A Chelating Triscarbene Ligand and Its Hexacarbene Iron Complex

Abstract

A free tricarbene is most likely a long‐lived intermediate in the formation of the first hexacarbene iron complex 1 (R = Me) from trimethylated tris(1‐imidazolyl)borate, n‐butyllithium, iron chloride, and tetraphenylborate. This tripodal C,C′,C″‐chelating ligand, for which the authors predict a brilliant future, is an isomer of Trofimenko's tris(1‐pyra‐zolyl)borate and represents a novel class of negatively charged six‐electron donors with the greatest possible similarity to the cyclopentadienyl anion.

New homoleptic carbene transfer ligands and related coinage metal complexes

“…Recently, Siebert et al [9,10] described the synthesis and characterization of the first anionic imidazol-2-ylidenes, the 3-borane-1-alkylimidazol-2-ylidenes anions and their metal complexes [11]. The first chelating tricarbene ligand with the topology of Trofimenko's tris(pyrazolyl)borates, tris(3-methylimidazolin-2-ylidene-1-yl)borate, has been introduced in 1995 by Fehlhammer and co-workers [12] together with its hexacarbene iron(III) and cobalt(III) complexes [13,14]. The synthesis of monoanionic chelating dicarbene bis(imidazolinylidene)borates and their use as ligands in various homoleptic and heteroleptic palladium(II), platinum(II), gold(I) [15] and nickel(II) [16] complexes has been recently described.…”

Synthetic Bioinorganic Chemistry: Scorpionates Turn 50

“…3). In addition, related ligands based on carbene [34,35], phosphine [36,37], thioether [38], thione [39][40][41], and selone [39] donor moieties have been studied during the past 20 years or so and will be discussed in more detail below (Fig. 4).…”

“…The coordination chemistry of the tris(carbene)borates, first reported by Fehlhammer in 1996 [34], was very limited [97] until Smith et al described in 2005 an improved synthetic route to analogous ligands bearing bulkier alkyl and aryl substituents [98]. These ligands, like the ubiquitous N-heterocyclic carbenes (NHCs) [99,100], are primarily strong σ-donors and only weak π-acceptors [101].…”

Syntheses, structures and electrochemical properties of homoleptic ruthenium(III) and osmium(III) complexes bearing two tris(carbene)borate ligands

“…Many polydentate N-heterocyclic carbenes have also been designed, and they allow preparation of organometallic compounds with a variety of geometries [6,7]. Among the polydentate N-heterocyclic carbenes, the tripodal tris(N-heterocyclic carbene)borate ligands (such as A and B, Chart 1), with a framework similar to that of the classic ligand tris(pyrazolyl)borate (Tp, C, Chart 1), have been of considerable interest due to their tripodal framework and chelating effect [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. In contrast to the versatile coordination and organometallic chemistry of tris(pyrazolyl)borate [27,28], metal complexes with tridentate N-heterocyclic carbene ligands A and B have been limited to several metal ions.…”

“…No product was isolated. It is noted that only six-coordinate homoleptic Fe(III) and Co(III) complexes were isolated from the reactions of Fe(II) or Co(II) precursor with tris(3-alkylimidazol-2-ylidene)hydroborate [HB(R-ImH) 3 ] [8,10].We also used XPS to probe the donating properties of carbene ligand in 1a and 1b. The bonding energies of Ru 3d 5/2 and Os 4f 7/2 of 1a, 1b and other related complexes are listed in Table 1.…”