Thank you for sharing your question with the Wefugee Community!
First of all, if you are still in the asylum procedure, you should not go to the Turkish embassy to extend your passport.
Also in Germany, in general, you will need a valid passport to marry (next to the documents you already mentioned). However, every civil servant in the "Standesamt" can decide independently how to procede in the individual case. You may be lucky, that your documents will be accepted as they are. You should also explain, that you are not allowed to ask for any service from the Turkish embassy as an asylum seeker. I would recommend you to contact your local Standesamt or maybe even talk to some different authorities (i.e. in another city/region) to discuss your situation.
Good luck and please get back to us with any further questions!
All the best,