Cycloheptadienyl complexes

Complexes containing the 5-electron cycloheptadienyl ligand are prepared by methods similar to those used for cyclohexadienyl complexes, viz. 

Some reactions of cyclohepta- and cyclohexa-dienyl iron tricarbonyl complexes resemble the reactions of the jr-cyclopentadienyl iron analogues. However, ring addition reactions which give diene derivatives occur more readily [263c], e.g. 

---

Triphenylmethyl fluoroborate will also abstract a hydride ion from tri-carbonyleyclohexa-l,3-dieneiron to give the cyclohexadienyl complex [Fe(CO)3(C H7)] BF4 (5,9, 76), analogous to the cycloheptadienyl complex [Fe(CO)3(C7H9)l BF4 described above. 

The analogous cycloheptadienyl complex (5 equation 1) was similarly prepared by Dauben and Ber-telli,4 but the acyclic pentadienyl systems were a little more difficult to obtain. The triphenylmethyl cation does not remove hydride from tricarbonyl(frans-pentadiene)iron (6 equation 2). The corresponding c/s-pentadiene complex (7 equation 3) cannot be prepared directly from the diene and an iron carbonyl,... 

Cyclodiphospho(III)azane-bridged bis(amido) complexes, with Zr(IV) and Hf(IV), 4, 793 Cyclodisilazanes, preparation, 3, 444 Cycloetherification, with alkynes, 10, 673 Cycloheptadienyl complexes, with chromium carbonyls,... 

The alkoxy ir -allylic derivatives underwent alkoxyl exchange very readily when treated with the appropriate alcohol containing a little mineral acid (10" M)(e.g. methoxy-ethoxy and vice versa). These reactions are believed to go via an intermediate carbonium ion stabilised by the delocalised electron system of the tt-allylic group. Methoxy tt-allylic complexes derived from 2,5-dimethylhexa-2,4-diene, cyclohepta-1,3-diene and cycloocta-1,3-diene on heating lost methanol irreversibly to give a8-unsaturated tr-allylic complexes e.g. cyclohepta-1,3-diene first gave a tt-methoxycycloheptenyl and then a TT -cycloheptadienyl complex. 

The cobalt complex 117 reacted with but-2-yne in the presence of HBF, to afford the cycloheptadienyl complex 118 (Scheme 7.45) [63]. The alkyne moiety is inserted into the C-C bond of the cyclopentadiene ring. 

Iron carbonyl complexes containing 77 -alkyl-77 -allyl coordinated hydrocarbon ligands are obtained in several ways. Nucleophilic addition to cationic iron complexes containing 77 -pentadienyl ligands yields (pentenediyl)iron complexes. Oxidatively-induced reductive elimination of these complexes can be utilized as a means to generate 1,2,3-trisubstituted cyclopropanes.The reaction of cationic cycloheptadienyl complexes (Scheme 22) with appropriate nucleophiles also yields the alkyl-allyliron carbonyl complexes. Fe(CO)s also reacts with a- or /3-pincnc in refluxing dioxane (Scheme 22) to produce an alkyl-allyliron complex. Recently, 1,2- and 1,4-disubstituted [(pentadienyl)Fe(CO)3] cations were shown to react with carbon nucleophiles, such as sodium dimethylmalonate, to yield 77 77 -allyl complexes as products. 

A complementary set of reactions has been found to take place when starting with [(77 -CsMes)Co(iil)( 7 -allyl)OTf derivatives 234 as 77 -cycloheptadienyl complexes 235 were obtained via a [3 - - 2 -f 2]-cycloaddition (Equation (40)). ... 

The catalyst-free 5-1-1-cycloaddition reaction between C, A(-cyclic A -acyl azome-thine imines (134) with isocyanides (135) formed imin-l,3,4-oxadiazin-6-one derivatives (136) in high to excellent yields (99%) under mild conditions (Scheme 42). The cobalt-mediated / -pentadienyl (137)/alkyne (138) 5-1-2-cycloaddition reaction yielded /, -cycloheptadienyl complexes (139) under kinetic control. The initial cycloadducts are isomerized to the final >/ -cycloheptadienyl complexes (140) (Scheme 43). The Ru(I)-catalysed intra- and intermolecular 5 4- 2-cycloaddition reactions of 3-acyloxy-l,4-enynes and alkynes produced adducts with highly functionalized seven-membered rings. The reaction sequence includes a 1,2-acyloxy migration. The catalyst-free 5 4- 2-cycloaddition reaction of 2-vinylaziridines with sulfonyl isocyanates in CH2CI2 yielded seven-membered cyclic ureas in high yields (up to 90%). ... 

Cycloheptadienyliron complexes also frequently show examples of internal nucleophile addition [214,215,224—227]. Steric effects are conventionally cited to explain the tendency of cycloheptadienyl complexes to give internal addition products (whereas cydohexadienyl complexes react at the termini). There is kinetic evidence to support this, as cycloheptadienyl complexes have been shown to be less reactive than cydohexadienyl complexes [223]. The CH2 of the cydohexadienyl complexes, and the CHjCHj of the cydohepadienyl complexes fold out away from the metal in these structures, and in the cydoheptadienyl case, each CH2 blocks a terminus of the Jt system. NudeophUic attack is displaced to the internal positions, forming ij, r] products in competition with the 1 products from the normal addition pathway [214,215,224—230]. With larger metals [Ru(CO)3 and Os(CO)3], this effect becomes more pronounced, and the products can predominate [230,231]. The nature of the nudeophile can also influence the preferred pathway (see Section 14.4). With soft nudeophiles, cydoheptadienyl complexes show the terminal addition pathway, while hard nudeophiles add internally [232]. Further... 

Starting from 2,4,6-octatriene and pivaldehyde, the conjugated homoallylic alcohol 8 is obtained as the sole product. Cycloheptatriene-derived complexes react with aldehydes and C02 to afford mixtures of the isomeric 1,3- and 1,4-cycloheptadienyl carbinols or acids, respectively. Interestingly, analogous reactions with methyl chloroformate or dimethyl carbamoyl chloride produce the conjugated dienyl ester 9 or amide 10 as unique products [19,20]. 

Functionalization of cycloheptadienyl-Mo(CO)2CpPF (l).1 This complex (1), prepared as shown, reacts with carbon nucleophiles to give products of stereoselective allylic substitution. 

U(11-C7H7)2] K[X3U Oi-11 ri - C7H7)UX5] The C7H7 rings are planar 358 Inverse cycloheptadienyl 413 sandwich complexes 5 ... 

Cycloheptadienyl-iron complexes. Cyclohcptadienyl-Fe(CO), reacts with nucleophiles to give mixtures of products, usually in low yield. However, complexes 1, in which one CO ligand is replaced by triphenylphosphinc or triphenyl phosphite, react with most nucleophiles at the dienyl terminus and in high yield. Hydride abstraction followed by reaction with a second nucleophile results in a regio- and stereocontrol led substitution at the opposite terminus and again anti to the metal. Decomplexation affords ri.v-5,7-disub-stituted cycloheptadienes. 

Some progress has been made in performing asymmetric variations of this chemistry. Addition of the anion of sulfoximine ester (272) to achiral (cycloheptadienyl)iron cation complex (271, L = P(OPh)3), followed by desullu-rization, affords enantiomerically enriched (273, 50% ee) (Scheme 77). In a similar manner, addition of the enolate derived from a chiral iV-acyloxazolidinone (274) to achiral (cyclohexadienyl)iron cation complex (275) and subsequent auxiliary removal affords (276, 70% ee). 

Initial attempts to prepare 7r-cycloheptatrienyl-iron tricarbonyl complexes were not successful—the products often being 7r-cycloheptadienyl-iron tricarbonyl derivatives (60). In 1964 Mahler, Jones, and Pettit (162) reported the synthesis of a complex [(C7H7)Fe(CO)3] BF4 by the following route ... 

Beck and co-workers (84,8.5) utilized the anionic carbonylmetallates [M(C0)5] (M = Mn, Re) and [WCp(CO),] in nucleophilic addition reactions with cationic hexadienyl, cyclohexadienyl, cycloheptadienyl, and cyclooctadienyl complexes of iron and ruthenium to give heterobimetal lie complexes with rj iV-hydrocarbon bridges. The reaction of [Fe(i7 -... 

The preparation by this route of the complexes (r 6-benzene)(t 4-l,3-cyclohex-adiene)Ru(O), (t74-l, 5-cyclooctadiene)(r 6-l,3,5-cyclooctatriene)Ru(0), bis(rjs-2,4-cycloheptadienyl)Ru(Il), and bis(i7S-cyclopentadienyl)Ru(II) is described here. These complexes are of interest in catalysis and in preparative chemis-... 

---