There are some that are iron based. I haven't used them. But, I can see that if they do make it out of field trials they could be really popular with the chemically reluctant.
Few alternatives exist to using the chemical herbicide 2,4-D and its allies to reduce broadleaf weeds in turfgrass or glyphosphate in landscapes. Currently, there are approximately five iron-based commercial products registered by the EPA's Biopesticide Division and labeled for broadleaf weed control. Demand will likely result in additional iron-based herbicides being brought onto the market. These selective, broadleaf herbicides contain the active ingredient chelated iron. Fundamentally, these iron (Fe) products are similar to liquid products that treat micronutrient deficiencies in plants and are considered mineral based materials.
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Testing needs to be conducted on warm season grasses such as Bermuda and zoysia.
https://extension.umd.edu/resource/iron-based-herbicides