Three types of isomers have been reported for eight-coordinate, dodecahedral, rhenium(V) centers: cis and trans isomers for the cations [ReH2(mhp)2(PPh3)2]+ (where mhp = the anion of 2-methyl-6-hydroxypyridine), E and Z isomers of the type ReH5(PPh3)2L (where L = an unsymmetrically substituted aromatic amine such as 2-aminopyridine or 4-phenylpyrimidine), and the enantiomers of ReH5(PPh3)2[NH(CH3)C2H5]. This report describes a new type of isomer pair for eight-coordinate, dodecahedral, rhenium(V) centers of the form ReH4(chelate)(PPh3)2 (where chelate = an aromatic imine that is metallated at the 2 position of an aromatic ring bound to the carbon of the imine functional group). The latter isomers appear to be associated again with the particular edge of the dodecahedron that is bridged by the chelating ligand. Determinations of Arrhenius activation energies, activation enthalpies, and activation entropies for interconversion of E and Z isomers as well as the monochelate isomers in addition to the same properties for the chemical exchange of phosphorous centers in the complex ReH5(PPh3)3 suggests a single mechanism for isomer interconversions. The interconversion mechanism conforms to a dodecahdron-square antiprism-dodecahedron process. Recent reports have shown that certain platinum metal centers will cyclometallate with ferrocenylimine complexes through a bond to the imine nitrogen and the 2 carbon of the substituted Cp ring. A similar complex with a rhenium(V) center was made from the reaction of ReH7(PPh3)2 with a ferrocenylimine. The resultant bimetallic complex is found to be a pair of isomers which, again, arise from the location of the chelating ligand on the dodecahedron. The resultant isomers afford an unusual system in which the iron center moves between two distinct steric and electronic environments in a periodic fashion.

Isomers and their interconversions for eight-coordinate, dodecahedral, rhenium(V) centers supported by four or five hydride ligands

253rd National Meeting (2017)

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