The chemistry of titanocene bisborane complexes Cp2Ti (HBcat') 2 (1a-g)(HBcat'= catecholborane or a substitued catecholborane) and monoborane complexes Cp2Ti (HBcat')(L)(2-4)(L= PMe3, PhSiH3, or PhCCPh) is reported. These complexes are unusual σ- complexes. The BH bond in the catecholborane of 1 acts as a two-electron-donor ligand. The 4-tert-butyl version 1a was studied in depth and underwent ligand substitution ...