The move will save the Senators space under the salary cap. Schaefer has three years and US$6.7 million left on his deal while Donovan has one year left at $925,000. The 30-year-old Schaefer had 12 goals and 34 assists in 77 games with the Senators last season.
He added a goal and five assists in 20 playoff games.
The 32-year-old Donovan had six goals and 11 assists in 76 games with the Bruins last season.