Stable Organopalladium(II) and Organoruthenium(II) Complexes with Spin-Labeled Phosphine Ligands

Abstract

Palladium(II) and ruthenium(II) complexes containing aminoxyl radical-substituted triphenylphosphine ligands are reported. The novel spin-labeled phosphine ligands [(p-(4,4,5,5,-tetramethylimidazolinyl-1-oxyl-3-oxide)phenyl)diphenylphosphine] (1) and [(p-(Noxyl-tert-butylamino-2-)phenyl)diphenylphosphine] (2) react with PdCl 2 to yield trans-Pd[1] 2 Cl 2 and trans-Pd [2] 2 Cl 2 (complexes 3 and 4, respectively), which show exchange-coupled EPR spectra. This through-space, intramolecular coupling provides a method of determining the number of radical phosphines coordinated to the Pd(II) center. Systems with only one coordinated phosphine show EPR spectra typical of the ligand. Phosphine 2 reacts with [(η 3 -C 3 H 5 )PdCl] 2 and [(η 6 -p-cymene)RuCl 2 ] 2 to form the mononuclear metal phosphine adducts (η 3 -C 3 H 5 )Pd[2]Cl ( 5) and (η 6 -p-cymene)Ru[2]Cl 2 (6). All complexes show broad, shifted 1 H NMR spectra, and magnetic susceptibility measurements confirm the presence of one (complexes 5, 6) or two (complexes 3, 4) radicals per complex accordingly. The X-ray crystal structures of Pd[2] 2 Cl 2 and (η 3 -C 3 H 5 )Pd[2]Cl are also reported. Complexes 5 and 6 are unusual examples of stable organometallic systems with peripheral free radicals, i.e., spin-labeled organometallics.

Experimental and Theoretical Studies of Magnetic Exchange in Silole‐Bridged Diradicals

“…[37] The torsion angles between the nitroxide moiety and the phenyl ring are 20.98 and 3.28 for molecule A and 23.18 and 1.88 for molecule B, respectively. While the first torsion angle values are not uncommon in phenyl-substituted nitroxide radicals (see above), the second ones are unusual, [38,39] and closer to the range of values reported for benzoquinonimine-N-oxide derivatives (3.38). [40,41] To check whether this structure reflects either a benzenoid or a quinonoid form in the crystal lattice, the 2,5-diphenylthienyl bond lengths for 12, crystal structures SUSNEZ, [36] FEJRUH (benzenoid forms), [37] VIZBUB [42] and QIPQAH (quinonoid forms) [43] were compared (see Figure S2 and Table S5 in the Supporting Information).…”

Discrepancy between the Spin Distribution and the Magnetic Ground State for a Triaminoxyl Substituted Triphenylphosphine Oxide Derivative

“…Previous studies on such systems showed that it is possible to selectively obtain the radical without oxidizing the P III center when Ag 2 O is used as oxidant. [9,12,15] This proved not to be the case here, only a partial oxidation was observed independent of the stoichiometry considered. The oxidation was therefore conducted as in route A to obtain the triradical 1.…”

“…However, the later appear in good agreement with those found usually. [11,12,17,18] Figure 2 shows the crystalline organization in the bc and ac planes. The molecular stacking can be described as a superposition of layers along the a axes.…”

trans-Dichloridobis{[4-(dimethylamino)phenyl]diphenylphosphane}palladium(II)

“…For a review on related compounds, see: Spessard & Miessler (1996). For related compounds, see: Burrow et al (1994); DiMeglio et al (1990); Edwards et al (1998); Ferguson et al (1982); Grushin et al (1994); Kitano et al (1983); Leznoff et al (1999); Meij et al (2003); Meijboom et al (2006a,b); Meijboom & Omondi (2010). For the synthesis of the starting materials, see: Drew & Doyle (1990).…”