Andrew F. Dyke

Organic chemistry of dinuclear metal centres. Part 3. µ-Carbene complexes of iron and ruthenium from alkynes viaµ-vinyl cations

Protonation of the complexes [M2(CO)(µ-CO){µ-C(O)C2R2}(η-C5H5)2][M = Fe or Ru; R2= H2, Ph2, H(Me), or H(Ph)] with HBF4·OEt2 results in rapid carbon–carbon bond cleavage and formation of the µ-vinyl cations [M2(CO)2(µ-CO){µ-C(R)C(H)R}(η-C5H5)2]+, containing a cis arrangement of R groups. Addition of HBF4·OEt2 to [Ru2(CO)(µ-CO){µ-C(O)C2Me2}(η-C5H5)2] produces the cation [Ru2(CO)(µ-CO)({µ-C(H)(O)C2Me2}(η-C5H5)2]+, which isomerises slowly to [Ru2(CO)2(µ-CO){µ-C(Me)C(H)Me}(η-C5H5)2]+. The µ-vinyl cations exist in solution as isomers with cis and trans orientations of terminal ligands, shown by variable-temperature n.m.r. to interconvert; cis isomers additionally display a fluxional oscillation of the µ-vinyl ligand. Treatment of the cations with Na BH4 yields µ-carbene complexes [M2(CO)2(µ-CO){µ-C(R)CH2R}(η-C5H5)2] in good yield, also as cis and trans isomers which interconvert in solution. These result from hydride addition to the β-carbon of the µ-vinyl, but addition to the α-carbon is apparent in the low-yield co-formation of the terminal ethylene complex [Ru2(CO)(µ-CO)2(C2H4)(η-C5H5)2] from the cation [Ru2(CO)2(µ-CO)(µ-CHCH2)(η-C5H5)2]+. Addition of sodium tetrahydroborate to [Ru2(CO)(µ-CO){µ-C(H)(O)C2Me2}(η-C5H5)2]+ provides the complex [Ru2(CO)(µ-CO){µ-C(Me)C(Me)CH2}(η-C5H5)2], completing a conversion of metallacyclic CO to CH2. Regeneration of the µ-vinyl cation [M2(CO)2(µ-CO)(µ-CHCH2)(η-C5H5)2]+ is achieved by treatment of [M2(CO)2(µ-CO){µ-C(H)Me}(η-C5H5)2] with [CPh3][BF4].

Organic chemistry of dinuclear metal centres. Part 1. Combination of alkynes with carbon monoxide at di-iron and diruthenium centres: crystal structure of [Ru2(CO)(µ-CO){µ-σ:η3-C(O)C2Ph2}(η-C5H5)2]

Under u.v. radiation a variety of alkynes (HC2H, MeC2Me, PhC2Ph, MeO2CC2CO2Me, MeC2H, PhC2H, and PhC2Me) reacts with [Fe2(CO)4(η-C5H5)2] to form complexes [Fe2(CO)(µ-CO){µ-σ : η3-C(O)C2R2}(η-C5H5)2] in 10–90% yields. Only PhC2Ph produces an analogous complex with [Ru2(CO)4(η-C5H5)2], but [Ru2(CO)(µ-CO){µ-σ:η3-C(O)C2Ph2}(η-C5H5)2] undergoes alkyne exchange on heating in toluene with HC2H, MeC2Me, MeC2H, PhC2H, or PhC2Me to afford the appropriate [Ru2(CO)(µ-CO){µ-σ:η3-C(O)C2R2}(η-C5H5)2] in near quantitative yield. The linking of alkyne and CO to produce a dimetallacyclopentenone ring was established through an X-ray diffraction study of the title compound. Crystals are orthorhombic, space group Pbca, with Z= 8 in a unit cell of dimensions a= 14.797,(3), b= 17.805(8), and c= 16.739(8)A. The structure was solved by heavy-atom methods and refined by least squares to R 0.033 for 3 726 diffractometer-measured reflection intensities. The molecule contains a dimetallacyclopentenone ring in which the ethylenic bond is η2-bound to ruthenium, so that the bridging C(O)C(Ph)C(Ph) ligand is σ-co-ordinated to one ruthenium and η3-co-ordinated to the other. Compounds [M2(CO)(µ-CO){µ-σ : η3-C(O)C(R′)C(R2)}(η-C5H5)2](M = Fe or Ru) in which R1≠ R2 exist as isomers as a result of linking of either end of the alkyne with CO. Steric factors appear to determine the relative stability of the isomers when one of R is H, but electronic factors are influential when neither is H. The dimetallacyclopentenones are fluxional, undergoing synchronous carbonyl ‘insertion’ into, and elimination from, the dimetallacycle. Free energies of activation appear dependent upon the size of the ‘alkyne’ substituents. In boiling toluene, carbonyl elimination from the dimetallacycle in [Fe2(CO)(µ-CO){µ-σ : η3-C(O)C2(CO2Me)2}(η-C5H5)2] becomes irreversible, and the dimetallacyclobutene complex [Fe2(CO)2(µ-CO){µ-C2(CO2Me)2}(η-C5H5)2] is formed quantitatively as cis and trans isomers. Only cis-[Ru2(CO)2(µ-CO){µ-C2(CO2Me)2}(η-C5H5)2] is generated when [Ru2(CO)(µ-CO)(µ-σ : η3-C(O)C2Ph2}(η-C5H5)2] is heated with MeO2CC2CO2Me. The ease with which carbon–carbon bond-making and -breaking occurs at the di-iron and diruthenium centres is recognised.

Combination of alkynes with µ-carbenes at a dimetal centre, and X-ray structure of [Fe2(CO)(µ-CO){µ-η1,η3-C(CO2Me)C(CO2Me)CHMe}(η-C5H5)2]: implications for metathesis and alkyne polymerisation

Bridging methylcarbenc complexes [M2(CO)2-(µ-CO)(µ-CHMe)(η-C5H5)2](M = Fe or Ru) react with alkynes RC2′R1(R = R1= H, Me, CO2Me; R = Me, R1= H) under u.v. irradiation to produce complexes [M2(CO)(µ-CO)(µ-η1,η3-CRCR1CHMe)(η-C5H5)2], shown through an X-ray diffraction study of [Fe2(CO)(µ-CO)-{µ-η1,η3-C(CO2Me)C(CO2Me)CHMe}(η-C5H5)2] to arise from linking of the µ-carbene and alkyne.

A convenient entry into diruthenium chemistry

Abstract In boiling toluene, diphenylacetylene is readily displaced from the dimetallocycle [Ru 2 (CO)(μ-CO) {μ-C(O)C 2 Ph 2 } (η-C 5 H 5 ) 2 ] by a variety of reagents (P(OMe) 3 , SO 2 , R 2 CN 2 , Ph 2 PCH 2 ) to produce [Ru 2 (CO){P(OMe) 3 }(μ-CO) 2 - (η-C 5 H 5 ) 2 ] or [Ru 2 (CO) 2 (μ-CO)(μ-L)(η-C 5 H 5 ) 2 ] (L  SO 2 , CR 2 , CH 2 ) in high yield.

Organic chemistry of dinuclear metal centres. Part 12. Synthesis, X-ray crystal structure, and reactivity of the di-µ-alkylidene complex [Ru2(CO)2(µ-CHMe)(µ-CMe2)(η-C5H5)2]: alkylidene linking

Upon treatment with methyl-lithium followed by HBF4·OEt2 a carbon monoxide ligand of the µ-alkylidene complex [Ru2(CO)2(µ-CO)(µ-CMe2)(η-C5H5)2](1) is converted into µ-ethylidyne, giving [Ru2(CO)2(µ-CMe)(µ-CMe2)(η-C5H5)2]+(2). This is deprotonated readily by water to form the µ-vinylidene complex [Ru2(CO)2(µ-CCH2)(µ-CMe2)(η-C5H5)2](3), which quantitatively regenerates (2) with HBF4·OEt2. Addition of NaBH4 to (2) results in hydride attack on µ-CMe to yield the di-µ-alkylidene complex [Ru2(CO)2(µ-CHMe)(µ-CMe2)(η-C5H5)2](4) as cis and trans isomers. The structure of the trans isomer has been established by X-ray diffraction. Crystals are triclinic, space group P, with Z= 2 in a unit cell for which a= 8.474(2), b= 7.802(3), c= 12.989(5)A, α= 99.42(3), β= 96.96(3), and γ= 107.73(3)°. The structure was solved by heavy-atom methods and refined to R 0.026 (R′ 0.031) for 4 092 independent intensities. A ruthenium–ruthenium single bond of 2.701(1)A is symmetrically bridged by ethylidene [mean Ru–C 2.079(3)] and isopropylidene [mean Ru–C 2.107(3)A] ligands to form an approximately planar Ru2C2 ring with a non-bonding Me2C··CHMe distance of 3.20 A. Upon thermolysis the alkylidenes link to evolve Me2CCHMe, Me2CHCHCH2, and Et(Me)CCH2. The absence of C4 and C6 hydrocarbons indicates that the alkylidene coupling occurs intramolecularly, and the electronic and stereochemical requirements of this process are discussed. Unlike mono-µ-alkylidene complexes, [Ru2(CO)2(µ-CO)(µ-CR2)(η-C5H5)2], the cis and trans forms. of (4) do not interconvert thermally below 145 °C, but u.v. irradiation effects a slow trans to cis isomerisation. U.v. irradiation of (4) in the presence of dimethyl acetylenedicarboxylate promotes ethylidene–alkyne linking to form [Ru2(CO)(µ-CMe2){µ-C(CO2Me)C(CO2Me)CHMe}(η-C5H5)2], but with ethyne both of the alkylidenes are lost and the ruthenium–ruthenium double-bonded complex [Ru2(µ-CO)(µ-C2H2)(η-C5H5)2] is produced.

Organic chemistry of dinuclear metal centres. Part 14. Synthesis, X-Ray structure, and reactivity of the ruthenium–ruthenium double-bonded complex [Ru2(μ-CO)(μ-C2Ph2)(η-C5H5)2]

Ultraviolet irradiation of the metallacycle [Ru2(CO)(μ-CO){μ-C(O)C2Ph2}(η-C5H5)2] (1) in tetrahydrofuran (thf) gives the complex [Ru2(μ-CO)(μ-C2Ph2)(η-C5H5)2] (2), shown by X-ray diffraction to have a ruthenium–ruthenium double bond [RuRu 2.505(1) A] bridged transversely by a diphenylacetylene ligand. The loss of two molecules of CO in forming (2) is reversible; under 100 atm of CO at 50 °C complex (2) is converted into (1) in 60% yield. Treatment of unsaturated complex (2) with diazoalkanes RCHN2 (R = H, Me, or CO2Et) results in the corresponding uptake of two alkylidene units to form [Ru2(CO)(μ-CHR){η-C(Ph)C(Ph)CHR}(η-C5H5)2], existing as isomers for R = Me or CO2Et due to differing orientations of the μ-CHR substituent. The structure of [Ru2(CO)(μ-CH2){μ-C(Ph)C(Ph)CH2}(η-C5H5)2] (3) has been established by X-ray diffraction, revealing that one methylene co-ordinates to the dinuclear metal centre while the other links with the alkyne. There are non-bonding C–C distances of 3.07 A between the two μ-carbons of the complex, but only 2.78 A separating the μ-CH2 carbon and the CH2 carbon of the C(Ph)C(Ph)CH2 ligand. On thermolysis the latter two carbons link, accompanied by other processes, to afford [Ru2(CO)(μ-CO){μ-C(Ph)C(Ph)CHMe}(η-C5H5)2] (5). A co-product of the reaction of diazoethane with (2) is the di-μ-vinyl complex [Ru2(CO) (μ-CHCH2){μ-C(Ph)CHPh}(η-C5H5)2] (8). X-ray diffraction reveals that the two β-carbons of the vinyl groups are 2.99 A apart and it is these rather than the two μ(α) carbons (3.06 A apart) which link on thermolysis, affording complex (5) once more. Thermolysis of [Ru2(CO)(μ-CHCO2Et){μ-C(Ph)C(Ph)CH(CO2Et)}(η-C5H5)2] does not effect carbon–carbon bond formation. Instead, CO is ejected and its site occupied by an oxygen of a carboethoxy group in the complex [Ru2(μ-CHCO2Et){μ-C(Ph)C(Ph)CHC(O)OEt}(η-C5H5)2]. Treatment of complex (1) with BH3·thf or LiMe–HBF4–NaBH4 converts the metallacyclic ketone group into CH2 or CHMe respectively, yielding [Ru2(CO)(μ-CO){μ-C(Ph)C(Ph)CHR}(η-C5H5)2] (R = H or Me). The nature of the processes observed on thermolysis of complexes (3) and (8) suggests the importance of least-motion effects in determining the course of carbon–carbon bond formation at a dinuclear metal centre.

Stereochemical control of alkyne oligomerisation at a diruthenium centre: X-ray structures of [Ru2(CO)(µ-CO)(µ-C4H4CMe2)(η-C5H5)2] and [Ru2(µ-CO){µ-C4(CO2Me)4CH2}(η-C5H5)2]

The µ-carbene complexes [Ru2(CO)2(µ-CO)(µ-CMe2)(η-C5H5)2] and [Ru2(CO)2(µ-CO)(η-CH2)(η-C5H5)2] undergo double insertion with ethyne and dimethyl acetylenedicarboxylate, respectively, to yield the title compounds; these complexes have been shown by X-ray diffraction to contain five-carbon chains of differing stereochemistry, attributed to the different steric demands of the carbene substituents.

Sequential conversion of ethyne into μ-vinylidene, μ-methylcarbyne and μ-methylcarbene at a di-ruthenium centre: X-ray structures of [Ru2(CO)2(μ-CO) (μ-CCH2) (η-C5H5)2] and [Ru2(CO)2(μ-CO) (μ-CCH3) (η-C5H5)2] [BF4]

The ethyne-derived demetallocycle [Ru 2 (CO) (μ-CO){μ-C(O)C 2 H 2 }(η-C 5 H 5 ) 2 isomerises in boiling toluene to yield the μ-vinylidene complex [Ru 2 (CO) 2 (μ-CO)(μ-CCH 2 ) (η-C 5 H 5 ) 2 ], which on protonation with dry HBF 4 provides the μ-carbyne complex [Ru 2 (CO) 2 (μ-CO)(μ-CCH 3 )(η-C 5 H 5 ) 2 ][BF 4 ]; the structure of each product has been determined by X-ray diffraction. The μ-carbyne cation is attacked by hydride to produce the μ-methylcarbene complex [Ru 2 (CO) 2 (μ-CO)(μ-CHCH 3 )(η-C 5 H 5 ) 2 ].

Sequential methylene addition to an alkyne coordinated at a diruthenium centre

Abstract The metalmetal double-bonded μ-alkyne complex [Ru2(μ-CO)(μ-C2Ph2) (η-C5H5)2] (1) reacts with diazomethane at 0°C to yield Ru2(CO)(η-CH2) {μ-C(Ph)C(Ph)CH2} (η-C5H5)2] (2) incorporating two methylene units, one bridging the metal atoms and one linked with the alkyne. Upon heating, a second carboncarbon bond formation occurs to link the methylene groups and give [Ru2(CO)(μ-CO) {μ-C(Ph)C(Ph)C(H)Me} (η-C5H5)2 (3); the structures of 1 and 2 were established by X-Ray diffraction.

Organic chemistry of binuclear metal centres. Part 6. µ-Vinylidene and µ-ethylidyne diruthenium complexes: crystal structures of cis-[Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2] and cis-[Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4]

The dimetallacycles [Ru2(CO)(µ-CO){µ-C(O)C2HR}(η-C5H5)2](R = H or Ph) isomerise in boiling toluene to the µ-vinylidene complexes [Ru2(CO)2(µ-CO)(µ-CCHR)(η-C5H5)2], shown by a deuterium-labelling experiment to involve an intramolecular hydrogen shift. Protonation of the µ-CCH2 complex with HBF4·OEt2 gives the µ-ethylidyne species [Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4], which deprotonates readily when treated with water, triethylamine, or methyl-lithium; with NaBH4 the cation is attacked by hydride to produce the µ-ethylidyne complex [Ru2(CO)2(µ-CO)(µ-CHMe)(η-C5H5)2]. Successive addition of methyl-lithium and HBF4·OEt2 to [Ru2(CO)4(η-C5H5)2] also yields the complex [Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4], whose subsequent conversion to [Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2] or [Ru2(CO)2(µ-CO)(µ-CHMe)(η-C5H5)2] provides an excellent route to these complexes. Similar successive addition of phenyl-lithium, HBF4·OEt2, and NaBH4 to [Ru2(CO)4(η-C5H5)2] gives [Ru2(CO)2(µ-CO)(µ-CHPh)(η-C5H5)2] in high yield. The molecular structures of cis-[Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2] and cis-[Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4] have been determined by X-ray diffraction studies. Crystals of both compounds are monoclinic, space group P21/n with Z= 4 and unit-cell dimensions a= 8.620(6), b= 15.712(9), c= 10.844(8)A, β= 92.57(4)° and a= 9.121(2), b= 9.724(3), c= 20.666(6)A, β= 106.42(3)° respectively. The structures were solved by heavy-atom methods and refined by least squares to give final residuals R of 0.051 and 0.026 for 2 503 and 3 044 unique, observed, diffractometer data respectively. Both cis-[Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2] and cis-[Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2]+ show approximate Cs symmetry in the solid state, with Ru–Ru single bond distances of 2.696(1) and 2.714(1)A respectively. In both cases each ruthenium atom is co-ordinated by terminal carbonyl and η-cyclopentadienyl ligands in addition to bridging carbonyl and hydrocarbon (vinylidene and ethylidyne) groups. The geometry and orientation of the bridging vinylidene ligand is consistent with a C–C bond order of two [C–C 1.326(11)A] and contact carbon bonding to the Ru2 fragment via donor and acceptor interactions of σ and π symmetry in the Ru2C plane. The µ-ethylidyne ligand in cis-[Ru2(CO)2(µ-CO)(µ-CMe)(η-C5H5)2][BF4] shows average Ru–C distances shorter than those of the η-vinylidene ligand in cis-[Ru2(CO)2(µ-CO)(µ-CCH2)(η-C5H5)2][1.937(4)vs. 2.030(7)A], and has a longer C–C distance [1.462(6)A] consonant with a C(sp)-C(sp3) single bond. These geometric features, and the reactivity of the cationic µ-ethylidyne complex towards nucleophiles, are explained in terms of a simple molecular orbital model.