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The diiron complex [Fe2{μ-к1(O):η1(C):η3(C)–C(N(Me)(Xyl))C(H) C(Me)C(O)OMe}(μ-CO)(Cp)2] (2) has been obtained from the diiron bridging vinyliminium [Fe2{μ-η1:η3–C(Me) C(H)C N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] (1; Xyl = 2,5-C6H3Me2) upon treatment with NaH in the presence of CH2 C CMe2, followed by chromatography on alumina with MeOH as eluent. The reaction consists in the incorporation of a methylcarboxylate unit, assembled from CO and MeO−, into the bridging vinyliminium ligand. The resulting complex 2 exhibits a C4 fragment bridging the two iron centres through the carbonyl oxygen atom and the allylidene moiety. The X-ray molecular structure of 2 has been determined.

The zwitterionic vinyliminium complex [Fe2{μ-η1:η3-C(R′) C(S)C N(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (2a) (R′ = p-Me-C6H4 (Tol), Xyl = 2,6-Me2C6H3) undergoes electrophilic addition at the S atom by HSO3CF3, MeSO3CF3, SiMe3Cl, BrCH2Ph, ICH2CH CH2 affording the complexes [Fe2{μ-η1:η3-C(Tol) C(SX)C N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][Y] (X = H, Y = SO3CF3, 4a; X = Me, Y = SO3CF3, 4b; X = SiMe3, Y = Cl, 4c; X = CH2Ph, Y = Br, 4d; X = CH2CH CH2, Y = I, 4e). Compound 2a and the corresponding vinyliminium complexes 2b and 2c (R′ = CH2OH, 2b; R′ = Me, 2c) react also with etherated BF3 leading to the formation of the corresponding S-adducts [Fe2{μ-η1:η3-C(R′) C(SBF3)C N(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R′ = Tol, 5a; R′ = CH2OH, 5b; R′ = Me, 5c). In analogous reactions, the zwitterionic vinyliminium complexes undergo S-metalation upon treatment with in situ generated [Fp]+[SO3CF3]− [Fp = Fe(CO)2(Cp)], leading to the formation of [Fe2{μ-η1:η3-C(R′) C(S–Fp)C N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3](R′ = CH2OH, 6a; R′ = Me, 6b; R′ = Bun, 6c). Similarly, zwitterionic vinyliminium containing Se in the place of S also undergo Se-electrophilic addition. Thus, the complexes [Fe2{μ-η1:η3-C(R′) C(SeX)C N(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = X = Me, R′ = Tol, 7a; R = Xyl, R′ = Me, X = Fp+, 7b) are obtained upon treatment of the neutral zwitterionic precursors with MeSO3CF3 and [Fp][SO3CF3], respectively. Alkylation at the S or Se atom of the bridging ligand is also accomplished by CH2Cl2, used as solvent, although the reaction is slower compared to more efficient alkylating reagents. The complexes formed by this route are [Fe2{μ-η1:η3-C(R′) C(E-CH2Cl)C N(Me)(R)}(μ-CO)(CO)(Cp)2][X] [E = S, R = Xyl, R′ = Tol, X = Cl, 8a; E = S, R = Xyl, R′ = Me, X = Cl, 8b; E = Se, R = R′ = Me, X = BPh4, 8c]. Finally, treatment of the zwitterionic vinyliminium complexes with I2 results in the oxidative coupling with formation of S–S (disulfide) or Se–Se (diselenide) bond. The reactions, performed in the presence of NaBPh4 afford the tetranuclear complexes [Fe2{μ-η1:η3-C(R′) C(E)C N(Me)(R)}(μ-CO)(CO)(Cp)2]2[BPh4]2 [R = Xyl, R′ = CH2OH, E = S, 9a; R = Xyl, R′ = Me, E = S, 9b; R = Xyl, R′ = Bun, E = S, 9c; R = Xyl, R′ = Me, E = Se, 9d; R = Me, R′ = Bun, E = Se, 9e]. The molecular structures of 4a, 8c and 9e have been determined by X-ray diffraction studies.

The bridging diiron thiocarbyne complex [Fe2{μ-CS(Me)}(μ-CO)(CO)2(Cp)2]ISO 3 CF 3 ] (1) reacts with activated olefins (methyl acrylate, acrylonitrile, styrene, diethyl maleate), in the presence of Me 3 NO and NaH, to give the corresponding μ-allylidene complexes [Fe 2 {μ-η 1 :η 3 -C α (SMe)C β (R')C γ (H)(R")} (μ-CO)(CO)(Cp) 2 ] (R" = CO 2 Me, R'= H, 3a; R" = CN, R'= H, 3b; R" = C 6 H 5 , R'= H, 3c; R" = R' = CO 2 Et, 3d). The coupling reaction of olefin with thiocarbyne is regio- and stereospecific, leading to the formation of only one isomer. C-C bond formation occurs between the less substituted alkene carbon and the thiocarbyne. Moreover, olefinic hydrogens of the bridging ligands are mutually trans. The reactions of 3a-b with MeSO 3 CF 3 result, selectively, in the formation of the cationic μ-sulphonium allylidene complexes [Fe 2 [μ-η 1 :η 3 -C α (SMe 2 )C β (H)C γ (H)(R)}(μ-CO)(CO)(Cp)2][SΟ 3 CF 3 ] (R = CΟ 2 Me, 4a; R = CN, 4b). Compound 4a undergoes displacement of the SMe 2 group by nucleophiles such as NaBH 4 , NBu 4 CN and NaOMe, affording the complexes [Fe 2 ( μ-η 1 :η 3 -C α (R)C β (H)C γ H)(CΟ 2 -Me)}(μ-(CO)(Cp) 2 ] (R = H, 5a; R = CN, 5b; R = OMe, 5c), respectively. The molecular structures of 3a and 5a have been determined by X-ray diffraction studies.

Primary alkynes R′C CH [R′ = Me3Si, Tol, CH2OH, CO2Me, (CH2)4C CH, Me] insert into the metal–carbon bond of diruthenium μ-aminocarbynes [Ru2{μ-CN(Me)(R)}(μ-CO)(CO)(MeCN)(Cp)2][SO3CF3] [R = 2,6-Me2C6H3 (Xyl), 1a; CH2Ph (Bz), 1b; Me, 1c] to give the vinyliminium complexes [Ru2{μ-η1:η3-C(R′) CHC N(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] [R = Xyl, R′ = Me3Si, 2a; R = Bz, R′ = Me3Si, 2b; R = Me, R′ = Me3Si, 2c; R = Xyl, R′ = Tol, 3a; R = Bz, R′ = Tol, 3b; R = Bz, R′ = CH2OH, 4; R = Bz, R′ = CO2Me, 5a; R = Me, R′ = CO2Me, 5b; R = Xyl, R′ = (CH2)4C CH, 6; R = Xyl, R′ = Me, 7a; R = Bz, R′ = Me, 7b; R = Me, R′ = Me, 7c]. The related compound [Ru2{μ-η1:η3-C[C(Me) CH2] CHC N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3], (9) is better prepared by reacting [Ru2{μ-CN(Me)(Xyl)}(μ-CO)(CO)(Cl)(Cp)2] (8) with AgSO3CF3 in the presence of HC CC(Me) CH2 in CH2Cl2 at low temperature.In a similar way, also secondary alkynes can be inserted to give the new complexes [Ru2{μ-η1:η3-C(R′) C(R′)C N(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = Bz, R′ = CO2Me, 11; R = Xyl, R′ = Et, 12a; R = Bz, R′ = Et, 12b; R = Xyl, R′ = Me, 13). The reactions of 2–7, 9, 11–13 with hydrides (i.e., NaBH4, NaH) have been also studied, affording μ-vinylalkylidene complexes [Ru2{μ-η1:η3-C(R′)C(R″) C(H)N(Me)(R)}(μ-CO)(CO)(Cp)2] (R = Bz, R′ = Me3Si, R″ = H, 14a; R = Me, R′ = Me3Si, R″ = H, 14b; R = Bz, R′ = Tol, R″ = H, 15; R = Bz, R′ = R″ = Et, 16), bis-alkylidene complexes [Ru2{μ-η1:η2-C(R′)C(H)(R″)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (R′ = Me3Si, R″ = H, 17; R′ = R″ = Et, 18), acetylide compounds [Ru2{μ-CN(Me)(R)}(μ-CO)(CO)(C CR′)(Cp)2] (R = Xyl, R′ = Tol, 19; R = Bz, R′ = Me3Si, 20; R = Xyl, R′ = Me, 21) or the tetranuclear species [Ru2{μ-η1:η2-C(Me)CCN(Me)(Bz)}(μ-CO)(CO)(Cp)2]2 (23) depending on the properties of the hydride and the substituents on the complex. Chromatography of 21 on alumina results in its conversion into [Ru2{μ-η3:η1-C[N(Me)(Xyl)]C(H)C CH2}(μ-CO)(CO)(Cp)2] (22). The crystal structures of 2a[CF3SO3] · 0.5CH2Cl2, 12a[CF3SO3] and 22 have been determined by X-ray diffraction studies.

The diiron frame Fe 2 Cp 2 CO 2 allows the coordination of a variety of carbene ligands, including heteroatom substituted (Fischer type) and alkylidenes, in both bridging and terminal coordination modes. Synthetic strategies have been devised for obtaining aminocarbenes and thiocarbenes, by nucleophilic addition on the corresponding bridging amino- and thio-carbyne cationic complexes [Fe 2 (μ-CX)(μ-CO)(CO) 2 (Cp) 2 ][SO 3 CF 3 ] (X = SMe, NMe 2 , N(Me)Xyl), respectively. A more general approach to the synthesis of diiron complexes bridged by carbenes, exploits the electrophilic character of the sulphonium complex [Fe 2 {μ-C(CN)(SMe 2 )}(μ-CO)(CO) 2 (Cp) 2 ][SO 3 CF 3 ] and the facile displacement of the SMe 2 moiety by nucleophiles. These methods afford a large variety of heteroatom (N, P, O, S) substituted carbene complexes and also μ-alkylidenes. Terminally bonded alkynyl methoxy carbene complexes have been obtained by the classical Fischer method, consisting in nucleophilic addition at a terminal CO, to generate an acyl intermediate, followed by oxygen atom methylation. The coordination to diiron cationic complexes makes the alkynylmethoxy carbene ligands very reactive towards the addition of nucleophiles, like amines and carbanions. These additions are regio- and stereoselective, occurring exclusively at the alkynyl moiety. Finally, new multidentate and functionalized bridging ligands are described. They are anchored to the diiron frame through an aminocarbene, or an alkylidene binding end, or both. These ligands result from intramolecular couplings and rearrangements which involve the μ-aminocarbyne, the terminally bonded nitrile ligands and acetylides.

The vinyliminium complexes [Fe2{μ-η1:η3-C(R′) C(R′)C N(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = Me, R′ = Et, 1a; R = Me, R′ = Ph, 1b; R = R′ = Me, 1c; R = Xyl, R′ = Me, 1d; R = Xyl, R′ = Et, 1e; R = Xyl, R′ = Ph, 1f; Xyl = 2,6-Me2C6H3), react with MeLi affording the corresponding μ-vinylalkylidene complexes [Fe2{μ-η1:η3-C(R′)C(R′) CHN(Me)(R)}(μ-CO)(CO)(Cp){C5H4(Me)}] (2a–f). The formation of 2a–f is believed to proceed via nucleophilic attack at the Cp ligand, followed by hydrogen migration from the resulting cyclopentadiene to the iminium carbon. Similarly, the complex [Fe2{μ-η1:η3-C(Ph) C(Ph)C N(Me)(Xyl)}(μ-CO)(CO)(Cp)2][SO3CF3] reacts with PhLi to give [Fe2{μ-η1:η3-C(Ph)C(Ph) CHN(Me)(Xyl)}(μ-CO)(CO)(Cp){C5H4(Ph)}] (4). Treatment of 2a with CF3SO3CH3 results in methylation of the nitrogen, yielding the complex [Fe2{μ-η1:η3-C(Et)C(Et)CH(NMe3)}(μ-CO)(CO)(Cp){C5H4(Me)}][CF3SO3] (5). Analogously, the μ-vinylalkylidene complexes [Fe2{μ-η1:η3-C(R′)C(R″) CHN(Me)(R)}(μ-CO)(CO)(Cp)2], (R = Me, R′ = Tol, R″ = H, 3a; R = Me, R′ = SiMe3, R″ = H, 3b; R = Me, R′ = R″ = Et, 3c; R = Me, R′ = R″ = Ph, 3d; R = Bz, R′ = Tol, R″ = H, 3e; R = Bz, R′ = SiMe3, R″ = H, 3f; R = Bz, R′ = COOMe, R″ = H, 3g; R = Bz, R′ = R″ = COOMe, 3h; R = Bz, R′ = R″ = Me, 3i; Bz = CH2Ph), react with CF3SO3CH3 to give the corresponding ammonium-functionalized μ-allylidene complexes [Fe2{μ-η1:η3-C(R′)C(R″)CH(NMe2R)}(μ-CO)(CO)(Cp)2][CF3SO3] (6a–i). The molecular structures of 5 and 6c have been elucidated by X-ray diffraction studies. Finally, protonation of [Fe2{μ-η1:η3-C(Et)C(Et) CH(NMe2)}(μ-CO)(CO)(Cp)2] (3c), with HBF4, affords the complex [Fe2{μ-η1:η3-C(Et)C(Et)CH(NHMe2)}(μ-CO)(CO)(Cp)2]][BF4] (7).

The diiron complexes [Fe(Cp)(CO){μ-η 2 :η 2 -C[N(Me)(R)]N C(C 6 H 3 R′)C CH(Tol)}Fe(Cp)(CO)] (R = Xyl, R′ = H, 3a ; R = Xyl, R′ = Br, 3b ; R = Xyl, R′ = OMe, 3c ; R = Xyl, R′ = CO 2 Me, 3d ; R = Xyl, R′ = CF 3 , 3e ; R = Me, R′ = H, 3f ; R = Me, R′ = CF 3 , 3g ) are obtained in good yields from the reaction of [Fe 2 {μ-CN(Me)(R)}(μ-CO)(CO)( p -NCC 6 H 4 R′)(Cp) 2 ] + (R = Xyl, R′ = H, 2a ; R = Xyl, R′ = Br, 2b ; R = Xyl, R′ = OMe, 2c ; R = Xyl, R′ = CO 2 Me, 2 d; R = Xyl, R′ = CF 3 , 2e ; R = Me, R′ = H, 2f; R = Me, R′ = CF 3 , 2g ) with TolC CLi. The formation of 3 involves addition of the acetylide at the coordinated nitrile and C–N coupling with the bridging aminocarbyne together with orthometallation of the p -substituted aromatic ring and breaking of the Fe–Fe bond. Complexes 3a – e which contain the N(Me)(Xyl) group exist in solution as mixtures of the E - trans and Z - trans isomers, whereas the compounds 3f,g , which posses an exocyclic NMe 2 group, exist only in the Z-cis form. The crystal structures of Z - trans - 3b , E - trans - 3c , Z - trans - 3e and Z - cis - 3g have been determined by X-ray diffraction experiments.

A terminally coordinated CO ligand in the complexes [Fe2{μ-CN(Me)R}(μ-CO)(CO)2(Cp)2][SO3CF3] (R = Me, 1a; R = Xyl, 1b; Xyl = 2,6-Me2C6H3), is readily displaced by primary and secondary amines (L), in the presence of Me3NO, affording the complexes [Fe2{μ-CN(Me)R}(μ-CO)(CO)(L)(Cp)2][SO3CF3] (R = Me, L = NH2Et, 4a; R = Xyl, L = NH2Et, 4b; R = Me, L = NH2Pri, 5a; R = Xyl, L = NH2Pri, 5b; R = Xyl, L = NH2C6H11, 6; R = Xyl, L = NH2Ph, 7; R = Xyl, L = NH3, 8; R = Me, L = NHMe2, 9a; R = Xyl, L = NHMe2, 9b; R = Xyl, = NH(CH2)5, 10). In the absence of Me3NO, NH2Et gives addition at the CO ligand of 1b, yielding [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(O)NHEt}(Cp)2] (11). Carbonyl replacement is also observed in the reaction of 1a–b with pyridine and benzophenone imine, affording [Fe2{μ-CN(Me)R}(μ-CO)(CO)(L)(Cp)2][SO3CF3] (R = Me, L = Py, 12a; R = Xyl, L = Py, 12b; R = Me, L = HN CPh2, 13a; R = Xyl, L = HN CPh2, 13b). The imino complex 13b reacts with p-tolylacetylide leading to the formation of the μ-vinylidene-diaminocarbene compound [Fe2{μ-η1:η2- C C(Tol)C(Ph)2N(H)CN(Me)(Xyl){(μ-CO)(CO)(Cp2)] (15) which has been studied by X-ray diffraction.

The reaction of the μ-aminocarbyne complex [Fe 2 {μ-CN(Me)(Xyl)}(μ-CO)(CO)(NCCMe 3 )(Cp) 2 ][SO 3 CF 3 ] ( 2 ) (Xyl=2,6-Me 2 C 6 H 3 ) with tolylacetylide, followed by treatment with HSO 3 CF 3 affords the complex [Fe 2 {μ-η 1 :η 3 C(Tol)CC(CMe 3 )N(H)CN(Me)(Xyl)}(μ-CO)(CO)(Cp 2 )][SO 3 CF 3 ] ( 3 ) (Tol=4-MeC 6 H 4 ). The X-ray molecular structure of 3 reveals the peculiar character of the bridging ligand, which exhibits both η 1 :η 2 allene and aminocarbene nature. The formation of 3 proceeds through several intermediate species, which have been detected by IR spectroscopy. Addition of HSO 3 CF 3 at an early stage of the reaction between 2 and LiCCTol leads to the formation of the imine complex [Fe 2 {μ-CN(Me)Xyl}(μ-CO)(CO){NHC(CCTol)CMe 3 }(Cp) 2 ][SO 3 CF 3 ] ( 6 ) indicating that the first step of the reaction consists in the acetylide addition at the coordinated NCCMe 3 . The molecular structure of 6 has been elucidated by an X-ray diffraction study.

Reaction of [Fe2(μ-CS)(μ-CSMe)Cp2(CO)2]+ (1) with sodium N,N-dimethyldithiocarbamate [Me2dtc]Na affords a mixture of the dithiocarbene [Fe Fe(μ-CS){μ-C(SMe)S C(S)NMe2}Cp(CO)] (2) and the thiocarbyne [Fe2(μ-CS)(μ-CSMe)(μ-S2CNMe2)Cp2] (3). Complex 2 is quantitatively converted into 3 by photochemical irradiation. The X-ray molecular structure of 3 demonstrates the presence of three bridging ligands and exhibits the shortest FeFe interaction found in similar systems [2.453(1) A]. Complex 3 can also be obtained by reacting [Me2dtc]− with the di-solvento thiocarbyne [Fe2(μ-CS)(μ-CSMe)(NCMe)2Cp2]+ (1a). By contrast no stable addition product has been isolated in analogous reactions involving the thiocarbyne [Fe2(μ-CO)(μ-CSMe)Cp2(CO)2]+ (1b). The [Me2dtc]− nucleophilic addition at the μ-C to form [Fe2(μ-CO){μ-C(CN)SC(S)NMe2}Cp2(CO)2] (4a) is obtained starting from [Fe2(μ-CO){μ-C(CN)(SMe2)}Cp2(CO)2]SO3CF3 (1d). Photochemical reaction of the cyanocarbene 4a causes intramolecular ring closure affording [Fe Fe(μ-CO){μ-C(CN)S C(S)NMe2}Cp2(CO)] (5a).

The complexes [Fe2{μ-CN(Me)R}(μ-CO)(NCMe)(CO)(Cp)2]SO3CF3 (R=Me, 2a; 2,6-Me2C6H3, 2b; CH2Ph, 2c), easily obtained from the corresponding [Fe2{μ-CN(Me)R}(μ-CO)(CO)2(Cp)2]SO3CF3 (1a–c) precursors, react with NBu4CN affording the cyano complexes [Fe2{μ-CN(Me)R}(μ-CO)(CN)(CO)(Cp)2] (3a–c) by displacement of the MeCN ligand. The analogous reaction with NBu4Cl leads to the formation of [Fe2{μ-CN(Me)R}(μ-CO)(Cl)(CO)(Cp)2] (4a–b). The μ-hydride complexes [Fe2{μ-CN(Me)R}(μ-H)(CO)2(Cp)2] (5a–b) have been prepared by reaction of 1a–b with NaBH4. The corresponding diruthenium compound [Ru2(μ-CNMe2)(μ-H)(CO)2(Cp)2] (6) has been similarly obtained from [Ru2(μ-CNMe2)(μ-CO)(NCMe)(CO)(Cp)2]SO3CF3. The X-ray molecular structure of 5a is that expected for cis isomers of this family of compounds. It shows a chiral conformation of the C5H5 ligands and the crystals are a conglomerate of enantiomeric individuals. NMR spectra of the various compounds, which are indicative of the presence of α–β or cis–trans isomeric mixtures, are reported and discussed.

The reaction of [M2{μ-CN(Me)R}(μ-CO)(CO)2(Cp)2]SO3CF3 (M=Fe, R=Me, 1a; M=Fe, R=CH2Ph 1b, M=Ru, R=CH2Ph, 1c) with a mixture of KH and acetonitrile affords [(Cp)(CO) MC{NMe(R)}N(H)C(Me)C (CN)] (2a–c). The X-ray structure of 2a (M=Fe, R=Me) shows the formation of a pyrrole-like metallaring FeC(2)NC(4)C (5). The double bond character of the C(4)C(5) interaction [1.309(7)] suggests the enammine nature of the N(H)C(Me)C(CN) fragment which originates from condensation of two acetonitrile molecules. A mechanism for the formation of 2a–c is proposed in light of the 13C-NMR and IR evidence. Complex 2a can be methylated at the N-end of the hexocyclic CN group, forming a cationic metallacyclo complex containing the CCN+Me nitrilium moiety.

The reaction of [Fe(CO) 2 (SR)(Cp)] (R=Et, Ph; Cp=η-C 5 H 5 ) with [Mn(CO) 2 (thf)(C 5 H 4 Me)] (thf=tetrahydrofuran), under photolytic conditions, leads to the formation of the novel heterodinuclear bridged thiolate complexes [FeMn(μ-CO)(μ-SR)(CO) 2 (Cp)(C 5 H 4 Me)] in low yields. [FeMn(μ-CO)(μ-SEt)(CO) 2 (Cp)(C 5 H 4 Me)] consists of a mixture of cis and trans isomers which have been separated and characterized by IR and NMR spectroscopy. The μ-phosphido complex [FeMn(μ-CO)(μ-PPh 2 )(CO) 2 (Cp)(C 5 H 4 Me)] has been prepared analogously from [Fe(CO) 2 (PPh 2 )(Cp)] and [Mn(CO) 2 (thf)(C 5 H 4 Me)]. Variable temperature NMR spectra of the latter heterodinuclear complex, in CDCl 3 , show the presence of an equilibrium mixture of the two interconverting cis and - trans isomers. The X-ray molecular structure of cis -[FeMn(μ-CO)(μ-SEt)(CO) 2 (Cp)(C 5 H 4 Me)] shows a bonded Fe–Mn interaction [2.617(2) A] reinforced by a μ-CO and a μ-SEt ligands. The molecule contains chiral centers at the iron, manganese and sulfur atoms and the diastereoisomer under study exhibits optimized non bonded contacts between the alkyl groups.

The reactions of [Ru2{μ-CN(Me)R}(μ-CO)(CO)2(Cp)2]SO3CF3 (R=Me 1a, CH2Ph 1b; Cp=η-C5H5) with Li2Cu(CN)R′2 (R′=Me, Bun, Ph) result in CC bond formation at the CO ligand affording the acyl complexes [Ru2{μ-CN(Me)R}(μ-CO)(COR′)(CO)(Cp)2] 2. The crystal structure of [Ru2{μ-CNMe2)(μ-CO)(COPh)(CO)(Cp)2] 2a reveals the double bond character of the μ-CN group and the interligand interaction involving the acyl oxygen and the μ-CNMe2 moiety. Type 2 complexes are also formed by reacting 1a–b with LiR′ (R′=Me, Bun, Ph), whereas reactions with ClMgCH2Ph yield both [Ru2{μ-CN(Me)R}(μ-CO)(COCH2Ph)(CO)(Cp)2] and [Ru2{μ-CN(Me)R}(μ-CO)(CO)2(η4-C5H5CH2Ph)(Cp)]. A comparison of the reactivity of 1a–b with that of the corresponding diiron complexes [Fe2{μ-CN(Me)R}(μ-CO)(CO)2(Cp)2]SO3CF3 is also presented.

The heteropolynuclear cyano-bridged complexes [(C5H5)Fe(CO)(CNMLn)(CNM′L′n)], {MLn = M′L′n = (C5H5)Fe(CO)2 or W(CO)5, MLn = (C5H5)Fe(CO)2, M′L′n = W(CO)5} and mixed isocyanide complexes [(C5H5)Fe(CO)(CNMLn)(CNR)], {MLn = W(CO)5, R = CPh3; MLn = (C5H5)Fe(CO)2, R = CH3} have been obtained by metallation or alkylation of the two terminal CN ligands of K[(C5H5)Fe(CO)(CN)2]. Comparison of the bonding properties of the CNMLn and CNR ligands, based upon their relevant spectroscopic data, are discussed. Furthermore, two new isomeric heterobinuclear cyano-bridged complexes of the form [(C5H5)(CO)2FeCNW(CO)5] and [(C5H5)(CO)2FeNCW(CO)5] have been synthesized and fully characterized by spectroscopic techniques. Finally the reactions with nucleophiles of the last two compounds have been also examined.

Electrochemistry of the μ-cyanoalkylidene complexes [Fe 2 (CO) 2 (cp) 2 ( μ -CO){ μ -C(CN)(X)}] n + ( n = 0, X = CN, H, Me, SMe, OMe, OEt, OPh, OCH 2 CH=CH 2 , PEt 2 , piperidinyl; n = 1, X = PMe 2 Ph) in nonaqueous solutions shows a one-electron reduction to the corresponding paramagnetic monoanions, which have been characterized by EPR spectroscopy. The presence of the positive charge in [Fe 2 (CO) 2 (cp) 2 (μ-CO){μ-C(CN)(PMe 2 Ph)}] + makes the one-electron addition significantly easier than to the neutral complexes. None of the 19-electron anions are fully stable and all undergo slow decomposition reactions, the rates of which are a function of the X substituent. Access to the radical anion intermediates [Fe 2 (CO) 2 (cp) 2 (μ-CO){μ-C(CN)(X)}] − does not trigger Electron Tra Chain catalytic substitution reactions of CO by phosphines, but allows these reactions to be successfully carried out by different methods, such as chemical reduction, CO photolysis and use of Me 3 NO. The CO-substituted derivatives [Fe 2 (cp) 2 (CO)(PMe 2 Ph)(μ-CO){μC(CN)(X) (X = CN, H, SMe) and [Fe 2 (cp) 2 ( μ -CO)( μ -dppm){ μ -C(CN)(X)}], (X = H, CN; dppm = Ph 2 PCH 2 PPh 2 ) were obtained. The one-electron reduction of the monophosphine-substituted complexes is fully irreversible and occurs at potentials 0.3–0.4 V more negative than those of the corresponding precursors. The different methods for promoting CO displacement in the μ-alkylidene complexes have been compared; the photolytic method affords the highest yields.

Repeated stepwise addition of CH 3 SO 3 CF 3 and Bu 4 NCN to the diisocyanide complex [Ru 2 (CO) 2 (Cp) 2 (CNBz) 2 ] (Cp = η -C 5 H 5 ; BzCH 2 Ph) has led to the formation of the new bis- μ -aminoalkylidene complex [Ru 2 (CO) 2 (Cp) 2 { μ -C(CN)N(Me Bz} 2 ], which has been characterized by X-ray diffraction. The crystal contains a racemic mixture of the isomer with the same chirality at the amine nitrogens. The molecule conforms to a C 2 idealized symmetry. Selected bond distances are RuRu 2.662(1), Ru( μ -C) 2.088 (av), μ -CN(amine) 1.479 (av) A. All the intermediate species: [Ru 2 (CO) 2 (Cp) 2 ( μ -CNBz){ μ -CN(Me)Bz}SO 3 CF 3 , [Ru 2 (CO) 2 (Cp) 2 { μ -CNBz)} μ -C(CN)N(Me)Bz}] and [Ru 2 (CO) 2 (Cp) 2 { μ -CN(Me)Bz}{ μ -C(CN)-N(Me)Bz}]SO 3 CF 3 have been isolated and characterized spectroscopically. Attempts to extend the synthetic method to the iron diisocyanide [Fe 2 (CO) 2 (Cp) 2 (CNBz) 2 ] led to [Fe 2 (CO)(CNBz)(Cp) 2 ( μ -CO){ μ -CN(Me)Bz} SO 3 CF 3 and [Fe 2 (CO)(CNBz)-(Cp) 2 ( μ -CO)} μ -C(CN)N(Me)Bz}] but not to the bis(aminoalkylidene) derivative.

The complex [Fe 2 (CO) 2 (Cp) 2 (μ-CS)(μ-CSMe)]SO 3 CF 3 ( 1 ) reacts with N n Bu 4 NCO to give [Fe 2 (CO) 2 (Cp) 2 (μ-CS){μ-CNC(O)SMe}] ( 2 ). This reaction has been carried out separately for both the cis and trans isomers of 1 . Complex cis - 2 undergoes S -methylation with MeOSO 2 CF 3 affording the novel thiocarbyne derivative [Fe 2 (CO) 2 (Cp) 2 (μ-CSMe) {μ-CNC(O)SMe}]SO 3 CF 3 ( 3 ), into which in turn an additional NCO − anion inserts to yield the bis(μ-acylisocyanide) complex [Fe 2 (CO) 2 (Cp) 2 {μ-CNC(O)SMe} 2 ] ( 4 ). All the reactions described are stereospecific and the derivatives 2–4 do not exhibit cis-trans isomerization.

The isocyanide complex [RU 2 CP 2 (CO) 3 (CNCH 2 Ph)], obtained by the reaction of [RU 2 CP 2 (CO) 4 ] with CNCH 2 Ph in the presence of Me 3 NO, has been N-alkylated, yielding the cationic μ-alkylidyne complex [Ru 2 CP 2 (CO) 3 {μ-CN(Me)CH 2 Ph}]SO 3 CF 3 . The compound yielded undergoes nueleophilic addition using NaBH 4 or NaBu 4 CN at the μ-C alkylidyne carbon to give the novel μ-aminoalkylidene complexes [Ru 2 Cp 2 (CO){μ-C(X)N(Me)CH 2 Ph}] (X = H, CN). The derivative with X = CN adopts the expected geometry and an idealized C s symmetry if the phenyl substituent is ignored. The relevant bond distances are as follows: RuRu, 2.711(1) A; Ru-μ-C(carbene), 2.090(4) A (ave.); C(carbene)-N, 1.477(5) A; N-C(alkyl), 1.474(5) A (ave.).

The reactions of [Fe 2 {μ-C(CN)SMe 2 }(μ-CO)(CO) 2)(Cp)[in2 ]SO 3 CF 3 (Cp = η-C 5 H 5 ) with alcohols and alkoxides have been investigated. Nucleophilic attack of the oxygen atom on the μ-C carbon with displacement of the Me 2 S molecule was observed in all cases. The resulting μ-cyanoalkoxycarbene derivatives [Fe 2 {μ-C(CN)OR}(μ-CO)(CO) 2 (Cp) 2 ] (R = Me, 2a ; Et, 2b ; i Pr, 2c ; CH 2 Ph, 2d ; CH 2 CHCH 2 , 2e ; CH 2 CH 2 NMe 2 , 2f ; CH 2 CH 2 OH, 2g ; C 6 H 5 , 3a ; C 6 H 4 - o -NO 2 , 3b ) have been characterized spectroscopically. The complex [Fe 2 {μ-C(CN)OCH 2 CHCH 2 }(μ-CO)(CO) 2 (Cp) 2 ] ( 2e ) undergoes a photolytically-promoted intramolecular CO substitution by the olefinic termination to give [Fe Fe{μ-C(CN)OCH 2 CH CH 2 }(μ-CO)(CO)(Cp) 2 ] ( 5 ), which was be subjected to an X-ray diffraction study. Some structural features were as expected, in particular the location of Cp in a cis disposition with respect to the CN group. The molecule is asymmetric as a consequence of the coordination of the allyl in the place of a terminal CO group; the configurations of the four chiral centres are discussed.

A new and improved method for the synthesis of M(CO)3(PMTA) (M = W, Mo)from M(CO)6 and PMTA (MeN(CH2Ch2NMe2)2) is described. The tridentate nitrogen ligand in W(CO)3(PMTA) is replaced, under relatively mild conditions, by tertiary phosphines (PME3, PEt3, PMe2Ph, PMePh2, PhP(CH2CH2PPh2)2, CH3C(CH2PPh2)3, and Ph2P(CH2)nPPh2 where n = 1, 2) and arenes (C6H6, MeC6H5, p-Me2C6H4,C6Me6,C6H5C1), which provides a general synthetic method for the preparation of W(CO)3(PR3)3 and (CO3(η6-arene) complexes. The reactions W(CO)3(L)3 [L = PMe3, PEt3, PMe2Ph, PMePh2, PhP(CH2Ch2PPh2)2, and CH3C(Ch2PPh2)3]with CF3SO3H in CH2Cl2 solution yield the hydrido derivaties W (H)(CO)3(L)+3 which were characterized by their 1H and 31 P NMR spectra at different temperatures. These studies show the W(H)(CO)3(L)+3 complexes to be fluxional as a result of both hydride and phosphine ligand migration.

The reactions of the metallacyclic complex [Cp(CO)FeC(S)SC(Fp)S] (1) (Cp = η-C5H5) with Group IB and IIB metal compounds have been investigated. Electrophilic addition at the thione sulphur atom has been observed in all cases. The reactions of 1 with the coinage metal complexes [MX(PPh3)]n (M = Cu, X = I, n = 4; M = Ag, X = Cl, n = 4; M = Au, X = Cl, n = 1) in the presence of TlPF6 give the adducts [Cp(CO)FeC{SM(PPh3)}SC(Fp)S]PF6 (2), which have been characterizded spectroscopically. The mercury salt [HgMe]PF6 reacts similarly with 1 to afford [Cp(CO)FeC(SHgMe)SC(Fp)S]PF6 (3), whereas mercury dihalides give products that have been shown by an X-ray diffraction study in the case in which X = Br to be halogen-bridged dimers of the type [Cp(CO)FeC(SHgX2)SC(Fp)S]2. The bromine-bridged dimer displays Ci symmetry. The coordination around the Hg atoms involves four normal and one weak bonds, and the geometry can be described as a distorted trigonal bipyramid. Zinc chloride reacts with 1 to give an air-sensitive unstable derivative that is tentatively formulated as [Cp(CO)FeC(SZnCl2)SC(Fp)S].

Reaction of FpC(S)SMLn (Fp = Fe(η-C5H5)(CO)2; MLn = Fp (1a), Re(CO)5 (1b)) with MeC(O)Cl affords [FpCS]Cl and LnMSC(O)Me (3);1a reacts with (CF3CO)2O to yield [Fp(CO)]CF3CO2 and FpSC(O)CF3 (5). In both cases the reactions have been shown to occur via the unstable S-acylated intermediates [FpC[SC(O)R]SMLn]+ (R = CF3, Me). Alkylation of 1a with RBr (R = Me, Et, CH2Ph, CH2CHCH2) or CF3SO2OR (R = Me, Et) followed by treatment of the stable S-alkylated derivatives [FpC(SR)SFp]+ with I− provides a useful alternative method for the synthesis of a variety of FpC(S)SR.

Displacement by [FpCS 2 ] − (Fp = Fe(η-C 5 H 5 )(CO) 2 ) of the halide in EClMe 3 (E = Si, Sn) and Ru(η-C 5 H 5 )(I)(CO) 2 affords the new ferriodithiocarboxylato complexes Me 3 ES(S)CFp ( 2a, 2b ) and (η-C 5 H 5 )(CO) 2 RuS(S)CFp ( 6 ). The latter and its congeners FpC(S)SML n (ML n = Re(CO) 5 , Fp) are alkylated at the thione-S to give the salt-like compounds [FpC(SR)SML n ]CF 3 SO 3 ) (R = Me, Et) ( 7 ) in high yield. FpC(S)SMe acts as a strong S donor ligand towards the neutral metal carbonyl fragments M(CO) 5 (M = Cr, Mo, W) and Mn(η-C 5 H 4 X)(CO) 2 (X = H, Me) but with Co 2 (CO) 8 , only the cluster MeSCCo 3 (CO) 9 ( 14 ) is obtained.