Synthesis and Characterization of the Metal(I) Dimers [Ar′MMAr′]: Comparisons with Quintuple‐Bonded [Ar′CrCrAr′]

Abstract

Metal-metal bonding in the dimeric chromium complex [Ar'CrCrAr'] (Ar' = C 6 H 3 -2,6(2,6-iPr 2 C 6 H 3 ) 2 is derived from the interaction of two d 5 {CrAr'} fragments whose valence electrons are paired to form a quintuple bond. [1][2][3][4][5] The ready synthesis [1] of this complex by the simple reduction of an aryl metal halide precursor [6] suggests the possible formation of similar complexes by other transition metals. Such complexes might exhibit unprecedented types of interactions between metals of various d n configurations, and their isolation and characterization would permit informative comparisons with the chromium species. Herein, we report the synthesis, structural and spectroscopic characterization of the iron and cobalt derivatives [Ar'MMAr'] (M = Fe (1) or Co (2)) and clarify that, although they bear a structural resemblance to [Ar'CrCrAr'], their metal-metal bonding has little in common with that of the chromium analogue.Complexes 1 [7b] with the potassium-graphite intercalate KC 8 in tetrahydrofuran. The metal dimers crystallized as very dark red (1) or very dark green (2) solids. They were initially characterized by X-ray crystallography, [8] which revealed that they had a dimeric structure (Figure 1 and Figure 2, respectively; selected structural data are provided in the Figure legends).The overall trans-bent C ipso MMC ipso core configuration is similar to that in [Ar'CrCrAr'].[1] This resemblance is misleading, however, and masks profound differences both in the metal-metal and the metal-ligand interactions. In a manner which appears to be similar to that in [Ar'CrCrAr'], the iron and cobalt atoms are h 1 bonded to an ipso-carbon center from the central aryl ring of the terphenyl ligand and are also h 6 bonded to a flanking ring of a terphenyl ligand attached to the other metal center within the dimer. However, in complexes 1 and 2, these flanking-ring interactions are much stronger than those in [Ar'CrCrAr'], as indicated by the

Ligand Field Strength Mediates Electron Delocalization in Octahedral [(HL)2Fe6(L′)m]n+ Clusters

“…The metal-to-metal distance ( d Fe–Fe = 2.597(2)–2.765(1) Å) in all instances is within the range where Fe–Fe bonding is invoked. 12b–d,21 …”

Limitations of mass spectrometric methods for the characterization of polydisperse materials

“…Our previous work with Mössbauer spectroscopy52, 53 has indicated that Fe may be included in a ferritin‐like metal storage polymer. Recent work on interactions between metal cations and aromatic systems indicates other possibilities for covalent or ionic complexes: the addition of metal ions to spider silk54 where the metal ions apparently were coordinated to the silk protein and perhaps form covalent bonds; the synthesis of a neutral aromatic gallium species with an octahedral structure;55 formation of an aromatic metallabenzene containing two gallium atoms;56, 57 complexes involving Fe and Co;58 formation of 'clam‐like' structures in aqueous solution between Rb and Cs cations and two anionic aromatic systems 59. The interaction of metal ions with aromatic systems as in the large molecules of coal and petroleum asphaltenes has not been explored in any detail but may offer exciting chemistry.…”

Synthesis of a Cyclic Co2Sn2 Cluster Using a Co– Synthon

“…The cobalt atoms are η 6 -coordinated by the flanking 2,6-diisopropylphenyl rings with a very short cobalt–centroid distance (1.560(1) Å), which suggests a particularly strong cobalt-arene interaction, cf. >0.1 Å shorter than the η 6 -arene interactions in [Ar′CoCoAr′] (1.764(2) Å), 15 [(nacnac)Co(η 6 -C 7 H 8 )] (1.747(2), nacnac = HC{C(Me)N(2,6-Me 2 C 6 H 3 )} 2 ) 16 and [(η 6 -C 7 H 8 )CoAr*] (1.659(1) Å, Ar* = C 6 H-2,6(C 6 H 2 -2,4,6- i Pr 3 ) 2 -3,5- i Pr 2 ). 17 The average C–C bond length within the metal-coordinated aryl rings is nearly 0.025 Å longer than those in the noncoordinated rings.…”

“…The existence of d-π* backbonding is also underlined by the substantial upfield shift of the aryl resonances of the coordinated Dipp groups (4.76 and 4.56 ppm) in the 1 H NMR spectrum. 15 , 18…”