Trimethylsilylated Allyl Complexes of the Heavy Alkali Metals, M[1,3-(SiMe₃)₂C₃H₃](thf)_n (M = K, Cs)

Abstract

Reaction of elemental cesium with 1,3-bis(trimethylsilyl)propene produces the corresponding substituted allyl derivative. The complex and its previously prepared potassium counterpart form the THF solvates K[1,3-(SiMe3)2C3H3](thf)3/2 and Cs[1,3-(SiMe3)2C3H3](thf), respectively, which crystallize as coordination polymers in the solid state. In the case of the cesium complex, the packing is polymeric in two dimensions. As was previously found for the potassium complex, the cesium compound is an initiator for methyl methacrylate polymerization.

Complexes with Sterically Bulky Allyl Ligands: Insights into Structure and Bonding

“…With potassium and the heavier alkali metals, allyl complexes are uniformly found as coordination polymers. The potassium salt of the AЈ anion, for example, has been crystallized as DME and thf solvates, {K[AЈ](dme)} ϱ [45] and {K[(AЈ)(thf) 3/2 ]} ϱ , [29] and also as the base-free complex, {K[AЈ]} ϱ . [19] The tetrahydrofurfuryl-substituted derivative of the AЈ anion has been crystallized as its potassium salt, [33] and the dimethylsilyl ansa-bis(silylcyclohexenyl)-dipotassium complex {K 2 [(η 3 -C 6 H 4 SiMe 3 -6) 2 SiMe 2 ]-(thf) 3 } ϱ has been isolated as a thf solvate.…”

“…The cesium compound {Cs[AЈ](thf)} ϱ forms a strictly linear chain of metal atoms. [29] The immediate environment around the cesium in {Cs[AЈ](thf)} ϱ consists of a thf ligand and two π-bound allyl ligands; there are close intermolecular contacts to methyl groups at 3.67 and 3.95 Å that serve to raise the formal coordination number from 5 to about 7.…”

Alkali Metal Complexes of Silyl‐Substituted ansa‐(Tris)allyl Ligands: Metal‐, Co‐Ligand‐ and Substituent‐Dependent Stereochemistry

“…Structural studies on intermolecularly solvated potassium silylallyls have revealed that these compounds tend to exist as zigzag coordination polymers or oligomers in which the allyl ligands adopt µ:η 3 :η 3 -coordination modes, with incorporation of solvent molecules such as thf completing the metal coordination environment. [14,15,34] The polymeric nature of allylpotassium compounds is a consequence of the larger ionic radius of the cation, which also seems to enable more un-symmetrical bonding of the allyl ligand, as witnessed by potassium-carbon bond lengths to the terminal allyl carbon atoms that differ by greater than 0.2 Å in some instances. [34] Complexes of ansa-bis (silylallyl) 2-(R 3 Si = various silyl groups), with main group and transition metals are also well known.…”

“…[14,15,34] The polymeric nature of allylpotassium compounds is a consequence of the larger ionic radius of the cation, which also seems to enable more un-symmetrical bonding of the allyl ligand, as witnessed by potassium-carbon bond lengths to the terminal allyl carbon atoms that differ by greater than 0.2 Å in some instances. [34] Complexes of ansa-bis (silylallyl) 2-(R 3 Si = various silyl groups), with main group and transition metals are also well known. [28,29] The individual allylmetal units within alkali metal ansa-bis(silylallyl) complexes, such as [Me 2 Si{(C 3 H 3 SiMe 3 )Li(tmeda)} 2 ] (2), do not interact with each other via µ-bridging interactions, and are structurally similar to their monoallyl counterparts such as 1.…”

A tetrameric allyl complex of sodium, and computational modeling of the 23Na–allyl chemical shift

“…Compounds with lithium are known as monomers [3,16], dimers [7,19], cyclic oligomers [20], and coordination polymers [21,22]. With potassium and the heavier alkali metals, only coordination polymers are known [7,16,19,23,24]. Until recently, only a single complex displaying Na-allyl interactions had been structurally authenticated, the monomeric Na(1-PhC 3 H 4 )(pmdta) [25].…”