A homogeneous catalytic system based on a suitable Ni(II) diimine derivative and methylaluminoxane affords predominantly syndiotactic polypropylene at subambient temperatures. The polymer microstructure is that expected for a "chain-end" mechanism of steric control. NMR analysis of polymer samples carrying selectively C-13-enriched end groups indicates a largely prevailing 1,2 regiochemistry for the insertion of propene into Ni-(CH3)-C-13 bonds in the initiation step and a syndiotactic steric control already effective in the second propagation step.