Templating and Selection in the Formation of Macrocycles Containing [{P(μ-NtBu)2}(μ-NH)]n Frameworks: Observation of Halide Ion Coordination

Abstract

Amination of [ClP(μ‐NtBu)]2 (1) using NH3 in THF gives the cyclophospha(III)zane dimer [H2NP(μ‐NtBu)]2 (2), in good yield. 31P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et3N show that almost quantitative formation of the cyclic tetramer [{P(μ‐NtBu)}2(μ‐NH)]4 (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre‐organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58–67 % using various reaction scales. The isolation of the major by‐product of the reaction (ca. 0.5–1 % of samples of 3), the pentameric, host–guest complex [{P(μ‐NtBu)2}2(μ‐NH)]5(HCl)⋅2 THF] (4⋅2 THF), gives a strong indication of the mechanism involved. In situ 31P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl− ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent‐ and anion‐dependent. The X‐ray structures of 2 and 4⋅2 THF are reported.

Guest Binding via N−H⋅⋅⋅π Bonding and Kinetic Entrapment by an Inorganic Macrocycle

“…The high bond energy of P−N single bonds and their low polarity underpin the stability of a diverse range of previously reported phosphazane compounds, and provide a good foundation for the development of a new range of robust inorganic macrocycles . Of particular interest is the pentameric host macrocycle 1 (Figure ), toroidal shape, large void volume, endo ‐cyclic N‐H functionalities, and exo ‐cyclic t Bu groups of which make it a highly unusual, sterically hindered H‐bonding host.…”

“…b) Comparison of the solid‐state structures of [ 1 ⊂I − ] and [ 2 ⊂I − ]; single‐crystal structure [ 1 ⊂I − ] from Ref. .…”

Synthesen mit anionischen Templaten

“…Wasserstoffbrücken spielen auch eine wichtige Rolle bei den von Wright et al beschriebenen halogenidgesteuerten Templatsynthesen einer Reihe von Makrocyclen mit [{P(μ‐N t Bu) 2 }(μ‐NH)] n ‐Grundgerüsten 14. Die Makrocyclen lassen sich durch Reaktion von [ClP(μ‐N t Bu)] 2 mit [NH 2 P(μ‐N t Bu)] 2 unter basischen Bedingungen herstellen.…”

“… Reaktion von [ClP(μ‐N t Bu)] 2 mit [NH 2 P(μ‐N t Bu)] 2 , die in Gegenwart von Chlorid (oder anderen Halogeniden) unter Bildung des Pentamers 8 als Hauptprodukt verläuft. Ohne Halogenidtemplat wird bevorzugt das entsprechende Tetramer gebildet 14…”

Synthesis and structure of cationic guanidinate-bridged bimetallic {Li7M} cubes (M = Mn, Co, Zn) with inverse crown counter anions

“…27 A pentameric structural motif related to 3 was also observed in the mercury-based inverse crown [{(F 3 C) 2 CHg} 5 (m 5 -Cl) 2 ], although in this instance the macrocycle was pre-synthesized and the chloride guest added subsequently.…”