How does diplomacy work when the invader - Putin - isn't receptive to negotiations or compromise? He's violated international law, purposely continues to target civilians among other war crimes and makes deals with the Saudis to reduce oil production and damage the world economy.
So let's negotiate what? Please Mr Putin stop killing innocent civilians and you can have the territory you invaded plus freely sell your fossil fuels without restrictions? Sorry we got in your way? Ridiculous.