α-Ethoxyvinyllithium: An Unexpected Polymeric Structure—Tetrameric Subunits Linked by LiCπ Interactions

Abstract

Two different Li environments characterize the solvent‐free, polymeric structure of 1 in the crystal. A tetrameric chain is formed by Li atoms, which are coordinated by two O and three or five C atoms. In contrast, 1 exists as isolated tetramers in THF. The C(Li)O carbenoid character of 1 results in an elongated CO bond and in lithium bridging.

The Electrophilic Nature of Carbenoids, Nitrenoids, and Oxenoids

“…96 Furthermore, R-ethoxyvinyllithium 167, a polymer in the solid state, shows a seven-linemultiplet in THF at -90 °C, indicating a tetramer structure (Scheme 40) with three lithiums at each carbon, which is confirmed by 6 Li-1 H HOESY experiments. 97 These results are nicely in agreement with the calculated structures of LiCH 2 OH 134 and its aggregates; see Scheme 41.…”

“…Not unexpectedly, the carbenoid nature of 167 is also documented by the 13 C NMR spectrum of the carbenoid carbon atom: ∆δ ) 60.7 ppm, as compared to ∆δ ) 54.4 ppm of the tetrameric vinyllithium. 97 The general features of the crystal structure of the sparteine-complexed carbamoyloxy-3-trimethylsilylallyllithium (-)-sparteine 200 123 (Scheme 55) correspond closely to those of 194 and 195 (Scheme 53). Lithium in 200 is not bridging the C1-O bond because a more favorable dipole-stabilized fivemembered ring chelate is formed which overcomes the energy diffence between the most stable calculated Li-bridged isomer 134A and the tetrahedral 134B (13.6 kcal mol -1 ; see section 1.4.1.1.4).…”

“…132 R-Ethoxyvinyllithium 167 crystallizes in tetramer units as a polymer complexed with THF; see Scheme 55. 97 Most significantly the C1-O bonds (142.1-143.6 pm, mean value 142.8 pm) are remarkably elongated as compared to those in vinyl ethers (∼136 pm). 138 Furthermore, all carbenoid C-O bonds are bridged by lithium.…”

Applications of the Laddering Principle — A Two-Stage Approach to Describe Lithium Heterocarboxylates

“…A recent survey10 tallied only two examples of unsolvated organolithium polymers involving any laddered portions, [LiOPh] ∞ 25 and [LiC(OEt)=CH 2 )] ∞ ,26 among several solvated examples and several unsolvated, finite ladders. This demonstrates two important points: 1) that solvation does not preclude polymerization, and may even encourage it in some cases (e.g.…”

Carbanion generation through tin-lithium exchange of vinyl-, aryl-, and hetarylstannanes

“…It should also be apparent that the reverse could also occur: the synthesis of a dilithiobutadiene from a stannole via double tin-lithium exchange. The application of this process is shown in Equation 35. 60 The excess of MeLi was necessary to drive the equilibrium completely to the right.…”