Phosphinoalkylsilyl chemistry: tripodal and mesomolecular complexation




Gossage, Robert Arthur

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The preparation of the modified silane [special characters omitted]; a phosphinoalkylsilane or PSi) via an alkylzirconium intermediate is reported. The synthesis of [special characters omitted] was carried out by the reaction of organolithium reagents with chloro-silanes at low temperature. The PSi compounds are isolated as air-sensitive, thermally stable and very viscous liquids. The reactivity of two of the silanes was investigated with the platinum group metal complex [special characters omitted] (cod = cycloocta-1,5-diene). In both cases, square planar platinum (II) complexes were isolated. The reactivity of [special characters omitted] produces five coordinate M (III) complexes which undergo stereomutation. The isomerisation of the syn to anti forms of [special characters omitted] has been examined at several temperatures via NMR spectroscopy and the activation parameters determined for the conversion of the syn to the intermediate isomer form [special characters omitted]. The implications of the stereomutation phenomona are discussed in relation to catalysis. None of the isomers of this complex forms a stable six coordinate adduct when reacted with a number of common nucleophiles. The analogous compound where M = Ir and related complexes of the formula [special characters omitted] are reactive towards CO to form stable six coordinate adducts containing two M-P and one M-Si, M-H, M-CO and a M-Cl bond. Some of these adducts can be made directly by the reaction of the PSi ligand precursor with [special characters omitted] (M = Rh, Ir) at room temperature. The reaction of the silane [special characters omitted] produces six coordinate complexes directly. For M = Ir, the compound reacts with CO to produce a six coordinate cation by displacement of a chloride ligand, the latter of which then acts as a non-coordinating counterion. A series of organosilicon dendrimers of the type : [special characters omitted] ([G-1] : x = 3, y = 2 = q = 0; [6-2] : y = 3, x = 9 , z = q = 0; [G-3] : z = 3, y = 9, X = 27, q = 0; [G-4] : q = 3, z = 9, y = 27, x = 81) are sythesised and examined spectroscopically. All of the dendrimers are air stable liquids. Species G3 has a marked tendency to undergo what appears to be self-condensation polymerisation. End and core group substitution is presented for a carbosilane dendrimer containing one shell of identical exterior Si atoms. The dendrimeric end groups can be modified by the replacement of a terminal chloride by fluoride, hydrogen, alkyl groups or metal complexes. The selective removal of a core phenyl group can be accomplished with the strong acid [special characters omitted]. The resulting silyl triflate can in turn be used as a precusor to a silyl ether, hence facilitating selective core group modification.



Silane, Complex compounds, Transition metal compounds