Structure and dynamics of crowns containing the phenyldinaphthylmethane subunit (a three-bladed propeller): observations of correlated rotation of the propeller blades and certain ether segments

Abstract

We describe some crowns (dinaphthopolyoxacycloalkanins) containing the phenyldinaphthylmethane subunit, regarded as a propeller, the aryl rings (blades) of which are fluxional, twisting about the arylmethine bonds. This torsional propeller movement is fluxional at room temperature on the n.m.r. timescale for some crowns, with AGf2+2M of ca. 10-1 1 kcal mol-', while for others (regarded as locked propellers at room temperature), A G f , is ca. 19 kcal mol-'. Whether fluxional in solution or no, the crowns and their salt complexes commonly exhibit just one propeller isomer in the solids; X-ray crystal structures of one example of a crown (4), and one example of a salt complex ( 7 ) , are described in this paper. Crystal data for (4): C,H4,0,~0.5(CH3)2C0, monoclinic, space group P2,/n, a = 14.403(2), b = 13.428(1), c = 17.797(3)A, p = 93.18(1)", R = 0.070. Crystal data for (7):C4,H440,KNCS~(CH3),C0, monoclinic, space group P2,/c, a = 12.721 (1 ), b = 15.1 97(1), c = 22.038(3) A, p = 92.55(1)", R = 0.065. N.m.r. spectroscopic evidence in solution suggests more than one propeller isomer in solution for fluxional crowns with six oxygen donors, while for locked crowns there is only one. The single observable process (two-ring flip) for the fluxional crowns with 5 and 7 oxygen donors exchanges environments of the two differentiable naphthyl rings and phenyl edges for pairs of isomers which cannot themselves be differentiated by n.m.r. spectroscopy.A lower energy flip exchanges differentiable isomers via a flip of one naphthyl and one phenyl ring for the six-donor crowns. The flexing of the polyether segments in it locked propeller has been shown to be correlated with the twisting of its propeller, using a combination of dynamic n.m.r. studies with 'H and 2H nuclei.

Catalytic Activities of CuSO4/Al2O3 in Dehydrogenation of Arenes by Dioxygen

“…Unless stated otherwise, all reagents and chemicals were obtained commercially and used without further purification. The preparation of 6- tert -butyl-2-naphthol ( 5c ) and 2,6-di- tert -butylhydroquinone ( 1e ) was performed as described in literature. 5,5‘-Diacenaphthene ( 7a ) was prepared by the oxidative coupling of acenaphthene using Pb(OAc) 4 .…”

“…Evaporation of the combined filtrate under reduced pressure left 6 (0.2 g, 98%) as a brownish solid. The crude product was further purified by treatment with active carbon to give light brownish 6 (0.19 g, 94%); mp 239−241 °C (lit . mp 239−242 °C).…”

Structural properties of methoxy derivatives of benzyl bromide, determined from powder X-ray diffraction data

“…For the methoxy group at the 4-position, on the other hand, the methyl group lies out of the plane of the phenyl ring, with the C͑4͒O-CH 3 bond pointing almost perpendicular to the plane of the ring. These conformational features are commonly observed in crystal struc- tures of other molecules containing 3,4,5-trimethoxyphenyl rings ͑with hydrogen atoms in the 2-and 6-positions͒ ͑Saad et Wallet et al, 1995;Lockhart et al, 1987;Krygowski et al, 2001͒. In contrast to the conformational properties discussed above for 3,5-dimethoxyphenyl rings, as found in 3,5-DMBB, it is apparent that there is much less latitude for conformational variation in 3,4,5trimethoxyphenyl rings. In the 3,4,5-TMBB molecule, the bromine atom of the CH 2 Br group also lies out of the plane of the phenyl ring, and is oriented outwards from the same face of the phenyl ring as the methoxy group at the 4-position.…”

On the possible isomerisation pathway for triarylmethanes Ar3CX, including propeller crowns

“…Indeed, the activation energy barriers to propeller flipping are from 10-19 kcal mol-' in this series. 8 An idealised Ph,C-structure is given in Figure 5, which shows the convention of labelling the torsion angles which we follow from the BDS paper. Analysis of propeller crown data shows no clear difference between the unusual isomer and the other six, but the geometrical parameters for this isomer are at the extremes of the range.…”