Cluster Condensation by Thermolysis: Synthesis of a Rhomb-Linked Re12Se16 Dicluster and Factors Relevant to the Formation of the Re24Se32 Tetracluster

The cluster cis -[Re 6 Se 8 (PEt 3 ) 4 I 2 ] undergoes substitution reactions with neutral ligands L in the presence of AgSbF 6 to afford the cis- disubstituted clusters [Re 6 Se 8 (PEt 3 ) 4 L 2 ] 2+ (L = MeCN ( 6 ), t -BuCN, DMF, Me 2 SO ( 9 )). Cluster 6 reacts with pyridine to give [Re 6 Se 8 (PEt 3 ) 4 (py) 2 ] 2+ . Retention of stereochemistry was demonstrated from 31 P NMR spectra and the crystal structure of [ 9 ](SbF 6 ) 2, which revealed the two Me 2 SO ligands to be O-bonded at adjacent Re sites of the face-capped octahedral [Re 6 (μ 3 -Se) 8 ] 2+ core. The clusters cis -[Re 6 Se 8 (PEt 3 ) 4 L 2 ] 2+ are of interest as possible precursors to oligomeric clusters under thermolysis conditions where one or both ligands L are removed. Thermolysis of orange-red [ 6 ](SbF 6 ) 2 (180 °C, 24 h) afforded a brown-green crystalline product identified by an X-ray structure determination to contain the dicluster [Re 12 Se 16 (PEt 3 ) 8 (MeCN) 2 ] 4+ ( 11 ). Two [Re 6 Se 8 ] 2+ cluster units are bridged by a Re 2 Se 2 rhomb to afford the centrosymmetric core [Re 12 (μ 3 -Se) 14 (μ 4 -Se) 2 ] 4+, established recently for the dicluster [Re 12 Se 16 (PEt 3 ) 10 ] 4+ . The two acetonitrile ligands occur in a trans orientation on the two cluster units. From consideration of the crystal structure of the precursor compound [ 6 ](SbF 6 ) 2 (reported earlier), the relative orientation of cluster pairs could be responsible for the formation of trans - 11 . Diclusters of the type cis -[Re 12 Se 16 (PEt 3 ) 8 L 2 ] 4+ are required for potential thermolytic conversion to the cyclic tetracluster [Re 24 Se 32 (PEt 3 ) 16 ] 8+ . Factors relevant to the formation of this unknown cluster type are considered.