Iron complexes pincer

Interestingly, the activity of the corresponding cobalt catalyst possessing a pincer-type ligand is higher than that of the iron complex. In addition, the cobalt complex also acts as a catalyst in asymmetric mtermolecular cyclopropanations. 

Figure 3,158 Synthesis of iron(ll) pincer carbene complexes.

Figure 3,159 Reactivity ofth e iron (II) pincer carbene dibromide complex.

Directed activation of a C(sp )-H bond by an iron complex was much less investigated than the reaction of C(sp )-H bonds. Li reported the phosphine-directed C (sp )-H to form an iron pincer complex (e.g., [80]). Ohki and Tatsumi reported that Cp Fe complexes bearing imidazolium salts undergo cyclometalation through C-H activation or can cleave the C-H bond of a heteroarene [81]. 

Recently, another study on the synthesis of the novel (PNP) pincer ligands based on phosphoramidites and their corresponding iron complexes (116a-b) was reported... 

Multidentate donor ligands specifically the pincer-type motif [EDE] (D = pyridyl, phenyl E = PR2, NR2, SR) with tridentate coordinating ligand framework have the advantage that they can simultaneously increase the electronic density and stabilize the coordination sphere of a transition metal. This can have suhstantial effects on the catalytic activity of the transition metal complexes. As an example, iron-hased pincer-type complexes present high catalytic activity for different reactions, such as hydrogenation (1—3), hydrosilylation (4,5), and hydroho-ration (6). 

A few drops of NH4CI aqueous solution are added to the residue obtained from the synthesis of pincer ligand in a Schlenk flask to quench any excess nbutyllithium and discarded as hazardous waste. The residues from the synthesis of iron complex after hydrolysis are discarded as heavy metal wastes. 

Within the same triad, iron has the smaller ionic radius compared with ruthenium [20], although electronically and structurally the two elements should form the same complexes. They essentially do, but when a second pincer carbene ligand is coordinated, it coordinates with one NHC moiety in abnormal coordination mode [476] as opposed to ruthenium, where both pincer carbene ligands are coordinated normally [468], In the absence of coordinating anions (BPh instead of bromide) octahedral cationic complexes are formed instead of square pyramidal neutral ones (see Figure 3.158). The additional n-donor ligand compensates the positive charge electronically. 

Electronic Structures of Reduced Manganese, Iron, and Cobalt Complexes Bearing Redox-Active Bis(imino)pyridine Pincer Ligands... 

An analogous series of bis(imino)pyridine iron dicarbonyl complexes was also synthesized (Figure 7.7) [38]. Unlike ( PDI)FeN2, ( PDI)Fe(CO)2 exhibits clean and reversible electrochemistry, allowing quantitative measurement of the potentials for one-electron oxidation and reduction. The combined metrical, spectroscopic, and computational data established that the cationic iron dicarbonyl complex [( PDI)Fe(CO)2][BAr 4j is best described as a low-spin iron(I) compound with a neutral bis(imino)pyridine chelate. Both EPR and DFT calculations support a principally iron-based SOMO with significant d 2 character. In the limit where the neutral iron dicarbonyl ( PDI)Fe(CO)2 is viewed in its low-spin Fe(II) canonical form, one-electron oxidation to [( PDI)Fe(CO)2] is pincer-based and results in a net reduction of the metal to Fe(I). 

As with the ketimine variant of the pincer, we initiated this chemistry by the reduction of the iron dibromide complex ( " PDAl)FeBr2 ( PDAl = 2,6(2,6- Pr2-CgH3N=CH)2C5H3N) [40],... 

Iron pincer complexes (147), easily prepared from 2,6-bis(diisopropyl-phosphinomethyl)pyridine and iron(III) bromide, are excellent catalysts for hydrogenation of acetophenones and have been characterized by X-ray crystallography and H- and 3 P-NMR."< 2... 

Transition-metal-catalyzed ring-opening functionalizations of donor - acceptor cyclopropanes have also been developed (Table 2.2). Addition of carbon nucleophiles to activated VCPs 69b and 69c in the presence of iron catalysts induced ring opening of the three-membered ring [81, 82]. A palladium pincer complex catalyzed ring-opening borylation of VCP 69c with 62(011)4 to produce... 

Scheme 15 Iron pincer complex (30) catalysed hydrogenation of (a) CO2 and (b) bicarbonate to formate salt...

A possible catalytic cycle for the hydrogenation of CO2 to formate catalysed by the iron pincer complex 30 is as follows (Fig. 15) (1) Formation of the hydrido-formato complex 31 by direct electrophilic attack of CO2 on the rran -dihydride 30,... 

Fig. 15 Proposed mechanism for the hydrogenation of CO2 to formate salt catalysed by the iron pincer complex 30...

Reactions of carbon monoxide involving iron pincer complexes were first reported by Chirik and coworkers [45] in 2006. They showed that stirring a pentane slurry of the... 

Heterobimetallic iron-platinum and iron-palladium complexes based on the pincer funetionalized ferrocene Fc-NCN (NCN = [4-C6H2(CH2NMe2-2,6)2] ) are available by the synthesis protocol shown in Scheme 3 [49, 50],... 

The particular features of phosphonium salts were exploited for a number of synthetic applications in 2014. Phosphonium chloride salts found applications as chlorine source and as modifiers for homogeneous catalyst systems. As an example, Muller, Rosenthal and co-workers reported the study of a chromium-based catalyst for the selective tri-merization of ethylene. A phosphonium precursor of the type i cyclo-(PR2CH2CH(OH) )2][Br]2) was used for the preparation of iron(n) complexes containing unsymmetrical P-N-P pincer ligands (Scheme 5). The group of Prof. Morris tested these compounds as catalysts for the asymmetric hydrogenation of ketones and imines. ... 

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