This would be a neatly literal translation, if it weren't for the problem that "promising", when used as an adjective, tends to mean "likely". The phrase does seem to have some currency on the web, I have looked for a reputable source and failed to find one. Here is a typical example of use of the phrase by somebody translating into English, in spite of clearly having limited knowledge of the English language:
"To this effect, the Promising Seller, has agreed to obtain from the relevant Local Authorities the authorization to subdivide the Land in order to allow the selling of the Immovable having attached to that transfer of ownership the corresponding land use and development rights on the Stand on which the Immovable is built, in favour of the Promising Buyer. "
http://74.125.77.132/search?q=cache:v5oT7SzujfIJ:www.pamgold...|lang_fr