Tricarbonylphthalaldehydechromium complex can be prepared using a ‘one pot’ procedure starting from tricarbonylbenzenechromium: the protection of one aldehyde function by chiral diamines leads to the formation of two diastereoisomers of the monoaminal of the phthlaldehyde complexes, efficient precursors of enantiopure ortho-substituted alkenyl arene complexes.