Synthesis and crystal structures of alkali-metal (+)-neomenthylcyclopentadienyl complexes

Abstract

Polymeric alkali-metal (+)-neomenthylcyclopentadienyl complexes [M(η⁵-C₅H₄R)]_∞ (M = Li 1a, Na 2a or K 3a) and [M(η⁵-C₅H₄R)L]_∞ [M = Na, L = tetrahydrofuran (thf) 2b; M = K, L = thf 3b, L = 1,2-dimethoxyethane (dme) 3c] and monomeric neomenthylcyclopentadienyl(N,N,N′,N′-tetramethylethane-1,2-diamine)lithium 1b have been synthesized and characterised by single-crystal X-ray analyses. Compounds 1a, 2a, 2b and 3c have multidecker polymeric chain structures with average M-Cp (centroid) (M = Li, Na or K) distances of 2.010 Å (Li), 2.437 and 2.503 Å (Na), and 2.874 Å (K). The average Cp^R–M–Cp^R angles are 166.9 (Li), 170.2 and 135.1 (Na), and 135.5° (K), respectively. The (+)-neomenthyl groups on successive cyclopentadienyl rings are oriented along the polymeric zigzag chain with approximate twist angles of 116.2 (1a), 91.1 (2a), 179.9 (2b) and 165.8° (3c) respectively. In the monomeric half-sandwich compound 1b the lithium atom is bonded to the pentahapto cyclopentadienyl ring at a metal-to-centre distance of 1.910 Å.