A series of Rh I complexes featuring cationic diphosphinometal ligands (PMP n+ ) has been synthesized, and the effect of the dative Rh I → M n+ interactions on other ligands coordinated to the Rh I center were studied. The Rh−CO bond strength in square pyramidal [(PMP)Rh(CO)X] n+ -type complexes (X = Cl, H) is dominated by the charge of the metalloligand. Complex [(PZnP)Rh(CO)H](NTf 2 ) 2 ( 7) was evaluated for its competence in hydroformylation catalysis. Computational analysis of octahedral [(PMP)Rh(CO) 2 H] n+ model complexes revealed a strengthening of the Rh−CO bond trans to the metalloligand with increasing atomic number of the metalloligand.