Synthesis and Structures of Mono- and Bis(amidinate) Complexes of Aluminum

How to Decarbonize N-Heterocyclic Carbenes (NHCs): The simple Alane Adducts (NHC) ⋅ AlR3 (R=H, Me, Et)

The reaction of the amine-stabilized alane (NMe3) ⋅ AlH3 1 with the backbone-saturated N-heterocyclic carbene (NHC) SIDipp (SIDipp=1,3-bis-{2,6-di-iso-propyl-phenyl}-imidazolidin-2-ylidene) at 0 °C yielded the NHC alane adduct (SIDipp) ⋅ AlH3 2. Reaction at elevated temperatures or prolonged reaction at room temperature gave the product of a ring expansion reaction (RER) of the NHC, (NMe3) ⋅ AlH(RER-SIDippH2) 3 ⋅ (NMe3). Subsequent reaction of the latter with sterically less hindered NHCs (IMeMe {=1,3,4,5-tetramethyl-imidazolin-2-ylidene}, IiPrMe {=1,3-di-iso-propyl-4,5-dimethyl-imidazolin-2-ylidene}, and IiPr {=1,3-di-iso-propyl-imidazolin-2-ylidene}) afforded the NHC-stabilized RER-products (NHC) ⋅ AlH(RER-SIDippH2) 3 ⋅ (NHC) (NHC=IMeMe, IiPrMe, IiPr), while no reaction was observed with the sterically more demanding NHCs IDipp (=1,3-bis-{2,6-di-iso-propyl-phenyl}-imidazolin-2-ylidene), SIDipp and ItBu (=1,3-di-tert-butyl-imidazolin-2-ylidene). The compounds 3 ⋅ (NHC) were also obtained starting from (SIDipp) ⋅ AlH3 2 and NHC at room temperature. Heating solutions of (SIDipp) ⋅ AlH3 2 without additional base to 95 °C resulted in decarbonization of the NHC and substitution of the carbene carbon atom with aluminum hydride under loss of ethene. Subsequent dimerization afforded cis-[AlH{μ-N(Dipp)CH2CH2N(Dipp)}]2 4_dimer. Heating solutions of the NHC-ligated aluminum alkyls (SIDipp) ⋅ AlR3 2R (R=Me, Et) to 145 °C instead led to complete scission of the NHC backbone with evolution of ethene and isolation of the dialkylaluminium(III) amidinates {DippNC(R)NDipp}AlR2 5R (R=Me, Et).

Diverse Reactivity of Amidinate-Supported Boron Centers with the Hypersilyl Anion and Access to a Monomeric Secondary Boron Hydride

Diverse reactivity of the bulky tris(trimethylsilyl)silyl substituent [Si(SiMe3)3], also known as the hypersilyl group, was observed for amidinate-supported dichloro- and phenylchloroborane complexes. Treatment of the dichloroborane with potassium tris(trimethylsilyl)silyl led to the activation of the backbone β-carbon center and formation of saturated four-membered heterocyclic chloroboranes R'{Si(SiMe3)3}C(NR)2BCl [R' = Ph, R = Cy (3); R' = Ph, R = iPr (6); R' = tBu, R = Cy (8)], whereas the four-membered amidinate hypersilyl-substituted phenyl borane 4 {PhC(NCy)2B(Ph)[Si(SiMe3)3]} was observed for the case of an amidinate-supported phenylchloroborane. The highly deshielded 11B NMR spectroscopic resonance and the distinct difference in the 29Si NMR spectrum confirmed the presence of a σ-donating hypersilyl effect on compounds 3, 6, and 8. Reaction of 3 with the Lewis acid AlCl3 led to the formation of complex 11 in which an unusual cleavage of one of the C-N bonds of the amidinate backbone is observed. Nucleophilic substitution at the boron center of saturated chloroborane 3 with phenyllithium generated the phenylborane derivative 12, whereas the secondary monomeric boron hydride 13 was observed after treatment with alane (AlH3). All compounds (2-13) have been fully characterized by NMR spectroscopy and single-crystal X-ray structure determination studies.

Alkali Metal Complexes of a Bis(diphenylphosphino)methane Functionalized Amidinate Ligand: Synthesis and Luminescence

A novel bis(diphenylphosphino)methane (DPPM) functionalized amidine ligand (DPPM-C(N-Dipp)2 H) (Dipp=2,6-diisopropylphenyl) was synthesized. Subsequent deprotonation with suitable alkali metal bases resulted in the corresponding complexes [M{DPPM-C(N-Dipp)2 }(Ln )] (M=Li, Na, K, Rb, Cs; L=thf, Et2 O). The alkali metal complexes form monomeric species in the solid state, exhibiting intramolecular metal-π-interactions. In addition, a caesium derivative [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 was obtained by cleavage of a diphenylphosphino moiety, forming an unusual six-membered ring structure in the solid state. All complexes were fully characterized by single crystal X-ray diffraction, NMR spectroscopy, IR spectroscopy as well as elemental analysis. Furthermore, the photoluminescent properties of the complexes were thoroughly investigated, revealing differences in emission with regards to the respective alkali metal. Interestingly, the hexanuclear [Cs{PPh2 CH2 -C(N-Dipp)2 }]6 metallocycle exhibits a blue emission in the solid state, which is significantly red-shifted at low temperatures. The bifunctional design of the ligand, featuring orthogonal donor atoms (N vs. P) and a high steric demand, is highly promising for the construction of advanced metal and main group complexes.

Comparison of Ligand Architecture on Vapor Deposition Precursors: Synthesis, Characterization, and Reactivity of Volatile Cadmium Bis-Amidinate Complexes

The lack of low-temperature (<200 °C) and easy-to-handle vapor deposition precursors for cadmium has been a limitation for cadmium chalcogenide ALD. Here, the cadmium amidinate system is presented as a scaffold for vapor deposition precursor design because the alkyl groups can be altered to change the properties of the precursor. Thus, the molecular structure affects the precursor stability at elevated temperature, onset of volatility, and reactivity. Cadmium bis-N,N-diisopropylacetamidinate (1) was synthesized and evaluated for its thermal stability, volatility, and reactivity-properties relevant to ALD precursors. Compounds 2, cadmium bis-N,N-diisopropyltertertiarybutylamidinate, and 3, cadmium bis-N,N-diisopropylbutylamidinate, are analogous to 1 and were synthesized by substituting the alkyl group on the bridging carbon during amidinate synthesis. All three compounds are volatile under reduced pressure, and thermal stability studies showed 1 and 3 to be stable at 100 °C in solution for days to weeks, while 2 decomposed at 100 °C within 24 h. Solution phase reactivity studies show 1 to be reactive with thiols at room temperature in a stoichiometric manner. No reactivity with either bis-silyl sulfides or alkyl sulfides was observed up to 110 °C over more than 3 days. Overall, the cadmium amidinate compounds presented here show potential as precursors in ALD/CVD processing, which can contribute to research critical for semiconductor processing.

Magnetic Anisotropy: Structural Correlation of a Series of Chromium(II)-Amidinate Complexes

Systematic substituent variations on amidinate ligands bring delicate changes of CrN₄ coordination in a family of chromium(II) complexes with the common formula of Cr(RNC(CH₃)NR)₂, where R = iPr (1), Cy (2), Dipp (Dipp = 2, 6-diisopropylphenyl) (3), and tBu (4). With the largest substituent group, 4 shows the largest distortion of the N₄ coordination geometry from square-planar to seesaw shape, which leads to its field-induced single-molecule magnet (SMM) behavior. This is an indication that 4 has the strongest axial magnetic anisotropy and/or optimized magnetic relaxation process. Combined with high-frequency/field electron paramagnetic resonance (HF-EPR) experiments and ab initio calculations, we deduce that the smallest energy gap between ground ⁴Ψ₀ and the first excited ⁴Ψ₁ orbitals in 4 contributes the most to its strongest magnetic anisotropy. Moreover, the lower E value of 4 ensures its being a field-induced SMM. Specifically, the D and E values were found to be correlated to the dihedral angle between the ΔN₁CrN₂ and ΔN₃CrN₄ triangles, indicating that distortion from ideal square-planar geometry to the seesaw help increase axial magnetic anisotropy and suppress the transversal part. Thus, the study on this system not only expands the family of Cr(II)-based SMMs but also contributes to a deeper understanding of magneto-structural correlation in four-coordinate Cr(II) SMMs.

Synthesis, structure, and catalytic activity of dinuclear aluminium bis(amidinate) and bis(guanidinate) complexes

The ring-opening polymerization grand prix: Bis(amidinate)s outpaced their bis(guanidinate) competitors and won the race, while the drivers’ engines using acidic co-initiators collapsed before take-off.

Neutral and cationic enantiopure group 13 iminophosphonamide complexes

Synthesis and reactivity of enantiopure iminophosphonamide ligand L-H (L = [Ph2P{N(R)CH(CH3)Ph}2]) with group 13 metal compounds has been investigated. The reaction of L-H with LiAlH4 afforded the aluminium monohydride complex [L2AlH]. The monochloride complexes [L2MCl] (M = Al, Ga) were accessed by reacting corresponding MCl3 (M = Al, Ga) with L-Li. Furthermore, the tetracoordinated aluminium cation [L2Al]+[GaCl4]- and gallium cation [L2Ga]+[AlCl4]- were obtained by chloride abstraction from [L2MCl] (M = Al, Ga), respectively. The title complexes represent the first examples of enantiopure group 13 metal complexes coordinated by chiral iminophosphonamides. All complexes have been characterized by single crystal X-ray diffraction, multinuclear NMR, EA and IR studies.

Lithium amide catalyzed hydroboration of nitriles

An operationally facile hydroboration of nitriles is reported that utilizes the stable and inexpensive catalyst LiN(SiMe₃)₂. The reaction displayed good tolerance of functional groups and also converted carbonyl derivatives.

Aluminum complexes with new non-symmetric ferrocenyl amidine ligands and their application in CO2 transformation into cyclic carbonates

A set of alkyl aluminum complexes supported by non-symmetric ferrocenyl amidine ligands were used as catalysts for the preparation of cyclic carbonates from epoxides and carbon dioxide using Bu₄NI as a co-catalyst.

Bimetallic Co/Al nanoparticles in an ionic liquid: synthesis and application in alkyne hydrogenation

CoAl- and Co₃Al-NPs are effective catalysts for alkyne-to-alkane hydrogenation with DIBAL-H as a co-catalyst under mild conditions (2 bar H₂, 30 °C).

Polymerization of alkyl diazoacetates initiated by the amidinate/Pd system: efficient synthesis of high molecular weight poly(alkoxycarbonylmethylene)s with moderate stereoregularity

The initiating ability of a new system, amidinate/Pd, for the polymerization of diazoacetates is described.

Coordination behavior of bidentate bis(carbenes) at alkali metal bis(trimethylsilyl)amides

Crystallization of LiN(SiMe₃)₂ from 2,2,5,5-tetramethyltetrahydrofuran yields the base-free tetramer. Strong carbenes monomerize the lithium bis(trimethylsilyl)amides, whereas the heavier congeners from carbene-stabilized dimers [AN(SiMe₃)₂]₂ with A = Na, K.

Catalytic bond forming reactions promoted by amidinate, guanidinate and phosphaguanidinate compounds of magnesium

The synthesis and catalytic properties of a series of magnesium compounds consisting of monoanionic, N,N'-chelating ligands (N∩N = amidinates, guanidinates, phosphaguanidinates) is reported. The compounds were synthesized by (i) insertion of a carbodiimide into an existing Mg-C or Mg-N bond, or (ii) protonolysis of an organomagnesium compound by a neutral pre-ligand. Structural analyses of mono- or bis-(chelate) compounds with general formula Mg(N∩N)X(L)n and Mg(N∩N)2(L)n (X = halide, aryloxide, amide; L = Et2O, THF; n = 0, 1 or 2) have been performed and the influence that the ligand substituent patterns have on the solid-state structures has been probed. Selected examples of the compounds were tested as (pre)catalysts for the polymerization of lactide, the dimerization of aldehydes and the hydroacetylenation of carbodiimides.

Formation and reactivity of an (alkene)peroxoiridium(III) intermediate supported by an amidinato ligand

An Ir(I) complex of an acetamidinato ligand was synthesized by reaction of N,N'-diphenylacetamidine, PhN[double bond, length as m-dash]C(Me)NHPh, with either MeLi and [{Ir(cod)}2(μ-Cl)2] or [{Ir(cod)}2(μ-OMe)2] and was characterized by X-ray crystallography as a mononuclear complex, [Ir{PhNC(Me)NPh}(cod)] (1; where cod = 1,5-cyclooctadiene). Reaction of 1 with CO afforded a dinuclear carbonyl complex, [{Ir(CO)2}2{μ-PhNC(Me)NPh-κN:κN'}2] (2), as indicated by EI mass spectrometry and solution- and solid-state IR spectroscopy [νCO (n-pentane) = 2067, 2034 and 1992 cm(-1)]. Activation of O2 by 1 in solution at 20 °C was irreversible and produced an (alkene)peroxoiridium(iii) intermediate, [Ir{PhNC(Me)NPh}(cod)(O2)] (3), which was characterized by one- and two-dimensional NMR techniques and IR spectroscopy (for 3, νOO = 860 cm(-1); for 3-(18)O2, νOO = 807 cm(-1)). Complex 3 oxidized PPh3 to OPPh3, and its decay in the absence of added substrates followed by reaction with cod yielded 4-cycloocten-1-one and a minor amount of 1. In comparison with the results for the previously reported guanidinato complex [Ir{PhNC(NMe2)NPh}(cod)(O2)] (4), the formation of 3 and its reaction with PPh3 are significantly faster, indicating considerable ligand effects in these reactions.

Synthesis and characterisation of magnesium complexes containing sterically demanding N,N′-bis(aryl)amidinate ligands

Reaction between N,N′-bis(aryl)amidines and di-n-butylmagnesium affords magnesium amidinates, where the steric bulk of the ligand influences both the solid state and solution behaviour of these complexes.

Aluminium(III) amidinates formed from reactions of `AlCl' with lithium amidinates

The disproportionation of AlCl(THF)n (THF is tetrahydrofuran) in the presence of lithium amidinate species gives aluminium(III) amidinate complexes with partial or full chloride substitution. Three aluminium amidinate complexes formed during the reaction between aluminium monochloride and lithium amidinates are presented. The homoleptic complex tris(N,N'-diisopropylbenzimidamido)aluminium(III), [Al(C13H19N2)3] or Al{PhC[N(i-Pr)]2}3, (I), crystallizes from the same solution as the heteroleptic complex chloridobis(N,N'-diisopropylbenzimidamido)aluminium(III), [Al(C13H19N2)2Cl] or Al{PhC[N(i-Pr)]2}2Cl, (II). Both have two crystallographically independent molecules per asymmetric unit (Z' = 2) and (I) shows disorder in four of its N(i-Pr) groups. Changing the ligand substituent to the bulkier cyclohexyl allows the isolation of the partial THF solvate chloridobis(N,N'-dicyclohexylbenzimidamido)aluminium(III) tetrahydrofuran 0.675-solvate, [Al(C19H27N2)2Cl]·0.675C4H8O or Al[PhC(NCy)2]2Cl·0.675THF, (III). Despite having a twofold rotation axis running through its Al and Cl atoms, (III) has a similar molecular structure to that of (II).

Synthetic and catalytic intermediates in a magnesium promoted Tishchenko reaction

Magnesium-aryloxide and -amide compounds supported by amidinate ligands are accessible in two-steps from a suitable Grignard reagent. Both species are active for the dimerization of benzaldehyde. The slower initiation by the aryloxide was exploited in the isolation of a bis-mesitylaldehyde adduct.