AbstractThe catalytic one‐bond isomerization (transposition) of 1‐alkenes is an emerging approach to Z‐2‐alkenes. Design of more selective catalysts would benefit from a mechanistic understanding of factors controlling Z selectivity. We propose here a reaction pathway for cis‐Mo(CO)₄(PCy₃)(piperidine) (3), a precatalyst that shows high Z selectivity for transposition of alpha olefins (e. g., 1‐octene to 2‐octene, 18 : 1 Z : E at 74 % conversion). Computational modeling of reaction pathways and isotopic labeling suggests the isomerization takes place via an allyl (1,3‐hydride shift) pathway, where oxidative addition of fac‐(CO)₃Mo(PCy₃)(η²‐alkene) is followed by hydride migration from one position (cis to allyl C³ carbon) to another (cis to allyl C¹ carbon) via hydride/CO exchanges. Calculated barriers for the hydride migration pathway are lower than explored alternative mechanisms (e. g., change of allyl hapticity, allyl rotation). To our knowledge, this is the first study to propose such a hydride migration in alkene isomerization.