More Arrows in the Quiver: New Pathways and Old Problems with Heavy Alkaline Earth Metal Diphenylmethanides

Abstract

Progress in the field of sigma-bonded alkaline earth organometallics has been handicapped by numerous complications, such as high reactivity, low solubility, and the limited availability of suitable starting materials. Here we present two synthetic methods, hydrocarbon elimination and desilylation, as alternative routes into this chemistry. A novel barium diphenylmethanide was prepared using these routes delineating that both methods provide a powerful, versatile synthetic access route to an extended library of organometallic alkaline earth derivatives.

Heavy Grignard Reagents: Synthesis, Physical and Structural Properties, Chemical Behavior, and Reactivity

“…The importance of d‐orbital participation in calcium derivatives has been verified by various quantum chemical calculations at very “simple” systems, such as hydrides, halides, and others . Earlier reviews summarize some aspects of the reaction portfolio of organocalcium compounds . In the next chapters we focus on recent examples in order to delineate the broad and fruitful chemistry of these heavy Grignard reagents.…”

Alkali Metal Diphenylmethanides: Synthetic, Computational and Structural Studies

“…. [30] For the alkali metals, the second apical coordination may be filled by a donor molecule. However, if the metal diameter is larger than the crown cavity, steric shielding provided by the macrocycle becomes less effective, since the metal is located above the plane of crown donor atoms.…”

“…The metal coordination number is 8, with unexceptional metalÀoxygen (crown) bond lengths ranging from 2.733(5) to 2.845(5) ; metal-THF distances are slightly shorter (2.67-2.71(4) ). It is instructive to compare the charge-separated [K [18] [30] Despite very similar ionic radii (1.38 (K + ) vs 1.35 (Ba 2 + ) for six-coordinate species) [31] the compounds do not adopt the same ion association mode, rather the slightly smaller, more polarizing barium center prefers coordination to the anionic ligands. With a reduced charge density, the slightly larger potassium cation is sufficiently stabilized by metal-donor interactions, a result confirmed by previous theoretical studies.…”

“…Extensive structural data are available on the macrocycle coordination to alkali metals, but their detailed influence on the ion association in organometallic compounds remains to be fully understood. Well‐documented cation/macrocycle matches such as potassium or barium and [18]crown‐6 afford full encapsulation of the cation by the crown cavity; the apical positions were filled by ligand molecules as demonstrated in [Ba[18]crown‐6][(CHPh 2 ) 2 ] 30. For the alkali metals, the second apical coordination may be filled by a donor molecule.…”

Alkaline Earth Organometallics

“…153 Bis(tris(trimethylsilyl)methyl)calcium, [C(SiMe 3 ) 3 ] 2 Ca 115, is made from the reaction of K[C(SiMe 3 ) 3 ] and CaI 2 in benzene and crystallizes from a heptane/benzene solution. 303 Crystallized in the form of its 18-crown-6 ether derivative 116 (Figure 60), the complex displays direct Ba-C bonds of 3.065 (3) Lithiation of the multidentate O-substituted phosphine 2-MeOC 6 H 4 CH(P(tolyl-p) 2 ) with LiBu n produces the dimeric salt 119. 3.0 Å with CaÁ Á ÁH distances of 2.5 Å ).…”