EPR Spectra of [Cr(CO)₂L(η-C₆Me₆)]⁺ (L = PEt₃, PPh₃, P(OEt)₃, P(OPh)₃):  Analysis of Line Widths and Determination of Ground State Configuration from Interpretation of ³¹P Couplings

Abstract

The preparation and characterization of [Cr(CO)2L(η-C6Me6)] (L = PEt3, PPh3, P(OEt)3 and P(OPh)3, are reported. One-electron oxidation affords unstable Cr(I) cations, [Cr(CO)2L(η-C6Me6)]+, EPR spectra of which are reported. Detailed analysis of the anisotropic 31P hyperfine interaction indicates that, in frozen CH2Cl2/THF, the phosphine and phosphite complexes have 2A‘ and 2A‘‘ ground states, respectively. The hyperfine anisotropy can be accounted for by dipolar interaction of the 31P nucleus with spin density on Cr and, in the case of the phosphite complexes, with ∼0.01 P 3p y spin density resulting from π-backbonding. Line width anomalies observed in EPR spectra of these and other Cr(I) and Mn(II) “piano stool” complexes can be understood in terms of molecular distortions resulting from solvation in frozen solutions.

A low‐spin iron with CN and CO as intrinsic ligands forms the core of the active site in [Fe]‐hydrogenases

“…The rhombic 2.10 EPR signal in [Fe]-hydrogenases has g values at 2.099, 2.041, 2.001 (Clostridium pasteurianum, hydrogenase-I [24]), at 2.108, 2.046 and 2.003 (D. vulgaris [23]), at 2.101, 2.050 and 2.005 (M. elsdenii [26]), at 2.100, 2.038, 1.994 (Desulfovibrio desulfuricans ATCC 7757 [31], and at 2.10, 2.04, 2.01 (Trichomonas vaginalis [32]). Such a set of g values is often found in low-spin d 5 transition metal complexes [33,34]. In view of the FTIR and EPR properties of the active sites of [Fe]-hydrogenases, we propose that the rhombic 2.10 EPR signal of [Fe]-hydrogenases is due to an unpaired spin mainly localized on a rhombic low-spin Fe(III) ion in a tetragonally distorted, strong octahedral ligand field with thiols, CO and CN as ligands.…”

Redox routes to arenechromium complexes of two-, three- and four-electron alkynes; structure and bonding in paramagnetic [Cr(CO)L(η-RCCR)(η-arene)]+

“…We now show how this oxidation process, in leading to a stronger metal-alkyne bond and weaker metal-carbonyl bonds, results in a change in the substitutional reactivity of [Cr(CO) 2 (η-RC᎐ ᎐ ᎐ CR)(η-C 6 Me 6 )] (R = Ph or C 6 H 4 OMe-p). Whereas the alkyne is displaced from [Cr(CO) 2 (η-RC᎐ ᎐ ᎐ CR)(η-C 6 Me 6 )] by two-electron donor ligands, L, such as isocyanides and phosphites, to give [Cr(CO) 2 L(η-C 6 Me 6 )], 3 The structures of 1 and 1 ؉ are shown in Figs. 1 and 2 and important bond distances and angles for these complexes, as…”

Can Acetylenedithiolate Act as a Tetradentate Bridging Ligand?

“…This observation points to a SOMO, which is predominantly localized at ruthenium. [7] In order to compare the effect of the oxidation on both metal atoms the ruthenium center was furnished with an IR probe. For this purpose complex 4 was synthesized, in which the phosphine in 3 is replaced by 2,6-dimethylphenylisocyanide.…”