Scandium Terminal Imido Chemistry

Diverging Reactivity in Anilidophosphine Supported Group III Complexes

We report the synthesis of scandium and yttrium halide complexes with bidentate, monoanionic anilidophosphine (PN) ligands and the general formula (PN)2MX (M = Sc (1-X), Y (2-X); X = Cl (1-Cl/2-Cl), X = I (1-I/2-I). Attempts to functionalize these complexes by salt metathesis reaction revealed that the chlorido complexes are quite unreactive precursors, whereas the iodo complexes readily engage in a broad variety of reactions. We report the azide complexes (1-N3 and 2-N3) as well as the heavy cyanate complexes with the general formula (PN)2M(OCPn) (M = Sc; Pn = P (1-OCP), Pn = As (1-OCAs) and M = Y; Pn = P (2-OCP), Pn = As (2-OCAs)). Furthermore, the amido and phosphanido complexes of the general formula (PN)2M(PnHMesityl) with Pn = N (1-NHMes, 2-NHMes) and Pn = P (1-PHMes, 2-PHMes) are reported. Attempts to synthesize benzyl complexes of the general type (PN)2M(Benzyl) with M = Sc, Y, La revealed drastic differences in the reactivity of the group III metal ions. While the scandium and yttrium complexes displayed elimination of KPN without the formation of defined metal complexes, for lanthanum, defined C-H activation chemistry has been observed, yielding -ate complex 3-CH.

Alkylamido lutetium complexes as prospective lutetium imido precursors: synthesis, characterization and ligand design

Mixed alkylamido lutetium complexes, LiPrLu(CH2SiMe3)(NHCPh3) (7CPh3) and LiPrLu(CH2SiMe3)(NHDipp) (7Dipp) (LiPr = 2,5-[iPr2P = N(4-iPrC6H4)]2C4H2N-), were synthesized by addition of a bulky primary amine, NH2R (R = CPh3, Dipp) (Dipp = 2,6-iPr2C6H3) to the dialkyl complex LiPrLu(CH2SiMe3)2 (6). Unlike complexes supported by the related pincer ligand LPh (LPh = 2,5-[Ph2P = N(4-iPrC6H4)]2C4H2N-) these species proved resistant to C-H cyclometalative processes. Attempts to access lutetium imdes via addition of 4-dimethylaminopyridine (DMAP) to 7CPh3 and 7Dipp promoted disproportionation, affording 0.5 equivalents of the corresponding bisamide complexes LiPrLu(NHCPh3)2 (8CPh3) and LiPrLu(NHDipp)2 (8Dipp), respectively, as well as 0.5 equivalents of LiPrLu(CH2SiMe3)2, which decomposed in the presence of DMAP. Incorporation of internal Lewis bases was accomplished by replacing the N-aryl substituents in LiPr with 4,6-dimethylpyrimidine groups (LPm, 11). The correspondng dialkyl lutetium complex LPmLu(CH2SiMe3)2 (12) was prepared, from which loss of SiMe4 occured over a period of hours in benzene-d6 solution.

Lanthanide (Substituted-)Cyclopentadienyl Bis(phosphinimino)methanediide Complexes: Synthesis and Characterization

Design and synthesis of high-performance single-molecule magnets (SMMs) have long been a research focus. Inspired by the best dysprosium(III) metallocene SMMs and dysprosium(III) bis(methanediide) SMMs, we assumed dysprosium SMMs, which had electrical neutrality by combining the two types of ligands. As the Dy3+ center is coordinated by one (substituted-)cyclopentadienyl (CpR) ligand and one methanediide ({C(PPh2NSiMe3)2}2-) ligand on the axial sites, this ideal structure with linear Ccarbene-Dy-Cpcent would strengthen the magnetic anisotropy and exhibit excellent SMM properties. However, it is not easy to synthesize it in this configuration. We for the first time obtained [Y{C(PPh2NSiMe3)2}(CpR)(THF)] (CpR = Cp(1), Cp tBu(2), Cp*(3), Cp = C5H5, Cp tBu = C5H4 tBu, Cp* = C5Me5) through the reactions of NaCp/KCpR and [Y{C(PPh2NSiMe3)2}(I)(THF)2]. In the molecular structures of 1-3, except for the two expected ligands, one coordination tetrahydrofuran (THF) molecule was also found in each complex. The P-C-P values of 1-3 were 135.46(7), 136.421(8), and 131.43(10)°, respectively, which were far less than 180°. The Ccarbene-Y-Cpcent of 1-3 deviated significantly from the linear shape, which was 118.021, 129.459, and 118.331°, respectively. Such a coordination environment makes the dysprosium congener [Dy{C(PPh2NSiMe3)2}(Cp*)(THF)] (4) whose Ccarbene-Dy-Cpcent (118.295°) was too small to maintain axiality and which almost exhibited no SMM properties. Even though the first exploration of lanthanide (substituted-)cyclopentadienyl bis(phosphinimino)methanediide complexes did not live up to our expectation, it provided great experiences for the future success of high-performance lanthanide (substituted-)cyclopentadienyl methanediide SMMs.

Cascade C-H Activation and Two C-C Bond Forming in Reaction of Azalutetacyclopentadiene with 2-Methylbenzonitriles

Azametallacyclopentadienes are an important class of metallacycles as the key intermediates in metal-promoted or catalyzed carbon-carbon coupling reaction of nitriles and alkynes. Rare-earth azametallacyclopentadienes have shown various reactivity toward nitriles, depending on the substituents of nitriles. The reaction of azalutetacyclopentadienes toward 2-methylbenzonitriles has been investigated in this work, which selectively affords the fused 7-5-6-membered azalutetacycles as products. Computational studies reveal that the reaction of azalutetacyclopentadienes toward 2-methylbenzonitriles selectively initiates with the remote activation of the benzylic C-H bond by the Lu-N bond, followed by the intramolecular nucleophilic attack from the deprotonated benzylic carbon to form a C-C bond. Subsequently, the high ring strain promoted the generation of the uncoordinated carbanion dissociated from the lutetium center, which then undergoes intramolecular nucleophilic attack toward C=N triple bond to give the final product containing fused 7-5-6-membered azalutetacycle. This work not only achieves highly selective three-step cascade reaction to form a unique class of rare-earth metallacycle, but also provides a new idea for the transformation of unsaturated substrates with C-H bonds that can be activated.

Terminal dysprosium and holmium organoimides

Terminal rare-earth-metal imide complexes TptBu,MeLn(NC6H3iPr2-2,6)(dmap) of the mid-late rare-earth elements dysprosium and holmium were synthesized via double methane elimination of Lewis acid stabilized dialkyl precursors TptBu,MeLnMe(GaMe4) with primary aniline derivative H2NC6H3iPr2-2,6 (H2NAriPr). Exploiting the weaker Ln-CH3⋯[GaMe3] interaction compared to the aluminium congener, addition of the aniline derivative leads to the mixed methyl/anilido species TptBu,MeLnMe(HNAriPr) which readily eliminate methane after being exposed to the Lewis base DMAP ([double bond, length as m-dash]N,N-dimethyl-4-aminopyridine). Under the same conditions, [AlMe3]-stabilized dimethyl rare-earth-metal complexes transform immediately to Lewis acid bridged imides TptBu,MeLn(μ2-NC6H3Me2-2,6)(μ2-Me)AlMe2 (Ln = Dy, Ho). DMAP/THF donor exchange is accomplished by treatment of TptBu,MeLn(NC6H3iPr2-2,6)(dmap) with 9-BBN in THF while the terminal imides readily insert carbon dioxide to afford carbamate complexes.

Rare-Earth Metal Phosphinidene Complexes: A Trip from Bridging One to Terminal One

ConspectusAs phosphorus analogues of alkylidene (or carbene) and imido (or nitrene) complexes, phosphinidene complexes have received great attention not only for their fundamental scientific merits but also for their ability to build new phosphorus-containing molecules. A large number of phosphinidene complexes in bridging, mononuclear, or terminal coordination modes have been synthesized, and their reactivity has been extensively explored. However, the synthesis of rare-earth metal (scandium, yttrium, and lanthanide metal) phosphinidene complexes lagged behind the transition metal and actinide congeners for decades. Rare-earth metal ions are among the hardest Lewis acids, whereas phosphinidene ligands are soft Lewis bases; rare-earth metal-phosphinidene coordination is thus mismatched based on the Pearson's HSAB principle. The bridging rare-earth metal phosphinidene complexes were not reported until 2008, and the synthesis of the mononuclear and terminal species is even more challenging, which has only recently been achieved.Our group reported a bis(μ2-phosphinidene)dineodymium complex in 2008. In the following >10 years, we have been pursuing the terminal rare-earth metal phosphinidene complexes. Due to the high instability of rare-earth metal-phosphorus multiple bonds, the synthesis and stabilization of these complexes are extremely difficult. Finally, by using suitable phosphinidene ligands and supporting ligands, we obtained the first mononuclear rare-earth metal phosphinidene complex in 2018 and the first terminal rare-earth metal phosphinidene complex in 2020. In these more than ten years of research, we have also found some interesting reactivity of the rare-earth metal phosphinidene complexes. The rare-earth metal bridging phosphinidene complexes can act as two-electron reductants based on the oxidative coupling of two phosphinidene ligands into a diphosphene ligand. The mononuclear rare-earth metal phosphinidene complexes catalyze the hydrogenation of terminal alkenes under mild conditions, and the joint experimental/DFT studies indicate that the hydrogenation reaction proceeds in a 1,2-addition/elimination mechanism rather than the common σ-bond metathesis mechanism. These reactivities are new and important for the rare-earth metal complexes. In addition, the ligand design in our study may contribute to the synthesis of rare-earth metal-arsenic multiple bonding complexes and alkaline-earth metal-phosphorus multiple bonding complexes, which have not yet been realized. Herein, we present an account of our investigations into rare-earth metal phosphinidene complexes, a trip from bridging one to terminal one. To give the readers an overall image of the development of the rare-earth metal phosphinidene complexes, some findings from other researchers are also included.

Tripodal tris(siloxide) ligand supported trivalent rare-earth metal complexes and redox reactivity

Tripodal tris(siloxide) ligand supported rare-earth metal complexes LLn(III) (Ln = Ce, Pr, Tb, Y, Lu) were synthesized. The Ce(III) complex was oxidized with [N(C6H4Br)3][SbCl6] to a Ce(IV) chloride complex, which reacted with tBuONa to form a Ce(IV) tert-butoxide complex, one displaying a reduction potential cathodically shifted relative to that of Ce(IV) chloride complex.

A Terminal Yttrium Phosphinidene

Terminal, nondirectional ionic "multiple" bond interactions between group 15 elements and rare-earth metals (Ln) have remained a challenging target until present. Although reports on terminal imide species have accumulated in the meantime, examples of terminal congeners with the higher homologue phosphorus are yet elusive. Herein, we present the synthesis of the first terminal yttrium organophosphinidene complex, TptBu,MeY(═PC6H3iPr2-2,6)(DMAP)2, according to a double-deprotonation sequence previously established for organoimides of the smaller rare-earth metals. Subsequent deprotonation of the primary phosphane H2PC6H3iPr2-2,6 (H2PAriPr) with discrete dimethyl compound TptBu,MeYMe2 in the presence of DMAP under simultaneous methane elimination generated a terminal multiply bonded phosphorus. The primary phosphide intermediates TptBu,MeYMe(HPAriPr) and TptBu,MeYMe(HNPAriPr)(DMAP) are isolable species and were also obtained and fully characterized for holmium and dysprosium. The Lewis acid-stabilized yttrium phosphinidene TptBu,MeY[(μ2-PAriPr)(μ2-Me)AlMe2] was obtained by treatment of H2PAriPr with TptBu,MeYMe(AlMe4) but could not be converted into a terminal phosphinidene via cleavage of trimethylaluminum. The corresponding reaction of H2PAriPr with TptBu,MeYMe(GaMe4) led to adduct [GaMe3(PH2AriPr)] rather than to the formation of a yttrium phosphinidene. The yttrium-phosphorus interaction in the obtained organophosphide and phosphinidene complexes was scrutinized by 31P/89Y NMR spectroscopy and DFT calculations, unambiguously supporting the existence of multiple bonding.

Regioselective C-H alkylation of anisoles with olefins by cationic imidazolin-2-iminato scandium(iii) alkyl complexes

A new type of rare-earth alkyl complexes supported by monoanionic imidazolin-2-iminato ligands were synthesised and structurally characterised by X-ray diffraction and NMR analyses. The utility of these imidazolin-2-iminato rare-earth alkyl complexes in organic synthesis was demonstrated by their performance in highly regioselective C-H alkylation of anisoles with olefins. With as low as 0.5 mol% catalyst loading, various anisole derivatives without ortho-substitution or 2-methyl substituted anisoles reacted with several alkenes under mild conditions, producing the corresponding ortho-Csp2-H and benzylic Csp3-H alkylation products in high yield (56 examples, 16-99% yields). Control experiments revealed that rare-earth ions, ancillary imidazolin-2-iminato ligands, and basic ligands were crucial for the above transformations. Based on deuterium-labelling experiments, reaction kinetic studies, and theoretical calculations, a possible catalytic cycle was provided to elucidate the reaction mechanism.

Selective Cleavage of the Strong or Weak C-C Bonds in Biphenylene Enabled by Rare-Earth Metals

Selective cleavage of C-C bonds within arene rings is of great interest but remains elusive, especially for the molecules possessing the active and inert C-C bonds. Here, we report that the active and inert C-C bonds of biphenylene could be controllably cleaved by the reaction of biphenylene, potassium graphite, and rare-earth complexes with different metal centers. For scandium, the bond activation occurs at the C_aryl-C_aryl single bond, yielding 9-scandafluorene. For Lu, the reaction goes through ring contraction of the aromatic ring in biphenylene to provide benzopentalene dianionic lutetium. The origin of the selectivity and the reaction mechanism were illustrated by the isolation of intermediates and DFT calculations.

Synthesis and Characterization of a Bridging Cerium(IV) Nitride Complex

Complexes featuring lanthanide-ligand multiple bonds are rare and highly reactive. They are important synthetic targets to understand 4f/5d-bonding in comparison to d-block and actinide congeners. Herein, the isolation and characterization of a bridging cerium(IV)-nitride complex: [(TriNOx)Ce(Li₂μ-N)Ce(TriNOx)][BAr^F₄] is reported, the first example of a molecular cerium-nitride. The compound was isolated by deprotonating a monometallic cerium(IV)-ammonia complex: [Ce^IV(NH₃)(TriNOx)][BAr^F₄]. The average Ce═N bond length of [(TriNOx)Ce(Li₂μ-N)Ce(TriNOx)][BAr^F₄] was 2.117(3) Å. Vibrational studies of the ¹⁵N-isotopomer exhibited a shift of the Ce═N═Ce asymmetric stretch from ν = 644 cm^-1 to 640 cm^-1, and X-ray spectroscopic studies confirm the +4 oxidation state of cerium. Computational analyses showed strong involvement of the cerium 4f shell in bonding with overall 16% and 11% cerium weight in the σ- and π-bonds of the Ce═N═Ce fragment, respectively.

A Borane Lewis Acid in the Secondary Coordination Sphere of a Ni(II) Imido Imparts Distinct C-H Activation Selectivity

Two borane-functionalized bidentate phosphine ligands that vary in tether length have been prepared to examine cooperative metal-substrate interactions. Ni(0) complexes react with aryl azides at low temperatures to form structurally unusual κ2-(N,N)-N3Ar adducts. Warming these adducts affords products of N2 extrusion and in one case, a Ni-imido compound that is capped by the appended borane. Reactions with 1-azidoadamantane (AdN3) provide a distinct outcome, where a proposed nickel imido intermediate activates the sp2 C-H bonds of arenes, even in the presence of benzylic C-H sites. Combined experimental and computational mechanistic studies demonstrate that the unique reactivity is a consequence of Lewis-acid-induced polarization of the Ni-NR bond, potentially providing a synthetic strategy for chemoselective reaction engineering.

Versatile Coordination Modes of Multidentate Neutral Amine Ligands with Group 1 Metal Cations

This work comprehensively investigated the coordination chemistry of a hexa-dentate neutral amine ligand, namely, N,N',N"-tris-(2-N-diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN), with group-1 metal cations (Li+, Na+, K+, Rb+, Cs+). Versatile coordination modes were observed, from four-coordinate trigonal pyramidal to six-coordinate trigonal prismatic, depending on the metal ionic radii and metal's substituent. For comparison, the coordination chemistry of a tetra-dentate tris-[2-(dimethylamino)ethyl]amine (Me6Tren) ligand was also studied. This work defines the available coordination modes of two multidentate amine ligands (DETAN and Me6Tren), guiding future applications of these ligands for pursuing highly reactive and elusive s-block and rare-earth metal complexes.

Open-Shell Early Lanthanide Terminal Imides

Group 3- and 4f-element organometallic chemistry and reactivity are decisively driven by the rare-earth-metal/lanthanide (Ln) ion size and associated electronegativity/ionicity/Lewis acidity criteria. For these reasons, the synthesis of terminal "unsupported" imides [Ln═NR] of the smaller, closed-shell Sc(III), Lu(III), Y(III), and increasingly covalent Ce(IV) has involved distinct reaction protocols while derivatives of the "early" large Ln(III) have remained elusive. Herein, we report such terminal imides of open-shell lanthanide cations Ce(III), Nd(III), and Sm(III) according to a new reaction protocol. Lewis-acid-stabilized methylidene complexes [Tp^tBu,MeLn(μ₃-CH₂){(μ₂-Me)MMe₂}₂] (Ln = Ce, Nd, Sm; M = Al, Ga) react with 2,6-diisopropylaniline (H₂NAr^iPr) via methane elimination. The formation of arylimide complexes is governed by the Ln(III) size, the Lewis acidity of the group 13 metal alkyl, steric factors, the presence of a donor solvent, and the sterics and acidity (pK_a) of the aromatic amine. Crucially, terminal arylimides [Tp^tBu,MeLn(═NAr^iPr)(THF)₂] (Ln = Ce, Nd, Sm) are formed only for M = Ga, and for M = Al, the Lewis-acid-stabilized imides [Tp^tBu,MeLn(NAr^iPr)(AlMe₃)] (Ln = Ce, Nd, Sm) are persistent. In stark contrast, the [GaMe₃]-stabilized imide [Tp^tBu,MeLn(NAr^iPr)(GaMe₃)] (Ln = Nd, Sm) is reversibly formed in noncoordinating solvents.

Reactivity of Mixed Methyl-Aminobenzyl Guanidinate Lutetium Complex towards iPrN=C=NiPr, CS2 and Ph2PH

A heteroleptic terminal alkyl lutetium complex stabilized by a bulky guanidinato ligand, LLu(CH2C6H4NMe2-o)(Me)(THF) (1) (L = (PhCH2)2NC(NC6H3iPr2-2,6)2) has been synthesized by treatment of LLu(CH2C6H4NMe2-o)2 with AlMe3 (1 equiv) via an...

A monoanionic pentadentate ligand platform for scandium-pnictogen multiple bonds

A new monoanionic pentadentate ligand is designed to accommodate Sc = E bonds (E = N, P). The imido complex is stable enough to isolate and characterize, and reacts rapidly with CO₂. The phosphinidene, on the other hand, is highly reactive and induces C-C bond cleavage to yield a phosphido-pyridyl complex which also undergoes rapid reacton with CO₂.

Charge frustration in ligand design and functional group transfer

Molecules with different resonance structures of similar importance, such as heterocumulenes and mesoionics, are prominent in many applications of chemistry, including 'click chemistry', photochemistry, switching and sensing. In coordination chemistry, similar chameleonic/schizophrenic entities are referred to as ambidentate/ambiphilic or cooperative ligands. Examples of these had remained, for a long time, limited to a handful of archetypal compounds that were mere curiosities. In this Review, we describe ambiphilicity - or, rather, 'charge frustration' - as a general guiding principle for ligand design and functional group transfer. We first give a historical account of organic zwitterions and discuss their electronic structures and applications. Our discussion then focuses on zwitterionic ligands and their metal complexes, such as those of ylidic and redox-active ligands. Finally, we present new approaches to single-atom transfer using cumulated small molecules and outline emerging areas, such as bond activation and stable donor-acceptor ligand systems for reversible 1e^- chemistry or switching.

Synthesis and Reactivity of Acyclic Germanimines: Silyl Rearrangement and Cycloadditions

We report the synthesis of aromatic germanimines [(HMDS)₂Ge═NAr] (Ar = Ph, Mes, Dipp; Mes = 2,4,6-Me₃C₆H₂, Dipp = 2,6-iPr₂C₆H₃) and an investigation into their associated reactivity. [(HMDS)₂Ge═NPh] decomposes above -30 °C, while [(HMDS)₂Ge═NDipp] engages in an intramolecular reaction at 60 °C. [(HMDS)₂Ge═NMes] was shown to rearrange via a 1,3-silyl migration to give [(HMDS){(SiMe₃)(Mes)N}Ge(NSiMe₃)] in a 1:7 equilibrium mixture at room temperature. These latter germanimines react with unsaturated polar substrates such as CO₂, ketones, and arylisocyanate via a [2 + 2] cycloaddition pathway.

Yttrium germole dianion complexes with Y-Ge bonds

The reactions of dipotassium 3,4-dimethyl-2,5-bis(trimethylsilyl)-germole dianion K2[1] with YCl3 and Cp*YCl2 (Cp* = cyclopentadienyl) in THF at room temperature afforded the dianion salt [(K-cryptand-222)2][1-YCl3] (K2[2]) and the dimeric complex [1-Y-Cp*]2 (3), respectively. While the polymeric complex {[(1)2-Y-K(toluene)]2}n (4) was obtained from the reaction of K2[1] and half molar equivalent of YCl3(THF)3.5 in toluene at 80 °C. The germole dianions in complexes 3 and 4 feature η5/η1 coordination interactions with the yttrium atoms. They represent the first examples of rare earth (RE) complexes containing RE-Ge bonds other than the RE-GeR3 structural type.

Insertion of Metal-Substituted Silylene into Naphthalene's Aromatic Ring and Subsequent Rearrangement for Silaspiro-Benzocycloheptenyl and Cyclobutenosilaindan Derivatives

Synthesis of silacycle compounds are of fundamental and application importance. Herein we report the first example of insertion of metal-substituted silylene fragment into naphthalene's aromatic ring. More significantly, this insertion is followed by interesting rearrangements to yield silaspiro-benzocycloheptenyl and cyclobutenosilaindan derivatives. The formation of cyclobutenosilaindan derivative includes the C-C bond cleavage and 4π electrocyclization steps; the formation of silaspiro-benzocycloheptenyl derivative is more complicated, including the C-C bond cleavage, reversible 4π electrocyclization, C-H bond activation and C-Si bond cleavage. DFT investigations were carried out to shed light on the mechanistic aspects of these two rearrangements. The formed cyclobutenosilaindan potassium can readily react with PhOH, MeOTf, EtOTf, PhCH₂ Cl or PhCOCl at room temperature to afford the hydrogen, alkyl, benzyl or benzoyl substituted cyclobutenosilaindans in high yields.

Enantioselective Hydroboration of Ketones Catalyzed by Rare-Earth Metal Complexes Containing Trost Ligands

Four chiral dinuclear rare-earth metal complexes [REL¹]₂ (RE = Y(1), Eu(2), Nd(3), La (4)) stabilized by Trost proligand H₃L¹ (H₃L¹ = (S,S)-2,6-bis[2-(hydroxydiphenylmethyl)pyrrolidin-1-ylmethyl]-4-methylphenol) were first prepared, and all were characterized by X-ray diffraction. Complex 4 was employed as the catalyst for enantioselective hydroboration reaction of substituted ketones, and the corresponding secondary alcohols with excellent yields and high ee values were obtained using reductant HBpin. The same result was also achieved using the combination of lanthanium amides La[N(SiMe₃)₂]₃ with Trost proligand H₃L¹ in a 1:1 molar ratio. The experimental findings and DFT calculation revealed the possible mechanism of the enantioselective hydroboration reaction and defined the origin of the enantioselectivity in the current system.

Synthesis and versatile reactivity of scandium phosphinophosphinidene complexes

M=E/M≡E multiple bonds (M = transition metal, E = main group element) are of significant fundamental scientific importance and have widespread applications. Expanding the ranges of M and E represents grand challenges for synthetic chemists and will bring new horizons for the chemistry. There have been reports of M=E/M≡E multiple bonds for the majority of the transition metals, and even some actinide metals. In stark contrast, as the largest subgroup in the periodic table, rare-earth metals (Ln) were scarcely involved in Ln=E/Ln≡E multiple bonds. Until recently, there were a few examples of rare-earth monometallic alkylidene, imido and oxo complexes, featuring Ln=C/N/O bonds. What are in absence are rare-earth monometallic phosphinidene complexes with Ln=P bonds. Herein, we report synthesis and structure of rare-earth monometallic phosphinidene complexes, namely scandium phosphinophosphinidene complexes. Reactivity of scandium phosphinophosphinidene complexes is also mapped out, and appears to be easily tuned by the supporting ligand.

Reactivity of Ce(iv) imido compounds with heteroallenes

The reactivity of alkali metal capped Ce(iv) imido compounds [M(DME)₂][CeNAr^F(TriNOx)] (1-M with M = K, Rb, Cs and Ar^F = 3,5-bis(trifluoromethyl)phenyl) with CO₂ and organic isocyanates has been evaluated.

Cerium-carbon dative interactions supported by carbodiphosphorane

A set of complexes containing dative interactions between a rare-earth metal and carbon are reported. Complex 2, Br₃Ce(CDP)(THF), with a Ce←C bond was synthesized by the reaction of CeBr₃ with a carbon(0) ligand, carbodiphosphorane (CDP). More significantly, a trivalent cerium complex 3, [BrCe(CDP)₂](BPh₄)₂, with two σ dative interactions C→Ce←C was also isolated, which represents an unusual example of two dative interactions formed with the same atom in a molecule. Furthermore, π donation by the second lone-pair electrons of the CDP ligand is rather weak. Single-crystal X-ray diffraction shows that the Ce-C bond lengths in these complexes are comparable with those in cerium(iii)-carbene species. Density functional theory calculations support the dative interaction formation in these complexes and the strength of σ-donation in 3 is stronger than that in 2.

Alternative (κ1-N:η6-arene vs.κ2-N,N) coordination of a sterically demanding amidinate ligand: are size and electronic structure of the Ln ion decisive factors?

The amine elimination reaction of equimolar amounts of ansa-bis(amidine) C₆H₄-1,2-{NC(tBu)NH(2,6-iPr₂C₆H₃)}₂ (L¹H) and [(Me₃Si)₂N]₂Yb(THF)₂ affords a bis(amidinate) Yb^II complex [C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}₂]Yb(THF) (1) in 68% yield. Complex 1 features a rather rare η¹-amido:η⁶-arene coordination of both amidinate fragments to the Yb^II ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 1 by I₂ regardless of the molar ratio of reagents (2 : 1 or 1 : 1) leads to the formation of the Yb^III species [{(2,6-iPr₂C₆H₃)[double bond, length as m-dash]NC(tBu)NH}-C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}]YbI₂(THF)₂ (2) in which only one amidinate fragment is coordinated to the ytterbium ion in κ²-N,N'-chelating coordination mode, while the second NCN fragment is protonated in the course of the reaction and is not bound to the metal ion. The outcome of the salt metathesis reaction of LaCl₃ with lithium amidinates [C₆H₄-1,2-{NC(tBu)N(2,6-R₂C₆H₃)}₂Li₂] (R = Me, iPr) is proven to be strongly affected by the substituent 2,6-R₂C₆H₃ on the amidinate nitrogens. When R = iPr, the salt metathesis reaction occurs smoothly and results in the formation of an ate-chloro-amidinate complex [C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}₂]La(μ²-Cl)Li(THF)(μ²-Cl)₂Li(THF)₂ (3) in which the La^III ion is coordinated by both amidinate fragments in a "classic"κ²-N,N'-chelating fashion. In the case of R = Me, the reaction requires prolonged heating for completion. Moreover, the salt metathesis reaction is accompanied by the fragmentation of the ligand and affords a trinuclear chloro-amidinate complex [C₆H₄-1,2-{NC(tBu)N(2,6-Me₂C₆H₃)}₂]La{[(tBu)C(N-2,6-Me₂C₆H₃)₂]La(THF)}₂(μ²-Cl)₄(μ³-Cl)₂ (4) containing one dianionic ansa-bis(amidinate) and two monoanionic [(tBu)C(N-2,6-Me₂C₆H₃)₂] amidinate fragments. DFT calculations are conducted to determine the factor that governs this change in coordination mode and, in particular, the effect of the metal oxidation state.

Rare-earth metal and actinide organoimide chemistry

Elaborate synthesis schemes pave the way to f-element and group 3 complexes with multiply bonded imido ligands displaying intriguing reactivity.

Pentamethylcyclopentadienyl ruthenium “pogo stick” complexes with nitrogen donor ligands

The preparation and reactivity of an imidazolin-2-iminato ruthenium complex with a rare one-legged piano-stool (“pogo stick”) geometry is reported.

de Oliveira-Filho AG, Braga AAC. Unveiling the potential of scandium complexes for methane C–H bond activation: a computational study

Sc(i) complexes activate methane C–H bonds under mild conditions.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Synthesis of homometallic divalent lanthanide organoimides from benzyl complexes

The reaction of LnI2(thf)2 with benzyl potassium affords the homoleptic benzyl complexes [Ln(CH2Ph)2]n of samarium, europium, and ytterbium. In the cases of Eu and Yb, the treatment of [Ln(CH2Ph)2]n with one equivalent of 2,6-diisopropylaniline gives access to tetrameric organoimide complexes [(thf)Ln(μ3-NDipp)]4, representing the first examples of homometallic Ln(ii) imides. This study revealed that the Yb(ii) organoimide chemistry is significantly different from that of calcium.