Solvent-resistant structures of base-free lithium and potassium allyl complexes, M[(SiMe₃)_nC₃H_5-n] (M = Li,n= 3; M = K,n= 2)

Abstract

The structures of unsolvated {Li[1,1 0 ,3-(SiMe 3 ) 3 C 3 H 2 ]} 2 ([LiA 00 ] 2 ) and {K[1,3-(SiMe 3 ) 2 C 3 H 3 ]} ? ([KA 0 ] ? ) are reported. The base-free complex LiA 00 is a dinuclear species in the solid state in which the two Li atoms are bridged by the allyls in a m 2 -Z 1 , Z 2 fashion. The LiÀ ÀC s-bonded distance is 2.232(7) Å ; the LiÀ ÀC Z 2 -interaction occurs at distances of 2.230(7) Å and 2.241(6) Å . Density functional theory calculations on [Li(C 3 H 5 )] 2 and {Li[1,1 0 ,3-(SiH 3 ) 3 C 3 H 2 ]} 2 indicate that inclusion of the silyl groups is critical to reproducing the distortions observed in [LiA 00 ]. The structure of the solvated Li(C 3 H 5 )(thf) 2 complex is calculated to be stable as a dimer, consistent with previous measurements on allyllithium in THF solution. Like related DME and THF solvates, [KA 0 ] ? is a coordination polymer with potassium ions linked by bridging p-allyl ligands; in [KA 0 ] ? the polymer takes the form of helical chains with a broad range of KÀ ÀC distances (2.87-3.15 Å ).

An η3‐Bound Allyl Ligand on Magnesium in a Mechanochemically Generated Mg/K Allyl Complex

“…Thea llyl bridging between K1 and K2 (C28ÀC30) is fully delocalized (D C-C = 0.004 ), and displays m 2 -h 3 :h 3 bonding to the potassium atoms,w ith average K À Cd istances of 3.050 (to K2) and 3.012 (to K1). Ther ange of distances is similar to that observed in the coordination polymers [26] Polymerization Results…”

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

“…Unsubstituted allyllithium is known to be dimeric in thf solution, [41] and calculations at the DFT level indicate that even the substituted complex {Li[C 3 -1,1Ј,3-(SiH 3 ) 2 H 3 ]-(thf) 2 } 2 would be stable as a dimer. [19] Support for this conclusion is found in a related lithium complex formed from the tetrahydrofurfuryl-substituted derivative of the AЈ ligand ( Figure 2). [33] The dimeric complex has Li1-O1 and Li2-O2 bond lengths that are indistinguishable at 1.87 Å, and the C-C allyl bonds are slightly more delocalized (∆ = 0.052 Å) than in {Li [1,1Ј,3- Figure 3).…”

“…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. [32] All five compounds are coordination polymers with potassium ions linked by bridging π-allyl ligands.…”

“…In other cases, the presence of substituent groups aids in crystallization, so that solid-state structures may be obtained; calculations suggest that the X-ray crystal structure of the lithium dimer {Li[1,1Ј,3-(SiMe 3 ) 3 C 3 H 2 ]} 2 is related to that of the unsubstituted complex, which is known to be a dimer from cryoscopy, but which has not been structurally authenticated. [19] Of even greater interest is the use of substituted allyl ligands to support entirely new classes of metal complexes. Discussed below are the thermally stable, electron-deficient transition metal bis(allyl) compounds M[1,3-(SiMe 3 ) 2 -C 3 H 3 ] 2 (M = Cr, 12-e -; [16] Fe, 14-e -; [20] Co, 15-e - [21,22] ); they have no monomeric counterparts with unsubstituted ligands.…”

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

“…Their solid-state structures display considerable variety as well. 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].…”