Ewan J. M. Hamilton

Unusual Cationic Tris(Dimethylsulfide)-Substituted closo-Boranes: Preparation and Characterization of [1,7,9-(Me2S)3-B12H9] BF4 and [1,2,10-(Me2S)3-B10H7] BF4

Rational syntheses of trisubstituted sulfur-bearing closo-boranes are presented. In the development of these syntheses unusual cationic closo-boranes [1,7,9-(Me(2)S)(3)-B(12)H(9)](+) (3) and [1,2,10-(Me(2)S)(3)-B(10)H(7)](+) (4) have been identified. These were initially recognized to be intermediates in the formation of the neutral trisubstituted species 1,7-(Me(2)S)(2)-9-(MeS)-B(12)H(9) (1) and 1,10-(Me(2)S)(2)-2-(MeS)-B(10)H(7) (2), respectively. Stable tetrafluoroborate salts were prepared and isolated, and their structures are presented. They are believed to represent the first structural determinations of cationic borane clusters of any type.

Probing Interligand Electron Transfer in the 1MLCT S1 Excited State of trans-Mo2L2L′2 Compounds: A Comparative Study of Auxiliary Ligands and Solvents

The interligand charge dynamics of the lowest singlet metal-to-ligand charge-transfer states (1MLCT S1 states) of a series of quadruply bonded trans-Mo2(NN)2(O2C-X)2 paddlewheel compounds are investigated, where NN is a π-accepting phenylpropiolamidinate ligand and O2C-X (X = Me, tBu, TiPB, or CF3) is an auxiliary carboxylate ligand. The compounds show strong light absorption in the visible region due to MLCT transitions from the Mo2 center to the NN ligands. The transferred electron density was followed by femtosecond time-resolved infrared (fs-TRIR) spectroscopy with vibrational reporters such as the ethynyl groups on the NN ligands. The observed fs-TRIR spectra show that these compounds have asymmetric 1MLCT S1 excited states where the transferred electron mainly resides on a single NN ligand. The presence of interligand electron transfer (ILET) is suggested to explain the shape of the ν(C≡C) bands and the influence of auxiliary ligands and solvents on the interligand electronic coupling. The ILET in the 1MLCT S1 state is shown to be sensitive to the functional groups on the auxiliary ligands while being less responsive to changes in solvents.