Synthetic, Reactivity, and Structural Studies on Half‐Sandwich (η⁵‐C₅Me₅)Be and Related Compounds: Halide, Alkyl, and Iminoacyl Derivatives

Abstract

The half-sandwich compounds [(eta(5)-C(5)Me(5))BeX] (X=Cl, 1 a; Br, 1 b), readily prepared from the reaction of the halides BeX(2) and M[C(5)Me(5)] (M=Na or K), are useful synthons for other (eta(5)-C(5)Me(5))Be organometallic compounds, including the alkyl derivatives [(eta(5)-C(5)Me(5))BeR] (R=Me, 2 a; CMe(3), 2 b; CH(2)CMe(3), 2 c; CH(2)Ph, 2 d). The latter compounds can be obtained by metathetical exchange of the halides 1 with the corresponding lithium reagent and exhibit NMR signals and other properties in accord with the proposed formulation. Attempts to make [(eta(5)-C(5)Me(5))BeH] have proved fruitless, probably due to instability of the hydride toward disproportionation into [Be(C(5)Me(5))(2)] and BeH(2). The half-sandwich iminoacyl [(eta(5)-C(5)Me(5))Be(C(NXyl)Cp')] and [(eta(5)-C(5)Me(4)H)Be(C(NXyl)Cp')]3, 6 where Xyl=C(6)H(3)-2,6-Me(2) and Cp'=C(5)Me(5) or C(5)Me(4)H, are formed when the beryllocenes [Be(C(5)Me(5))(2)], [Be(C(5)Me(4)H)(2)], and [Be(C(5)Me(5))(C(5)Me(4)H)] are allowed to react with CNXyl. Isolation of three different iminoacyl isomers from the reaction of the mixed-ring beryllocene [(eta(5)-C(5)Me(5))Be(eta(1)-C(5)Me(4)H)] and CNXyl, namely compounds 5 a, 5 b, and 6, provides compelling evidence for the existence in solution of different beryllocene isomers, generated in the course of two very facile processes that explain the solution dynamics of these metallocenes, that is the 1,5-sigmatropic shift of the Be(eta(5)-Cp') unit around the periphery of the eta(1)-Cp' ring, and the molecular inversion rearrangement that exchanges the roles of the two rings.

Synthesis and Characterization of Cp*Be‐F‐Al(ORF)3

“…The chemistry of beryllium compounds was mainly developed in the 1960s, but is getting rising attention in the last decade 1–8. Many neutral and anionic beryllium compounds are known, but the preparative chemistry of cationic Be complexes is by far less developed.…”

Alkaline Earth Organometallics

“…58 No hydride resonance could be found in the 1 H NMR spectrum, however, and 1 H, 9 Be, and 13 C{ 1 H} NMR indicated that the only products were a mixture of 10 and unreacted (C 5 Me 5 )BeBr. 58 No hydride resonance could be found in the 1 H NMR spectrum, however, and 1 H, 9 Be, and 13 C{ 1 H} NMR indicated that the only products were a mixture of 10 and unreacted (C 5 Me 5 )BeBr.…”

“…Three isomers have been isolated 58 ; at À78 C, isomer C is formed exclusively and reversibly, suggesting that it has the lowest barrier to C-C coupling reactions. It has four possible isomers if both the Z 5 /Z 1 -and the "molecular inversion" rearrangements that are proposed to occur in Cp 2 Be are operative (Scheme 2, A-D).…”

“…58 The reaction of M[C 5 Me 5 ] (M¼ Na, K) with BeX 2 (OEt 2 ) 2 (X ¼ Cl, Br) generates both halide derivatives in high yield. The chloride derivative 13 can be prepared in 20% yield from the reaction of (C 5 Me 5 ) 2 Mg with BeCl 2 (OEt 2 ) 2 in Et 2 O; the yield rises to 55% in refluxing toluene/diethyl ether.…”

On the Origin of the Enhanced Acidity of Chalcocyclopentadienes (Cyclopentadiene Chalcogenols) in the Gas Phase

“…Cyclopentadiene and its derivatives have received a great deal of attention as ligands for alkaline earth and d and f transition metals. [1][2][3][4][5][6][7][8] Their ligand capabilities are closely related to the aromatic character of the five-membered ring when it captures an extra electron and becomes a 6p-electron system. The aromaticity of the cyclopentadienyl anion is also responsible for the significant acidity of cyclopentadiene, both in the gas phase and in solution.…”