Well known grievances? I simply cannot agree with you there. Those are points for which we only have the Russian governments word, and dozens of denials from other governments across the globe.

Not to mention, the reasoning for the war has changed dramatically over and over, from "stop the Nazis!" To "oh they were totally going to join NATO and attack us!!!" To "The security of Europe!" And now "they were gonna get nukes!"

Never mind the fact that the Ukraine already gave up their nukes in exchange for Russia's assurances they wouldn't do exactly this. Or the fact that NATO obviously doesn't need the Ukraine as members since Russia can't even win a land war with a military a fraction of their size right across the border. Or any of the other facts Russia has bald faced lied about repeatedly.

Given the above factors I find it highly unlikely Putin was looking for or interested in any diplomatic out. He was looking for an excuse.