Diphenylphosphino(phenyl pyridin-2-yl methylene)amine palladium(II) complexes: Chemoselective alkene hydrocarboxylation initiators

The heteroditopic, P-N-chelating ligand diphenylphosphino(phenyl pyridin-2-yl methylene)amine (1) has been synthesised via a simple ‘one-pot’ procedure and its donor characteristics assessed. The neutral [MX(Y)(1-κ²-P-N)] (3, M = Rh, X = Cl, Y = CO; 4, M = Pd, X = Y = Cl; 5, M = Pd, X = Cl, Y = Me; 6, M = Pt, X = Y = Cl; 7, M = Pt, X = Cl, Y = Me; 8, M = Pt, X = Y = Me) and cationic [Pd(Me)(MeCN)(1-κ²-P-N)][Z] (9, Z = B{3,5-(CF₃)₂-C₆H₃}4; 10, Z = PF₆) complexes of 1 have been prepared and characterised. The solid-state structures of complexes 3, 4, 6 and 7 have been established by X-ray crystallography. Reactions of [PdCl(Me)(1-κ²-P-N)] towards CO and ^tBuNC have been investigated, affording the corresponding η¹-acyl (12) and -iminoacyl (14) complexes, respectively. Similar insertion chemistry is observed for the cationic derivative 9. Treatment of the acyl complex 12 with ethene at elevated pressure establishes an equilibrium between the starting material and the product resulting from insertion, 13. Under catalytic conditions, combination of palladium(II) with 1 in MeOH affords a selective initiator for the formation of 4-oxo-hexanoic acid methyl ester (15) from CO/ethene (38 bar, 90 °C).     

Si-Fluoro substituted quasisilatranes (N → Si) FYSi(OCH2CH2)2NR

The reaction of fluorosilanes XYSiF₂ (X = Y = F; X = F, Y = Ph; X = Ph, Y = Me) with diethanolamines and their O-trimethylsilyl derivatives affords novel Si-fluoro substituted quasisilatranes 3, 5 and 9. These compounds were characterized by the multinuclear NMR spectroscopy and X-ray diffraction analysis. Experimental and theoretically calculated electron density distribution functions in crystal structure of 9 have shown that the N → Si coordination bond corresponds to polar bond with pronounced ionic contribution. Calculated N → Si bond order in the compound 9 does not exceed 1/3 of the normal Si-N bond. A strong N → Si coordination bond exists in compounds 3, 5 and 9 the length of which varies in the range 1.98-2.175 Å.     

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.     

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.     

Titanium complexes bearing aromatic-substituted β-enaminoketonato ligands: Syntheses, structure and olefin polymerization behavior

A series of titanium complexes [(Ar)NC(CF₃)CHC(R)O]₂TiCl₂ (4b: Ar = -C₆H₄OMe(p), R = Ph; 4c: Ar = -C₆H₄Me(p), R = Ph; 4d: Ar = -C₆H₄Me(o), R = Ph; 4e: Ar = α-Naphthyl, R = Ph; 4f: Ar = -C₆H₅, R = t-Bu; 4g: Ar = -C₆H₄OMe(p); R = t-Bu; 4h: Ar = -C₆H₄Me(p); R = t-Bu; 4i: Ar = -C₆H₄Me(o); R = t-Bu) has been synthesized and characterized. X-ray crystal structures reveal that complexes 4b, 4c and 4h adopt distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4b-c and 4f-i are active catalysts for ethylene polymerization and ethylene/norbornene copolymerization, and produce high molecular weight polyethylenes and ethylene/norbornene alternating copolymers. In addition, the complex 4c/MMAO catalyst system exhibits the characteristics of a quasi-living copolymerization of ethylene and norbornene with narrow molecular weight distribution.     

Synthesis and X-ray structure of cationic β-diimine palladium complexes containing π-methallyl ligand

High yield of cationic palladium β-diimine complexes [(CH₂(MeCNAr)₂)Pd(η³-C₄H₇)][Y] (Ar = C₆H₅, Y = PF₆ (8); 2-Me-C₆H₄, Y = PF₆ (9); 2,6-Me₂-C₆H₃, Y = PF₆ (10); 2,6-iPr₂-C₆H₃, Y = PF₆ (11), Y = B(3,5-(CF₃)₂-C₆H₃)₄ (12)) have been obtained by an oxidative addition of the methallyloxyphosphonium salts (5, 6) to a preformed complex Pd(dba)₂ (7) in the presence of the β-iminoamine ligands (1-4).These complexes are thermally stable and have been characterized by ¹H and ¹³C{¹H} NMR as well as IR spectroscopy. The structure of the cationic allyl palladium complex (12) has been solved by X-ray crystallography.     

Secondary bonding in functionalized organotellurium compounds: preparation and structural characterization of bis(acetamido)tellurium(IV) diiodide and bis(4-methylbenzoylmethyl)tellurium(II)

Elemental tellurium inserts, under mild conditions, between C-I bond of iodoacetamide to afford bis(acetamido)tellurium(IV) diiodide (NH₂COCH₂)₂TeI₂, 1. Heating of N-bromomethylphthalimide with activated tellurium powder however, resulted in the formation of bis(phthalimido)methane, 2, instead of the expected product bis(phthalimidomethyl)tellurium(IV) dibromide. The IR spectrum of 1 is indicative of intramolecular Te?OC interaction which is also substantiated by its single-crystal structure. The compound with planar small-bite chelating organic ligands acquires butterfly shape that imparts almost perfect C_2v molecular symmetry but unlike other organotellurium(IV) iodides, the solid state structure of 1 is devoid of any intermolecular Te?I or I?I secondary interactions owing to the presence of intramolecular Te?O secondary bonds as well as intermolecular N-H?O, N-H?I and C-H?I hydrogen bonds. Bis(4-methylbenzoylmethyl)telluride (4-MeC₆H₄COCH₂)₂Te, 3b, prepared by the reduction of the corresponding dibromide, is the first structurally characterized acyclic dialkyltelluride and interestingly, does not involve intramolecular Te?OC interaction invariably present in the parent dihalides (4-YC₆H₄COCH₂)₂TeX₂ (Y = H, X = I 4a; Y = H, X = Br 5a; Y = MeO, X = Br 5c). Weak intermolecular Te?Te and C-H?O hydrogen bonds appear to be the non covalent intermolecular associative forces that dominate its crystal packing in the solid state of this Te(II) derivative. The dialkyltellurides (4-YC₆H₄COCH₂)₂Te, (Y = H, 3a, Me, 3b) undergo oxidation in presence of (SCN)₂ to give the corresponding bis(isothiocyanato)tellurium(IV) derivatives and form 2:1 adducts with Pt(II) and Pd(II) chlorides.     

Novel hydridotris(pyrazolyl)borate ruthenium(II) complexes containing the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane: Synthesis and evaluation of DNA binding properties

A series of half-sandwich ruthenium(II) complexes containing κ³(N,N,N)-hydridotris(pyrazolyl)borate (κ³(N,N,N)-Tp) and the water-soluble phosphane 1,3,5-triaza-7-phosphaadamantane (PTA) [RuX{κ³(N,N,N)-Tp}(PPh₃)_2−n(PTA)_n] (n = 2, X = Cl (1), n = 1, X = Cl (2), I (3), NCS (4), H (5)) and [Ru{κ³(N,N,N)-Tp}(PPh₃)(PTA)L][PF₆] (L = NCMe (6), PTA (7)) have been synthesized. Complexes containing 1-methyl-3,5-diaza-1-azonia-7-phosphaadamantane(m-PTA) triflate [RuCl{κ³(N,N,N)-Tp}(m-PTA)₂][CF₃SO₃]₂ (8) and [RuX{κ³(N,N,N)-Tp}(PPh₃)(m-PTA)][CF₃SO₃] (X = Cl (9), H (10)) have been obtained by treatment, respectively, of complexes 1, 2 and 5 with methyl triflate. Single crystal X-ray diffraction analysis for complexes 1, 2 and 4 have been carried out. DNA binding properties by using a mobility shift assay and antimicrobial activity of selected complexes have been evaluated.     

Nitrile ligands activation in dinuclear aminocarbyne complexes

The diiron complexes [Fe(Cp)(CO){μ-η²:η²-C[N(Me)(R)]NC(C₆H₃R′)CCH(Tol)}Fe(Cp)(CO)] (R = Xyl, R′ = H, 3a; R = Xyl, R′ = Br, 3b; R = Xyl, R′ = OMe, 3c; R = Xyl, R′ = CO₂Me, 3d; R = Xyl, R′ = CF₃, 3e; R = Me, R′ = H, 3f; R = Me, R′ = CF₃, 3g) are obtained in good yields from the reaction of [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(p-NCC₆H₄R′)(Cp)₂]⁺ (R = Xyl, R′ = H, 2a; R = Xyl, R′ = Br, 2b; R = Xyl, R′ = OMe, 2c; R = Xyl, R′ = CO₂Me, 2d; R = Xyl, R′ = CF₃, 2e; R = Me, R′ = H, 2f; R = Me, R′ = CF₃, 2g) with TolCCLi. The formation of 3 involves addition of the acetylide at the coordinated nitrile and C-N coupling with the bridging aminocarbyne together with orthometallation of the p-substituted aromatic ring and breaking of the Fe-Fe bond. Complexes 3a-e which contain the N(Me)(Xyl) group exist in solution as mixtures of the E-trans and Z-trans isomers, whereas the compounds 3f,g, which posses an exocyclic NMe₂ group, exist only in the Z-cis form. The crystal structures of Z-trans-3b, E-trans-3c, Z-trans-3e and Z-cis-3g have been determined by X-ray diffraction experiments.     

Mono- and bimetallic platinum(II) and palladium(II) complexes containing fluorinated benzothiolates

The new mononuclear palladium(II) and platinum(II) [M(p-SC₆F₄(CF₃))₂(dppe)] complexes M = Pd 1a, Pt 2a; [M(o-SC₆H₄(CF₃))₂(dppe)] M = Pd 1d, Pt 2d as well as the previously known [M(SC₆F₅)₂(dppe)] M = Pd 1b, Pt 2b and [M(p-SC₆HF₄)₂(dppe)] M = Pd 1c, Pt 2c, have been used as metalloligands for the preparation of the heteroleptic bimetallic complexes [M₂(μ-SRf)₂(dppe)₂](SO₃CF₃)₂ M = Pd, Rf = p-C₆F₄(CF₃) 3a, C₆F₅3b, p-C₆HF₄3c, o-C₆H₄(CF₃) 3d; M = Pt, Rf = p-C₆F₄(CF₃) 4a, C₆F₅4b, p-C₆HF₄4c and o-C₆H₄(CF₃) 4d. Variable temperature ¹⁹F NMR experiments show that the fluorothiolate bridged bimetallic compounds are fluxional in solution whereas mononuclear complexes are not. The solid state X-ray diffraction structures of [Pd(p-SC₆HF₄)₂(dppe)] (1c), [Pt(SC₆F₅)₂(dppe)] (2b) and [Pt(o-SC₆H₄(CF₃))₂(dppe)] (2d) show square-planar coordination around the metal centers. The solid state molecular structure of the compound [Pt₂(μ-o-SC₆H₄(CF₃))₂(dppe)₂](SO₃CF₃)₂ (4d), exhibit a planar [Pt₂(μ-S)₂] ring with the sulfur substituents in an anti configuration.     

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.     

Incorporation of a tripodal ligand with a (N,O,O)-donor set into a new family of nickel and cobalt spin clusters

The reaction of Ni(OAc)₂, NiX₂ (X = Cl, Br) or CoCl₂ with the proligand 2-amino-2-methyl-1,3-propanediol (ampdH₂) affords a new family of tetranuclear complexes. The syntheses of [Ni₄(OAc)₄(ampdH)₄] (1) and [M₄X₄(ampdH)₄] (M = Ni, X = Cl, 2; M = Ni, X = Br, 3; M = Co, X = Cl, 4) are reported, together with the single crystal X-ray structures of 1, 2 and 4 and the magnetochemical characterization of 1, 3 and 4. Each member of this family of complexes displays a low symmetry structure that incorporates a {M₄O₄} core unit based on a distorted cubane. Magnetic measurements reveal ferromagnetic exchange interactions for 1, 3 and 4. These give rise to S = 4 ground state spins for the tetranuclear Ni complexes and an anisotropic effective S′ = 2 ground state for the Co complex.     

Diastereomeric half-sandwich Ru(II) cationic complexes containing amino amide ligands. Synthesis, solution properties, crystal structure and catalytic activity in transfer hydrogenation of acetophenone

The cationic complexes [(η⁶-arene)Ru(N,O-amino amide)X]Y (arene = p-cymene or indane; N,O-amino amide = (l)-proline amide or (l)-phenylalanine amide; X = Cl or I; Y = Cl, I or PF₆) have been synthesised and fully characterized by spectroscopic and analytical methods. In several cases (1a, 3a, 4a, 4b, 5) the metal configuration has been definitively established by X-ray analysis on single crystal. The lability of the metal center in solution has been studied by ¹H NMR and CD techniques. The highest configurational stability has been found in the complexes of the type [(η⁶-indane)Ru(N,O-proline amide)Cl]Y (4a,b). The complexes 1b, 2a-b, 3b, 4b and 5 are good precatalysts for the transfer hydrogenation of acetophenone in basic i-PrOH, with ee up to 76% at 30 °C. An ESI(+)-MS study of pre-catalytic solutions has provided useful information on the catalytic mechanism.     

Zwitterionic diiron vinyliminium complexes: Alkylation, metalation and oxidative coupling at the S and Se functionalities

The zwitterionic vinyliminium complex [Fe₂{μ-η¹:η³-C(R′)C(S)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (2a) (R′ = p-Me-C₆H₄ (Tol), Xyl = 2,6-Me₂C₆H₃) undergoes electrophilic addition at the S atom by HSO₃CF₃, MeSO₃CF₃, SiMe₃Cl, BrCH₂Ph, ICH₂CHCH₂ affording the complexes [Fe₂{μ-η¹:η³-C(Tol)C(SX)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][Y] (X =  H, Y = SO₃CF₃, 4a; X = Me, Y = SO₃CF₃, 4b; X = SiMe₃, Y = Cl, 4c; X = CH₂Ph, Y = Br, 4d; X = CH₂CHCH₂, Y = I, 4e).Compound 2a and the corresponding vinyliminium complexes 2b and 2c (R′ = CH₂OH, 2b; R′ = Me, 2c) react also with etherated BF₃ leading to the formation of the corresponding S-adducts [Fe₂{μ-η¹:η³-C(R′)C(SBF₃)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂] (R′ = Tol, 5a; R′ = CH₂OH, 5b; R′ = Me, 5c).In analogous reactions, the zwitterionic vinyliminium complexes undergo S-metalation upon treatment with in situ generated [Fp]⁺[SO₃CF₃]⁻ [Fp = Fe(CO)₂(Cp)], leading to the formation of [Fe₂{μ-η¹:η³-C(R′)C(S-Fp)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃](R′ = CH₂OH, 6a; R′ = Me, 6b; R′ = Buⁿ, 6c).Similarly, zwitterionic vinyliminium containing Se in the place of S also undergo Se-electrophilic addition. Thus, the complexes [Fe₂{μ-η¹:η³-C(R′)C(SeX)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (R = X = Me, R′ = Tol, 7a; R = Xyl, R′ = Me, X = Fp⁺, 7b) are obtained upon treatment of the neutral zwitterionic precursors with MeSO₃CF₃ and [Fp][SO₃CF₃], respectively.Alkylation at the S or Se atom of the bridging ligand is also accomplished by CH₂Cl₂, used as solvent, although the reaction is slower compared to more efficient alkylating reagents. The complexes formed by this route are [Fe₂{μ-η¹:η³-C(R′)C(E-CH₂Cl)CN(Me)(R)}(μ-CO)(CO)(Cp)₂][X] [E = S, R = Xyl, R′ = Tol, X = Cl, 8a; E = S, R = Xyl, R′ = Me, X = Cl, 8b; E = Se, R = R′ = Me, X = BPh₄, 8c].Finally, treatment of the zwitterionic vinyliminium complexes with I₂ results in the oxidative coupling with formation of S-S (disulfide) or Se-Se (diselenide) bond. The reactions, performed in the presence of NaBPh₄ afford the tetranuclear complexes [Fe₂{μ-η¹:η³-C(R′)C(E)CN(Me)(R)}(μ-CO)(CO)(Cp)₂]₂[BPh₄]₂ [R = Xyl, R′ = CH₂OH, E = S, 9a; R = Xyl, R′ = Me, E = S, 9b; R = Xyl, R′ = Buⁿ, E = S, 9c; R = Xyl, R′ = Me, E = Se, 9d; R = Me, R′ = Buⁿ, E = Se, 9e].The molecular structures of 4a, 8c and 9e have been determined by X-ray diffraction studies.     

Axial and equatorial carbene ligands of dimanganese and dirhenium monocarbene complexes: Synthesis, characterisation and structural studies

The binuclear alkoxycarbene complexes [M₂(CO)₉{C(OEt)C₄H₃Y}] (M = Mn, Y = S(1), O(2); Re, Y = S(3), O(4)) were synthesised and characterised, giving axial carbene ligands for the dimanganese complexes, and equatorial carbene ligands for the dirhenium complexes. Aminolysis of these complexes with ammonia and n-propylamine yielded complexes [M₂(CO)₉{C(NHR)C₄H₃Y}] (R = H, M = Mn, Y = S(5), O(6); Re, Y = S(7), O(8); R = propyl, M = Mn, Y = S(9), O(10); Re, Y = S(11), O(12)). For the smaller NH₂-substituted carbene ligands, the X-ray structures determined showed equatorial carbene ligands for both dimanganese and dirhenium complexes, while the NHPr-substituted carbene complexes retained the original configurations of the precursor alkoxy carbene complex, indicating that the steric effects of both the M(CO)₅-fragment and the carbene ligand substituent can affect the coordination site of the carbene ligands of Group VII transition metal complexes in the solid state.     

Ruthenium hydride complexes of chiral and achiral diphosphazane ligands and asymmetric transfer hydrogenation reactions

The half-sandwhich ruthenium chloro complexes bearing chelated diphosphazane ligands, [(η⁵-Cp)RuCl{κ²-P,P-(RO)₂PN(Me)P(OR)₂}] [R = C₆H₃Me₂-2,6] (1) and [(η⁵-Cp^∗)RuCl{κ²-P,P-X₂PN(R)PYY′}] [R = Me, X = Y = Y′ = OC₆H₅ (2); R = CHMe₂, X₂ = C₂₀H₁₂O₂, Y = Y′ = OC₆H₅ (3) or OC₆H₄^tBu-4 (4)] have been prepared by the reaction of CpRu(PPh₃)₂Cl with (RO)₂PN(Me)P(OR)₂ [R = C₆H₃Me₂-2,6 (L¹)] or by the reaction of [Cp^∗RuCl₂]_n with X₂PN(R)PYY′ in the presence of zinc dust. Among the four diastereomers (two enantiomeric pairs) possible for the “chiral at metal” complexes 3 and 4, only two diastereomers (one enantiomeric pair) are formed in these reactions. The complexes 1, 2, 4 and [(η⁵-Cp)RuCl{κ²-P,P-Ph₂PN((S)-^∗CHMePh)PPhY}] [Y = Ph (5) or N₂C₃HMe₂-3,5 (S_CS_PR_Ru)-(6)] react with NaOMe to give the corresponding hydride complexes [(η⁵-Cp)RuH{κ²-P,P-(RO)₂PN(Me)P(OR)₂}] (7), [(η⁵-Cp^∗)RuH{κ²-P,P′-X₂PN(R)PY₂}] [R = Me, X = Y = OC₆H₅ (8); R = CHMe₂, X₂ = C₂₀H₁₂O₂, Y = OC₆H₄^tBu-4 (9)] and [(η⁵-Cp)RuH{κ²-P,P-Ph₂PN((S)-^∗CHMePh)PPhY}][Y = Ph (10) or N₂C₃HMe₂-3,5 (S_CS_PR_Ru)-(11a) and (S_CS_PS_Ru)-(11b)]. Only one enantiomeric pair of the hydride 9 is obtained from the chloro precursor 4 that bears sterically bulky substituents at the phosphorus centers. On the other hand, the optically pure trichiral complex 6 that bears sterically less bulky substituents at the phosphorus gives a mixture of two diastereomers (11a and 11b). Protonation of complex 7 using different acids (HX) gives a mixture of [(η⁵-Cp)Ru(η²-H₂){κ²-P,P-(RO)₂PN(Me)P(OR)₂}]X (12a) and [(η⁵-Cp)Ru(H)₂{κ²-P,P-(RO)₂PN(Me)P(OR)₂}]X (12b) of which 12a is the major product independent of the acid used; the dihydrogen nature of 12a is established by T₁ measurements and also by synthesizing the deuteride analogue 7-D followed by protonation to obtain the D-H isotopomer. Preliminary investigations on asymmetric transfer hydrogenation of 2-acetonaphthone in the presence of a series of chiral diphosphazane ligands show that diphosphazanes in which the phosphorus centers are strong π-acceptor in character and bear sterically bulky substituents impart moderate levels of enantioselectivity. Attempts to identify the hydride intermediate involved in the asymmetric transfer hydrogenation by a model reaction suggests that a complex of the type, [Ru(H)(Cl){κ²-P,P-X₂PN(R)PY₂}(solvent)₂] could be the active species in this transformation.     

Synthesis and characterization of some new mononuclear ruthenium complexes containing 4-(un)substituted dipyridylpyrazole ligands

A mononuclear ruthenium complex [Ru(bpy)₂(bpp)](PF₆) (1) and its halogenated and nitro derivatives [Ru(bpy)₂(Xbpp)](PF₆) (bpy = 2,2′-bipyridine; bpp = 3,5-bis(2-pyridyl)pyrazole; X = Cl, 2; X = Br, 3; X = I, 4; X = NO₂, 5) have been synthesized and characterized by ¹H NMR, ¹³C NMR, HRMS, elemental analysis. Complexes 2–5 have been further confirmed by X-ray diffraction. Their UV–Vis and emission spectroscopies, electrochemical measurements and acid–base properties are described. The results presented here reveal that the introduction of Cl, Br, I and NO₂ groups to the coordinated bpp⁻ ligand makes the absorption and emission maxima of the parent complex 1 blue-shifted, the oxidation potential of the Ru^II/Ru^III couple increased and the pK_a value decreased obviously. In addition, significant quenching of the emission by these groups is also observed.     

Synthesis and characterization of aluminum complexes of 2-pyrazol-1-yl-ethenolate ligands

The synthesis and the characterization of some new aluminum complexes with bidentate 2-pyrazol-1-yl-ethenolate ligands are described. 2-(3,5-Disubstituted pyrazol-1-yl)-1-phenylethanones, 1-PhC(O)CH₂-3,5-R₂C₃HN₂ (1a, R = Me; 1b, R = Bu^t), were prepared by solventless reaction of 3,5-dimethyl pyrazole or 3,5-di-tert-butyl pyrazole with PhC(O)CH₂Br. Reaction of 1a or 1b with (R¹ = Me, Et) yielded N,O-chelate alkylaluminum complexes (2a, R = R¹ = Me; 2b, R = Bu^t, R¹ = Me; 2c, R = Me, R¹ = Et). Compound 1a was readily lithiated with LiBuⁿ in thf or toluene to give lithiated species 3. Treatment of 3 with 0.5 equiv of MeAlCl₂ or AlCl₃ yielded five-coordinated aluminum complexes [XAl(OC(Ph)CH{(3,5-Me₂C₃HN₂)-1})₂] (4, X = Me; 5, X = Cl). Reaction of 5 with an equiv of LiHBEt₃ generated [Al(OC(Ph)CH{(3,5-Me₂C₃HN₂)-1})₃] (6). Complex 6 was also obtained by reaction of 3 with 1/3 equiv of AlCl₃. Treatment of 5 with 2 equiv of AlMe₃ yielded complex 2a, whereas with an equiv of AlMe₃ afforded a mixture of 2a and [Me(Cl)AlOC(Ph)CH{(3,5-Me₂C₃HN₂)-1}] (7). Compounds 1a, 1b, 2a-2c and 4-6 were characterized by elemental analyses, NMR and IR (for 1a and 1b) spectroscopy. The structures of complexes 2a and 5 were determined by single crystal X-ray diffraction techniques. Both 2a and 5 are monomeric in the solid state. The coordination geometries of the aluminum atoms are a distorted tetrahedron for 2a or a distorted trigonal bipyramid for 5.     

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.     

Influence of the transannular interaction in spiro-heterocycles containing Ge(IV) and Sn(IV). A comparative study

[D(CH₂CH₂S)₂]M(XCH₂CH₂Y) 1-8 (M = Ge, Sn; D = O, S; X = Y = S, O and X = S, Y = O) spirocycles were synthesized to analyze the influence of the metal center replacement and the donor atom hardness on the strength of the transannular bond and the hypercoordination phenomena. The compounds were characterized by IR, Raman and NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy, E.I. mass spectrometry and elemental analysis. The molecular and crystal structures of compounds 3, 4, 6-8 and Ge(SCH₂CH₂S)₂ (9) were obtained by X-ray diffraction analyses. They all exhibit five-coordinate central atoms due to transannular metal coordination (M?D) except 4, which displays a dimeric structure formed by the fusion of two five-membered rings resulting in a cyclic-distannoxane unit, {[O(CH₂CH₂S)₂]Sn(SCH₂CH₂O)}₂. The relationship between the nature of the metal center and the differences found between the two germanium and tin series are discussed.