Stepwise Synthesis and Coordination Compound of an Inorganic Cryptand

Abstract

Modeled on organics: The inorganic cryptand [P2{O(SiiPr2)2}2{SiMe2(OSiMe2)2}] (see figure; C black, O orange, P red, Si blue) can be synthesized by a stepwise lithiation/silylation process. A first coordination compound of this ligand was obtained from its reaction with Li[Al(ORF)4].

Structural Study of Mismatched Disila-Crown Ether Complexes

“…Careful theoretical studies on the basicity of O(SiH 2 Me 2 ) 2 and OEt 2 revealed that the lower electrostatic attraction in siloxanes results from the repulsion between the positively charged Si atoms and Lewis acids [11]. This proceeding has recently been extended on cyclosiloxanes [12], which were previously described as pseudo crown ethers or inorganic crown ethers [13][14][15]. However, the structural analogy to organic crown ethers is poor, since siloxanes feature O atoms linked by -SiMe 2 -rather than -CH 2 CH 2 -.…”

“…The Me groups at the Si atoms adopt an approximately staggered conformation with average dihedral angles of 84.2(2) • at Si1/Si2 and 59.8(2) • at Si3/Si4. Worth mentioning is the unusual orientation of Si4: In all hitherto known sila-crown ether complexes, the Si atoms bonded to coordinating O atoms are approximately arranged in plane with the crown ether O atoms [12][13][14][15]18,19,23]. In contrast to this, Si4 is considerably located beneath the mean plane of the coordinating O atoms.…”

“…[18]crown-6 with Li + and Na + The hybrid ligand 1,2-disila [18]crown-6 was synthesized in a single step reaction from 1,2-dichlorodisilane and pentaethylene glycol (Scheme 2). Prior studies have shown that Li + matches well with 1,2-disila [12]crown-4 and Na + with 1,2-disila [15]crown-5 [18], so that the two cations together with 1,2-disila [18]crown-6 are supposed to fulfil the criteria of a mismatch. Reaction of 1,2-disila [18]crown-6 with lithium hexafluorophosphat in a 1:1 stoichiometry yielded a highly viscous oil.…”

“…As a result, the ligand exceeds with its ring diameter the ionic radius of the Lewis acid. Since particularly Si-based crown ethers show limited flexibility [11][12][13][14][15]18,19], we expected not all O crown atoms to participate in the coordination of the metal center [20][21][22]. The first mismatch structure of a hybrid crown ether was very recently published and is constituted of 1,2-disila [18]crown-6 and Ca(OTf) 2 (OTf = − OSO 2 CF 3 ) [23].…”

“…Compared to the hitherto known lithium complexes of hybrid sila-crown ethers, the Li1-O1 bond length is elongated, which may be the result of the strongly twisted ligand. Typically, the O atoms in sila-crown ethers complexes adopt an approximately planar conformation [13][14][15]18,19]. The disilane fragment in 1 is roughly coplanar to the thereon bonded O atoms O1 and O2, but the organic part of the ligand is strongly twisted and is wrapped around the metal center.…”