CpFe+ salt

Recently the first examples of complexes between the four-membered amidinato-Group 13 metal(l) heterocycles and transition metal fragments were reported. Complexes of the type CpFe(CO)2[M(X) But(NR)2 ] (M = Al, Ga, In X = Cl, Br R = Pri, Gy) were formed in salt-elimination reactions between Na[CpFe(CO)2] and [But(NR)2]MX2. A series of complexes between the four-membered amidinato-Group 13 metal(l) heterocycles and Group 10 metal(O) fragments have been prepared according to Scheme 35. ... 

A carbon-iron bond is also formed by the reaction of the cyclopropenium salt 185 with dicarbonyl(i/5-cyclopentadienyl)(trimethylsilyl)iron [92], (Scheme 69) In the reaction with benzocyclobutenylidene- 5-cyclopentadienyliron(II) hexafluorophosphate 186, CpFe(CO)2R (R=cyelo-C3H5, CH2-cyclo-C3H5) is converted to the allene and butadiene complexes, 187 and 188, respectively [93]. (Scheme 70)... 

We found no evidence for isomerization of the a,6-dialkoxy-alkylidene complexes CpFe(C0)L[C(0Et)CH20R] (9,, 15) to alkylated carboalkoxymethyl salts CpFe(C0)L(CH2C(OR)(OEt) ) under ambient conditions. Indeed the solution chemistry of a,6-dialkoxyethylidene complexes parallels that of a-alkoxyethylidene compounds CpFe(C0)L[C(0R)CH3]+, in that 9,14,15 quantitatively revert to 5-7 upon treatment with excess io3i3e in CH2C12. We did, however, prepare samples of the ethylated carboalkoxymethyl... 

One equivalent of LiHBEt3 or LiHB(sec-butyl)3 in THF at -80° consumed the phosphine substituted a,8-dialkoxyethylidene salts 9a, b and delivered 73% yields of the formylmethyl complex CpFe(CO)PPh3(CH2CHO) (21) as the only isolable organometallic compound. The product 21 can be accounted for by an electrophile... 

The results of studies employing CpFe(C0)2 complexes within Scheme 4 offer more mechanistic insight into the reaction chemistry of a,3-dialkoxyethyl complexes. One equivalent of LiHBEt3 thus reduced the a-ethoxy-6-methoxyethylidene salt 14a in THF (-80°), but the product corresponded to addition of one hydride— an a-ethoxy-6-methoxyethyl CpFe(C0)2 complex (16a). After pre-... 

We synthesized cationic y2-acetyl compounds 28,25 by combining iron acetyl complexes CpFe(C0)L(C0CH3) (g7) [L=C0,PPh3] with a coordinatively unsaturated (16-electron) metal carbonyl salt CpM(CO)n+[M=Fe,n=2 M=Mo,n=3], as indicated in Scheme 5. Thus... 

The intent of these experiments was to demonstrate intermediacy of 33 via O-protonation and elimination of the ethylidene salt CpFe(C0)2(CHMe)+, which would rearrange to CpFe (CO) 2 (n2-CH2 CH2)+. We feel however that additional studies are required in order to adequately study the interaction of organometallic hydride reagents and bimetallic y2 acyl complexes. 

Isolation of 3-cyclopropenyl metal compounds by this method has been achieved so far for iron and rhenium metals only. Thus, the reaction of Na[CpFe(CO)J (NaFp) with cyclopropenylium salts at -70 °C, in THF, gave 3-Fp-cyclopropene complexes (equation 194)2 267. The X-ray crystal structure of the most stable iron complex 3-Fp-C3Ph3 exhibits a regular cyclopropene C—C single and double bond distances (151 and 129 pm), and a characteristic distance of 208 pm for the Fe—C (T-bond267. The H NMR (CS2) spectrum of the 3-Fp-C3Ph,H complex displays a singlet at S = 2.63 ppm, of the cyclopropen yl proton at the 3-position. ... 

The 77-cyclopentadienyliron dicarbonyl dimer and the mixed metal carbonyl 7r-cyclopentadienyliron-manganese heptacarbonyl are protonated by strong acids to form isolatable salts, namely [CpFe(CO)2]2H +PF6 and [CpFeMn(CO)7H]+PF6 . The ruthenium dimer [CpRu(CO)2]2 behaves similarly, although no salt was isolated (63). 

Metal-based nucleophiles may react with activated haloarenechromium complexes leading to substitution of the halides. The reaction of Collmarfs reagent Na2[Fe(CO)4] with chloro-arenetricarbonylchromium complexes in THF/N-methylpyrrolidinone produces the yellow anionic dinuclear complexes 91a in 45 % yield (Scheme 40) as a result of an ipso SNAr [64]. Spectroscopic data suggest that complex 91a adopts the rj6 structure as opposed to the alternative //5 -cyclohexadieny 1 carbene structure 92. Similarly, it has been reported by the same group that the potassium salt of [CpFe(CO)2] participates in ipso nucleophilic attack on chloroarenechromium substrates, producing dinuclear complexes 91b in 92 % yield (Scheme 40) [65]. 

The yellow CpFe1 (//6-arene) salts (most commonly BF4 or PF6 ) are usually stable up to at least 200 °C, are stable in concentrated sulfuric acid, and are very resistant towards oxidation (until recently, it was believed that they could not be oxidized [23] vide infra). They are not easy to reduce either [23] (vide infra). The chloride salts [CpFe+( f -arene) Cl- are water-soluble they are formed upon hydrolysis following ligand-exchange reactions between ferrocene and the arene in the presence of aluminum chloride [21]. Such aqueous solutions may sometimes be directly used for nucleophilic reactions [22] (vide infra). The BF4- salts are also sometimes quite soluble in water, but the PF6- salts are much less so. Electrophilic reactions that are readily undergone by the free arenes, such as Friedel-Crafts reactions, are no longer possible on the CpFe+( /6-arene) complexes [19, 23]. On the other hand, a range of nucleophilic reactions that are impossible or very difficult to carry out with free arenes become possible under ambient or mild conditions with the CpFe+()/6-arene) complexes (Scheme 2) [16-20]. 

Scheme 4. Fast C-H activation reaction in the 19-electron complex [CpFe (r/6-C6Me6)] with 02 and quantitative salt effect of Na+PF6 in THF.

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