Anakin attacking Mace is his final act, I think, in turning to the Dark Side. Did Palpatine know what Anakin would do?
Was he betting on Anakin telling Mace, Mace coming to arrest him, goading Mace into a duel and then Anakin attacking Mace in his defense and consequently turning to the Dark Side?
It's unclear, since in the novelisation we only have the scene from Anakin's perspective; however, it's likely that in this, as in most things, Palpatine was playing what TV Tropes calls a Xanatos Gambit - a plan where any outcome is to the player's benefit.
After revealing himself to Anakin, if Anakin exposed him to the Jedi the Jedi would certainly come to arrest him. This would give Palpatine an excellent excuse to execute Order 66, the purpose of which had always been to put down a Jedi coup. It would also most likely give him an opportunity to complete Anakin's fall to the Dark Side.
If Anakin did NOT expose him, then he knows that Anakin has chosen him over the Jedi. He now has a loyal follower directly inside the Jedi council, and can continue to manipulate things behind the scenes and gather information until he has enough evidence against the Jedi to justify executing Order 66 anyway. Anakin will continue to come to him for guidance and training, and Anakin's fall will be completed one way or the other.
No matter what Anakin did at that point, Palpatine had set up the pieces so that any outcome would be to his own advantage. It's his signature move, after all - he did the same thing when he set the Trade Federation against Naboo, and throughout the Clone Wars.
Palpatine knew it was one of Anakin's options, but he didn't know which course of action Anakin would take in the end.
From the movie transcript:
PALPATINE: Are you going to kill me?
ANAKIN: I would certainly like to.
PALPATINE: I know you would. I can feel your anger. It gives you focus, makes you stronger.
ANAKIN raises his lightsaber to PALPATINE's throat. There is a tense moment, then ANAKIN relaxes, and then turns off his lightsaber.
ANAKIN: I am going to turn you over to the Jedi Council.
PALPATINE: Of course you should. But you're not sure of their intentions, are you? What if I am right and they are plotting to take over the Republic?
ANAKIN: I will quickly discover the truth of all this.
PALPATINE: You have great wisdom, Anakin. Know the power of the dark side. The power to save Padme.
ANAKIN stares at him for a moment.
PALPATINE turns and moves to his office.
PALPATINE: (continuing) I am not going anywhere. You have time to decide my fate. Perhaps you'll reconsider and help me rule the galaxy for the good of all . . .
PALPATINE sits behind his desk.
Palpatine leaves it up to Anakin. His hope is mainly that Anakin decides not to tell Windu and the rest of the council about his true identity, but instead joins him so that they can rule the galaxy together. Order 66 was going to be called anyway, so the Jedi would have been killed regardless of Anakin's decision.
Even when disarmed and practically helpless (lightning aside), Palpatine still uses the promise of being able to save Padme as a way to sway Anakin to his side, which ultimately works and causes Anakin to stop Windu from delivering the final blow. However, he didn't know that Anakin would do this. For pretty much his whole life, Palpatine has just been manipulating people and playing the probabilities. He's cold and calculating, but even he can't do anything with complete certainty. It's what makes him such a good villain.
