Preparation, Characterization, and Structural Analyses of [Rh(chp)(NBD)]2 and [Rh(chp)(NBD)]2(PF6). Isolation of a Paramagnetic d7-d8 Binuclear Radical and Its d8-d8 Precursor

David C. Boyd, Robert Szalapski, Kent R Mann

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Single-crystal X-ray studies of [Rh(chp)(NBD)]2 and its one-electron oxidation product [Rh(chp)-(NBD)]2PF6·CH2Cl2 (chp = 6-chloro-2-hydroxypyridinate; NBD = norbornadiene) have been completed. Crystal data for [Rh(chp)(NBD)]2 at 22 °C: space group P21/c; Z = 4; a = 14.639 (2) Å, b = 10.483 (3) Å, c = 15.271 (3) Å, β = 103.04 (2)°, V = 2283 (2) Å3; R = 0.024, Rw= 0.034 for 3784 reflections with F2 > σ(Fo2). Crystal data for [Rh(chp)(NBD)]2PF6·CH2Cl2 at -72 °C: space group P1*; Z = 2; a = 10.160 (4) Å, b = 12.770 (5) Å, c = 13.129 (7) Å, α = 75.70 (4)°, β = 68.39 (4)°, γ = 67.94 (3)°, V = 1456.0 (1.1) Å3; R = 0.061, Rw= 0.060 for 3237 reflections with Fo2> σ(Fo2). [Rh(chp)(NBD)]2 contains two square-planar Rh(I) units that intersect with a dihedral angle of 49° bridged by two hydroxypyridinate ligands. The molecule is structurally similar to the previously characterized [Rh(mhp)(COD)]2 (mhp = 6-methyl-2-hydroxypyridinate; COD = 1,5-cyclooctadiene). The Rh-Rh distance is relatively short (3.040 (1) Å) for d8 d8 complexes, which is consistent with our observations of a low-energy dσ*→ pσ electronic spectral band and its ease of oxidation. Addition of AgPF6 to CH2Cl2 solutions produces the stable d8 d7, mixed-valence complex [Rh(chp)(NBD)]2PF6.CH2Cl2. This complex is paramagnetic (μeff = 1.76 μB; EPR g1= 2.08, g2= 2.21, and g3= 2.25) and shows a broad signal for g1 that is consistent with two equivalent Rh(I1/2) atoms. The crystal structure of the d8 d7 radical indicates that its geometry is similar to the d8 d8 parent, but the Rh-Rh distance is considerably shorter (2.819 (1) Å). The shortening of the Rh-Rh distance is consistent with the 1/2 bond order expected for a (dσb)2(dσ*)1 electronic configuration in the radical.

Original languageEnglish (US)
Pages (from-to)790-795
Number of pages6
Issue number3
StatePublished - Mar 1 1989

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