Optically Active P sub(5)-Deltacyclenes: A Unique Cage-Inversion Reaction and Some Transition-Metal Complexes of the Rearranged Cage

Cage-chiral P sub(5)-deltacyclene 1 is available as a pair of highly enriched P-C cage enantiomers 1' and 1 double prime , which exist as pairs of epimers a and b. Deprotonation of cage atom P1 initiates a rearrangement reaction, in which P1 and the neighboring carbon atom C4, together with its substituent, change places to form optically active iso-P sub(5)-deltacyclene enantiomers 6 double prime and 6', again as pairs of epimers. The CD spectra of related pairs of optically active cages 1 and 6 consist of almost mirror-symmetric curves, an indicator of mirror-symmetric cage structures. This surprising result was verified by an absolute structure determination of the W(CO) sub(5) complex 9a double prime . With the exception of the two cage nuclei that had changed places in relation to starting material 1', all other cage nuclei of rearrangement product 6a double prime occupy mirror-symmetric positions. To the best of our knowledge, this represents the first cage-inversion reaction of an optically active compound. P1 is the only active donor center of 6 involved in the bonding of M(CO) sub(5) fragments (M = Cr, Mo, W). The chiroptical properties of Cr(CO) sub(5) complex 7a' and W(CO) sub(5) complex 9a double prime are almost mirror-symmetric and resemble those of the free cages 6' and 6 double prime , respectively. The coordinated transition-metal complex fragments do not contribute significantly to the Cotton effects of the P-C cage. A DFT analysis of the deprotonated cage anions [1 - H] super(-) and [6 - H] super(-) predicts a driving force of -20.3 kcalmol super(-1) for the rearrangement reaction. Cage-chiral P-C cage compounds are a new class of chiral ligands. A stereoselective rearrangement performed with highly enriched P sub(5)-deltacyclene enantiomers is accompanied by a unique cage inversion, which results in almost mirror-symmetric CD curves of related pairs of P sub(5)-deltacyclene/iso-P sub(5)-deltacyclene enantiomers. The absolute structure of a W(CO) sub(5) complex enantiomer confirms the observation.