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Hypercoordination by Multiple Dangling Benzylmethoxy Ligands in Highly Crowded Triaryltin Bromide [(2-MeOCH2 C6 H4
Henk S van den Bogaard1, Hemant K Sharma1, Alejandro Mettta-Magaña1
1Department of Chemistry and Biochemistry, The University of Texas at El Paso, El Paso, TX 79968, USA.
Abstract:
The reaction between the Grignard reagent formed from Mg and 2-bromobenzylmethyl ether and SnCl4 produced four products: [2-(MeOCH2 )C6 H4 ]3 SnBr (1), [2-(MeOCH2 )C6 H4 ]2 SnX2 (2, X2 =Br2 (a) and BrCl (b)), [{2-(MeOCH2 )C6 H4 }3 Sn]2 (3), and [{2-(MeOCH2 )C6 H4 }2 SnBr]2 O (4). In the case of 1, two of the three dangling arm O atoms coordinate to the central tin atom with O-Sn internuclear distances of 2.53 (O1) and 2.91 (O2) Å, the shorter interaction being trans to the Br atom, the other trans to a phenyl carbon atom. In the case of 2a the resulting hexacoordinate structure exhibits two very short O-Sn interactions of 2.42 and 2.50 Å, well below the sum of the VdW radii of O and Sn, 3.69 Å. The sterically crowded ditin compound 3 was obtained in trace amounts and the structure demonstrates no dangling O-Sn interactions. General changes in structure compared to other distannane systems are reflective of the great steric crowding. Distannoxane 4, has a Sn-O-Sn bond angle of 148.1(2)° which is larger compared to other distannoxane structures. The intermolecular interactions between Sn-O 2.470(3) and 2.521(3)Å and 2.665(3) and 2.629(3)Å for Sn1 and Sn2 respectively are responsible for a distorted octahedral geometry around the two tin atoms. The various 119 Sn, 13 C and 1 H NMR spectra are in accord with their structural analysis for 1 and 2, and in the solid state 13 C NMR spectrum of 1 the dangling methylene group is observable whereas is solution there is a rapid dynamic equilibrium resulting in a single resonance for all methylene groups.
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