Homoleptic structures alkoxides

The X-ray crystal structure of homoleptic thorium alkoxide [Th(OCH-t-Pr2)4]2 (299) is shown in Fig. 44. Each thorium atom adopts a distorted trigonal bipyramidal geometry, and the Th208 core can be viewed as two trigonal bipyramids fused along a common axial-equatorial edge. 

Since 1980 an increasing number of single-crystal X-ray structure determinations has been carried out and it is not feasible to describe more than a representative number in detail. A number of reviews have been published. In fact only a few homoleptic metal alkoxides have been structurally characterized and the majority of structures determined involve metal complexes containing other ligands besides the alkoxo group. Therefore most of the structural data in this chapter are reported in tabular form. 

Only a few structures of homoleptic uranium alkoxides have been reported. The hexamethoxide [U(OMe)6] is a mononuclear molecule with an octahedral UOe fi amework. The mixed valency [U(iv), U(v)] complex [U2(jU.-OBu )3(OBu )6] has... 

The major types of the molecular structures for the heteroleptic derivatives appear to be the same or very close to those characteristic of homoleptic alkoxides. They can be classified as follows ... 

The homoleptic derivatives of Mo and W(VI) are rather scarcely studied. The only structurally characterized complex, W(OMe)5, possesses the molecular structure analogous to those of alkoxide halids, i.e. a dimer built up of two edge-sharing octahedra. The structure of monooxo homometallic derivatives is unknown and their individuality appears questionable. The only dioxocom-plex of molybdenum(V) isolated as pyridin solvate demonstrates the [Ti(OMe)w]-type structure (Table 12.19). 

A monoamide complex was obtained with [OCtBu(2-CH2-NC5H3-6-Me)2] as a co-ligand (Fig. 19) [127]. The overall structure features are very similar to the aforementioned homoleptic Sm-system except that a monodentate alkoxide ligand has been replaced by a N(SiMe3)2 group. The amide group makes the complex soluble in aliphatic hydrocarbons. 

Simple CH-alkoxides continue to reveal surprising new structure chemistry and the composition of Ln(OMe)3 and Ln(OEt)3 is not yet determined. Mononuclear lanthanide aryloxide complexes are well-examined and are the only fully characterized 3-coordinate, homoleptic Ln(OR)3 species. The variation of the steric environment in pure CH- and CHF-alkoxides with respect to volatility (molecular mass optimization) seems to be rather exhausted. It was shown that functionalization can ensure volatility and although the entire MOCVD-busi-ness gets somewhat stuck, CHF- and CHdo-alkoxides are promising alternatives to the /J-diketonates. Sol gel technology can fall back on highly soluble CH- and CHdo-alkoxides. 

Hitchcock, P.B., Lappert, M.F., and MacKinnon, A.l. (1988) Use of a highly hindered phosphino-alkoxide ligand in the formation of monomeric homoleptic lanthanoid metal complexes X-ray structures of [Ln(r -OCBu2CH2PMe2)3] (Ln = Y or Nd). Journal of the Chemical Society, Chemical Communications, 1557-1558. 

The homoleptic sterically hindered thiolate complex [Mo2(TMT)g] containing Mo— Mo triple bonds was first prepared by a multistep reaction (35). The X-ray crystal structure showed a staggered configuration for the thiolate ligands with an Mo— Mo distance of 2.228(1) A (35). They were synthesized subsequently by a simple one-step synthesis involving the reaction of M0CI4 with the TIPT anion in 1,2-dimeth-oxyethane and structurally characterized. A study of their chemistry showed them to be rather unreactive compared with their alkoxide analogues (36). 

Although many heterobimetallic alkoxides were characterized structurally (cf. Section III. A), the crystal structure of the first homoleptic heterotrimetallic isopropoxide [Ba Zr2(0-/-Pr)9 (/i-0-(-Pr)2Cd(/t-0-/-Pr)]2 was recently elucidated (39a). 

ClFeLM. (69), C1CuLai, and ClCuLra and ClCuLZr (70), ClLa(LZr)2, and Cl2LaLZr (71) were synthesized even in the cases of central metals that can form the homoleptic derivatives EL . In spite of inherent difficulties in the X-ray structural elucidation of metal alkoxides (72), it was possible to determine X-ray structures of the chloride bridged dimers [Cd(u-Cl)L7r]2 (73) and [Pr(LA1)2(ft-Cl)Pr-i-OH]2 (74). 

Only a few complexes containing Ce(IV)-carbon bonds have been structurally characterized so far. Salt metathesis reactions utilizing mixed alkoxide nitrate Ce(IV) precursors [Eq. (63)] [311], as well as the oxidative salt elimination of K[Ce(COT)]2 ate complexes with silver iodide, led to isolable organocerium(IV) species [Eq. (64)] [80e]. The oxidation of the homoleptic Ce(III) alkoxide Ce(OCrBu3)3 with benzoquinone yielded a dinuclear heteroleptic Ce(IV) complex [Eq. (65)] [312]. 

SOLID STATE AND MOLECULAR STRUCTURES 15.3.4.1 Prototypal Structures for Homoleptic Alkoxides... 

Glycols are highly reactive towards metal alkoxides to form homoleptic and mixed alkoxo-glycolate derivatives. This alcohol exchange reaction (see Section 7.10.3.1.3) is driven by the formation of chelated or bridged structures with both (dianionic) OCR2CR2O—... 

The reactions of M2(OBu )e (M = Mo, W) with less sterically demanding alcohols RCH2OH (R = C-C4H7, C-C5H9 c-CeHii, PP) afford a series of structurally related homoleptic alkoxides M4(OCH2R)i2 according to Eq. (2.196) ... 

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