Chemistry and Electrochemistry of the Heterodinuclear Complex CIPd(dppm)2PtCl: A M–M′ Bond Providing Site Selectivity.

The heterodinuclear d9-d9 title compound 1, whose crystal structure has been solved, reacts with dppm [bis(diphenylphosphino)methane] in the presence of NaBF4 to generate the salt [ClPd(μ-dppm)2Pt(Β¹-dppm)][BF4] (2a), which contains a Pt-bound dangling dppm ligand. 2a has been characterized by ¹H and 31P NMR, Fourier transform Raman [ν(Pd-Pt) = 138 cm-1], and UV-vis spectroscopy [λmax(dσ-dσ∗) = 366 nm]. In a similar manner, [ClPd(μ-dppm)2Pt(Β¹-dppm=O)][BF4] (2b), ligated with a dangling phosphine oxide, has been prepared by the addition of dppm=O. The molecular structure of 2b has been established by an X-ray diffraction study. 2a reacts with 1 equiv of NaBH4 to form the platinum hydride complex [(Β¹-dppm)Pd(μ-dppm)2Pt(H)][BF4] (3). Both 2a and 3 react with an excess of NaBH4 to provide the mixed-metal d10-d10 compound [Pd(μ-dppm)3Pt] (4). The photophysical properties of 4 were studied by UV-vis spectroscopy [λmax(dσ-dσ∗) = 460 nm] and luminescence spectroscopy (λemi = 724 nm; τe = 12 ± 1 μs, 77 K). The protonation of 1 and 4 leads to [ClPd(μ-dppm)2(μ-H)PtCl]+ (5) and 3, respectively. Stoichiometric treatment of 1 with cyclohexyl or xylyl isocyanide yields [ClPd(μ-dppm)2Pt(CNC6H11)]Cl (6a) and [ClPd(μ-dppm)2Pt(CN-xylyl)]Cl (6b) ligated by terminal-bound CNR ligands. In contrast, treatment of 1 with the phosphonium salt [C≡NCH2PPh3]Cl affords the structurally characterized A-frame compound [ClPd(μ-dppm)2(μ-C=NCH2PPh3)PtCl]Cl (6c), spanned by a bridging isocyanide ligand. The electrochemical reduction of 2a at -1.2 V vs SCE, as well as the reduction of 5 in the presence of dppm, leads to a mixture of products 3 and 4. Further reduction of 3 at -1.7 V vs SCE generates 4 quantitatively. The reoxidation at 0 V of 4 in the presence of Cl- ions produces back complex 2a. The whole mechanism of the reduction of 1 has been established. [ABSTRACT FROM AUTHOR]