As an occupied territory, it doesn't have any legitimate institutions (such as a recognised government, banks, courts, etc.) — only a foreign occupation regime. Same way as Germany's Reichskommissariats and Reichprotektorats during WW2 were never legitimate entities despite being de facto governed by Germany.
This means than no contract (private or public) with a Crimean entity can be internationally recognised and will be easily contested by any court/arbitrage outside of the RF.
In addition to this, there's a moral concern of giving legitimacy to a foreign occupation. There's just no way to justify this unless one supports the mentioned occupation, with following systemic abuse of human rights, change of ethnic composition and militarisation.