Inorganic Chemistry, Vol.47, No.19, 9069-9080, 2008
Unsymmetrical platinum(II) phosphido derivatives: Oxidation and reductive coupling processes involving platinum(III) complexes as intermediates
Reaction of the trinuclear [NBu4](2)[(R-F)(2)Pt(mu-PPh2)(2)Pt(mu-PPh2)(2)Pt(R-F)(2)] (1, R-F = C6F5) with HCl results in the formation of the unusual anionic hexanuclear derivative [NBu4](2)[[{(R-F)(2)Pt(mu-PPh2)(2)Pt(mu-PPh2)(2)Pt(mu-Cl)}(2)] (4, 96 e(-) skeleton) through the cleavage of two Pt-C6F5 bonds. The reaction of 4 with TI(acac) yields the trinuclear [NBu4][(R-F)(2)Pt(mu-PPh2)(2)Pt(mu-PPh2)(2)Pt(acac)] (5, 48 e(-) skeleton), which is oxidized by Ag+ to form the trinuclear compound [(R-F)(2)Pt(mu-PPh2)(2)Pt(mu-PPh2)(2)Pt(acac)][ClO4] (6, 46 e(-) skeleton) in mixed oxidation state Pt(III)-Pt(III)-Pt(II), which displays a Pt-Pt bond. The reduction of 6 by [NBu4][BH4] gives back 5. The treatment of 6 with Br- (1:1 molar ratio) at room temperature gives a mixture of the isomers [(PPh2RF)(R-F)Pt(mu-PPh2)(mu-Br)Pt(mu-PPh2)(2)Pt(acac)], having Br trans to R-F (7a) or Br cis to R-F (7b), which are the result of PPh2/C6F5 reductive coupling. The treatment of 5 with I-2 (1:1 molar ratio) yields the hexanuclear [{(PPh2RF)(R-F)Pt(mu-PPh2)(mu-I)Pt(mu-PPh2)(2)Pt(mu-I)}(2)] (8, 96 e(-) skeleton), which is easily transformed into the trinuclear compound [(PPh2RF)(R-F)Pt(mu-PPh2)(mu-I)Pt(mu-PPh2)(2)Pt(I)(PPh3)] (9, 48 e-skeleton). Reaction of [(R-F)(2)Pt(mu-PPh2)(2)Pt(mu-PPh2)(2)Pt(NCMe)(2)] (10) with I-2 at 213 K for short reaction times gives the trinuclear platinum derivative [(R-F)(2)Pt(mu-PPh2)(2)Pt(mu-PPh2)(2)Pt(I)(2)] (11, 46e skeleton) in mixed oxidation state Pt(III)-Pt(III)-Pt(II) and with a Pt-Pt bond, while the reaction at room temperature and longer reactions times gives 8. The structures of the complexes have been established by multinuclear NMR spectroscopy. In particular, the Pt-195 NMR analysis, carried out also by F-19-Pt-195 heteronuclear multiple-quantum coherence, revealed an unprecedented shielding of the Pt-195 nuclei upon passing from Pt(II) to Pt(III). The X-ray diffraction structures of complexes 4, 5, 6, 9, and 11 have been studied. A detailed study of the relationship between the complexes has been carried out.