Metathesis reactions can accelerate the construction of complex products from relatively simple starting materials through the catalytic exchange of their component functional groups. While olefin and alkyne 2 metathesis are the most well-developed reactions in this category, other isofunctional reactions including carbonyl-olefin metathesis (COM) have been the focus of increasing attention (Figure ). However, despite notable progress, many functional group metathesis reactions remain unknown. For example, alkyl halides and olefins are two abundant functional groups in organic chemistry, but there is currently no way to achieve their metathetical exchange (Figure ). Alkyl halides and olefins can be combined through radical pathways or via Heck reactions, but fragment exchange is not a typical outcome. Indeed, it is not obvious how the known strategies for functional group-olefin metathesis chemistries might be expanded to include alkyl halides. Nevertheless, the realization of an alkyl-halide olefin metathesis (AHOM) reaction could enable a variety of novel synthetic strategies for small molecule and materials synthesis. Here, we introduce the first strategy to achieve AHOM using diazene catalysis. The inspiration for this chemistry arose from our work in catalytic carbonyl-olefin metathesis (COM), 4a, 8 which has resulted in the development of a number of ring-opening, ring-closing, and ROMP 11 reactions. The key intermediate underpinning these reactions is the hydrazonium ion (i.e. a protonated azomethine imine), which is formed by condensation of a 1,2-dialkyhydrazine catalyst with the carbonyl component and which achieves metathesis by reversible [3+2]-cycloaddition with the olefin component. The key realization for the current work was that the same hydrazonium intermediate might instead be accessed by alkylation of a diazene followed by tautomerization. If viable, this alternative hydrazonium synthesis could enable the engagement of a broad range of alkylating agents in metathesis reactions with olefins.