Synthesis, Stuctural Characterization, and Stereospecificity in the Formation of Bimetallic Rhodacarborane Clusters Containing Rh-H-B Bridge Interactions

Article abstract of DOI:10.1021/ja00290a031

Reactions of (COD=η⁴-1,5-cyclooctadiene; R=Ph; Et; Ph, Me) with resulted in the formation of bimetallic rhodacarborane clusters containing Rh-Rh bonds supported by Rh-H-B interactions. 2 (2) is formed stereospecifically as the nature of the Rh-H-B interactions determines a specific stereoisomer and of the six possible only the structure of 2 is observed.The synthesis, characterization, and X-ray structure determinations of analogues of 2 containing differing phosphine ligands demonstrate this stereospecificity to be of thermodynamic origin, arising from polyhedral repulsions on adjacent carborane ligands.The characterization of (8) as well as experiments observing the formation of 2 result in a general mechanism for their formation involving hydrogenation of the COD ligand to cyclooctene via phosphine ligand disproportionation. 2 (2) crystallizes in the triclinic space group P1 with unit cell parameters a=11.118(2) Angstroem, b=13.456(3) Angstroem, c=18.390(3) Angstroem, α=93.09(2) deg, β=76.22(1) deg, γ=76.90(2) deg, Z=2. 2 (3) crystallizes in the monoclinic space group P2₁/c with unit cell parameters a=11.153(6) Angstroem, b=15.228(9) Angstroem, c=18.844(10) Angstroem, β=91.83(2) deg, Z=4. 2 (5) crystallizes in the monoclinic space group P2₁/c with unit cell parameters a=18.035(6) Angstroem, b=13.156(4) Angstroem, c=26.905(8) Angstroem, β=113.34(2) deg, Z=4. (8) crystallizes in the monoclinic space group P2₁/n with unit cell parameters a=14.043(7) Angstroem, b=32.638(13) Angstroem, c=10.059(4) Angstroem, β=98.98(3) deg, Z=4.