Iron bis pyridine

Checkers substituted white FeCl for bis(pyridine)iron(H) chloride. 

Checkers substituted white FeClj for bis(pyridine)iron(II) chloride. 

Bis(imino)pyridine iron complex 5 as a highly efficient catalyst for a hydrogenation reaction was synthesized by Chirik and coworkers in 2004 [27]. Complex 5 looks like a Fe(0) complex, but detailed investigations into the electronic structure of 5 by metrical data, Mossbauer parameters, infrared and NMR spectroscopy, and DFT calculations established the Fe(ll) complex described as 5 in Fig. 2 to be the higher populated species [28]. 

Further investigations revealed that this hydrogenation is accelerated in pentane solution. These results are shown in brackets in Table 3 [31]. Under optimized reaction conditions high catalyst TOF up to 5,300 were achieved when 10 was used. In the absence of both hydrogen and nitrogen, 10 was converted into the q -arene complexes such as the bis(imino)pyridine iron q -phenyl complex, 10-Phenyl, and the corresponding q -2,6-diisopropylphenyl complex, 10-Aryl, in the 85 15 ratio in... 

Scheme 7 Intramolecular arene coordination in bis(imino)pyridine iron complex 10...

Bis(imino)pyridine iron complex 5 acts as a catalyst not only for hydrogenation (see 2.1) but also for hydrosilylation of multiple bonds [27]. The results are summarized in Table 10. The reaction rate for hydrosilylations is slower than that for the corresponding hydrogenation however, the trend of reaction rates is similar in each reaction. In case of tra s-2-hexene, the terminal addition product hexyl (phenyl)silane was obtained predominantly. This result clearly shows that an isomerization reaction takes place and the subsequent hydrosilylation reaction dehvers the corresponding product. Reaction of 1-hexene with H2SiPh2 also produced the hydrosilylated product in this system (eq. 1 in Scheme 18). However, the reaction rate for H2SiPh2 was slower than that for H3SiPh. In addition, reaction of diphenylacetylene as an atkyne with phenylsilane afforded the monoaddition product due to steric repulsion (eq. 2 in Scheme 18). 

Scheme 23 Flydrosilylation catalyzed by a bis(imimo)pyridine iron complex...

The comparison of a bis(imino)pyridine iron complex and a pyridine bis (oxazoline) iron complex in hydrosilylation reactions is shown in Scheme 24 [73]. Both iron complexes showed efficient activity at 23°C and low to modest enantioselectivites. However, the steric hindered acetophenone derivatives such as 2, 4, 6 -trimethylacetophenone and 4 -ferf-butyl-2, 6 -dimethylacetophenone reacted sluggishly. The yields and enantioselectivities increased slightly when a combination of iron catalyst and B(CeF5)3 as an additive was used. 

Scheme 24 The comparison of a bis(imino)pyridine iron complex and a pyridine bis(oxazoline) iron complex for hydrosilylation of ketones...

In 2009, Chirik reported a hydrogen-mediated reductive enyne cyclization catalyzed by the bis(imino)pyridine iron complex 5 (Scheme 37) [119]. In the... 

As an alternative method for the C-C bond formation, oligomerization and polymerization reactions of olefins catalyzed by a bis(imino)pyridine iron complex are also well known (Scheme 40) [121-124]. 

A head-to-head dimerization of a-olefin catalyzed by a bis(imino)pyridine iron complex has been reported by Small and Marcucci [126]. This reaction delivers linear internal olefins (up to 80% linearity) from a-oleftns. The linearity of products, however, depends on the catalyst structure and the reaction conditions. 

Fink and Babik reported that propylene polymerization was achieved by a bis (imino)pyridine iron complex with Ph3C[B(C6p5)]4] and ttialkylaluminium as additives [127]. Both 3-methyl-"butyl and "butyl endgroups were observed by NMR spectrum when ttiisobutylaluminium as an activator was used, whereas the only "propyl endgroup was formed in case of triethylaluminium activation. In addition, this polymerization proceeds two times faster with than without a hydrogen atmosphere, but the value decreases and the M IM value rises up. 

Synthesis of 2,6-Bis(imino)pyridine Iron(II) and Cobalt(II) Halides. 110... 

Bis(imino)pyridine Iron Halide/MAO and Cobalt Halide/MAO Catalysts. 120... 

Scheme 2 Synthesis of bis(arylimino)pyridine iron(II) and cobalt(II) halides...

The capacity of bis(arylimino)pyridine iron(II) (5) and cobalt(II) halides (6) to act as precatalysts for the polymerisation and oligomerisation of ethylene was first demonstrated when toluene solutions of 5 or 6 were treated with excess MAO... 

The active species generated when bis(arylimino)pyridine iron (5) and cobalt (6) halides are activated with MAO was, by analogy with metallocene catalysts, initially considered to be a highly reactive mono-methylated cobalt(II) or iron(II) cation of the form LM-Me+ bearing a weakly coordinating counter-anion such as [X-MAO]-(X = halide, Me). To examine this theory a number of spectroscopic investigations have been directed towards identifying the active species (vide infra). 

Scheme 7 Proposed chain propagation and transfer process in bis(imino)pyridine iron and cobalt catalysts...

Table 3 Other co-catalysts that have been employed to activate bis(arylimino)pyridine iron dihalides (5)...

The introduction of metal alkyls to an MAO-activated bis(imino)pyridine iron catalyst has also been the subject of a number of studies. Both AlMe3 and AlEt3 have been added to 5a/MAO-based polymerisation catalysts leading to polyethylene displaying a bimodal distribution similar to that observed using 5a/M AO,... 

In contrast, the related diamines 45 and 46 [cf. (3,5-/-Pr2C6H2-4-NH2)2CH2 above] give, on treatment with 2,6-diacetylpyridine, oligomeric polyimines that can be readily complexed with iron dichloride to afford 47 and 48, respectively (Fig. 14). Notably, on activation with MAO, 47 and 48 are active catalysts for ethylene polymerisation and indeed perform more efficiently at elevated temperatures than those of the original bis(imino)pyridine iron precatalyst 5 [166],... 

The use of two or more different catalysts in the same reactor, sometimes known as in situ reactor blending or tandem catalysis, has been widely employed industrially as means of controlling the properties of a polyolefin (e.g. molecular weight and the molecular weight distribution). Recent years have seen a variety of reports emerge on the use of bis(imino)pyridine iron/cobalt systems as one component of the process [169, 170, 171, 172, 173, 174, 175, 176, 177,178, 179],... 

Heterogeneous tandem catalysis involving at least one of the components being supported has also been reported [178, 179]. For example, calcosilicate has recently been used as an effective carrier for simultaneous immobilisation of a dual-functional system based on a bis(imino)pyridine iron compound and a zirconocene to form a heterogeneous catalyst precursor. On activation with triethylaluminium, ethylene was converted to LLDPE the layered structure of the calcosilicate was used to account for the improved thermal stability and higher molecular weights of the LLDPE formed [179],... 

Table 4 Selected non-bis(imino)pyridine iron and cobalt precatalyst/activator combinations for ethylene oligomerisation/polymeiisation... 

Replacement of both pyridine rings of bipyridine by imidazole has a much greater effect than replacement by thiazole and the [Fe N6]2+ derivative of 2,2 -biimidazole 34 (Dq(Ni2+)=1080 cm-1) is purely high spin [41]. The spin-crossover behaviour of tris(2,2/-bi-imidazoline)iron(II) salts seems somewhat unexpected in light of this and the relatively low a-donor power as indicated by the small Dq(Ni2+) value (1030 cm-1) for 36. 

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