Palladium (II) complexes with mono-oxide 1,1′-bis(diphenylphosphino)metallocene ligands [Fe(η-C5Me4PPh2)(η-C5Me4P{O}Ph2)] and [Os(η-C5H4PPh2)(η-C5H4P{O}Ph2)]

The monoxides [Fe(η⁵-C₅Me₄PPh₂)(η⁵-C₅Me₄P{O}Ph₂)] (1) and [Os(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄P{O}Ph₂)] (2) have been prepared by treatment of the corresponding diphosphines with CCl₄ and methanol.These ligands react with [Pd(PhCN)₂Cl₂] to give dichloride complexes of different structure.The dimeric complex [{Os(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄P{O}Ph₂)}PdCl(μ-Cl)]₂ (4) contains the monodentate P-coordinated osmocene ligand with the free P{O}Ph₂ group, while the octamethylferrocene ligand gives the chelate k²-P,O complex [{Fe(η⁵-C₅Me₄PPh₂)(η⁵-C₅Me₄P{O}Ph₂)}PdCl₂] (3).The structures of 3 and 4 have been determined crystallographically.Treatment of 3 and 4 with silver salts in CH₂Cl₂ or acetonitrile leads to the corresponding dicationic complexes[{M(η⁵-C₅R₄PPh₂)(η⁵-C₅R₄P{O}Ph₂)}Pd(MeCN)_x]²⁺ (5, M = Fe, R = Me; 6, M = Os, R = H). Complex 5 decomposes upon isolation, in contrast 6 is rather stable, probably due to Os-Pd bonding. The dichlorides 3 and 4 catalyze catalytic amination of p-bromotoluene with N-(4-tolyl)morpholine with lower activity than (dppf)PdCl₂, however they perform comparable to (dppf)PdCl₂ activity in coupling of p-bromotoluene with p-methoxyphenyl boronic acid.     

Versatility in the mode of coordination {(N), (N,O), (C,N) or (C,N,O)} of [(η-C5H5)Fe{(η-C5H4)-CHN-(C6H4-2OH)}] to palladium(II)

The study of the reactivity of the ferrocenyliminoalcohol [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-CHN-(C₆H₄-2OH)}] (1b) with Na₂[PdCl₄] or Pd(OAc)₂ has allowed the isolation and characterization of the heterotrimetallic complexes: trans-[Pd{(η⁵-C₅H₅)Fe[(η⁵-C₅H₄)-CHN-(C₆H₄-2OH)]}₂Cl₂] (2b), [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2O)]Fe(η⁵-C₅H₅)}{(η⁵-C₅H₅)Fe[(η⁵-C₅H₄)-CHN-(C₆H₄-2OH)]}] (3b) and trans-[Pd{(η⁵-C₅H₅)Fe[(η⁵-C₅H₄)-CHN-(C₆H₄-2O)]}₂] (4b). Ligand 1b acts as a (N) (in 2b) or a (N,O)⁻ (in 4b) ligand; while in 3b the two units of the iminoalcohol exhibit simultaneously different modes of binding {(N) and [C(sp², ferrocene),N,O]²⁻}. The crystal structures of 2b · 3H₂O and 3b · 1/2CHCl₃ are also reported and confirm the mode of binding of the ligand in these compounds. The relative importance of the factors affecting the preferential formation of products (2b-4b) is also discussed. The study of the reactivity of 3b with PPh₃ has enabled the obtention of the cyclopalladated complexes [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2O)]Fe(η⁵- C₅H₅)}(PPh₃)] (6b) and [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2OH)]Fe(η⁵-C₅H₅)}Cl(PPh₃)] (7b), in which 1b behaves as a [C(sp², ferrocene),N,O]²⁻ (in 6b) or [C(sp², ferrocene),N]⁻ (in 7b) ligand. Treatment of 3b with MeO₂C-CC-CO₂Me produces [Pd{[(MeO₂C-CC-CO₂Me)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2O)]Fe(η⁵-C₅H₅)}] (8b), that arises from the bis(insertion) of the alkyne into the σ[Pd-C(sp², ferrocene)] bond. The comparison of the results obtained for 1b and [C₆H₅-CHN-(C₆H₄-2OH)] (1a) has allowed to establish the influence of the substituents on the imine carbon on their reactivity in front of palladium(II) as well as on the lability of the Pd-ligands bond. ⁵⁷Fe Mössbauer studies of 2b-4b and 6b provide conclusive evidence of the effect induced by the mode of binding of 1b on the environment of the iron(II).     

From straight chain to macrocyclic complexes containing mixed sulfur/nitrogen donors and coordinated 1,3-diynes

The acid-mediated reaction of [{Co₂(CO)₆(μ-η²-HOCH₂CC-)}₂] (1) with the meta- and para-substituted aminothiophenols, 3-NH₂-C₆H₄SH and 4-NH₂-C₆H₄SH, affords the straight chain species, [{Co₂(CO)₆(μ-η²-(3-NH₂-C₆H₄S)CH₂CC-)}₂] (2) and [{Co₂(CO)₆(μ-η²-(4-NH₂-C₆H₄S)CH₂CC-)}₂] (3), respectively. The molecular structure of 3 reveals the presence of two isomeric forms differing in the relative disposition of the S-aryl groups. Conversely, reaction of 1 with the ortho-substituted aminothiophenol, 2-NH₂-C₆H₄SH, furnishes the 10-membered macrocyclic species [{Co₂(CO)₆}₂{cyclo-μ-η²:μ-η²-CH₂C₂C₂CH₂SC₆H₃-NH-2}] (4) along with the linear chain complex [{Co₂(CO)₆(μ-η²-(2-NH₂-C₆H₄S)CH₂CC-)}₂] (5). On the other hand, treatment of 1 with the ortho-substituted mercaptopyridine, 2-SH-C₅H₄N, in the presence of HBF₄ gives the salt [{Co₂(CO)₆(μ-η²-(2-S-C₅H₄NH)CH₂CC-)}₂](BF₄)₂ (6a) in good yield; work-up in the presence of base affords the neutral complex [{Co₂(CO)₆(μ-η²-(2-S-C₅H₄N)CH₂CC-)}₂] (6b). Single crystal X-ray diffraction studies have been reported on 3-5 and 6a.     

Construction of optically active multimetallic systems of rhodium(I), palladium(II), and ruthenium(II) with a P-chiral tetraphosphine ligand

The treatment of optically P-chiral tetraphosphine, (3S,6R,9R,12S)-6,9-di-tert-butyl-2,2,3,12,13,13-hexamethyl-3,6,9,12-tetraphosphatetradecane (1), with rhodium(I), palladium(II), and ruthenium(II) complex precursors led to the selective formation of mono-, di-, or trinuclear homo- or heterometallic complexes, [Rh(1)]SbF₆ (4), [{Rh(nbd)}₂(1)](SbF₆)₂ (3), [{Pd(η³-allyl)}₂(1)](SbF₆)₂ (5), [{RuCl(η⁵-C₅(CH₃)₅)}₂(1)] (6), and [{RuCl₂(η⁶-benzene)}₂(PdCl₂)(1)] (8). These complexes were characterized by NMR and X-ray crystallographic analysis.     

Amidoamine-based dendrimers with end-grafted Pd-Fe units: Synthesis, characterization and their use in the Heck reaction

The synthesis and characterization of novel amidoamine-based metallodendrimers with heterobimetallic end-grafted amidoferrocenyl-palladium-allyl chloride units is described. Dendrimer (Fe((η⁵-C₅H₄PPh₂)(η⁵-C₅H₄))C(O)HNCH₂CH₂NHC(O)CH₂CH₂)N[CH₂CH₂N(CH₂CH₂C(O)NHCH₂CH₂NH-C(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂)))₂]₂ (9-Fe) and the corresponding metal species (Fe((η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))(η⁵-C₅H₄))C(O)HNCH₂CH₂NHC(O)CH₂CH₂)N[CH₂CH₂N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))))₂]₂ (9-Fe-Pd) were prepared by a consecutive divergent synthesis methodology including addition-amidation cycles, standard peptide coupling, and coordination procedures. For comparative reasons also the monomeric and dimeric molecules (Fe(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄C(O)NHⁿC₃H₇)) (5-Fe) and [Fe(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄C(O)NHCH₂)]₂ (6-Fe) as well as N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂)))₃ (7-Fe) and [CH₂N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂)))₂]₂ (8-Fe) were prepared from Fe(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄CO₂H) (3). Using [Pd(η³-C₃H₅)Cl]₂ (4) as palladium source heterobimetallic metallodendrimers (Fe(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))(η⁵-C₅H₄C(O)NHⁿC₃H₇)) (5-Fe-Pd), [Fe(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))(η⁵-C₅H₄C(O)NHCH₂)]₂ (6-Fe-Pd), N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))))₃ (7-Fe-Pd) and [CH₂N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))))₂]₂ (8-Fe-Pd) were synthesized. Additionally, seleno-phosphines of 5-Fe-Se and 9-Fe-Se, respectively, were prepared by addition of elemental selenium to 5-Fe or 9-Fe to estimate their σ-donor properties.The palladium-containing amidoamine supports are catalytically active in the Heck-Mizoroki cross-coupling of iodobenzene with tert-butyl acrylate. The catalytic data are compared to those obtained for the appropriate mononuclear and dinuclear compounds 5-Fe-Pd and 6-Fe-Pd. This comparison confirms a positive cooperative effect. The mercury drop test showed that (nano)particles were formed during catalysis, following on heterogeneous carbon-carbon cross-coupling.     

Cyclopalladation of N-phenyl-4-ferrocenylmethylpyrazoles: Crystal structure of [Pd{κ-C,N-C6H4-1-[(3,5-Me2-C3N2)-CH2-(η-C5H4)Fe(η-C5H5)]}Cl(PPh3)] · CH2Cl2

The synthesis and characterization of pyrazole derivatives of general formula [C₆H₄-4-R-1-{(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}] [R = OMe (1a) or H (1b)] with a ferrocenylmethyl substituent are described.The study of the reactivity of compounds 1 with palladium(II) acetate has allowed the isolation of complexes (μ-AcO)₂[Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}]₂ (2) [R = OMe (2a) or H (2b)] that contain a bidentate [C(sp², phenyl), N]⁻ ligand and a central “Pd(μ-AcO)₂Pd” unit.Furthermore, treatment of 2 with LiCl produced complexes (μ-Cl)₂[Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}]₂ (3) [R = OMe (3a) or H (3b)] that arise from the replacement of the acetato ligands by the Cl⁻.Compounds 2 and 3 also react with PPh₃ giving the monomeric complexes [Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}X(PPh₃)] {X⁻ = AcO⁻ and R = OMe (5a) or H (5b) or X⁻ = Cl⁻ and R = OMe (6a) or H (6b)}, where the phosphine is in a cis-arrangement to the metallated carbon atom. Treatment of 3 with thallium(I) acetylacetonate produced [Pd{κ²-C,N-C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}(acac)] (7) [R = OMe (7a) or H (7b)]. Electrochemical studies of the free ligands and the cyclopalladated complexes are also reported. The dimeric complexes 3 also react with MeO₂C-CC-CO₂Me (in a 1:4 molar ratio) giving [Pd{(MeO₂C-CC-CO₂Me)₂C₆H₃-4-R-1-[(3,5-Me₂-C₃N₂)-CH₂-(η⁵-C₅H₄)Fe(η⁵-C₅H₅)]}Cl] (8) [R = OMe (8a) or H (8b)], which arise from the bis(insertion) of the alkyne into the σ{Pd-C(sp², phenyl)} bond of 3.     

Knoevenagel condensation of [NC-CH2C(O)-NH-CH(CO2Et)-S]2 with ferrocenecarbaldehyde and the activation of the σ(C-S) bond of [(η-C5H5)Fe{(η-C5H4)-CHC(CN)-C(O)-NH-CH(CO2Et)-CH2-S-}]2 induced by palladium(II)

The results obtained from the Knoevenagel condensation between the aldehydes R-CHO {with R=4-MeO-C₆H₄, 4-NO₂-C₆H₄, 4-Cl-C₆H₄, C₆H₅, 2,4,6-Me₃-C₆H₂ or (η⁵-C₅H₅)Fe(η⁵-C₅H₄)} and [NC-CH₂C(O)-NH-CH(CO₂Et)-S]₂ under different experimental conditions are reported. These studies have allowed the isolation and characterisation of three optically pure polyamides of general formula [R-CHC(CN)-C(O)-NH-CH(CO₂Et)-CH₂-S-]₂ with R=4-MeO-C₆H₄ (3a), 4-NO₂-C₆H₄ (3b) or (η⁵-C₅H₅)Fe(η⁵-C₅H₄) (3f). The reactions of 3f with Na₂[PdCl₄] or Pd(AcO)₂ are also studied. The treatment of Pd(AcO)₂ with 3f in a 2:1 molar ratio in refluxing toluene leads to the formation of [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-CHC(CN)-C(O)-NH-C(CO₂Et)CH₂}] (5f). Electrochemical studies based on cyclic voltammetry of compounds 3f and 5f are also reported.     

Synthesis of new chloro methyl niobium and tantalum complexes with silyl-cyclopentadienyl ligands: X-ray crystal structure of [Ta{η-C5H3(SiMe3)2}Cl2Me2]

Trichloro methyl [Nb{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Cl₃Me] (X = Cl, 2; Me, 3), dichloro dimethyl [Nb{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Cl₂Me₂] (X = Cl, 4; Me, 5) and tetramethyl [Nb{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Me₄] (X = Me, 6; Cl, 7) niobium complexes were synthesized by treatment of starting tetrachloro derivatives [Nb{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Cl₄] (X = Cl, 1a; Me, 1b) with dimethyl zinc or chloro methyl magnesium in different proportions and conditions. A mixture of trichloro methyl and dichloro dimethyl tantalum complexes [Ta{η⁵-C₅H₃(SiClMe₂)(SiMe₃)}Cl_4−xMe_x] (x = 1, 8; 2, 9) in a 2:1 molar ratio was obtained in the reaction of [Ta{η⁵-C₅H₃(SiClMe₂)(SiMe₃)}Cl₄] (1c) with 0.5 equivalents of ZnMe₂ in toluene at low temperature. 8 could be isolated as single compound when 1 equivalent of 1c was added to the mixtures of 8 and 9, while the reaction of 1c with 1.5 equivalents of dimethyl zinc gave 9 as unitary product. However, [Ta{η⁵-C₅H₃(SiMe₃)₂}Cl₄] (1d) reacts with 0.5 equivalents of alkylating reagent giving the trichloro methyl compound [Ta{η⁵-C₅H₃(SiMe₃)₂}Cl₃Me] (10) in good yield. On the other hand, [Ta{η⁵-C₅H₃(SiMe₃)₂}Cl₄] (1d) reacts with 2 equivalents of MgClMe in hexane at room temperature giving a mixture of dichloro dimethyl and chloro trimethyl complexes[Ta{η⁵-C₅H₃(SiMe₃)₂}Cl_4−xMe_x] (x = 2, 11; 3, 12), while the use of 4 equivalents of MgClMe converts 1c into the tetramethyl derivative [Ta{η⁵-C₅H₃(SiClMe₂)(SiMe₃)}Me₄] (13). Finally, a tetramethyl tantalum complex [Ta{η⁵-C₅H₃(SiMe₃)₂}Me₄] (14) was prepared by reaction of [Ta{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Cl₄] (X = Cl, 1c; Me, 1d) with 5 (X = Cl) or 4 (X = Me) equivalents of MgClMe in diethyl ether (X = Cl) or hexane (X = Me), respectively, as solvent. All the complexes were studied by IR and NMR spectroscopy and the molecular structure of the complex 11 was determined by X-ray diffraction methods.     

Study of the reactivity of palladacycles containing [C(sp, ferrocene),N,S] or [C(sp),N,S] terdentate ligands with symmetric alkynes

The study of the reactivity of the cyclopalladated complex [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] (1c) with the alkynes R¹-CC-R¹ (with R¹ = CO₂Me, Ph or Et) is reported.Compound 1c reacts with the equimolar amount of MeO₂C-CC-CO₂Me in refluxing CH₂Cl₂ to give [Pd{[(MeO₂C-CC-CO₂Me)(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] (2c), which arises from the monoinsertion of the alkyne into the σ[Pd-C(sp², ferrocene)] bond.However, when the reaction was performed using Ph-CC-Ph or Et-CC-Et no evidence of the insertion of these alkynes into the σ[Pd-C(sp², ferrocene)] bond was detected.In contrast with these results, when 1c was treated with the Tl[BF₄] followed by the removal of the TlCl formed and the subsequent addition of MeO₂C-CC-CO₂Me the reaction gave 2c and [Pd{[(MeO₂C-CC-CO₂Me)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}][BF₄] (3c); but when the alkyne was R¹-CC-R¹ (with R¹ = Ph or Et), the ionic palladacycles [Pd{[(R¹-CC-R¹)₂(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}][BF₄] · CH₂Cl₂ [with R¹ = Ph (5c) or Et (6c)] were isolated. In compounds 3c, 5c and 6c, the mode of binding of the butadienyl unit is η³. The reactions of 2c, 3c, 5c and 6c with PPh₃ are also reported. The results obtained from these studies reveal that the σ(Pd-S) bond in 2c is more prone to cleave than in 4c-6c. X-ray crystal structures of 2c, 5c and [Pd{[(MeO₂C-CC-CO₂Me)(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl(PPh₃)] (7c), are also described. Compound 7c arises from 2c by cleavage of the Pd-S bond and the incorporation of a PPh₃ in the coordination sphere of the palladium. A parallel study focused on the reactions of [Pd{[2-CH₂-4,6-Me₂-C₆H₂]-CHN-(C₆H₄-2-SMe)}Cl] (1d) (with a [Csp³,N,S]⁻ terdentate group) with the three alkynes reveals that the σPd-C(sp², ferrocene)] bond of 1c is more reactive than the σ[Pd-C(sp³)] bond of 1d.     

Carbon-rich organometallic materials derived from 4-ethynylphenylferrocene

Using 4-ethynylphenylferrocene (1) as the building block, a new series of rigid-rod alkynylferrocenyl precursors consisting of fluoren-9-one unit, 2-bromo-7-(4-ferrocenylphenylethynyl)fluoren-9-one (2a), 2,7-bis(4-ferrocenylphenylethynyl)fluoren-9-one (2b), 2-trimethylsilylethynyl-7-(4-ferrocenylphenylethynyl)fluoren-9-one (3) and 2-ethynyl-7-(4-ferrocenylphenylethynyl)fluoren-9-one (4) have been prepared in moderate to good yields. The acetylene complex 4 is a useful precursor for the synthesis of well-defined carbon-rich ferrocenyl heterometallic complexes, trans-[(η⁵-C₅H₅)Fe(η⁵-C₅H₄)C₆H₄CCRCCPt(PEt₃)₂Ph] (5), trans-[(η⁵-C₅H₅)Fe(η⁵-C₅H₄)C₆H₄CCRCCPt(PBu₃)₂CCRC≡CC₆H₄(η⁵-C₅H₄)Fe(η⁵-C₅H₅)] (6), trans-[(η⁵-C₅H₅)Fe(η⁵-C₅H₄)C₆H₄CCRCCM(dppm)₂Cl] (M=Ru (7), Os (8)) (R=fluoren-9-one-2,7-diyl). All new complexes have been characterized by FTIR, NMR and UV-Vis spectroscopies and fast atom bombardment mass spectrometry (FABMS). The molecular structures of 1, 2a, 4, 6 and 8 have been determined by single-crystal X-ray studies where an ironiron through-space distance of nanosized dimension (ca. 42 Å) is observed in the trimetallic molecular rod 6. The electronic absorption, luminescence and electrochemical properties of these carbon-rich molecules were investigated and the data were correlated with the theoretical results obtained by the method of density functional theory.     

Schiff bases containing ferrocenyl and thienyl units and their utility in the palladium catalyzed allylic alkylation of cinnamyl acetate

The synthesis and characterization of two new ferrocenyl Schiff bases: [Fc-CHN-(CH₂)_n-(C₄H₃S)] (2) {Fc represents (η⁵-C₅H₅)Fe(η⁵-C₅H₄)- and n = 1(2a) or 2(2b)} containing the thienyl (C₄H₃S) group are reported. NMR studies indicate that 2 have the anti-(E) conformation in solution and the X-ray crystal structure of 2a confirms that it also adopts the anti-(E) form in the solid state. Ligands 2 have been tested in the palladium catalyzed allylic alkylation of (E)-3-phenyl-2-propen-1-yl (cinnamyl) acetate using sodium diethyl 2-methylmalonate as nucleophile. The reaction of 2 with [Pd(η³-1-Ph-C₃H₄)(μ-Cl)]₂ in the presence of a slight excess K[PF₆] produced [Pd(η³-1-Ph-C₃H₄){Fc-CHN-(CH₂)_n-(C₄H₃S)}][PF₆] {n = 1(5a) or 2(5b)}, which are the intermediates of this catalytic process. NMR studies of 5 reveal the coexistence of several isomers in solution. The stoichiometric reactions of 5 with the nucleophile are also reported. The comparison of the results obtained for 2, [Fc-CHN-(C₆H₄-2SMe)] (1a) and [(2,4,6-Me₃-C₆H₂)-CHN-(C₆H₄-2SMe)] (1b) has allowed to establish the importance of the nature of the substituents on the imine group on the regioselectivity of the process.     

Palladium(II)-allyl complexes containing chiral N-donor ferrocenyl ligands

A study of the reactivity of enantiopure ferrocenylimine (S_C)-[FcCHN-CH(Me)(Ph)] {Fc =  (η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-} (1a) with palladium(II)-allyl complexes [Pd(η³-1R¹,3R²-C₃H₃)(μ-Cl)]₂ {R¹ = H and R² = H (2), Ph (3) or R¹ = R² = Ph (4)} is reported. Treatment of 1a with 2 or 3 {in a molar ratio Pd(II):1a = 1} in CH₂Cl₂ at 298 K produced [Pd(η³-3R²-C₃H₄){FcCHN-CH(Me)(Ph)}Cl] {R² = H (5a) or Ph (6a)}. When the reaction was carried out under identical experimental conditions using complex 4 as starting material no evidence for the formation of [Pd(η³-1,3-Ph₂-C₃H₃){FcCHN-CH(Me)(Ph)}Cl] (7a) was found. Additional studies on the reactivity of (S_C)-[FcCHN-CH(R³)(CH₂OH)] {R³ = Me (1b) or CHMe₂ (1c)} with complex 4 showed the importance of the bulk of the substituents on the palladium(II) allyl-complex (2-4) or on the ferrocenylimines (1) in this type of reaction. The crystal structure of 5a showed that: (a) the ferrocenylimine adopts an anti-(E) conformation and behaves as an N-donor ligand, (b) the chloride is in acis-arrangement to the nitrogen and (c) the allyl group binds to the palladium(II) in a η³-fashion. Solution NMR studies of 5a and 6a and [Pd(η³-1,3-Ph₂-C₃H₃){FcCHN-CH(Me)(CH₂OH)}Cl] (7b) revealed the coexistence of several isomers in solution. The stoichiometric reaction between 6a and sodium diethyl 2-methylmalonate reveals that the formation of the achiral linear trans-(E) isomer of Ph-CHCH-CH₂Nu (8) was preferred over the branched derivative (9). A comparative study of the potential utility of ligand 1a, complex 5a and the amine (S_C)-H₂N-CH(Me)(Ph) (11) as catalysts in the allylic alkylation of (E)-3-phenyl-2-propenyl (cinnamyl) acetate with the nucleophile diethyl 2-methylmalonate (Nu⁻) is reported.     

A synthetic, structural and reactivity study of [(η-C4R4)Co(η-C5H4X)] complexes, R = Me or Et; X = CHO, CHCHFc, CHCH(η-C5H4)Co(η-C4Ph4), CHC(CN)2: Unexpected formation of [(η-cyclopentadienyl)(η-3,4,5,6-tetraethyl-α-pyrone)cobalt]

The tetraethyl- and tetramethyl-cyclobutadiene complexes [(η⁴-C₄R₄)Co(η⁵-C₅H₄CHO)] R = Et, 5, R = Me, 7, and [(η⁴-C₄R₄)Co(η⁵-C₅H₄CO₂Me)] R = Et, 6, R = Me, 8, are conveniently prepared by photolysis of the corresponding isocobaltocenium cations [(η⁴-C₄R₄)Co(η⁶-C₆H₅Me)]⁺ in acetonitrile, and subsequent treatment with Na[C₅H₄CHO] or Na[C₅H₄CO₂Me]. The aldehydes 5 and 7 undergo Wittig and Knoevenagel reactions with [FcCH₂PPh₃]I and CH₂(CN)₂, to form [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH=CHFc)] and [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH=C(CN)₂], 11 and 15, respectively. The Horner-Wittig reaction of [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH₂P(O)(OEt)₂] with [(η⁴-C₄Ph₄)Co(η⁵-C₅H₄CHO)] yields [(η⁴-C₄R₄)Co(η⁵:η⁵-C₅H₄CHCH-C₅H₄)Co(η⁴-C₄Ph₄)], 12 and 13. [(η⁴-C₄Me₄)Co(η⁵-C₅H₄CHO)] also reacts with t-BuLi and FcLi to furnish the corresponding secondary alcohols, 16 and 17, respectively. Surprisingly, the attempted direct synthesis of 5 by reaction of Na[C₅H₅] and ethyl formate with [(η⁴-C₄Et₄)Co(CO)₂I], 1, instead yielded [(η⁵-C₅H₅)Co(η⁴-3,4,5,6-tetraethyl-α-pyrone)], 18, and a mechanistic proposal is advanced. The X-ray crystal structures of 1, 7, 8, 11(Z), 15 and 18, and also the isocobaltocenium salts [(η⁴-C₄Et₄)Co(η⁶-C₆H₅Me)][PF₆], 2, and [(η⁴-C₄Et₄)Co(η⁶-1,3,5-C₆H₃Me₃)][PF₆], 4, are reported.     

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.     

Mono and dinuclear complexes of half-sandwich platinum group metals (Ru, Rh and Ir) bearing a flexible pyridyl-thiazole multidentate donor ligand

The mononuclear cationic complexes [(η⁶-C₆H₆)RuCl(L)]⁺ (1), [(η⁶-p-ⁱPrC₆H₄Me)RuCl(L)]⁺ (2), [(η⁵-C₅H₅)Ru(PPh₃)(L)]⁺ (3), [(η⁵-C₅Me₅)Ru(PPh₃)(L)]⁺ (4), [(η⁵-C₅Me₅)RhCl(L)]⁺ (5), [(η⁵-C₅Me₅)IrCl(L)]⁺ (6) as well as the dinuclear dicationic complexes [{(η⁶-C₆H₆)RuCl}₂(L)]²⁺ (7), [{(η⁶-p-ⁱPrC₆H₄Me)RuCl}₂(L)]²⁺ (8), [{(η⁵-C₅H₅)Ru(PPh₃)}2(L)]²⁺ (9), [{(η⁵-C₅Me₅)Ru(PPh₃)}₂(L)]²⁺ (10), [{(η⁵-C₅Me₅)RhCl}₂(L)]²⁺ (11) and [{(η⁵-C₅Me₅)IrCl}₂(L)]²⁺ (12) have been synthesized from 4,4′-bis(2-pyridyl-4-thiazole) (L) and the corresponding complexes [(η⁶-C₆H₆)Ru(μ-Cl)Cl]₂, [(η⁶-p-ⁱPrC₆H₄Me)Ru(μ-Cl)Cl]₂, [(η⁵-C₅H₅)Ru(PPh₃)₂Cl)], [(η⁵-C₅Me₅)Ru(PPh₃)₂Cl], [(η⁵-C₅Me₅)Rh(μ-Cl)Cl]₂ and [(η⁵-C₅Me₅)Ir(μ-Cl)Cl]₂, respectively. All complexes were isolated as hexafluorophosphate salts and characterized by IR, NMR, mass spectrometry and UV-vis spectroscopy. The X-ray crystal structure analyses of [3]PF₆, [5]PF₆, [8](PF₆)₂ and [12](PF₆)₂ reveal a typical piano-stool geometry around the metal centers with a five-membered metallo-cycle in which 4,4′-bis(2-pyridyl-4-thiazole) acts as a N,N′-chelating ligand.     

Trimethylstannyl (diphenylphosphino)acetate: a source of (diphenylphosphino)acetate ligand in the synthesis of coordination compounds

Trimethylstannyl (diphenylphosphino)acetate (1), which is readily accessible from potassium (diphenylphosphino)acetate and trimethylstannyl chloride, may serve as the source of (diphenylphosphino)acetate anion in the preparation of coordination compounds. Thus, the reactions between [M(cod)Cl₂] (M = Pd and Pt; cod = η²:η²-cycloocta-1,5-diene) and two equivalents of 1 give [M(Ph₂PCH₂CO₂-κ²O,P)₂] (2 and 3), while the reaction of [{Pd(μ-Cl)Cl(PFur₃)}₂] (4; Fur = 2-furyl) with one equivalent of 1 yields [SP-4-3]-[PdCl(Ph₂PCH₂CO₂-κ²O,P)(PFur₃)] (5). The reactions of 1 with the dimers [{Rh(η⁵-C₅Me₅)Cl(μ-Cl)}₂] and [{Ru(η⁶-1,4-MeC₆H₄(CHMe₂))Cl(μ-Cl)}₂] (at 1-to-metal ratio 1:1) produce O,P-chelated complexes as well, albeit as stable adducts with the liberated Me₃SnCl: [RhCl(η⁵-C₅Me₅)(Ph₂PCH₂CO₂-κ²O,P)] · Me₃SnCl (6) and[RuCl(η⁶-1,4-MeC₆H₄(CHMe₂))(Ph₂PCH₂CO₂-κ²O,P)] · Me₃SnCl (8). The related complexes with P-monodentate (diphenylphosphino)acetic acid, [RhCl₂(η⁵-C₅Me₅)(Ph₂PCH₂CO₂H-κ,P)] (7) and [RuCl₂(η⁶-1,4-MeC₆H₄(CHMe₂))(Ph₂PCH₂CO₂H-κP)] (9), were obtained by bridge splitting in the dimers with the phosphinocarboxylic ligand. All new compounds were characterized by spectral methods and combustion analyses, and the structures of 2 · 3CH₂Cl₂, 3, 4, 5, 6 and 8 were determined by X-ray crystallography.     

Large bite bisphosphite, 2,6-C5H3N{CH2OP(-OC10H6)(μ-S)(C10H6O-)}2: Synthesis, derivatization, transition metal chemistry and application towards hydrogenation of olefins

Large bite bisphosphite ligand, 2,6-C₅H₃N{CH₂OP(-OC₁₀H₆)(μ-S)(C₁₀H₆O-)}₂ (2), is obtained by reacting chlorophosphite, {-OC₁₀H₆(μ-S)C₁₀H₆O-}PCl (1) with 2,6-pyridinedimethanol in presence of triethylamine.Treatment of 2 with aqueous solution of H₂O₂ or elemental sulfur resulted in the formation of bis(oxide) or bis(sulfide) derivatives, 2,6-C₅H₃N{CH₂OP(E)(-OC₁₀H₆)(μ-S)(C₁₀H₆O-)}₂ (3, E = O; 4, E = S) in quantitative yield.The 10-membered cationic chelate complex, [RuCl(η⁶-C₁₀H₁₄)η²-2,6-C₅H₃N{CH₂OP(-OC₁₀H₆)(μ-S)(C₁₀H₆O-)}₂-κP,κP]Cl (5) is produced in the reaction between [Ru(p-cymene)(μ-Cl)(Cl)]₂ and bisphosphite 2, whereas the neutral chelate complex, cis-[Rh(CO)Cl{2,6-C₅H₃N{CH₂OP(-OC₁₀H₆(μ-S)C₁₀H₆O-)}₂}-κP,κP] (6) is isolated in the reaction of 2 with 0.5 equiv.of [Rh(CO)₂Cl]₂.Compound 2 on treatment with M(COD)Cl₂ (M = Pd, Pt) produce the chelate complexes, [MCl₂{η²-2,6-C₅H₃N{CH₂OP(-OC₁₀H₆)(μ-S)(C₁₀H₆O-)}₂}-κP,κP] (7, M = Pd;10, M = Pt).Similarly the reaction of bisphosphite 2 with Pd(COD)MeCl affords cis-[PdMe(Cl)η²-2,6-C₅H₃N{CH₂OP(-OC₁₀H₆)(μ-S)(C₁₀H₆O-)}₂-κP,κP] (8).Treatment of 2 with [Pd(η³- C₃H₅)Cl]₂ in the presence of AgClO₄ furnish the cationic complex, [Pd(η³-C₃H₅)η²-2,6-C₅H₃N{CH₂OP(-OC₁₀H₆)(μ-S)(C₁₀H₆O-)}₂-κP,κP]ClO₄ (9). The binuclear complex, [Au₂Cl₂{2,6-C₅H₃N{CH₂OP(-OC₁₀H₆)(μ-S)(C₁₀H₆O-)}₂}-κP,κP] (11) is obtained in the reaction of compound 2 with two equiv. of AuCl(SMe₂), where the ligand exhibits bridged bidentate mode of coordination. All the complexes are characterized by the ¹H NMR, ³¹P NMR, elemental analysis and mass spectroscopy data. The cationic ruthenium complex 5 is proved to be an active catalyst for the hydrogenation of styrene and α-methyl styrene.     

Cyclopentadienylnickel thiolate complexes: synthesis, molecular structures and electrochemical detection of sulfur dioxide adducts

Simple reactions between Ni(η⁵-C₅H₅)(PR₃)Br and the Schiff-base thiols, 4-HSC₆H₄NC(H)C₄H₂SBr-4^′ (1) and 4-HSC₆H₄NC(H)C₄H₃S (2), or organothiols, HSC₆H₄F-4 and HSC₆H₄NH₂-4, produced cyclopentadienylnickel thiolates of the formulae, Ni(η⁵-C₅H₅)(PR₃)(SC₆H₄NC(H)C₄H₂SBr-4) (3), Ni(η⁵-C₅H₅)(PR₃)(SC₆H₄NC(H)C₄H₃S) (4) or Ni(η⁵-C₅H₅)(PR₃)(SC₆H₄X-4) (R=Ph, X=F (6) or NH₂ (7) and R=Bu, X=F (5) or NH₂ (8)) which were characterized by a combination of analytical techniques. Complexes 3, 6 and 7 were structurally characterized by X-ray crystallography, showing that they possess the familiar trigonal geometry around the nickel center. These complexes react with sulfur dioxide, with 5, 6, 7 and 8 exhibiting substantial differences between the redox potentials of the pre- and post-SO₂ compounds to suggest that these complexes can be developed as potentiometric SO₂ sensors.     

Factors affecting the lability of the σ(M-X) bond in cycloplatinated and cyclopalladated complexes containing [C(sp, ferrocene),N,X] or [C(sp, phenyl),N,X] (X = S, N) terdentate ligands

The reactions of the cyclometallated complexes [M{[(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl] [with M = Pt (5a) or Pd (5b)] with PPh₃ under different experimental conditions are reported. These studies have allowed the isolation of [M{[(η⁵-C₅H₃)-CHN-C₆H₄-2-SMe]Fe(η⁵-C₅H₅)}(PPh₃)]X [M = Pt and X⁻ = Cl⁻ (6a) or (7a) or M = Pd and X⁻ = Cl⁻ (6b) or (7b)] and the neutral complex [Pd{[(η⁵-C₅H₃)-CHN-(C₆H₄-2-SMe)]Fe(η⁵-C₅H₅)}Cl(PPh₃)] (8b). In 6-7a,b the ferrocenyl Schiff base behaves as a [C(sp², ferrocene),N,S]⁻ group while in 8b it acts as a [C(sp², ferrocene),N]⁻ ligand. The X-ray crystal structure of 7b confirms the mode of binding of the ferrocenyl ligand. The comparison of the results obtained and those reported for [M{(C₆H₄)-CHN-(CH₂-CH₂-2-SEt)}Cl] and [M{(C₆H₄)-CHN-(C₆H₄-2-SMe)}Cl] {with a [C(sp², phenyl),N,S]⁻ terdentate ligand} or [M{[(η⁵-C₅H₃)-CHN-(CH₂)₃-NMe₂]Fe(η⁵-C₅H₅)}Cl] {in which the ligand acts as a [C(sp², ferrocene),N,N′]⁻ group} have allowed the elucidation of the relative importance of the factors affecting the lability of the M-X (X = S or N′) and M-Cl bonds in cyclometallated compounds with [C,N,S]⁻ and [C(sp², ferrocene),N,X]⁻ ligands.     

Isocyanide insertion reactivity of dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [{Nb(η-C5H4SiMe3)(CH2Ph)2}2(μ-1,4-NC6H4N)]

The reactivity of dinuclear niobium and tantalum imido complexes with the isocyanide compound 2,6-Me₂C₆H₃NC has been studied. The trialkyl complexes [{NbR₃(CH₃CN)}₂(μ-1,3-NC₆H₄N)], [{NbR₃(CH₃CN)}₂(μ-1,4-NC₆H₄N)] and [{TaR₃(CH₃CN)}₂(μ-1,4-NC₆H₄N)] (R=CH₂SiMe₃) gave [{Nb(η²-RCNAr)₂R}₂(μ-1,3-NC₆H₄N)] (1), [{Nb(η²-RCNAr)₂R}₂(μ-1,4-NC₆H₄N)] (2) and [{Ta(η²-RCNAr)₂R}₂(μ-1,4-NC₆H₄N)] (3) (R=CH₂SiMe₃; Ar=2,6-Me₂C₆H₃), from the isocyanide insertion in two of the metal alkyl carbon bonds. The reaction of the isocyanide reagent with the di-alkyl mono-cyclopentadienyl derivatives [{Nb(η⁵-C₅H₄SiMe₃)R₂}₂(μ-1,3-NC₆H₄N)] (R=Me, CH₂Ph, CH₂SiMe₃), [{Nb(η⁵-C₅H₄SiMe₃)R₂}₂(μ-1,4-NC₆H₄N)] (R=Me, CH₂Ph (4), CH₂SiMe₃) and [{Ta(η⁵-C₅Me₅)(CH₂SiMe₃)₂}₂(μ-1,4-NC₆H₄N)] yielded [{Nb(η⁵-C₅H₄SiMe₃)(η²-RCNAr)R}₂(μ-1,3-NC₆H₄N)] (R=Me (5), CH₂Ph (6), CH₂SiMe₃ (7)), [{Nb(η⁵-C₅H₄SiMe₃)(η²-RCNAr)R}₂(μ-1,4-NC₆H₄N)] (R=Me (8), CH₂Ph (9), CH₂SiMe₃ (10)) and [{Ta(η⁵-C₅Me₅)(η²-Me₃SiCH₂CNAr)CH₂SiMe₃}₂(μ-1,4-NC₆H₄N)] (11) (Ar=2,6-Me₂C₆H₃), respectively, from a single insertion process. The reaction with the mono-alkyl complex [{Nb(η⁵-C₅H₄SiMe₃)(Me)Cl}₂(μ-1,4-NC₆H₄N)] gave [{Nb(η⁵-C₅H₄SiMe₃)(η²-MeCNAr)Cl}₂(μ-1,4-NC₆H₄N)] (12), produced from the isocyanide insertion in the metal-alkyl carbon bond. The alkyl-amido complex [{Nb(η⁵-C₅H₄SiMe₃)(Me)NMe₂}₂(μ-1,4-NC₆H₄N)] gave, from the preferential isocyanide insertion in the metal-amide nitrogen bond, [{Nb(η⁵-C₅H₄SiMe₃)(η²-Me₂NCNAr)Me}₂(μ-1,4-NC₆H₄N)] (13). The molecular structure of one of the alkyl precursors, [{Nb(η⁵-C₅H₄SiMe₃)(CH₂Ph)₂}₂(μ-1,4-NC₆H₄N)] (4), has been determined.