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(mu-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 degrees C, these reactions afforded (a) [Ir(cod)(mu-Cl)(Me2PCH2BMe2)] (1), (b) an equilibrium mixture of (Me2PCH2BMe2)(2), [{Rh(mu-Cl)(cod)}(2)] and [Rh(cod)(mu-Cl)(Me2PCH2BMe2)] (2), and (c) cis-[Pt(mu-Cl)(2)(Me2PCH2BMe2)(2)] (3), respectively. By contrast, reactions between the phenyl-substituted analogue, (Ph2PCH2BMe2)(2), and [{M(mu-Cl)(cod)}(2)] (cod = 1,5-cyclooctadiene; M = Ir and Rh) proceeded over the course of 1 hour at 20 degrees C to generate [M(cod)(mu-Cl)(Ph2PCH2BMe2)] (M = Ir (4) and Rh (5)), indicative of room temperature (Ph2PCH2BMe2)(2) dissociation. Room temperature reactions of (Ph2PCH2BMe2)(2) with [{Rh(mu-Cl)(coe)(2)}(2)] (coe = cyclooctene) using a 1 : 1 or 3 : 1 stoichiometry also afforded [{Rh(coe)(mu-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(mu-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.

Automated summary

A new synthesis method for (Me2PCH2BMe2)(2) and (Ph2PCH2BMe2)(2) was reported, which showed different reactivity at room temperature. The ligand precursor (Me2PCH2BMe2)(2) did not react with [{M(mu-Cl)(cod)}(2)] or [PtCl2(cod)], while the phenyl-substituted analogue (Ph2PCH2BMe2)(2) reacted readily with [{M(mu-Cl)(cod)}(2)] to generate the desired products.