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Novel Organoaluminum Lewis Acids via Selective Aluminum‐Tin Exchange Processes – Electrophilic Initiation by the Aluminum Halide and Ensuing Complexation by the Resulting Tin Halide
Author(s) -
Eisch John J.,
Mackenzie Katrin,
Windisch Harald,
Krüger Carl
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199901)1999:1<153::aid-ejic153>3.0.co;2-0
Subject(s) - chemistry , tin , halide , benzene , aluminium , lewis acids and bases , chloride , inorganic chemistry , adduct , reagent , electrophile , medicinal chemistry , polymer chemistry , organic chemistry , catalysis
With the goals of preparing novel carbaluminating reagents and mono‐ and bidentate organoaluminum Lewis acids, the scope and limitations of synthesizing the requisite organoalanes by the aluminum‐tin exchange between an aluminum halide and the appropriate organostannane have been examined in detail. The interactions of such tin precursors as 1,2‐bis(trimethylstannyl)ethyne, allyltri‐ n ‐butyltin, benzyltrimethyltin, and 1,2‐bis(trimethylstannyl)benzene and various aluminum chlorides of the type, R n AlCl 3– n (R = Me, Et), gave selective aluminum‐tin exchange at the sp‐ or sp 2 ‐hybridized carbon–tin bond and produced such organoalanes as allyl(methyl)aluminum chloride, benzylaluminum dichloride, 1,2‐bis(diethylalumino)ethyne, 1,2‐bis(dimethylalumino)benzene, 1,2‐bis[chloro(methyl)alumino]benzene, and 1,2‐bis(dichloroalumino)benzene in high yield. A complicating factor was the tendency of the R 3 SnCl by‐product to complex with the resulting organoalane. In some cases, exemplified by allyl(methyl)aluminum chloride, such complexation did not interfere with the carbaluminating action of the reagent; in other cases, exemplified by 1,2‐bis[chloro(methyl)alumino]benzene, the R 3 SnCl could be removed by means of π‐bases and reduced pressures; and in still other structures, as with 1,2‐bis(dichloroalumino)benzene, the tin chloride could not be dislodged at moderate temperatures. The structure and bonding in such tin halide–aluminum halide complexes in solution were investigated with the 1:1 adducts of AlCl 3 with Me 3 SnCl and with n Bu 3 SnCl, respectively, by means of multinuclear NMR spectroscopy. Furthermore, an XRD of the solid complex, Me 3 SnCl · AlCl 3 , was carried out. Such complexes were shown to consist of 1:1 ion pairs of the type [R 3 Sn + ][AlCl 4 − ] in dilute solution and of a chiral polymeric helix in the solid state wherein planar Me 3 Sn + units are linked to each other via bridging tetrachloroaluminate anions, Cl–(AlCl 2 )–Cl − . Treatment of such complexes with either benzyltriethylammonium chloride (one or two equivalents) or tetramethylphosphonium chloride leads to the displacement of Me 3 SnCl and the formation of the expected ionic complexes. Finally, the importance of such novel reagents and chelating Lewis acids to organic synthesis and olefin polymerization is discussed and elucidated.