Cyclooctadiene iridium complexes with phosphine and pentadienyl ligands

A comparison of the coordination behaviour of R2PCH2BMe2 (R = Me vs. Ph) ambiphilic ligands with late transition metals

A new synthesis that avoids the use of Me2PH is reported for (Me2PCH2BMe2)2, and this method was extended to the synthesis of (Ph2PCH2BMe2)2. The ligand precursor (Me2PCH2BMe2)2 did not react with [{M(μ-Cl)(cod)}2] (cod = 1,5-cyclooctadiene; M = Ir and Rh) or [PtCl2(cod)] at room temperature. However, after 12-48 hours at 65-70 °C, these reactions afforded (a) [Ir(cod)(μ-Cl)(Me2PCH2BMe2)] (1), (b) an equilibrium mixture of (Me2PCH2BMe2)2, [{Rh(μ-Cl)(cod)}2] and [Rh(cod)(μ-Cl)(Me2PCH2BMe2)] (2), and (c) cis-[Pt(μ-Cl)2(Me2PCH2BMe2)2] (3), respectively. By contrast, reactions between the phenyl-substituted analogue, (Ph2PCH2BMe2)2, and [{M(μ-Cl)(cod)}2] (cod = 1,5-cyclooctadiene; M = Ir and Rh) proceeded over the course of 1 hour at 20 °C to generate [M(cod)(μ-Cl)(Ph2PCH2BMe2)] (M = Ir (4) and Rh (5)), indicative of room temperature (Ph2PCH2BMe2)2 dissociation. Room temperature reactions of (Ph2PCH2BMe2)2 with [{Rh(μ-Cl)(coe)2}2] (coe = cyclooctene) using a 1 : 1 or 3 : 1 stoichiometry also afforded [{Rh(coe)(μ-Cl)(Ph2PCH2BMe2)}2] (6) or [RhCl(Ph2PCH2BMe2)3] (7), respectively, where the latter is a borane-appended analogue of Wilkinson's catalyst, and reactions of (Ph2PCH2BMe2)2 with [PtX2(cod)] (X = Cl or Me) yielded cis-[Pt(μ-Cl)2(Ph2PCH2BMe2)2] (8) and cis-[PtMe2(Ph2PCH2BMe2)2] (9). Compounds 1-9, (Me2PCH2BMe2)2 and (Ph2PCH2BMe2)2 were crystallographically characterized. In compounds 1-5 and 8, each chloride co-ligand is coordinated by the borane of an R2PCH2BMe2 ligand. Additionally, in the solid state structure of 6, each bridging chloride ligand interacts weakly with a pendent borane, and in 7, the chloride ligand is tightly coordinated to the borane of one Ph2PCH2BMe2 ligand and weakly coordinated to the borane of a second Ph2PCH2BMe2 ligand. By contrast, both boranes in 9 (and one of the three boranes in 7) are non-coordinated.

A SF5 Derivative of Triphenylphosphine as an Electron-Poor Ligand Precursor for Rh and Ir Complexes

The synthesis of the triarylphosphine, P(p-C₆H₄SF₅)₃ containing a SF₅ group, has been achieved. The experimental and theoretical studies showed that P(p-C₆H₄SF₅)₃ is a weaker σ-donor when compared with other substituted triarylphosphines, which is consistent with the electron-withdrawing effect of the SF₅ moiety. The studies also revealed a moderate air stability of the phosphine. The σ-donor capabilities of P(p-C₆H₄SF₅)₃ were estimated from the phosphorus-selenium coupling constant in SeP(p-C₆H₄SF₅)₃ and by DFT calculations. The behavior of P(p-C₆H₄SF₅)₃ as ligand has been investigated by the synthesis of the iridium and rhodium complexes [MCl(COD){P(p-C₆H₄SF₅)₃}], [MCl(CO)₂{P(p-C₆H₄SF₅)₃}₂] (M = Ir, Rh), or [Rh(µ-Cl)(COE){P(p-C₆H₄SF₅)₃}]₂, and the molecular structures of [IrCl(COD){P(p-C₆H₄SF₅)₃}] and [Rh(µ-Cl)(COE){P(p-C₆H₄SF₅)₃}]₂ were determined by single X-ray diffraction. The structures revealed a slightly larger cone angle for P(p-C₆H₄SF₅)₃ when compared to other para-substituted triarylphosphines.