Peralkylated Barium Complexes

Abstract

Beyond their archetypal Grignard-type reactivity [1] organoA C H T U N G T R E N N U N G metallic complexes of the heavier alkaline-earth metals are currently attracting a great deal of attention in homogeneous catalysis. [2, 3] The large ionic radii of divalent M II (M = Ca, Sr, Ba), the highly ionic nature of the respective metal-carbon s bonds, and the associated huge ligandexchange rates [4] imply high reactivity in catalytic transformations such as olefin polymerization, hydrosilylation, or hydroamination. Naturally, these bonding and reactivity attributes are most pronounced for Ba II and are held responsible for the lack of well-defined and crystallographically authenticated alkyl derivatives. In 1998, Westerhausen and coworkers presented the X-ray structure of the dimeric com- plex [((thf)Ba{CA C H T U N G T R E N N U N G (C CPh)(Ar)}) 2 ] with Ba À CA C H T U N G T R E N N U N G (alkenyl) bonds, which was obtained by the reaction of [(thf)Ba{PA C H T U N G T R E N N U N G (SiMe 3 ) 2 } 2 ]with diphenylbutadiyne.[5] Later on, the same group described the reaction of, which consists of a Ba 2 C 2 P 4 Zn 4 cuboid with Ba-Et-Zn moieties.[6] The majority of well-characterized dialkyl barium compounds, however, feature a-bound aryl and trialkylsilyl groups for stabilization. Representative examples include [Ba-

Surface Organobarium and Organomagnesium Chemistry on Periodic Mesoporous Silica MCM‐41: Convergent and Sequential Approaches Traced by Molecular Models

“…[19] With the aim of generating alkylated alkaline earth metal surface species, two grafting strategies were pursued. A sequential approach started from the pre-grafting of tailormade silylamide 1 [16] followed by alkylation (silylamide elimination) with AlEt 3 (TEA) to produce hybrid materials des-…”

“…On the other hand, the synthesis of [BaA C H T U N G T R E N N U N G (AlEt 4 ) 2 ]@MCM-41 (M4) by direct grafting of pre-isolated 2 [16] corresponded to a convergent protocol. The implications of the different grafting sequences for the generation of peralkylated barium surface species (M3 and M4) are also discussed with respect to/in light of the directly grafted materials Mg-A C H T U N G T R E N N U N G (AlMe 4 ) 2 @MCM-41 (M5) and TEA@MCM-41 (M6).…”

“…According to Scheme 1, material M2 was obtained by treating a dehydrated sample of parent M1 with 1 [16] (1.1 equiv) in hexane. Subsequent treatment of the isolated white hybrid material, M2, with an excess of TEA (6 equiv) gave a white mixture, from which material M3 was isolated after several hexane washings.…”

“…Subsequent treatment of the isolated white hybrid material, M2, with an excess of TEA (6 equiv) gave a white mixture, from which material M3 was isolated after several hexane washings. Likewise, by using a slight excess (1.1 equiv), the alkyl complexes 2 [16] , MgA C H T U N G T R E N N U N G (AlMe 4 ) 2…”

“…Herein, we report on surface organobarium chemistry (SOBaC) and SOMgC involving the silylamide Ba[N- [16] and tetraalkylaluminates [Ba- [16] and MgA C H T U N G T R E N N U N G (AlMe 4 ) 2 [17] as organometallic components, as well as channel-like hexagonal PMS MCM-41 as a support. Moreover, the reaction products of these organoalkaline earth metal complexes with HOSiA C H T U N G T R E N N U N G (OtBu) 3 as a molecular oxo surface were studied by single-crystal X-ray diffraction analysis.…”