I found the solution on my second try and it's a good one, but I think my first try also works. 1. Rg3+ , Kf8 2. Rf3 and white threatens mate in two moves with Rxf7 and black can only cover it temporarily by sacrificing his queen, like 2. - , Qxd4 3. Rxf7+ , Kg8 4. Rg7+ , Kh8 5. Qxd4 and mate soon follows with a discover check.
Or 2. - , Kg8 3. Rxf7 , Bxf7 4. Qxf7+ , Kh8 5. Qf6+ , Kg8 6. Rg3++
2. - , Rxe7 3. Qh8++ loses immediately.
nice deflection of the bishop