The “refugee-triggering” factor has often been mentioned in Western media as President Putin’s power tool in dealings with Europe. Admittedly, he could ramp up the military activity in Syria and release new waves of refugees across the Mediterranean if the West refused to play along.
However, the Russian involvement in Syria happened after the main groups of Syrian refugees had been displaced, as demonstrated by the graph below. Besides, a pressure by generating masses of refugees is too awkward to manage: Turkey sits in the middle, and this makes Erdogan, not Putin, the holder of this trump card in haggling with Europe.
The chaos of uncontrolled immigration to Europe was certainly a welcome bonus for Putin in his game of weakening Angela Merkel ahead of the 2017 German elections. But it was unlikely his deliberate calculation ahead of the Syria campaign.