Homoleptic Compounds Research Articles

Chloride Ion-Pairing with Ru(II) Polypyridyl Compounds in Dichloromethane

Chloride ion-pairing with a series of four dicationic Ru(II) polypyridyl compounds of the general form [Ru(bpy)3-x(deeb)x](PF6)2, where bpy is 2,2'-bipyridine and deeb is 4,4'-diethylester-2,2'-bipyridine, was observed in dichloromethane solution. The heteroleptic compounds [Ru(bpy)2(deeb)](2+) and [Ru(bpy)(deeb)2](2+) were found to be far less sensitive to ligand loss photochemistry than were the homoleptic compounds [Ru(bpy)3](2+) and [Ru(deeb)3](2+) and were thus quantified in most detail. X-ray crystal structure and (1)H NMR analysis showed that, when present, the C-3/C-3' position of bpy was the preferred site for adduct formation with chloride. Ion-pairing was manifest in UV-visible absorption spectral changes observed during titrations with TBACl, where TBA is tetrabutyl ammonium. A modified Benesi-Hildebrand analysis yielded equilibrium constants for ion-pairing that ranged from 13 700 to 64 000 M(-1) and increased with the number of deeb ligands present. A Job plot indicated a 2:1 chloride-to-ruthenium complex ratio in the ion-paired state. The chloride ion was found to decrease both the excited state lifetime and the quantum yield for photoluminescence. Nonlinear Stern-Volmer plots were observed that plateaued at high chloride concentrations. The radiative rate constants decreased and the nonradiative rate constants increased with chloride concentration in a manner consistent with theory for radiative rate constants and the energy gap law. Equilibrium constants for excited state ion-pairing abstracted from such data were found to be significantly larger than that measured for the ground state. Photophysical studies of hydroxide and bromide ion-pairing with [Ru(bpy)2(deeb)](2+) are also reported.

Synthesis and characterization of homoleptic chromium(III) complexes containing pyridine-2-thionato ligands and of the co-crystal (1:1) bis(pyridine-2-thionato)(pyridine-2-dithionato) chromium(III) tris(pyridine-2-thionato) chromium(III)

The reaction of [Cr(CO)6] with a series of heterocyclic bidentate (N,S) ligands in refluxing mesitylene afforded the homoleptic trischelate complexes [Cr(3-Me3SipyS)3] (2), [Cr(3-CF3pyS)3] (3) and [Cr(5-CF3pyS)3] (4), where R-pyS stands for the anion of the corresponding substituted pyridine-2-thione ligand. Studies in the solid state by X-ray diffraction showed that the reaction with the unsubstituted ligand HpyS yielded the compound [Cr(pyS)3]/[Cr(pyS)2(pySS)] (1), which is a two-component co-crystal comprising the homoleptic species [Cr(pyS)3] (1a) and the heteroleptic species [Cr(pyS)2(pySS)] (1b), in a 1:1 ratio. While the structure of the species [Cr(pyS)3] (1a) is analogous to that of other homoleptic compounds, [Cr(RpyS)3], the species [Cr(pyS)2(pySS)] (1b) is an unusual heteroleptic complex containing both pyridine-2-thionate and pyridine-2-dithionate ligands. All of the compounds obtained were characterized by microanalysis and FAB spectrometry, and by IR and UV–Vis spectroscopies. X-ray studies showed that in all cases the metal is in a distorted octahedral environment with the heterocyclic ligand acting as a bidentate (N,S) chelate system. The supramolecular organization in complexes (1) and (2) through hydrogen bonding, weak C–H⋯π and π–π interactions was analyzed.

Molecular and electronic structure of MM quadruply bonded complexes containing O2CC6H4N(Ph)2 supporting ligands

The complexes trans-M2(TiPB)2(O2CC6H4-4-NPh2)2 where M=Mo (I), and M=W (II) were prepared from the reaction between M2(TiPB)4 and the carboxylic acid Ph2N-4-C6H4CO2H (∼2equiv.) in toluene (TiPB=2,4,6-triisopropylbenzoate). The compounds were isolated as microcrystalline powders that are yellow, I or purple II, and are air-sensitive. Compound I was characterized by single-crystal X-ray crystallography and shown to have a centrosymmetric structure and a planar central C6H4-CO2M2O2C-C6H4 unit. Calculations indicate that the HOMO is principally M2δ with mixing of the filled π-orbitals of the N,N-diphenyl-4-aminobenzoate. Oxidation of I and II yield cationic species that have been characterized by EPR and UV–Vis–NIR spectroscopy. The radical cations show EPR spectra characteristic of M25+ centers having the MM configuration σ2π4δ1 and compound I+ shows a low energy NIR transition assignable to a ligand to metal charge transfer transition. The homoleptic compound Mo2(O2CC6H4-4-N-Ph2)4, III, was prepared from the reaction between Mo(CO)6 and Ph2N-4-C6H4CO2H in refluxing ortho-dichlorobenzene and is shown to exhibit similar spectroscopic features to those of I.

Capturing the geometry of the emissive state of a Cu(i) red emitter through strong intramolecular stacking forces

Condensation of ethylenediamine with fluorenone produces a diimine with two terminal fluorophores and a flexible central backbone, N,N'-bis-fluoren-9-ylidene-ethane-1,2-diamine (flen). The diimine reacts with [Cu(MeCN)(4)]BF(4) or CuI to produce a homoleptic compound of the stoichiometry [Cu(flen)(2)]BF(4) or [Cu(flen)(2)][CuI(2)] respectively. Both complexes emit in the red part of the spectrum, with a maximum around 720 nm and excited state lifetime of 0.2 μs in solution. The crystal structures of the complexes reveal almost an identical Cu(i)-diimine core where the predominant forces are the intramolecular π-π interactions between the fluorenone aromatic systems resulting in considerably distorted coordination environments. The negligible difference in the emission maximum between solution and solid state indicates that the vibrationally relaxed excited state, assigned as MLCT/IL, adopts a structure closely similar to the crystallographically determined one.

Diamine Bis(phenolate) as Supporting Ligands in Organoactinide(IV) Chemistry. Synthesis, Structural Characterization, and Reactivity of Stable Dialkyl Derivatives

The homoleptic compounds [U(salan-R2)2] (R = Me (1), tBu (2)) were prepared in high yield by salt-metathesis reactions between UI4(L)2 (L = Et2O, PhCN) and 2 equiv of [K2(salan-R2)] in THF. In contrast, the reaction of the tetradentate ligands salan-R2 with UI3(THF)4 leads to disproportionation of the metal and to mixtures of U(IV) [U(salan-R2)2] and [U(salan-R2)I2] complexes, depending on the ligand to M ratio. The reaction of K2salan-Me2 ligand with U(IV) iodide and chloride salts always leads to mixtures of the homoleptic bis-ligand complex [U(salan-Me2)2] and heteroleptic complexes [U(salan-Me2)X2] in different organic solvents. The structure of the heteroleptic complex [U(salan-Me2)I2(CH3CN)] (4) was determined by X-ray studies. Heteroleptic U(IV) and Th(IV) chloride complexes were obtained in good yield using the bulky salan-tBu2 ligand. The new complexes [U(salan-tBu2)Cl2(bipy)] (5) and [Th(salan-tBu2)Cl2(bipy)] (8) were crystallographically characterized. The salan-tBu2 halide complexes of U(IV) a...

Oxalate Bridged MM Quadruply Bonded Oligomers: Considerations of Electronic Structure and Synthetic Strategies

The electronic structures of oxalate bridged oligomers of MM quadruply bonded complexes (M = Mo or W) have been calculated by density functional theory. The calculations predict the formation of a δ band width ~1.0 eV. With increasing number of oxalate bridges, the metal-to-ligand (oxalate) charge transfer band moves to lower energy. Two synthetic approaches have been investigated. (1) The direct reaction between oxalic acid and the homoleptic compound M2(T i PB)4, where T i PB = 2,4,6-triisopropylbenzoate and (2) the metathetic reaction between the herein reported salt Mo2(T i PB)2(CH3CN)4(BF4)2 and ( n Bu4N+)2(oxalate2−). Neither reaction yielded the desired oligomers though the latter resulted in the formation of the molecular triangle [Mo2(T i PB)2(O2CCO2)]3.

Synthesis and Stability of Homoleptic Metal(III) Tetramethylaluminates

Whereas a number of homoleptic metal(III) tetramethylaluminates M(AlMe(4))(3) of the rare earth metals have proven accessible, the stability of these compounds varies strongly among the metals, with some even escaping preparation altogether. The differences in stability may seem puzzling given that this class of metals usually is considered to be relatively uniform with respect to properties. On the basis of quantum chemically obtained relative energies and atomic and molecular descriptors of homoleptic tris(tetramethylaluminate) and related compounds of rare earth metals, transition metals, p-block metals, and actinides, multivariate modeling has identified the importance of ionic metal-methylaluminate bonding and small steric repulsion between the methylaluminate ligands for obtaining stable homoleptic compounds. Low electronegativity and a sufficiently large ionic radius are thus essential properties for the central metal atom. Whereas scandium and many transition metals are too small and too electronegative for this task, all lanthanides and actinides covered in this study are predicted to give homoleptic compounds stable toward loss of trimethylaluminum, the expected main decomposition reaction. Three of the predicted lanthanide-based compounds Ln(AlMe(4))(3) (Ln = Ce, Tm, Yb) have been prepared and fully characterized in the present work, in addition to Ln(OCH(2)tBu)(3)(AlMe(3))(3) (Ln = Sc, Nd) and [Eu(AlEt(4))(2)](n). At ambient temperature, donor-free hexane solutions of Ln(AlMe(4))(3) of the Ln(3+)/Ln(2+) redox-active metal centers display enhanced reduction to [Ln(AlMe(4))(2)](n) with decreasing negative redox potential, in the order Eu ≫ Yb ≫ Sm. Whereas Eu(AlMe(4))(3) could not be identified, Yb(AlMe(4))(3) turned out to be isolable in low yield. All attempts to prepare the putative Sc(AlMe(4))(3), featuring the smallest rare earth metal center, failed.

Synthesis and Characterization of Homoleptic and Heteroleptic Cobalt, Nickel, Copper, Zinc and Cadmium Compounds with the 2‐(Tosylamino)‐N‐[2‐(tosylamino)benzylidene]aniline Ligand

AbstractThe electrochemical oxidation of anodic metal (cobalt, nickel, copper, zinc and cadmium) in an acetonitrile solution of the Schiff‐base ligand 2‐(tosylamino)‐N‐[2‐(tosylamino)benzylidene]aniline (H2L) afforded the homoleptic compounds [ML]. The addition of 1,1‐diphenylphosphanylmethane (dppm), 2,2′‐bipyridine (bipy) or 1,10‐phenanthroline (phen) to the electrolytic phase gave the heteroleptic complexes [NiL(dppm)], [ML(bipy)] and [ML(phen)]. The crystal structures of H2L (1), [NiL] (2), [CuL] (3), [NiL(dppm)] (4), [CoL(phen)] (5), [CuL(bipy)] (6) and [Zn(Lphen)] (7) were determined by X‐ray diffraction. The homoleptic compounds [NiL] and [CuL] are mononuclear with a distorted square planar [MN3O] geometry with the Schiff base acting as a dianionic (NamideNamideNimineOtosyl) tetradentate ligand. Both compounds exhibit an unusual π–π stacking interaction between a six‐membered chelate ring containing the metal and a phenylic ring of the ligand. In the heteroleptic complex [NiL(dppm)], the nickel atom is in a distorted tetrahedral [NiN3P] environment defined by the imine, two amide nitrogen atoms of the L2– dianionic tridentate ligand and one of the phosphorus atoms of the dppm molecule. In the other heteroleptic complexes, [CoL(phen)], [CuL(bipy)] and [ZnL(phen)], the metal atom is in a five‐coordinate environment defined by the imine, two amide nitrogen atoms of the dianionic tridentate ligand and the two bipyridine or phenanthroline nitrogen atoms. The compounds were characterized by microanalysis, IR and UV/Vis (Co, Ni and Cu complexes) spectroscopy, FAB mass spectrometry and 1H NMR ([NiL] and Zn and Cd complexes) and EPR spectroscopy (Cu complexes).

Synthesis and characterisation of trigonal C2-chiral di- and tetra-substituted bis(oxazoline) alkyl zinc complexes and their reactivity towards protic reagents

A series of zinc(ii) alkyl complexes stabilised by the C(2)-chiral bis(oxazoline) ligand ((R(1),R(2))BOX, with R(1) = (4S)-tBu, R(2) = H (a); R(1) = (4S)-Ph, R(2) = H (b); R(1) = (4R)-Ph, R(2) = (5S)-Ph (c)), has been synthesised and structurally characterised. ((R(1),R(2))BOX)H ligands react with ZnEt(2) in toluene to give the heteroleptic three-coordinate compounds of ((R(1),R(2))BOX)ZnEt, 1a, 1b and 1c in high yield. However, when the addition of (BOX)H ligands (a-b) over ZnEt(2) is "uncontrolled", the formation of homoleptic four-coordinate compounds are favoured (2a-b), but not for the more sterically crowded ligand (c). The zinc-ethyl derivatives (1a-c) react readily with protic reagents such as acetic acid (HOAc) and methanol (MeOH). For compounds 1a-c a redistribution of ligands is observed leading preferentially to homoleptic compounds, except for the bulkier ligand c providing a three-coordinate complex identified as ((Ph,Ph)BOX)Zn(OMe), 4c. The reaction of acetylacetone (acacH) with compounds 1a-c leads straightforwardly to the more stable four-coordinate compounds corresponding to ((R(1),R(2))BOX)Zn(η(2)-acac), 5a-c. The potential of these compounds as initiators for the copolymerisation of epoxides with CO(2) was investigated.

Bis(dimethylsilyl)amide Complexes of the Alkaline-Earth Metals Stabilized by β-Si−H Agostic Interactions: Synthesis, Characterization, and Catalytic Activity

The syntheses of the homoleptic compounds Ae[N(SiMe2H)2]2(THF)x (Ae = Ca, x = 1, 2; Sr, x = 2/3, 3; Ba, x = 0, 4) are reported. They can be prepared by salt metathesis involving the alkaline-earth metal iodides and KN(SiMe3)2 (1) or by transamination between Ae[N(SiMe3)2]2(THF)2 and HN(SiMe2H)2. These precursors constitute convenient starting materials for the subsequent preparation of {LnO}AeN(SiMe2H)2 heteroleptic complexes of the large alkaline-earth metals, as exemplified by the syntheses of {LO3}AeN(SiMe2H)2 ({LO3}− = 2-{(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methyl}-4,6-di-tert-butylphenolate; Ae = Ca, 5; Sr, 6; Ba, 7). Both homo- and heteroleptic complexes are stabilized in the solid state by secondary β-Si−H agostic interactions. The structures of the kinetically stable {LO3}BaN(SiMe2H)2 (7) and those of its potassium synthetic precursors 1 and {LO3}K·KN(SiMe2H)2 (8) are described, and the catalytic activity of the heteroleptic complexes in the ring-opening polymerization of lactide is presented.

Hydrogen bond supramolecular self-assembly in nickel(II) dithiophosphates, Ni[S 2P(OR) 2] 2, R = sec-Bu, iso-Bu, and their bis(pyrazole) adducts

The reaction between nickel(II) nitrate and potassium phosphorus-1,1-dithiolates (di- sec-butyl and di- iso-butyl) in methanol yields 2:1 complexes which were characterized by FT-IR and NMR spectroscopy. 2:1 pyrazole adducts of both compounds were also obtained. The X-ray diffraction analysis of the compounds reveals square planar, four-coordination geometry for the homoleptic compounds and a six-coordinated distorted octahedral geometry for the adducts. In Ni[S 2P(OBu s) 2] 2 the molecules are associated through C–H⋯O hydrogen bonds (2.652 Å), and in Ni[S 2P(OBu i) 2] 2 the molecules are associated through C–H⋯S hydrogen bonds (2.948 Å). The pyrazole adducts are associated through N–H⋯O bonds and N–H⋯S bonds from the pyrazole nitrogen atoms, to form supramolecular assemblies. Thus, Ni[S 2P(OBu s) 2(Pz) 2] 2 (Pz = pyrazole) forms bi-dimensional layers through N–H⋯O and N–H⋯S bonds (2.502 and 2.965 Å, respectively), whereas Ni[S 2P(OBu i) 2(Pz) 2] 2 forms linear chains with N–H⋯S bonds 2.728 Å. The dithiophosphato groups behave as isobidentate chelating ligands.

Group 13 Ligand Supported Heavy‐Metal Complexes: First Structural Evidence for Gallium–Lead and Gallium–Mercury Bonds

Heavy-metal complexes of lead and mercury stabilized by Group 13 ligands were derived from the oxidative addition of Ga(ddp) (ddp=HC(CMeNC(6)H(3)-2,6-iPr(2))(2), 2-diisopropylphenylamino-4-diisopropyl phenylimino-2-pentene) with corresponding metal precursors. The reaction of Me(3)PbCl and Ga(ddp) afforded compound [{(ddp)Ga(Cl)}PbMe(3)] (1) composed of Ga-Pb(IV) bonds. In addition, the monomeric plumbylene-type compound [{(ddp)Ga(OSO(2)CF(3))}(2)Pb(thf)] (2a) with an unsupported Ga-Pb(II)-Ga linkage was obtained by the reaction of [Pb(OSO(2)CF(3))(3)] with Ga(ddp) (2 equiv). Compound 2a falls under the rare example of a discrete plumbylene-type compound supported by a nonclassical ligand. Interesting structural changes were observed when [Pb(OSO(2)CF(3))(3)]2.H(2)O was treated with Ga(ddp) in a 1:2 ratio to yield [{(ddp)Ga(mu-OSO(2)CF(3))}(2)(OH(2))Pb] (2b) at below -10 degrees C. Compound 2b consists of a bent Ga-Pb-Ga backbone with a bridging triflate group between the Ga-Pb bond and a weakly interacting water molecule at the gallium center. Similarly, the reaction of mercury thiolate Hg(SC(6)F(5)) with Ga(ddp) (2 equiv) produced the bimetallic homoleptic compounds anti-[{(ddp)Ga(SC(6)F(5))}(2)Hg] (3a) and gauche-[{(ddp)Ga(SC(6)F(5))}(2)Hg] (3b), respectively, with a linear Ga-Hg-Ga linkage. Compounds 1-3 were structurally characterized and these are the first examples of compounds comprised of Ga-Pb(II), Ga-Pb(IV), and Ga-Hg bonds.

Bis(imidazolin-2-ylidene-1-yl)borate Complexes of the Heavier Alkaline Earths: Synthesis and Studies of Catalytic Hydroamination

Heteroleptic complexes of the heavier alkaline earth elements, calcium and strontium, containing bis(imidazolin-2-ylidene-1-yl)borate ligands may be synthesized by deprotonation of boronium salt ligand precursors with [KN(SiMe3)2] in the presence of CaI2 or SrI2. The silylamide complexes [{H2B(ImtBu)2}M{N(SiMe3)2}(THF)n] (M = Ca, n = 1; M = Sr, n = 2), containing N-tert-butyl-substituted imidazolin-2-ylidene fragments, are stable to intermolecular solution redistribution despite some evidence of solution fluxionality in the case of M = Ca. Attempts to synthesize heteroleptic iodide-containing species led to the isolation of the homoleptic compounds [{H2B(ImtBu)2}2MTHF)n] (M = Ca, n = 1; M = Sr, n = 2) most likely because of the reduced steric demands of the halide coligand. Although extension of the “one pot” synthetic method to precursors containing N-mesityl-substituted imidazoles resulted in extensive ligand degradation, use of [Ca{N(SiMe3)2}2(THF)2] as both base and group 2 element source provided the target heteroleptic silylamide complex. X-ray diffraction analyses demonstrated that the borate ligands adopt a facial η3-binding mode in which coordination is provided through the two N-heterocyclic carbene (NHC) donors and an additional agostic-type interacton from one hydrogen of the BH2 residue. Analysis of this ligand binding by DFT methods indicates that, although the bonds from the carbon centers are similar in character to those provided by neutral NHC ligands, the bonding is supplemented by an electrostatic component which is manifested as a coordination of a hydridic BH bond. The ionic nature of the overall interaction is sufficient to maintain the metal−ligand binding in the presence of amine donors and has allowed the evaluation of the Ca and Sr complexes [{H2B(ImtBu)2}M{N(SiMe3)2}(THF)n] as precatalysts for the intramolecular hydroamination of aminoalkenes. While the calcium catalyst provides activities commensurate with our previously reported β-diketiminato complex, [CH{C(Me)N(2,6-iPr2C6H3)}Ca{N(SiMe3)2}(THF)], the strontium derivative is superior in all cases.

Reactions of cationic transition metal acetonitrile complexes [M(CH3CN)n]m+ with GaCp*: novel gallium complexes of iron, cobalt, copper and silver

The reactions of the cationic transition metal acetonitrile complexes [M(CH3CN)n]m+ (m = 2: M = Fe, Co and m = 1: M = Cu, Ag) with GaCp* were investigated. The reaction of [Fe(CH3CN)6][BArF]2 (BAr(F) = [B{C6H3(CF3)2}4) with GaCp* leads to [Cp*Fe(GaCp*)3][BAr(F)] (1) via a redox neutral Cp* transfer and [Ga2Cp*][BAr(F)] as a by-product while the formation of [Cp*Co(GaCp*)3][BAr(F)]2 (2) from [Co(CH3CN)6][BAr(F)]2 is accompanied by oxidation of Co(II) to Co(III) with GaCp* as the oxidant. The reactions of [Cu(CH3CN)4][BAr(F)] and Ag[BPh4] with GaCp* lead to the formation of the homoleptic compounds [Cu(GaCp*)4][BAr(F)] (4) and [Ag(GaCp*)4][BPh4] (5), while treatment of Ag[CF3SO3] with GaCp* leads to the dimeric complex [Ag2(GaCp*)3(micro-GaCp*)2][CF3SO3]2 (6). All compounds were characterized by NMR spectroscopy, single crystal X-ray diffraction and elemental analysis.

Stepwise and one-pot syntheses of Ir(iii) complexes with imidazolium-based carbene ligands

We report the preparation, crystal structure, electrochemistry, and emission properties of Ir(Cinsertion markC:)3, where Cinsertion markC: is an N-heterocyclic carbene ligand. Two synthetic approaches are introduced for generating Ir(III) complexes bearing imidazolium-based carbene ligands whose precursors are [pypiH2][Cl] (1a) (pyridyl[1,2-a]{2-phenylimidazol}-3-ylidene chloride) and [pympiH2][Cl] (1b) (pyridyl[1,2-a-{2-(p-methoxy)phenylimidazol}-3-ylidene chloride). The first method is a stepwise reaction: treatment of [Ir(mu-Cl)(COD)]2, where COD is 1,5-cyclooctadiene, with 4 equiv. of the corresponding carbene (Cinsertion markC:) ligands in the presence of an excess amount of sodium methoxide affords Ir(III) dimers [Ir(mu-Cl)(Cinsertion markC:)2]2 (2a, Cinsertion markC: = pypi(-); 2b, Cinsertion markC: = pympi(-)). These chloro-bridged dimers 2a and 2b react with the corresponding carbene (Cinsertion markC:) ligands to form the desired homoleptic compounds Ir(Cinsertion markC:)3 (3a, Cinsertion markC: = pypi(-); 3b, Cinsertion markC: = pympi(-)). The second method, using a one-pot reaction of [Ir(mu-Cl)(COD)]2 with 6 equiv. of the corresponding carbene (Cinsertion markC:) ligands 1a and 1b in the presence of excess amounts of Ag2O, affords Ir(Cinsertion markC:)3. The two methods are convenient and reproducible procedures for the synthesis of Ir(Cinsertion markC:)3. Complexes 3a and 3b are obtained as mixtures of meridional and facial isomers, which can be separated by recrystallization or flash column chromatography.

Bis(trispivalatodimolybdenum (II))-μ-bis(4′-carboxylato-2,2′:6′,2″-terpyridine) Ruthenium (II)] (2+) Tetrafluoroborate. Preparation, Electronic Structure and Physical Properties

The homoleptic compound Ru(II)(L)2 where L = 4′-carboxylato-2,2′:6′,2″-terpyridine was employed as a bridge to link two [Mo2(O2CBut)3]+ units in the formation of the title complex: [Mo2(O2CBut)3]2-μ-Ru(II)L2] (2+) [BF4−]2, which has been characterized by 1H-NMR, UV–vis and emission spectroscopy, MALDI-TOF-MS and cyclic voltammetry. The electronic structure of the complex has been investigated by density functional theory employing Turbomole on the model complex cation [Mo2(O2CH)3]2-μ-(Ru(II)L2)2+. The intense blue color of the cation arises from M2 δ to bridge/terpyridine charge transfer.

Reinvestigation of the reaction of strontium and barium with iodobenzene and molecular structure of the heavy Grignard reagent [((thf) 2BaPh 2) 4 · (thf)BaO] with an oxygen-centered square Ba 5 pyramid

The direct synthesis of activated strontium and barium with iodobenzene in THF yields the corresponding THF complexes of phenylstrontium and phenylbarium iodide, respectively, which dismutate into the homoleptic compounds MPh 2 and MI 2. Already at low temperatures ether cleavage reactions take place and from this reaction, the oxygen-centered cage [((thf) 2BaPh 2) 4 · (thf)BaO] was isolated and its molecular structure determined.

Heteroleptic Phenylcalcium Derivatives via Metathesis Reactions of PhCa(thf)4I with Potassium Compounds

The metathesis reactions of (thf)4Ca(Ph)I with the corresponding potassium compounds KR yield the heteroleptic arylcalcium derivatives (thf)3Ca(Ph)[N(SiMe3)2] (1) and (thf)4Ca(Ph)PPh2 (2), due to the insolubility of KI in common organic solvents. However, the reaction of KCp and KOC6H2-2,6-tBu-4-Me with (thf)4Ca(Ph)I give the homoleptic compounds (thf)2CaCp2 (3) and (dme)CaCp2 (4) (depending on the solvent) as well as (thf)3Ca(OC6H2-2,6-tBu-4-Me)2 (5). Diphenylcalcium decomposed under these reaction conditions. The reaction of K[(Me3SiN)2CPh] with (thf)4Ca(Ph)I yields [{(thf)3Ca}2{4,4-Ph2-2,6-(C6H4)2C3N3}(μ-I)] (6). This dihydrotriazine derivative forms due to a slow liberation of benzonitrile from the starting N,N'-bis(trimethylsilyl)benzamidinate. A solvent change in order to shift the Schlenk equilibrium (2 PhCaICaPh2 + CaI2) toward the homoleptic diphenylcalcium leads immediately to ether cleavage reactions and the formation of [{(Et2O)CaPh2}4·(Et2O)CaO] (7), which precipitates from diethyl ether. Thi...

Synthesis and Thermolysis of Aluminum Amidinates: A Ligand-Exchange Route for New Mixed-Ligand Systems

A novel ligand-exchange route for the synthesis of amidinate-containing compounds of aluminum is explored. Syntheses of three new compounds, MeC(NiPr)2AlEt2 (4), EtC(NiPr)2AlMe2 (5), and (Me2NC(NiPr)2)2AlH (6), are presented. These mixed-ligand compounds are difficult to make in high yields by the more traditional routes of carbodiimide insertion or salt metathesis. The thermal reactivities of these compounds and their parent homoleptic compounds [MeC(NiPr)2]3Al (1), [Me2NC(NiPr)2](3)Al (2), and [EtC(NiPr)2]3Al (3) are explored in detail and analyzed with respect to their utility as potential atomic-layer-deposition precursors for aluminum-containing films. The major mechanism of thermal decomposition is found to be carbodiimide deinsertion to form aluminum alkyls or amides. Because of their thermal characteristics, both compounds 3 and 5 hold promise for use as precursors.

Highly efficient magnesium initiators for lactide polymerization

Two monomeric, six-coordinated magnesium complexes with bulky aminophenolate ligands [(Htbpoa)2Mg] (1) and [(Htbpca)2Mg(THF)2] (2), where Htbpoa =N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-methyl-1,3-dioxolaneamine and Htbpca =N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-cyclohexylamine have been prepared, characterized and employed as initiators for lactide polymerization. The crystal structure of the homoleptic compound 1 has been determined and shows that the six-coordinate magnesium atom in 1 is surrounded by two tridendate tbpoa ligands. In the solution, however, complex 1 exists in equilibrium with a five-coordinate species 1a having one oxolane fragment dangling. The tbpoa and tbpca ligands in 1 and 2 play a dual role, as the ancillary ligand stabilizing the monomeric magnesium species and as the initiating polymerization group.