Electron-Rich N-Heterocyclic Silylene (NHSi)–Iron Complexes: Synthesis, Structures, and Catalytic Ability of an Isolable Hydridosilylene–Iron Complex

Unprecedented silicon(ii)→calcium complexes with N-heterocyclic silylenes

The first N-heterocyclic silylene (NHSi) complexes of any s-block element to date are reported for calcium: [(η⁵-C₅Me₅)₂Ca←:Si(O-C₆H₄-2-^tBu){(N^tBu)₂CPh}] and [(η⁵-C₅Me₅)₂Ca←:Si(N^tBuCH)₂]. The synthesis, structure, bonding analysis by DFT methods and the reactivity towards oxygen containing substrates is discussed.

Synthesis, structure and reactivity of a donor-stabilised silylene with a bulky bidentate benzamidinato ligand

A novel donor-stabilised silicon(ii) complex with an SiN₃ skeleton was synthesised and its reactivity profile was characterised (reactions with N₂O, S₈, Se, Te, Me₃SiN₃, PhSCH₂N₃ and [Fe(CO)₅]).

Can low-valent silicon compounds be better transition metal ligands than phosphines and NHCs?

We investigated the potential application of low-valent silicon compounds as transition metal ligands by computing the most important ligand properties and compared them to the generally used carbene and phosphine ligands.

Steric effects in the reactions of amidinate germylenes with ruthenium carbonyl: isolation of a coordinatively unsaturated diruthenium(0) derivative

Coordinatively unsaturated germylene-bridged diruthenium(0) complexes have been prepared by treating [Ru₃(CO)₁₂] with amidinate germylenes of the type Ge(R¹bzamR²)(HMDS), but only when the amidinate contains just one very bulky R group (^tBu) (not two).

N-heterocyclic silylene complexes in catalysis: new frontiers in an emerging field

A review of all existing N-heterocyclic silylene (NHSi) complexes involved in catalysis. Remarkably few examples exist, but already show promise as an emerging new generation of catalysts with the potential to tune catalyst activities and selectivities.

Bis-N-heterocyclic carbene (NHC) stabilized η6-arene iron(0) complexes: synthesis, structure, reactivity, and catalytic activity

Reaction of FeCl2 with the chelating bis-N-heterocyclic carbene (NHC) bis-(N-Dipp-imidazole-2-ylidene)methylene (abbreviated {((Dipp)C:)2CH2}) (Dipp = 2,6-di-isopropylphenyl) affords the complex [FeCl2{((Dipp)C:)2CH2}] (1) in high yield. Reduction of complex 1 with excess KC8 with a 10-fold molar excess of PMe3 affords the Fe(II) complex [FeH{((Dipp)C:)2CH2}(PMe3)(η(2)-PMe2CH2)] (2) as a mixture of three stereoisomers. Complex 2, the first example of any iron(II) complex bearing mutually an NHC and PMe3 ligand, is likely obtained from the in situ, reductively generated 16 VE Fe(0) complex, [Fe{((Dipp)C:)2CH2}(PMe3)2] (2'), following intramolecular C-H activation of one of the phosphorus-bound CH3 groups. Complex 2 is unstable in aromatic solvents and forms, via a novel synthetic transformation involving intramolecular reductive elimination and concomitant PMe3 elimination, the Fe (0) arene complex [Fe{((Dipp)C:)2CH2}(η(6)-C6D6)] (4-d6) in C6D6. Complex 4-d6 represents the first example of an NHC stabilized iron (0) arene complex. The transformation from 2 to 4-d6 can be accelerated at higher temperature and at 60 °C forms immediately. Alternatively, the reduction of 1 in the presence of toluene or benzene affords the complexes [Fe{((Dipp)C:)2CH2}(η(6)-C7H8)] (3) and [Fe{((Dipp)C:)2CH2}(η(6)-C6H6)] (4), selectively and in good yields. DFT calculations characterizing the bonding situation in 3 and 4 reveal similar energies of the HOMO and LUMO orbitals, with the LUMO orbital of both complexes located on the Dipp rings of the bis-NHC. The HOMO orbital reflects a π-back-bonding interaction between the Fe(0) center and the chelating NHC ligand, while the HOMO-1 is associated with the arene interaction with the Fe(0) site. The calculations do not suggest any noninnocence of the coordinated arene in either complex. Moreover, the (57)Fe Mössbauer spectrum of 4 at 80K exhibits parameters (δ = 0.43 mm·s(-1); ΔEQ = 1.37 mm·s(-1)) which are consistent with a five-coordinate Fe(0) system, rendering 3 and 4 the first examples of well-defined authentic Fe(0)-η(6)-arene complexes of the type [Fe(η(6)-arene)L2] (L = η(1 or 2) neutral ligand, mono or bidentate). Some reactivitiy studies of 3 are also reported: The reaction of 3 with excess CO selectively yields the five-coordinate piano-stool complex [Fe{((Dipp)C:)2CH2}(CO)3] (6) in near quantitative yields, while the reaction of complex 3 with C6D6 under heating affords by toluene elimination 4-d6. The catalytic ability of 4 was also investigated with respect to amide reduction to amines, for a variety of substrates using Ph2SiH2 as a hydride source. In all cases good to excellent yields to the corresponding amines were obtained. The use of 4 as a precatalyst represents the first example of a well-defined Fe(0) complex to effect this catalytic process.