Aluminum complexes incorporating bidentate amido phosphine ligands

A series of aluminum complexes supported by o-phenylene-derived amido phosphine ligands, N-(2-diphenylphosphinophenyl)-2,6-dimethylanilide ([Me-NP]-) and N-(2-diphenylphosphinophenyl)-2,6-diisopropylanilide ([iPr-NP]-), have been prepared. The reactions of trialkylaluminum with H[Me-NP] and H[iPr-NP], respectively, in refluxing toluene produced the corresponding dialkyl complexes [Me-NP]AlR(2) and [iPr-NP]AlR(2) (R = Me, Et). Deprotonation of H[Me-NP] with n-BuLi in THF at -35 degrees C followed by addition of AlCl(3) in toluene at -35 degrees C afforded [Me-NP]AlCl(2), which was subsequently reacted with 2 equiv of trimethylsilylmethyllithium in toluene to give [Me-NP]Al(CH(2)SiMe(3))(2). The aluminum complexes were all characterized by (1)H, (13)C, (31)P, and (27)Al NMR spectroscopy. The solid-state structures of monomeric, four-coordinate [Me-NP]AlEt(2) and [iPr-NP]AlMe(2) and five-coordinate [Me-NP]AlCl(2)(THF) were determined by X-ray crystallography. The (1)H NMR studies of [Me-NP]AlEt(2), [Me-NP]Al(CH(2)SiMe(3))(2), and [iPr-NP]AlEt(2) indicate diastereotopic alpha-hydrogen atoms in these molecules. Heteronuclear COSY and NOE experiments suggest that the phosphorus donor in [Me-NP]Al(CH(2)SiMe(3))(2) and [iPr-NP]AlEt(2) is coupled to only one of the diastereotopic alpha-hydrogen atoms that is virtually antiperiplanar with respect to the phosphorus atom.     

Synthesis and spectroscopic properties of elongated ruthenium dihydrogen complexes: temperature and isotope dependence of H-H distances

Several dihydrogen complexes of ruthenium of the form [Cp/Cp*Ru(P-P)H(2)](+) (P-P = chelating diphosphine ligand) have been prepared by reaction of the corresponding neutral chloride complexes with H(2) in the presence of NaB(ArF)(4). Treatment with D(2) or T(2) gas leads to incorporation of deuterium or tritium in the dihydrogen ligand. Measurement of the resulting H-D and H-T couplings as a function of the temperature and magnetic field gives results consistent with computational studies which predict that the H-H bond distance will increase with temperature and will be significantly shortened by isotopic substitution. The degree of the observed temperature dependence is found to be a critical function of the ancillary ligand set.     

Regulating function of methyl group on the strength of dihydrogen bond in HBeH-HCCH and HMgH-HCCH complexes

The regulating function of methyl group on the strength of dihydrogen bond was investigated in HBeH-HCCH and HMgH-HCCH complexes at the MP2/6-311++G(3df,2p) level. The bond lengths, infrared spectra, interaction energies, and charge transfers were analyzed. The presence of methyl group in the proton acceptor enhances the strength of dihydrogen bond, whereas its presence in the proton donor weakens the strength of dihydrogen bond. The charge analyses indicate that the methyl group in the proton donor and acceptor is electron-donating, thus the methyl group in the proton donor plays a negative role, whereas in the proton acceptor it plays a positive role in the formation of dihydrogen bond.     

H-H and N-H bond cleavage of dihydrogen and ammonia with a bifunctional parent imido (NH)-bridged diiridium complex

Hydrogenation and protonation of parent imido complexes have attracted much attention in relation to industrial and biological nitrogen fixation. The present study reports the structure and properties of the highly unsaturated diiridium parent imido complex [(Cp*Ir)(2)(μ(2)-H)(μ(2)-NH)](+) derived from deprotonation of a parent amido complex. Because of the Lewis acid-Br?nsted base bifunctional nature of the metal-NH bond, the parent imido complex promotes heterolysis of H(2) and deprotonative N-H cleavage of ammonia to afford the corresponding parent amido complexes under mild conditions.     

Gold(I) complexes with tertiary phosphine sulfide ligands

Phosphine sulfides and their gold(I) complexes with general formula R₃P=S—Au—X (X = Cl^–, Br^– or CN^–) were prepared and characterized by elemental analyses, i.r. and ³¹P-n.m.r. spectroscopy. A decrease in the i.r. frequency of the P=S bond in the ligands upon complexation, is indicative of S coordination to gold (I). The ³¹P-n.m.r. spectra revealed that electronegativity of the substituents and angles between them were the two most important factors influencing the ³¹P-n.m.r. chemical shifts. The phosphorus resonance was observed to be more downfield in alkyl substituted phosphine sulfides as compared to the aryl substituted phosphine sulfides. Ligand scrambling in the Cy₃P=S—Au—CN complex in solution, to form [(Cy₃P=S)₂Au]⁺ and [Au(CN)₂]^–, was investigated by ¹³C and ¹⁵N-n.m.r. spectroscopy. Equilibrium constants (K _eq) for scrambling of the Cy₃P=S—Au—CN complex and for its analogue, Cy₃P=Se—Au—CN were measured by integrating the ¹³C-n.m.r. at 297 K and were found to be 0.147 and 1.81 respectively.     

Activation of H-H and H-O bonds at phosphorus with diiron complexes bearing pyramidal phosphinidene ligands

The complex [Fe(2)Cp(2)(μ-PMes*)(μ-CO)(CO)(2)] (Mes* = 2,4,6-C(6)H(2)(t)Bu(3)), which in the solid state displays a pyramidal phosphinidene bridge, reacted at room temperature with H(2) (ca. 4 atm) to give the known phosphine complex [Fe(2)Cp(2)(μ-CO)(2)(CO)(PH(2)Mes*)] as the major product, along with small amounts of other byproducts arising from the thermal degradation of the starting material, such as the phosphindole complex [Fe(2)Cp(2)(μ-CO)(2)(CO){PH(CH(2)CMe(2))C(6)H(2)(t)Bu(2)}], the dimer [Fe(2)Cp(2)(CO)(4)], and free phosphine PH(2)Mes*. During the course of the reaction, trace amounts of the mononuclear phosphide complex [FeCp(CO)(2)(PHMes*)] were also detected, a compound later found to be the major product in the carbonylation of the parent phosphinidene complex, with this reaction also yielding the dimer [Fe(2)Cp(2)(CO)(4)] and the known diphosphene Mes*P═PMes*. The outcome of the carbonylation reactions of the title complex could be rationalized by assuming the formation of an unstable tetracarbonyl intermediate [Fe(2)Cp(2)(μ-PMes*)(CO)(4)] (undetected) that would undergo a fast homolytic cleavage of a Fe-P bond, this being followed by subsequent evolution of the radical species so generated through either dimerization or reaction with trace amounts of water present in the reaction media. A more rational synthetic procedure for the phosphide complex was accomplished through deprotonation of the phosphine compound [FeCp(CO)(2)(PH(2)Mes*)](BF(4)) with Na(OH), the latter in turn being prepared via oxidation of [Fe(2)Cp(2)(CO)(4)] with [FeCp(2)](BF(4)) in the presence of PH(2)Mes*. To account for the hydrogenation of the parent phosphinidene complex it was assumed that, in solution, small amounts of an isomer displaying a terminal phosphinidene ligand would coexist with the more stable bridged form, a proposal supported by density functional theory (DFT) calculations of both isomers, with the latter also revealing that the frontier orbitals of the terminal isomer (only 5.7 kJ mol(-1) above of the bridged isomer, in toluene solution) have the right shapes to interact with the H(2) molecule. In contrast to the above behavior, the cyclohexylphosphinidene complex [Fe(2)Cp(2)(μ-PCy)(μ-CO)(CO)(2)] failed to react with H(2) under conditions comparable to those of its PMes* analogue. Instead, it slowly reacted with HOR (R = H, Et) to give the corresponding phosphinous acid (or ethyl phosphinite) complexes [Fe(2)Cp(2)(μ-CO)(2)(CO){PH(OR)Mes*}], a behavior not observed for the PMes* complex. The presence of BEt(3) increased significantly the rate of the above reaction, thus pointing to a pathway initiated with deprotonation of an O-H bond of the reagent by the basic P center of the phosphinidene complex, this being followed by the nucleophilic attack of the OR(-) anion at the P site of the transient cationic phosphide thus formed. The solid-state structure of the cis isomer of the ethanol derivative was determined through a single crystal X-ray diffraction study (Fe-Fe = 2.5112(8) ?, Fe-P = 2.149(1) ?).     

Synthesis and characterization of diiron ethanedithiolate complexes with monosubstituted phosphine ligands

Reactions of (μ-edt)Fe₂(CO)₆ (edt = SCH₂CH₂S) (1) with the monophosphine ligands Ph₂PCH₂Ph, Ph₂PC₆H₁₁, Ph₂PCH₂CH₂CH₃, or P(2-C₄H₃O)₃ in the presence of Me₃NO?2H₂O afforded (μ-edt)Fe₂(CO)₅L [L = Ph₂PCH₂Ph, 2; Ph₂PC₆H₁₁, 3; Ph₂PCH₂CH₂CH₃, 4; P(2-C₄H₃O)₃, 5] in 70–88% yields. Complexes 2–5 were characterized by spectroscopy and single crystal X-ray diffraction analysis. The phosphorus of 2–5 is in an apical position of the distorted octahedral geometry of iron.     

Catalytic properties of palladium complexes with silica-anchored phosphine ligands in vinyl exchange reaction

Catalytic properties of Pd complexes with phosphine ligands anchored to silica have been studied. The valence state of Pd and the acidity of the alcohol were found to influence the rate of vinyl exhange. A possible reaction mechanism is proposed.

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New rhodium---ruthenium heterobimetallic complexes with bridging bi- or tri-dentate phosphine ligands

The mononuclear chelated complex [RuCl(Cp)(η²-dppa)] has been synthesised and reacted with [Rh₂Cl₂(CO)₄] to form the heterobimetallic complex [(Cp)Ru(μ-CO)₂{(μ-Ph₂PN(H)PPh₂}RhCl₂]. Complexes of [RuCl(Cp){(PPh₂)₂CHCH₂PPh₂}] have been reacted with [Rh₂Cl₂(CO)₄] or [RhCl(CO)₂(p-toluidene)]. Characterisation of these new ruthenium complexes was carried out using ³¹P-NMR, FAB mass spectroscopy, elemental analysis and IR spectrophotometry.     

Synthesis and electrochemistry of phenyl-functionalized diiron propanedithiolate complexes with bidentate phosphine ligands

Carbonyl substitution reactions of [μ-(SCH₂)₂CHC₆H₅]Fe₂(CO)₆ with bidentate phosphine ligands, cis-1,2-bis(diphenylphosphine)ethylene (cis-dppv) and N,N-bis(diphenylphosphine)propylamine [(Ph₂P)₂N-Pr-n], yielded an asymmetrically substituted chelated complex [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(k ²-dppv) and a symmetrically substituted bridging complex [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄[μ-(PPh₂)₂N-Pr-n] under different reaction conditions. Both complexes were fully characterized by spectroscopic methods and by X-ray crystallography. Their electrochemical behaviors were observed by cyclic voltammetry, and the catalytic electrochemical reduction of protons from acetic or trifluoroacetic acid to give dihydrogen mediated by complex [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(k ²-dppv) was investigated.     

Luminescent complexes with ligands containing C=N bond

Data on luminescent complexes with azomethine ligands are generalized and systematized. The synthesis and luminescent properties of complexes with acyclic and cyclic azomethines are considered.     

Preparation, characterization and structure of ruthenium phosphine complexes containing non-innocent ligands

Phosphine ruthenate complexes containing the non-innocent ligands 4-chloro-1,2-phenylenediamine (opda-Cl) and 3,3′,4,4′-tetraamminebiphenyl (diopda) were synthesized and characterized by means of X-ray diffraction, electrochemistry, ³¹P{¹H} NMR and electronic spectroscopies. Crystals of cis-[RuCl₂(dppb)(bqdi-Cl)] complex were isolated as a mixture of two conformational isomers due to different positions of the chlorine atoms of the o-phenylene ligand in relation to the P1 atom of the phosphine moiety.     

Nonpolar dihydrogen bonds--on a gliding scale from weak dihydrogen interaction to covalent H-H in symmetric radical cations [HnE-H-H-EHn]+

The electronic structures and bonding patterns for a new class of radical cations, [HnE-H-H-EHn]+ (EHn=element hydride, E=element of Groups 15-18), have been investigated by applying quantum-chemical methods. All structures investigated give rise to symmetric potential energy minimum structures. We envisage clear periodic trends. The H--H bond length is shorter for elements toward the bottom of the periodic table of elements, and a short H--H bond corresponds to accumulation of electron density in the central H--H region. All [HnE-H-H-EHn]+ of Groups 15-17 are thermodynamically unstable towards loss of either H2 or H. The barriers for these dissociations are rather low. The Group 18 congeners, except E=Xe, appear to be global minima of the respective potential energy surfaces. The findings are discussed in terms of H2 bond activation, and a general mechanistic scheme for the standard reduction process 2H+ + 2e(-) --> H2 is given. Finally, it is proposed that some of the symmetric radical cations are likely to be observed in mass spectrometric or matrix isolation experiments.