Electron-poor 2,3-dihydro-1,3-diborolyl ruthenium compounds: Synthesis, complexation, oxidative addition, capping, and stacking reactions

The addition products of lithium alkyls and the pentaalkyl-2,3-dihydro-1,3- diborole derivatives 5a-f react with [{(C5Me5)RuCl}(4)] and [{(C5Me4Et)RuCl }(4)] to form the violet sandwich compounds 2*c-f and 2<^>c, f. These forma lly 16 VE complexes are in fact electron-poor 18 VE species, because a high -lying combination of sigma(B-C) orbitals interacts with the d(xz) orbital of the Ru atom. Addition of tert-butyl isocyanide to 2*a, or 2*d leads to t he isonitrile complexes 6*a, and 6*d, as indicated by the spectroscopic dat a and X-ray structure analyses. At low temperature the interaction of 2*a, c, or e with Hz yields the classic dihydride complexes 7*a, c, and e, respe ctively. which have been studied by NMR. Oxidative addition of H3B . THF to the ruthenium atom of 2*a or c, followed by a reductive elimination of H-2 and migration of the boranediyl group gives the yellow closo-RuC3B3 ruthen acarboranes 8*a and 8*c, respectively. The reaction of [(C2H4),RhCl](2) and 2*c generates the tetranuclear complex 9*c.