It is permissible for a man to lead his wife in prayer, and the woman should stand behind the man, because it is not permissible for her to stand with him, because when the Prophet (peace and blessings of Allaah be upon him) led Anas and the orphan in prayer, he made Umm Sulaym – who was the mother of Anas – stand behind them. 

It is also indicated by the report narrated from Anas ibn Maalik, that the Messenger of Allaah (peace and blessings of Allaah be upon him) led him and his mother or maternal aunt in prayer. He said, “He made me stand to his right and he made the woman stand behind us.” (narrated by Muslim, al-Masaajid wa Mawaadi’ al-Salaah, 1056). 

Al-Kaasaani said: If there is a woman praying with the imaam, he should make her stand behind him. 

Ibn Rushd al-Hafeed said: there is no dispute concerning the fact that a lone woman may pray behind the imaam and that if there is also a man present, the man should pray beside the imaam and the woman should pray behind him. 

See Ahkaam al-Imaamah wa’l-I’timaam by al-Muneef, p. 319-320 

And Allaah knows best.