Tetranuclear rhodium clusters with facial cyclooctatetraene ligands

摘要

Molecular tetrarhodium cluster complexes with facial (#mu#_3-) cyclooctatetraene ligands are synthesized from Rh_4(CO)_(12) 2 and 1,3,5,7-cyclooctatetraene (cot) or 1,4-(SiMe_3)_2C_8H_6, respectively. The reactions proceed in a cooperative fashion, with all four metal atoms of the cluster being involved. Reaction of 2 with cot at low temperature (boiling n-pentane) only gives the mono-cot complex Rh_4(CO)_8(#mu#_3-C_8H_8) 4, whereas at higher temperature (boiling n-heptane) the bis-cot cluster complex Rh_4(CO)_6(#mu#_3-C_8H_8)(#eta#~4-C_8H_8) 5 is formed exclusively. Complex 4 is also prepared from 5 and Fe(CO)_5. From 2 and 1,4-(SiMe_3)_2C_8H_6 in boiling n-pentane only the complex Rh_4(CO)_6{#mu#_3-C_8H_6(SiMe_3)_2}(#eta#~4-C_8H_6(SiMe_3)_2) 6 is obtained in quantitative yield. Substitution of the apical ligands in 4 with 1,4-(SiMe_3)_2, and in 5 with 1,3-cyclohexadiene or 1,5-cyclooctadiene gives the complexes Rh_4(CO)_6(#mu#_3-C_8H_8){#eta#~4-C_8H_6(SiMe_3)_2} 7, Rh_4(CO)_6(#mu#_3-C_8H_8)(#eta#~4-C_6H_8) 8 and Rh_4(CO)_6(#mu#_3-C_8H_8)(#eta#~4-C_8H_(12)) 9, respectively. The crystal and molecular structures of 4, 5, 6, 7, 8 and 9 were determined. The apical C_8H_6R_2 ligands in 5, 6 and 7 attain the 1,2,5,6-#eta#~4-coordination mode through non-adjacent double bonds.