times revenue, an extremely rich valuation.

The third investor also said that Goldman is taking a 4.5 percent fee from the money invested into the fund.

The placement memorandum may be distributed on Wednesday, though that does not give investors a lot of time to weigh a $2 million investment. Even then, the memorandum is not expected to have a lot of financial detail.

(Reporting by Matthew Goldstein and Joe Giannone; Editing by Tim Dobbyn)

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