Cyclodimethylsiloxane (Me₂SiO)_m (m = 3–6) Ring Transformations on Reactions with AgSbF₆; Crystal Structure of Ag(Me₂SiO)₇SbF₆

Abstract

The reaction of D m (D = Me 2 SiO, m = 3-6) with silver hexafluoroantimonate in liquid SO 2 affords a mixture of AgD n SbF 6 (n = 6-8) complexes. Upon the addition of CH 3 CN, Ag + -directed ring transformations are effected, which allows for the isolation of neat D n (n = 6-8). The AgD n + cations are rare examples of Lewis acid donor complexes of siliconWe recently reported the preparation of Li + -cyclodimethylsiloxane host-guest cations directly from their components [1] and provided rare examples of silicon ethers behaving as Lewis bases as shown in Equation (1 ) with large anions, no other examples of a metal-cation-siloxane adduct have been reported. Metal-cation-siloxane salt formation is favored by large anions, which minimizes the unfavorable lattice-energy changes. Therefore, the question as to whether the formation of the complexes could be extended to the use of commercially available salts with smaller anions as the starting materials remains. The Ag + cation is regarded as a soft Lewis acid [3] and has a low affinity to oxygen donor ligands.[4] Nevertheless, we report below the first examples of the transition-metal-cation-siloxane SbF 6 -salts of AgD n + (n = 6-8) formed by the reactions of D m (m = 3-6) with AgSbF 6 in liquid SO 2 . Unlike the Li[Al] case, transformation of the siloxane rings occur with Ag + acting as a template for the formation of the most thermodynamically stable metal-cation-cyclodimethylsiloxane complex. The formation of macrocyclic ethers by the reaction of AgAsF 6 with (CH 2 O) 3 or ethylene oxide was described by Roesky and his coworkers.[5] However, no similar ring transformation reactions of cyclodimethylsiloxanes under mild conditions have been previously reported.[6] Ring-opening polymerization of D m (m = 3-6) has been widely investigated, and these results are also of interest in this context. [a]

Coordination and Oligomerisation of the Siloxanephosphane Cage Compound [P2{(SiMe2)2O}3]

“…It was not possible to isolate the salt 4 ] in a crystalline state, however, we succeeded in removing the lithium ion from the ligand 5 by adding a small amount of THF to the reaction mixture, and obtained the free ligand 5 as colourless crystals. The structural solution and refinement was carried out in the monoclinic space group P2 1 /n, and undoubtedly revealed the formation of the dimeric ligand with a rectangular arrangement of the four phosphorus atoms as shown in Figure 5.…”

“…The Al À P bonds are between 253.5 and 256.0 pm long. Analogously, from the reaction of 2 with GaEt 3 the compound [ (4) 4 ] by two analytical methods, namely, NMR spectroscopy and electrospray mass spectrometry (ESI-MS). The 31 P{ 1 H} NMR spectrum of such a reaction mixture in a C 6 H 5 CF 3 /C 6 D 6 solvent mixture revealed a quartet signal of four peaks with nearly equal intensities after several days.…”

“…From these reactions, mixtures of the complex cations [Ag@D6] + , [Ag@D7] + and [Ag@D8] + could be obtained. [4] These results showed that cyclosiloxanes can be considered as inorganic analogues of the well-established crown ether ligands. In this respect the cage […”

“…[2] In 2006 the group of Passmore was able to synthesise complexes of the ligands (SiMe 2 O) 5 and (SiMe 2 O) 6 (D5 and D6, respectively) systematically by reactions with the lithium salt of the weakly coordinating anion [AlA C H T U N G T R E N N U N G (OR F ) 4 ] À . [3] In the obtained products [Li@D5] 4 ], the lithium ion is located in the middle of the almost planar siloxane rings. In the same year, ring transformations were observed in reactions of the cyclosiloxanes Dn (n = 3-6) with AgSbF 6 .…”

“…[1] In this paper we describe the application of the salt Li[Al-A C H T U N G T R E N N U N G (OR F ) 4 ] (R F = CA C H T U N G T R E N N U N G (CF 3 ) 3 ) as a reagent for a dimerisation of a main-group-element cage compound. This reaction yields a new macrocyclic molecule, which could not be obtained by classical synthetic strategies.…”