Alkene alkylation can occur by polar, radical and metal coordinative mechanisms, where relative rates, regioselectivities and efficiencies depend on the alkene substituent pattern. 1 Among radical methods, metal hydride hydrogen atom transfer (MHAT) cross-coupling has emerged as an effective strategy to append alkyl groups to alkenes, even to generate quaternary carbons, with consistent Markovnikov selectivity, chemoselectivity and tolerance of multiple alkene substitution patterns. Prior methods have relied on radical capture of classic π-electrophiles (Fig. , left) 3 or on dual catalysis to engage σ-electrophiles, whereby the MHAT catalytic cycle intersects a secondary cycle: nickel, 4 chromium, 5 copper 6 or iron . We recently reported this latter cross-coupling-iron-iron dual catalysis-to enable complex fragment coupling by a putative MHAT/ SH2 fragment mechanism (Figure ). As in the seminal report by MacMillan, an SH2 pathway was suggested by 1) a marked increase in diastereoselectivity that accompanied addition of the iron porphyrin cocatalyst, as well as 2) side products that indicated radical intermediates and 3) absence of an open valence cis-to the carbon ligand on iron that might otherwise indicate C-C bond formation by reductive elimination. This is similar to the reasoning that suggests iron hydrides can functionalize alkenes by an MHAT mechanism, which might itself be considered a metal hydride SH2 reaction.