I think the Iranian leadership in the 80s were more interested in creating an Islamic republic of Iraq than in outright annexation.
I've actually been toying with an Iranian TL for a while now, but I'm not sure how plausible the POD is;
It's that in 1730 the Turks win the battle of Nahavand, securing western Persia for their Safavid client Tahmasp II. When the Russian evacuate the capsian sea coast in 1732 Tahmasp reoccupies this area, which serves as a springboard for advances into central Persia. The Safavids gradually reform their military and political structures under Ottoman tutelage and in the 1740s/50s defeat the Afghans and restore their empire to ts pre-1722 borders.
they then assert their independence from teh Ottomans (not hard as the Turks were in VERY poor shape by the later eighteenth century), and then don't bother anyone until 1800-1803, when they loose a war witht eh Russians over Georgia. They then stagnate for a while before loosing to the Russians again in 1825, when much of Azerbyjan is annexed to Russia (basically the same gains as in OTL).
However, with the persian dynasty better established, with stronger administrative systems and more legitimacy these defeats trigger a series of reforms comparable to the Ottoman Tanzimat and in the Crimean war the Persians ally with the British and regiaon the lands lost in 1825.
Thereafter a significant programme of modernisation gets underway, with the construction of telegraph and rail lines, irrigation projects and educational reforms, whilst the Persians expand into central asia. Unfortunately all this costs money and with the worldwide financial collapse of the miod 1870s Persia goes bankrupt. The Europeans take advantage of this to impose a set of financial controls on the govenment, limiting military spending and leading directly to the loss of the central Asian empire, whcih the Russians take over.
This proves unnacceptable to the former Persian ruling class (and to army officers retired on half pay) and in 1886 they stage a natioanlist coup, analogous to the Egyptian revolution of 1881 but backed by enough military force that European intervention isn't an option. A constitution is enacted in 1887 which transfers most power to a parliament with an elected lower house.
By the 1890s oil revenue from Baku and foreign investment is triggering massive economic growth, enough to support the creation of armed forces comparable (not quite equal) in power with those of the ottoman Empire
And that's as far as I've thought, any thoughts on plausibility/where it goes from here