Pentamethylcyclopentadienyl-rhodium and -iridium complexes. Part 21. Neutral and cationic β-diketonato-, η3-allylic, and NN″-triazenido-complexes: the X-ray crystal structure of the binuclear complex [Rh2(C5Me5)2(acac)2][BF4]2

Abstract

The synthesis and properties of the (β-diketonato-complexes [M(η⁵-C₅Me₅)X(R¹COCHCOR²)][M = Rh, X = Cl, R¹= R²= Me, R¹= R²= CF₃, R¹= Me, R²= Prⁿ, R¹= Me, R²= OEt, or R¹= Me, R²= CF₃; M = Rh, R¹= R²= Me, X = Br, I, N₃, or OAc (acetate); and M = Ir, X = Cl, R¹= R²= Me, or R¹= R²= CF₃] obtained from [M₂(η⁵-C₅Me₅)₂Cl₄][M = Rh (1a) or Ir (1b)] and Na[R¹COCHCOR²] are reported. Iridium forms a stable complex [Ir(η⁵-C₅Me₅)(acac)₂] in which the two acac (MeCOCHCOMe) groups are OO′- and C-bonded respectively; no exchange is detectable on the ¹H n.m.r. time scale. The complex [Rh(η⁵-C₅Me₅)Cl(acac)] undergoes substitution when treated with N-bromo- or N-iodo-succinimide to give [Rh(η⁵-C₅MC₅)Cl(MeCOCYCOMe)](Y = Br or I). Reaction of [Rh(η⁵-C₅Me₅)Cl(MeCOCHCOR²)] with AgX gives binuclear [Rh₂(η⁵-C₅Me₅)₂(MeCOCHCOR²)₂][X]₂(R₂= Me, Prⁿ, or OEt; X = PF₆ or BF₄). The complex [Rh₂(η⁵-C₅Me₅)₂(acac)₂][BF₄]₂(14a) has been shown by X-ray crystallography to contain two bridging acac ligands. OO′-bonded to one rhodium and C-bonded to the other. A major contributor to the structure of the acac ligand is the β-diketone form, although a delocalised β-diketonate form also plays an important role. The η⁵-C₅Me₅ ring in (14a) is distorted towards an ‘ene-enyl’ structure, the shortest C[graphic omitted]C (‘ene’) bond being trans to the Rh–C(acac)σ-bond. Reaction of [Rh₂(η⁵-C₅Me₅)₂(acac)₂][PF₆]₂ with L gives [Rh(η⁵-C₅Me₅)L(acac)][PF₆][L = PPh₃, P(OEt)₃, Bu^tNC, py, NH₂Me, or NHMe₂]; similarly prepared are [Rh(η⁵-C₅Me₅)L(CF₃COCHCOCF₃)][PF₆](L = MeCN or PPh₃). Reaction of (1a) with RNHNNR and base or Ag[N₃R₂] gives the NN″-bonded triazenido-complexes [Rh(η⁵-C₅Me₅)Cl(N₃R₂)](R = Ph, p-MeC₅H₄, or p-ClC₅H₄); the NN′-bonded acetamidinato-complex [Rh-(η⁵-C₅Me₅)Cl(PhNCMeNPh)] is prepared similarly. On reaction with L in the presence of Ag[PF₆] these give [Rh(η⁵-C₅Me₅)L(RNXNR)][PF₆][X = N, R = Ph, L = MeCN or P(OMe)₃; X = CMe, R = Ph, L = MeCN or PPh₃. The azido-complex [Rh₂(η⁵-C₅Me₅)₂(N₃)₄] forms adducts [Rh₂(η⁵-C₅Me₅){N₃)₄(RNHNNR)] with RNHNNR (R = Ph or p-MeC₆H₄). The η³-1-methylallyl complex [Rh(η⁵-C₅Me₅)(η³-1-MeC₃H₄)Cl] also forms the cationic complexes [Rh(η⁵-C₅Me₅)(η³-1-MeC₃H₄)L][PF₆][L = MeCN, P(OMe)₃, PPh₃, or NH₂Et] on reaction with L in the presence of Ag[PF₆].