Sulfur as a heteroatom in metallaborane structures: Cyclopentadienylcobalt thiaboranes

The series of cobaltathiaboranes CpCoSBnHn (n = 6, 7, 8, 9, 10) related to the experimentally known CpCoSB8H8 and CpCoSB10H10 have been investigated by density functional theory. The lowest energy CpCoSBnHn (n = 6–10) structures are the closo deltahedra in accord with expectations for these 2n + 2 Wadean skeletal electron systems. In the lowest energy such structures the sulfur atom is located at a lowest degree vertex and the cobalt atom at a highest degree vertex. An alternative bicapped octahedral CpCoSB6H6 structure having the sulfur atom at a degree 3 capping vertex lies only ∼7 kcal/mol above the bisdisphenoid global minimum. For the 12-vertex CpCoSB10H10 system the three possible structures based on a B10CoS regular icosahedron lie more than 50 kcal/mol in energy below any non-icosahedral structures. The relative energy ordering of ortho < meta < para for these icosahedral CpCoSB10H10 structures is the opposite of the relative energy ordering of para < meta < ortho for the well-known icosahedral dicarbaboranes C2B10H10. One of the low-energy nine-vertex CpCoSB7H7 structures B7CoS-3 (Fig. 3) appears to be a frozen intermediate in the diamond-square-diamond process interconverting two isomeric tricapped trigonal prisms through a capped square antiprism intermediate.

Density functional theory of CpCoSBn–2Hn–2 (n = 8, 9, 10, 11, 12) indicates a preference for the most spherical closo deltahedra with the sulfur atom at a low degree vertex and the cobalt atom at a high degree vertex.Figure optionsDownload as PowerPoint slide