BDI∗MgX(L) where X = nBu and OtBu and L = THF, py and DMAP. The rates of kinetic exchange of L where BDI∗ = CH{C(tBu)N-2,6-iPr2C6H3}2

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BDI∗MgnBu(THF) and rac-LA to produce heterotactic PLA have been shown to increase from Pr=0.5–0.65 from DCM to neat THF. The increase in concentration of THF from MTHF=0 in toluene to neat THF is shown to occur by THF dissociation as deduced by 1H NMR studies. In related systems where X=nBu and OtBu and with ligands L=THF, py and DMAP similar processes occur by which external exchange of L occurs with added free ligand. For X=nBu and L=THF, the activation parameters for the dissociation process are ΔH╪=7.0±0.5kcalmol−1 and ΔS╪=−11.6±0.4calmol−1 and for X=OtBu and L=THF are ΔH╪=11.1±1.0kcalmol−1 and ΔS╪=−3.3±3.9calmol−1. The BDI∗(R=tBu) is notably larger than BDI(R=Me) and this limits the use of THF to coordinate during catalysis. The three coordinate complex BDI∗MgnBu has been structurally characterized by single crystal X-ray crystallography: where Mg–N=2.010(4) and 2.026(4)Å and Mg–C=2.117(5)Å, with N–Mg–N=94.2(2)° and N–Mg–C=130.0(2)° and 135.8(2)°. The related complexes BDI∗MgnBu(L), where L=py and DMAP have similar structural features.