Designing the spatial environment around a metal center is a critical issue in terms of the electronic and/or steric properties and hence the reactivity of organometallic complexes. Chemists have thus focused on the design of the structural, electronic, and dynamic properties of supported ligands, as demonstrated in the field of ,e.g., homogenous catalysis, supramolecular chemistry, and materials science. One well-known strategy for reversibly modulating the electronic/spatial environment around metal centers is based on a ligand-substitution process on metal centers bearing multifunctional ligands including a hemi-labile coordination moiety (L') in the presence of an external Lewis base (LB) (Figure , left). However, these processes often yield an equilibrium mixture that is difficult to separate. In this context, we have reported the reversible, recyclable, and pressure-responsive room-temperature-chemisorption of carbon monoxide (CO) on a zero-valent nickel complexes that bear multifunctional multipurpose carbene ligands, namely N-phosphine oxide-substituted imidazolinylidenes (SPoxIms) and the corresponding imidazolylidenes (PoxIms) (Figure , left). (S)PoxIm ligands in tetrahedral (S)PoxImNi(CO)n complexes selectively adopt either a -C-(n = 3) or -C,O-(n = 2) coordination mode, which can be interconverted through the addition/exclusion of CO.