NO˙ disproportionation by a {RhNO}⁹pincer-type complex

Abstract

The reactivity of the {RhNO} complex [Rh(PCPBu)(NO)]˙ (1˙) with NO˙ was studied. A disproportionation reaction takes place in which NO is released quantitatively, while the complex Rh(PCPBu)(NO)(NO) (2), with coordinated nitrite, is formed. The new complex 2 was fully characterized by multinuclear NMR techniques, IR and X-ray diffraction. The X-ray structure reveals a square pyramidal geometry with an N-bound nitro ligand trans to the C of the PCP ligand and a bent nitrosyl ligand in the apical position. IR measurement of released NO confirms that one equivalent forms for each molecule of 1˙. Infrared spectroscopic experiments with 1˙-NO and NO˙ suggest that the reaction occurs through the intermediacy of a dinitrosyl complex. In addition, DFT calculations were performed to provide more evidence on the structure of the intermediates and to support the observed reactivity.

Photoinduced linkage isomers in a model ruthenium nitrosyl complex: Identification and assignment of vibrational modes

“…Finally, the long-time irradiation of the complex induces release of NO followed by the formation of nitrous oxide N 2 O. Supposedly, the mechanism of the N 2 O release comprises the formation of a {Ru-(κ 2 -ONNO)} intermediate, similar to known reactions [60,[62][63][64][65].…”

“…Nevertheless, in the absence of reference data for a coordinated Ru-N 2 O compound, we cannot unambiguously exclude that the detected vibrational mode belongs to a coordination state of N 2 O. The formation of a complex with coordinated dinitrogen N 2 can be ruled out due to the fact that the ν(N-N) band would be expected at much lower wavenumbers (≈2100 cm The mechanism of N 2 O formation in solution when starting from a nitrosyl compound could comprise the formation of monometallic {M-(κ 2 -ONNO)} (bonding through two oxygen atoms) or bimetallic {M 2 -μ-(NOON)} (bonding through bridged nitrogen atoms) intermediates [62][63][64][65]. Also, the ability of hyponitrite compounds to release N 2 O in the solid state after light excitation has been reported [60].…”

Structure and Reactivity of NO/NO+/NO−Pincer and Porphyrin Complexes

“…Although most of the work published by our group has been focused on these complexes, [28,41,42] in recent years we have also explored reactivity of a complex with an asymmetric PCN pincer scaffold. [40] In this case, obtention of the tetradentate species proved to be challenging, since the route analogous to that shown in Scheme 2 yielded pentacoordinate Rh(PCN)(NO)(Cl) (20) due to residual chloride in solution.…”

“…We have also studied the NO * disproportionation reaction mediated by a rhodium pincer complex. [42] This reactant consists of a radical {RhNO} 9 Notably, N 2 O could already be detected when adding only one equivalent of NO. This, together with observation of an isosbestic point between the FTIR signals of [Rh(PCP)(NO] * and Rh(PCP)(NO)(NO 2 ), suggests a fast reaction with short-lived intermediates.…”

“…Reaction of (6 * ) with O 2 was tested in an attempt to isolate a NO * disproportion intermediate, but instead it was found to result in coordination of oxygen to the metallic center, as is shown in Scheme 15. [42] However for the case of the PCN ligand, whereas reaction of (19 * ) with air does also yield [Rh(PCN)(NO)(NO 2 )], coordination of the oxygen molecule was not observed. [40] Reaction with excess O 2 resulted in decomposition of (19 * ) into several products as evidenced by 31 P-NMR (unpublished data).…”