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The reaction between the tricobalt cluster FcCCo3(CO)9 (1) (where Fc = ferrocenyl) and the redox-active diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) affords the new cluster (3) in refluxing 1,2-dichloroethane or toluene. The cluster FcCCo3(CO)7(bma) (2), a logical precursor to 3, was observed in solution by IR spectroscopy when cluster 1 and bma were refluxed in the low boiling point solvent CH2Cl2; however, putative 2 could not be isolated due to its rapid conversion to the final product 3. Cluster 3 has been fully characterized in solution by IR and NMR (13C and 31P) spectroscopy and in the solid state by X-ray diffraction analysis. , as the CH2Cl2 solvate, crystallized in the triclinic space group P 1 , a = 10.4704(6), b = 14.6033(8), c = 14.787(1) A , α = 102.973(5), β = 94.517(8), γ = 90.197(5)°, V = 2195.9(2) A 3 , Z = 2, D calc = 1.653 g cm −3 ; R = 0.0411, R w = 0.0449 for 3602 observed reflections with 13σ(I). Cyclic voltammetric investigations of 3 in CH2Cl2 reveal the presence of three reversible redox responses assigned to the 0/1+, 0/1−1, and 1−/2− redox couples. The nature of the HOMO and the two lowest unoccupied molecular orbitals (LUMO and SUMO) in 3 has been determined by carrying out extended Huckel calculations on the model compound , the results of which are discussed relative to the observed electrochemistry of 3 and related cluster compounds.

The imido-capped cluster Ru3(CO)10(μ3-NPh) (1) reacts with PPh3 under thermal and Me3NO activation to give the corresponding phosphine-substituted clusters Ru3(CO)9(PPh3)(μ3-NPh) (2) and Ru3(CO)8(PPh3)2(μ3-NPh) (3). Both d2 and 3 have been isolated and fully characterized in solution by IR and 31P NMR spectroscopy, and the solid-state structure of each new cluster compound has been established by X-ray diffraction analysis. 2 crystallizes in the monoclinic space group P21/n: a=13.091(2), b=11.405(2), c=22.687(4)A3, β=99.80(1)°, V=3338(1) A3, Z=4, Dcalc=1.808 g cm−3; R=0.0399, Rw=0.0511 for 3515 observed reflections. 3, as the CH2Cl2 solvate, crystallizes in the triclinic space group P 1 : a=9.5678(8), b=14.425(1), c=17.986(1) A α=81.692(5), β=88.078(6), γ=77.716(6)°, V=2400.1(3) A 3 , Z=2, D calc =1.640 g cm −3 ; R=0.0439, R w =0.0479 for 3570 observed reflections. The X-ray data establish the site of the first PPh3 group at an axial position in the cluster 2 while cluster 3 derives from the formal replacement of an equatorial CO group on an adjacent ruthenium center in 2 by the second PPh3 group. These results confirm the highly stereo- and regioselective ligand substitution reactivity attendant in this particular imido-capped cluster. The redox properties of 1–3 have also been explored by cyclic; voltammetry at a platinum electrode in THF solvent.

The alkyne-bridged compounds Co 2 (CO) 6 (μ-R′CCR) where R′  H, R,  Ph, t Bu; R′  Me, R  Ph) have been examined for their reactivity with the redox-active diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma). Thermal and Me 3 NO-induced activation of each Co 2 (CO) 6 (μ-R′CCR) compound initiallyfurnishes the binuclear compounds Co 2 (CO) 4 (bma)(μ-R′CCR) ( 1c , R′  H, R  Ph; 2c , R′  H, R  t Bu; 3c , R′  Me, R  Ph), all of which are shown to possess a chelating bma ligand. These compounds exhibit a reversible chelate-to-bridge bma ligand isomerization that proceeds by a pathway involving dissociative CO loss. The stability of the chelating isomers is dependent on the steric bulk of the alkyne substituents, with the bridging isomer ( 1b, 2b, 3b ) being favored at ambient temperature only in the case of Co 2 (CO) 4 (bma)(μ-HCC t Bu) ( 2b ). Regioselective phosphine attack at the least-substituted alkyne carbon is observed at temperatures above 60 °C to afford the corresponding zwitterionic hydrocarbyl compounds Co 2 (CO) 4 [μ-η 2 :η 2 :η 1 :η 1 -RCC(R′)PPh 2 CC(PPh 2 )C(O)OC (O)] ( 1z, 2z, 3z ). Depending on the ease of separation, the new compounds have been characterized by IR and NMR spectroscopy, and the molecular structure of the bridged compound 2b and all three zwitterionic hydrocarbyl compounds have been determined by X-ray crystallography. 1z crystallizes in the triclinic space group P 1 : a = 9.8093(7) A , b = 12.215(1) A , c = 15.744(2) A , α = 98.251(8)°, β = 95.060(8)°, γ = 90.640(7)°, V = 1859.1(3) A 3 , Z = 2, d calc = 1.426 g cm −3 ; R = 0.0365, R w = 0.0469 for 2749 observed reflections. 2b crystallizes in the triclinic space group P 1 : a = 11.1272(7) A , b = 12.142(1) A , c = 13.565(1) A , α = 97.123(7)°, β = 94.951(6)°, γ = 100.197(6)°, V = 1778.8(2) A 3 , Z = 2, d calc = 1.453 g cm −3 ; R = 0.0469, R w = 0.0484 for 3357 observed reflections. 2z crystallizes in the monoclinic space group P2 1 /n: a = 9.465(7) A , b = 20.071(8) A , c = 18.389(6) A , β = 98.88(5)°, V = 3452(3) A 3 , Z = 4, d calc = 1.498 g cm −3 ; R = 0.0544, R w = 0.0589 for 3114 observed reflections. 3z , as the CH 2 Cl 2 solvate, crystallizes in the triclinic space group P 1 : a = 9.732(3) A , b = 12.286(2) A , c = 16.715(3) A , α = 98.39(1)°, β = 102.91(2)°, γ = 91.93(2)°, V = 1922.6(8) A 3 , Z = 2, d calc = 1.550 g cm −3; R = 0.0730, R w = 0.0825 for 2896 observed reflections. The X-ray data on 1z, 2z, and 3z confirm the site of phosphine attack on the coordinated alkyne ligand and the presence of the eight-electron hydrocarbyl ligand that accompanies this reaction. The redox properties of the zwitterionic compounds Co 2 (CO) 4 [μ-η 2 :η 2 :η 1 :η 1 -RCC(R′)PPh 2 CC(PPh 2 )C(O)OC (O)] have been examined by cyclic coltammetry, and the data discussed relative to the coordination mode adopted by the bma ligand and the redox properties exhibited by the related alkyne-bridged compound Co 2 (CO) 4 (bma)(μ-PhCCPh) (chelating and bridging isomers). Extended Huckel calculations on the model compound Co 2 (CO) 4 [μ-η 2 :η 2 :η 1 :η 1 -HCC(H)PH 2 CC(PH 2 )C(O)OC (O)] have been carried out and are used in a discussion concerning the site of electron reduction and oxidation in 1z, 2z , and 3z .

The new compound Pt(1,5-COD)(1,2-O2C6H4)(1) (where COD=cyclooctadiene) has been prepared from the reaction between Pt(1,5-COD)Cl2 and the disodium salt of catechol. Pt(1,5-COD)(1,2-O2C6H4) has been isolated and structurally characterized by X-ray diffraction analysis, which confirms the monomeric nature of this compound and the chelating mode adopted by the ancillary 1,5-COD and catecholate ligands. Pt(1,5-COD)(1,2-O2C6H4) crystallized in the monoclinic space groupP21/n,a=10.208(1) A,b=10.3829(8) A,c=11.473(2) A, β=103.817(9)°,V=1180.9(2) A3,Z=4,d calc=2.314 g·cm−3;R=0.0307,R w =0.0445 for 1216 observed reflections withI>3σ(I). Cyclic voltammetric studies on1 reveal an irreversible oxidation (E =0.78 V) and an irreversible reduction (E =−1.99 V) in CH2Cl2 solution. The nature of the HOMO and LUMO in Pt(1,5-COD)(1,2-O2C6H4) was examined by using the model compound Pt(ethylene)2(1,2-O2C6H4), with the results discussed relative to compound1.

The reaction of the disodium salt of 2,2-dicyano-1,1-ethylenedithiol (i-mnt) with the cyclopentadienyl compound Cp∗Ru(NO)Cl2 in methanol gives the new piano-stool compound Cp∗Ru(NO)(i-mnt), (1), in high yield. 1 has been isolated and characterized in solution by IR and NMR (1H and 13C NMR) spectroscopic methods, and the solid-state structure has been confirmed by X-ray diffraction analysis. Cp∗Ru(NO)(i-mnt) crystallizes, as the CH2Cl2 solvate, in the orthorhombic space group Pbcm, a = 9.8872(6) A, b = 13.5269(8) A, c = 15.0557(8) A, V = 2013.6(2) A3, Z = 4, d calc = 1.621 g · cm−3; R = 0.0330, Rw = 0.0353 for 1068 observed reflections with I> 3[sgrave](I). The observed Ru-N-O bond angle of 168.9(7)° in the X-ray structure of 1 confirms the near linear nature of the nitrosyl linkage. The oxidation/reduction properties of 1 have been explored by cyclic voltammetry, which revealed the presence of a quasi-reversible one-electron reduction (0/1−) and an irreversible oxidation. A comparison of the elec...

The sulfido-bridged cluster Ru 3 (CO) 9 ( μ 3 -S) 2 ( 1 ) has been allowed to react with the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in the presence of Me 3 NO to give the new cluster Ru 3 (CO) 7 (bpcd)( μ 3 -S) 2 ( 2 ) in 61% yield. The ancillary bpcd in 2 is bound at one of the basal ruthenium sites in a chelating fashion, being derived by the replacement of axial and equatorial CO groups. This cluster represents the first example of a cluster derived from Ru 3 (CO) 9 ( μ 3 -S) 2 that contains a chelating diphosphine ligand. Cluster 2 has been characterized in solution by IR and NMR ( 1 H and 31 P) spectroscopies and in the solid state by X-ray diffraction analysis. Ru 3 (CO) 7 (bpcd)( μ 3 -S) 2 , which exists as two crystallographically independent molecules in the unit cell, crystallizes in the monoclinic space group P2 1 /c, a= 19.451(1), b = 21.865(2) A , Z = 8, D calc = 1.702 cm −3 ; R = 0.0411 , R w = 0.0447 for 5622 observed reflections. The redox properties of 2 were explored by cyclic voltammetry in MeCN, which revealed the presence of a reversible one-electron reduction process (bpcd based) and an irreversible oxidation (metal based). The natture of the HOMO and LUMO in 2 has been examined by carrying out extended Huckel MO calculations on the model cluster Ru 3 (CO) 7 (H 4 -bpcd)( μ 3 -S) 2 , and the results are discussed relative to the observed electrochemistry.

The alkynyl-bridged triruthenium cluster Ru 3 (CO) 9 9 μ 2 -H( μ 3 - ν 2 -C t Bu) ( 1 ) reacts with the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3,-dione (bpcd) in the presence of Me 3 NO to afford the new cluster Ru 3 (CO) 7 ( μ 2 -H)( μ 3 - ν 2 -CC t Bu)(bpcd) ( 2 ) in 76% yield. The diphosphine ligand in 2 is bound at the unique ruthenium atom in a chelating fashion, and is the first example of a cluster-coordinated bpcd ligand. Cluster 2 has been characterized in solution by IR and NMR ( 1 H and 31 P) spectroscopy and in the solid state by X-ray diffraction analysis. Ru 3 (CO) 7 ( μ 3 - ν 2 -CC t Bu)(bpcd), as the CH 2 Cl 2 solvate, crystallizes in the monoclinic space group P2 1 /c: α = 21.190(1), b = 12.345(1) A , c = 17.272(1) A , β = 95.075(5)°, V = 4500.5(5) A , 3 , Z = 4, d calc = 1.667 g cm −3 ; R = 0.399, R w = 0.0432 for 3255 observed reflections. The redox properties of 2 were explored by cyclic voltammetry, which revealed the presence of a reversible one-electron reduction process (bpcd based) and an irreversible oxidation (metal based). The nature of the HOMO and LUMO in 2 has been examined by carrying out extended Huckel MO calculations on the model cluster Ru 3 (CO) 7 ( μ 2 -H)( μ 3 - ν 2 -CCHH 4 -bpcd), and the results are discussed with respect to the observed electrochemistry. The propensity of cluster 2 to undergo P-C bond cleavage is discussed in the light of other diphosphine ligand work.

The NMR 13C spin-lattice relaxation times of the phenyl group and equatorial carbonyl carbons in Ru3(CO)9(μ3-CO)(μ3-NPh) were measured as a function of temperature and resonance frequency in the solvent methylene chloride, and at several temperatures in chloroform. Phenyl T1s were used to calculate the diffusion coefficients characterizing molecular tumbling, D⊥, and spinning of the phenyl group, Ds; carbonyl relaxation times yielded the parallel diffusion coefficient, D∥. Values of D⊥ calculated using the standard motional narrowing assumption were incorrectly observed to be frequency dependent, and in marked error (by as much as a factor of two) from results obtained using the non-motionally narrowed equations. The spinning diffusion coefficients, Ds, were an order of magnitude greater than either D⊥ or D∥, but somewhat lower than the rate of the equivalent rotation of free benzene in the same solvents, indicating the existence of a barrier to internal rotation of the phenyl group. Fenske-Hall and extended Huckel calculations revealed that the barrier arises primarily from steric interactions between the ortho protons of the phenyl group and the carbon atom of the equatorial carbonyls.

The reaction between the cyclopentadienyliridium complexes Cp∗ Ir(L)Cl2 (where L = PMe3, PPh3, CN-t-Bu) and disodium maleonitriledithiolate (Na2mnt) yields the corresponding mnt-substituted compounds Cp∗ Ir(PMe3)(mnt) (1), Cp∗ Cp∗ Ir(PPh3)(mnt) (2) and Cp∗ Ir(CN-t-Bu)(mnt) (3). All of these new compounds have been isolated in high yield and characterized in solution by IR and NMR spectroscopy. The solid state structures of 2 and 3 were determined by single-crystal X-ray diffraction analysis. 2 crystallizes in the triclinic space group P 1 with a = 10.4557(8) A , b = 10.630(1) A , c = 14.894(1) A , α = 91.382(8)°, β = 90.141(6)°, γ = 118.182(7)° , V = 1458.5(3) A 3 and Z = 2 . Full-matrix least-squares refinement yielded R = 0.0281 for 3425 (I > σ(I)) reflections. 3 crystallizes in the monoclinic space group P21/n with a = 8.9609(7) A , b = 20.343(1) A , c = 11.9115(9) A , β = 94.168(6)°, V = 2165.(6) A 3 and Z = 4. Full-matrix least-squares refinement yielded R = 0.0245 for 2266 (I> 3 σ (I)) reflections. The redox properties of 1–3 have been explored by cyclic and rotating disc electrode voltammetric techniques in MeCN and CH2Cl2 solvents. Each of these compounds exhibit a well-defined one-electron oxidation wave that is assigned to the 0/ + 1 redox couple, along with a + 1/ + 2 redox wave, the reversibility of which is highly dependent on the nature of the ancillary two-electron donor ligand (L) and the solvent. Extended Huckel calculations have been performed on the model compounds CpIr(PH3)(mnt) and CpIr(CNH)(mnt), with the results used in a discussion of the nature of the HOMO and LUMO levels in 1–3.

The reaction betweencis-Ru(bpy)2Cl2 (where bpy=bipyridine) and the diphosphine ligand 1,1′-bis(diphenylphosphino)ferrocene (dppf) in the presence of AgBF4 has led to the isolation of the title compound [Ag(dppf)Cl]2. [Ag(dppf)Cl]2 has been structurally characterized by X-ray diffraction analysis, which confirms the bridging mode adopted by the ancillary dppf ligand and the centrosymmetric nature of this molecule. Dimeric [Ag(dppf)Cl]2 crystallizes in the triclinic space group\(P\bar 1\),a=11.426(1) A,b=11.509(1) A,c=12.786(1) A, α=68.96(2)°, β=70.66(2)°, γ=71.24(2)°,V=1441(1) A3,Z=1,dcalc=1.608 g·cm−3;R=0.0445,Rw=0.0566 for 4486 observed reflections withl>3σ(l)

Treatment of cis- or trans-CpRe(CO)2Br2 (1) with Ph3SnH yields the corresponding dihydride CpRe(CO)2H2 (2) and Ph3SnBr. Conducting the same reaction in the presence of pyridine or Et3N gives trans-CpRe(CO)2(SnPh3)2 (3). The molecular structure of 3 has been determined by X-ray crystallography. 3 crystallizes in the monoclinic space group P2 1 c with a=25.099(2), b=9.4205(8), c=16.388(2) A , β=103.632(8)°, V=3765.7(6) A 3 , and D calc =1.777 g cm −3 for Z=4 . The refined structure gave R and Rw values of 0.0317 and 0.0444, respectively, for 3753 observed reflections. A plausible mechanism for the formation of the dihydride CpRe(CO)2H2 that involves the chain-propagating radicals CpRe(CO)2Br. and CpRe(CO)2H. is presented.

The reaction between the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and the dirhenium compound Re2(CO)8(μ-H)(μ-η1,η2-C  CPh) in CH2Cl2 at room temperature proceeds by CO loss to give the dirhenium complex Re2(CO)7(bpcd)(μ-H)(η1-C  CPh) (1). This new complex was characterized in solution by IR and NMR (1H and 31P) spectroscopy and in the solid state by X-ray diffraction analysis. Re2(CO)7(bpcd)(μ-H)(η1-C  CPh) crystallizes in the triclinic space group P1: a = 11.3900(9), b = 13.3921(9), c = 14.275(1) A, α = 84.280(6)°, β = 89.678(6)°γ = 69.240(6)°, V = 2024.9(3) A3, Z = 2, dcalc = 1.862 g cm−3 R = 0.0221, Rw = 0.243 for 4066 observed reflections. The bpcd ligand in 1 adopts a chelating mode with a linear phenylacetylide ligand being located on the adjacent rhenium center cis to the bpcd ligand. This complex represents the first structurally characterized example of a hydrido-bridged dirhenium complex possessing both a linear acetylide ligand and a chelating diphosphine ligand.

Treatment of disodium 1,2,5-thiadiazole-3,4-dithiol (Na 2 tdas) with the cyclopentadienyl complex Cp*Ru(NO)Cl 2 in MeOH gives the corresponding 1,2,5-thiadiazole-3,4-dithiolate-substituted complex Cp * Ru(NO)(tdas) in 61% yield. The product has been characterized in solution by IR and NMR ( 1 H and 13 C) spectroscopies, and the molecular structure of Cp * Ru(NO)(tdas) has been established by X-ray diffraction analysis. Cp * Ru(NO)(tdas) crystallizes in the monoclinic space group P2 1 / c with a =26.204(2), b =8.4915(6), c =14.2339(9) A, β=90.739(5)°, V =3166.9(3) A 3 and Z =8. Full-matrix least-squares refinement yielded R =0.0338 for 3151 ( I >3σ( I )) reflections. The redox properties of Cp * Ru(NO)(tdas) were examined by cyclic and rotating disk electrode voltammetric techniques. Two electrochemical responses were observed and assigned to 0/+1 and 0/ − 1 redox couples. Both of these redox couples are quasi-reversible. It is suggested that the stability of the 0/−1 redox couple is modulated by an EC scheme, whereby the initial reduction product [Cp * Ru(NO)(tdas)] ·− undergoes a bending of the nitrosyl ligand. The nitrosyl bending is observable at low temperature in THF solvent. The nature of the HOMO and LUMO levels in Cp * Ru(NO)(tdas) has been determined by extended Huckel molecular orbital calculations, the results of which are discussed with respect to the electrochemical data.

The hydroformylation of 1 -pentene using the benzylidyne-capped cluster PhCCO3(CO)9 has been examined by cylindrical internal reflectance (CIR) spectroscopy. At 130°C, cluster fragmentation is observed and the formation of aldehydes is shown to coincide with fragmentation of PhCCO3(CO)9 by CIR spectroscopy. These results are discussed in relationship to the observations previously reported by Withers and Seyferth (Inorg. Chem. 22 (1983) 2931) on PhCCO3(CO)9 and its polymer-bound analogues. CIR spectral data for the CO2(CO)8-catalyzed hydroformylation of 1-pentene are also presented for comparative purposes.

The hydroformylation of 1-pentene has been examined with the catalyst precursor PhCCo3(CO)7(LL) (where LL=cis-Ph2PCHCHPPh2) under mild batch conditions at 130°C and 600 psi H2/CO (1:1). Extensive cluster fragmentation is observed at the end of the hydroformylation reaction based on the isolation of the initially charged cluster in < 10% yield. Cylindrical internal reflectance (CIR) spectroscopy has been used to study the stability of the PhCCo3(CO)7(LL) cluster and the nature of cluster fragmentation species present in the working catalyst solution. Cluster fragmentation to [Co(CO)4]− occurs early in the reaction prior to alkene hydroformylation, followed by the formation of the phosphine-substituted complexes [Co(CO)3(LL)]+ and [Co(CO)2(LL)]−. The CIR data allow for the timing of the fragmentation of the cluster to be assigned with confidence and support the batch reaction data regarding the extensive fragmentation cluster observed. The effect of the ancillary phosphine ligand on the stability of the initially charged cluster is discussed and the CIR data is compared with the results obtained from the parent cluster PhCCo3(CO)9 under similar conditions.

The reaction between 1,1′-bis(diphenylphosphino)ferrocene (dppf) and the tricobalt cluster PhCCo 3 (CO) 9 ( 1 ) yields the disubstituted cluster PhCCo 3 (CO) 7 (dppf) ( 2 ). The dppf ligand in 2 bridges adjacent cobalt centers via axial coordination. Ligand substitution leading to 2 may be achieved by thermolysis, oxidative decarbonylation using trimethylamine oxide, and by electrontransfer chain (ETC) catalysis using sodium benzophenone ketyl. The isolated yield of 2 ranged from 50 to 70% in all cases. Solution characterization of 2 by FT-IR and 31 P NMR spectroscopy is presented along with the single-crystal X-ray diffraction results. The dppf-bridged cluster PhCCo 3 (CO) 7 (dppf)·(toluene) crystallized in the monoclinic space group P 2 1 / c with a = 13.560(3), b = 17.339(3), c = 21.482(3) A, β = 106.81(1)°, V = 4835(1) A 3 and Z = 4. Block-cascade least-squares refinement yielded R = 0.0630 for 5055 ( I > 3σ( I )) reflections. The redox reactivity of 2 was examined by cyclic voltammetry, which revealed the presence of two irreversible oxidations that are attributed to the oxidation of the dppf ligand and the cluster core along with the observation of an irreversible reduction that exhibits cyclic voltammetric curve crossing. All of the redox processes are discussed with respect to existing tricobalt cluster redox chemistry.

The stability of diphosphine-substituted cobalt clusters derived from Co4(CO)10(μ4-PPh)2 has been examined under hydroformylation conditions using Cylindrical Internal Reflectance (CIR) spectroscopy. The monodentate phosphine clusters Co4(CO)8(PPh3)2(μ4-PPh)2 (1) and Co4(CO)8[P(OMe)3]2(μ4-PPh)2 (2) undergo rapid P-ligand loss to give the corresponding monosubstituted cluster Co4(CO)9P(μ4-PPh)2 [where P=PPh3 or P(OMe)3] and Co4(CO)10(μ4-PPh)2 at 130 °C. No hydroformylation activity was observed at 130 °C. Increasing the reaction temperature to 150 °C affords the parent cluster as the only observable organometallic species. 1-Pentene hydroformylation is observed at 150 °C, and the working catalyst solution shows no evidence for the fragmentation of Co4(CO)10(μ4-PPh)2 to HCo(CO)4. In contrast, the bidentate-substituted dimethylphosphino(ethane) (dmpe) cluster Co4(CO)8(dmpe)(μ4-PPh)2 (3) appears to function as a hydroformylation catalyst without phosphine loss or declusterification at 130 °C. The greater stabilization of the dmpe-substituted cluster relative to the monodentate phosphine systems and the absence of cluster fragmentation, which has recently been reported in the hydroformylation of 1-pentene using Co4(CO)10(μ4-PPh)2, are discussed.

MeJ(p,-PPh)-] (3-). IR analysis reveals a 51:49 mixture of solvent-separated and acyl oxygen-[Li'] contact ion pairs, respectively at -70 OC. Use of the Grignard reagents t-BuMgCI or MeMgBr gives the 49-electron cluster [FeCo,(CO),(p,-PPh)']. [MeO][Li] reacts with 1 at a cobalt-bound CO group at -78 OC to furnish the methoxycarbonyl cluster [FeCo2(CO),(C(0)OMe}(p3-PPh)-] (59, which is shown by IR analysis to exist exclusively as an ester oxygen-[Li'] contact ion pair. NMR analysis suggests that 5- rearranges to the p,-methoxyphosphido cluster [F~CO,(CO)~(~~-P P~OM~)-] (87 at ambient temperature as the major product. Treatment of 1 with methanolic [Et,N][OH] in THF at -70 OC gives the corresponding methoxycarbonyl and hydroxycarbonyl clusters in a 55:45 ratio, respectively, as determined by IR band-shape analysis. The reactivity and stability of these new anionic clusters are discussed.

NMR spin-lattice relaxation times of the phenyl, cyclopentadienyl, and terminal carbonyl 13 C nuclei in the title compound were measured as a function of temperature in the solvent chloroform. The phenyl carbon T 1 's were used to calculate the diffusion coefficient characterizing the ring's net spinning rate. Internal rotation rates of the cyclopentadienyl groups, R(Cp), were found to be far greater than R(Ph) at all temperatures, indicating that the barrier to phenyl group rotation is not due to inter-ring steric repulsions. Rather, it can be attributed to an electronic interaction of the bridging carbonyl's π* orbital with the phenyl π system through the metal 2e and carbynyl 2p orbitals. This is only the second system in which a bridging carbonyl/capping group orbital interaction has been observed and the first for which the barrier range to internal rotation has been experimentally determined

C 24 H 37 CoO 5 P 4 •C 7 H 8 cristallise dans P2 1 /c avec a=9,861, b=11,172, c=32,935 A, β=82,91 o , Z=4; affinement jusqu'a R=0,0758. Les atomes de Co sont dans un arrangement triangulaire avec le coordinat benzylidene en tant que chapeau, completant le cœur polyedrique nido. Un coordinat dmpe=Me 2 PCH 2 CH 2 PMe lie deux atomes de Co, tandis que l'autre coordinat dmpe chelate un seul atome Co

The reaction of the methylidyne-bridged cluster HRu3(CO)10(μ-COMe) (1) with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and Me3NO furnishes HRu3(CO)8(μ-COMe)(bpcd) (2) and HRu3(CO)8(Ph2PH)[μ-PPh2C CC(O)CH2C(O)] (3) as the major and minor products, respectively. The 1H and 31P NMR data indicate that the bpcd ligand in 2 is chelated to one of the ruthenium atoms that is bridged by the hydride and methylidyne ligands. Thermolysis of 2 is accompanied by P–Ph bond cleavage and elimination of benzene to yield Ru3(CO)7(μ3-COMe)[μ-P(Ph)C C(PPh2)C(O)CH2C(O)] (4). Compound 4 consists of a triangular ruthenium core that is face-capped by μ3-COMe methylidyne and μ-P(Ph)C C(PPh2)C(O)CH2C(O) phosphido ligands. The kinetics for the conversion of 2 → 4 have been measured in toluene solvent over the temperature range 320–343 K, and based on the observed activation parameters and the inhibitory effect of added CO on the reaction, a rate-limiting step involving a dissociative loss of CO is supported. Heating 4 in the presence of H2 afforded the phosphinidene-capped cluster H3Ru3(CO)7(μ3-PPh)[μ-C C(PPh2)C(O)CH2C(O)] (5). Crystallographic analysis of 5 has confirmed the loss of the methylidyne moiety and the cleavage of the phosphido PhP–C(dione) bond, and the presence of three edge-bridging hydrides is supported by 1H NMR spectroscopy. The reaction of 4 with added PPh3 and PMe3 has been investigated; the uptake of a single phosphine ligand occurs regiospecifically at one of the phosphido-bound ruthenium centers to give Ru3(CO)6L(μ3-COMe)[μ-P(Ph)C C(PPh2)C(O)CH2C(O)] (PPh3, 6; PMe3, 7). Compound 6 contains 48e- and exhibits a structural motif similar to that found in 4. Compound 7 readily adds a second PMe3 ligand to yield the bis-substituted cluster Ru3(CO)6(PMe3)2(μ2-COMe)[μ-P(Ph)C C(PPh2)C(O)CH2C(O)] (8). The solid-state structure of 8 confirms the loss of two ruthenium–ruthenium bonds and the conversion of the original face-capping μ3-COMe ligand to a μ2-COMe moiety that tethers two non-bonding ruthenium centers. The two PMe3 ligands in 8 coordinate to the same ruthenium center, and the 9e- P(Ph)C C(PPh2)C(O)CH2C(O) ligand binds all three ruthenium atoms through the phosphine, phosphido, alkene, and carbonyl moieties. Near-UV irradiation of 8 leads to loss of CO and polyhedral contraction of the triruthenium frame to yield the 48e- cluster Ru3(CO)5(PMe3)2(μ3-COMe)[μ-P(Ph)C C(PPh2)C(O)CH2C(O)] (9).

The reaction between the tetracobalt cluster Co4(CO)10(μ4-PPh)2 (1) and [Et4N][OH] (1.1 equivalents of a 1.3 M solution in MeOH) has been examined in THF at -78°C. Low-temperature IR analysis reveals the presence of both the hydroxycarbonyl cluster [Co4(CO)9(μ4-PPh)2(CO2H)-] [2-] and the methoxycarbonyl cluster [Co4(CO)9(μ4-PPh)2(CO2Me)-] [3-] as a result of hydroxide and methoxide attack, respectively, on a terminal carbonyl group in 1. IR band-shape analysis indicates that [2-] and [3-] exist in a 77:23 ratio at -72°C. Addition of excess [Li+] (as [CF3SO3][Li]) to solutions of [2-] and [3-] affords [3-] in quantitative yield at -72°C. The thermal stability and reactivity of these anionic clusters are discussed and comparisons made to the structural similar formyl and acetyl clusters derived from 1.

The reaction between Fe 2 (CO) 6 (μ 2 -S) 2 ( 1 ) and (THF)Cu(η 5 -Cp*) (where Cp* = C 5 Me 5 ) has been examined in THF at −78 °C. Rapid and efficient insertion of the carbene like fragment Cu(η 5 -Cp*) into the SS bond of 1 affords the mixed-metal arachno cluster Fe 2 (CO) 6 (μ 3 -S) 2 Cu(η 5 -Cp*) ( 2 ). Reaction of 1 with LiEt 3 BH and MeLi at −78 °C gives the corresponding cluster radical anion Fe 2 (CO) 6 (μ 3 -S) 2 Cu(η 5 -Cp*) ·− ( 3 ) without the spectroscopic intermediacy of CO-based reduction products. The thermal stability of 2 and 3 is described.

The rhenium anion [(η 5 -C 5 Me 5 )Re(CO) 2 Br − ] (2 − ) has been prepared in high yield from the reaction of lateral or diagonal (η 5 -C 5 Me 5 )Re(CO) 2 Br 2 with alkyl/aryllithium and Grignard reagents, trialkylborohydrides, and one-electron reducing agents. The molecular structure of 2 − (as the [PPP + ] salt) was established by X-ray crystallography. [(η 5 -C 5 Me 5 )Re(CO) 2 Br] [PPP] crystallizes in the orthorhombic space group Pbca

The kinetics for the bridge-to-chelate isomerization of the dppe ligand in H 4 Ru 4 (CO) 10 (dppe) have been investigated by UV-vis and NMR spectroscopies over the temperature range of 308-328 K. The isomerization of the ligand-bridged cluster 1,2-H4Ru4(CO)io(dppe) (1-br) was found to be reversible by 31 P NMR spectroscopy, affording a K eq = 15.7 at 323 K in favor of the chelating dppe isomer 1-ch. The forward (k 1 ) and reverse (k -1 ) first-order rate constants for the reaction have been measured in different solvents and in the presence of ligand-trapping agents (CO and PPh 3 ). On the basis of the activation parameters and reaction rates that are unaffected by added CO and PPh 3 , a sequence involving the nondissociative migration of a phosphine moiety and two CO groups between basal ruthenium centers is proposed and discussed.

Controlled thermolysis of the mixed-metal clusters RCCo 2 NiCp(CO) 6 (R = H, Ph) with the chiral diphosphine ligand 3,4-bis(diphenylphosphino)-5-methoxy-2(5 H )-furanone (bmf) leads to CO substitution and formation of the corresponding bmf-bridged clusters RCCo 2 NiCp(CO) 4 (bmf) (R = H, Ph). These clusters exist in solution as a non-interconverting mixture of diastereomers, as determined by NMR spectroscopy. Whereas the benzylidyne-capped cluster PhCCo 2 NiCp(CO) 4 (bmf) decomposes in 1,2-dichloroethane (DCE) during prolonged heating at 83 °C, thermolysis of HCCo 2 NiCp(CO) 4 (bmf) affords the new phosphido-bridged cluster Co 2 NiCp(CO) 4 [μ 2 ,η 2 ,η 1 -C(H)C C(PPh 2 )C(O)OCH(OMe)](μ-PPh 2 ) under the same conditions. This latter cluster has been isolated and characterized in solution by IR and NMR spectroscopies and the solid-state structure determined by X-ray diffraction analysis. The structural highlights for Co 2 NiCp(CO) 4 [μ 2 ,η 2 ,η 1 -C(H)C C(PPh 2 )C(O)OCH(OMe)](μ-PPh 2 ) include the regioselective cleavage of the P–C(furanone ring) bond, coupled with polyhedral opening of the Co 2 Ni core and attack on the CpNi center by the other phosphine moiety of the bmf ligand. The diastereoselectivity accompanying the formation of cluster Co 2 NiCp(CO) 4 [μ 2 ,η 2 ,η 1 -C(H)C C(PPh 2 )C(O)OCH(OMe)](μ-PPh 2 ) is discussed relative to steric effects within the cluster polyhedron.

The reaction of the μ3-benzylidyne capped cluster PhCCo3(CO)9 (1) with 2, 3-bis(diphenylphosphino)maleic anhydride (L-L) has been examined at 75 °C in toluene solvent. The major product isolated was not the expected diphosphine complex PhCCo3(CO)7(L-L) but rather the new cluster Co3(CO)6(μ2-η2-η1(O))(μ2-PPh2) (2). It is shown that the μ3-benzylidyne ligand in 1 is transformed into a bridging benzylidene ligand as a result of the formal insertion into one of the PC bonds of the ancillary 2, 3-bis(diphenylphosphino)maleic anhydride ligand. Formation of a μ2-phosphido group accompanies this transformation. Cluster 2 has been characterized by IR and 31P1H NMR spectroscopy. Single-crystal X-ray diffraction analysis establishes the presence of the new six-electron μ2-benzylidene-η2-η1(diphenylphosphino)maleic anhydride ligand. 2 crystallizes in the monoclinic space group P21/n, a=11.538(1), b=17.0754(8), c=19.506(1) A, β=92.108(7)°, Z=4, Dcalc=1.557 g cm−3, R=0.0392, Rw=0.0432 for 2012 observed reflections. Cluster 2 provides the experimental basis for enhanced μ3-CCo bond reactivity as opposed to CoCo bond reactivity. The significance of 2 is discussed in the context of cluster catalysis and ligand-modulated reactivity of the μ3-benzylidyne ligand in 1.

The syntheses of new tantalum compounds containing an ancillary azido ligand(s) are described. The tantalum compound with the composition Ta(NMe2)4(N3) has been synthesized in high yield from the reaction of TaCl(NMe2)4 with NaN3 in THF. The solid-state structure reveals a dimeric architecture based on Ta2(NMe2)8(μ-N3)2 (1), where the eight-membered dimetallocyclic ring possesses a chair-like conformation with bridging azido ligands binding the two Ta(NMe2)4 moieties. Solution molecular weight measurements and electronic structure calculations predict 1 to exist as a monomer at room temperature. 1 reacts with the formamidine iPrNC(H)NHiPr to furnish fac-Ta(NMe2)3(η1-N3)[iPrNC(H)NiPr] (2) and Me2NH; compound 2 has been characterized by IR and 1H NMR spectroscopy and X-ray diffraction analysis. Treatment of 1 with p-toluidine affords the trinuclear compound Ta3(NMe2)5(μ-NMe2)(μ-NC6H4Me-4)2(NC6H4Me-4)(μ-N3)2(η1-N3) (3). Compound 3 contains three non-bonded tantalum atoms that are ligated by edge-bridging imido, amido, and azido ligands. The molecular structure of 3 has been determined by X-ray crystallography, and the unprecedented presence of terminal and bridging imido, amido, and azido ligands in a single tantalum compound confirmed. The bonding in 3 has been examined by DFT, and these data are discussed relative to the crystallographic structure. Compounds 1–3 represent the first structurally characterized examples of heteroleptic tantalum compounds that possess an all-nitrogen coordination sphere with at least one azido ligand.

EPR spectra are reported for four metal complexes of 2,3-bis(diphenylphosphino)maleic anhydride (BMA), [Co(2)(PhCCR)(CO)(4)(eta-BMA)](-), R = Ph, H, [Co(2)(PhCCPh)(CO)(4)(mgr;-BMA)](-), and [PhCW(CO)(2)(BMA)Cl](-), as well as the radical anions, [BMA](-) and [BPCD](-), BPCD = 4,5-bis(diphenylphosphino)cyclopentene-1,3-dione. At room temperature, all spectra are 1:2:1 triplets due to hyperfine coupling to two equivalent (31)P nuclei with coupling to two equivalent (1)H nuclei for [BPCD](-) and unresolved coupling to one or two (59)Co nuclei for the Co complexes with chelating or bridging BMA, respectively. The (31)P couplings are temperature dependent, ca. -3 and -13 mG K(-)(1) for the metal complexes and ligand radical anions, respectively. At low temperature, the spectrum of [BMA](-) shows the presence of symmetric and asymmetric PPh(2) rotational conformers, related by the thermodynamic parameters DeltaH degrees = -0.8 +/- 0.2 kJ mol(-)(1) and DeltaS degrees = 4 +/- 1 J mol(-)(1) K(-)(1) and interconverted with activation parameters DeltaH() = 18.2 +/- 0.4 kJ mol(-)(1), DeltaS() = -30 +/- 2 J mol(-)(1) K(-)(1). The temperature dependence of the (31)P couplings is explained by a negative spin-polarization contribution toa(P)and a positive contribution due to P 3s character; the latter increases with the asymmetry of the PPh(2) conformations. The range of conformations accessible to the metal complexes is less than for the ligand radical anions, and accordingly the temperature dependence is significantly smaller.

C 39 H 43 Co 4 O 9 P 3 •C 7 H 8 cristallise dans P2 1 avec a=10,634, b=20,674, c=12,189 A, β=112,44 o , Z=2; affinement jusqu'a R=0,044. L'arrangement rectangulaire des atomes Co est plan et presente deux chapeaux formes par les groupes η 4 -phenylphosphinidene, donnant ainsi un cœur polyedre closo

The diphosphine-bridged ruthenium dimer Ru 2 (CO) 6 [((Z)Ph 2 PCHCHPPh 2 ] ( 1 ) reacts with added PMe 3 under photochemical and thermal conditions and by Me 3 NO-induced activation at the phosphine-substituted ruthenium center to give Ru 2 (CO) 5 (PMe 3 )[(Z)Ph 2 PCHCHPPh 2 ] ( 2 ). The entering PMe 3 is found to adopt axial and equatorial sites in 2 , as confirmed by solution 1 H and 31 P NMR spectroscopy measurements. The solid-state structure of the equatorially substituted isomer 2e has been established by X-ray diffraction analysis. 2e cystallizes in the triclinic space group P 1 : a = 10.8602(7), b = 10.801(9), c = 15.680(1) A , α = 79.788(6), β = 82.838(6), y = 66.450(5)°, V = 1714.6(2) A 3 , Z = 2, D calc = 1.578 g cm −3 ; R = 00574, R w = 0.0627 for 3695 observed reflections with 1>3 σ(1).

Eight new catecholate- and naphthalenediolate-substituted pentamethylcyclopentadienylruthenium, compounds have been prepared from the reaction between Cp ∗ Ru(NO)Cl 2 and the appropriate aromatic diol in methanolic KOH. Each new compound has been isolated and fully characterized in solution by IR and NMR ( 1 H and 13 C) spectroscopy, in addition to X-ray diffraction analysis which has established the solid-state structure of the naphthalenediolate compound Cp ∗ Ru(NO)(2,3-O 2 C 10 H 6 ). Cp ∗ Ru(NO)(2,3-O 2 C 10 H 6 ) crystallizes, as the CH 2 Cl 2 solvate, in the monoclinic space group P 2 1 / n with a = 11.0176(8), b = 16.041(2), c = 13.0504(9) A , β = 112.024(6)° , V = 2138.1(3) A 3 and Z =4. Full-matrix least-squares refinement yielded R =0.0376 for 1893 ( l .3 ϱ ( l )) reflections. Cyclic voltammetric studies have been carried out, and two redox responses were observed, assignable to the 0/1− and 0/1+ redox couples. Whereas the reduction wave in each of the compounds is essentially independent of the nature of the ancillary diolate ligand, the stability of the oxidation couple is modulated by the electronic properties of the diolate ligand. The molecular orbital properties of several model CpRu(NO)(diolate) compounds were explored by extended Huckel calculations. The calculated HOMO and LUMO energies of each compound displayed good agreement with the cyclic voltammetry data, allowing for generalizations to be made concerning the site of electron addition to and electron removal from the new Cp ∗ Ru(NO)(diolate) compounds.

The reaction between the pentamethylcyclopentadienyl complex Cp*Ru(NO)Cl2 and oxalic acid in methanolic KOH affords the corresponding oxalate compound Cp*Ru(NO)(ox) in moderate yield. The title complex has been isolated and characterized in solution by IR and NMR (1H and13C) spectroscopy, and the solid-state structure has been established by X-ray diffraction analysis, which confirmed the presence of the chelating oxalate ligand in Cp*Ru(NO)(ox). Cp*Ru(NO)(ox) crystallizes in the triclinic space group $$P\bar 1$$ ,a=7.0875(9) A,b=8.589(2) A,c=12.784(4) A, α=73.58(2)°, β=88.93(2)°, γ=66.86(2)°,V=682.7(8) A3,Z=2,d calc=1.724 g·cm−3; R=0.053, Rw=0.071 for 1561 observed reflections withI>3σ(I).

The new compound Cp ∗ Ru(NO)(dmit) has been prepared from Cp ∗ Ru(NO)Cl 2 and 1,3-dithiol-2-thione-4,5-dithiolate (dmit), prepared in situ from 4,5-bis(benzoylthio)-1,3-dithiol-2-thione in ethanolic sodium ethoxide, in moderate yield. The product has been isolated and characterized in solution by IR and NMR ( 1 H and 13 C) spectroscopies. The solid-state structure of Cp ∗ Ru(NO)(dmit) has been confirmed by single-crystal X-ray diffraction analysis. The electrochemical behavior of Cp ∗ Ru(NO)(dmit) has been studied by cyclic and rotating disk electrode voltammetries, revealing the existence of two well-defined one-electron responses that have been assigned to the 0/+1 and 0/−1 redox couples. The composition of the HOMO and LUMO levels in the model compound CpRu(NO)(dmit) has been determined by carrying out extended Huckel molecular orbital calculations. The MO data indicate that the HOMO in CpRu(NO)(dmit) is best described as a dmit-based orbital (78%) which contains a small amount of Ru (d x 2 − y 2 )/NO (py) character, while the LUMO is best represented by an antibonding overlap of the Ru ( d xy ) and π ∗ NO ( p x ) orbitals. A comparison of the MO and electrochemical data from Cp ∗ Ru(NO)(dmit) with the structurally related dithiolate compounds Cp ∗ Ru(NO) (mnt) and Cp ∗ Ru(NO)(tdas) is presented. It has been found that Cp ∗ Ru(NO)(dmit) exhibits a more easily oxidized 0/+1 redox couple as compared to the mnt and tdas compounds. This results from the presence of a high-lying [dmit] 2− donor orbital that leads to a high-energy antibonding interaction between the Cp ∗ Ru(NO) and dmit fragments, which in turn produces a destabilized HOMO.

The reaction between Cp*Ru(NO)Cl2 and the heterocyclic compound 2,3-quinoxalinediol in the presence of methanolic KOH leads to the formation of the new piano-stool compound Cp*Ru(NO)(2,3-quinoxalinediolate) (1). Product isolation and characterization by solution spectroscopic methods (1H and13C NMR and IR) are described. The solid-state structure of Cp*Ru(NO)(2,3-quinoxalinediolate) confirms the replacement of each chloride ligand in Cp*Ru(NO)Cl2 by an oxygen group of the 2,3-quinoxalinediol ligand. Cp*Ru(NO)(2,3-quinoxalinediolate) crystallizes in the orthorhombic space group Pbca, a=14.846(1) A,b=12.718(1) A,c=18.255(2) A,V=3446.7(5) A3,Z=8,d calc=1.643 g·cm−3;R=0.0364,R w=0.0393 for 1245 observed reflections withI>3σ(I). The observed Ru−N−O bond angle of 156.3(7)° in the X-ray structure of1 confirms the nonlinear nature of the nitrosyl linkage. This bend in the nitrosyl moiety away from the quinoxalinediolate ligand presumably results from solid-state packing forces and does not derive from electronic interactions, on the basis of extended Huckel molecular orbital calculations. The MO properties of1 are compared with other Cp*Ru(NO)-substituted complexes previously synthesized in these laboratories.

Recent advances in high surface area (HSA) electrode materials have played an important role in the development of high-performance batteries and fuel cells. HSA electrodes can significantly increase the power-density of batteries and fuel cells by enhancing the heterogeneous electrochemical reaction rate and concurrently reducing battery and fuel cell size and weight. The compactness of HSA electrodes can also reduce the ohmic potential drop, which has the clear advantage of reducing power losses. This paper reports results on utilizing direct metallization of porous substrates to prepare new HSA electrode materials. Specifically, Nickel HSA electrode materials, relevant to the Ni-Cd and metal-hydride rechargeable batteries, were prepared on porous carbon substrates by direct thermolysis of organometallic precursors and/or electroless Ni plating. SEM and XPS characterization results indicate a Ni metallic film was conformally coated over the porous carbon skeleton. The real electroactive areas were determined electrochemically in NaOH solution and results will be discussed in correlation with the metallization conditions.