Selection of a Pentameric Host in the Host–Guest Complexes {[{[P(μ‐NtBu)]₂(μ‐NH)}₅]⋅I}⁻[Li(thf)₄]⁺ and [{[P(μ‐NtBu)]₂(μ‐NH)}₅]⋅HBr⋅THF

Abstract

The structures of the host-guest complexes [[[[P(mu-NtBu)]2(mu-NH)]5]I]-.[Li(thf)4]+ [2.I[Li(thf)4]] and [[[P(mu-NtBu)]2(mu-NH)]5].HBr.THF (2.HBr.THF) show that increased distortion of the framework of the pentameric macrocycle [[[P(mu-NtBu)]2(mu-NH)]5] (2) occurs with the larger halide ions. Theoretical studies show that the thermodynamic stabilities of the model host-guest anions [2.X]- (X=Cl, Br, I) are in the order Cl- approximately Br->I-, that is, the reverse of the templating trend observed experimentally. These studies support the view that the selection of the pentamer 2 over the tetramer [[[P(mu-NtBu)]2(mu-NH)]4] (1) is kinetically controlled, a conclusion which is also consistent with the previous observation that the frameworks of 1 and 2 are not in dynamic equilibrium with each other.

The Selenium‐Based Hexameric Macrocycle [(Se)P(μ‐NtBu)2P(μ‐Se)]6

“…[8] The greater proportion of the cis isomer of 1 over the trans may have an influence on the formation of a macrocyclic (rather than oligomeric or polymeric) product. [1,3,4] Owing to the low solubility of the macrocycle 2 in organic solvents (such as CHCl 3 , toluene, and THF), further elucidation of the chemical environments and bonding of the Se atoms in its macrocyclic backbone using 77 Se NMR spectroscopy was not possible. This situation, and the fact that only the dimer [(Se=)P(mNtBu) 2 P(m-Se)] 2 + could be observed in the positiveion electrospray mass spectrum of 2 (m/z 726), meant that the exact nature and size of the macrocycle could not be ascertained prior to its structural characterization.…”

“…The result of this arrangement is that (unlike in 2) there are no available donor atoms for metal coordination within the backbones of these macrocycles. Significantly, in 2 (where there are no organic substituents bonded to the m-Se atoms), a cisoid geometry of the m-Se atoms with respect to the P 2 N 2 rings is adopted (similar to that seen in the related nitrogen-based torocycles [{P(m-NtBu)} 2 (m-NH)] n (n = 4, 5), Scheme 1), [3,4] thus allowing donor Se atoms to be available for potential metal coordination.…”

“…Like the related nitrogen macrocycles [{P(mNtBu)} 2 (m-NH)] n (n = 4, 5), [3,4] the P 2 N 2 ring units are approximately perpendicular to the mean plane of the macrocycle (dihedral angles 95.4-97.68) so that the molecules have a toroidal shape. An interesting feature of the structure of the solvate is the presence of the lattice THF molecule within the sheath of the tBu groups in 2, above the centroid of the macrocycle (Figure 1 b).…”

“…[1,2] The tetrameric, nitrogen-bridged macrocycle [{P(m-NtBu)} 2 (m-NH)] 4 (Scheme 1 a) is obtained by the condensation of the dimers [ClP(m-NtBu)] 2 and [(NH 2 )P-(m-NtBu)] 2 in the presence of Et 3 N. [3] However, the pentameric homologue is produced exclusively if this reaction is undertaken in the presence of I À ions, resulting in the hostguest complex [{P(m-NtBu)} 2 (m-NH)] 5 I À (Scheme 1 b). [4] The toroidal structures of the tetramer and pentamer and the presence of endo NÀH functionalities combine the appearance and host-guest characteristics of organic macrocycles such as calixarenes and porphyrins.…”

A Modular Approach to Inorganic Phosphazane Macrocycles

“…[23,24] However, pentameric NH-bridged macrocycles are obtained in the presence of excess of halide ions (X À , particularly I À ) (n = 5). [25,26] The observation of templating in a molecular inorganic system of this type is extremely rare and is directly analogous to macromolecular organic systems. [27,28] It has also been shown that hexameric S-and Se-bridged macrocycles, [E=P(m-N t Bu) 2 P(m-E)] 6 (E = S, Se) (D, Scheme 2) of this class containing alternating P III /P V -skeletons can be readily obtained via the Wurtz-type coupling reactions of the dimers [(Cl)(E = )P(m-N t Bu)] 2 although the yields are low (ca.…”