Pentamethylcyclopentadienylrhodaborane chemistry. Part 3. The reaction of [{Rh(η5-C5Me5)Cl2}2] with closo-[B10H10]2– and arachno-B10H12-6,9-(PMe2Ph)2, and the characterisation of some novel rhodaboranes by X-ray diffraction analysis and nuclear magnetic resonance spectroscopy

Abstract

Reaction of the rhodaborane synthon [{Rh(η⁵-C₅Me₅)Cl₂}₂] with closo-[B₁₀H₁₀]^2–- in dichloromethane solution results in the rapid insertion, in reasonable yield, of a Rh(η⁵-C₅Me₅) vertex to give orange, air-stable crystals of [1-(η⁵-C₅Me₅)-closo-1-RhB₁₀H₁₀](1). When methanol is also present the major product (40% yield) is the related orange, air-stable, methoxy derivative [1-(η⁵-C₅Me₅)-closo-1-RhB₁₀H₉-2-(OMe)](2). X-Ray diffraction analysis of (2) established a triclinic unit cell, space group P, with a= 1 407.7(2), b= 878.9(1), c= 835.9(2) pm, α= 111.19(1), β= 103.44(1),γ= 92.24(1)°, and Z= 2. Detailed n.m.r. data on (1) and (2) are also discussed. Reaction of [{Rh(η⁵-C₅Me₅)Cl₂}₂] with the bis-ligand adduct arachno-B₁₀H₁₂-6,9-(PMe₂Ph)₂ affords yellow, air-stable crystals of the dichloromethane solvate [7-(η⁵-C₅Me₅)-nido-7-RhB₁₀H₁₁-8-Cl-11-(PMe₂Ph)]·CH₂Cl₂(3)[monoclinic, space group P2₁/n, with a= 1 520.4(2), b= 1 228.3(3), c= 1 622.3(2) pm, β= 102.24(1)°, and Z= 4]. A notable feature of the structure is the presence of three bridging H atoms in the five-atom RhB₄ open face of the nido cluster. Two-dimensional [¹¹B–¹¹B]-COSY,[¹H–¹H]{¹¹B}-COSY, and ¹H-{¹¹B(selective)} n.m.r. experiments revealed further interesting features of this cluster species. Treatment of (3) with an excess of the ligand PMe₂Ph in the presence of H₂O or O₂ gave a 63% yield of the novel twelve-vertex nido-rhodaoxaborane [7-(η⁵-C₅Me₅)-nido-7,12-RhOB₁₀H₉-8-Cl-11-(PMe₂Ph)](4). Orange-red, air-stable crystals of (4) were monoclinic, space group P2₁/n, with a= 867.7(2), b= 1 984.4(4), c= 1 551.8(3) pm, β= 102.08(2)°, and Z= 4. The cluster structure of (4) is closely related to that of (3) but with the unique oxygen atom replacing two bridging hydrogens in the open face. Detailed n.m.r. data are also presented and discussed.