Diastereoselective Self‐Assembly of Low‐Symmetry Pd_nL_2n Nanocages through Coordination‐Sphere Engineering**

Abstract

Metal‐organic cages (MOCs) are popular host architectures assembled from ligands and metal ions/nodes. Assembling structurally complex, low‐symmetry MOCs with anisotropic cavities can be limited by the formation of statistical isomer libraries. We set out to investigate the use of primary coordination‐sphere engineering (CSE) to bias isomer selectivity within homo‐ and heteroleptic PdnL2n cages. Unexpected differences in selectivities between alternative donor groups led us to recognise the significant impact of the second coordination sphere on isomer stabilities. From this, molecular‐level insight into the origins of selectivity between cis and trans diastereoisomers was gained, highlighting the importance of both host‐guest and host‐solvent interactions, in addition to ligand design. This detailed understanding allows precision engineering of low‐symmetry MOC assemblies without wholesale redesign of the ligand framework, and fundamentally provides a theoretical scaffold for the development of stimuli‐responsive, shape‐shifting MOCs.

Photoswitchable catalysis by a self-assembled molecular cage

“…This combination of ligands was selected for their shape complementarity. [60][61][62][63][64] On its own, ligand 2 is known 65 to react with palladium(II) ions to form a [Pd3(2)6] 6+ double-walled triangle in acetonitrile and a [Pd4(2)8] 8+ double-walled square in DMSO, 65 which we also observe (Figure 2aiv, SI S8 and S9).…”

“…Finally, a single crystal suitable for X-ray diffraction unambiguously confirmed the heteroleptic species as cis-[Pd2(E-1)2( 2)2](BF4)4 (Figure 2c, CCDC: 2343887, SI S10.4), in line with expectations from shape complementarity prediction. [60][61][62][63][64] The cage has a Pd•••Pd separation of 9.92 Å. The pyridyl units are not significantly twisted (angles between the trans pyridyl rings range from 16 to 22 °), and therefore the ortho-pyridyl hydrogen-bond donors project into the cavity for optimal guest binding and catalysis.…”

Shape‐Complementary Multicomponent Assembly of Low‐Symmetry Co(III)Salphen‐Based Coordination Cages

“…pioneered the electronic route [35] while Fujita exploited the combination of bulky lutidines and lean pyridines around cis ‐protected [Pd(en)] fragments to assemble rectangles and prismatic cages [36,37] . We recently expanded this principle by grouping bulky donors around ‘naked’ Pd(II) centers, yielding heteroleptic cis ‐ [38] and trans‐ [Pd 2 L 2 L′ 2 ] [39] as well as unique 1+3 two‐component [Pd 2 LL′ 3 ] cages [39–43] . Ribas, Reek and co‐workers generated heteroleptic cuboids by saturating metallo‐macrocycles with bridging ligands [44] .…”

Formkomplementäre Multikomponenten Assemblierung von Niedrigsymmetrischen Co(III)Salphen Koordinationskäfigen

“…leisteten Pionierarbeit bezüglich der Verwendung elektrostatischer Effekte [35] während Fujita die Kombination von sperrigen Lutidinen und sterisch weniger anspruchsvollen Pyridinen um cis ‐geschützte [Pd(en)]‐Fragmente nutzte, um Rechtecke und prismatische Käfige zu assemblieren [36,37] . Vor kurzem haben wir dieses Prinzip erweitert, indem wir sperrige Donorgruppen um „nackte“ Pd(II)‐Zentren gruppiert haben, was die Selbstassemblierung zu heteroleptischen cis ‐ [38] und trans‐ [Pd 2 L 2 L′ 2 ] [39] sowie einzigartigen 1+3 Zweikomponenten [Pd 2 LL′ 3 ] Käfigen ermöglichte [39–43] . Ribas, Reek und Mitarbeiter erzeugten heteroleptische Quader durch Sättigung von Metallo‐Makrozyklen mit verbrückenden Liganden [44] .…”