Macquarie Group is a warm favourite to buy the investment banking business Sal Oppenheim in Europe, numerous newspaper and wire reports over the last day suggest.Deutsche Bank is the likely buyer of the private banking assets of Oppenheim, Dow Jones reported.Macquarie has used the last year to make select purchases of investment banking and fund management assets in North America. Picking up Oppenheim (based in Luxembourg but largely serving a German market) would be its first significant acquisition in Europe in some years.