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Some reactions of metal-metal bonds with fluoro-olefins Tsai, James Hwa-San

Abstract

Current interest in metal-metal bonded systems has been largely confined to the synthesis of such compounds, and little is known of the chemical behaviour of the metal-metal bonds. One of the simplest systems to study was the tin-tin bond, and thus the additions of fluoro-olefins to hexamethylditin were examined. Such additions were found to occur readily under ultraviolet irradiation which suggests that the formation of (CH₃)₃Sn radicals is an important feature of the reaction mechanism. The formation of adducts such as (CH₃)₃Sn(CF₂CF₂)nSn(CH₃)₃ (n = 1 or 2) , (CH₃)₃SnCF₂CF(CF₃)Sn(CH₃)₃, (CH₃)₃Sn(CFHCF₂)nSn(CH₃) ₃ (n = 1 or 2), and (CH₃) ₃Sn(CH₂CF₂)nSn(CH₃)₃(n = 1 or 2) , as well as the occurrence of secondary reactions leading to products of the type (CH₃)₃Sn(CF₂CF₂)nH (n = 1,2, or 3), (CH₃) ₃SnCF₂CF(CF₃)H, and other analogous compounds are discussed. The (CH₃)₃Sn radical was found to have nucleophilic character, and to attack exclusively on the group marked with an asterisk in the following olefins: [ Formulas omitted ]. The factors responsible for the orientation of such unsymmetric olefins with respect to the (CH₃)₃Sn radical are considered. The compound (CH₃)₃Sn-Mn(CO)₅, containing a mixed metal-metal bond, was also shown to be very reactive, but to behave differently toward a variety of olefins. A two-carbon insertion into the tin-manganese bond was readily achieved by the reaction with tetrafluoroethylene at 50° under ultraviolet irradiation, which again might suggest that a free-radical mechanism is involved. Two interesting dimers, i.e., the "boat and chair" forms of [CF₂=CFMn(CO) ₄] ₂, containing both σ- and π-bonds were formed, presumably through the decomposition of the adduct (CH₃)₃SnCF₂CF₂Mn(CO)₅. With trifluoroethylene, neither adduct nor dimer is obtained but the novel fluorovinyl-transition metal compounds cis- and trans-(CFH=CF)Mn(CO)₅ were formed. When reacted with trifluorochloroethylene, CF₂=CFCOMn(CO)₅ was predominantly obtained, as well as cis- and trans-(CFCl=CF)Mn(CO)₅ in small yields. The reaction with ethylene caused the cleavage of the manganese-carbonyl bond rather than the tin-manganese bond, forming (CH₃) ₃Sn-Mn(CO) ₄(π-C₂H₄) . The catalytic activity of (CH₃) ₃Sn-Mn(CO) ₅ in the hydrogenation of ethylene was also examined. Detailed spectroscopic studies were made for the products obtained in the pure state.

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