Geometrically Specific Imino Complexes of the [Re6(μ3-Se)8]2+ Core-Containing Clusters

The reactions of nitrile complexes of the [Re-6(mu(3)-Se)(8)](2+) core-containing clusters, [Re-6(mu(3)-Se)(8)(PEt3)(n)-(CH3CN)(6-n)](2+) [n=5 (1); n=4, cis- (2) and trans- (3); n=0 (4)], with organic azides C6H5CH(CH3)N-3 and C6H5CH2N3 produced the corresponding cationic imino complexes of the general formula [Re-6(mu(3)-Se)(8)-(PEt3)(n)(L)(6-n)](2+) [L=PhN=CHCH3: n=5 (5); n=4, cis- (6) and trans- (7); n=0 (8) and L=HN=CHPh: n=5 (9); n=4, cis- (10) and trans- (11)]. These novel complexes were characterized by NMR spectroscopy (H-1 and P-31) and single-crystal X-ray diffraction. A mechanism involving the migration of one of the groups on the azido alpha-C atom to the alpha-N atom of the azido complex, concerted with the photo-expulsion of N-2, was invoked to rationalize the formation of the imino complexes. Density functional theory (DFT) calculations indicated that due to the coordination with and activation by the cluster core, the energy of the electronic transition responsible for the photo-decomposition of a cluster-bound azide is much reduced with respect to its pure organic counterpart. The observed geometric specificity was rationalized by using the calculated and optimized preferred ground-state conformation of the cluster-azido intermediates.