Additions and intramolecular migrations of nucleophiles in cationic diruthenium μ-allenyl complexes

The diruthenium μ-allenyl complex [Ru₂(CO)(NCMe)(μ-CO){μ-η¹:η²-C(H)CC(Me)(Ph)}(Cp)₂][BF₄], 3b, reacts with halide anions to yield the neutral derivatives [Ru₂(CO)₂(X){μ-η¹:η²-C(H)CC(Me)(Ph)}(Cp)₂] [X = Cl, 4b; X = Br, 4c; X = I, 4d]. Complex 4b undergoes isomerization to the unprecedented bridging vinyl-chlorocarbene species [Ru₂(CO)(μ-CO){μ-η¹:η³- C(Cl)C(H)C(Me)(Ph)}(Cp)₂], 10, upon filtration of a CH₂Cl₂ solution through an alumina column.Complex 3b reacts with an excess of NaBH₄ to give five products: the allene complex [Ru₂(CO)₂{μ-η²:η²- CH₂CC(Me)(Ph)}(Cp)₂], 5; the hydride species trans-[Ru₂(CO)₂(μ-H){μ-η¹:η²-CHCC(Me)(Ph)}(Cp)₂], 6, and cis-[Ru₂(CO)₂(μ-H){μ-η¹:η²-CHCC(Me)(Ph)}(Cp)₂], 8; the vinyl-alkylidene [Ru₂(CO)(μ-CO){μ-η¹:η³- C(H)C(H)C(Me)(Ph)}(Cp)₂], 9; and the cluster [Ru₃(CO)₃(μ-H)₃(Cp)₃], 7.Studies on the thermal stabilities of 5, 6, 8 and 9 have suggested a plausible mechanism for the formation of these complexes and for the synthesis of 10.     

Formation of multifunctional ligands by nucleophilic addition of alcohols and thiols to the alkyne groups in compound C5H5FeC5H4CCSCCH: Reactivity studies

The multifunctional ligands [(Z)-FcCCSC(H)C(H)XR] [X = O, R = Me (2a); X = O, R = Et (2b); X = S, R = Ph (3); X = S, R = C₆F₅ (5)] and [(Z,Z)-Fc(SR)CC(H)SC(H)C(H)SR] [R = Ph (4), C₆F₅ (6)] have been prepared through hydroalkoxylation and hydrothiolation processes of the alkyne groups in the compound FcCCSCCH 1. Reactions between compound 3 and the carbonyl metals Co₂(CO)₈, Os₃(CO)₁₀(NCMe)₂ and Fe₂(CO)₉ have allowed the synthesis of the polynuclear compounds [(Z)-{Co₂(CO)₆}(μ-η²-FcCCSC(H)C(H)SPh)] 9, [(Z)-Os₃(CO)₉(μ-CO){μ₃-η²-FcCCSC(H)C(H)(SPh)}] 10 and [(Z)-{Fe₃(CO)₉}[μ₃,η³-(CCS)-FcCCSC(H)C(H)(SPh)] 11. All the compounds have been characterized by elemental analysis, ¹H and ¹³C{¹H} NMR spectroscopy, mass spectrometry and the crystal structure of compounds [(Z)-FcCCSC(H)C(H)OMe] 2a and [{Co₂(CO)₆}₂(μ-η²:η²-FcCCSCCSiMe₃)] 7 have been solved by X ray diffraction analysis.     

Reactivity of silyl-substituted heterobimetallic iron-platinum hydride complexes towards unsaturated molecules: Part II. Insertion of trifluoropropyne and hexafluorobutyne into the platinum-hydride bond

Insertion of hexafluorobutyne into the Pt-H bond of the heterobimetallic complexes [(OC)₃Fe{Si(OMe)₃}(μ-Ph₂PXPPh₂)Pt(H)(PPh₃)] (1a X = CH₂; 1b X = NH) yields the σ-alkenyl complexes [(OC)₃Fe{μ-Si(OMe)₂(OMe)}(μ-Ph₂PXPPh₂)Pt{C(CF₃)C(H)CF₃}] (3a X = CH₂; 3b X = NH). This insertion reaction is accompanied by dissociation of the platinum bound PPh₃ ligand and saturation of the vacant coordination site by a dative μ−η²-Si-O → Pt interaction. Addition of the Pt-H bond of 1a across the triple bond of 3,3,3-trifluoropropyne affords in a regiospecific manner [(OC)₃Fe{μ-Si(OMe)₂(OMe)}(μ-dppm)Pt{C(CF₃)CH₂}] (2) having the trifluoromethyl substituent on the α-carbon. Addition of RNC to 3 affords the isocyanide adducts [(OC)₃Fe{Si(OMe)₃}(μ-Ph₂PXPPh₂)Pt(CNR){C(CF₃)C(H)CF₃}] (4a R = t-Bu, X = CH₂; 4b R = 2,6-xylyl, X = CH₂; 4c R = 2,6-xylyl, X = NH). In dichloromethane solution 3a is gradually transformed into the C₄F₆-bridged compound [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt(CO)] 5. The Pt-bound carbonyl ligand of 5 is displaced by xylylisocyanide or trimethylphosphite affording the derivatives [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt(CNxylyl)] 6 and [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt{P(OMe)₃}] 7. The molecular structures of 4a, 5 and 6 have been determined by X-ray diffraction studies.     

Medium size macrocycles incorporating combinations of coordinated-1,3-diyne units, oxygen donors and group 14 elements

Two approaches have been employed to prepare medium size macrocycles incorporating combinations of coordinated-1,3-diyne units, oxygen donors and group 14 elements. In the first approach, the acid-catalysed reaction of [{Co₂(CO)₆(μ-η²-HOCH₂CC)}₂] (1a) with either C₆H₅OH, C₆H₄-1,4-(OH)₂ or C₆H₄-1,2-(OH)₂ was found to form in good to moderate yield the nine-membered [{Co₂(CO)₆}₂{cyclo-μ-η²:μ-η²-CH₂C₂C₂CH₂OC₆H₄}₂] (2) and the eight-membered macrocycles, [{Co₂(CO)₆}₂{cyclo-μ-η²:μ-η²-CH₂C₂C₂CH₂-2,3-C₆H₂-1,4-(OH)₂}] (3) and [{Co₂(CO)₆}₂{cyclo-μ-η²:μ-η²-CH₂C₂C₂CH₂-3,4-C₆H₂-1,2-(OH)₂}] (4), respectively. In contrast, treatment of the bis-lithiated derivative of 1a with Cl₂SiR¹R² affords the silicon-containing nine-membered macrocycles [{Co₂(CO)₆}₂{cyclo-μ-η²:μ-η²-OCH₂C₂C₂CH₂OSiR¹R²}] (5a R¹ = R² = Me; 5b R¹ = R² = Ph; 5c R¹ = Me, R² = Ph). Similarly, the germanium analogue of 5b, [{Co₂(CO)₆}₂{cyclo-μ-η²:μ-η²-OCH₂C₂C₂CH₂OGePh₂}] (6) can be prepared from Cl₂GePh₂. Single crystal X-ray diffraction studies have been reported on 2, 3, 5a, 5b and 6.     

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.     

Rhenium(I) tricarbonyl complexes with bispyridine ligands attached to sulfur-rich core: Syntheses, structures and properties

Rhenium(I) tricarbonyl complexes with bispyridine ligands bearing sulfur-rich pendant, Re(CO)₃(Medpydt)X (Medpydt = dimethyl 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylate; X = Cl, 1; X = Br, 2) and Re(CO)₃(MebpyTTF)X (MebpyTTF = 4,5-bis(methyloxycabonyl)-4′,5′-(4′-methyl-2,2′-dipyrid-4-ylethylenedithio)-tetrathiafulvalene; X = Cl, 5; X = Br, 6), were prepared from the reactions between Re(CO)₅X (X = Cl, Br) and Medpydt or MebpyTTF, respectively. Hydrolysis of the above complexes afforded the analogues with carboxylate derivatives, Re(CO)₃(H₂dpydt)X (X = Cl, 3; X = Br, 4) and Re(CO)₃(H₂bpyTTF)X (X = Cl, 7; X = Br, 8). The crystal structures for complexes 1 · 2H₂O, 5 and 6 were determined using X-ray single crystal diffraction. UV-Vis absorption spectra of the rhenium complexes show the intraligand and MLCT transitions. Electrochemical behaviors of all new compounds were studied with cyclic voltammetry. Upon irradiation, complexes 3-6 exhibit blue to red emissions in fluid solutions at the room temperature. The performance of complexes 3, 4, 7 and 8 as photosensitizers for anatase TiO₂ solar cells was preliminarily investigated as well.     

Photophysical properties and computational investigations of tricarbonylrhenium(I)[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]L and tricarbonylrhenium(I)[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]L derivatives (X = N-CH3, O, or S; L = Cl, pyridine)

We report a combined experimental and computational study of new rhenium tricarbonyl complexes based on the bidentate heterocyclic N-N ligands 2-(4-methylpyridin-2-yl)benzo[d]-X-azole (X = N-CH₃, O, or S) and 2-(benzo[d]-X-azol-2-yl)-4-methylquinoline (X = N-CH₃, O, or S). Two sets of complexes are reported. Chloro complexes, described by the general formula Re(CO)₃[2-(4-methylpyridin-2-yl)benzo[d]-X-azole]Cl (X = N-CH₃, 1; X = O, 2; X = S, 3) and Re(CO)₃[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]Cl (X = N-CH₃, 4; X = O, 5; X = S, 6) were synthesized heating at reflux Re(CO)₅Cl with the appropriate N-N ligand in toluene. The corresponding pyridine set {Re(CO)₃[2-(4-methylpyridin-2-yl)benzo-X-azole]py}PF₆ (X = N-CH₃, 7; X = O, 8; X = S, 9) and {Re(CO)₃[2-(benzo[d]-X-azol-2-yl)-4-methylquinoline]py}PF₆ (X = N-CH₃, 10; X = O, 11; X = S, 12) was synthesized by halide abstraction with silver nitrate of 1-6 followed by heating in pyridine and isolated as their hexafluorophosphate salts. All complexes have been fully characterized by IR, NMR, electrochemical techniques and luminescence. The crystal structures of 1 and 7 were obtained by X-ray diffraction. DFT and time-dependent (TD) DFT calculations were carried out for investigating the effect of the organic ligand on the optical properties and electronic structure of the reported complexes.     

Synthesis, photochemistry, and electrochemistry of ruthenium(II) polypyridyl complexes anchored by dicobalt carbonyl units

A novel hybrid complex system of ruthenium polypyridyl complexes anchored by dicobalt carbonyl units, [Ru(bpy)₂{phen-C{Co₂(CO)₄(dppm)}C-tolyl}](PF₆)₂ (1) and [Ru(bpy)₂{tolyl-C{Co₂(CO)₄(dppm)}C-phen-C{Co₂(CO)₄(dppm)}C-tolyl}](PF₆)₂ (2), has been prepared from the dicobalt carbonyl complex Co₂(CO)₆(dppm) (dppm = bis(diphenylphosphino)methane) and the ruthenium complex [Ru(bpy)₂(phen--tolyl)](PF₆)₂ (3) or [Ru(bpy)₂(tolyl--phen--tolyl)](PF₆)₂ (4).The present Ru-Co₂ hybrid complexes 1 and 2 are nonluminescent at room temperature, although precursor ruthenium polypyridyl complexes, such as 3 and 4, clearly show phosphorescence from the ³MLCT excited state. The emission quenching of these hybrid complexes indicates the intramolecular energy transfer from the ruthenium polypyridyl unit to the dicobalt carbonyl unit(s) and then to the ground state by a radiationless deactivation process accompanied by a vibrational relaxation of the dicobalt carbonyl unit(s). This interpretation is supported by spectral change measurements along with constant potential electrolysis and electrochemical data.     

Chalcogen-capped ruthenium carbonyl clusters derived from diphosphazane mono- and dichalcogenides of the type X2P(E)N(R)PX2 and X2P(E)N(R)P(E)X2 (E = S or Se)

Reactions of Ru₃(CO)₁₂ with diphosphazane monoselenides Ph₂PN(R)P(Se)Ph₂ [R = (S)-∗CHMePh (L⁴), R = CHMe₂ (L⁵)] yield mainly the selenium bicapped tetraruthenium clusters [Ru₄(μ₄-Se)₂(μ-CO)(CO)₈{μ-P,P-Ph₂PN(R)PPh₂}] (1, 3). The selenium monocapped triruthenium cluster [Ru₃(μ₃-Se)(μ_sb-CO)(CO)₇{κ²-P,P-Ph₂PN((S)-∗CHMePh)PPh₂}] (2) is obtained only in the case of L⁴. An analogous reaction of the diphosphazane monosulfide (PhO)₂PN(Me)P(S)(OPh)₂ (L⁶) that bears a strong π-acceptor phosphorus shows a different reactivity pattern to yield the triruthenium clusters, [Ru₃(μ₃-S)(μ₃-CO)(CO)₇{μ-P,P-(PhO)₂PN(Me)P(OPh)₂}] (9) (single sulfur transfer product) and [Ru₃(μ₃-S)₂(CO)₅{κ²-P,P-(PhO)₂PN(Me)P(OPh)₂}{μ-P,P-(PhO)₂PN(Me)P(OPh)₂}] (10) (double sulfur transfer product). The reactions of diphosphazane dichalcogenides with Ru₃(CO)₁₂ yield the chalcogen bicapped tetraruthenium clusters [Ru₄(μ₄-E)₂(μ-CO)(CO)₈{μ-P,P-Ph₂PN(R)PPh₂}] [R = (S)-∗CHMePh, E = S (6); R = CHMe₂, E = S (7); R = CHMe₂, E = Se (3)]. Such a tetraruthenium cluster [Ru₄(μ₄-S)₂(μ- CO)(CO)₈{μ-P,P-(PhO)₂PN(Me)P(OPh)₂}] (11) is also obtained in small quantities during crystallization of cluster 9. The dynamic behavior of cluster 10 in solution is probed by NMR studies. The structural data for clusters 7, 9, 10 and 11 are compared and discussed.     

Heterometallic Pt-Ag and Pt2Ag transition metal complexes

Complexes of type {cis-[Pt](μ-σ,π-CCPh)₂}AgX (3a, [Pt] = (bipy′)Pt, X = FBF₃; 3b, [Pt] = (bipy′)Pt, X = FPF₅; 3c, [Pt] = (bipy)Pt, X = OClO₃; 3d, [Pt] = (bipy′)Pt, X = BPh₄; bipy′ = 4,4′-dimethyl-2,2′-bipyridine; bipy = 2,2′-bipyridine) are accessible by combining cis-[Pt](CCPh)₂ (1a, [Pt] = (bipy′)Pt; 1b, [Pt] = (bipy)Pt) with equimolar amounts of [AgX] (2a, X = BF₄; 2b, X = PF₆; 2c, X = ClO₄; 2d, X = BPh₄). In 3a-3d the platinum(II) and silver(I) ions are connected by σ- and π-bonded phenyl acetylide ligands. When the molar ratio of 1 and 2 is changed to 2:1 then trimetallic [{cis-[Pt](μ-CCPh)₂}₂Ag]X (8a, [Pt] = (bipy)Pt, X = BF₄; 8b, [Pt] = (bipy′)Pt, X = PF₆; 8c, [Pt] = (bipy)Pt, X = BF₄) is produced. The solid state structure of 8a was determined by single X-ray crystal structure analysis. In 8a the silver(I) ion is embedded between two parallel oriented cis-[Pt](CCPh)₂ units. Within this structural arrangement the phenyl acetylides of individual [Pt](CCPh)₂ entities possess a μ-bridging position between Pt(II) and Ag(I). In addition, a very weak dative Pt → Ag interaction is found (Pt-Ag 2.8965(3) Å). The respective silver carbon distances Ag-C_α (2.548(7), 2.447(7) Å) and Ag-C_β (3.042(7), 2.799(8) Å)(PtC_αC_βPh) confirm this structural motif.Complexes 8a-8c isomerize in solution to form trimetallic [{cis-[Pt](μ-σ,π-CCPh)₂}₂Ag]X (9a, [Pt] = (bipy)Pt, X = BF₄; 9b, [Pt] = (bipy′)Pt, X = PF₆; 9c, [Pt] = (bipy)Pt, X = ClO₄). In the latter molecules the organometallic cation [{cis-[Pt](μ-σ,π- CCPh)₂}₂Ag]⁺ is set-up by two nearly orthogonal positioned [Pt](CCPh)₂ entities which are hold in close proximity by the group-11 metal ion. Within this assembly all four PhCC units are η²-coordinated to silver(I). A possible mechanism for the formation of 9 is presented.     

Amination and Suzuki coupling reactions catalyzed by palladium complexes coordinated by cobalt-containing monodentate phosphine ligands with bis-trifluoromethyl substituents on bridged arylethynyl: Observation of some unusual metal-containing compounds

Two cobalt-containing bulky monodentate phosphines {[(μ-PPh₂CH₂PPh₂)Co₂(CO)₄][(μ,η-(^tBu)₂PCCAr]} (4cm: Ar = 3-CF₃C₆H₄; 4cmm: Ar = 3,5-(CF₃)₂C₆H₃) were prepared from the reaction of Co₂(CO)₆(μ-PPh₂CH₂PPh₂) (3) with each corresponding alkynes (^tBu)₂PCCAr. Both compounds were converted to their oxidized forms {[(μ-PPh₂CH₂PPh₂)Co₂(CO)₄][(μ,η-(^tBu)₂P(O)CCAr]} (4cmO: Ar = 3-CF₃C₆H₃; 4cmmO: Ar = 3,5-(CF₃)₂C₆H₃) in the presence of oxide. Further reactions of 4cm and 4cmm with Pd(OAc)₂ gave palladium complexes {[(μ-PPh₂CH₂PPh₂)Co₂(CO)₄][(μ,η-(^tBu)₂PCC(Ar)-κC¹)]Pd(μ-OAc)} 5cm (Ar = 3-CF₃C₆H₃) and 5cmm (Ar = 3,5-(CF₃)₂C₆H₂), respectively. By contrast, reactions of 4cm and 4cmm with Pd(COD)Cl₂ gave products, [{μ-P,P-PPh₂CH₂PPh₂}Co₂(CO)₃(μ-CO){μ,η-(^tBu)₂PCCAr}]-PdCl₂] 8cm and 8cmm, respectively, with unique bonding modes. Several crystallines of [(4cm)₂Pd₃(μ-Cl)(μ-CO)₂)(μ-Cl)]₂ (9) were obtained along with crystallines of 8cm during the crystallization process. The crystal structures of all three compounds, 4cmmO, 8cmm and 9 were determined by single-crystal X-ray diffraction methods. Fair to excellent efficiencies were observed for employing 4cmm/palladium salt as catalytic precursor in amination as well as in Suzuki coupling reactions.     

The influence of alkane spacer of bis(diphenylphosphino)alkanes on the nuclearity of silver(I): Syntheses and structures of P,P′-bridged clusters and coordination polymers involving dithiophosphates

The effect of the length of alkane spacer in diphosphines on the nuclearity of Ag(I) complexes containing dialkyl dithiophosphates (dtp) ligands has been investigated. 1,1-Bis(diphenylphosphino)methane (dppm) yielded tetranuclear [Ag₄(dppm)₂{S₂P(OEt)₂}₄] (1), [Ag₄(dppm)₂{S₂P(OⁱPr)₂}₄] (3), trinuclear [Ag₃(dppm)₃{S₂P(OEt)₂}₂](PF₆) (2), and a dinuclear [Ag₂(dppm)₂{S₂P(OⁱPr)}](PF₆) (4). The increase in spacer length from one methylene in dppm to two in 1,2-bis(diphenylphosphino)ethane (dppe) resulted in the formation of polymeric, [Ag(dppe){S₂P(OR)₂}]_∞ (R = Et, 5a and 5a′; ⁱPr, 5b), and [Ag₄(μ₃-Cl)(dppe)_1.5{S₂P(OR)₂}₃]_∞ (R = Et, 6a; ⁱPr, 6b). Compounds 5a, 5b, 6a and 6b were reported earlier [C.W. Liu, B.-J. Liaw, L.-S. Liou, J.-C. Wang, Chem. Commun. (2005) 1983]. Further increase in the chain length to four methylene units in 1,4-bis(diphenylphosphino)butane (dppb) yielded dppb-bridged polymers, [Ag(dppb){S₂P(OEt)₂}]_∞ (7) and [Ag₂(dppb){S₂P(OEt)₂}₂]_∞ (8). In all the polynuclear compounds, diphosphines acted as P,P′-bridging ligands, while the dtp ligands (S,S′-donors) adopted varieties of coordination patterns: S,S′-chelating (5, 7), S,S′-bridging (4), bimetallic-triconnective, μ₂:η²,η¹ (1, 3, 8), bimetallic-diconnective, μ₂:η² (2, 3) and trimetallic-triconnective, μ₃:η²,η¹ (6). Some of the complexes exhibit argentophilicity with Ag?Ag distances in the range, 2.918-3.360 Å. Concomitant bridging of two silver atoms either by dppm and dtp ligands (1, 3 and 4) or two dtp ligands (8) lead to close silver-silver contacts. The diphosphines (dppe and dppb) with longer spacer appeared to favor 1D or 2D polymers due to the flexibility of the spacer within the diphosphine unit by adopting anti conformation as opposed to syn conformation of the dppm linker is revealed in complexes.     

Reactivity and electrochemical behavior of ruthenium dithiolene complexes with coordinatively unsaturated metal centers: cycloaddition and dimerization reactions

The novel ruthenium dithiolene complexes [(arene)Ru{S₂C₂(COOMe)₂}] (arene = C₆H₆ (1a), C₆H₄(Me)(iPr) (1b), C₆Me₆ (1c)) were synthesized. The equilibrium between complex 1a and the corresponding dimer [(C₆H₆)Ru{S₂C₂(COOMe)₂}]₂ (1a′) was confirmed in solution. The reaction of complex 1a with dimethyl- or diethylacetylene dicaboxylate gave the alkene-bridged adducts [(C₆H₆)Ru{S₂C₂(COOMe)₂}{C₂(COOR)₂}] (R = Me (2a), Et (3a)) as [2 + 2] cycloaddition products formally. The reactions of complex 1a with diazo compounds also gave the alkylidene-bridged adducts [(C₆H₆)Ru{S₂C₂(COOMe)₂}(CHR)] (R = H (4a), SiMe₃ (5a), COOEt (6a)) as [2 + 1] cycloaddition products. The electrochemical behavior of complex 1a was investigated. The reductant of complex 1a was a stable species for several minutes. The oxidant of complex 1a was very unstable; the cation 1a⁺ formed was immediately converted to the corresponding cationic dimer 1a′⁺. The cationic dimer 1a′⁺ was stable for several minutes, and it was rapidly and quantitatively converted to the neutral complex 1a when it was reduced.     

Syntheses and molecular structures of some compounds containing many-atom chains end-capped by tricobalt carbonyl clusters

Several complexes containing Co₃ carbonyl clusters end-capping carbon chains of various lengths are described. Pd(0)/Cu(I)-catalysed reactions between {Co₃{μ₃-C(CC)₂Au(PPh₃)}(μ-dppm)(CO)₇ and I(CC)₂SiMe₃ or FcCCI gave {Co₃{μ₃-C(CC)_xR}(μ-dppm)(CO)₇ [x = 4, R = SiMe₃3; x = 3, R = Fc 8]; treatment of 3 with NaOMe and AuCl(PPh₃) gave 4 [x = 4, R = Au(PPh₃)]. Related preparations of Co₃{μ₃-C(CC)₂[Ru(PP)Cp′]}(μ-dppm)_n(CO)_9−2n [PP = (PPh₃)₂, Cp’ = Cp, n = 1, 5; PP = dppe, Cp′ = Cp^∗, n = 1, 6; 0, 7] are also described. Syntheses of bis-cluster complexes {Co₃(μ-dppm)(CO)₇}₂(μ-C_x) (x = 14, 12; 16, 9; 18, 11; 26, 10) - the latter being the longest cluster-capped C_x chains so far described - and the mercury-bridged compounds Hg{(CC)_xC[Co₃(μ-dppm)(CO)₇]}₂ (x = 1, 13; 2, 14) are reported. The molecular structures of 7, 12, 13 and 14, as well as of Co₃(μ₃-CCCSiMe₃)(μ-dppm)(CO)₆(PPh₃) (15) and Co₃{μ₃-CC(O)OEt}(μ-dppm)(CO)₇ (16), are reported.     

Synthesis, characterization, reactivity and computational studies of new rhenium(I) complexes with thiosemicarbazone ligands derived from 4-(methylthio)benzaldehyde

N-thioamide thiosemicarbazone derived from 4-(methylthio)benzaldehyde (R = H, HL¹; R = Me, HL² and R = Ph, HL³) have been prepared and their reaction with fac-[ReX(CO)₃(CH₃CN)₂] (X = Br, Cl) in methanol gave the adducts [ReX(CO)₃(HLⁿ)] (1a X = Cl, n = 1; 1a′ X = Br, n = 1; 1b X = Cl, n = 2; 1b′ X = Br, n = 2; 1c X = Cl, n = 3; 1c′ X = Br, n = 3) in good yield.All the compounds have been characterized by elemental analysis, mass spectrometry (ESI), IR and ¹H NMR spectroscopic methods. Moreover, the structures of HL², HL³, HL³·(CH₃)₂SO and 1b′·H₂O were also elucidated by X-ray diffraction. In 1b′, the rhenium atom is coordinated by the sulphur and the azomethine nitrogen atoms (κS,N³) forming a five-membered chelate ring, as well as three carbonyl and bromide ligands. The resulting coordination polyhedron can be described as a distorted octahedron.The structure of the dimers is based on rhenium(I) thiosemicarbazonates [Re₂(L¹)₂(CO)₆] (2a), [Re₂(L²)₂(CO)₆] (2b) and [Re₂(L³)₂(CO)₆] (2c) as determined by X-ray studies. Methods of synthesis were optimized to obtain amounts of these thiosemicarbazonate complexes. In these compounds the dimer structures are achieved by Re-S-Re bridges, where S is the thiolate sulphur from a κS,N³-bidentate thiosemicarbazonate ligand.Some single crystals isolated in the synthesis of 2b contain [Re(L⁴)(L²)(CO)₃] (3b) where L⁴ (=2-methylamine-5-(para-methylsulfanephenyl)-1,3,4-thiadiazole) is originated in a cyclization process of the thiosemicarbazone. Furthermore, the rhenium atom is coordinate by the sulphur and the thioamidic nitrogen of the thiosemicarbazonate (κS,N²) affording a four-membered chelate ring.     

Synthesis, characterization and reactivity of tribenzylphosphine rhodium and iridium complexes

New rhodium and iridium complexes, with the formula [MCl(PBz₃)(cod)] [M = Rh (1), Ir (2)] and [M(PBz₃)₂(cod)]PF₆ [M = Rh (3), Ir (4)] (cod = 1,5-cyclooctadiene), stabilized by the tribenzylphosphine ligand (PBz₃) were synthesized and characterized by elemental analysis and spectroscopic methods. The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. The addition of pyridine to a methanol solution of 1or 2, followed by metathetical reaction with NH₄PF₆, gave the corresponding derivatives [M(py)(PBz₃)(cod)]PF₆ [M = Rh (5), Ir (6)]. At room temperature in CHCl₃ solution, 4 converted spontaneously to the ortho-metallated complex [IrH(PBz₃)(cod){η²-P,C-(C₆H₄CH₂)PBz₂}]PF₆ (7) as a mixture of cis/trans isomers via intramolecular C-H activation of a benzylic phenyl ring. The reaction of 3 or 4 with hydrogen in coordinating solvents gave the dihydrido bis(solvento) derivative [M(H)₂(S)₂(PBz₃)₂]PF₆ (M = Rh, Ir; S = acetone, acetonitrile, THF), that transformed into the corresponding dicarbonyls [M(H)₂(CO)₂(PBz₃)₂]PF₆ by treatment with CO. Analogous cis-dihydrido complexes [M(H)₂(THF)₂(py)(PBz₃)₂]PF₆ (M = Rh, Ir) were observed by reaction of the py derivatives 5 and 6 with H₂.     

Observations on reaction pathways of dicobalt octacarbonyl with alkynyl amines

Treatments of a bis(diphenylphosphino)methylene (dppm) bridged dicobalt complex, Co₂(CO)₆(dppm) (4), with propargylamine and 4-ethynylaniline at 25 °C for 24 h gave [(dppm)Co₂(CO)₄(μ-HCCCH₂NH₂)] (5) and [(dppm)Co₂(CO)₄(μ-HCCC₆H₄NH₂)] (6), respectively. Interestingly, only alkynyl amines bridged dicobalt complexes were obtained rather than the previously observed coupling products. The results are in acceptance with the proposed mechanism which describes the formation of the coupling products {[Co₂(CO)₆(μ-HCC-)]-CH₂NH}₂CO (1) and {[Co₂(CO)₆(μ-HCC-)]-C₆H₄N}₂ (2) from the reaction of Co₂(CO)₈ with propargylamine and 4-ethynylaniline, respectively. Similar results were attained for the reactions of 4 with propioamide and 1-ethynylcyclohexylamine at 25 °C for 24 h which yielded [(dppm)Co₂(CO)₄(μ-HCCC(O)NH₂)] (7) and [(dppm)Co₂(CO)₄(μ-HCCC₆H₁₀NH₂)] (8), respectively.Reaction of 1-ethynylcyclohexylamine with one molar equivalent of Co₂(CO)₈ in THF at 25 °C for 15 min gave an alkyne bridged dicobalt complex, [Co₂(CO)₆(μ-HCCC₆H₁₀NH₂)] (9). Direct treatment of 3-ethynlaniline with one molar equivalent of Co₂(CO)₈ in THF at 25 °C for 1 h gave an alkyne bridged dicobalt complex, [Co₂(CO)₆(μ-HCCC₆H₄NH₂)] (11) and an azobenzene derivative, {[Co₂(CO)₆(μ-HCC)]C₆H₄N}₂ (10).Further treatments of 8, 9, and 11 with one molar equivalent of Sanger’s reagent, 2,4-dinitrofluorobenzene, in THF at25 °C for 48 h gave [(dppm)Co₂(CO)₄(μ-HCCC₆H₁₀NHC₆H₃(NO₂)₂)] (13), [Co₂(CO)₆(μ-HCCC₆H₁₀NHC₆H₃(NO₂)₂)] (14), and [Co₂(CO)₆(μ-HCCC₆H₄NHC₆H₃(NO₂)₂)] (15), respectively.     

The effect of titanium alkoxides in the synthesis of heterobimetallic complexes by titanocene(III) alkoxide-induced metal-metal bond cleavage of metal carbonyl dimers

A series of titanocene(III) alkoxides L₂Ti(III)OR where L = Cp, R = Et(1b), ^tBu(1a), 2,6-Me₂C₆H₃(1c), 2,6-^tBu₂-4-Me-C₆H₂(1d), or L = Cp*, R = Me(2e), ^tBu(2a), Ph(2f) was synthesized and subjected to reaction with [CpM(CO)₃]₂ [M = Mo, W], [CpRu(CO)₂]₂, and Co₂(CO)₈. The Ti(III) precursors 1a, 1c, 2a, 2e, and 2f reacted with [CpM(CO)₃]₂ [M = Mo, W] to form heterobimetallic complexes L₂Ti(OR)(μ-OC)(CO)₂MCp [M = Mo, W], of which Ti and M are linked by an isocarbonyl bridge. Reactions of these Ti(III) complexes with Co₂(CO)₈ resulted in formation of Ti-Co₁ heterobimetallic complexes, from 2a, 2e, or 2f, or Ti-Co₃ tetrametallic complexes, Cp₂Ti(O^tBu)(μ-OC)Co₃(CO)₉ from 1a, 1b, or 1c. The products were characterized by NMR, IR, and X-ray crystallography. Reaction mechanisms were proposed from these results, in particular, from steric/electronic effects of titanium alkoxides.     

The cyclopalladation reaction of 2-phenylaniline revisited

2-Phenylaniline reacted with Pd(OAc)₂ in toluene at room temperature for 24 h in a one-to-one molar ratio and with the system PdCl₂, NaCl and NaOAc in a 1 (2-phenylaniline):1 (PdCl₂):2 (NaCl):1 (NaOAc) molar ratio in methanol at room temperature for one week to give the dinuclear cyclopalladated compounds (μ-X)₂[Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}]₂ [1a (X = OAc) and 1b (X = Cl)] in high yield. Moreover, the reaction between 2-phenylaniline and Pd(OAc)₂ in one-to-one molar ratio in acid acetic at 60 °C for 4 h, followed by a metathesis reaction with LiBr, allowed isolation of the dinuclear cyclopalladated compound (μ-Br)₂[Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}]₂ (1c) in moderate yield. A parallel treatment, but using monodeuterated acetic acid (DOAc) as solvent in the cyclopalladation reaction, allowed isolation of a mixture of compounds 1c, 1c_d1 [Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄](μ-Br)₂[Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)-3-d-C₆H₃] and 1c_d2 (μ-Br)₂[Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)-3-d-C₆H₃}]₂ in moderate yield and with a deuterium content of ca. 60%. 1a and 1b reacted with pyridine and PPh₃ affording the mononuclear cyclopalladated compounds [Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}(X)(L)] [2a (X = OAc, L = py), 2b (X = Cl, L = py), 3a (X = OAc, L = PPh₃) and 3b (X = Cl, L = PPh₃)] in a yield from moderate to high. Furthermore, 1a reacted with Na(acac) · H₂O to give the mononuclear cyclopalladated compound 4 [Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}(acac)] in moderate yield. ¹H NMR studies in CDCl₃ solution of 2a, 2b, 3a, 3b and 4 showed that 2a and 3a presented an intramolecular hydrogen bond between the acetato ligand and the amino group, and were involved in a dynamic equilibrium with water present in the CDCl₃ solvent; and that the enantiomeric molecules of 2b and 4 were in a fast exchange at room temperature, while they were in a slow exchange for 2a, 3a and 3b. The X-ray crystal structures of 3b and 4 were determined. 3b crystallized in the triclinic space group with a = 9.9170(10), b = 10.4750(10), c = 12.0890(10) Å, α = 98.610(10)°, β = 94.034(10)° and γ = 99.000(10)° and 4 in the monoclinic space group P2₁/a with a = 11.5900(10), b = 11.2730(10), c = 12.2150(10) Å, α = 90°, β = 107.6560(10)° and γ = 90°.     

Synthesis,structure, and electrochemistry of pyridinecarboxamide cobalt(III) complexes; the effect of bridge substituents on the redox properties

Two series of complexes of the types trans-[Co^III(Mebpb)(amine)₂]ClO₄ {Mebpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-methylbenzene dianion, and amine = pyrrolidine (prldn) (1a), piperidine (pprdn) (2a), morpholine (mrpln) (3a), benzylamine (bzlan) (4a)}, and trans-[Co^III(cbpb)(amine)₂]X {cbpb²⁻ = N,N-bis(pyridine-2-carboxamido)-4-chlorobenzene dianion, and amine = pyrrolidine (prldn), X = PF₆ (1b), piperidine (pprdn), X = PF₆ (2b), morpholine (mrpln), X = ClO₄ (3b), benzylamine (bzlan), X = PF₆ (4b)} have been synthesized and characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structure of 1a has been determined by X-ray diffraction. The electrochemical behavior of these complexes, with the goal of evaluating the effect of axial ligation and equatorial substitution on the redox properties, is also reported. The reduction potential of Co^III, ranging from −0.53 V for (1a) to −0.31 V for (3a) and from −0.48 V for (1b) to −0.22 V for (3b) show a relatively good correlation with the σ-donor ability of the axial ligands. The methyl and chloro substituents of the equatorial ligand have a considerable effect on the redox potentials of the central cobalt ion and the ligand-centered redox processes.