The complexes of titanium tetrachloride with one or two molecules of formaldehyde have been studied with ab initio SCF-MO methods. Several structures of the H2CO-TiCl4, (H2CO)2-TiCl4, and (H2CO-TiCl4)2 complexes have been considered, and the rearrangements between them have been discussed. The interaction between formaldehyde and TiCl4 has been analyzed in terms of molecular orbital interactions, and the effects produced by complex formation have been rationalized. © 1992, American Chemical Society. All rights reserved.