The synthesis and characterisation of constrained geometry scandium and aluminium permethylindenyl complexes ^Me2SB(^RN,I*)ScCl(THF) (R = ⁱPr (1), ⁿBu (2) and Ph (3)), ^Me2SB(^iPrN,I*)Sc(O-2,6-ⁱPr-C₆H₃)(THF) (4), ^Me2SB(^iPrN,I*)Sc(O-2,4-^tBu-C₆H₃)(THF) (5), ^Me2SB(^nBuN,I*)Sc(O-2,6-ⁱPr-C₆H₃)(THF) (6), ^Me2SB(^PhN,I*)Sc(O-2,6-ⁱPr-C₆H₃)(THF) (7), ^Me2SB(^tBuN,I*)AlCl(THF) (8), ^Me2SB(^tBuN,I*)Al(O-2,6-Me-C₆H₃)(THF) (9) and ^Me2SB(^tBuN,I*)Al(O-2,4-^tBu-C₆H₃)(THF) (10) are reported. All complexes were characterised by NMR spectroscopy. Solid-state structures of 2–4, 6 and 8–10 were determined by X-ray crystallography. Ring-opening polymerisation of L- and rac-lactide using all complexes with the exception of 6 show first-order dependence on monomer concentration and produced polylactide with unimodal molecular weight distribution. First-order dependence on catalyst concentration was determined from L-lactide polymerisation using 4 and 9. Moderately heterotactic polylactide (P_r = 0.53–0.68) was achieved from rac-lactide polymerisation using 4, 5, 7 and 9. The effects of the metal centre (Sc and Al), the amido substituent (ⁱPr, ^tBu, ⁿBu and Ph) and the aryloxide initiating group (O-2,6-Me-C₆H₃, O-2,6-ⁱPr-C₆H₃ and O-2,4-^tBu-C₆H₃) on the catalytic activity are discussed.