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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 1,3bis(acy1oxy)tetraalkyldistannoxanes 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 - polycyclostannanes, obtained either by the palladiumcatalyzed decomposition of dialkylstannanes or by reduction of dichlorodialkylstannanes with metals, are also very good latent catalysts for silicone curing. When incorporated into reactive mixtures under nitrogen, they do not catalyze the condensation. Upon exposure to air, they are oxidized to active catalysts which cure silicones. These di-or polystannanes can be considered airactivated latent organotin catalysts.In the plastics industry, the most important reactions catalyzed by bis(acy1oxy)dialkylstannanes' are the curing of silicones, which need to be cured to show their interesting elastomeric properties? the preparation of polyurethanes? which has to be accelerated when high production rates are needed, and esterification processes. Organotin catalysts are used in these reactions because of their high efficiency, their low cost, and their moderate toxicity. Such high efficiency may cause inconvenience, however, as condensation or addition reactions start as soon as reactants and catalyst are mixed t~g e t h e r .~ We recently designed and prepared new latent organotin catalysts, bis-[2-(acyloxy)dkyl] diorganostannanes,6 which provide long pot-lives for the mixtures into which they have been incorporated and which can be activated at will by heating. These tetraorganostannanes are inactive, but upon heating, they undergo an anti @-elimination reaction leading to 0 (5) Jousseaume, B.; Gouron, V.; Maillard, B.; Pereyre, M.; Franc&, J.-M. Organometallics 1990,9,1330. Jousseaume, B.; Gouron, V.; Pereyre, M.; FrancBs, J.-M. Appl. Organomet. Chem. 1991,5, 136. Gouron, V.; Jousseaume, B.; Pereyre, M.; Verlhac, J. B.; Franc&, J.-M. In Chemistry and Technology of Silicon and Tin; Oxford University Press, Oxford Science Publishers: Oxford, U.K., p 239. Franc&, J.-M.; Gouron, V.; Jousseaume, B.; Pereyre, M. Eur. Pat. 338947, 1989; 421891,1991. (6) Jousseaume, B.; Noiret, N.; Pereyre, M.; Franc& J.-M.; Petraud, M. Organometallics 1992,11,3910. Jousseaume, B.; Guillou, V.; Noiret, N.; Pereyre, M.; Franch, J.-M. J. Organomet. Chem. 1993, 450, 91. Jousseaume, B.; Noiret, N.; Pereyre, M.; FrancBs, J.-M. J. Chem. SOC., Chem. Commun. 1992, 739.