The 28-year-old Reynolds pitched in 71 games for the Rockies in 2012, posting a 3-1 record and 4.40 ERA in 57.1 innings. He struck out 51 and walked 17. Reynolds has appeared in 144 games over the last two years, the third-most in baseball among lefties.
"We are excited to add a versatile and experienced left-handed reliever to the bullpen," Diamondbacks general manager Kevin Towers said in a statement. "He's very familiar with our division and has been a workhorse for the last couple seasons, so we expect he can continue to do that for us."
Wheeler, 24, broke into the big leagues in 2012, appearing in 50 games for the Diamondbacks, hitting .239 with one home run and driving in 10 runs. Wheeler excelled at Triple-A Reno before his call-up, hitting .351 with 15 homers and 90 RBI.