Syntheses and ligand properties of 1,3-dit-butyl-2,3-dihydro-1,3-diboroles. Rhodium-(η5-2,3-dihydro-1,3-diborole) and rhodium-(η5-2,3-dihydro-1,3-diborolyl) complexes

Of the new 1,3-dit-butyl-2,3-dihydro-1,3-diboroles (1a,b), the pentaalkyl derivative 1b reacts with [(C2H4)2RhCl]2 to give the Cl-bridged dimer 2b. The single crystal structure analysis of 2b reveals that the hydrogen atoms H2 and H22 in the two-positions are located on the opposite side of the dihydrodiborole rings than the rhodium atoms, with formation of 3c/2e C–H⇀B bonds. The chlorine bridges in 2b are cleaved with MeLi in toluene to give the arenediborolylrhodium sandwich 3b. The tetraalkyl-1,3-diborole (1a) reacts with MeLi or KH and then [(C2H4)2RhCl]2 in toluene to give the sandwich 3a. Treatment of 2b with MeLi in the presence of the 1,3-diborole (1b) provides the 16 VE 1,3-diborolyl-1,3-diborolrhodium complex 4b. With CpNa 2b forms the 1,3-diborole sandwich 6b, which has a 3c/2e C–H⇀B bond, whereas with Cp*Li the hydrido complex 7b with a Rh–H bond is obtained.