Diisocyanide Tertiary Phosphine Complexes

Rh2L2(dppm)2 (L = 2,5-diisocyano-2,5-dimethylhexane). The Rh2(I) bond distance in Rh2(dimen)2( dppm)f is 3.161(1) A, which is typical for dppm complexes of Rh2(I), but which requires that the dimer bridges undergo considerable conformational distortion to accommodate such a short distance. The absorption spectrum of Rh2(dimen)2(dTOm)2 shows an absorption due to la2u 2a g at 565 nm, and Rh2L2(dppm)2 shows an absorbance due to this transition at 595 nm. Dirhodium(I) complexes with a bridging dppm or dpam [dpam = l,2-bis(dipheny-larsino)methane)] ligand and monodentate isocyanide have similar structures with close Rh-Rh separations. Examples of such conmlexes are Rh2(RNC)4(dppm)2 (R = tert-Bu, n-Bu, Ph) and Rh2(n-BuNC)4(dpam)2 

The addition of chloride ion to solutions of these isocyanide Rh2(I) complexes causes a change in their electron transfer characteristics. In the presence of chloride ion the one-electron oxidized complex Rh2(dimen)2(dppm)2 is no longer stable, but it now rapidly disproportionates into Rh2(dimen)2(dppm) and Rh2(di-men)2(dppm)2  

The effect of chloride ion is to form a bridge between the rhodium centers, thereby facilitating the electron transfer between metal centers. This result shows that in the photoreactions of Rh2(I) complexes in the presence of HCl, disproportionation reactions of odd-electron intermediates can provide pathways for the generation of the oxidized and reduced products that are observed. 

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