Russian translation: онлайновая система торговли между компаниями
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Explanation: Under 'operativnye' you might also use 'v realnom vremeny'. Business-to-business supposes companies, as offered above, but I still think businessmen are at the frontline, so you may use this term. And finally, why 'torgi, not 'torgovlya'? Because under marketplace business solicitaion is meant.
Explanation: The "onlainovaya" part can really be substituted by "internet" adjective, it's up to you. Definition of a birzha is a marketplace for entrepreneurs (the connotation is to exclude individuals and count only businesses). All in all, "veduschaya internet birzha" or "veduschaya onlainovaya birzha" succinctly describes your translation phrase.