Chromium Nitrosyl Complexes Research Articles

Recent advances in the chemistry of nitrosyl complexes of chromium

AbstractA review of the chemistry of nitrosyl complexes of chromium published since 2002 is given including coordination complexes as well as organometallic complexes. The syntheses, electronic structures, optical absorption spectra, electron paramagnetic resonance parameters, photochemistry, reactivity, and magnetic properties of the complexes are presented.

Group 6 Metal Complexes of the η5-Pentamethyl[60]fullerene

A molybdenum pentamethyl[60]fullerene bromo tricarbonyl complex, Mo(η5-C60Me5)Br(CO)3 (3), was successfully synthesized by the reaction of C60Me5Br (2) with Mo(CO)3(EtCN)3. Treatment of 3 with I2 afforded an iodo complex, Mo(η5-C60Me5)I(CO)3 (4). The reaction employing C60Me5K (5) prepared from C60Me5H (1) and KH, followed by treatment with Mo(CO)3(EtCN)3 and then Diazald, gave a nitrosyl complex, Mo(η5-C60Me5)(NO)(CO)2 (6). Complex 6 was converted to a molybdenum(IV) complex, Mo(η5-C60Me5)Cl2(NO)(CO) (7), by the reaction with PCl5. A molybdenum(VI) complex, Mo(η5-C60Me5)O2Br (8), was obtained by exposure of 3 in air. Tungsten- and chromium-nitrosyl complexes, W(η5-C60Me5)(NO)(CO)2 (9) and Cr(η5-C60Me5)(NO)(CO)2 (10), were synthesized similarly to 6. Complex 10 gave a dithiocarbonate complex, Cr(η5-C60Me5)(η5-S2COEt)(NO) (11) through the reaction among 10, ethanol, and carbon disulfide. Compounds 1, 3, 4, 6, 8, and 11 were characterized by X-ray crystallography.

Electron-Transfer Reactions of Nitrosyl and Superoxo Metal Complexes

Novel chromium nitrosyl complexes L(H2O)CrNO(2+) (L = L(1) = 1,4,8,11-tetraazacyclotetradecane, L(2) = meso-Me 6-1,4,8,11-tetraazacyclotetradecane) are oxidized by Ru(bpy)3(3+) to LCr(H2O)2(3+) and NO with rate constants k = 2.22 M(-1) s(-1) (L(1)) and 6.83 (L(2)). Analogous reactions of the superoxo complexes L(H2O)CrOO(2+) are only slightly faster, k = 45 M(-1) s(-1) (L(1)) and 15 M(-1) s(-1) (L(2)). A related rhodium complex L(2)(H2O)RhOO(2+) has k = 15.8 M(-1) s(-1). These results, combined with our earlier data for the oxidation of Cr(aq)NO(2+) and Cr(aq)OO(2+), suggest only a modest role for thermodynamics in determining the kinetics of oxidation. This behavior is even more pronounced in the oxidation of rhodium hydrido and hydroperoxo complexes, with the latter reacting more than 10(5)-fold faster despite being thermodynamically less favored by more than 0.3 V. The X-ray crystal structure of [L(1)(H2O)CrNO](ClO4)2 supports the limiting Cr(III)-NO(-) description for the complex cation.

Electron Spin Relaxation in Chromium-Nitrosyl Complexes.

A new method to prepare Cr(NO)(H(2)O)(5)(2+) from dichromate and NH(2)OH is reported. The chromium nitrosyls Cr(NO)(EHBA)(+) and Cr(NO)(EHBA)(2) (EHBA = 2-ethyl-2-hydoxybutyrate) were prepared by a literature reaction and characterized by continuous wave electron paramagnetic resonance and two-pulse electron spin echo spectroscopy at X-band. The g values are characteristic of a single unpaired electron in a predominantly d(xy)() orbital. In fluid and glassy solutions Cr(NO)(EHBA)(2) is a mixture of cis and trans isomers. Rotation of the methyl groups in the EHBA ligands causes an increased rate of spin echo dephasing at temperatures between 40 and 120 K. For the EHBA complexes echo envelope modulation is observed at temperatures below about 40 K that is attributed to inequivalent coupling to protons of the slowly rotating methyl groups. Both the effect of the methyl rotation on spin echo dephasing and the depth of the proton modulation are dependent on the number of ethyl groups in the ligand, and thus the spin echo experiments provide confirmation of the number of EHBA ligands in the complexes. The spin-lattice relaxation rates for the chromium-nitrosyl complexes at temperatures near 100 K are similar to values reported previously for Cr(V) complexes, which also have a single unpaired electron in a predominantly d(xy)() orbital. For Cr(NO)(H(2)O)(5)(2+), Cr(NO)(EHBA)(+), and Cr(NO)(EHBA)(2) the dominant contribution to spin-lattice relaxation between 12 and 150 K is the Raman process with a Debye temperature, theta(D), of 110-120 K. For Cr(NO)(CN)(5)(3)(-) the data are consistent with a Raman process (theta(D) = 135 K) and a contribution from a local mode, which dominates above about 60 K. The formally low-spin d(5) chromium nitrosyl complexes relax about 5 orders of magnitude more slowly than low-spin d(5) Fe(III) porphyrins, which is attributed to the absence of a low-lying excited state.

Novel cyano-bridged nitrosyl complexes of chromium(I) with amino- and aminoethyl-pyridines

New compounds of chromium(I), from the interaction of potassium pentacyanonitrosylchromate(I) monohydrate, K3[CrNO(CN)5]·H2O with 2-, 3- and 4-aminopyridines, pyridine-2-hydrazide, 2(2-aminoethyl)pyridine and 4(2-aminoethyl)pyridine are described. The products possess the empirical formula, CrNO(CN)2(L)2, for which a cyano-bridged polymeric structure is proposed. Chromium(I) has a low-spin-d5 configuration in these complexes.

Organometallic nitrosyl chemistry. 22. New halo nitrosyl complexes of chromium resulting from the reactions of halogens with (.eta.5-C5R5)Cr(CO)(NO)L (R = H, Me; L = CO, PPh3)

Le traitement de (η 5 -C 5 H 5 )Cr(CO) 2 (NO) avec l'iode dans CH 2 Cl 2 donne [(η 5 -C 5 H 5 )Cr(NO)I] 2 . Preparation des complexes a 17 electrons (η 5 -C 5 H 5 )Cr(NO)(L)I avec L=PPh 3 , P(OPh) 3 , P(OEt) 3 . Proprietes physiques

Synthesis, structure and properties of the chromium nitrosyl complexes of [CrNO(CN) x(en) y] n± type

The series of the nitrosyl chromium complexes of types [CrNO(CN) x(en) y] n± were synthesized and investigated: I, K[CrNO(CN) 2(en)(OH)·4H 2O; II, [CrNO(CN) 2(en)(H 2O)]; III, Cr 2(NO) 2(CN) 4(en) 3]; IV, [Cr 2(NO) 2(CN) 2(en) 4] Cl 2·2H 2O; V, [Cr 2(NO) 2(en) 5]Cl 4·6H 2O. The complexes III–V were found to be the dimers which bridge ethylenediamine Their structure was determined by the magnetic and spectroscopic (EPR, UV-VIS and IR) methods. The influence of the coordinated ligands upon the electronic structure of the molecular unit {CrNO} was determined.

Electron Spin Resonance Studies of Chromium Nitrosyl Complexes

The electron paramagnetic resonance results of three chromium nitrosyl complexes are reported (pentacyano, penta-aquo, and penta-amino). Hyperfine structure with the nucleus of the metal as well as with the nuclei of some of the ligands is observed. We attempt to explain the interaction with the ligand nuclei by mixing the ground state with excited states (charge transfer) by means of the exchange with the unpaired electron. Different possibilities for the configuration of the ground state are discussed.