Low-Valence Anionic α-Diimine Iron Complexes: Synthesis, Characterization, and Catalytic Hydroboration Studies

The synthesis of rare anionic heteroleptic and homoleptic alpha-diimine iron complexes is described. Heteroleptic BIAN (bis(aryl)iminoacenaphthene) complexes 1-[K([18]c-6)-(thf)(0.5)] and 2-[K([18]c-6)(thf)(2)] were synthesized by reduction of the [(BIAN)FeBr2] precursor complex using stoichiometric amounts of potassium graphite in the presence of the corresponding olefin. The electronic structure of these paramagnetic species was investigated by numerous spectroscopic analyses (NMR, EPR, Fe-57 Mossbauer, UV-vis), magnetic measurements (Evans NMR method, SQUID), and theoretical techniques (DFT, CASSCF). Whereas anion 1 is a low-spin complex, anion 2 consists of an intermediate-spin Fe(III) center. Both complexes are efficient precatalysts for the hydroboration of carbonyl compounds under mild reaction conditions. The reaction of bis(anthracene) ferrate(1-) gave the homoleptic BIAN complex 3-[K([18]c-6)(thf)], which is less catalytically active. The electronic structure was elucidated with the same techniques as described for complexes 1-[K([18]c-6)(thf)(0.5)] and 2-[K([18]c-6)(thf)(2)] and revealed an Fe(II) species in a quartet ground state

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Direct synthesis of an anionic 13-vertex closo-cobaltacarborane cluster

Reaction of 1,2-bis(diphenylphosphino)-ortho-carborane (L) with [K(thf){((Mes)BIAN)Co(eta(4)-cod)}] (1, (Mes)BIAN = bis(mesityliminoace-naphthene)diimine, cod = 1,5-cyclooctadiene) affords an anionic 13-vertex closo-cobaltacarborane cluster (2) in one step. The mechanism of this transformation has been studied by experimental and quantum chemical techniques, which suggest that a series of outer-sphere electron transfer and isomerisation processes occurs. This work shows that low-valent metalate anions are promising reagents for the synthesis of anionic metallacarborane clusters

A comparative study of biradicaloids as ligands in iron tetracarbonyl complexes

Iron tetracarbonyl complexes of the biradicaloids [P(μ-N-Ter)]₂ (Ter: 2,6-dimesitylphenyl) and [P(μ-C-IPr)]₂ (IPr: 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) have been isolated. These two biradicaloids act here as σdonating, monodentate ligands. Experimental and theoretical data suggest that they can best be described in their zwitterionic resonance structures in these complexes. Single-crystal XRD and IR spectroscopy reveal that the donor strength of both is comparable to N-heterocyclic carbenes (NHCs). [P(μ-C-IPr)]₂ is a slightly stronger donor than [P(μ-N-Ter)]₂. Furthermore, an improved, scalable, and facile synthesis of both biradicaloids is presented.ISSN:1551-7004ISSN:1424-6369ISSN:1424-6376ISSN:1551-701

Aufbau‐ und Abbaureaktionen von weißem Phosphor induziert durch N‐heterocyclische Carbenkomplexe von Nickel(0)

The reaction of zerovalent nickel compounds with white phosphorus (P-4) is a barely explored route to binary nickel phosphide clusters. Here, we show that coordinatively and electronically unsaturated N-heterocyclic carbene (NHC) nickel(0) complexes afford unusual cluster compounds with P-1, P-3, P-5 and P-8 units. Using [Ni(IMes)(2)] [IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene], electron-deficient Ni3P4 and Ni3P6 clusters have been isolated, which can be described as superhypercloso and hypercloso clusters according to the Wade-Mingos rules. Use of the bulkier NHC complexes [Ni(IPr)(2)] or [(IPr)Ni(eta(6)-toluene)] [IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene] affords a closo-Ni3P8 cluster. Inverse-sandwich complexes [(NHC)(2)Ni2P5] (NHC=IMes, IPr) with an aromatic cyclo-P-5(-) ligand were identified as additional products