At this point, it's likely that an attack on Iran has already been decided upon. These negotiations are doomed to fail from the start. Why? Because the US and allies are demanding that Iran have no nuclear enrichment capability at all. Not not enriching beyond reactor levels, but no enrichment at all. Enriching nuclear material is a right every nation has under international law. They're trying to impose harsher conditions on Iran than numerous other non-nuclear weapon states.
They know Iran wants to build a nuclear power grid. They're offering a fig leaf program that would provide fuel for their power plants, but in a way that would give them zero independent control over their own reactor supply lines. They want Iran completely incapable of creating any nuclear enrichment whatsoever. And this is after the US and allies have already violated previous agreements with Iran more than once.
Imagine what that would look like. Iran agrees to Washington's terms. They become completely dependent on the US and allies for their reactor fuel. But they're still geopolitical rivals with Israel. One day AIPAC starts up the propaganda machine again. They start applying pressure in Washington to cut off the Iranian reactor fuel shipments. They succeed, and now Iran's cities are in the dark.
Considering the diplomatic history, there is zero chance Iran is going to make its power grid dependent on the US alliance. It would be willing to sign an agreement preventing enrichment beyond reactor levels, (same as the old agreement.) But there is zero chance Iran is going to agree to give up enrichment entirely.
The US and allies are demanding something they know that Iran cannot possibly give them. This is why it's likely that a war has already been decided upon. You don't make a poison pill your unshakeable demand, unless you want them to fail.
My prediction? The Iranian nuclear facilities will be destroyed by Israeli nuclear bunker-busting bombs. The first nuclear weapons ever fired in anger since WW2 will be used against the sites. Israel will not admit this. Rather, it will continue to refuse to officially say whether it even has nukes at all. Residual fallout and radiation will be blamed on the nuclear material found inside the facilities.