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Evrard D, Clement S, Lucas D, Hanquet B, Knorr M, Strohmann C, Decken A, Mugnier Y, Harvey PD: Chemistry and electrochemistry of the heterodinuclear complex ClPd (dppm) 2PtCl: a M-M' bond providing site selectivity. Inorg Chem. 2006 Feb 6;45(3):1305-15.
The heterodinuclear d (9)-d (9) 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 (mu-dppm) 2Pt (eta (1)-dppm)][BF4] (2a), which contains a Pt-bound dangling dppm ligand. 2a has been characterized by 1H and 31P NMR, Fourier transform Raman [nu (Pd-Pt) = 138 cm (-1)], and UV-vis spectroscopy [lambda (max)(dsigma-dsigma*) = 366 nm]. In a similar manner, [ClPd (mu-dppm) 2Pt (eta (1)-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 [(eta (1)-dppm) Pd (mu-dppm) 2Pt (H)][BF4] (3). Both 2a and 3 react with an excess of NaBH4 to provide the mixed-metal d (10)-d (10) compound [Pd (mu-dppm) 3Pt] (4). The photophysical properties of 4 were studied by UV-vis spectroscopy [lambda (max)(dsigma-dsigma*) = 460 nm] and luminescence spectroscopy (lambda (emi) = 724 nm; tau (e) = 12 +/- 1 micros, 77 K). The protonation of 1 and 4 leads to [ClPd (mu-dppm) 2 (mu-H) PtCl]+ (5) and 3, respectively. Stoichiometric treatment of 1 with cyclohexyl or xylyl isocyanide yields [ClPd (mu-dppm) 2Pt (CNC6H11)] Cl (6a) and [ClPd (mu-dppm) 2Pt (CN-xylyl)] Cl (6b) ligated by terminal-bound CNR ligands. In contrast, treatment of 1 with the phosphonium salt [C [triple bond] NCH2PPh3] Cl affords the structurally characterized A-frame compound [ClPd (mu-dppm) 2 (mu-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. |
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