Kevin A. Mead

Replacement of hydrido-ligands in triruthenium complexes by triphenylphosphinegold groups. Crystal structures of [AuRu3(µ-COMe)(CO)10(PPh3)], [AuRu3(µ-H)2(µ3-COMe)(CO)9(PPh3)], and [Au3Ru3(µ3-COMe)(CO)9(PPh3)3]

The compound [AuMe(PPh3)] reacts under mild conditions (diethyl ether, ambient temperatures) with the compounds [M3(µ-H)(µ-COMe)(CO)10] and [Ru3(µ-H)3(µ3-COMe)(CO)9] to give the complexes [AuM3(µ-COMe)(CO)10(PPh3)][M = Fe (1) or Ru (2)], [AuRu3(µ-H)2(µ3-COMe)(CO)9(PPh3)](3), [Au2Ru3(µ-H)(µ3-COMe)(CO)9(PPh3)2](4), and [Au3Ru3(µ3-COMe)(CO)9(PPh3)3](5). Spectroscopic properties of the new species are reported and discussed, and the structures of (2), (3), and (5) have been established by X-ray diffraction studies. The structure of [AuRu3(µ-COMe)(CO)10(PPh3)](2) can be regarded as a molecule of [Ru3(µ-H)(µ-COMe)(CO)10] in which the bridging hydrido-ligand is replaced by a bridging AuPPh3 group, thus producing a ‘butterfly’ metal atom core (interplanar angle 117°) with the gold atom occupying a ‘wing-tip’ site. The COMe ligand bridges the body of the butterfly on the convex side. The Au–Ru bonds [2.760(2) and 2.762(2)A] are ca. 0.1 A shorter than the non-bridged Ru–Ru bonds [2.845(2) and 2.839(3)A] but the bridged Ru–Ru bond is significantly longer at 2.879(2)A. Crystals of (2) are triclinic, space group P, and the asymmetric unit comprises two molecules of complex. The structure has been refined to R 0.075 for 4 868 intensities measured to 20 = 40° at 220 K. In [AuRu3(µ-H)2(µ3-COMe)(CO)9(PPh3)](3) the carbyne ligand triply bridges an equilateral triangle [Ru–Ru 2.865(2)–2.879(2)A] of ruthenium atoms, while on the opposite side of the triangle there are two edge-bridging hydrido-ligands and one edge-bridging AuPPh3 group. Each ruthenium atom carries three terminal carbonyl ligands, giving octahedral co-ordination if the Ru–Ru bonds are ignored. The molecule has approximate Cs symmetry, not required crystallographically. The structure is triclinic, space group P, and has been refined to R 0.042 for 3 247 intensities measured to 2θ= 45° at 293 K. The complex [Au3Ru3(µ3-COMe)(CO)9(PPh3)3](5) crystallises with half a molecule of CH2Cl2 per molecule of (5) incorporated into the crystals. Again the carbyne ligand triply bridges a near-equilateral triangle of Ru atoms [Ru–Ru 2.895(3)–2.929(2)A], but on the opposite side of this triangle one gold atom is co-ordinated to form a tetrahedron [Au–Ru 2.818(2), 2.825(2), and 2.987(2)A]. The two faces of this tetrahedron adjacent to the long Au–Ru bond are each further triply bridged by AuPPh3 ligands. The two Au–Au distances in this bicapped tetrahedral structure are 2.930(1) and 3.010(1)A; the difference between these probably arises from the packing of the bulky triphenylphosphine ligands. Crystals of (5) are monoclinic, space group P21/n, and the structure has been refined to R 0.050 for 4 279 intensities measured to 2θ= 45° at 293 K.

Heteronuclear metal complexes with bridging methoxymetylidyne ligands: X-ray crystal structures of [AuRu3(µ2-COMe)(CO)10(PPh3)] and [Fe3Pt(µ3-H)(µ3-COMe)(CO)10(PPh3)]

Heteronuclear cluster compounds can be prepared from reactions between [M3(µ-H)(µ-COMe)(CO)10](M = Fe or Ru) and [ AuMePPh3], or between the tri-iron compound and [Pt(C2H4)2(PPh3)]; the structures of [AuRu3(µ2-COMe)(CO)10(PPh3)] and [Fe3Pt(µ3-H)(µ3-COMe)(CO)10(PPh3)] have been established by X-ray diffraction.

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.

Organic chemistry of dinuclear metal centres. Part 7. Ylides in the synthesis of organodiruthenium complexes: X-ray crystal structure of [Ru2(CO)2(µ-CO)(µ-CH2)(η-C5H5)2]

Heating [Ru2(CO)(µ-CO){µ-C(O)C2Ph2}(η-C5H5)2] with an ylide Ph3PCHR in toluene at reflux rapidly yields µ-alkylidene complexes [Ru2(CO)2(µ-CO)(µ-CHR)(η-C5H5)2](R = H, 70%; Me, 35%; Et, 28%; or Ph, 57%). A similar reaction with Ph3PCHCHCH2 gives only a 13% yield of the analogous product [Ru2(CO)2(µ-CO)(µ-CHCHCH2)(η-C5H5)2], the major product (33%) being the isomeric substituted allyl complex [Ru(CO){η3-C3H4[Ru(CO)2(η-C5H5)]-1}(η-C5H5)]. Upon u.v. irradiation the latter undergoes rearrangement, with Ru–Ru bond formation, to give the former, believed to proceed via a 16-electron σ-allyl species. Further u.v. irradiation of [Ru2(CO)2(µ-CO)(µ-CHCHCH2)(η-C5H5)2] releases a CO ligand and brings the alkylidene vinyl substituent into co-ordination, forming [Ru2(CO)(µ-CO)(µ-CHCHCH2)(η-C5H5)2] in high yield. The two metal atoms in the complex [Ru(CO){η3-C3H4[Ru(CO)2(η-C5H5)]-1]}(η-C5H5)] are also brought into bonding with one another when the allyl is protonated, yielding the methylvinyl cation [Ru2(CO)2(µ-CO)(µ-CHCHMe)(η-C5H5)2]+. Treatment of the cation with NaBH4 results in hydride addition to the β-carbon of the vinyl, producing [Ru2(CO)2(µ-CO)(µ-CHEt)(η-C5H5)2] in good yield. The µ-CH2 complex [Ru2(CO)2(µ-CO)(µ-CH2)(η-C5H5)2] is not formed when [Ru2(CO)(µ-CO){µ-C(O)C2Ph2}(η-C5H5)2] and CH2N2 are heated together, but thermally more robust diazoalkanes, CH(CO2Et)N2 and Ph2CN2, afford [Ru2(CO)2(µ-CO){µ-CH(CO2Et)}(η-C5H5)2] and [Ru2(CO)2(µ-CO)(µ-CPh2)(η-C5H5)2] respectively. The latter suffers from steric crowding and readily ejects a CO to give [Ru2(CO)(µ-CO)(µ-CPh2)(η-C5H5)2], in which a double bond of one phenyl ring is co-ordinated to ruthenium. Under CO pressure this transformation is reversed. The complex [Ru2(CO)2(µ-CO)(µ-SO2)(η-C5H5)2] is formed in high yield when SO2 is bubbled through a boiling toluene solution of [Ru2(CO)(µ-CO){µ-C(O)C2Ph2(η-C5H5)2]. Crystals of [Ru2CO)2(µ-CO)(µ-CH2(η-C5H5)2] are triclinic, space group P, with Z= 2 in a unit cell for which a= 6.771(2), b= 9.315(2), c= 11.864(5)A, α= 103.12(3), β= 100.61(3), and γ= 103.40(2)°. The structure has been solved by heavy-atom methods and refined to R0.0365 (R′ 0.0359) for 2 725 independent intensities. The two Ru(CO)(η-C5H5) moieties are held together by a single Ru–Ru bond [2.707(1)A] which is symmetrically bridged by CO and CH2 groups. The interplanar angle between the two bridge systems is 161° with the convex side facing the terminal (cis) carbonyl groups. The molecule has idealised Cs(m) symmetry.

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.

Stepwise synthesis of tungsten–platinum or –gold bonds bridged by alkylidyne ligands: X-ray crystal structures of [Pt3W2(µ3-CR)2(CO)4-(η-C5H5)2(cod)2](cod cyclo-octa-1,5-diene), [Pt2W3(µ-CR)2(µ3-CR)(CO)6(η-C5H5)3], and [AuW2(µ-CR)2(CO)4(η-C5H5)2][PF6]

The synthesis of metal complexes with bonds between tungsten and platinum or gold, bridged by tolylidyne ligands, is described; and the molecular structures of the species [Pt3W2(µ3-CR)2(CO)4(η-C5H5)2(cod)2](cod = cyclo-octa-1,5-diene), [Pt2W3(µ-CR)2(µ3-CR)(CO)6(η-C5H5)3], and [AuW2(µ-CR)2(CO)4(η-C5H5)2][PF6](R = C6H4Me-4) have been established by X-ray crystallography.

Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 6. Synthesis of platinum–chromium and –tungsten compounds. X-Ray crystal structure of [(Me3P)(OC)4W{µ-C(OMe)C6H4Me-4}Pt(PMe3)2]

Addition of light petroleum solutions of [M{C(OMe)C6H4R-4}(CO)5](M = Cr or W, R = Me or CF3) to ethylene-saturated solutions of [Pt(cod)2](cod = cyclo-octa-1,5-diene), to which two molar equivalents of tertiary phosphine had been added, afforded the heteronuclear dimetal complexes [(OC)5[graphic omitted](PR3)2](R = Me, PR3 PMe3 or PMe2Ph; R = CF3, PR3= PMe3) and [(OC)5[graphic omitted](PR3)2](R = Me or CF3, PR3= PMe3 or PMe2Ph), characterised by 31P and 1H n.m.r. spectroscopy. The compounds [(OC)5[graphic omitted](PMe2Ph)2], [(OC)5[graphic omitted](PMe2Ph)2], and [(OC)5[graphic omitted](PMe3)2] were similarly obtained from [W{C(OMe)Me}(CO)5], [Cr([graphic omitted]H2)(CO)5], and [W(CPh2)(CO)5], respectively. Although [PtW(µ-CPh2)(CO)5(PMe3)2] is a relatively unstable complex, reaction with trimethylphosphine affords air-stable [(Me3P)(OC)4[graphic omitted](PMe3)2] as a single isomer. A similar enhanced thermal and oxidative stability relative to the pentacarbonyl species is also observed with the compounds [(Me3P)(OC)4[graphic omitted](PMe3)2] and [(R3P)(OC)4[graphic omitted](PR3)2](PR3= PMe3 or PMe2Ph). A single-crystal X-ray diffraction study on the complex [PtW{µ-C(OMe)-C6H4Me-4}(CO)4(PMe3)3]shows that the tungsten–platinum bond [2.825(1)A] is asymmetrically bridged by a C(OMe)C6H4Me-4 group [C–W 2.37(1)A; C–Pt 2.03(1)A], that the co-ordination of the W atom is close to octahedral, and that the Pt atom is in a near-planar environment. The crystals are orthorhombic, space group Pna21(no. 33), with Z= 4 in a unit cell of dimensions a= 18.180(6), b= 10.720(3), c= 14.697(4)A. The structure has been elucidated by heavy-atom methods from 3 882 independent intensities measured to 2θ= 60° at 200 K, and refined to R 0.044.

Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 18. Synthesis of the complexes [MW(µ-CC6H4Me-4){µ-(σ : η2-CO)}(CO)(η-C5H5)3](M = Ti or Zr) and the crystal structure of the titanium–tungsten compound

The compounds [M(CO)2(η-C5H5)2](M = Ti or Zr) react with [W(CC6H4Me-4)(CO)2(η-C5H5)] when heated in toluene to give the dimetal compounds [MW(µ-CC6H4Me-4)(µ-CO)(CO)(η-C5H5)3], characterised by n.m.r. and i.r. spectroscopy. The structure of the titanium–tungsten compound has been established by a single-crystal X-ray diffraction study. As expected, the titanium–tungsten bond [2.977(4)A] is bridged by the CC6H4Me-4 ligand [Ti–C 2.19(3) and W-C 1.91(2)A, with double-bond character in the linkage to tungsten], and one of the two linear terminal carbonyl ligands on the W atom forms a η2-donor bond to the Ti atom. The bridge system itself is nearly planar; but although the two cyclopentadienyl ligands on the Ti atom are at normal bonding distances and are approximately equivalently related to the bridge plane, they are in a staggered orientation to one another. The third cyclopentadienyl ligand completes the bonding around the W atom. The high thermal stability and relative inertness of the molecule can be ascribed, at least in part, to the compact arrangement of inert bulky ligands around the metal centres.

Organic chemistry of dinuclear metal centres. Part 4. µ-Carbene and µ-vinyl complexes of ruthenium from allenes

Heating [Ru2(CO)(µ-CO){µ-C(O)C2Ph2}(η-C5H5)2] with an allene R1CHCCHR2(R1= R2= H or Me; R1= H, R2= Me) in toluene at 100 °C displaces diphenylacetylene and produces allyl complexes [Ru(CO){η3-C3H4–nMen[2-Ru(CO)2(η-C5H5)]}(η-C5H5)](2, n= 0, yield 90%; 3, n= 1, 70%; 4, n= 2, 10%). A Ru–Ru bond is broken in this process but is regenerated upon protonation of (2) with HBF4, which yields the µ-vinyl species [Ru2(CO)2(µ-CO){µ-C(Me)CH2}(η-C5H5)2][BF4. Treatment of this with NaBH4 effects hydride addition to the µ-vinyl to form the µ-dimethylcarbene complex [Ru2(CO)2(µ-CO)(µ-CMe2)(η-C5H5)2] in 77% yield. Similar sequential addition of H+ and H– to (3) gives [Ru2(CO)2(µ-CO){µ-C(Me)Et}(η-C5H5)2] in 60% yield, but (4) does not transform to a µ-CEt2 complex. The molecular structure of [Ru2(CO)2(µ-CO)(µ-CMe2)(η-C5H5)2] was established by X-ray diffraction. The two ruthenium atoms are 2.712(1)A apart and are bridged symmetrically by the carbonyl and the dimethylcarbene ligands. The interplanar angle between the two bridge systems is 153°. Each Ru atom carries one terminal carbonyl group and one cyclopentadienyl ligand. These cyclopentadienyl ligands lie in an eclipsed cis orientation, skew to the Ru ⋯ Ru axis, on the convex side of the bridge system, giving the molecule as a whole Cs symmetry. The mean Ru–C (carbene) separation is 2.113(4)A and the plane of the carbene ligand coincides with the molecular mirror plane. The structure is triclinic and has been refined to R 0.018 for 2 001 intensities measured on a four-circle diffractometer. In solution the complex exists as both cis and trans isomers which interconvert rapidly on the n.m.r. time-scale above room temperature. This, and related behaviour of the complex [Ru2(CO)2(µ-CO)(µ-CMe2)(PMe2Ph)(η-C5H5)2], is interpreted in terms of a bridge ⇌ terminal carbene exchange. Minor products of the synthesis of [Ru2(CO)2(µ-CO)(µ-CMe2)(η-C5H5)2] are the isomers [Ru2(CO)2(µ-H){µ-C(Me)CH2}(η-C5H5)2] and [Ru2(CO)2(µ-H){µ-CHC(H)Me}(η-C5H5)2]; the former is dominant in solution but an X-ray diffraction study revealed the latter as the solid-state structure. The molecule comprises two Ru(CO)(η-C5H5) fragments joined by a Ru–Ru bond [2.857(2)A] which is bridged by hydrido- and 2-methylvinyl ligands. The vinyl ligand spans the Ru–Ru bond in a σ, η2 mode, with a Ru–C(σ) separation of 2.013(4)A and Ru–C(π) separations of 2.189(4) and 2.275(4)A. The hydrido-ligand bridges with a small degree of asymmetry, but lies coplanar with the Ru (1)Ru(2)(µ-C) metallacycle. The terminal ligands on each ruthenium atom are arranged to give the molecule an overall cis configuration. However, the carbonyl ligands are not perfectly eclipsed, the torsion angle (O)C–Ru–Ru–C(O) being 15.7(2)°. The structure is monoclinic, and has been refined to R 0.028 for 2 041 intensities measured on a four-circle diffractometer at 200 K.