Pentacarbonyl[(E)-3-ferrocenyl-1-methoxy-2-propenylidene]chromium1

[193070-49-4]  · C19H14CrFeO6  · (MW 446.16)

(cyclopropanation,2,3 Dötz benzannulation,2,3 Michael addition,4 NLO chromophore5)

Physical Data: mp 105-107 °C.

Solubility: soluble in hexane, diethyl ether, tetrahydrofuran, ethanol, and most organic solvents.

Form Supplied in: dark violet solid.

Analysis of Reagent Purity: 1H NMR (200 MHz, CDCl3) d4.22 (s, 5H), 4.60 (br s, 4H), 4.70 (s, 3H), 7.19 (d, J = 15.0 Hz, 1H), 7.52 (d, J = 15.0 Hz, 1H); 13C NMR (75.5 MHz, CDCl3) d 65.6, 69.9, 70.3, 72.6, 78.3, 137.5, 138.0, 217.1, 224.2, 326.0; IR (KBr) n 3020 (s), 2401 (w), 2361 (w), 2054 (m), 1939 (s), 1575 (m), 1541 (w), 1423 (w), 1217 (s); UV-visible (hexane, 10-5 - 10-7 M) lmax = 543.2, 462.8 nm; LRMS (70 eV, EI) m/z (%) 446 (M+, 20), 418 (15), 332 (30), 306 (80), 270 (90), 237 (25), 220 (45), 205 (46), 186 (75), 149 (40), 121 (100); HRMS (70 eV, EI) calculated for C19H14CrFeO6 (M+) 445.9545, found 445.9564. Analysis calculated for C19H14CrFeO6: C, 51.15; H, 3.16. Found: C, 51.22; H, 3.06. Cyclic voltammogram (potentials measured in 0.1 M Bu4NClO4-MeCN and given in V with respect to Fc/Fc+): oxidation, E° (1st) = 0.135, Epa (2nd) = 0.501, Epc = 0.418; reduction, E° = 0.460, Epc = -1.617.

Preparative Methods: to a solution of pentacarbonyl(1-methoxyethylidene)chromium (6.3 g, 25 mmol) in diethyl ether (150 mL) at room temperature were successively added triethylamine (13.94 mL, 100 mmol), ferrocenecarbaldehyde (6.42 g, 30 mmol) and chlorotrimethylsilane (9.52 mL, 75 mmol). The mixture was stirred at room temperature for 48 h. Silica gel (ca. 25 g) was then added, and the solvent was removed under reduced pressure. The residue was loaded onto a silica gel column under N2. Elution with hexane gave 8.35 g (18.72 mmol, 75%) of pentacarbonyl[(E)-3-ferrocenyl-1-methoxy-2-propenylidene]chromium as a dark violet solid. Rf = 0.30 (hexane).

Purification: column chromatography on silica gel using hexane as eluent.

Handling, Storage, and Precautions: as a solid the reagent is quite air-stable and can easily be handled in the air. To prevent oxidation, store in the dark under nitrogen atmosphere and refrigerate. In solution this carbene complex is slightly air-sensitive particularly in the presence of light. NMR experiments and reactions are best carried out under an inert atmosphere.

Introduction

Heterobinuclear organometallic complex containing a push-pull p-system with a low second-order NLO response. This reagent has been mainly used for the diastereoselective intermolecular cyclopropanation of electronically neutral alkenes. The reaction of this compound with alkynes to give substituted phenols and with alkyllithiums to generate b-substituted alkylcarbene complexes is also known.

Cyclopropanation Reactions

2-Ferrocenylvinyl carbene complex of chromium (1) reacts with electronically neutral alkenes in an intermolecular fashion to give the corresponding 2-ferrocenylvinylcyclopropanes with high diastereoselectivity (1).2,3 The reaction occurs under thermal conditions using an excess of the alkene. Either monosubstituted olefins or 1,2-disubstituted olefins with a cyclic or acyclic structure undergo cyclopropanation by this heterobimetallic carbene complex (1).

Dötz Benzannulation Reactions

The thermal reaction of 2-ferrocenylvinyl carbene complex (1) with terminal alkynes (1-hexyne) or conjugated enynes (2-methylbut-1-en-3-yne) affords regioselectively 2,4,6-trisubstituted phenol derivatives (2).2,3 This result demonstrates that the Dötz benzannulation reaction is highly favored over the cyclopropanation process.3

Michael Additions

2-Ferrocenylalkenyl carbene complex (1) behaves as a Michael acceptor. Alkyllithiums react with complex (1) at -78 °C to provide after purification by silica gel column chromatography the corresponding b-substituted alkylcarbene complexes with moderate yields (3).4 Higher chemical yields are observed in these conjugate addition reactions when analogous carbene complexes bearing a bulky alkoxy group (pentacarbonyl[(E)-3-ferrocenyl-1-[(1R*,2S*,5R*)-menthyloxy]-2-propenylidene]chromium and pentacarbonyl[(E)-3-ferrocenyl-1- [(1R,2S,5R)-8-phenylmenthyloxy]-2-propenylidene]chromium) are employed. In addition, the later chiral nonracemic derivative leads to the Michael adducts with high levels of asymmetric induction.4

Second-order Nonlinear Optical (NLO) Response

The molecular first hyperpolarizability b of 2-ferrocenylalkenyl chromium carbene complex (1) was determined by hyper-Rayleigh scattering experiments.5 The b values ranged from 47 × 10-30esu in hexane (ε532 = 11 933 × 104 L mol-1 cm-1) to 110 × 10-30 esu in acetonitrile (ε532 = 6844  × 104 L mol-1 cm-1). Carbene complexes with a longer polyene linker between the donor and the acceptor groups show higher b values. The highest b value: 2420 × 10-30 esu in acetonitrile (ε532 = 22 950 × 104 L mol-1 cm-1) has been reported for compound 2.

Related Reagents.

Pentacarbonyl[(E)-3-ferrocenyl-1-[(1R*,2 S*,5R*)-menthyloxy]-2-propenylidene]chromium;4 pentacarbonyl[(E)-3-ferrocenyl-1-[(1R,2S,5R)-8-phenylmenthyloxy]-2-propenylidene]chromium;4,6 pentacarbonyl[(E)-3-ferrocenyl-1-methoxy-2-propenylidene]tungsten.5 See also: pentacarbonyl(1-ferrocenyl-1-methoxymethylene)chromium.7


1. (a) Herndon, J. W., Coord. Chem. Rev. 1999, 181, 177. (b) Sierra, M. A., Chem. Rev. 2000, 100, 3591.
2. Barluenga, J.; Fernández-Acebes, A.; Trabanco, A. A.; Flórez, J., J. Am. Chem. Soc. 1997, 119, 7591.
3. Barluenga, J.; López, S.; Trabanco, A. A.; Fernández-Acebes, A.; Flórez, J., J. Am. Chem. Soc. 2000, 122, 8145.
4. Barluenga, J.; Fernández-Acebes, A.; Flórez, J., unpublished results.
5. Jayaprakash, K. N.; Ray, P. C.; Matsuoka, I.; Bhadbhade, M. M.; Puranik, V. G.; Das, P. K.; Nishihara, H.; Sarkar, A., Organometallics 1999, 18, 3851.
6. Barluenga, J.; Fernández-Rodríguez, M. A.; Aguilar, E.; Fernández-Mari, F.; Salinas, A.; Olano, B., Chem. Eur. J. 2001, 7, 3533.
7. (a) Connor, J. A.; Lloyd, J. P., J. Chem. Soc. Dalton 1972, 1470. (b) Connor, J. A.; Lloyd, J. P., J. Chem. Soc. Perkin 1 1973, 17. (c) Dötz, K. H.; Dietz, R.; Neugebauer, D., Chem. Ber. 1979, 112, 1486.

José Barluenga, Alvaro Fernández-Acebes & Josefa Flórez

Instituto Universitario de Química Organometálica ‘Enrique Moles’ (Unidad Asociada al CSIC), Universidad de Oviedo, Oviedo, Spain



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