Addition and oxidative addition reactions of some cationic complexes of rhodium(I)

Article abstract of DOI:10.1021/ic50102a032

The four-coordinate cationic complex {Rh[P(OCH₃)₃]₄}B(C₆H ₅)₄ reversibly adds carbon monoxide to form {Rh(CO)[P(OCH₃)₃]₄}[B(C₆H ₅)₄ and also reacts with the acetylenes C₂R₂ (R = CF₃ and CO₂CH₃) to give {Rh[P(OCH₃)₃]₄C₂R ₂}B(C₆H₅)₄. {Rh[P(n-C₄H₉)₈]₄}B(C ₆H₅)₄ adds hydrogen irreversibly to form cis-{Rh[P(n-C₄H₉)₃]₄H ₂}B(C₆H₅)₄ whereas the corresponding reactions involving {Rh[P(OR)₃]₄}B(C₆H₅)₄ (R = CH₃ and C₆H₅) to give cis-{Rh[P(OR)₃]₄H₂}B(C₆H ₅)₄ are reversible. Treatment of the five-coordinate complex {Rh[P(OCH₃)₃]₅}B(C₆H ₅)₄ with hydrobromic and hydriodic acids in ethanol gives trans-{Rh[P(OCH₃)₃]₄HBr}B(C₆H ₅)₄ and trans-{Rh[P(OCH₃)₃]₄HI}B(C₆H ₅)₄, respectively. However prolonged reaction of {Rh[P(OCH₃)₃]₅}B(C₆H ₅)₄ with hydrobromic acid yields cis-{Rh[P(OCH₃)₃]₄Br₂}B(C ₆H₅)₄. The addition of an equimolar amount of bromine to {Rh[P(OCH₃)₃]₅}B(C₆H ₅)₄ gives trans-{Rh[P(OCH₃)₃]₄Br₂}B(C ₆H₅)₄ together with a small amount of the cis form. In contrast the corresponding reaction involving iodine affords cis-{Rh[P(OCH₃)₃]₄I₂}B(C ₆H₅)₄ as the sole product. {Rh[P(OCH₃)₃]₄}B(C₆H ₅)₄ reacts with methyl iodide to form trans-{Rh[P(OCH₃)₃]₄(CH₃)I}B(C ₆H₅)₄. The cations RhL₄⁺{L = P(OR)₃ [R = CH₃, C₂H₅, and i-C₃H₇] and P(CH₃)₂C₆H₅} and RhL₅⁺ [L = P(OR)₃ (R = CH₃ and C₂H₅)] react with the allyl halides C₃H₅X (X = Cl and Br) to give Rh(π-C₃H₅)L₄²⁺ or RhX(π-C₃H₅)L₃⁺. The product formed is shown to depend on the ligand involved and on the reaction conditions.