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

BDI*(MgBu)-Bu-n(THF) and rac-LA to produce heterotactic PLA have been shown to increase from P-r = 0.5-0.65 from DCM to neat THF. The increase in concentration of THF from M-THF = 0 in toluene to neat THF is shown to occur by THF dissociation as deduced by H-1 NMR studies. In related systems where X = Bu-n and (OBu)-Bu-t and with ligands L = THF, py and DMAP similar processes occur by which external exchange of L occurs with added free ligand. For X = Bu-n and L = THF, the activation parameters for the dissociation process are Delta H double dagger = 7.0 +/- 0.5 kcal mol(-1) and Delta S double dagger = -11.6 +/- 0.4 cal mol(-1) and for X = (OBu)-Bu-t and L = THF are Delta H double dagger = 11.1 +/- 1.0 kcal mol(-1) and Delta S double dagger = -3.3 +/- 3.9 cal mol(-1). The BDI*(R = Bu-t) is notably larger than BDI (R = Me) and this limits the use of THF to coordinate during catalysis. The three coordinate complex BDI*(MgBu)-Bu-n has been structurally characterized by single crystal X-ray crystallography: where Mg-N = 2.010(4) and 2.026(4) angstrom and Mg-C = 2.117(5) angstrom, with N-Mg-N = 94.2(2)degrees and N-Mg-C = 130.0(2)degrees and 135.8(2)degrees. The related complexes BDI*(MgBu)-Bu-n(L), where L = py and DMAP have similar structural features. (C) 2015 Elsevier Ltd. All rights reserved.