The basic problems with getting Persia to join the Central Powers:
(1) There was a teen-aged Shah who had a hard time resisting Russian and British pressure.
(2) While there were nationalists in the Majlis who resented the British and Russians, even they were also worried about the Turks (who made no secret of their desire to annex border areas).
(3) Jihad propaganda in favor of the Central Powers was less effective than in some other parts of the Muslim world--it attracted some Arabs and Kurds, but with the ethnic Persian population it foundered on the Shia-Sunni split and fear of Turkish imperialism:
"The notion of global Islamic solidarity behind the Ottoman Sultan-Caliph was a fantasy, particularly in the Shia world. Rauf Bey's incursion across the border had reignited centuries-old hostility between Sunni Turks and Shia Persians, very nearly pushing Persia into war--against the Ottoman Empire..." Sean McMeekin,
The Berlin-Baghdad Express: The Ottoman Empire and Germany's Bid for World Power (Harvard UP 2010), p. 283
https://books.google.com/books?id=6k5HzkboGvcC&pg=PA283
"Furthermore, holy war propaganda had mobilized only a handful of Arabs and Kurds along the Turkish-Persian border, along with some south Persian tribes. Elsewhere, the call for jihad had produced little response, falling victim to Persian fears of the Turks and to the Shiite-Sunni schism..." Donald M. McKale,
War by Revolution: Germany and Great Britain in the Middle East in the Era of World War I (Kent State UP 1998), p. 134
https://books.google.com/books?id=j6-bKj5eaqcC&pg=PA134