While the trigonal pyramidal geometry (C3v symmetry) results in high-lying dyz and dxz orbitals because of antibonding interactions with the σ-donating ligand orbitals, a trigonal planar geometry (D3h symmetry) affords lower-lying dyz and dxz orbitals because of the reduced spatial overlap with ligand orbitals. The lower-lying dyz and dxz orbitals of trigonal planar Cu I sites have a less favorable energy match with the σu* orbital of the H2 molecule, thus minimizing π-backbonding to H2.