Alkaline earth metal aryloxides

Although the development of metal atom vapour technology over the past three decades has shown tremendous utility for the synthesis of a wide range of organometallic compounds (many of which were inaccessible by conventional techniques), the use of this technique for the synthesis of metal alkoxides and related derivatives does not appear to have been fully exploited. In 1990, Lappert et al. demonstrated the utility of this technique for the synthesis of M—O—C bonded compounds by the isolation of alkaline earth metal aryloxides. 

Recently, mild solid-state chemistiy, involving the treatment of the metals in the presence of the ligand and a flux agent in the absence of a solvent, has been highly successful towards the preparatirHi of various heavy alkaline-earth metal aryloxides, including the heterobimetaUic species [AM(ODpp)3] (ODpp or 2,6-diphenylphenoxide) (A = Na, K M = Ca-Ba) [241] or [Li2Ba(ODpp)4] [164],... 

The stereochemistry of Mg and the heavier alkaline earth metals is more flexible than that of Be and, in addition to occasional compounds which feature low coordination numbers (2, 3 and 4), there are many examples of 6, 8 and 12 coordination, some with 7, 9 or 10 coordination, and even some with coordination numbers as high as 22 or 24, as in SrCdn, BaCdn and (Ca, Sr or Ba)Zni3. " Strontium is 5-coordinate on the hemisolvate [Sr(OC6H2Bu3)2(thf)3]. jthf which features a distorted trigonal bipyramidal structure with the two aryloxides in equatorial positions. ... 

Salt metathesis [Eq. (7)] is a well-established route in the synthesis of a variety of alkaline-earth metal alkyls [186,208-210], allyls [211-214], benzylates [149,178], cyclopentadienides [17, 108, 215-219], pentadienyls [220], fluorenyls [17, 221], indenyls [222], amides [112, 113, 223], p-diketiminates [112], guanidinates [15, 194], aUcoxides [224], aryloxides [224], silanides [210, 225-228], thiolates [229], phosphanides [230, 231], selenolates [229], and germanides [232, 233]. However, the route has been rarely used for the synthesis of more reactive alkyl and aryl metal complexes, largely due to issues pertaining to ether cleavage chemistry as metathesis typically requires the presence of an ethereal solvent. 

Metal exchange reactions have been used in the preparation of heavy alkali organometallics by reaction of alkali metal alkoxide or aryloxide with an organolithium reagent under precipitation of lithium alkoxide/aryloxide. For these reactions, careful ligand choice enables the separation of the two solid reaction products. Two variants of this reaction for alkaline-earth metal organometallics... 

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