The soft scorpionate ligand hydrotris(6-tert-buty1-3-thiopyridazinyl)borate (Tn) was found to exhibit pronounced photoreactivity. Full elucidation of this process revealed the formation of 6-tert-butylpyr-idazine-3-thione (PnH) and 4,5-dihydro-6-tert-butylpyr-idazine-3-thione (H(2)PnH). Under exclusion of light, no solvolytic reactions occur, allowing the development of high-yield preparation protocols for the sodium, potassium, and thallium salts and improving the yield for their derived copper boratrane complex. The photoreactivity is relevant for all future studies with electron-deficient scorpionate ligands.