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DIIRON-HYDRIDE COMPLEXES - SYNTHESIS, STRUCTURE, AND REACTIVITY OF TRANS-[FE-2(CO)(4)(MU-H)(MU-CO)(MU-PCY(2))(MU-PH(2)PCH(2)PPH(2))]

HOGARTH, G; LAVENDER, MH; SHUKRI, K; (1995) DIIRON-HYDRIDE COMPLEXES - SYNTHESIS, STRUCTURE, AND REACTIVITY OF TRANS-[FE-2(CO)(4)(MU-H)(MU-CO)(MU-PCY(2))(MU-PH(2)PCH(2)PPH(2))]. ORGANOMETALLICS , 14 (5) 2325 - 2341.

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Abstract

The diphosphine-stabilized diiron complex [Fe-2(CO)(6)(mu-CO)(mu-dppm)] (dppm = Ph(2)PCH(2)PPh(2)) reacts readily with dicyclohexylphosphine upon UV irradiation to give the phosphido-hydrido complex [Fe-2(CO)(4)(mu-H)(mu-CO)(mu-PCy(2))(mu-dppm)] (1) shown to contain a trans arrangement of phosphorus-containing ligands, which is maintained throughout reactions. Two general types of reactivity are noted for 1, namely, insertion of unsaturated compounds into the diiron-hydride moiety with concomitant loss of carbon monoxide and hydride elimination reactions, which may or may not occur with carbonyl loss. Insertion of ethyne affords [Fe-2(CO)(4)(mu-HC=CH2)(mu-PCy(2))(mu-dppm)] (2). With propyne, an inseparable mixture of isomers [Fe-2(CO)(4)(mu-MeC=CH2)(mu-PCy(2))(mu-dppm)] (3a) and [Fe-2(CO)(4)(mu-HC=CHMe)(mu-PCy(2))(mu-dppm)] (3b) is formed in a 2.5:1 ratio, while with phenylethyne, regioselective insertion yields only the beta-alkenyl complex [Fe-2(CO)(4)(mu-HC=CHPh)(mu-PCy(2))(mu-dppm)] (4). The ''windshield-wiper'' sigma-pi alkenyl fluxionality of these complexes has been monitored by both H-1 and P-31 NMR spectroscopy, the former revealing that the fluxional process does not interconvert the beta-hydrogen atoms. The free energies of activation vary considerably between alpha- and beta-substituted alkenyl complexes, an effect which is believed to be steric in origin. Unactivated disubstituted alkynes do not react with 1; however, the activated alkyne dimethyl acetylenedicarboxylate (DMAD) readily inserts to afford the metallacyclic complex [Fe-4(CO)(4){eta(2)-C(CO(2)Me)=CH-C(OMe)=O}(mu-PCy(2))(mu-dppm)] (5) as a result of cis-trans vinyl isomerization and ester carbonyl coordination. Addition of allene to 1 affords 3a via selective proton transfer to the external carbons. Carbon dioxide is unreactive toward 1, but carbon disulfide readily inserts to yield the dithioformato complex [Fe-2(CO)(4)(mu-S2CH)(mu-PCy(2))(mu-dppm)] (6). Organic isothiocyanates (RNCS) also insert into 1, giving N-thioformamido [Fe-2(CO)(4)(mu-RNCHS)(mu-PCy(2))(mu-dppm)] (7a-c; R = allyl, Et, Ph) and formimidoyl [Fe-2(CO)(4)(mu-RN=CH)(mu-PCy(2))(mu-dppm)] (8a,b) complexes. Both result from selective hydride transfer to carbon, which occurs with sulfur loss in the case of the latter. Heating a toluene solution of 7b leads to the formation of 8b as a result of sulfur loss. Another formimidoyl complex [Fe-2(CO)(4)(mu-(t)BuN=CH)(mu-PCy(2))(mu-dppm)] (8d) has been prepared as the only product from the reaction of 1 with tert-butyl isocyanide, while in contrast 1 is unreactive toward nitriles. Both N-thioformamido 7 and formimidoyl 8 complexes contain an sp(2)-hybridized nitrogen and partial carbon-nitrogen double-bond character. Chromatography of 1 on alumina in the presence of dichloromethane affords [Fe-2(CO)(4)(mu-OH)(mu-PCy(2))(mu-dppm)] (9) together with chloro-bridged [Fe-2(CO)(4)(mu-Cl)(mu-PCy(2))(mu-dppm)] (10). The latter is more easily prepared upon reaction of 1 with hydrochloric acid. Addition of iodine to 1 yields the analogous iodo-bridged complex [Fe-2(CO)(4)(mu-I)(mu-PCy(2))(mu-dppm)] (11) in moderate yield.Thermolysis of 1 in the presence of diphenylphosphine affords mixtures of [Fe-2(CO)(4)(mu-PPh(2))(mu-PCy(2))(mu-dppm)] (12) and [Fe-2(CO)(4)(mu-PPh(2))(2)(mu-dppm)] (13). In a separate experiment, thermolysis of 12 with diphenylphosphine did not afford 13, indicating that phosphido-bridge exchange occurs prior to the formation of the electron-precise bis(phosphido)-bridged species. Thermolysis of 1 alone results in benzene elimination to yield [Fe-2(CO)(5)(mu-PCy(2))(mu-PhPCH(2)PPh(2))] (14). Complexes 1, 2, 4, 7a, 8a, and 11 were characterized by single-crystal X-ray diffraction analyses. Crystal data: for 1, space group P ($) over bar 1, a = 10.2577(34) Angstrom, b = 13.0315(81) Angstrom, c = 15.8986(71) Angstrom, alpha = 81.902(43)degrees, beta = 84.672(31)degrees, gamma = 72.272(38)degrees, Z = 2, 4136 reflections, R = 0.068; for 2, space group P ($) over bar 1, a = 11.7987(15) Angstrom, b = 12.8813(16) Angstrom, c = 17.0025(9) Angstrom, alpha = 73.670(8)degrees, beta = 77.770(8)degrees, gamma = 64.870(8)degrees, Z = 2, 6506 reflections, R = 0.046; for 4, space group P ($) over bar 1, a = 12.5326(15) Angstrom, b = 12.5939(16) Angstrom, c = 18.4748(25) Angstrom, alpha = 105.240(10)degrees, beta = 91.975(10)degrees, gamma = 118.025(10)degrees, Z = 2, 7416 reflections, R = 0.051; for 7a, space group P ($) over bar 1, a = 11.9777(39) Angstrom, b = 13.5843(36) Angstrom, c = 13.7530(51) Angstrom, alpha = 88.912(26)degrees, beta = 89.293(28)degrees, gamma = 78.931(25)degrees, Z = 2, 4235 reflections, R = 0.061; for 8a, space group P2(1)/c, a = 11.8267(32) Angstrom, b = 15.5264(29) Angstrom, c = 27.1868(71) Angstrom, alpha = 90 degrees, beta = 91.366(22)degrees, gamma = 90 degrees, Z = 4, 3252 reflections, R = 0.088; for 11, space group P ($) over bar 1, a = 11.8975(20) Angstrom, b = 12.9829(16) Angstrom, c = 16.6072(25) Angstrom, alpha = 72.937(12)degrees, beta = 76.891(13)degrees, gamma = 64.089(11)degrees, Z = 2, 5957 reflections, R = 0.069.

Type:Article
Title:DIIRON-HYDRIDE COMPLEXES - SYNTHESIS, STRUCTURE, AND REACTIVITY OF TRANS-[FE-2(CO)(4)(MU-H)(MU-CO)(MU-PCY(2))(MU-PH(2)PCH(2)PPH(2))]
Keywords:RAY CRYSTAL-STRUCTURE, R = PH, MOLECULAR-STRUCTURE, PLATINUM METALS, DIMOLYBDENUM COMPLEXES, INSERTION REACTIONS, FLUXIONAL BEHAVIOR, ALKYNE INSERTION, DOUBLE-BOND, DERIVATIVES
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Chemistry

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