The first synthesis of 1,4,7-tri-tert-butyl-1,4,7-triazacyclononane ((t)Bu(3)tacn) and its adamantyl analog Ad(3)tacn are described. Cr-II, Mn-II, Fe-II, Co-II, Ni-II, and Cu-I compounds of (t)Bu(3)tacn are reported: the steric properties of this ligand enforce four-coordinate geometries except in the case of five-coordinate Cr-II, enabling design of pseudotetrahedral compounds bearing this tridentate redox-inert ancillary ligand.