New Ruthenium Nitrosyl Complexes with Tris(1-pyrazolyl)methane (tpm) and 2,2'-Bipyridine (bpy) Coligands. Structure, Spectroscopy, and Electrophilic and Nucleophilic Reactivities of Bound Nitrosyl

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Inorganic Chemistry, 45 (21): 8608--8617 (2006)
DOI: 10.1021/ic061062e


Ru(bpy)(tpm)NO(ClO4)3 tpm = tris(1-pyrazolyl)methane; bpy = 2,2'-bipyridine was prepd. in a stepwise procedure that involves the conversion of Ru(bpy)(tpm)Cl+ into the aqua and nitro intermediates, followed by acidification. The diamagnetic complex crystallizes to exhibit distorted octahedral geometry around the metal, with the Ru-N(O) bond length 1.774(12) \AA and the RuNO angle 179.1(12)°, typical for a RuNO6 description. The Ru(bpy)(tpm)NO3+ ion (I) was characterized by 1H NMR and IR spectroscopies (nNO = 1959 cm-1) and through d. functional theory calcns. Intense electronic transitions in the 300-350-nm region are assigned through time-dependent (TD)DFT as intraligand p $\rightarrow$ p* for bpy and tpm. The dp $\rightarrow$ p*(bpy) metal-to-ligand charge-transfer transitions appear at higher energies. Aq. cyclic voltammetric studies show a reversible wave at 0.31 V (vs. Ag/AgCl, 3 M Cl-), which shifts to 0.60 V in MeCN, along with the onset of a wave of an irreversible process at -0.2 V. The waves are assigned to the 1- and two-electron redns. centered at the NO ligand, leading to species with RuNO7 and RuNO8 configurations, resp. Controlled potential redn. of I in MeCN led to the Ru(bpy)(tpm)NO2+ ion (II), revealing a significant downward shift of nNO to 1660 cm-1 as well as changes in the electronic absorption bands. II was also characterized by ESR, showing an anisotropic signal at 110 K that arises from an S = 1/2 electronic ground state; the g-matrix components and hyperfine coupling tensor resemble the behavior of related RuNO7 complexes. Both I and II were characterized through their main reactivity modes, electrophilic and nucleophilic, resp. The addn. of OH- into I generated the nitro complex, with kOH = 3.05 $\times$ 106 M-1 s-1 (25°). This value is among the highest obtained for related nitrosyl complexes and correlates with ENO+/NO, the 1-electron redox potential. Complex II is a robust species toward NO release, although a conversion to I was obsd. in the presence of O2. This reaction afforded a 2nd-order rate law with k = 3.5M-1 s-1 (25°). The stabilization of the NO radical complex is attributed to the high pos. charge of the precursor and to the geometrical and electronic structure as detd. by the neutral tpm ligand. on SciFinder(R)



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