AbstractHerein we report the synthesis of three heteroleptic first‐row transition metal(II) complexes containing carbazolido NNN pincer ligands and conversion to the corresponding metal(I)‐carbonyl complexes via a reductive carbonylation route. These complexes are precatalysts for the hydrophosphination of activated alkenes, affording a cobalt‐catalysed hydrophosphination process that solely and selectively yields the β addition (anti‐Markovnikov) product. The scope of this transformation has been investigated using a variety of activated alkenes. Isolation and characterisation of substrate‐coordinated intermediates reveal available coordination sites, which provide insight into the proposed catalytic cycle.magnified image