The reactivity of the labile cluster Os3(CO)10(MeCN)2 (1) with the monofunctionalized heterocyclic ligands 6-R-2,2′-bipyridine (where R = Et, Ph) has been investigated. The alkyl-substituted heterocycle 6-Et-2,2′-bipyridine reacts with 1 in refluxing CH2Cl2 to give an isomeric mixture of HOs3(CO)9(N2C12H11) due to cyclometalation of the side-chain ethyl group (2) and ortho metalation of the unsubstituted bipyridine ring (3). The solid-state structure of the latter cluster, HOs3(CO)9(N2C10H6-6-Et) (3), has unequivocally established the site of the C-H bond activation in the product. Treatment of 1 with the aryl-substituted ligand 6-Ph-2,2′-bipyridine proceeds similarly with ortho metalation at the ancillary phenyl group and the C-6′ ortho site of the unsubstituted bipyridine ring, as verified by 1H NMR spectroscopy. The X-ray diffraction structure of the thermodynamically more stable bipyridine-metalated cluster HOs3(CO)9(N2C10H6-6-Ph) (5) has been determined. The course of these reactions is discussed with respect to our recent study involving the reaction of cluster 1 with the ligand 6-Me-2,2′-bipyridine.

Displacement of the labile THF molecules in BrRe(CO)3(THF)2 (1) by the diphosphine ligands 2-(ferrocenylidene)-4,5-bis(diphenylphosphino)4-cyclopenten-1,3-dione (fbpcd) and 2-(3-ferrocenylprop-2-ynylidene)-4,5-bis(diphenylphosphino)4-cyclopenten- 1,3-dione (fpbpcd) yields the mononuclear compounds fac-BrRe(CO)3(fbpcd) (2) and fac-BrRe(CO)3(fpbpcd) (3), respectively. The new ligand fpbpcd ligand has been synthesized from 3-ferrocenylpropynal and the parent diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) through a Knoevenagel condensation. 2 and 3 have been isolated and fully characterized by IR and NMR spectroscopies (1H and 31P), ESI mass spectrometry, and X-ray diffraction analysis in the case of 3. The electrochemical properties of compounds 2 and 3 have been examined by cyclic voltammetry, and the nature of the HOMO and LUMO levels in these systems has been confirmed by MO calculations at the extended Hückel level. The redox and MO data are discussed relative to the redox and orbital properties of related functionalized diphosphines based on the bpcd platform.

Treatment of Os(CO)(10)(MeCN)(2) (1) with the heterocyclic ligand 6-methyl-2,2'-bipyridine (6-Me-2,2'-bpy) at room temperature leads to the formation of the isomeric hydride-bridged clusters HOs3(CO)(9)(mu(2)-CH2N2C10H7) (2) and HOs3(CO)(9)(mu(2)-N2C11H9) (3). The cyclometalation of the ancillary 6-Me group in 2 and the ortho metalation of the nonsubstituted pyridyl ring in 3 have been confirmed by spectroscopic and crystallographic methods. Thermolysis of 2 leads to the formation of 3 and the dihydride cluster H2Os3(CO)(8)(mu(3)-N2C11H8) (4); the latter cluster, whose structure has been crystallographically determined, derives from a formal loss of CO and C-H bond activation of the methylene moiety in 2. Heating 2 in the presence of ligand-trapping agents proceeds with the release of the 6-Me-2,2'-bpy ligand and formation of Os-3(CO)(9)L-3 [where L = CO, P(OMe)(3)]. The kinetics for the reaction between 2 and added ligand have been investigated by UV-vis and NMR spectroscopies and found to be first-order in starting cluster and independent of the incoming ligand. Parallel kinetic experiments employing the deuterated cluster DOs3(CO)(9)(mu(2)-CD2N2C10H7) (2-d(3)), which was prepared from cluster 1 and 6-Me-d(3)-2,2'-bpy, confirm the existence of a primary kinetic isotope effect (KIE) of 1.78 at 323 K. The KIE data and the calculated activation parameters [Delta H-double dagger = 21.7(4) kcal/mol; Delta S-double dagger = -13(1) eu] are strongly suggestive of a reaction scheme involving a rate-limiting reductive coupling of the bridging hydride ligand and cyclometalated alkyl moiety in 2 to furnish a putative sigma complex containing an intact methyl group bound to the Os-3 cluster, prior to the generation of the unsaturated cluster Os-3(CO)(9)(mu-N2C11H10). Thermolysis of 3 in the presence of added P(OMe)(3) does not furnish free 6-Me-2,2'-bpy but proceeds by a ligand-induced displacement of the methyl-substituted pyridyl ring and formation of the cluster compound HOs3(CO)(9)[P(OMe)(3)](mu(2)-N2C11H9) (5). The kinetics for the reaction between 3 and P(OMe)(3) have been studied over the temperature range 333-356 K, and on the basis of the observed activation parameters [Delta H-double dagger = 13.0(3) kcal/mol; Delta S-double dagger = -30(1) eu] and the first-order dependence on the cluster and ligand, an associative process that involves P(OMe)(3) ligand attack on the cluster and release of the methyl-substituted pyridyl ring in the rate-limiting step is proposed.

The reaction of the redox-active diphosphine ligand 2-(ferrocenylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (fbpcd) with PtCl2(1,5-cod) furnishes the platinum(II) compound PtCl2(fbpcd) (2). Treatment of 2 with disodium maleonitriledithiolate (Na(2)mnt) yields the chelating thiolate compound Pt(mnt)(fbpcd) (3). Both 2 and 3 have been fully characterized in solution by IR, UV-Vis, and NMR spectroscopies, and their molecular structures established by X-ray crystallography. The redox properties of the fbpcd ligand and compounds 2 and 3 have been investigated by cyclic voltammetry, and the composition of the HOMO and LUMO levels in these systems have been determined by extended Huckel MO calculations, the results of which are discussed with respect to electrochemical data. (C) 2008 Elsevier Ltd. All rights reserved.

Treatment of Os3(CO)10(MeCN)2 (1) with the heterocyclic ligand 6-methyl-2,2′-bipyridine (6-Me-2,2′-bpy) at room temperature leads to the formation of the isomeric hydride-bridged clusters HOs3(CO)9(μ2-CH2N2C10H7) (2) and HOs3(CO)9(μ2-N2C11H9) (3). The cyclometalation of the ancillary 6-Me group in 2 and the ortho metalation of the nonsubstituted pyridyl ring in 3 have been confirmed by spectroscopic and crystallographic methods. Thermolysis of 2 leads to the formation of 3 and the dihydride cluster H2Os3(CO)8(μ3-N2C11H8) (4); the latter cluster, whose structure has been crystallographically determined, derives from a formal loss of CO and C−H bond activation of the methylene moiety in 2. Heating 2 in the presence of ligand-trapping agents proceeds with the release of the 6-Me-2,2′-bpy ligand and formation of Os3(CO)9L3 [where L = CO, P(OMe)3]. The kinetics for the reaction between 2 and added ligand have been investigated by UV−vis and NMR spectroscopies and found to be first-order in starting cluster and independent of the incoming ligand. Parallel kinetic experiments employing the deuterated cluster DOs3(CO)9(μ2-CD2N2C10H7) (2-d3), which was prepared from cluster 1 and 6-Me-d3-2,2′-bpy, confirm the existence of a primary kinetic isotope effect (KIE) of 1.78 at 323 K. The KIE data and the calculated activation parameters [ΔH⧧ = 21.7(4) kcal/mol; ΔS⧧ = −13(1) eu] are strongly suggestive of a reaction scheme involving a rate-limiting reductive coupling of the bridging hydride ligand and cyclometalated alkyl moiety in 2 to furnish a putative sigma complex containing an intact methyl group bound to the Os3 cluster, prior to the generation of the unsaturated cluster Os3(CO)9(μ-N2C11H10). Thermolysis of 3 in the presence of added P(OMe)3 does not furnish free 6-Me-2,2′-bpy but proceeds by a ligand-induced displacement of the methyl-substituted pyridyl ring and formation of the cluster compound HOs3(CO)9[P(OMe)3](μ2-N2C11H9) (5). The kinetics for the reaction between 3 and P(OMe)3 have been studied over the temperature range 333−356 K, and on the basis of the observed activation parameters [ΔH⧧ = 13.0(3) kcal/mol; ΔS⧧ = −30(1) eu] and the first-order dependence on the cluster and ligand, an associative process that involves P(OMe)3 ligand attack on the cluster and release of the methyl-substituted pyridyl ring in the rate-limiting step is proposed.

The reaction of the pincer diphosphine ligand 4,6-bis(diphenylphosphinomethyl)-m-xylene (dppx) with the metal cluster compounds PhCCo3(CO)9 and Ru6(μ6-C)(CO)17 has been explored. Both clusters react with dppx to afford the simple substitution products [PhCCo3(CO)8]2(dppx) and [Ru6(μ6-C)(CO)16]2(dppx), where two cluster units are tethered by the pincer ligand. The molecular structures of the title products and the 2:1 cluster-pincer ligand stoichiometry have been established by X-ray crystallography. The stability of [PhCCo3(CO)8]2(dppx) and [Ru6(μ6-C)(CO)16]2(dppx) has been investigated under gentle thermolysis conditions (ca. 55–65°C). Both dppx-substituted clusters are unstable with [PhCCo3(CO)8]2(dppx) decomposing and [Ru6(μ6-C)(CO)16]2(dppx) transforming into the diphosphine-bridged cluster Ru6(μ6-C)(CO)15(μ-dppx) as the major observable product. The identity of the latter cluster has been ascertained by IR and NMR spectroscopies and mass spectrometry.

The reaction between the triosmium cluster 1,2-Os-3(CO)(10)(MeCN)(2) and the diphosphine pincer ligand 4,6-bis(diphenylphosphinomethyl)-m-xylene (dppx) has been examined and found to yield the pincer-bridged cluster 1,2-Os-3(CO)(10)(dppx) (2) as the major product, in addition to the pincer-bridged cluster 1,2-Os-3(CO)(10)[1-diphenylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinomethyl)phenyl}-propan-2-ol] (3) in trace amounts (< 2% yield). Both cluster products have been isolated and their molecular structures determined by crystallographic analyses. The structural highlights of compounds 2 and 3, which represent the first examples of pincer-ligated metal clusters, are discussed. The origin of the functionalized diphosphine ligand in 3 is traced to the ethanol solvent that was used in the recrystallization of the dppx ligand. (c) 2006 Elsevier B.V. All rights reserved.

Knoevenagel condensation of ferrocenecarboxaldehyde with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) yields the new diphosphine ligand 2-(ferrocenylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (fbpcd) in near quantitative yield. The reaction of fbpcd with the activated cluster 1,2-Os3(CO)10(MeCN)2 has been examined, with the diphosphine-bridged cluster 1,2-Os3(CO)10(fbpcd) (2b) observed as the major product. Cluster 2b is unstable and transforms into the corresponding chelating isomer 1,1-Os3(CO)10(fbpcd) (2c) on heating. The kinetics associated with the conversion of 2b→2c have been studied over the temperature range of 313-343 K by 1H NMR and UV–vis spectroscopies. On the basis of the observed activation parameters, a nondissociative isomerization process that involves a transient μ2-bridged phosphine moiety is presented. Near-UV irradiation of cluster 2c leads to CO loss and ortho-metalation of the one of the ancillary phenyl groups to give the hydride cluster HOs3(CO)9[μ-PhP(C6H4)CC(PPh2)C(O)CCH(C5H4FeCp)C(O)] (3) as a 45:55 mixture of diastereomers. The fbpcd ligand and clusters 2b, 2c, and 3 have been isolated and characterized in solution by IR and NMR (1H and 31P) spectroscopies, and by X-ray diffraction analysis in the case of the hydride-bridged cluster 3.

The α-diimine ligand 1,10-phenanthroline (phen) reacts with the activated cluster 1,2-Os3(CO)10(MeCN)2 to afford the carbonyl-bridged cluster 1,1-Os3(CO)9(μ-CO)(phen), which has been characterized by IR and NMR spectroscopies and X-ray diffraction analysis. Replacement of the 1,5-cyclooctadiene (cod) ligand in 1,1-Os3(CO)10(cod) by phen proceeds sluggishly over a 24 h period, showing less than 5% conversion to 1,1-Os3(CO)9(μ-CO)(phen).

Knoevenagel condensation of 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) with thiophene-2-carboxaldehyde furnishes the second-generation unsaturated diphosphine ligand 2-(2-thienylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (1,tbpcd) in high yield. The substitution chemistry of the rhenium compounds BrRe(CO)(5) and BrRe(CO)(3)(THF)(2) with tbpcd has been investigated and found to produce fac-BrRe(CO)(3)(tbpcd) (2). Compounds I and 2 have been isolated and fully characterized in solution by IR and NMR (H-1 and P-31) spectroscopies, in addition to mass spectrometry, and X-ray crystallography. The redox properties of 1 and 2 have been examined by cyclic voltammetry, and these data are discussed relative to the results obtained from extended Huckel MO calculations and emission spectroscopic studies, as well as related ligand derivatives previously prepared by us. Our data indicate that the lowest excited state in tbpcd and fac-BrRe(CO)(3)(tbpcd) arises from a pi -> pi* intraligand (IL) transition confined exclusively to the tbpcd ligand. (c) 2007 Elsevier Ltd. All rights reserved.

The reaction of the pincer diphosphine ligand 4,6-bis(diphenylphosphinomethyl)- m -xylene (dppx) with the metal cluster compounds PhCCo 3 (CO) 9 and Ru 6 (μ 6 -C)(CO) 17 has been explored. Both clusters react with dppx to afford the simple substitution products [PhCCo 3 (CO) 8 ] 2 (dppx) and [Ru 6 (μ 6 -C)(CO) 16 ] 2 (dppx), where two cluster units are tethered by the pincer ligand. The molecular structures of the title products and the 2:1 cluster-pincer ligand stoichiometry have been established by X-ray crystallography. The stability of [PhCCo 3 (CO) 8 ] 2 (dppx) and [Ru 6 (μ 6 -C)(CO) 16 ] 2 (dppx) has been investigated under gentle thermolysis conditions (ca. 55–65°C). Both dppx-substituted clusters are unstable with [PhCCo 3 (CO) 8 ] 2 (dppx) decomposing and [Ru 6 (μ 6 -C)(CO) 16 ] 2 (dppx) transforming into the diphosphine-bridged cluster Ru 6 (μ 6 -C)(CO) 15 (μ-dppx) as the major observable product. The identity of the latter cluster has been ascertained by IR and NMR spectroscopies and mass spectrometry.

The Knoevenangel condensation between 9-anthracenecarboxaldehyde and the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione (bpcd) takes place rapidly in CH2Cl2/MeOH solution in the presence of molecular sieves (4 Å) to produce the functionalized ligand 2-(anthracen-9-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione. The title compound has been isolated and characterized in solution by IR, NMR, and UV-vis spectroscopies, and the solid-state structure has been established by X-ray diffraction analysis. 2-(anthracen-9-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione crystallizes in the triclinic space group P−1, a=10.227(2) Å, b=13.865(2) Å, c=15.905(2) Å, α=112.157(2)°, β=101.424(2)°, γ=100.065(3)°, V=1968.5(5) Å3, Z=2, and d calc=1.101 Mg/m3; R=0.0873, R w=0.2604 for 7452 reflections with I>2σ(I). The cyclic voltammetric behavior for 2-(anthracen-9-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopentene-1,3-dione has been studied, and the observed redox data and results from extended Hückel MO calculations are discussed relative to the parent ligand bpcd.

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.

Quinoxaline-functionalized, cage-annulated oxa- and thiacrown ethers have been synthesized as possible specific metal host systems. The synthesis and characterization of quinoxaline-functionalized, cage-annulated oxa- and thiacrown ethers have been described. The characterization of these host systems have been fully achieved in solution by using various techniques such as IR, 1H NMR, and 13C NMR spectroscopic methods, high-resolution mass spectrometry (HRMS), elemental microanalysis, and X-ray crystallographic analysis in case of one quinoxaline-functionalized, cage-annulated oxacrown ether compound. The synthesis of the diphosphine ligand 2,3-bis(diphenylphosphino)-N-p-tolylmaleimide (bmi) is described. The substitution of the MeCN ligands in the activated cluster 1,2-Os3(CO)10(MeCN)2 by the diphosphine ligand bmi proceeds rapidly at room temperature to furnish a mixture of bridging and chelating Os3(CO)10(bmi) isomers and the ortho-metalated product HOs3(CO)9[μ-(PPh2)C=C{PPh(C6H4)}C(O)N(tolyl-p)C(O)]. Thermolysis of the bridging isomer 1,2-Os3(CO)10(bmi) under mild conditions gives the chelating isomer 1,1-Os3(CO)10(bmi), whose molecular structure has been determined by X-ray crystallography. The kinetics for the ligand isomerization have been investigated by UV-vis and 1H NMR spectroscopy in toluene solution over the temperature range of 318-348 K. On the basis of kinetic data conducted in the presence of added CO and the Eyring activation parameters, a non-dissociative phosphine migration across one of the Os-Os bonds is proposed. Orthometalation of one of the phenyl groups associated with the bmi ligand is triggered by near-UV photolysis of the chelating cluster 1,1- Os3(CO)10(bmi).

The ligand substitution behavior of the tetrahedrane clusters RCCo2Mo(eta(5)-indenyl)(CO)(8) [R=H (1); Ph (3)] with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) has been investigated. Thermolysis of cluster 1 with bpcd in CH2Cl2, 1,2-dichloroethane, or toluene affords the bped-bridged cluster HCCo2Mo(eta(5)-indenyl)(CO)(6)(mu-bpcd) (2) as the initial product. Cluster 2 is unstable and undergoes decomposition upon prolonged heating. Unlike cluster 1, heating the benzylidyne-capped cluster 3 with bpcd in either CH2Cl2 or 1,2-dichloroethane furnishes the thermally unstable mixed-metal cluster Co2MoCp(eta(5)-indenyl)(CO)(5)[mu(2),eta(2),eta(1)-C(Ph)C=C(PPh2)C(O)CH2C(O)](mu-PPh2) (4) and the carbyne-bridged dinuclear compound CoMo(eta(5)-indenyl)(mu CPh)(CO)(2)(mu-bpcd)Cl (5) as the principal reaction products. Thermolysis of 3 with added bpcd in toluene gives 4 as the sole observed product. Compounds 2, 4, and 5 have been fully characterized in solution, and the solid-state structures of 2 and 5 have been established by X-ray crystallography. The structure of 2 consists of a triangular Co2Mo core that is capped by the methylidyne group and that contains a bpcd ligand that bridges the two cobalt centers. The X-ray structure of 5 provides support for the partial fragmentation of the original cluster through the loss of a cobalt vertex and the abstraction of a chlorine atom from the chlorinated solvent. The presence of a bridging carbyne moiety that spans the Co-Mo vector and a bpcd ligand that is chelated to the cobalt center by the two phosphine groups and attached to the molybdenum center by the alkene pi bond of the dione ring are confirmed. The reactivity differences exhibited by clusters 1 and 3 are discussed, and these data are briefly contrasted with that of the cyclopentadienyl counterpart PhCCo2Mo(eta(5)-Cp)(CO)(8). (c) 2006 Elsevier B.V. All rights reserved.

The substitution chemistry of the activated clusters Os3(CO)10(MeCN)2 (1) and Os3(CO)10(1,5-cod) (2) has been investigated with the bidentate ligand 1,2-bis(dimethylphosphino)ethane (dmpe). Both starting clusters react rapidly with dmpe at room temperature to give the corresponding substitution product Os3(CO)10(dmpe) (3), whose isomeric composition is shown to depend on the nature of the starting cluster. Whereas the bridged cluster 1,2-Os3(CO)10(dmpe) (3b) was formed almost exclusively upon reaction with Os3(CO)10(MeCN)2, a near statistical mixture of bridging (3b) and chelating (3c) isomers of Os3(CO)10(dmpe) was found in the reaction employing Os3(CO)10(1,5-cod). Both dmpe isomers have been characterized in solution by 3iP NMR spectroscopy and their solid-state structures established by X-ray crystallography. The bridged cluster 1,2-Os3(CO)10(dmpe) crystallizes in the monoclinic space group P21/n, a = 9.867(2) Å, b = 17.081(3) Å, c = 14.198(2) Å, β = 95.902(3)°, V = 2380.4(6) Å3, Z = 4, and d calc = 2.793 Mg/m3; R = 0.0435, R w = 0.0466 for 3519 reflections with I > 2σ(I). The chelated cluster 1,1-Os3(CO)10(dmpe) crystallizes in the orthorhombic space group C222(1), a = 8.329(3) Å, b = 19.028(6) Å, c = 15.008(5) Å, V = 2379(1) Å3, Z = 4, and d calc = 2.795 Mg/m3; R = 0.0390, R w = 0.0718 for 2360 reflections with I > 2σ(I).

The triosmium cluster 1,2-Os-3(CO)(10)(MeCN)(2) reacts rapidly with the diphosphine ligand 2,3-bis(diphenylphosphino)-N-p-tolylmaleimide (bmi) at room temperature to give bmi-bridged cluster 1,2-Os-3(CO)(10)(bmi) (2b) as the major product, along with the chelating isomer 1,1-Os-3(CO)(10)(bmi) (2c) and the hydride-bridged cluster HOs3(CO)(9)[mu-(PPh2)C=C{PPh(C6H4)}C(O)N(tolyl-p)C(O)] (3) as minor by-products. All three cluster compounds have been isolated and fully characterized in solution by IR and NMR spectroscopies (H-1 and P-31), and X-ray crystallography in the case of 2c. Cluster 2b is unstable and readily isomerizes to 2c in quantitative yield on mild heating. The kinetics for the conversion of 2b -> 2c have been measured over the temperature range of 318-348 K in toluene solution, and based on the observed activation parameters a nondissociative isomerization process that proceeds via a transient 12-bridged phosphine moiety is presented. Near-UV photolysis of cluster 2c at room temperature affords HOs3(CO)(9)[mu-(PPh2)C=C {PPh(C6H4)}C(O)N(tolyl-p)C(O)] (3) with a quantum yield of 0.017. The reactivity of clusters 2b, 2c, and 3 is discussed with respect to related diphosphine-substituted Os-3(CO)(10)(P-P) clusters prepared by our groups. (c) 2006 Elsevier B.V. All rights reserved.