Design and Synthesis of Isocyanide Ligands for Catalysis: Application to Rh‐Catalyzed Hydrosilylation of Ketones

New isocyanide ligands with meta‐terphenyl backbones were synthesized. 2,6‐Bis[3,5‐bis(trimethylsilyl)phenyl]‐4‐methylphenyl isocyanide exhibited the highest rate acceleration in rhodium‐catalyzed hydrosilylation among other isocyanide and phosphine ligands tested in this study. ¹H NMR spectroscopic studies on the coordination behavior of the new ligands to [Rh(cod)₂]BF₄ indicated that 2,6‐bis[3,5‐bis(trimethylsilyl)phenyl]‐4‐methylphenyl isocyanide exclusively forms the biscoordinated rhodium–isocyanide complex, whereas less sterically demanding isocyanide ligands predominantly form tetracoordinated rhodium–isocyanide complexes. FTIR and ¹³C NMR spectroscopic studies on the hydrosilylation reaction mixture with the rhodium–isocyanide catalyst showed that the major catalytic species responsible for the hydrosilylation activity is the Rh complex coordinated with the isocyanide ligand. DFT calculations of model compounds revealed the higher affinity of isocyanides for rhodium relative to phosphines. The combined effect of high ligand affinity for the rhodium atom and the bulkiness of the ligand, which facilitates the formation of a catalytically active, monoisocyanide–rhodium species, is proposed to account for the catalytic efficiency of the rhodium–bulky isocyanide system in hydrosilylation.     

Alkali Metal and Alkaline Earth Metal Complexes with the Bis(borane‐diphenylphosphanyl)amido Ligand – Synthesis,Structures, and Catalysis for Ring‐Opening Polymerization of ϵ‐Caprolactone

The syntheses of lithium and alkaline earth metal complexes with the bis(borane‐diphenylphosphanyl)amido ligand ( 1 ‐ H ) of molecular formulas [{κ²‐N(PPh₂(BH₃))₂}Li(THF)₂] ( 2 ) and [{κ³‐N(PPh₂(BH₃))₂}₂M(THF)₂] [(M = Ca ( 3 ), Sr ( 4 ), Ba ( 5 )] are reported. The lithium complex 2 was obtained by treatment of bis(borane‐diphenylphosphanyl)amine ( 1 ‐ H ) with lithium bis(trimethylsilyl)amide in a 1:1 molar ratio via the silylamine elimination method. The corresponding homoleptic alkaline earth metal complexes 3 – 5 were prepared by two synthetic routes – first, the treatment of metal bis(trimethylsilyl)amide and protio ligand 1 ‐ H via the elimination of silylamine, and second, through salt metathesis reaction involving respective metal diiodides and lithium salt 2 . The molecular structures of lithium complex 2 and barium complex 5 were established by single‐crystal X‐ray diffraction analysis. In the solid‐state structure of 2 , the lithium ion is ligated by amido nitrogen atoms and hydrogen atoms of the BH₃ group in κ²‐coordination of the ligand 1 resulting in a distorted tetrahedral geometry around the lithium ion. However, in complex 5 , κ³‐coordination of the ligand 1 was observed, and the barium ion adopted a distorted octahedral arrangement. The metal complex 5 was tested as catalyst for the ring opening polymerization of ?‐caprolactone. High activity for the barium complex 5 towards ring opening polymerization (ROP) of ?‐caprolactone with a narrow polydispersity index was observed. Additionally, first‐principle calculations to investigate the structure and coordination properties of alkaline earth metal complexes 3 – 5 as a comparative study between the experimental and theoretical findings were described.     

Unusual complex chemistry of rare-Earth elements: large ionic radii-small coordination numbers

Because of their large ionic radii and relatively low oxidation states rare-earth elements generally form complexes which have high coordination numbers and weak metal-ligand bonds. They are often not suitable for homogeneous catalysis on account of their instability of configuration in solution. Complexes of the corresponding metal atoms with low coordination numbers may be an improvement. This type of complex can be obtained in the classical way by the introduction of bulky ligands, and recently, they were also prepared in reactions with ligand groups which offer remarkable metal-ligand bond features. This concept is demonstrated for complexes with bulky bis(trimethylsilyl)amido ligands [N(SiMe(3))(2)](-) and "slim" phosphoraneiminato ligands (NPR(3)(-)). Their suitability as catalysts for the ring-opening polymerization of lactones is reported as well.     

Tris[bis(trimethysilyl)amido]zinkate von Lithium und Calcium

Tris[bis(trimethylsilyl)amido]zincates of Lithium and Calcium Calcium-bis[bis(trimethylsilyl)amide] and Bis[bis(trimethylsilyl)amido]zinc yield in 1,2-dimethoxyethane quantitatively Calcium-bis{tris[bis(trimethylsilyl)- amido]zincate} · 3DME. When THF is chosen as a solvent, the two reactants and the zincate form a temperature-independent equilibrium, whereas in benzene no reaction occurs. The tris[bis(trimethylsilyl)amido]zincate anion displays characteristic ¹³C{¹H) and ²⁹Si{¹H] chemical shifts of 7 and ?8 ppm, respectively; the nature of the solvent, the cation and the complexating ligands don't influence the IR nor NMR data of the zincate anion and thus verify that [Ca(DME)₃]²⁺ and {Zn[N(SiMe_{3 2}]₃}^? appear as solvent separated ions, which is also confirmed by their insolubility in hydrocarbons.     

Synthesis,Characterization, and Structure of Some Silicon Containing Diorganotin(IV) Complexes of Salicylaldehyde Thiosemicarbazones

Abstract

Four diorganotin(IV) complexes, bis[(trimethylsilyl)methyl]tin salicylaldehyde thiosemicarbazonate monohydrate(1), bis[(trimethylsilyl)methyl]tin 3-methoxysalicylaldehyde thiosemicarbazonate (2), bis[(trimethylsilyl)methyl]tin 5-tert-butyl-3-methylsalicylaldehyde thiosemicarbazonate (3), and bis[(trimethylsilyl)methyl]tin 2-oxylnaphthaldehyde thiosemicarbazonate (4) have been synthesized by reactions of (Me₃SiCH₂)₂SnCl₂ with the corresponding semicarbazone. The four complexes were characterized by IR and NMR spectroscopy and elemental analyses. The X-ray studies of compounds 1 and 4 showed that the thiosemicarbazone ligands act as tridentate ligands chelating to the central tin atoms, and thus the tin atoms were five coordinated in trigonal bipyramidal geometry for both compounds.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

Syntheses,Crystal Structure and Reactivity of Tin(II) Bis[N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide]

Metallation of N‐(diphenylphosphanyl)(2‐pyridylmethyl)amine with n‐butyllithium in toluene yields lithium N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide ( 1 ), which crystallizes as a tetramer. Transamination of N‐(diphenylphosphanyl)(2‐pyridylmethyl)amine with an equimolar amount of Sn[N(SiMe₃)₂]₂ leads to the formation of monomeric bis(trimethylsilyl)amido tin(II) N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide ( 2 ). The addition of another equivalent of N‐(diphenylphosphanyl)(2‐pyridylmethyl)amine gives homoleptic tin(II) bis[N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide] ( 3 ). In these complexes the N‐(diphenylphosphanyl)(2‐pyridylmethyl)amido groups act as bidentate bases through the nitrogen bases. At elevated temperatures HN(SiMe₃)₂ is liberated from bis(trimethylsilyl)amido tin(II) N‐(diphenylphosphanyl)(2‐pyridylmethyl)amide ( 2 ) yielding mononuclear tin(II) 1,2‐dipyridyl‐1,2‐bis(diphenylphosphanylamido)ethane ( 4 ) through a C–C coupling reaction. The three‐coordinate tin(II) atoms of 2 and 4 adopt trigonal pyramidal coordination spheres.     

Zur Elektronenstruktur hochsymmetrischer Verbindungen der f‐Elemente. 41 Synthese,Kristall‐, Molekül‐ und Elektronenstruktur eines Bis(cyclohexylisonitril)‐Addukts des Grundkörpers Tris(bis(trimethylsilyl)amido)erbium(III) sowie Elektronenstrukturen ausgewählter Monoaddukte

Electronic Structures of Highly Symmetrical Compounds of f Elements. 41 Synthesis, Crystal, Molecular and Electronic Structure of a Bis(cyclohexylisonitrile) Adduct Derived from the Tris(bis(trimethylsilyl)amido)erbium(III) Moiety and Electronic Structures of Selected Mono Adducts The reaction of tris(bis(trimethylsilyl)amido)erbium(III) (Er(btmsa)₃) with two equivalents of cyclohexylisonitrile yields the corresponding bis adduct [Er(btmsa)₃(CNC₆H₁₁)₂] ( 1 ). Complex 1 crystallizes in the monoclinic space group C2/c with a = 2542.9(11) pm, b = 1208.4(4) pm, c = 1783.0(2) pm, β = 122.39(3)°, V = 4.638(5)·10⁹ pm³, Z = 4 and R = 0.0380. The structure of compound 1 features the five coordinate Er³⁺ central ion in a nearly exact trigonal bipyramidal environment, with three btmsa ligands in the equatorial and the two cyclohexylisonitrile molecules in the axial positions. On the basis of the absorption spectra of bis adduct 1 and the mono(tetrahydrofuran) as well as the mono(triphenylphosphine oxide) adducts [Er(btmsa)₃(THF)] ( 2 ) and [Er(btmsa)₃(OPPh₃)] ( 3 ), respectively, the underlying truncated crystal field (CF) splitting patterns of these compounds could be derived, and simulated by fitting the free parameters of a phenomenological Hamiltonian. Reduced r.m.s. deviations of 13.0 cm^?1 (42 assignments), 16.0 cm^?1 (63 assignments) and 17.5 cm^?1 (55 assignments) could be achieved for compounds 1 , 2 and 3 , respectively. Making use of the phenomenological CF parameters of the fits, the experimentally based non‐relativistic molecular orbital schemes of complexes 1 , 2 and 3 were set up, and compared with that of base‐free Er(btmsa)₃.     

Generation of cationic indenyl silylamide gadolinium and scandium complexes [(Ind)Ln{N(SiMe3)2}]+[B(C6F5)4]- and their reactivity for 1,3-butadiene polymerization

Highly efficient cis-polymerization of butadiene was achieved by using new bis(indenyl) silylamide rare earth complexes with the cooperation of both a borate salt and i-Bu3Al; treatment of these complexes with organoboron compounds unexpectedly yielded new cationic mono(indenyl) amido species relevant to polymerization.     

配合物(ArO)2Yb(NPh2)2K(THF)4(Ar=C6H2-t-Bu3-2,4,6)的合成、分子结构和催化行为

Reaction of anhydrous YbC13 with 2 equiv, of sodium 2,4,6-tri-tert-butylphenoxide (ArONa, Ar=C6H2-t-Bu3-2,4,6) and 2 equiv, of potassium diphenyl amide in THF afforded the first bis(aryloxo) amido-lanthanide complex of (ArO)2Yb(NPh2)2K(THF)4 (1). In 1, the ytterbium and potassium were bridged via diphenyl amido ligands.The ytterbium metal center was coordinated to two oxygen atoms of aryloxide ligands and two nitrogen atoms of diphenyl amido ligands in a conventional distorted tetrahedral fashion, while the potassium interacted in η^2-fashion with two phenyl rings of the diphenyl amido ligands besides four THF molecules. 1 displayed moderate catalytic activities for the polymerization of methyl methacrylate and acrylonitrile.     

First Homoleptic Rare Earth Carbazolates: Synthesis,Crystal Structures,Spectroscopic and Thermal Investigations of Divalent 1[Ln(NC12H8)2] with Ln = Europium and Ytterbium

The compounds [Ln(NC₁₂H₈)₂], Ln = Eu and Yb, were obtained in solvent free reactions of the rare earth elements europium and ytterbium with the amine carbazole. Single crystals of both compounds were grown from the melt syntheses, no recrystallization from solvents was necessary. The new compounds are the first examples of homoleptic carbazolates of the rare earth elements furthermore exhibiting divalent lanthanides. In absence of any solvent, carbazole as the sole coordination partner shows η⁶‐π‐coordination in addition to the μ₁‐ and μ₂‐coordination of the nitrogen atoms. This results in a one‐dimensional chain structure of dimers with a formal C.N. of 6 for the rare earth elements and thus being low for divalent lanthanides. The products were investigated by X‐ray single crystal and powder diffraction, Mid IR, Far IR and Raman spectroscopy, and with DTA/TG regarding their thermal behaviour. Both compounds [Ln(NC₁₂H₈)₂], Ln = Eu (1) and Yb (2) , crystallize isotypic in the triclinic space group P1.     

Synthesis of new organophosphorus‐substituted mono‐ and bis(trimethylsilyl)amines with PCH2N fragments and their derivatives

Convenient procedures for the synthesis of new organophosphorus‐substituted mono‐ and bis(trimethylsilyl)amines with PCH₂N moiety are proposed, starting from trimethylsilyl esters of organophosphorus acids, as well as 1,3,5‐trialkylhexahydro‐1,3,5‐triazines and N‐alkoxymethyl bis(trimethylsilyl)amines as aminomethylating reagents. Certain properties of the resulting compounds are presented. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:71–77, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20580     

Highly Efficient Hydrophosphonylation of Aldehydes and Unactivated Ketones Catalyzed by Methylene‐Linked Pyrrolyl Rare Earth Metal Amido Complexes

A series of rare earth metal amido complexes bearing methylene‐linked pyrrolyl‐amido ligands were prepared through silylamine elimination reactions and displayed high catalytic activities in hydrophosphonylations of aldehydes and unactivated ketones under solvent‐free conditions for liquid substrates. Treatment of [(Me₃Si)₂N]₃Ln(μ‐Cl)Li(THF)₃ with 2‐(2,6‐Me₂C₆H₃NHCH₂)C₄H₃NH ( 1 , 1 equiv) in toluene afforded the corresponding trivalent rare earth metal amides of formula {(μ‐η⁵:η¹):η¹‐2‐[(2,6‐Me₂C₆H₃)NCH₂](C₄H₃N)LnN(SiMe₃)₂}₂ [Ln=Y ( 2 ), Nd ( 3 ), Sm ( 4 ), Dy ( 5 ), Yb ( 6 )] in moderate to good yields. All compounds were fully characterized by spectroscopic methods and elemental analyses. The yttrium complex was also characterized by ¹H NMR spectroscopic analyses. The structures of complexes 2 , 3 , 4 , and 6 were determined by single‐crystal X‐ray analyses. Study of the catalytic activities of the complexes showed that these rare earth metal amido complexes were excellent catalysts for hydrophosphonylations of aldehydes and unactivated ketones. The catalyzed reactions between diethyl phosphite and aldehydes in the presence of the rare earth metal amido complexes (0.1 mol %) afforded the products in high yields (up to 99 %) at room temperature in short times of 5 to 10 min. Furthermore, the catalytic addition of diethyl phosphite to unactivated ketones also afforded the products in high yields of up to 99 % with employment of low loadings (0.1 to 0.5 mol %) of the rare earth metal amido complexes at room temperature in short times of 20 min. The system works well for a wide range of unactivated aliphatic, aromatic or heteroaromatic ketones, especially for substituted benzophenones, giving the corresponding α‐hydroxy diaryl phosphonates in moderate to high yields.     

New Sn(IV) and Ti(IV) bis(trimethylsilyl)amides in d,l-lactide polymerization, SEM characterization of polymers

Ring-opening polymerization of d,l-lactide initiated with new chlorotris(bis(trimethylsilyl) amido) tin(IV), tetrakis(bis(trimethylsilyl)amido) tin(IV) and titanium(IV) was investigated. New complexes reveal practically quantitative conversion degrees and produced polymers with higher molecular weight with respect to reference alkoxo-species.The X-ray crystal structure of chlorotris(bis(trimethylsilyl)amido) tin (IV) was investigated. Axial enantiomerism of [SnCl{N(SiMe₃)₂}₃] molecules in solution was studied by high-field dynamic NMR, the value of Gibbs activation energy ΔG^‡ = 59.5 kJ/mol.Field emission SEM investigation of bulk polymer samples and thin films on conductive Al foil revealed a stratified fibrous textures in the bulk polymers, as well as nanoscaled topographical features due to coils and entanglements of individual macromolecules in thin films.     

Zur elektronenstruktur hochsymmetrischer Verbindungen der ⨍-elemente–XXIII. Wie groß sind die Kristallfeldaufspaltungseffekte bei den Tris (bis (trimethylsilyl) amido)-Komplexen der Lanthanoiden?

The σ and π absorption spectrum of the ³H₄→³P₀ transition has been measured at room temperature on an oriented single crystal of tris(bis(trimethylsilyl)amido)praseodymium (III) as well as the room temperature magnetic circular dichroism spectrum of the compound dissolved in a mixture of toluene and methylcyclohexane in the ratio 1:1. From these data the crystal field (CF) splitting of the ground ³H₄ manifold was derived. An approximate set of CF parameters was obtained which qualitatively reproduces the experimental levels. The magnitude of the CF parameters demonstrates that the three bis(trimethylsilyl)amido ligands produce an unusually large crystal field.     

2‐(1 H‐1,2,3‐Triazol‐4‐yl)‐Pyridine Ligands as Alternatives to 2,2′‐Bipyridines in Ruthenium(II) Complexes

The synthesis of a variety of 2‐(1H‐1,2,3‐triazol‐4‐yl)‐pyridines by click chemistry is demonstrated to provide straightforward access to mono‐functionalized ligands. The ring‐opening polymerization of ε‐caprolactone initiated by such a mono‐functionalized ligand highlights the synthetic potential of this class of bidentate ligands with respect to polymer chemistry or the attachment onto surfaces and nanoparticles. The coordination to Ru^II ions results in homoleptic and heteroleptic complexes with the resultant photophysical and electrochemical properties strongly dependent on the number of these ligands attached to the Ru^II core.     

Filling a Niche in “Ligand Space” with Bulky,Electron-Poor Phosphorus(III) Alkoxides

The chemistry of phosphorus(III) ligands, which are of key importance in coordination chemistry, organometallic chemistry and catalysis, is dominated by relatively electron-rich species. Many of the electron-poor P^III ligands that are readily available have relatively small steric profiles. As such, there is a significant gap in “ligand space” where more sterically bulky, electron-poor P^III ligands are needed. This contribution discusses the coordination chemistry, steric and electronic properties of P^III ligands bearing highly fluorinated alkoxide groups of the general form PR_n(OR^F)_3−n, where R=Ph, R^F=C(H)(CF₃)₂ and C(CF₃)₃; n=1–3. These ligands are simple to synthesize and a range of experimental and theoretical methods suggest that their steric and electronic properties can be “tuned” by modification of their substituents, making them excellent candidates for large, electron-poor ligands.     

Ring opening polymerization of α‐amino acid N‐carboxyanhydrides catalyzed by rare earth catalysts: Polymerization characteristics and mechanism

Five rare earth complexes are first introduced to catalyze ring opening polymerizations (ROPs) of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (BLG NCA) and L ‐alanine NCA (ALA NCA) including rare earth isopropoxide (RE(OiPr)₃), rare earth tris(2,6‐di‐tert‐butyl‐4‐methylphenolate) (RE(OAr)₃), rare earth tris(borohydride) (RE(BH₄)₃(THF)₃), rare earth tris[bis(trimethylsilyl)amide] (RE(NTMS)₃), and rare earth trifluoromethanesulfonate. The first four catalysts exhibit high activities in ROPs producing polypeptides with quantitative yields (>90%) and moderate molecular weight (MW) distributions ranging from 1.2 to 1.6. In RE(BH₄)₃(THF)₃ and RE(NTMS)₃ catalytic systems, MWs of the produced polypeptides can be controlled by feeding ratios of monomer to catalyst, which is in contrast to the systems of RE(OiPr)₃ and RE(OAr)₃ with little controllability over the MWs. End groups of the polypeptides are analyzed by MALDI‐TOF MS and polymerization mechanisms are proposed accordingly. With ligands of significant steric hindrance in RE(OiPr)₃ and RE(OAr)₃, deprotonation of 3‐NH of NCA is the only initiation mode producing a N‐rare earth metallated NCA ( i ) responsible for further chain growth, resulting in α‐carboxylic‐ω‐aminotelechelic polypeptides after termination. In the case of RE(BH₄)₃(THF)₃ with small ligands, another initiation mode at 5‐CO position of NCA takes place simultaneously, resulting in α‐hydroxyl‐ω‐aminotelechelic polypeptides. In RE(NTMS)₃ system, the protonated ligand hexamethyldisilazane (HMDS) initiates the polymerization and produces α‐amide‐ω‐aminotelechelic polypeptides. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of ligands based on naphthalene peri-substituted by Group 15 and 16 elements and their coordination chemistry

The synthetic aspects of chemistry of ligands based on naphthalene peri-substituted by heavier Group 15 elements (P, As, Sb, Bi) or Group 16 elements (S, Se, Te) are discussed in this review. An overview of coordination chemistry of these ligands is also given. In general, the area is dominated by bis(phosphines) Nap(PR₂)₂ and dithiolates Nap(SR)₂ (Nap = naphthalene-1,8-diyl), and most of the ligands act with chelating rigid C₃-backbones. Whilst all known bis(phosphine) complexes with Ni, Pd and Pt contain unmodified Nap(PR₂)₂ moieties, the reactions with a variety of metal carbonyls sometimes result in P–C bond cleavage within the ligand. A range of gold complexes with Nap(PR₂)₂ ligands have been investigated for material applications. NapP₂ ligands other than phosphines are also described, these include 1,2-diphosphaacenaphthenes, bis(phosphonites) and bis(phosphine oxides). Group 16 peri-dichalcogenolates used as ligands include NapS₂, NapSe₂ and NapSSe systems, but no tellurium congeners. Heterodentate ligands discussed in this review include those with NapPN, NapPO, NapPS, NapPF, NapPC and NapSN motifs. Ligands with heavier Group 15 donor atoms (NapAs₂, NapSb₂) are also reported. All possible oxides of the dithioles (monooxide to tetraoxide) as ligands are also discussed. Areas of interest for further work are outlined.     

Verbrückende Koordination von Gallium–Gallium‐Bindungen durch Chelatliganden – Grenzen der Beständigkeit von Digallium‐Verbindungen

Bridging Coordination of Gallium–Gallium Bonds by Chelating Ligands – Limitations of the Stability of Digallium Derivatives The reactions of bis[bis(trimethylsilyl)methyl]‐di(μ‐acetato)digallium(Ga–Ga) ( 2 ) with lithium‐2‐amido‐1‐methylbenzimidazole in the molar ratios of 1 to 1 or 1 to 2 yielded by the precipitation of lithium aceatate new digallium compounds, in which the intact Ga–Ga bonds were bridged by two chelating ligands. The replacement of only one acetato group gave compound 5 , that possesses two different bridging ligands with the benzimidazole group coordinated by its terminal amido function and that nitrogen atom of the heterocycle which is not attached to a methyl group. If both acetato groups were replaced by imdazole ligands, two products were obtained, in which the chelates are transferred in each other either by a mirror plane parallel to the Ga–Ga bond (cis, 6 ) or by a twofold rotational axis perpendicular to the element–element bond (trans, 7 ). 7 is thermodynamically favored and was irreversibly formed by heating of the mixture. 5 and 7 were characterized by crystal structure determinations and have Ga atoms in a chiral environment. Weaker donor ligands such as diphenyl(lithiomethyl)(piperidinomethyl)silane, which in principal is able to coordinate via its carbanionic carbon atom and more weakly via its sterically shielded piperidino nitrogen atom, led to the cleavage of the Ga–Ga bond. The mononuclear compound 8 was isolated, in which the Ga atom is attached to one bis(trimethylsilyl)methyl group and two (piperidinomethyl)silyl substituents. Furthermore, the synthesis of a dialkyl‐bis(1,3‐dionato)digallium derivative ( 9 ) is reported, in which the chelating 1,3‐dionato groups are terminally coordinated to the Ga atoms of the unsupported Ga–Ga bond.