Preparations and Properties of Some Gationic Palladium(II) Complexes of the Di-t-butylnitroxide Radical

Abstract

Cationic palladium(II) complexes of the di-t-butylnitroxide radical, [Pd(But2NO)(L-L)]X (L-L=2,2′-bipyridine, 1,10-phenanthroline, N-substituted 2-pyridylmethyleneamine and bis(triphenylphosphine); X−=ClO4-and/or BPh4−), were prepared. 1H NMR spectra of the complexes indicate that the nitroxide forms a three membered ring with the palladium atom. The N-methyl- and N-ethyl-2-pyridylmethyleneamine complexes exist as two geometrical isomers in solution, whose ratios are 1 : 1 and 1 : 0.2, respectively. In the N-butyl and N-p-tolyl analogs, however, only one of the isomers exists in solution. These results are interpreted in terms of steric repulsion between the t-butyl groups and N-substituents. The bipyridine complex reacts with dialkyl disulfides in the presence of catalytic amounts of bipyridine to give a sulfur-bridged dimeric complex, [Pd(bipyridine)(SR)]2(ClO4)2(R=Me and Pr), and a free nitroxide radical.

Synthesis and molecular structure of titanium complexes containing a reduced TEMPO radical

“…Evans et al recently reported a novel TEMPO complex of Sm containing both h 1 and h 2 -coordinated TEMPO ligands. 18 h 2 -coordination is common for TEMPO complexes of most transition metals; [11][12][13][14][15][16][17][18] for the early metals h 2 -coordination was observed for the homoleptic Ti(ONR 2 ) 4 (R = Me, 26 Et 27 ). In this communication, we report the X-ray structures of two titanium compounds containing anionic TEMPO ligands and demonstrate that the binding mode of these ligands depends sensitively on the ancillary ligation at titanium.…”

“…Applications of this versatile molecule include its use as a mild yet selective oxidant of primary and secondary alcohols, 1,2 as a spin-label in the study of complex chemical environments, [3][4][5][6] as a mediator of controlled/living free radical polymerization, 7,8 and in the mechanistic study of radical reactions. Inorganic chemists have extensively studied the fundamental coordination chemistry of the nitroxide moiety to transition metals 9,10 Mn, 11 Co, 12 Cu, 13 Zn, 9 Mo, 14,15 Rh, 14 Pd, 16,17 lanthanides, 18 the p-block metalloids such as B 19 and Si, 20 and the s-block metals Li, Na, and Mg. 21 A number of these compounds have been investigated in the search for new molecular magnets. 22 TEMPO often serves as an odd-electron Lewis base towards electrophilic metal centers; surprisingly, only a limited number of metal complexes with monoanionic TEMPO ligands have been reported.…”

“…22 TEMPO often serves as an odd-electron Lewis base towards electrophilic metal centers; surprisingly, only a limited number of metal complexes with monoanionic TEMPO ligands have been reported. 11,12,[15][16][17][18]21,23 The synthesis of TEMPO and di-tert-butylnitroxide complexes of Ti, Zr and Hf was previously reported, 24,25 but little is known about the coordination geometry and oxidation state of the radical-derived ligand. Evans et al recently reported a novel TEMPO complex of Sm containing both h 1 and h 2 -coordinated TEMPO ligands.…”