Synthesis and Structure of Group 4 Iminophosphonamide Complexes

Lanthanide complexes with a new luminescent iminophosphonamide ligand bearing phenylbenzothiazole substituents

A new iminophosphonamine Ph2P(HNPbt)(NPbt) (1, HL) bearing chromophore 2-(phen-2'-yl)-1,3-benzothiazole (Pbt) substituents was synthesized and introduced into lanthanide complexes. It was found that salt metathesis reactions between KL (2) generated in situ and LnCl3 lead to the formation of tris-iminophosphonamide complexes [LnL2]L (Ln = Y (3), Sm (4), Gd (5), Dy (6)), regardless of the 2/LnCl3 ratio. Compounds 3-6 consist of a cationic fragment [LnL2]+, where the lanthanide atom is surrounded by two rigidly κ4-coordinated ligands, and an L- anion residing in the outer coordination sphere. Iminophosphonamine 1 shows a rare excitation wavelength-dependent two-band luminescence in the solid state. For compounds containing the deprotonated form, namely potassium salt KL and complexes of Gd and Dy, a single-band luminescence with the color changing from turquoise to orange was observed. The Sm complex reveals a set of a few narrow well-resolved bands corresponding to the f-f transitions against the background of the outer-sphere ligand's emission.

Role of Bis(phosphinimino)methanides as Universal Ligands in the Coordination Sphere of Metals across the Periodic Table

The coordination chemistry of bis(phosphinimino)methanide ligands is widespread and accompanies a large number of metal ions in the periodic table ranging from lithium to neptunium. This unique class of ligand systems show copious coordination chemistry with the main-group, transition, rare-earth, and actinide metals and are considered to be among the most attractive ligand systems to researchers. The bis(phosphinimino)methanide metal complexes offer an extensive range of applications in various fields and have been demonstrated as one of the universal ligand systems to stabilize the metal ions in not only their usual but also their unusual oxidation states. The main-group and transition metal chemistry using bis(phosphinimino)methanides as ligands was last updated almost a decade ago. In this review, we provide a comprehensive overview of various state-of-the-art bis(phosphinimino)methanide-supported metal complexes by dealing with their synthesis, characterization, reactivity, and catalytic studies which were not included in the last critical reviews.

Aluminium alkyl complexes supported by imino-phosphanamide ligand as precursors for catalytic guanylation reactions of carbodiimides

Herein, we report the synthesis, characterisation, and application of three aluminium alkyl complexes, [κ2-{NHIRP(Ph)NDipp}AlMe2] (R = Dipp (2a), Mes (2b); tBu (2c), Dipp = 2,6-diisopropylphenyl, Mes = mesityl, and tBu = tert-butyl), supported by unsymmetrical imino-phosphanamide [NHIRP(Ph)NDipp]- [R = Dipp (1a), Mes (1b), tBu (1c)] ligands as molecular precursors for the catalytic synthesis of guanidines using carbodiimides and primary amines. All the imino-phosphanamide ligands 1a, 1b and 1c were prepared in good yield from the corresponding N-heterocyclic imine (NHI) with phenylchloro-2,6-diisopropylphenylphosphanamine, PhP(Cl)NHDipp. The aluminium alkyl complexes 2a, 2b and 2c were obtained in good yield upon completion of the reaction between trimethyl aluminium and the protic ligands 1a, 1b and 1c in a 1 : 1 molar ratio in toluene via the elimination of methane, respectively. The molecular structures of the protic ligands 1b and 1c and the aluminium complexes 2a, 2b and 2c were established via single-crystal X-ray diffraction analysis. Complexes 2a, 2b and 2c were tested as pre-catalysts for the hydroamination/guanylation reaction of carbodiimides with aryl amines to afford guanidines at ambient temperature. All the aluminium complexes exhibited a high conversion with 1.5 mol% catalyst loading and broad substrate scope with a wide functional group tolerance during the guanylation reaction. We also proposed the most plausible mechanism, involving the formation of catalytically active three-coordinate Al species as the active pre-catalyst.

An Unsymmetric Imino-Phosphanamidinate Ligand and its Y(III) Complex: Synthesis, Characterization, and Catalytic Hydroboration of Carbonyl Compounds

An imino-phosphanamide ligand, [NHI^iPr2Me2P(Ph)NH-2,6-ⁱPr₂C₆H₃] (LH), containing two different N-substituents was prepared by the direct reaction of the lithium salt of N-heterocyclic imine (NHI) with phenylchloro-2,6-diisopropylphenyl phosphanamine, PhP(Cl)NH-2,6-ⁱPr₂-C₆H₃. Reaction of LH with Y(N(SiMe₃)₂)₃ afforded the heteroleptic complex, [{L}Y(N(SiMe₃)₂)₂] (1), by elimination of HN(SiMe₃)₂. Compound 1 was characterized by multinuclear NMR and X-ray crystallography. In the complex, the Y(III) center was found to be tetracoordinate in a distorted tetrahedral geometry. The ligand, imino-phosphanamidinate, [L]^-, functions in a chelating manner, and its coordination to Y(III) results in a distorted 4-membered YPN₂ ring. As a proof of principle of its activity, 1 was used as a precatalyst for the hydroboration of various aldehydes and ketones using HBpin as the hydrogen source. The hydroboration reaction was rapid and clean even with low catalyst loadings (0.01-0.1 mol %). In addition, a very good functional group tolerance was observed in these reactions.

Thermal Decomposition In Situ Monitoring System of the Gas Phase Cyclopentadienyl Tris(dimethylamino) Zirconium (CpZr(NMe2)3) Based on FT-IR and QMS for Atomic Layer Deposition

We developed a newly designed system based on in situ monitoring with Fourier transform infrared (FT-IR) spectroscopy and quadrupole mass spectrometry (QMS) for understanding decomposition mechanism and by-products of vaporized Cyclopentadienyl Tris(dimethylamino) Zirconium (CpZr(NMe₂)₃) during the move to process chamber at various temperatures because thermal decomposition products of unwanted precursors can affect process reliability. The FT-IR data show that the -CH₃ peak intensity decreases while the -CH₂- and C=N peak intensities increase as the temperature is increased from 100 to 250 °C. This result is attributed to decomposition of the dimethylamido ligands. Based on the FT-IR data, it can also be assumed that a new decomposition product is formation at 250 °C. While in situ QMS analysis demonstrates that vaporized CpZr(NMe₂)₃ decomposes to N-ethylmethanimine rather than methylmethyleneimine. The in situ monitoring with FT-IR spectroscopy and QMS provides useful information for understanding the behavior and decomposes of CpZr(NMe₂)₃ in the gas phase, which was not proven before. The study to understand the decomposition of vaporized precursor is the first attempt and can be provided as useful information for improving the reliability of a high- advanced ultra-thin film deposition process using atomic layer deposition in the future.

Alkali metal complexes of an enantiopure iminophosphonamide ligand with bright delayed fluorescence

Alkali metal complexes of an enantiopure iminophosphonamide bearing chiral centers at both nitrogen atoms are described. They show bright phosphorescence and thermally activated delayed fluorescence (TADF).

The enantiomerically pure ligand P,P-diphenyl-N,N′-bis((R)-1-phenylethyl)phosphinimidic amide (1; (R)-HPEPIA) was synthesized and subsequently deprotonated with alkali metal precursors to yield dimeric complexes [M₂{(R)-PEPIA}₂] (M = Li (2), Na (3), K (4), Rb (5)). The cesium compound [M{(R)-PEPIA}] (6) crystallized as a cocrystal composed of dimeric ([Cs₂{(R)-PEPIA}₂] (6_d) and 1D-polymeric ([Cs{(R)-PEPIA}]_n) (6_p) species in a 1 : 1 ratio. The coordination polymer 6_p features a unique sinus-shaped configuration of repeating –Cs–N–P–N–Cs–N–P–N– units. Unusual photoluminescence (PL) properties were found for solid 1–6: in contrast to the fluorescent ligand 1, the alkali metal complexes show phosphorescence at low temperatures (<100 K) and thermally activated delayed fluorescence (TADF) above ∼150 K. The latter provides for PL quantum yields up to 36% (3) at ambient temperature. DFT calculations support that both 1 and 2–6_d have similar singlet and triplet excited states with energy separations of a few tens of meV. The strongly enhanced intersystem crossing (ISC) in the metal complexes, resulting in TADF, is attributed to their dimeric structure. This suggests that the fluorophore dimerization may serve as a tool to effect ISC for the design of TADF emitters.

Simple entry into N-tert-butyl-iminophosphonamide rare-earth metal alkyl and chlorido complexes

New series of rare-earth metal dialkyls [(NPN^tBu)Ln(CH₂SiMe₃)₂(THF)_n] (Ln = Sc,n= 0 (2), Ln = Y,n= 1 (3)) and monoalkyls [(NPN^tBu)₂Ln(CH₂SiMe₃)] (Ln = Y (4), Nd (6), Sm (7)), [(NPN^tBu)₂Sc(THF)CH₃] (5) are achieved by protolysis of highly basic ligand Ph₂P(N-tBu)(NH-tBu) = (NPN^tBu)H (1). Further alkyl abstraction, alkyl/Cl exchange reactions and X-ray structure analyses of thus obtained new complexes are presented.

The half-sandwich 18- and 16-electron arene ruthenium iminophosphonamide complexes

Novel arene ruthenium iminophosphonamides are electron-rich complexes due to a strong σ,π-donor zwitterionic ligand.

Understanding the directed ortho lithiation of (R)-Ph2P(NCO2Me)NHCH(Me)Ph. NMR spectroscopic and computational study of the structure of the N-lithiated species

The multinuclear magnetic resonance and computational study of the structure of N-lithium (R)-Ph₂P(NCO₂Me)NHCH(Me)Ph revealed the origin of its diastereoselective ortho lithiation.

Zirconium complexes supported by an N-perfluoro-arylated diamidopyridyl ligand: synthesis of hydrazinediido complexes

The N-perfluoro-phenylated pyridyldiamine H2N2(PFP)N(py) (1) has been prepared by a palladium-catalyzed coupling of hexafluorobenzene and the diamine (H2NCH2)2C(CH3)(2-C5H4N) using the palladacycle trans-di(μ-acetato)bis[o-(di-o-tolylphosphino)benzyl]palladium(II) as catalyst. Reactions of H2N2(PFP)N(py) and Zr(NMe2)4 at room temperature or 90 °C led to the complexes [(N(PFP)N2(TFAP)N(py))ZrF(NMe2)] (2) and [(N2(TFAP)N(py))ZrF2] (3) in which one or two dimethylamido groups replaced one or two ortho fluorine atoms of the pentafluorophenyl groups in the ligand. Reaction of Me3SiX (X = Cl, I) with [(N2(TFAP)N(py))ZrF2] (3) resulted in the formation of mixed halogenated complexes [(N2(TFAP)N(py))ZrFI] (4) and [(N2(TFAP)N(py))ZrFCl] (5) in which the axially bound fluorido ligand is substituted. Reaction of [(N2(TFAP)N(py))ZrF2] (3) with LiNHNPh2 afforded the monohydrazido(1-) complex [(N2(TFAP)N(py))ZrF(NHNPh2)] (6) which was converted to the dimeric fluoro-potassium bridged hydrazinediido complex [Zr(N2(TFAP)N(py))FNNPh2K]2 (7) using KHMDS. The corresponding reaction with LiHMDS yielded the monomeric, donor free complex [Zr(N2(TFAP)N(py))NNPh2] (8).

Ethylene and 1-hexene polymerization using zirconium iminophosphonamide complexes

Ethylene polymerization was studied using a variety of iminophosphonamide (PN2) complexes of zirconium. Bis(PN2) dichloride complexes [Ph2P(NR′)2]2ZrX2 (X = Cl; 1a: R′ = p-tolyl; 1b: R′ = Bn; 1c: R′ = C6F5) or dimethyl complexes (X = Me; 2a: R′ = p-tolyl; 2b: R′ = Bn) and cyclopentadienyl(PN2)zirconium dichloride complexes [η5-C5R′′5][R2P(NR′)2]ZrCl2 (3a: R′ = p-tolyl, R = Ph, R′′ = H; 3b: R′ = SiMe3, R = Et, R′′ = H; 3c: R′ = C6F5, R = Ph, R′′ = H; 3e: R′ = 3,5-(CF3)2Ph, R = Ph, R′′ = H; 3f: R′ = 3,5-(CF3)2Ph, R = Ph, R′′ = Me) or dimethyl analogs [η5-C5H5][R2P(NR′)2]ZrMe2 (4a: R′ = p-tolyl, R = Ph; 4b: R′ = SiMe3, R = Et) were evaluated under a range of conditions using methylaluminoxane (PMAO) activator. Complexes 1 and 2 behave as precursors to single-site polymerization catalysts under the conditions studied, while complexes 3 or dialkyls 4 show more complex behavior and formation of poly(ethylene) with a bimodal molecular weight distribution. In contrast, activation of dialkyl complexes 4 with [Ph3C][B(C6F5)4] and polymerization in the presence of small amounts of PMAO or TIBAL as scavenger, led to single-site behavior. PMAO reacts with the neutral dialkyls via ligand abstraction to produce a number of P-containing species that may explain the multi-site behavior observed when using this activator. Dialkyls 4 react cleanly with [Ph3C][B(C6F5)4] in haloarene or even dichloromethane solution to furnish the corresponding cationic alkyls 5, which were characterized by multinuclear NMR spectroscopy. Fluxional dinuclear species are formed in the presence of excess dialkyl and these are susceptible to C—H activation to form µ-Me,µ-CH2 complexes one of which could be isolated in pure form. The cationic alkyls initiate the polymerization of 1-hexene at room temperature in chlorobenzene solution, but extensive chain transfer occurs and the systems are not living.Key words: single site, early metal olefin polymerization catalysis.