Summary: Upon exposure to air, 1, 2-bis (acyloxy) tetraalkyldistannanes incorporated in mixtures of either silicone oils and curing agent, or of isocyanates and alcohols, are oxidized to 1, 3-bis (acy1oxy) tetraalkyldi-stannoxanes which show excellent catalytic properties for curing silicones or for preparing polyurethanes. Under nitrogen, they induce longer pot-lives than the usua 1 bis (acy 1 oxy) d ia 1 ky Is tannane catalysts. Peru 1 ky 1- ...