Disiloxanediolates and Metallasilsesquioxanes of the Rare Earth Elements 

Abstract

This research report summarizes recent results in the chemistry of lanthanide disiloxanediolates and metallasilsesquioxanes. Both classes of compound can be regarded as realistic model compounds for silica-supported lanthanide catalysts. Heterobimetallic siloxanediolates of the lanthanidesThe chemistry of metallasiloxanes derived from silanediols, disiloxanediols and related Si-OH species continues to be an area of vigorous research activities [1][2][3][4][5][6][7] Lanthanide(III) disiloxanediolates a) Lanthanide(III) mono(disiloxanediolates)By now, the chemistry of lanthanide bis(disiloxanediolates) is well established, and some lanthanide tris(disiloxanediolates) have also been prepared and structurally characterized (vide infra) [9]. Only the synthesis of mono-substituted rare earth metal complexes derived from difunctional siloxanediolate ligands had not been achieved until recently. Thus far only one compound of this type has been synthesized and structurally 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Scheme 1An X-ray study confirmed the presence of the first mono(trisiloxanediolate) complex of a lanthanide element. The molecule contains a puckered eight-membered for hafnium and uranium [6,7,9]. In these cases, however, the trisiloxanediolate ligand is formed by ring-enlargement reactions starting from disiloxanediolate precursors. A prominent structural feature of compound 5 is the presence of a so-called "ate" complex resulting from retention of lithium chloride. "Ate" complexes are a common phenomenon in organolanthanide chemistry. Their formation involves retention of alkali halides formed during the course of a reaction, thereby reflecting the strong tendency of the large lanthanide ions to achieve high coordination numbers [11]. In compound 5 the situation is such that a complex of the type "[Ph 2 Si(OSiPh 2 O) 2 ]YbCl" is sterically highly unsaturated (coordination number 3 at Yb). In this case stabilitzation is achieved not only by coordination of one THF ligand but also through "ate" complex formation with retention of two equivalents of LiCl. One lithium chloride is connected to the central ytterbium via two bridging chloride ligands. The second LiCl is coordinated in a rather peculiar way by additional coordination of a siloxide oxygen atom to Li. In both cases, the coordination sphere around lithium is supplemented by two THF ligands (Fig. 1) [10]. Page 4 of 53Wiley-VCH ZAAC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 Accordingly these complexes have been termed "metallacrown" derivatives of scandium and yttrium [9]. In contrast, large Ln 3+ ions such as Pr 3+ , Nd 3+ or Sm 3+ do no fit into the center of the twelve-membered ...

Azido-Functionalized Aromatic Phosphonate Esters in RPOSS-Cage-Supported Lanthanide Ion (Ln = La, Nd, Dy, Er) Coordination

“…The rigid POSS-cage structure in combination with the phosphonate esters is assumed to enhance the excited-state lifetimes of the metal centers, paving the way for potential future molecular data storage and manipulation. For a comprehensive overview on POSS-cage as well as lanthanide POSS chemistry the reader is referred to the work of Edelmann and co-workers. − …”

Siloxane Coordination Revisited: Si−O Bond Character, Reactivity and Magnificent Molecular Shapes

“…In comparison to neutral (crown)ethers, these ligands have a negative charge and it is inevitable for the oxygen atom to interact with the metal centre. In this way, many silanolate salts have been characterized and also gained some fields of application, mainly catalysis [72–81] . Similar to the above mentioned silanolates compounds which bear ligands constituted of An ‐Si(R 2 )−O−Si(R 2 )‐ An ( An =any terminal anionic group), − Si(R 2 )−O−Si(R 2 ) − (silicide‐like) or related anionic moieties have been obtained.…”

Modern concepts and methods in the chemistry of polyhedral metallasiloxanes

“…30) and bent lanthanide π-complexes (Fig. 30, A) has been highlighted, where it was suggested that they may be referred to as "inorganic metallocenes" [138]. In our opinion, the similarity is only in terms of geometry because in 90, the siloxane fragments are covalently bonded to metal atoms and there is no π-bond formation.…”