Synthesis of the Highly Reduced [Fe₆C(CO)₁₅]^4– Carbonyl Carbide Cluster and Its Reactions with H⁺ and [Au(PPh₃)]⁺

Abstract

The reduction of [Fe6C(CO)16]2– (1) with NaOH in DMSO or with Na/naphthalene in THF affords the highly reduced [Fe6C(CO)15]4– (2) monocarbide tetraanion. The molecular structure of 2 has been crystallographically determined as its [Et4N]4[Fe6C(CO)15]·CH3CN salt, revealing an octahedral structure as expected for a hexanuclear cluster possessing 86 valence electrons. The stepwise protonation of 2 with strong acids such as HBF4·Et2O results first in the monohydride trianion [HFe6C(CO)15]3– (3) and then the purported dihydride dianion [H2Fe6C(CO)15]2– (4), as indicated by 1H NMR spectroscopy. Both 3 and 4 are not stable enough to be isolated and rapidly decompose, yielding the parent dianion 1. The reaction of 2 with a slight excess of Au(PPh3)Cl affords the aurated dianion [Fe6C(CO)15(AuPPh3)2]2– (5), which has been isolated and structurally characterized as its [Et4N]2[Fe6C(CO)15(AuPPh3)2]·2CH3CN salt. DFT calculations allowed us to study, from a computational point of view, the electronic features of the new compounds and possible reaction intermediates.

A Comparative Experimental and Computational Study of Heterometallic Fe‐M (M = Cu, Ag, Au) Carbonyl Clusters Containing N‐Heterocyclic Carbene Ligands

“…In contrast, in the presence of the bulkier IPr ligand, M ··· M contacts are essentially non‐bonding. This gives further support to the conclusion that metallophilic interactions are rather soft and strongly depends on the steric properties of the ancillary ligands employed in such complexes …”

“…Heterometallic complexes and clusters containing coinage metals in the +1 oxidation state were very attractive since they presented heterometallic bonds and metallophilic interactions, that is, attractive interactions between the closed shell d 10 centres Aurophilicity was investigated at first, in relation also to relativistic phenomena, followed by argentophilicity and cuprophilicity , . Several homoleptic and heteroleptic carbonyl clusters containing 2–8 coinage metals (also mixed ones) supported by Fe, Co, Mo, V and Ru carbonyl moieties were reported , , . These allowed to study the effects of the coinage metal, heterometal and ancillary ligands on the bonding within such heterometallic clusters.…”

Synthesis and Characterization of Heterobimetallic Carbonyl Clusters with Direct Au‐Fe and Au···Au Interactions Supported by N‐Heterocyclic Carbene and Phosphine Ligands

“…1) Iron carbonyl clusters surface‐decorated by [AuL] + fragments. This represents the largest class of heterobimetallic Au‐Fe carbonyl clusters, that comprises species such as Fe(CO) 4 (AuPPh 3 ) 2 , Fe(CO) 4 (AuNHC) 2 (NHC = IMes, IPr, IBu; IMes = C 3 N 2 H 2 (C 6 H 2 Me 3 ) 2 ; IPr = C 3 N 2 H 2 (C 6 H 3 i Pr 2 ) 2 ; IBu = C 3 N 2 H 2 (CMe 3 ) 2 ), [Fe 2 (CO) 8 (AuPPh 3 )] – , [Fe 3 (CO) 11 (AuPPh 3 )] – , [Fe 3 E(CO) 9 (AuPPh 3 )] – (E = O, S, Te),, Fe 3 E(CO) 9 (AuPPh 3 ) 2 (E = O, S),, [HFe 4 (CO) 12 (AuPPh 3 ) 3‐ n ] n– (n = 0, 1), Fe 4 C(CO) 12 (AuPEt 3 ) 2 , Fe 5 C(CO) 14 (AuPEt 3 ) 2 , [Fe 6 C(CO) 16 (AuPPh 3 )] –[13] and [Fe 6 C(CO) 15 (AuPPh 3 ) 2 ] 2– . These may be viewed as the result of the addition of [AuL] + (L = phosphine, N ‐heterocyclic carbene) fragments to the surface of an iron carbonyl cluster anion, i.e., [Fe(CO) 4 ] 2– , [Fe 3 (CO) 11 ] 2– , [Fe 2 (CO) 8 ] 2– , [Fe 3 E(CO) 9 ] 2– (E= O, S, Te), [HFe 4 (CO) 12 ] 3– , [Fe 4 C(CO) 12 ] 2– , [Fe 5 C(CO) 14 ] 2– , [Fe 6 C(CO) 16 ] 2– and [Fe 6 C(CO) 15 ] 4– .…”

Reactions of [Fe6C(CO)14(S)]2–: Cluster Growth, Redox, Sulfiding

“…of CO are required by the stoichiometry of the reaction, one in effect compensating for the change in cluster charge and the other allowing the cluster to change from closo (86e -) to nido (88e -). [8] The oxidative carbonylation of [1] 2to give [2] 0 can also be effected by acids. Addition of excess degassed HBF 4 •Et 2 O under an atmosphere of CO leads cleanly to [2] 0 with an 81 % isolated yield.…”

“…[1] Reduction gives [Fe 6 C(CO) 15 ] 4-. [2] We have started to investigate the possibility that [Fe 6 C(CO) 16 ] 2could be developed as a precursor to replicas for FeMoco and related clusters that are responsible for biological nitrogen fixation. [3] Arguably the most distinctive cofactor found in nitrogenase, hypervalent carbide ligands are absent from all other synthetic iron-sulfide clusters.…”