The synthesis of crowded peri-5-bromo-6-(organostannyl)acenaphthenes is described. Reaction of 5,6-dibromoacenaphthene with 1 equiv of n-BuLi at −40 °C in diethyl ether followed by addition of the appropriate organotin reagent at 0 °C gave 5bromo-6-(triphenylstannyl)acenaphthene (1), 5-bromo-6-(chlorodiphenylstannyl)acenaphthene (2), bis(6-bromoacenaphthen-5-yl)diphenylstannane ( 3), bis(6-bromoacenaphthen-5-yl)dibenzylstannane ( 4), bis(6-bromoacenaphthen-5-yl)dibutylstannane ( 6), and bis(6-bromoacenaphthen-5-yl)dichlorostannane ( 7) in low to medium yields (10−56%). 4 was converted into 5-iodo-6-bromoacenaphthene (5) by stirring overnight in the presence of a large excess of iodine. The new compounds were fully characterized spectroscopically. 119 Sn NMR spectra suggest and interaction between the tin atoms and the neighboring peri halogen atoms. Single-crystal X-ray studies on 1−4 and 6−8 revealed Sn•••X distances which are significantly less than the sum of the van der Waals radii, while DFT calculations indicate Wiberg bond indices of up to 0.11. Furthermore, there is evidence of the onset of 3c−4e bonding, though according to natural population analysis, the charge on tin is close to +2 in all compounds studied. Electrostatic interactions may thus be another important driving force for the close Br•••Sn interactions, along with the small covalent (donor−acceptor) contributions.
The efficiency and applicability of three different methods to synthesize polystannanes with different side chains are described. By means of dehydrogenative coupling utilizing the transition metal catalyst RhCl(PPh 3 ) 3 (Wilkinson's catalyst), n-Bu 2 SnH 2 reached the highest molar masses. Dehydrogenetive coupling in the presence of tetramethylethylenediamine could be best employed for (4-n-BuPh) 2 SnH 2 . Wurtz coupling using sodium in liquid ammonia was best suited for Ph 2 SnCl 2 . Next to the above-mentioned educts, n-Bu(Ph)SnX 2 (X = H or Cl (as appropriate for the particular route) was used for polymerization resulting in one of so far rare example of asymmetric polystannanes with high molecular masses.
(11)) have also been prepared, along with bromo-sulfur derivative Acenap(Br)(SEt) 15. All eleven chalcogen-tin compounds align a Sn-C Ph /Sn-Cl bond along the mean acenaphthene plane, and position a chalcogen lone-pair in close proximity to the electropositive tin centre promoting a weakly attractive intramolecular donor−acceptor E•••Sn-C Ph / E•••Sn-Cl 3c-4e type interaction to form. The extent of E→Sn bonding was investigated by X-ray crystallography and solution-state NMR and was found to be more prevalent in triorganotin chlorides 5-9 in comparison with triphenyltin derivatives 1-4. The increased Lewis acidity of the tin centre resulting from coordination of a highly electronegative chlorine atom was found to greatly enhance the lp(E)−σ*(Sn−Y) donor−acceptor 3c-4e type interaction, with substantially shorter E-Sn peri-distances observed in the solid for triorganotin chlorides 5-9 (~75% ∑r vdW ) and significant 1 J( 119 Sn, 77
In subsequent growth runs on (0001) seeds of 4H-SiC, the grown layers were used to study the growth rate and defect formation. Whereas the total pressure drastically influences the growth rate, there is almost no effect of varying the seed thickness on mass transport conditions. Using optical microscopy two different regions have been identified. One, being the (0001) plane and the other, being the so-called off-facet area. This leads to different growth regimes at the interface simultaneously.
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