Iron complexes imines

The direct reductive amination (DRA) is a useful method for the synthesis of amino derivatives from carbonyl compounds, amines, and H2. Precious-metal (Ru [130-132], Rh [133-137], Ir [138-142], Pd [143]) catalyzed reactions are well known to date. The first Fe-catalyzed DRA reaction was reported by Bhanage and coworkers in 2008 (Scheme 42) [144]. Although the reaction conditions are not mild (high temperature, moderate H2 pressure), the hydrogenation of imines and/or enam-ines, which are generated by reaction of organic carbonyl compounds with amines, produces various substituted aryl and/or alkyl amines. A dihydrogen or dihydride iron complex was proposed as a reactive intermediate within the catalytic cycle. 

Tridentate ligands for cobalt and iron catalysts. The catalysts discussed earlier in the section on ethene oligomerisation can also be used for making polymers, provided that they are suitably substituted. In Figure 10.30 we have depicted such a catalyst, substituted with isopropyl groups at the aryl substituents on the imine group, as in Brookhart s catalysts [49], The initiation is now carried out by the addition of MAO to a salt of the cobalt or iron complexes. The catalysts obtained are extremely active, but they cannot be used for polar substrates. 

For the quinone imine cyclization of iron complexes to carbazoles the arylamine is chemoselectively oxidized to a quinone imine before the cyclodehydrogenation [99]. The basic strategy of this approach is demonstrated for the total synthesis of the 3-oxygenated tricyclic carbazole alkaloids 4-deoxycarbazomycin B, hyellazole, carazostatin, and 0-methylcarazostatin (Scheme 17). 

Compound 79 reacts with 0(CH2)4 and NCMe in the presence of CFsSOsMe, like the iron complex 11 and the molybdenum and tungsten complexes 45 and 46, to give zwitterionic compounds [2-NO-2-PEt3-7-L-c/ow-2,l-CoCBioHio] [L = 0(CH2)4 (83), NCMe (84)]. Interestingly, the acetonitrile reaction gave in addition to 84 small amounts of the imine complex [7- N(Me) = C(H)Me -2-NO-2-PEt3-c/oio-2,l-CoCBioHio] (85), a product related to the iron and nickel compounds 34 and 78, respectively. The latter pair were the only products when 11 and 75, respectively, were... 

Over the past 15 years, we developed three procedures for the iron-mediated carbazole synthesis, which differ in the mode of oxidative cyclization arylamine cyclization, quinone imine cyclization, and oxidative cyclization by air (8,10,557,558). The one-pot transformation of the arylamine-substituted tricarbonyl(ri -cyclohexadiene) iron complexes 571 to the 9H-carbazoles 573 proceeds via a sequence of cyclization, aromatization, and demetalation. This iron-mediated arylamine cyclization has been widely applied to the total synthesis of a broad range of 1-oxygenated, 3-oxygenated, and 3,4-dioxygenated carbazole alkaloids (Scheme 5.24). 

Electrophilic aromatic substitution of 708 with the iron-coordinated cation 602 afforded the iron-complex 714 quantitatively. The iron-mediated quinone imine cyclization of complex 714, by sequential application of two, differently activated, manganese dioxide reagents, provided the iron-coordinated 4b,8a-dihydrocarbazole-3-one 716. Demetalation of the iron complex 716 with concomitant... 

Electrophilic substitution at the arylamine 709 using the complex salt 602, provided the iron complex 725 quantitatively. Sequential, highly chemoselective oxidation of the iron complex 725 with two, differently activated, manganese dioxide reagents provided the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-one (727) via the non-cyclized quinone imine 726. Demetalation of the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-one (727), followed by selective O-methylation, provided hyellazole (245) (599,600) (Scheme 5.70). 

Electrophilic aromatic substitution of the arylamine 780a using the iron-complex salt 602 afforded the iron-complex 785. Oxidative cyclization of complex 785 in toluene at room temperature with very active manganese dioxide afforded carbazomycin A (260) in 25% yield, along with the tricarbonyliron-complexed 4b,8a-dihydro-3H-carbazol-3-one (786) (17% yield). The quinone imine 786 was also converted to carbazomycin A (260) by a sequence of demetalation and O-methylation (Scheme 5.86). The synthesis via the iron-mediated arylamine cyclization provides carbazomycin A (260) in two steps and 21% overall yield based on 602 (607-609) (Scheme 5.86). 

The total synthesis of carbazomycin D (263) was completed using the quinone imine cyclization route as described for the total synthesis of carbazomycin A (261) (see Scheme 5.86). Electrophilic substitution of the arylamine 780a by reaction with the complex salt 779 provided the iron complex 800. Using different grades of manganese dioxide, the oxidative cyclization of complex 800 was achieved in a two-step sequence to afford the tricarbonyliron complexes 801 (38%) and 802 (4%). By a subsequent proton-catalyzed isomerization, the 8-methoxy isomer 802 could be quantitatively transformed to the 6-methoxy isomer 801 due to the regio-directing effect of the 2-methoxy substituent of the intermediate cyclohexadienyl cation. Demetalation of complex 801 with trimethylamine N-oxide, followed by O-methylation of the intermediate 3-hydroxycarbazole derivative, provided carbazomycin D (263) (five steps and 23% overall yield based on 779) (611) (Scheme 5.91). 

Terminally brominated PE as PE macroinitiator can be produced by other methods. It has been reported that vinyl terminated PE produced by a bis(phenoxy-imine)metal complex and MAO catalyst system (Mn = 1800, Mw/Mn = 1.70) was converted to terminally 2-bromoisobutyrate PE through the addition reaction of 2-bromoisobutyric acid to the vinyl chain end. Polyethylene-Wodc-poly( -bulyl acrylate) (PE-fo-PnBA) from terminally brominated PE by ATRP procedure has also been produced [68]. It was reported that degenerative transfer coordination polymerization with an iron complex can be used to prepare terminally brominated PE as a macroinitiator [69]. A Zn-terminated PE prepared using an iron complex and diethylzinc,... 

The chemistry of iron vinylidene complexes is dominated by the electrophilicity of the carbon atom adjacent to the iron organometallic unit. While addition of water leads to an acyl complex (i.e., the reverse of the dehydration shown in equation 10), addition of an alcohol leads to a vinyl ether complex. Similarly, other iron vinyl complexes can be prepared by the addition of thiolate, hydride, or an organocuprate (Scheme 33). " The nucleophilic addition of imines gave enaminoiron intermediates that could be further elaborated into cyclic aminocarbenes. This methodology has been used to provide access to /3-lactams and ultimately penicillin analogs, and good diastereoselectivities were observed (6 1-15 1) (Scheme 34). 04 Iso, vinylidene complexes are intermediates in cyclizations of alkynyl irons with substituted ketenes, acid chlorides, and related electrophiles an example is shown (equation 11). These cyclizations led to the formation of a series of isolable and characterizable cyclic vinyl iron complexes. 

The same iron complex also catalyzes the reaction of imines and diazo compounds to give d -aziridines (Sch. 31) [142]. 

The reaction of (—)-151 with imines such as 2-methyl-l-pyrrolidine illustrated in Scheme 33 affords complex 222. An X-ray structure of 222 shows that the coordinated imine is oriented perpendicular to the 1,2-azaborolyl ring. This orientation which contrasts with that assumed for 219 must be due to the greater steric bulk of the imine. Reaction of 222 with allylmagnesium bromide gives 223 with excellent stereoselectivity. Hydrolysis affords the free amine 224. The reactions illustrated in Schemes 32 and 33 demonstrate that 1,2-azaborolyl iron complexes can efficiently transfer chirality to B-bound organic substrates. The development of catalytic versions of these stoichiometric reactions would be a highly desirable extension of this work. 

Three-membered heterocycles. Decomposition of diazo compounds by the iron complex in the presence of imines leads to aziridines. An analogous reaction of diazoalkanes with aldehydes gives some epoxides and the rearrangement products (ketones) owing to the Lewis acidic nature of the catalyst. Ethyl diazoacetate behaves differently, as 1,2-aryl shift occurs during the reaction. ... 

Diimine Palladium and Imine Pyridine Iron Complexes with Halogenophenyl... 

The last example, Figure 15, is a bromo chloro macrocyclic iron complex. Bromine is CIP priority 1, chlorine is 2, the imine nitrogens 3 and 4, the pyridine nitrogen 5, and the amine nitrogens 6 and 7. The complex is pentagonal bipyramidal-seven coordinate, PB-7, the atoms on the axis are priority numbers 12- and the priority numbers for the atom in the plane are given in lowest sequential order, 35476. This clockwise order is symbolized as C. 

A third pathway leads via the quinone imine intermediates 38 to 3-hydro-xycarbazoles 41 (mode C in Scheme 12) [97, 98, 108, 109]. Oxidation of the complexes 36 with manganese dioxide afforded the quinone imines 38, which on treatment with very active manganese dioxide undergo oxidative cyclization to the tricarbonyl(ri" -4b,8a-dihydrocarbazol-3-one)iron complexes 39. Demetalation of 39 with trimethylamine iV-oxide and subsequent aromatization lead to the 3-hydro-xycarbazoles 41. The isomerization providing the aromatic carbazole system is a... 

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