Kirsty A. Macpherson

Organic chemistry of dinuclear metal centres. Part 13. Synthesis, structure, and reactivity of [Ru2(CO)4(η5: η5′-C5H4CH2C5H4)]

Reaction of [Ru3(CO)12] with bis(cyclopentadienyl)methane in boiling toluene gives [Ru2(CO)4(η5:η5′-C5H4CH2C5H4)](1) in good yield. The molecular structure has been determined by X-ray diffraction. The structure was solved by heavy-atom methods and refined by least squares to give a final R 0.045 for 3 009 unique, observed diffractometer data. Crystals of (1) are orthorhombic, space group Pbca, with Z= 16 in a unit cell of dimensions a= 18.066(9), b= 14.321(6), and c= 22.156(10)A. The molecule consists of a staggered (OC)2Ru–Ru(CO)2 unit bridged by a bis(cyclopentadienylene)methane ligand which is η5-bound to each ruthenium atom. I.r. spectroscopy reveals that this structure dominates in solution, but that a low concentration of a carbonyl-bridged isomer is also present. Sequential treatment of complex (1) with LiMe, tetrafluoroboric acid, and NaBH4 affords the bis-µ-ethylidene complex [Ru2(CO)2(µ-CHMe)2(η5:η5′-C5H4CH2C5H4)](7) the structure of which has also been determined by X-ray diffraction, and solved and refined as above to a final R 0.025 for 1 813 data. Crystals of (7) are monoclinic, space group P21/n(non-standard setting of P21/c, no.14), with Z= 4 in a unit cell of dimensions a= 8.702(3), b= 12.653(4), c= 14.508(6)A, and β= 98.01(3)°. The molecule contains an (OC)Ru–Ru(CO) unit bridged by two ethylidene groups so as to give a highly folded Ru2(µ-C)2 core. The methyl groups of the ethylidenes are oriented anti with respect to a bridging bis(cyclopentadienylene)methane ligand bound in an η5 : η5′ fashion as for complex (1). Although the µ-C ⋯µ-C distance in complex (7) is relatively short (3.11 A), thermolysis induces alkylidene linking less efficiently than for related η-C5H5 complexes with a non-folded geometry, a difference attributed to the reduced flexibility in (7) arising from the coupling of the η-C5 rings. Reaction of complex (1) with Li[BHEt3]–water affords the µ-methylene complex [Ru2(CO)2(µ-CO)(µ-CH2)(η5:η5′-C5H4CH2C5H4)]. Photolysis of (1) in the presence of diphenylacetylene gives [Ru2(CO)2(µ-CO)(µ-σ: σ-C2Ph2)(η5: η5′-C5 H4CH2C5H4)], containing a ‘parallel’ two-electron alkyne ligand. The Ru–Ru bond of (1) is cleaved by iodine to yield [Ru2I2(CO)4(η5:η5′-C5H4CH2C5H4)], which is readily converted into[Ru2Me2(CO)4(η5: η5′- C5H4CH2C5H4)] on treatment with Li[CuMe2].

Phosphorus-carbon bond cleavage at a di-iron centre: synthesis of μ-phosphidomethyl complexes [Fe2(CO)6(μ-CH2PR2)(μ-PR2)] from [Fe2(CO)6(μ-R2PCH2PR2)]

Abstract Upon heating in toluene at reflux the di-iron heptacarbonyl complexes [Fe 2 (CO) 6 (μ-CO)(μ-R 2 PCH 2 PR 2 )] (RPh, Me, Et, i Pr, OEt) lose carbon monoxide, resulting in phosphorus-methylene bond cleavage to give the μ- phosphidomethyl complexes [Fe 2 (CO) 6 (μ-CH 2 PR 2 )(μ-PR 2 )]. The ability of the phenyl group to stabilise the μ- CH 2 PR 2 ligand is seen in the thermolyses of the diphosphine complex [Fe 2 (CO) 6 (μ-CO)(μ-Ph 2 PCH 2 PMe 2 )], which undergoes selective Me 2 PCH 2 bond cleavage to yield [Fe 2 (CO) 6 (μ-CH 2 PPh 2 )(μ-PMe 2 )], and of the bis-diphosphine complexes [Fe 2 (CO) 4 (μ-CO)(μ-R 2 PCH 2 PR 2 )(μ-Ph 2 PCH 2 PPh 2 )] (RPh, Me), which results only in Ph 2 PCH 2 bond cleavage to give [Fe 2 (CO) 4 (μ-R 2 PCH 2 PR 2 )(μ-CH 2 PPh 2 )(μ-PPh 2 )]. The ubiquity of μ-CH 2 PPh 2 is attributed to the existence of a zwitterionic form in which positive charge residing on phosphorus is dispersed into the phenyl rings. The complexes [Fe 2 (CO) 4 (μ-R 2 PCH 2 PR 2 )(μ-CH 2 PPh 2 )(μ-PPh 2 )] exist as mixtures of geometric isomers a and b , identified by 31 P NMR spectroscopy and an X-ray diffraction study on the major isomer a of [Fe 2 (CO) 4 (μ-Me 2 PCH 2 PMe 2 )(μCH 2 PPh 2 )(μ-PPh 2 )] as its dichloromethane solvate, which contains a cis arrangement of phosphido and phosphidomethyl ligands with the diphosphine lying trans to the latter. Methyl substitution in the diphosphine backbone suppresses phosphorus-methylene bond cleavage and results instead in ortho-metalation and phosphorus-phenyl bond cleavage. Thus, on heating [Fe 2 (CO) 6 (μ-CO){μ-Ph 2 PCH(Me)PPh 2 }] carbon monoxide and benzene are lost and [Fe 2 (CO) 6 {μ-PhPCH(Me)P(Ph)(C 6 H 4 - o )}] is formed, structurally characterised by X- ray diffraction. Substitution of two methyl groups into the diphosphine backbone favours ortho -metalation more strongly still and UV irradiation of the chelate complex [Fe(CO) 3 {η 2 -Ph 2 PC(Me 2 )PPh 2 }] in the presence of iron pentacarbonyl yields [Fe 2 (CO) 6 {μ-PhPC(Me 2 )P(Ph)(C 6 H 4 - o )}] directly. The structure of [Fe 2 (CO) 6 (μ-CO){μ-Ph 2 PCH(Me)PPh 2 }] as its hexane solvate was examined by X-ray diffraction, for comparison with that of [Fe 2 (CO) 6 (μ- CO){μ-Ph 2 PCH 2 PPh 2 }]. The structure analysis was not satisfactory but no significant differences between the molecular structures were observed. The suppression of backbone P-C cleavage by methyl substitution is attributed to the destabilisation of the zwitterionic form of μ-CR 2 PPh 2 , which has negative charge residing on the carbon.

Organic chemistry of dinuclear metal centres. Part 8. Organo–iron–ruthenium chemistry. X-Ray structure of trans-[FeRu(CO)2(µ-CO)2(η-C5H5)2]

The iron–ruthenium complex [FeRu(CO)4(η-C5H5)2] is obtained in 60% yield from the reaction of Na[Fe(CO)2(η-C5H5)] with [RuI(CO)2(η-C5H5)]. In the solid state a trans-[FeRu(CO)2(µ-CO)2(η-C5H5)2] structure has been established by X-ray diffraction. Crystals are monoclinic, space group P21/c (no. 14), with Z= 2 in a unit cell for which a= 7.064(2), b= 12.518(3), c= 8.011(2)A, and β= 106.23(2)°. The structure was solved by heavy-atom methods and refined to R 0.0275 (R′ 0.0313) for 1 532 independent intensities. The molecule is disordered about a centre of inversion at the mid-point of the metal–metal bond, each metal site being occupied by half an iron and half a ruthenium atom, with an iron–ruthenium bond length of 2.626(1)A. In solution the cis-[FeRu(CO)2(µ-CO)2(η-C5H5)2] isomer is dominant, and shown by 13C n.m.r. to be undergoing cis⇌trans isomerisation with bridge ⇌ terminal carbonyl exchange at room temperature, but to be static at –80 °C. The complex is an excellent precursor of organo-iron–ruthenium chemistry. Treatment with alkynes R1C2R2(R1= R2= H, Me, Ph, or CO2Me; R11= Me or Ph, R2= H) under u.v. irradiation gives complexes [FeRu(CO)(µ-CO){µ-C(O)CR1CR2}(η-C5H5)2] in 20–65% yield as a result of alkyne–CO linkage. This link in the complexes derived from ethyne, propyne, and but-2-yne is broken upon protonation, generating µ-vinyl cations [FeRu(CO)2(µ-CO)(µ-CR1CHR2)(η-C5H5)2]+(R1= R2= H or Me; R1= H, R2= Me). These are attacked by hydride at the β carbon of the µ-vinyl to give µ-alkylidene complexes [FeRu(CO)2(µ-CO)(µ-CR1R2)(η-C5H5)2](R1= H, R2= Me or Et; R1= Me, R2= Et). Reaction of [FeRu(CO)(µ-CO){µ-C(O)CPhCPh}(η-C5H5)2] with Ph3PCHR or CH(CO2Et)N2 in boiling toluene also gives µ-alkylidene complexes [FeRu(CO)2(µ-CO)(µ-CHR)(η-C5H5)2](R = H, Me, or CO2Et) in good yield, through ready displacement of diphenylacetylene. The µ-CH2 complex is best obtained (75%) by treating [FeRu(CO)4(η-C5H5)2] with LiBHEt3 then water, and in a related manner sequential addition of methyl-lithium, HBF4·OEt2, and NaBH4 affords [FeRu(CO)2(µ-CO)(µ-CHMe)(η-C5H5)2]. Under u.v. irradiation alkynes react with µ-alkylidene complexes [FeRu(CO)2(µ-CO)(µ-CHR1)(η-C5H5)2] to give products of alkyne–alkylidene linking [FeRu(CO)(µ-CO)(µ-CR3CR2CHR1)(η-C5H5)2](R1= H or Me, R2= R3= H, Me, Ph, or CO2Me; R1= H or Me, R2= Me or Ph, R3= H). These exist as non-interconverting isomers in which the new C3 ligand is either bound σ to iron and σ, η2 to ruthenium or vice versa. The scope of organo-iron–ruthenium chemistry closely resembles that of the di-iron system but it is apparent that in reactivity terms there is an order: FeRu > Fe2 > Ru2.

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.

Phosphorus–carbon bond cleavage at a di-iron centre. Conversion of µ-R2PCH2PR2 to µ-R2PCH2 and µ-PR2: crystal structures of [Fe2(CO)4(µ-Ph2PCH2)(µ-PPh2)(µ-Me2PCH2PMe2)] and [Fe2(CO)6{µ-PhPCH(Me)P(Ph)(C6H4-O)}]

The µ-bis(phosphido)methane ligands in the complexes [Fe2(CO)7(µ-R2PCH2PR2)] and [Fe2(CO)5(µ-R2PCH2PR2)2](R = Me or Ph) undergo phosphorus–carbon bond cleavage on heating to give co-ordinated µ-R2PCH2 and µ-PR2; the pattern of cleavage is changed by methyl substitution, as in Ph2PCH(Me)PPh2, when loss of one phenyl group is accompanied by ortho-metallation of another.

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 dinuclear metal centres. X: Dimerization of allene at a diruthenium centre. X-Ray crystal structure of [Ru2(CO)2{μ-C(Me)CHCH2CCH2}(η-C5Me5)2]

Abstract Photolysis of [Ru2(CO)4(η-C5R52] (R = H or Me) in the presence of allene yields complexes [(η-C5R5)(CO)2RuCH 2C(CH2)C(CH2)CH2Ru(CO)2(η-C5R5)] and [Ru2(CO)2{(μ-C(Me)CHCH2CCH2)}(η-C5Me5)2], containing dimers of allene derived by C(2)C(2) and C(1)C(1) coupling, respectively. The molecular structure of [Ru2(CO)2 (μ-C(Me)CHCH2)CCH2(η-C5Me5)2] has been determined by X-ray diffraction. The structure was solved by heavy-atom methods and refined by least-squares to give a final R 0.047 for 4678 unique, observed diffractometer data. Crystals are monoclinic, space group P21 /c, with Z = 8 in a unit cell of dimensions a = 10.403(8), b = 28.804(27), c = 19.882(18) A, β = 117.14(6)°. The molecule is based on a trans-(η-C5Me5)(CO)RuRu(CO)(η-C5Me5) unit with one terminal and one semi-bridging carbonyl ligand This unit is bridged by a linear MeCCHCH2CCH2 six-carbon chain which is η2-bound to one ruthenium through two σ-bonds, making a metallacyclopentene ring, and to the other through an η2-interaction of an exocyclic double bond. The formation of the allene dimer products is attributed to the attack of Ru(CO)2(η-C5R5) radicals upon the C(1) or C(2) carbon of allene, followed by dimerization of the radicals so formed. The μ-allene species [Ru2(CO)2(μ-CH2CCH2)(η-C5H5)2] is obtained by photolysis of the μ-vinylidene complex [Ru2(CO)3(μ-CCH2)(η-C5H5)2] in acetonitrile, followed by the addition of diazomethane.

Activation of a µ3-ethylidyne ligand through oxidation–deprotonation: X-ray structure of [Ru3(µ3-CMe)(µ-CO)3(η-C5Me5)3][BF4]

Oxidation of the µ3-ethylidyne complex [Ru3(µ3-CMe)(µ-CO)3(η-c5Me5)3] yields [Ru3(µ3-CMe)(µ-CO)3(η-C5Me5)3]+(characterized by X-ray diffraction) and [Ru3(µ3-CMe)(µ-CO)3(η-C5Me5)3]2+; the latter deprotonates to give the µ3– vinylidene cation [Ru3(µ3-CCH2)(µ-CO)3(η-C5Me5)3]+ which reacts with methyl-lithium to form [Ru3(µ3-CEt)(µ-CO)3(η-C5Me5)3], completing a µ3-Cme th µ3-CEt homologaion.

The μ3-cyclopentadienylidene ligand: X-ray structure of [Ru4(CO)5 {P(OMe)3}(μ3-C5H4)2(η-C5H5)2]

Abstract UV irradiation of [Ru 2 (CO) 4 (η-C 5 H 5 ) 2 ] yields the tri- and tetra-ruthenium complexes [Ru 2 (CO) 4 (η-C 5 H 5 ){η-C 5 H 4 Ru(CO) 2 (η-C 5 H 5 )}] and [Ru 4 (CO) 6 (μ 3 -C 5 H 4 ) 2 (η-C 5 H 5 ) 2 ]. The μ 3 -C 5 H 4 ligand in the latter has been characterised through an X-ray diffraction study on [Ru 4 (CO) 5 {P(OMe) 3 }(μ 3 -C 5 H 4 ) 2 (η-C 5 H 5 ) 2 ].

Reactivity of bis(diphenylphosphino) methane at a di-iron centre: thermally induced rearrangements of dimetallacyclopentenone complexes [Fe2(CO)5{μ-σ:η3-C(O)CRCr}(μ-dppm)]

Abstract In toluene at 100°C the dimetallacyclopentenone complex [Fe2(CO)5{μ-σ:η3-C(O)CHCH}(μ-dppm)] (1a) isomerises to the μ-vinyl complex [Fe2(CO)6{μ-C(CH2)P(Ph2)CH2PPh2}] (2) via intramolecular nucleophilic attack of phosphorus on a carbon of the metallacycle, with an associated 1,2-hydrogen shift and CC bond cleavage. On further heating to 110°C, 2 in turn is transformed to isomeric [Fe2(CO)6−{μ-C(CH2Ph)P(Ph2)CH2PPh}] (3), arising from transfer of a phenyl group from phosphorus to carbon, and the complex [Fe2(CO)5−{μ-Ph2PCH2P(Ph)C6H4C(CH3)}] (4a), resulting from more complex rearrangement. Heating the complexes [Fe(CO)5−{μ-σ:η3(C(O)CRCH}(μ- dppm)] (R = Me (1b), Ph (1c)) gave only [Fe2(CO)2{μ-Ph2PCH2P(Ph)C6H4C(CH2R)}] (4b, 4c), the likely intermediates analogous to 2 and 3 not being detectable. The structures of 2, 3 and 4c were established by X-ray diffraction, providing an insight into the molecular manoeuvres involved in the rearrangements. In contrast to the ready thermolysis of 1a-c, in which the diphosphine and organic moieties lie cis to one another, the analogous trans complexes [Fe(CO)5{μ-σ:C(O)CRCR}(μ-dp pm)] (R = Me (1d), Ph (1e)) are stable in refluxing toluene, partly attributable to the inability of phosphorus to attack the distant metallacycle.