Group 11 Metal Complexes Coordinated by the (Nitronyl Nitroxide)‐2‐ide Radical Anion: Facile Oxidation of Stable Radicals Controlled by Metal–Carbon Bonds in Radical‐Metalloids

Abstract

A series of group 11 metal complexes coordinated by (nitronyl nitroxide)-2-ide radical anion NN-M(dtpb) [NN: nitronyl nitroxide; M: Cu I , Ag I , and Au I ; dtpb: 1,2-bis(di-2-tolylphosphanyl)benzene)] was prepared. Their structures, electrochemical properties, and related theoretical calculations were investigated. The oxidation potential (E ox , V vs. Fc/Fc + ) of the NN-moiety in these radical-metalloids significantly shifted to the negative direction in comparison to that of the unsubsti- [a] Preparation of NN + -Ag(dtpb)·SbF 6 -: In a glove box filled with argon, NN-Ag(dtpb) (100 mg, 0.131 mmol, 1.0 equiv.) was dissolved in CH 2 Cl 2 (4 mL). To this stirred solution, a CH 2 Cl 2 solution (4 mL) of TBPA + ·SbF 6 -(97 mg, 0.135 mmol, 1.0 equiv.) was added. After stirring for 30 min, the solution was concentrated to ca. 2 mL under reduced pressure. Et 2 O was added to the solution. The generating precipitate was collected and washed with Et 2 O, to give NN + -Ag(dtpb)·SbF 6 as a dark brown solid (124 mg, 95 %). Crystals suitable for X-ray crystal structure analysis were obtained by recrystallization from CH 2 Cl 2 /n-hexane. NN + -Ag(dtpb)·SbF 6 -: C 41 H 44 AgF 6 N 2 O 2 P 2 Sb, dark brown crystals; MW 1002.37; m.p. 183-184°C. MS (FAB + ) m/z 765 [NN + -Ag(dtpb)], (FAB -) m/z 235 [SbF 6 -].Preparation of NN + -Au(dtpb)·SbF 6 -: In a glove box filled with argon, NN-Au(dtpb) (95 mg, 0.111 mmol, 1.0 equiv.) was dissolved in CH 2 Cl 2 (2 mL). To this stirred solution, a CH 2 Cl 2 solution (2 mL) of TBPA + ·SbF 6 -(80 mg, 0.111 mmol, 1.0 equiv.) was added. After stirring for 30 min, the solution was concentrated to ca. 2 mL under reduced pressure. Et 2 O was added to the solution. The generating precipitate was collected and washed with Et 2 O, to give NN + -Au(dtpb)·SbF 6 as a yellow solid (104 mg, 86 %). Crystals suitable for X-ray crystal structure analysis were obtained by recrystallization from CH 2 Cl 2 /Et 2 O. NN + -Au(dtpb)·SbF 6 -: C 41 H 44 AuF 6 N 2 O 2 P 2 Sb, green crystals; MW 1091.47; m.p. 153°C (decomp.). MS (FAB + ) m/z 855 [NN + -Au(dtpb)], (FAB -) m/z 235 [SbF 6 -]; High resolution MS (FAB + ): found m/z 855.2544; calcd. for C 41 H 44 AuN 2 O 2 P 2 m/z 855. Geometrical Optimizations and Determination of SOMO Energies and NPA Charges of NN-M(dtpb):The geometrical optimizations were achieved using the X-ray structures for the initial input geometries. The determination of HOMO (SOMO) energies of NN-M(dtpb) were achieved using the Gaussian 09 program package [22] with a DFT method at the UB3PW91 level. [25] Basis sets employed were 6-31G(d,p) (for geometrical optimization) and 6-311++(d,p) (for NPA charge calculation [23] ) for C, H, N, O, P, and Cu atoms and Hay-Wadt double-zeta functions with Los Alamos relativistic effective core potential (LANL2DZ) [26] for Ag, Au, Pt, and Hg atoms (Figure 3a, Figure S6). Conflict of Interest:The authors declare no conflict of interest. from JSPS KAKENHI (Grant Number JP17K05790 for M. K. and K. O. and JP26102005 for S. S.).

Aurophilic Interactions in Multi‐Radical Species: Electronic‐Spin and Redox Properties of Bis‐ and Tris‐[(Nitronyl Nitroxide)‐Gold(I)] Complexes with Phosphine‐Ligand Scaffolds

“…We have previously reported that NN‐metal complex NN‐M‐L exhibited unique electrochemical behaviors in which the oxidation potential assignable to the NN moieties shifted abnormally to a negative potential [11c,12] . We also measured the cyclic voltammograms (CVs) of (NN‐Au) 2 ‐1 o , m , p and (NN‐Au) 3 ‐2 to investigate their electrochemical properties and to determine the effect of aurophilic interactions (Figures 8 and S5, and Table 1).…”

“…Third, the second oxidation potential of (NN‐Au) 2 ‐1 o was slightly higher than the oxidation potentials of (NN‐Au) 2 ‐1 m and (NN‐Au) 2 ‐1 p . We have reported that the oxidation potentials assignable to the NN moieties in NN‐M‐L are correlated with the natural population analysis (NPA) charges at the C2 carbon atom in the NN moiety [12] . The particular differences in the electrochemical properties of (NN‐Au) 2 ‐1 o suggest higher electron‐donating ability due to the aurophilic interaction, which causes a large negative and a small positive NPA charge compared with (NN‐Au) 2 ‐1 p (Table S8).…”

“…Recent progress in the chemistry of NN radicals has led to the direct introduction of the NN group to organic and organometallic platforms using a parent NN ( NN‐H ) as a synthetic unit, which can easily convert a nucleophilic radical anion by deprotonation at the C2‐position (Scheme 1). [8−14] To date, the properties of a series of organometallic NN radicals NN‐M−L [M: Hg II , [8] Pt II , [9] Pd II , [10] Au I , [11−13] Ag I , [12] Cu I ; [12,13] L: acetate (OAc), phosphine ligand (PR 3 ), 2,2′‐bipyridine ligand, and N ‐heterocyclic carbene ligand (NHC) as examples] have been investigated and their interesting redox [9,10,12] and electronic‐spin properties have been discovered [10,11] . We also found that NN‐Au‐L is an attractive cross‐coupling reagent for the introduction of an NN group in the reaction with aryl bromide or aryl iodide [11a] .…”

A Molecule Having 13 Unpaired Electrons: Magnetic Property of a Gadolinium(III) Complex Coordinated with Six Nitronyl Nitroxide Radicals

“…The synthetic route for Gd 3+ ·(1 – ) 3 is shown in Scheme . This method is similar to our previously reported method for preparing a series of organometallic nitronyl nitroxide (NN) radicals. ,− After the generation of an NN anion upon treatment of NN-H with sodium hydroxide, the resulting mixture was allowed to react with AuCl­(THT) (THT = tetrahydrothiophene) to afford Na + ·1 – (CCDC 2090754). Compound Na + ·1 – was converted to Gd 3+ ·(1 – ) 3 by treatment with gadolinium­(III) nitrate.…”

2-Imidazoline Nitroxide Derivatives of Cymantrene

“…The design of organometallic derivatives of nitroxide radicals [ 1 , 2 , 3 ] has a high potential for the development of new organic synthesis principles and the study of the mechanisms of catalytic reactions [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ] as well as for the creation of polyfunctional magnetoactive materials exhibiting diverse intra- and intermolecular interactions and spin-exchange coupling [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ,…”