Synthesis and structures of (3-methyl-2-pyridyl)diphenylphosphane derivatives of metal clusters

An unsymmetric bidentate ligand (3-methyl-2-pyridyl)diphenylphosphane (P(Mepy)Ph₂) is able to react with various tetranuclear transition metal clusters such as HRuCo₃(CO)₁₂, HRuRh₃(CO)₁₂ and Rh₄(CO)₁₂. The synthesis and crystal structures of HRuCo₃(CO)₁₀(P(Mepy)Ph₂) (1), HRuRh₃(CO)₁₀(P(Mepy)Ph₂) (2), RuRh₂(CO)₉(P(Mepy)Ph) (3) and Rh₆(CO)₁₄(P(Mepy)Ph₂) (4) are described. In 1, 2 and 4 the phosphane ligand replaces the carbonyls and acts as a bridging bidentate P-N group. The formation of 3 includes degradation of both the metal cluster core and the ligand itself. One of the P-C bonds in the ligand is cleaved and the ligand caps a metal triangle with a bridging phosphido group together with the nitrogen donor. The reaction between dinuclear Rh₂(CO)₄Cl₂ and P(Mepy)Ph₂ gives a binuclear Rh₂(μ-CO)Cl₂(P(Mepy)Ph₂)₂ (5) with bridging ligands in a head-to-tail arrangement. The crystal structure is also given.     

Regiospecific insertion into the Co–Co bond of the mixed-metal cluster Co2Rh2(CO)12 by an electron-poor alkyne: X-ray diffraction structure of the butterfly cluster Co2Rh2(CO)10(μ-HCCCO2Me)

The reaction between the mixed-metal tetrahedral cluster Co₂Rh₂(CO)₁₂ (1) and the electron-poor alkyne methyl propiolate in hexane at room temperature furnishes a mixture of products consisting of Co₃Rh(CO)₁₂ (2), Co₃Rh(CO)₁₀(μ-HCCCO₂Me) (3), Co₂Rh₂(CO)₁₀(μ-HCCCO₂Me) (4), and CoRh₃(CO)₉(μ-HCCCO₂Me)₃ (5). The isolation and solution spectroscopic data of these compounds are described, and the solid-state structure of Co₂Rh₂(CO)₁₀(μ-HCCCO₂Me) determined by X-ray diffraction analysis. The title cluster crystallizes in the triclinic space group. The solid-state structure of Co₂Rh₂(CO)₁₀(μ-HCCCO₂Me) provides proof for the regiospecific insertion of the methyl propiolate ligand into the Co–Co bond of the starting cluster Co₂Rh₂(CO)₁₂. The stability of clusters 3 and 4 in the presence of added methyl propiolate is discussed.     

Polymerization and Catalytic Properties of Cluster-Containing Monomers and Polymers

Summary : Cluster-containing monomers were obtained and characterized. Mono- and disubstituted products were obtained under mild conditions via the interaction of Rh₆(CO)₁₆ with 4-vinylpyridine (4-VPy). Substitution of labile acetonitrile ligand in Rh₆(CO)₁₅NCMe by allyldiphenylphosphine (AlPPh₂) yields Rh₆(CO)₁₄(µ,η²-PPh₂CH₂CHCH₂) with formation of π-complex. The copolymerization of cluster-containing monomers synthesized with traditional monomers has been studied. It was found that Rh₆- containing monomers change neither the ligand surroundings nor the structure of cluster monomer framework during polymerization reaction. Polymer-immobilized clusters were found to be active in hydrogenation reactions of cyclohexene.     

Exploring the Reactivity of Rh<Subscript>2</Subscript> (OAc)<Subscript>4</Subscript> with 2, 2′ -Dipyridylamine

A series of three new compounds obtained from the reaction of Rh₂(OAc)₄ and 2, 2 -dipyridylamine (Hdpa) under various conditions have been characterized. All are diamagnetic and have a Rh–Rh single bond. In Rh₂(dpa)₄, 1, there are four bridging dpa anions which bind the two Rh atoms through one pyridyl N atom and one amido N atom though two of these ligands interact further with a rhodium atom through the third N atom. In the other two compounds the Hdpa ligand is neutral. Thus Rh₂(OAc)₄(Hdpa)₂, 2, is an adduct of the well known complex dirhodium tetraacetate in which the two Hdpa ligands occupy axial positions. In the third compound, Rh₂(Hdpa)₂(OAc)₂Cl₂, 3, only two acetate bridges are present. One Hdpa molecule chelates equatorially each rhodium atom and the chloride ions are axially coordinated. The Rh–Rh distances are 2. 4005(6) and 2. 4042(8) Å for 1 and 2, respectively. For 3, the Rh–Rh distance of 2. 593(1) Å is significantly longer than those in 1 and 2 because of the presence of fewer bridging ligands.     

Oxidation of bridging groups by carboxylate coordinated ligands in palladium clusters

Thermolysis of tetranuclear palladium clusters Pd₄(-Q)₄ Pd₄(-Q)₄(-O₂CR)₄ (Q=CPh₂ or CO;R=Me, CMe₃, Ph, CH₂Cl or CF₃) has been found to involve innersphere oxidation of carbene or carbonyl ligands during which an oxygen atom transfer occurs from the carboxylate group to the carbene or carbonyl ligand. The thermolysis of the carbonyl clusters gives rise to the products of CO₂ insertion into the C–H bond of benzene or toluene used as solvents forming benzoic acid from benzene and a mixture of phenylacetic and toluic acids from toluene. The reaction of [Pd(OAc)₂(PPh₃)]₂ with HCO₂H includes the transfer of an O atom from formate ligand to the P atom and cleavage of the P-Ph bond accompanied by transfer of the Ph group from PPh₃ ligand to the palladium atom. The structure of the complex formed, [Pd(-O₂PPh₂)(C₆H₅)(PPh₃)]₂, has been resolved by X-ray analysis.     

High Nuclearity Bimetallic Rhodium–Palladium Carbonyl Cluster Complexes. Synthesis and Characterization of Rh6(CO)16[Pd(PBu t 3)]3 and Rh6(CO)16[Pd(PBu t 3)]4

The reaction of Rh₄(CO)₁₂ with Pd(PBu ^t ₃)₂ yielded the high nuclearity bimetallic hexarhodium-tripalladium cluster complex Rh₆(CO)₁₆[Pd(PBu ^t ₃)]₃, 10, in 11% yield. Compound 10 was converted to the hexarhodium-tetrapalladium cluster Rh₆(CO)₁₆[Pd(PBu ^t ₃)]₄, 11, in 62% yield by reaction with an additional quantity of Pd(PBu ^t ₃)₂. Both compounds were characterized crystallographically. Structurally, both compounds consist of an octahedral cluster of six rhodium atoms with sixteen carbonyl ligands analogous to that of the known compound Rh₆(CO)₁₆. Compound 10 also contains three Pd(PBu ^t ₃) groups that bridge three Rh–Rh bonds along edges of the Rh₆ octahedron to give an overall D₃ symmetry to the Rh₆Pd₃ cluster. Compound 11 contains four edge bridging Pd(PBu ^t ₃) groups distributed across the Rh₆ octahedron to give an overall D_2d symmetry to the Rh₆Pd₄ cluster. Each Rh–Pd connection in both compounds contains a bridging carbonyl ligand that helps to stabilize the bond between the Pd(PBu ^t ₃) groups and the Rh atoms. Both compounds can be regarded as Pd(PBu ^t ₃) adducts of Rh₆(CO)₁₆.     

Ruthenium Carbonyl Cluster Complexes with Phenylgermyl Ligands from the Reactions of Ph<Subscript>3</Subscript>GeH with Ru(CO)<Subscript>5</Subscript> and Ru<Subscript>3</Subscript>(CO)<Subscript>12</Subscript>

Four new triphenylgermylruthenium carbonyl compounds HRu(CO)₄GePh₃, 14; Ru(CO)₄(GePh₃)₂, 15; Ru₂(CO)₈(GePh₃)₂, 16; and Ru₃(CO)₉(GePh₃)₃(μ-H)₃, 17 were obtained from the reaction of Ru(CO)₅ with Ph₃GeH in hexane solvent at reflux, 68 °C. The major product 14 was formed by loss of CO from the Ru(CO)₅ and an oxidative addition of the GeH bond of the Ph₃GeH to the metal atom. This six coordinate complex contains one terminal hydrido ligand. Compound 15 is formed from 14 and contains two trans-positioned GePh₃ ligands in the six coordinate complex. Compound 16 contains two Ru(CO)₄(GePh₃) fragments joined by an Ru–Ru single bond. Compound 17 contains a triangular cluster of three ruthenium atoms with three bridging hydrido ligands and one terminal GePh₃ ligand on each metal atom. When heated to 125 °C, 14 was converted to the new triruthenium compound Ru₃(CO)₁₀(μ-GePh₂)₂, 18. Compound 18 consists of a triangular tri-ruthenium cluster with two GePh₂ ligands bridging two different edges of the cluster and one bridging CO ligand. Ru₃(CO)₁₂ was found to react with Ph₃GeH at 97 °C to yield three products: 15, and two new compounds Ru₃(CO)₉(μ-GePh₂)₃, 19 and Ru₂(CO)₆(μ-GePh₂)₂(GePh₃)₂, 20 were obtained. Compound 19 is similar to 18 having a triangular tri-ruthenium cluster but has three bridging GePh₂ ligands, one on each Ru–Ru bond. Compound 20 contains only two ruthenium atoms joined by a single Ru–Ru bond that has two bridging GePh₂ ligands and a terminal GePh₃ ligand on each metal atom. All compounds were characterized by a combination of IR, ¹H NMR, single-crystal X-ray diffraction analyses. This report is dedicated to Professor Dieter Fenske on the occasion of his 65th birthday for his many pioneering contributions to the chemistry of metal chalcogenide cluster complexes.     

Organometallic chemistry and homogeneous catalysis of Rh and Rh-Co mixed metal carbonyl clusters

The reactions of hydrosilane and/or alkyne as well as isonitriles with rhodium and rhodium cobalt mixed metal carbonyl clusters, e.g., Rh₄(CO)₁₂ and Co₂Rh₂(CO)₁₂, are studied. Novel mixed metal complexes, e.g., CoRh(CO)₅ (HCCBu ⁿ ), (R₃Si)₂Rh(CO) _n Co(CO)₄, Rh(R–NC)₄Co(CO)₄, Co₂Rh₂(CO)₁₀(HCCR), and Co₂Rh₂(CO)₉(HCCBu ⁿ ), are synthesized and identified. The catalytic activities of these rhodium and rhodium-cobalt mixed metal complexes are examined in hydrosilyation, silylformylation, and novel silylcarbocyclization reactions. Possible mechanisms for these reactions are proposed and discussed.     

Unsaturation in binuclear cyclopentadienylrhodium carbonyls: Comparison with their cobalt analogs

The Cp₂Rh₂(CO)_n (n = 4, 3, 2, 1) derivatives have been examined by density functional theory using the BP86 and MPW1PW91 functionals. The known tricarbonyl Cp₂Rh₂(CO)₃ is predicted to have a singly bridged structure with a predicted Rh–Rh single bond distance of ～2.70 Å in close agreement with the experimental value of 2.68 Å, determined by X-ray crystallography. In contrast to the cobalt analog, no evidence for a triply bridged Cp₂Rh₂(μ-CO)₃ structure was found. The known dicarbonyl Cp₂Rh₂(CO)₂ is predicted to have a doubly bridged structure with a predicted RhRh double bond distance of 2.58 Å in close agreement with the experimental RhRh double bond distance of 2.564 Å, found by X-ray crystallography for the permethylated derivative (η⁵-Me₅C₅)₂Rh₂(μ-CO)₂. The monocarbonyl Cp₂Rh₂(CO) is predicted to have a four-electron donor bridging carbonyl group with a Rh–O distance of ～2.5 Å and a RhRh double bond distance of ～2.54 Å. This differs from Cp₂Co₂(CO) which was previously predicted to have only a two-electron donor bridging carbonyl group with a long Co?O distance and a short CoCo distance of ～2.0 Å suggesting a formal triple bond. For Cp₂Rh₂(CO)₄ doubly bridged trans and cis isomers were found within ～1.0 kcal/mol in energy with non-bonding Rh?Rh distances of ～3.2 Å. However, these Cp₂Rh₂(CO)₄ isomers are predicted to be unstable with respect both to CO loss to give Cp₂Rh₂(CO)₃ and to fragmentation into two CpRh(CO)₂ units.     

The synthesis and structural characterization of Os3(CO)8[Si(OMe)3][μ-PMe2(C6H4](μ-H)2: An unusual unsaturated triosmium cluster complex

The reaction of Os₃(CO)₁₀(NCMe)[Si(OMe)₃](-H),1, with PMe₂Ph yielded the new complex Os₃(CO)₁₀(PMe₂Ph)[Si(OMe)₃](-H),2 by substitution of the MeCn ligand with the phosphine ligand. When heated to 125°C compound2 was decarbonylated and transformed into the new unsaturated cluster complex Os₃(CO)₈[-PMe₂(C₆H₄)][Si(OMe)₃](-H)₂,3 in 54% yield. Compound3 was characterized by a single crystal X-ray diffraction analysis, osmium bonds. The phenyl ring of the phosphine ligand has undergoneortho-metallation by a neighboring metal atom. A terminally coordinated Si(OMe)₃ ligand is coordinated to the third osmium atom. The cluster is unsaturated by the amount of 2 electrons, and there is an open coordination site on the siloxyl substituted osmium atom that is partially filled by a weak interaction with one of the -bonds of theortho-metalled phenyl ring. Complex3 reacts with CO at 1 atm to reform compound2 in 85% yield in 5 h at 40°C. Crystal Data: for3: space group = P2₁/n,a = 9.911(2) Å,b = 18.451(6) Å,c = 14.872(2) Å, = 95.64(2)°,Z = 4, 1994 reflections,R = 0.028.     

Synthesis and structure of Os3(μ-H)3(CO)9(μ3-Sn)Os3(μ-H)(CO)10(PEt2Ph): The first osmium cluster containing a face-capping tin atom

Pyrolysis a the cluster Os₃(µ-H h (CO)₁₀ (SnMe2 H) produced an as yet unidentified purple duster, which upon reaction with PEt₂Ph at room temperature, gave essentially a quantitative yield of the cluster Os₃(µ-H)₃(CO)₉(µ₃-Sn) Os₃(µ-H)(CO)₁₀(PEt₂Ph), 4. The X-ray structure of 4 (as the toluene solvate) shows that it consists Or two Os, triangles linked through a µ₄-Sn unit, such that one of the Os₃ triangle is µ₃-bonded to the Sn atom (Os-Sn range 2.689(2)–2.707(2) Å) and the other is bonded via a single covalent bond (Os-Sn = 2.643(2) Å). The phosphine ligand occupies the equatorial site on a second osmium atom a be latter Os₃ moiety that is syn to the Sn atom; the unique bridging hydride ligarid is believed to occupy a site that Acis to both the P and Sn atoms. Crystallographic data for compound4. 0.5C₇H₈: space group,P ; ca= 11862(4) Å,b = 12.940(4) Å,c = 16.513(5) Å, =68.96(3),=80.60(3)°,=62.49(2).R=0.029, 4118 observed reflections.     

Elektronenstruktur von Rh4(CO)12, ein Modell für linear und brückenförmig gebundenes CO an Rhodiumkatalysatoren

Electronic Structure of Rh₄(CO)₁₂, a Model for Linear- and Bridge-bonded CO on Rhodium Catalysts The electronic structure of the Rh₄(CO)₁₂ cluster containing both linear- and bridgebonded CO groups has been studied by the EHMO method and compared with that of the Ir₄(CO)₁₂ cluster with only linear-bonded CO ligands. The charge distribution shows a distinctly higher π-back donation for the bridge-bonded CO groups. This result is compared with experimental data such as bond lengths, force constants of the C? O stretching frequencies and XPS data. It allows further an interpretation of results of CO hydrogenation on supported rhodium catalysts and on rhodium model complexes.     

Triosmium cluster with the bridging aminooxime derivative of pinane: Synthesis,crystal structure and conformational analysis

The reaction of 1R,2R,5R-2-dimethylamino-2,6,6-trimethylbicyclo[3.1.1]heptane-3-one oxime (pinaneoxime) with Os₃(CO)₁₀(NCMe)₂ was used to synthesize the (μ-H)Os₃(μ-κ¹-O-N=C₁₂H₂₁N)(CO)₁₀ cluster with coordination of the ligand through the oxime O atom and invariable terpenoid structure. The structure of the synthesized cluster was determined by X-ray diffraction analysis. The theoretical conformational analysis of the above cluster in a solution and in crystal state was performed by a combined MM3/MERA method. The rotation of a ligand about the O(1)-N(2) bond was found impossible due to a high energy barrier (E > 550 kJ/mol).     

Structural characterization of the anions [Rh6(CO)15X]− [X = COEt and CO(OMe)]

The anions [Rh₆(CO)₁₅X]^?, with X = COEt and CO(OMe), have been studied by single-crystal X-ray diffraction. They contain octahedral rhodium clusters, with mean metalmetal distances of 2.779 and 2.765 », respectively. The carbonyl stereochemistry in the two anions is similar to that of Rh₆(CO)₁₆, with one terminal CO group replaced by the X ligand. The RhC(carbomethoxy) bond distance (1.96(2) ») is significantly shorter than the RhC(acyl) distance (2.06(2) »).     

Catalytic hydrogenation of 1,3-trans-pentadiene over Rh4(CO)12 supported on γ-Al2O3

Rh₄(CO)₁₂ anchored on γ-Al₂O₃ (Rh₄(CO)₁₂/Al₂O₃) has been studied as a catalyst for the hydrogenation of 1,3-trans-pentadiene. Under mild conditions (1 atm H₂ and temperatures between 60°C and 80°C) hydrogenation occurs at only one of the double bonds of the diene, and analysis of the products shows that the terminal double bond is preferentially hydrogenated. Hydrogenation of the second double bond of the conjugated diene occurring only after all the 1,3-trans-pentadiene has been consumed. In this respect Rh₄(CO)₁₂/Al₂O₃ behaves like toluene solutions of Rh₄(CO)₁₂. Anchoring of Rh₄(CO)₁₂ on the solid support gives a catalyst which is less active but more stable than toluene solutions of Rh₄(CO)₁₂. The effects of CO and of triphenylphosphine on catalytic activity and on specificity of Rh₄(CO)₁₂/Al₂O₃ have also been investigated and both shown to cause a reduction of the rate of hydrogenation of 1,3-trans-pentadiene.     

Ligand substitution in HC(O)CCo3(CO)9 with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd): Diphosphine ligand fluxionality, decarbonylation of the formyl moiety and competitive P-Ph bond cleavage reactivity

The reaction of the formyl-capped cluster HC(O)CCo₃(CO)₉ (1) with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in the presence of added Me₃NO leads to the production of the disubstituted cluster HC(O)CCo₃(CO)₇(bpcd) (2). Thermolysis of 2 in toluene at 60 °C gives the methylidyne-capped cluster HCCo₃(CO)₇(bpcd) (4) and the phosphido-bridged cluster Co₃(CO)₇[μ₂,η²,η¹-P(Ph)CC(PPh₂)C(O)CH₂C(O)] (5). Cluster 4 has been independently prepared from HCCo₃(CO)₉ and bpcd and shown to serve as the precursor to 5. The new clusters 2, 4, and 5 have been isolated and characterized in solution by IR and NMR (¹H and ³¹P) spectroscopies and their solid-state structures have been established by X-ray diffraction analyses. Both clusters 2 and 4 contain 48e- and exhibit triangular Co₃ cores with a chelating and bridging bpcd ligand in the solid state, respectively. The structure of 5 provides unequivocal support for the loss of the methylidyne capping ligand and P-Ph bond cleavage attendant in the activation of 4 and confirms the presence of the face capping seven-electron μ₂,η²,η¹-P(Ph)CC(PPh₂)C(O)CH₂C(O) ligand in the final product. The fluxionality displayed by the bpcd ligand in clusters 2 and 4 and the decarbonylation behavior of the formyl moiety in the former cluster are discussed relative to related alkylidyne-capped Co₃ derivatives.     

Further studies of the reactions of PtRu5(μ6-C)(CO)16 with alkynes: The preparation and structural characterizations of PtRu5(CO)13(μ-EtC2Et)(μ3-EtC2Et)(μ5-C) and Pt2Ru6(CO)17(μ-η5-Et4C5)(μ3-EtC2Et) (μ6-C)

The reaction of PtRu₅(CO)₁₆(μ₆-C),1 with 3-hexyne in the presence of UV irradiation produced two new electron-rich platinum-ruthenium cluster complexes PtRu₅(CO)₁₃(μ-EtC₂Et)(μ₃-EtC₂Et)(μ₅-C),2 (20% yield) and Pt₂Ru₆(CO)₁₇(μ-η⁵-Et₄C₅)(μ₃-EtC₂Et) (μ₆-C),3 (7% yield). Both compounds were characterized by single-crystal X-ray diffraction analyses. Compound2 contains of a platinum capped square pyramidal cluster of five ruthenium atoms with the carbido ligand located in the center of the square pyramid. A EtC₂Et ligand bridges one of the PtRu₂ triangles and the Ru-Pt bond between the apical ruthenium atom and the platinum cap. The structure of compound3 consists of an octahedral PtRu₅ cluster with an interstitial carbido ligand and a platinum atom capping one of the PtRu₂ triangles. There is an additional Ru(CO)₂ group extending from the platinum atom in the PtRu₅ cluster that contains a metallated tetraethylcyclopentadienyl ligand that bridges to the platinum capping group. There is also a EtC₂Et ligand bridging one of the PtRu₂ triangular faces to the capping platinum atom. Compounds2 and3 both contain two valence electrons more than the number predicted by conventional electron counting theories, and both also possess unusually long metal-metal bonds that may be related to these anomalous electron configurations. Crystal data for2, space group Pna2₁,a=19.951(3) Å,b=9.905(2) Å,c=17.180(2) Å,Z=2, 1844 reflections,R=0.036; for3, space group Pna2₁,α=13.339(1) Å,b=14.671(2) Å,c=11.748(2) Å, α=100.18(1)°, β=95.79(1)°, γ=83.671(9)°,Z=2, 3127 reflections,R=0.026.     

Synthesis, characterisation of two hexa-iron clusters with {Fe2S2(CO)x} (x = 5 or 6) fragments and investigation into their inter-conversion

Reaction of a trithiol ligand, 2-(mercaptomethyl)-2-methylpropane-1,3-dithiol (H₃L), with tri-iron dodecacarbonyl in toluene produces two hexa-iron clusters (1 and 2). The two clusters are characterised crystallographically and spectroscopically. NMR spectroscopy reveals that the cluster 2 exists in two conformations in equilibrium 2_anti ⇔ 2_syn and the equilibrium constant K_eq = 0.55 under CO atmosphere. In the cluster 2, the central {Fe₂S₂(CO)₆} sub-unit is flanked by two identical {Fe₂S₂(CO)₆} satellite sub-units through thiolate linkages whereas one of the thiolate linkages can further form Fe-S bond with the proximal Fe atom in one of the two satellite sub-units to produce the cluster 1 by expelling one CO. This conversion can be entirely reversed by continuously purging CO through the solution of the cluster 1. As suggested by DFT calculations, the conversion features a key step, the rotation of the Fe_prox(CO)₃ to expose a vacant site for exogenic ligand binding (the S atom from the central sub-unit in this case) with concomitant switch for one of the three CO ligands in the unit of Fe_prox(CO)₃ from terminal to bridging orientation. The conversion from the clusters 1-2 involving one CO uptake is much faster than its reverse process since the latter is an endergonic process characterised by large reaction barriers, as revealed by the DFT calculations.     

Reactions of linked tetrahedron clusters [Co2(CO)6(μ-HC2CH2O)-]2R with Rh2(CO)4Cl2 to give mixed-metal linked alkyne-bridged butterfly clusters containing C2Co2Rh2 unit

The reactions of compound Rh₂(CO)₄Cl₂, 1 with [Co₂(CO)₆(μ-HC₂CH₂O)-]₂R (R = C₆H₄, 2; (COCH₂)₂, 3; C₆H₄-1,4-(CO)₂, 4; (COCH)₂, 5; (CO)₂, 6) in benzene at 60 °C produce five new mixed-metal linked clusters Rh₂Co₂(CO)₁₀(μ₄,η²-HC₂CH₂O-R-OCH₂C₂H-μ)Co₂(CO)₆ (R = C₆H₄, 7a; (COCH₂)₂, 7b; C₆H₄-1,4-(CO)₂, 7c; (COCH)₂, 7d; (CO)₂, 7e) and five known linked octahedral clusters [Rh₂Co₂(CO)₁₀(μ₄,η²-HC₂CH₂O-)]₂R (R = C₆H₄, 8a; (COCH₂)₂, 8b; C₆H₄-1,4-(CO)₂, 8c; (COCH)₂, 8d; (CO)₂, 8e), respectively. Treatment of clusters 7a-8e in benzene at room temperature under air for 24 h with stirring afford the precursor clusters 2-6, respectively. The structure of cluster 7a has been determined by single-crystal X-ray diffraction. The linked cluster 7apossesses two isomers A and B in its structures, the Rh₂(CO)₄ unit inserts into one of two Co-Co bonds and coordinates to the Co₂C₂ core forming one distorted closo-Rh₂Co₂C₂ octahedron framework which is connected to the Co₂C₂ tetrahedron unit via C₆H₄(OCH₂)₂-1,4 as a bridging ligand. All clusters were characterized by C, H elemental analysis, IR and ¹H NMR spectroscopy.     

Facile Synthesis and Versatile Reactivity of an Unusual Cyclometalated Rhodium(I) Pincer Complex

The synthesis of the reactive PN(C^H) ligand 2‐di(tert‐butylphosphanomethyl)‐6‐phenylpyridine ( 1^H ) and its versatile coordination to a Rh^I center is described. Facile C?H activation occurs in the presence of a (internal) base, thus resulting in the new cyclometalated complex [Rh^I(CO)(κ³‐P,N,C‐ 1 )] ( 3 ), which has been structurally characterized. The resulting tridentate ligand framework was experimentally and computationally shown to display dual‐site proton‐responsive reactivity, including reversible cyclometalation. This feature was probed by selective H/D exchange with [D₁]formic acid. The addition of HBF₄ to 3 leads to rapid net protonolysis of the Rh?C bond to produce [Rh^I(CO)(κ³‐P,N,(C?H)‐ 1 )] ( 4 ). This species features a rare aryl C?H agostic interaction in the solid state, as shown by X‐ray diffraction studies. The nature of this interaction was also studied computationally. Reaction of 3 with methyl iodide results in rapid and selective ortho‐methylation of the phenyl ring, thus generating [Rh^I(CO)(κ²‐P,N‐ 1^Me )] ( 5 ). Variable‐temperature NMR spectroscopy indicates the involvement of a Rh^III intermediate through formal oxidative addition to give trans‐[Rh^III(CH₃)(CO)(I)(κ³‐P,N,C‐ 1 )] prior to C?C reductive elimination. The Rh^III–trans‐diiodide complex [Rh^I(CO)(I)₂(κ³‐P,N,C‐ 1 )] ( 6 ) has been structurally characterized as a model compound for this elusive intermediate.