Crystal structures, spectroscopic studies and photodenitrosylation reactions of stereoselectively formed dinitrosyl-molybdenum [Mo(bidentate-N,S)2(NO)2] complexes with 2-pyrimidinethiolate derivatives

Abstract

For the first time, the cis(NO,NO)-trans(S,S)-[Mo(dapymt)2(NO)2] (dapymt = 4,6-diamino-2-pyrimidinethiolate) (1) and cis(NO,NO)-trans(N,S)-[Mo(dmpymt)2(NO)2] (dmpymt = 4,6-dimethyl-2-pyrimidinethiolate) (2) complexes have been prepared by the reaction of [Mo(NO)2]2+ with thiolate ligands. These complexes were characterized using UV–Vis absorption spectroscopy, IR absorption spectroscopy and X-ray crystallography. The dapymt complex exhibits a trans(S,S)-type configuration similar to that of our briefly reported dinitrosyl complexes cis(NO,NO)-trans(S,S)-[Mo(pymt)2(NO)2] (pymt = 2-pyrimidinethiolate) (3) and cis(NO,NO)-trans(S,S)-[Mo(pyt)2(NO)2] (pyt = 2-pyridinethiolate) (4). The dmpymt complex is a novel example of cis(NO,NO)-trans(N,S) coordination. This new isomer was selectively formed based on the use of a sterically hindered ligand that lacked the ability to form hydrogen bonds. Under ambient light, the prepared dinitrosyl complexes released one of two nitric oxide (NO) molecules to yield the following μ-OH dinuclear complexes: [{(ON)Mo(L)2}(μ-OH)2] (L = dmpymt (2p), pymt (3p), or pyt (4p)). Following irradiation of the parent complex with visible light, one NO ligand was eliminated and the Mo atoms were bridged by two hydroxo ligands to form a symmetric Mo2O2 core. Over time, the complexes exhibited a drastic decrease in absorbance of the MLCT (Mo → π*(NO)) band. It was found that the presence of a pyri(mi)dine nitrogen atom in the ligand was important for this photoreaction. The primary coordination sphere of the central molybdenum ion changed from a six-coordinate geometry to a seven-coordinate geometry, and the coordination geometry around the Mo atom was observed to be that of a distorted pentagonal bipyramid. Further, the oxidation states of the Mo atoms also varied from 0 to +II with this reaction. The E1/2 values of 1–4, [Mo(o-atp-N,S)2(NO)2] (o-atp = o-aminothiophenolate) (5), [Mo(o-ap-N,O)2(NO)2] (o-ap = o-aminophenolate) (6) and [Mo(pic-N,O)2(NO)2] (pic = 2-picolinate) (7)) indicated that the [Mo(NO)2]2+ moiety could be easily oxidized according to the following reaction order: 6 < 5 < 1 < 4 < 2, 3, 7. The E1/2 value of the [Mo(NO)2]2+ moiety in the dinitrosyl complexes is considered to be related to the denitrosylation reaction rate.