Ring-Side-Arm Cooperativity in Cation Inclusion Complexes of 12-Membered Ring Lariat Ethers: Effect of Side-Arm Chain Length and a Clarification of Long-Side-Arm Binding Strengths

Article abstract of DOI:10.1021/jo00259a008

The alkali metal and ammonium cation binding properties of N-pivot, 12-crown-4 lariat ethers are recorded here.A reinvestigation of N-pivot lariat ethers having (CH2CH2O)nCH3 side arms is presented, and data are reported for fresh samples of these long chain compounds.Details of the X-ray crystal structures obtained for N-<(3-oxabutyl)methyl>aza-12-crown-4 are reported.The complex crystallizes in the tricyclic space group P<*>1 with cell constants a = 8.712 (2) Angstroem, b = 8.694 (3) Angstroem, c = 11.740 (3) Angstroem, α = 111.44 (2) deg, β = 90.76 (2) deg, γ = 103.50 (2) deg, and Z = 2 for D_c = 1.591 gcm^-1.Least-squares refinement based on 3723 observed reflections led to a final conventional R value of 0.052.All of the lariat ether donors bind to the alkali metal cation, with the macroring in the crown conformation.The 12-crown-4 system behaves, in many ways, like the 15- and 18-membered ring analogues.The presence of an octakis(ethyleneoxy) side arm does not diminish cation binding strength in this series as reported for the 15- and 18-membered ring compounds.Indeed, the fall off in binding constants previously reported for the longest chain examples of the latter families now appears to be due to sample decomposition rather than solvent encumbrance.