No, he could not and yes, the Russians have a system in place to prevent this. Here’s how it works:
The Russian nuclear launch control system is called “Kazbek”, it consists of three “nuclear briefcases”, codename “Cheget”. One briefcase each at the disposal of the President, Minister of Defence and Head of General Staff. Plus there are spare briefcases that are not currently in operation - spares etc.
The briefcases are locked and carried around by operator communications officers.
The whole Kazbek system is normally in “sleep mode” - you can press the buttons all you want, nothing will happen. The system activates only in case of a nuclear strike against Russia. The initial notification of a nuclear strike comes from the early warning system, the warning first arrives to a command post of the Nuclear Missile Forces (RVSN). If the attendant general validates the warning, the Kazbek goes live. It’s worth noting that the early warning system itself is pretty safe, though not entirely - in 1995 the Kazbek system was activated after a launch of a meteorological missile near Norway, because its trajectory was similar to a Trident missile. That was the only activation of Kazbek in history (aside from excercises).
When the Kazbek is live, the launch codes can be enetered and transmitted to the RVSN command post, ordering the launch. However the RVSN command post needs to receive signals from any TWO briefcases to launch the missiles. So no one person can unilaterally order the launch - there has to be at least two orders out of three people who have this right (the President, the Minister of Defence and the Head of General Staff).