Synthesis and structure of a heterotrimetallic (Li/Er/In), heptacyclic metallasiloxane cage compound ☆

Abstract

The unusual heterotrimetallic (Li/Er/In), heptacyclic metallasiloxane cage compound [{(Ph 2 SiO) 2 O} 3 {Li(THF) 2 } {InMe}]Er (2) has been prepared in 98% yield by reaction of the erbium bis(disiloxanediolate) derivative [{(Ph 2 SiO) 2 O} 2 {Li(THF) 2 } 2 ]ErCl (1) with trimethylindium, InMe 3 . The product was structurally characterized by single-crystal X-ray diffraction. © 2014 Elsevier B.V. All rights reserved. Well-defined molecular metal siloxides (=metallasiloxanes) comprising M-O-Si functionalities attract significant interest due to their diverse potential applications [1]. Not only are metal siloxides excellent molecular models for silica-supported heterogeneous metal catalysts [2], but they can also serve as precursors for new materials [3], nanoparticles [4], well-defined surface species [5], and homogeneous catalysts [6]. A particularly useful and versatile precursor for a large variety of metal siloxides is the simple and readily accessible 1,1,3,3-tetraphenyl-disiloxane-1,3-diol, (HO)SiPh 2 OSiPh 2 (OH), which forms stable complexes with virtually all metallic elements across the Periodic Table ranging from lithium to uranium [1,7]. Among these, lanthanide disiloxanediolates form a well-investigated class of compounds [1]. Most prominent are heterometallic lanthanide bis(disiloxanediolates) of the type [{(Ph 2 SiO) 2 O}{Li(S) n }] 2 LnCl(S) (Ln = rare-earth metal; S = Et 2 O, THF, DME; n = 1, 2 Initial reactivity studies revealed that unusual heterometallic products could be isolated from reactions of these lanthanide bis(disiloxanediolates) with Group 13 metal trialkyls. Scheme 2 illustrates the outcome of reactions of type A complexes (Ln = Sc, Y) with AlMe 3 and InMe 3 , resp. Treatment of the Sc complex with Yet another, completely different product was obtained when a praseodymium complex of type C was treated with trimethylindium (Scheme 3). This reaction resulted in double insertion of InMe 2 units into the 12-membered Si 4 O 6 Li 2 inorganic ring system attached to praseodymium and formation of the novel ionic product [Li(THF) In the present study, we found that a reaction of the type B erbium bis(disiloxanediolate) complex [{(Ph 2 SiO) 2 O} 2 {Li(THF) 2 } 2 ]ErCl (1) with trimethylindium yet again took an entirely different course (Scheme 4). The reaction of [{(Ph 2 SiO) 2 O} 2 {Li(THF) 2 } 2 ]ErCl (1) with trimethylindium was carried out in toluene solution using a molar ratio of 1:3 [8]. The reaction mixture was first stirred at r.t. and then refluxed for 1 h. After removal of a small amount of insoluble material (presumably Li[InMe 4 ]) by filtration, the product 2 crystallized directly from the concentrated filtrate in the form of colorless prisms. Meaningful NMR spectra of 2 could not be obtained due to the strongly paramagnetic nature of the Er 3+ ion. After all, as is characteristic for the chemistry of metal disiloxanediolates, the usual combination of spectroscopi