A series of oxophosphine (3,5-Me(2)Pz)(2)CHP-(R)(2)O (Pz = pyrazole; R = Bu-t (HL1), Cy (HL2)) and iminophosphine (3,5-Me(2)Pz)(2)CHP(R)(2)NAr = Cy, Ar = Ph (HL3); R = Ph, Ar = Ph (HL4), Ar = 2,6-Me-2-phenyl (HL5)) heteroscorpionate ligands were synthesized. Abstraction of the methide proton of these ligands by rare-earth-metal tris(alkyl)s, Ln(CH2SiMe3)(3)(THF)(2), afforded the corresponding zwitterionic bis(alkyl) complexes L(1-5)Ln(CH2SiMe3)(2)(THF) (L-1, Ln = Y (1a), Lu (1b); L-2, Ln = Y (2a), Lu (2b); L-3, Ln = Y (3a), Lu (3b); L-4, Ln = Y (4a), Lu (4b); L-5, Ln = Y (5a), Lu (5b), while metathesis reaction of the lithium salts of LiL3 and LiL4 with YCl3(THF)(2) or YBr3(THF)(2) followed by treatment with LiCH2SiMe3 and KN(SiHMe2)(2), respectively, afforded the first heteroscorpionate yttrium mixed halogen/alkyl or amido complexes L3-4Y(Cl)(CH2SiMe3)(THF) (L-3 (6a), L-4 (7a)), L3-4Y(Cl)(N(SiHMe2)(2))(THF) (L-3 (8a), L-4 (9a)), (LY)-Y-4(Br)(CH2SiMe3)(THF) (10a), and (LY)-Y-4(Br)(N(SiHMe2)(2))(THF) (11a). The structures of these complexes were well-defined, and the molecular structures of la, 2a, 3b, 4b, 5a, and 7a were further characterized by single crystal X-ray diffraction analysis. Complexes 1-5 showed similar high activity toward the ROP of rac-LA at room temperature, and both the alkyl species participated in initiation, of which the lutetium complexes exhibited slightly higher selectivity than their yttrium analogues (P-r = 0.85-0.89 vs 0.80-0.84) despite the bulkiness of the ligands. Interestingly, the mixed halogen complexes 6a-11a were single-site initiators, where the sigma-halogen moiety remaining on the central metal showed, for the first time, facilitating the heteroselectivity up to P-r = 0.98. This result sheds new light on designing specifically selective catalytic precursors.