J. Nicola Nicholls

High-Nuclearity Carbonyl Clusters: Their Synthesis and Reactivity

Publisher Summary This chapter discusses the synthesis and reactivity of high-nuclearity carbonyl clusters (HNCC). The chapter defines HNCC as homo- or heteronuclear carbonyl clusters of transition and main group metals containing five or more metal atoms, each of which is linked to the metal core by at least one M—M bond. The chapter discusses the chemistry of the HNCC in terms of reaction type rather than metal by metal. All the HNCC that have been characterized to date by X-ray crystallographybare listed in a table together with the methods used for their synthesis and references to their spectroscopic data. Synthetic methods used for the preparation of HNCC may be classified in to two broad categories, depending on whether or not they involve the use of redox conditions; they are—syntheses not involving redox conditions and syntheses requiring reducing or oxidizing conditions. The synthesis of HNCC by redox condensation involves the reaction of an anionic mononuclear or polynuclear carbonyl species with a neutral, cationic, or even anionic fragment. A relatively small number of HNCC have been synthesized by oxidation of other carbonyl clusters. The oxidation reactions of a number of large carbide clusters have been found to provide relatively selective synthetic routes to clusters of reduced nuclearity. Oxidation of HNCC often results in cluster fragmentation or, as a consequence of redox condensation. X-Ray diffraction has often been successful in the determination of hydrogen atom position in HNCC hydrides.

The synthesis of [Ru5C(CO)15] by the carbonylation of [Ru6C(CO)17] and the reactions of the pentanuclear cluster with a variety of small molecules: the X-ray structure analyses of [Ru5C(CO)15], [Ru5C(CO)15(MeCN)], [Ru5C(CO)14(PPh3)], [Ru5C(CO)13(PPh3)2], and [Ru5(µ-H)2C(CO)12{Ph2P(CH2)2PPh2}]

The hexaruthenium cluster [Ru6C(CO)17] reacts with CO at 70 °C and 80 atm to produce [Ru5C(CO)15](1) and [Ru(CO)5]. Complex (1) crystallises in space group P21/c with a= 16.448(3), b= 14.274(2), c= 20.834(4)A, β= 91.36(2)°, and Z= 8. The structure was found to be isomorphous with the analogue [Os5C(CO)15], and was refined to R= 0.051 for 3 256 diffractometer data. The five Ru atoms adopt a square-pyramidal geometry with an exposed carbido-atom lying 0.11 (2)A beneath the basal plane. Reaction of complex (1) with the nitrogen-donor ligand MeCN yields the adduct [Ru5C(CO)15(MeCN)](2) which exhibits a bridged butterfly arrangement of metal atoms with a central carbido-atom. The complex crystallises in space group P21/n with a= 14.116(6), b= 18.167(7), c= 10.276(4)A, β= 95.14(3)°, and Z= 4; the structure was solved by direct methods and difference techniques and refined to R= 0.047 for 1 604 diffractometer data. Reactions of complex (1) with tertiary phosphine ligands PR3[R = Ph (3) or MePh2(4)] or Ph2P(CH2)nPPh2[n= 1 (5) or 2 (6)] produce the substituted complexes [Ru5C(CO)15-m(PR3)m][m= 1 (3a, 4a), 2 (3b, 4b), or 3 (3c, 4c)] or [Ru5C(CO)13{Ph2P(CH2)nPPh2}][n= 1 (5) or 2 (6)]. The structures of these complexes are closely related to that of (1). Complex (3a) crystallises in space group Pn with a= 9.953(2), b= 12.247(2), c= 14.703(3)A, β= 91.23(2)°, and Z= 2, (3b) in space group P21/c with a= 15.923(4), b= 12.494(3), c= 25.210(7)A, β= 93.28(2)°, and Z= 4. Both structures were solved by a combination of direct methods and Fourier techniques and were refined to R= 0.021 for 3 305 reflections (3a) and R= 0.039 for 4 127 reflections (3b), respectively. Hydrogenation of (6) gives the dihydro-complex [Ru5(µ-H)2C(CO)12{Ph2P(CH2)2Ph2}] which crystallises in space group P21 with a= 12.210(4), b= 18.602(6), c= 18.409(6)A, β= 97.63(2)°, and Z= 4. The structure was solved using the same techniques as the other complexes and refined to R= 0.064 for 3 510 diffractometer data. Treatment of complex (1) with halide ions gives the anionic clusters [Ru5C(CO)15X]–(X = F, Cl, Br, or I) whose structures are similar to that of (2). Protonation of these anions gives the monohydrido-clusters [Ru5H(C)(CO)15X]. With Cl2 and Br2 complex (1) undergoes fragmentation to give dimers [Ru2(CO)6X4](X = Cl or Br); in contrast, reaction with I2 gives [Ru5C(CO)15I2].

Metal-carbido complexes of ruthenium and osmium

Abstract The methods available for the preparation of the carbonylcarbido clusters of ruthenium and osmium are summarised. The various techniques utilised in the determination of the structure of these compounds are reviewed and the reactivity the deca-, hexa- and pentanuclear carbido cluster compounds are described. The carbido atom in the higher nuclearity systems appears to stabilise the M n C unit against fragmentation, and allows investigation of an extensive chemistry of the metal cage.

The reductive activation of [M5C(CO)15](M=Ru or Os) and subsequent reactions of the dianion [Os5C(CO)14)2−, carbonylation of [M5C(CO)15](M=Ru or Os) and the crystal structures of [Os5C(CO)16], [N(PPh3)2]2[Os5C(CO)14], and [Os5C(CO)14{Au(PPh3)}2]

High pressure infrared (h.p.i.r.) studies indicate that the cluster [Ru5C(CO)15](1) adds carbon monoxide under relatively mild conditions (20 °C, 80 atm) to give [Ru5C(CO)16](2), while under more forcing conditions (90 °C, 80 atm) the cluster (2) reverts back to (1). The osmium analogue, [Os5C(CO)15](3), gives [Os5C(CO)16](4) at 70 °C and 50 atm but may be obtained in quantitative yield from an autoclave reaction in the absence of solvent. Complex (4) crystallises in space group P with a= 10.017(3), b= 15.823(5), c= 16.507(8)A, α= 96.78(3), β= 103.20(3), γ= 93.41(2)°, and Z= 4. The structure was solved by a combination of direct methods and Fourier-difference techniques and refined by blocked full-matrix least squares to R= 0.073 for 6 120 reflections. The five Os atoms define a ‘bridged-butterfly’ configuration with a carbide at the centre. There are four terminal carbonyl groups bound to the bridging metal atom and three to each of the other four metal atoms. A h.p.i.r. study of the reaction of (4) with H2 has shown that at a pressure of 75 atm and at temperatures around 90 °C the cluster [Os5H2(C)(CO)15](5) is produced. The electrochemical or chemical reduction of [M5C(CO)15][M = Ru (1) or Os (3)] produces the corresponding dianion [M5C(CO)14]2–[M = Ru (6) or Os (7)]. An X-ray analysis of the [N(PPh3)2]+ salt of (7) shows that the squarepyramidal Os5C core geometry of (3) is retained. One of the Os–Os bonds in the basal plane is symmetrically bridged by a carbonyl group. The remaining 13 carbonyl ligands are co-ordinated terminally, two each to the carbonyl-bridged metal atoms, and three each to the other three metal atoms. The salt crystallises in space group P with a= 13.244(6), b= 14.648(9), c= 21.963(14)A, α= 86.78(5), β= 85.54(5), γ= 81.22(5)°, and Z= 2. The structure was solved using the same techniques as for (4) and refined by blocked-cascade least squares to R= 0.065 for 5 780 observed diffractometer data. The dianion (7) reacts with two equivalents of [Au(PPh3)Cl] to give the neutral complex [Os5C(CO)14{Au(PPh3)}2](10) which has also been characterised crystallographically. In (10) the Os5C core shows significant distortions from square-pyramidal geometry. Two opposite Os(basal)–Os(apical) bonds are bridged by the Au atoms of the Au(PPh3) ligands and these two bonds are significantly longer than the other two unbridged Os(basal)–Os(apical) bonds. Two carbonyl groups are bonded terminally to the apical Os atom, and three each to the four basal Os atoms. This complex crystallises in space group P21/c with a= 20.307(4), b= 9.843(2), c= 27.980(6)A, β= 100.53(2)°, and Z= 4. The structure was solved and refined as for (7) to R= 0.060 for 7 013 observed diffractometer data.

Formation of new halogeno mixed-metal clusters by oxidative addition of triphenylphosphinegold(I) halides to [Ru5C(CO)15]: crystal and molecular structures of [Ru5C(CO)15{µ-Au(PPh3)}Cl] and [Ru5C(CO)14{µ-Au(PPh3)}(µ-Br)]

In CH2Cl2 the compound [Ru5C(CO)15] reacts with [Au(PPh3)X](X = Cl or Br) to form [Ru5C(CO)15{µ-Au(PPh3)}X] which loses one mole of CO to form [Ru5C(CO)14{µ-Au(PPh3)}(µ-X)], where X functions as a three-electron donor. The crystal structures of [Ru5C(CO)15{µ-Au(PPh3)}Cl] and [Ru5C(CO)14{µ-Au(PPh3)}(µ-Br)] are reported. The complex [Ru5C(CO)15{µ-Au(PPh3)}Cl] crystallizes in the triclinic space group P with a= 15.333(3), b= 15.865(3), c=18.813(7)A, α= 84.29(4), β= 84.41 (4), γ= 61.88(2)°, and Z= 4 with two distinct molecules per asymmetric unit. For 5 487 reflections the structure refined to R 0.0703 and R′ 0.0539. The molecule contains a bridged butterfly configuration of ruthenium atoms (seven Ru–Ru bonds) with the gold atom bridging the butterfly ‘hinge’ bond and the chloride attached terminally to the ruthenium that spans the wing tips of the butterfly. All ruthenium atoms remain bonded to the carbide atom, but the gold and chlorine show no interaction with the carbide. For [Ru5C(CO)14{µ-Au(PPh3)}(µ-Br)] the space group is monoclinic, P21/c, with a= 8.967(1), b= 29.767(7), c= 15.010(3)A, β= 92.16(1)°, and Z= 4. For 2 950 reflections, the refinement converged with R 0.0432 and R′ 0.0434. The molecule is best described as a distorted square pyramid of ruthenium atoms in which one apical to basal Ru–Ru bond is replaced by a bridging three-electron donating bromine. The complex is derived from the 15 carbonyl complex by displacement of one of the hinge carbonyls by the halide.

Site selectivity in the reactions of nucleophiles with [Ru5C(CO)15]: X-ray analysis of [Ru5C(CO)14(µ-η2-MeCO)(AuPPh3)] and [Ru5C(CO)13(η5-C5H5)(AuPPh3)], the first high nuclearity cyclopentadienylruthenium cluster

The cluster [Ru5C(CO)15]reacts with LiMe, followed by [Ph3PAu][Cl], to give [Ru5C(CO)14(µ-η2-MeCO)(AuPPh3)] while reaction with NaC5H5 followed by [Ph3PAu][ClO4], gives [Ru5C(CO)13(η5-C5H5)(AuPPh3)]; X-ray analysis has confirmed that the nucleophile has attacked a carbonyl ligand in the former case but a metal centre in the latter.

Reactions of [Ru5C(CO)15], involving bridging ligands : crystal and molecular structures of the complexes [Ru5(H)C(CO)14(SEt)], [Ru5(H)C(CO)13(PPh3)(SEt)], [Ru5(H)C(CO)12(PPh3)(SEt)], and [Ru5C(CO)13(PPh3){µ-Au(PPh3)}(µ-I)]

The cluster [Ru5C(CO)15] reacts with H2S, H2Se, and HSR (R = Me or Et) to give [Ru5(H)C(CO)14(SH)], [Ru5(H)C(CO)14(SeH)], and [Ru5(H)C(CO)14(SR)], respectively. The complex [Ru5(H)C(CO)14(SEt)] crystallises in space group P21/n with a= 15.315(3), b= 16.739(4), c= 10.286(3)A, β= 89.31(2)°, and Z= 4. The structure was solved by a combination of direct methods and Fourier-difference techniques, and refined by blocked-cascade least squares to R= 0.032 for 4134 observed diffractometer data. The Ru5 metal arrangement is intermediate between a square-based pyramid and a bridged ‘butterfly’ with a carbido-carbon at the centre of the cluster. The sulphur atom of the SEt group bridges one edge of the square pyramid where the Ru ⋯ Ru separation is 3.410(1)A. In the reaction of [Ru5C(CO)15] with HSEt the postulated intermediate [Ru5(H)C(CO)15(SEt)] was not isolated. The first product was [Ru5(H)C(CO)14(SEt)](4). When (4) is heated to 81 °C a further molecule of CO is lost and the complex [Ru5(H)C(CO)13(SEt)] isolated. A phosphine derivative of this complex was also prepared and characterised crystallographically; [Ru5(H)C(CO)13(PPh3)(SEt)](6) crystallises in space group P21/c with a= 15.892(2), b= 11.474(1), c= 21.387(2)A, β= 92.50(1)°, and Z= 4. The structure was solved and refined using the same techniques as for (4) to R= 0.036 for 5 861 reflections. The structure resembles that of (4) with the SEt group bridging a long Ru ⋯ Ru edge [3.438(1)A] but with one of the carbonyl groups on a Ru atom associated with the SEt bridge replaced by a phosphine ligand. An analogous reaction occurs when [Ru5C(CO)14{µ-Au(PPh3)}(µ-I)] is heated in heptane to give [Ru5C(CO)13{µ-Au(PPh3)}(µ-I)]. This complex also readily takes up phosphine to give [Ru5C(CO)13(PPh3){µ-Au(PPh3)}(µ-I)](12), which has been characterised crystallographically, crystallising in space group P with a= 9.899(3), b= 14.628(6), c= 18.788(7)A, α= 100.29(3), β= 91.31(3), γ= 93.69(3)°, and Z= 2. The structure was solved and refined as described above to R= 0.042 for 6 075 reflections. The general geometry of the Ru5C core observed in (6) is retained and the iodine ligand bridges a long Ru ⋯ Ru edge [3.526(1)A], and the Au(PPh3) group replaces the bridging hydride. Further heating of the cluster (6) results in the loss of a further CO ligand to give [Ru5(H)C(CO)12(PPh3)(SEt)](7) which may exist in two isomeric forms. The structure of one of the isomers shows that Ru–Ru bond formation has occurred and the geometry of the Ru5C core may be described as a centred, square-based pyramid. The SEt group now bridges a basal Ru–Ru edge [2.698(1)A] and the phosphine ligand is co-ordinated to a basal Ru atom. The complex (7) crystallises in space group P with a= 10.162(2), b= 13.807(4), c= 14.660(4)A, α= 78.20(2), β= 74.12(2), γ= 87.38(2)°, and Z= 2. This converged to R = 0.041 for 4 050 reflections. The adducts [Ru5C(CO)15{µ-Au(PPh3)}X](X =Cl or Br) and their derivatives [Ru5C(CO)14{µ-Au(PPh3)}X] react with PPh3 to eliminate‘ Au(PPh3)X ’ and produce [Ru5C(CO)14(PPh3)].

The metal—carbide stretching frequencies in the clusters [M5C(CO)15] (M = Ru, Os) and their derivatives as an aid to cluster structure determination

Abstract The IR spectra of a number of derivatives of the metal clusters [M 5 C(CO) 15 ] (M = Ru, Os) have been recorded, and the frequencies of the metal—carbide stretching modes measured. These are shown to depend in a simple manner on the cluster geometry, and the use of these frequencies as structural indicators is proposed. The observed frequencies are assigned to particular metal—carbide stretching modes.

Synthesis and X-ray crystallographic characterisation of the diphosphane bridged cluster [Ir4(CO)11PhPPPhlr4(CO)9(AuPEt3)2]

Deprotonation of [Ir4(CO)11PPhH2] followed by oxidation with Ag[ClO4] in the presence of [AuPEt3]+ affords the cluster [Ir4(CO)11PhPPPhIr4(CO)9(AuPEt3)2], which has been shown by an X-ray analysis to contain an Ir4 and an Ir4Au2 unit linked by adiphosphane (PhPPPh) ligand.

A high-pressure infrared study of the stability of some ruthenium and osmium clusters to CO and H2 under pressure

A high-pressure i.r. study has been made of the stability of some high-nuclearity carbonyl clusters of ruthenium and osmium to carbon monoxide and hydrogen, and of the thermal stabilities of these clusters under an inert atmosphere. In solution, the hexanuclear cluster [Os6(CO)18] reacts with CO (90 atm, 160 °C, 1 h) to produce the new pentanuclear cluster [Os5(CO)19] and [Os(CO)5]. In contrast, in the solid state [Os6(CO)18] adds 2 mol of CO to form [Os6(CO)20]. The pentanuclear carbonyl [Os5(CO)19] undergoes reaction with CO to give both [Os3(CO)12] and [Os2(CO)9], and with [Os2(CO)9] to give [Os7(CO)21]. On heating in an inert atmosphere [Os5(CO)19] loses CO to generate [Os5(CO)16]. This reaction is reversible. Reaction of [Os5(CO)16], [Os5H2(CO)16], [Os6(CO)18], or [Os6H2(CO)18] with H2 under moderate pressures and temperatures gives [OS4H4(CO)12] and [OsH2(CO)4]; [Os5(CO)19] first produces [Os5(CO)16] and proceeds to the same products. On carbonylation under pressure [Ru3(CO)12] yields [Ru(CO)5], and [Ru6(CO)17C] gives a mixture of [Ru5(CO)15C] and [Ru(CO)5]. Pyrolysis of [Ru6H2(CO)18] under argon at 120 °C gives the hexanuclear carbide [Ru6(CO)17C] in high yield.