Air activated organotin catalysts for silicone curing and polyurethane preparation

Abstract

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.

Reactions of hafnocene stannyl complexes with stannanes: implications for the mechanism of the metal-catalyzed dehydropolymerization of secondary stannanes

“…Interestingly, in addition to the expected product from a-elimination (10), there are other metal species observed during the course of the reaction. After heating a concentrated ( [11] i ¼80 mM) benzene-d 6 solution for 1 h at 100 8C, the major species observed by 1 H NMR spectroscopy were 10 (37%), unreacted 11 (29%), two intermediates 13 (17%) and 14 (7%), and three other minor products (10% total).…”

“…Observation of CpCp p Hf(Me)Cl (10). Complex 11 (0.0088 g, 0.015 mmol) and ferrocene (0.0025 g, 0.013 mmol) were weighed in a 1.00^0.01 mL volumetric flask, and toluene-d 8 was added to make 1.00 mL.…”

Tin in Catalysis

“…A comprehensive review on the state-of-the-art up to 1998 is given by Delmond and Dumartin. 32,40 The general reaction sequence for the preparation of the title compounds is given in Scheme 6.1.3. The main drawback at the time the review was written was, being insoluble, the compounds were difficult to characterize completely, thus hampering a good understanding of their reactivity at the solid-liquid interface.…”

“…four-coordination sphere in the dry solid state and at the solid-liquid interface. 40 An alternative synthetic route towards a functionally pure, as assessed by hr-MAS NMR, organotin trichloride grafted onto cross-linked polystyrene with the C11-spacer, [P-H] (1−t) [P-(CH 2 ) 11 -SnCl 3 ] t , was elaborated by extending the method used earlier for the SnBuPh 2 analog (Scheme 6.1.4) 41 The general reaction scheme for the synthesis of the polystyrenegrafted alkyltin trichloride compound, given in Scheme 6.1.4, avoids a priori potential tin contamination of the final catalysts that might result from the work-up procedures of the heterogeneous reaction mixture having contained SnCl 4 . The existence of such an Sn 2 O 2 ring core has not been formally identified, so far, in the grafted C4-and C6-analogs.…”

Organotin Compounds in Technology and Industry

“…The tetrabutyldiacyloxydistannanes are inert until they are air-oxidised to the distannoxanes when they become efficient catalysts [equation (25)]. 26 (25) Similarly the 2-carboxyethyltin compounds are non catalytic, but at elevated temperatures, ethene is eliminated to give the catalytic tin carboxylates [equation (26)]. …”