Putin is very fond of Novichok.
Putin has overseen and directed an illegitimate invasion of Ukraine, including countless war crimes.
Would he be so bold as to deploy tactical battlefield nuclear weapons, when he could instead draw upon his arsenal of Novichok agents and VX agents.
Are Ukranian forces well-prepared for such an attack? Ukranian civilian casualties would be vast, but Putin has proven that he has no scruples about killing innocent civilians.
Many Russian soldiers would probably also die, given their incompetence, but Putin cares not about the fate of his own troops either.
I’ve undoubtedly overlooked important issues why this would be militarily impractical, unfeasible, or logistically too difficult.