I'm sorry he won't be able to work in Germany with that Polish Temporary Residence Permits. Only If it should have been a Polish Permanent Residence permit then he would have been able to Work in Germany.PERMANENT RESIDENCE PERMITS HOLDERS in EU countries can be given a Residence Permits in a different Eu Country if they move there and meet up with the requirements. For him to work in Germany he would have to seek for a German Working visa if he's accepted then he will be able to come to Germany for Work purposes.
Best regards
Nelly