The reaction of (c-C6H11)7Si7O9(OH)3 (1a) with GaX3 (X = Cl or I) in the presence of Proton Sponge (C14H18N2) affords (c-C6H11)7Si7O12GaX- C14H18N2·H+ (2a, R = Cl; 2b, R = I). A single-crystal X-ray ...diffraction study of 2a reveals discrete ions with no significant interactions. Upon thermolysis both 2a and 2b liberate an equivalent of C14H18N2·H+X- to produce quantitative yields of (c-C6H11)7Si7O12Ga2 (3), a siloxy-bridged dimer which is isomorphous with previously characterized dimers containing Ti3+ and V3+. The reaction of 3 with Ph3PO affords (c-C6H11)7Si7O12Ga(OPPh3) (5), which was characterized by a single-crystal X-ray diffraction study. The reaction of trisilanol 1a with Ga(CH2SiMe3)3 affords 6, an interesting cluster derived from the reaction of two molecules of 1a with six molecules of Ga(CH2SiMe3)3 and six molecules of water.
Quartz crystal microbalance and scanning tunneling microscopy experiments have been used to demonstrate that self-assembled monolayers of thiophene on gold can be quantitatively replaced by ...absorption of methanethiol from the gas phase. Adsorption of thiophene on the gold surface results in the relaxation of the clean gold surface reconstruction and the formation of vacancy islands or “pits” in the gold. Subsequent annealing of the monolayer can result in the complete removal of the vacancy islands. Methanethiol displacement of thiophene monolayers that have been previously annealed to remove vacancy island “pits” does not generate additional “pits” in the gold surface. Thus, ordered methanethiol monolayers which are free from vacancy island “pits” in the underlying gold surface can be formed by displacement of annealed thiophene monolayers. These results provide strong additional evidence that the formation of vacancy islands in the gold during the formation of alkanethiol SAMs is directly associated with relaxation of the clean surface reconstruction, rather than conventional chemical etching of the surface by alkanethiol.
Alkanes are among the most abundant and unreactive of all organic compounds. Industrial use of these resources often relies upon free-radical activation of carbon-hydrogen bonds, often at high ...temperatures, thereby limiting the selectivities that can be achieved in any functionalization reaction. Consequently, the selective activation of C-H bonds by homogeneous transition-metal compounds has been a topic that has been of great interest to the organometallic community for many years. In this Account, mechanistic studies with a series of homogeneous rhodium organometallic complexes are summarized that provide for the first time a comparative evaluation of the relative equilibrium constants and rates of reaction for both alkane and arene hydrocarbon activation.
