(Arene)cyclopentadienylchromium Chemistry. Synthesis, EPR, NMR, and Cyclic Voltammetry of Neutral Compounds and Their Monocations

Koehler, F. H.; Metz, Bernhard; Strauss, W.

doi:10.1021/ic00121a019

Cited by 27 publications

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“…Compared to the hyperfine data of sim- [14,19] in 1 the hyperfine coupling to chromium is stronger, while that to the ligand protons is weaker. An even larger hyperfine interaction (AA C H T U N G T R E N N U N G ( 53 Cr) iso = 1.85 mT) has been observed for chromium exo-bonded to two [2.2]-A C H T U N G T R E N N U N G (1,4)cyclophane ligands.…”

Section: Resultsmentioning

confidence: 60%

“…Neither for 1 nor for 2 could the other CH 2 and C 6 H 4 signals be detected near d = 260 and À60 ppm, respectively. We ascribe this to the fact that 1 and 2 are not very soluble and that the half-widths of the arene proton signals of similar compounds are in the range of 5 kHz [14] so that, in the present case, they disappear in the noise. rings of [2.2]A C H T U N G T R E N N U N G (1,4)cyclophane is bonded to chromium.…”

Section: Resultsmentioning

confidence: 77%

“…[14] The most convenient starting material is [{(C 5 Me 5 )CrCl 2 } 2 ], [15] and therefore the synthesis of (C 5 Me 5 )CrA C H T U N G T R E N N U N G (arene) compounds consists of successive (C 5 Me 5 )Cr-transfer and reduction steps. First, the reactivity of [{(C 5 Me 5 )CrCl 2 } 2 ] is increased by addition of anhydrous aluminum halide, which labilizes the CrÀCl bonds and splits the dinuclear compound.…”

Section: Resultsmentioning

confidence: 99%

“…When this was done by heating a mixture of AlCl 3 , [2.2]A C H T U N G T R E N N U N G (1,4)cyclophane, and Al as reducing agent, no (C 5 Me 5 )CrA C H T U N G T R E N N U N G (arene)-type compound could be isolated, although the procedure had been successful for benzene and substituted congeners. [14] In retrospect, this must be ascribed to the particular bonding between chromium and [2.2]A C H T U N G T R E N N U N G (1,4)cyclophane (see below), which renders the target molecule thermally labile. When milder conditions were chosen (reaction in refluxing cyclohexane rather than in a melt of AlCl 3 and AlBr 3 ) only one (C 5 Me 5 )Cr fragment could be bonded to [2.2]A C H T U N G T R E N N U N G (1,4)cyclophane, and 1 (see Scheme 2) was obtained in analytically pure form, albeit in low yield.…”

Section: Resultsmentioning

confidence: 99%

“…The signal shifts relative to diamagnetic standards (see Experimental Section), that is, the paramagnetic shifts caused by the unpaired electron spin density at 305 K, were d A C H T U N G T R E N N U N G (1,4)cyclophane which is not bonded to chromium, because for the other benzene and CH 2 moieties the signals should appear near d = 260 and À60 ppm, respectively. [14] The assignment was based on the relative signal areas and the fact that for dipolar relaxation the signal half-width is proportional to r À6 where r is the Cr···H distance. From the analogous structure of 2 it is known that the distances of Cr from the C 6 H 4 and CH 2 protons are 5.07 and 5.28 , respectively.…”

Section: Resultsmentioning

confidence: 99%

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The reaction of [{(C5Me5)CrCl2}2] with [2.2](1,4)cyclophane gave [(C5Me5)Cr{[2.2](1,4)cyclophane}] (1) and [(C5Me5)Cr{[2.2](1,4)cyclophane}Cr(C5Me5)] (2), depending on the reaction conditions. X-ray structure analysis showed 2 to be a ministack which in turn is stacked in the lattice. The chromium atoms are 6.035 A apart, and the distortion of the benzene rings to boat-shaped moieties is less pronounced than in parent [2.2](1,4)cyclophane. The NMR and EPR spectra were consistent with a S=1/2 ground state for 1 and with two interacting S=1/2 centers in 2. Spin density was found in the ligand pi systems, where its sign was negative when the pi system was adjacent to chromium, while on the nonbonded benzene moiety of 1 it was positive. Cyclic voltammograms showed reductions to 1- and 2(2-), as well as oxidations to 1+, 2+, and 2(2+) which were quasireversible, whereas oxidations to 1(2+) and 2(3+) were irreversible. Interaction between the metal ions was revealed by a 260 mV separation of the redox waves belonging to 2+, and 2(2+). Both cations were isolated as [B(C6H5)4]- salts, which in solution decomposed to [2.2](1,4)cyclophane and [(C5Me5)Cr{(eta6-C6H5)B(C6H5)3}] (3). The 1H and 13C NMR spectra of 3 were in accordance with an S=1 ground state. Solid-state magnetic measurements of the dimetallic compounds showed antiferromagnetic interaction with J=-122 cm-1 for 2, J=-31 cm-1 for 2+ (ground state S=1/2), and J=-23.5 cm-1 for 2(2+) (with H=-JS1S2). The decrease of J in the series 2, 2+, and 2(2+) was traced to the number of unpaired electrons and, for the mixed-valent cation 2+, to additional double exchange.

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Section: Resultsmentioning

confidence: 60%

Section: Resultsmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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