The substitution of larger groups onto the ester moiety of various dirhodium(II) carboxamidates have led to the development of three catalysts for use in various transformations. These new chiral imidazolidinone-ligated catalysts, Rh-2(4S-EPPIM)(4), Rh-2(4S-BACIM)(4), and Rh-2(4S-BPPIM)(4), have been tested in a variety of systems, including carbon-hydrogen insertion, intramolecular cyclopropanation, and Hetero-Diels-Alder reactions. While all display high levels of selectivity, only Rh-2(4S-BACIM)(4) demonstrates higher levels of selectivity than its base catalyst, Rh-2(4S-MACIM)(4). These results show that increased levels of selectivity cannot be achieved through simply increasing the steric bulk around the active site. Instead, a delicate balance in steric distribution around the active site of the catalyst must be achieved to maximize selectivity with reactivity. (C) 2002 Elsevier Science B.V. All rights reserved.