Coordination-driven face-directed self-assembly of trigonal prisms. Face-based conformational chirality.
The coordination-driven self-assembly of four different trigonal prisms from 3 equiv of one of four different tetrapyridyl star connectors and 6 equiv of a platinum linker dication in nitromethane is presented. This face-directed approach affords high yields without template assistance. The prisms have been characterized by multinuclear and DOSY NMR and dual ESI-FT-ICR mass spectrometry. The use of a conformationally chiral star connector leads to a conformationally chiral prism when connector arm ends attached to a vertex have a strongly correlated twist sense and chirality is communicated across polyhedral faces, edges, and vertices. Molecular mechanics results suggest that in the smallest prism 3d collective effects dominate and the all-P and all-M conformers are strongly favored. NMR data prove that the two edges of the pyridine rings in the triflate salts of 3a-3d are distinct. An Eyring plot of rates obtained from line-shape analysis and 1-D EXCHSY NMR yields an activation enthalpy DeltaH(double dagger) of approximately 12 kcal/mol and activation entropy DeltaS(double dagger) of approximately -15 cal/mol x K for the edge interconversion process, compatible with pyridine rotation around the Pt-N bond. For 3c, this behavior is observed only up to approximately 318 K. At higher temperatures, the Eyring plot is again linear but follows a very different straight line, with a DeltaH(double dagger) of approximately 35 kcal/mol and DeltaS(double dagger) of approximately 60 cal/mol x K. This highly unusual result is further investigated and discussed in the following companion paper.
Caskey
Douglas C
DC
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA.
Yamamoto
Takuya
T
Addicott
Chris
C
Shoemaker
Richard K
RK
Vacek
Jaroslav
J
Hawkridge
Adam M
AM
Muddiman
David C
DC
Kottas
Gregg S
GS
Michl
Josef
J
Stang
Peter J
PJ
D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D011725:Pyridines / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013237:Stereoisomerism; D013696:Temperature
D011725:Pyridines