Cationic complexes of rhodium(I) and their reactivity toward air

Article abstract of DOI:10.1021/ic50102a031

The reaction of [C₈H₁₂RhCl]₂ with an excess of the ligands L = P(O-i-C₃H₇)₃, P(OCH₃)₂C₆H₅, POCH₃(C₆H₅)₂, P(CH₃)₂C₆H₅, and PCH₃(C₆H₅)₂ in methanol at room temperature or under refluxing conditions gives the four-coordinate cations RhL₄⁺ whereas the corresponding reaction involving the ligands L = P(OR)₃ (R = CH₃, C₂H₅, i-C₄H₉, and n-C₄H₉) and P(OCH₂)₃CCH₃ yields the five-coordinate species RhL₅⁺. However, by employing a rhodium:ligand ratio of 1:4 in those reactions involving the ligands P(OR)₃ (R = CH₃ and C₂H₅) the four-coordinate cations Rh[P(OR)₃]₄⁺ are obtained. Further the reaction of [C₈H₁₂RhCl]₂ with excess of the ligands L = P(CH₃)₂C₆H₅ and As(CH₃)₂C₆H₅ in methanol in the presence of air affords the stable oxygen-containing cations RhL₄O₂⁺. The cations RhL₄⁺, RhL₅⁺, and RhL₄O₂⁺ were characterized as the tetraphenylborates hexafluorophosphates, or perchlorates. The ionic compounds {Rh[P(OR)₃]₄}B(C₆H₅)₄ (R = CH₃, C₂H₅ and i-C₃H₇) and {Rh[P(OR)₃]₅}B(C₆H₅)₄ (R = CH₃, C₂H₅, i-C₄H₉, and n-C₄H₉) decompose in air to form the neutral derivatives Rh[P(OR)₃]₂B(C₆H₅)₄ containing one of the phenyl rings of the B(C₆H₅)₄ group bonded as an arene to the rhodium atom. The bonded B(C₆H₅)₄ group in Rh [P(OCH₃)₃]₂B(C₆H₅) ₄ is readily displaced by trimethyl phosphite and by the ligand (C₆H₅)₂PC₂H₄P(C ₆H₅)₂ to give the products {Rh[P(OCH₃)₃]₅}B(C₆H ₅)₄ and {Rh[(C₆H₅)₂PC₂H₄P(C ₆H₅)₂]₂}B(C₆H ₅)₄, respectively. The compound {Rh[P(OCH₃)₃]₅}PF₆ reacts with the dienes cycloocta-1,5-diene and bicyclo[2.2.1]hepta-2,5-diene in the presence of air to give the ionic derivatives {Rh(C₈H₁₂)[P(OCH₃)₃] ₂}PF₆ and {Rh(C₇H₈)[P(OCH₃)₃] ₃}PF₆, respectively. The nmr spectra of the various compounds are discussed.