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Protonolysis of lanthanide tris(tetramethylaluminate)s with two equivalents of 2,6‐diisopropylaniline affords LaIII and CeIII diimide compounds Ln[(μ‐NC6H3iPr2‐2,6)2AlMe2](thf)4 featuring a bidentate AlMe2‐linked diimido ligand. As revealed for the corresponding Ce(GaMe4)3‐reaction, formation of the diimide complexes proceeds via tetrametallic complexes of the type [Ce{(μ‐NC6H3iPr2‐2,6)(HNC6H3iPr2‐2,6)(MMe3)}]2 (Me=Al, Ga). Oxidation of the cerium(III) complex with hexachloroethane leads to a neutral CeIV diimide species. Partial protonolysis with phenylacetylene and hydrogenolysis via H3SiPh give conclusive insights into the reactive coordination sites of such diimide complexes. The [(NAr)2AlMe2] diimido scaffold not only provides a suitable platform for performing CeIII/CeIV redox chemistry in a metal alkyl environment but also engages in inherent LnIII imide reactivity. [ABSTRACT FROM AUTHOR]

Trinuclear rare-earth metal methylidene complexes with a Ln3(μ3-CH2)(μ3-Me)(μ2-Me)3 structural motif were synthesized by applying three protocols. Polymeric [LuMe3]n (1-Lu) reacts with the sterically demanding amine H[NSiMe3(Ar)] (Ar = C6H3iPr2-2,6) in tetrahydrofuran via methane elimination to afford isolable monomeric [NSiMe3(Ar)]LuMe2(thf)2 (4-Lu). The formation of trinuclear rare-earth metal tetramethyl methylidene complexes [NSiMe3(Ar)]3Ln3(μ3-CH2)(μ3-Me)(μ2-Me)3(thf)3 (7-Ln; Ln = Y, Ho, Lu) via reaction of [LnMe3]n (1-Ln; Ln = Y, Ho, Lu) with H[NSiMe3(Ar)] is proposed to occur via an “intermediate” species of the type [NSiMe3(Ar)]LnMe2(thf)x and subsequent C−H bond activation. Applying Lappert's concept of Lewis base-induced methylaluminate cleavage, compounds [NSiMe3(Ar)]Ln(AlMe4)2 (5-Ln; Ln = Y, La, Nd, Ho) were converted into methylidene complexes 7-Ln (Ln = Y, Nd, Ho) in the presence of tetrahydrofuran. Similarly, tetramethylgallate complex [NSiMe3(Ar)]Y(GaMe4)2 (6-Y) could be employed as a synthesis precursor for 7-Y. The molecular composition of complexes 4-Ln, 5-Ln, 6-Y and 7-Ln was confirmed by elemental analyses, FTIR spectroscopy, 1H and 13C NMR spectroscopy (except for holmium derivatives) and single-crystal X-ray diffraction. The Tebbe-like reactivity of methylidene complex 7-Nd with 9-fluorenone was assessed affording oxo complex [NSiMe3(Ar)]3Nd3(μ3-O)(μ2-Me)4(thf)3 (8-Nd). The synthesis of 5-Ln yielded [NSiMe3(Ar)]2Ln(AlMe4) (9-Ln; Ln = La, Nd) as minor side-products, which could be obtained in moderate yields when homoleptic Ln(AlMe4)3 were treated with two equivalents of K[NSiMe3(Ar)]. [ABSTRACT FROM AUTHOR]

The reaction of monomeric [(Tp tBu,Me)LuMe2] (Tp tBu,Me=tris(3-Me-5- tBu-pyrazolyl)borate) with primary aliphatic amines H2NR (R= tBu, Ad=adamantyl) led to lutetium methyl primary amide complexes [(Tp tBu,Me)LuMe(NHR)], the solid-state structures of which were determined by XRD analyses. The mixed methyl/tetramethylaluminate compounds [(Tp tBu,Me)LnMe({μ2-Me}AlMe3)] (Ln=Y, Ho) reacted selectively and in high yield with H2NR, according to methane elimination, to afford heterobimetallic complexes: [(Tp tBu,Me)Ln({μ2-Me}AlMe2)(μ2-NR)] (Ln=Y, Ho). X-ray structure analyses revealed that the monomeric alkylaluminum-supported imide complexes were isostructural, featuring bridging methyl and imido ligands. Deeper insight into the fluxional behavior in solution was gained by 1H and 13C NMR spectroscopic studies at variable temperatures and 1H-89Y HSQC NMR spectroscopy. Treatment of [(Tp tBu,Me)LnMe(AlMe4)] with H2N tBu gave dimethyl compounds [(Tp tBu,Me)LnMe2] as minor side products for the mid-sized metals yttrium and holmium and in high yield for the smaller lutetium. Preparative-scale amounts of complexes [(Tp tBu,Me)LnMe2] (Ln=Y, Ho, Lu) were made accessible through aluminate cleavage of [(Tp tBu,Me)LnMe(AlMe4)] with N, N, N′, N′-tetramethylethylenediamine (tmeda). The solid-state structures of [(Tp tBu,Me)HoMe(AlMe4)] and [(Tp tBu,Me)HoMe2] were analyzed by XRD. [ABSTRACT FROM AUTHOR]

The μ2-imide complexes [Ln(AlMe4)(μ2-Nmes*)]x(mes* = C6H2tBu3-2,4,6) (Ln = Y, La,Nd, Lu) are synthesized from homoleptic heterobimetallic complexesLn(AlMe4)3utilizing two distinct protocols:reaction with 2,4,6-tri-tert-butylaniline in hexanevia methane elimination or with potassium (2,4,6-tri-tert-butylphenyl)amide in toluene according to a salt metathesis–protonolysistandem reaction. Complexes [Ln(AlMe4)(μ2-Nmes*)]2(Ln = Y, Nd, Lu) revealed isomorphous solid-statestructures, featuring an asymmetrically bridged Ln2N2core with very short Ln–N distances (2.071(1)–2.155(3)Å). In the solid-state structure of the lanthanum derivativesimilar dimeric subunits assemble as La4Al4oligomersthrough μ2-η1:η2-bridging tetramethylaluminato moieties. [La(AlMe4)(μ2-Nmes*)]4displays La---arene interactions (2.702(6)Å) that are considerably shorter than the La(μ-CH3)aluminatobond lengths. [ABSTRACT FROM AUTHOR]

Homoleptic tetramethylaluminates Ln(AlMe 4 ) 3 react with KTp t Bu,Me (Tp t Bu,Me = tris(3- t Bu-5-Me-pyrazolyl)borato) to yield rare-earth-metal methylidene complexes (Tp t Bu,Me )Ln(μ 3 -CH 2 )[(μ-Me)AlMe 2 ] 2 (Ln = La, Ce, Nd). The lanthanum reaction is prone to additional C-H- and B-N-bond activation, affording coproducts La[HB(pz Me, t Bu )(pz CMe2,Me ) 2 ][(μ-CH 2 )(μ-Me)AlMe 2 ] 2 and [La(μ-pz t Bu,Me )(AlMe 4 ) 2 ] 2 (pz t Bu,Me = 3- t Bu-5-Me-pyrazolato). The protonolysis reaction of Ln(AlMe 4 ) 3 and Hpz t Bu,Me provides more efficient access to [Ln(μ-pz t Bu,Me )(AlMe 4 ) 2 ] 2 (Ln = La, Nd). Treatment of Ln(AlMe 4 ) 3 with KTp Me,Me led to methylidene complexes (Tp Me,Me )Ln(μ 3 -CH 2 )[(μ-Me)AlMe 2 ] 2 (Ln = Nd, Sm) or bis(tetramethylaluminate) complexes (Tp Me,Me )Ln(AlMe 4 ) 2 (Ln = Y, Lu). The neodymium reaction generated methine derivative (Tp Me,Me )Nd[(μ 4 -CH)(AlMe 2 ) 2 (μ-pz ,Me,Me )][(μ-Me)AlMe 2 ] as a minor coproduct. The reaction of Ln(GaMe 4 ) 3 (Ln = Y, La, Ce, Nd, Sm, Ho) with HTp t Bu,Me gave methylidene complexes (Tp t Bu,Me )Ln(μ 3 -CH 2 )[(μ-Me)GaMe 2 ] 2 (Ln = La, Ce, Nd, Sm) and alkyl complexes (Tp t Bu,Me )LnMe[(μ-Me)GaMe 3 ] (Ln = Y, Ho), while competing B-N bond activation reactions produced GaMe 2 [BH(Me)(μ-pz t Bu,Me ) 2 ] and (Tp t Bu,Me )Ln(η 2 -pz t Bu,Me )[(μ-Me)GaMe 3 ] (Ln = Y, Ho). The steric impact of the Tp R,Me ligands was examined by cone angle calculations. Rare-earth-metal methylidene complexes (Tp t Bu,Me )Ln(μ 3 -CH 2 )[(μ-Me)EMe 2 ] 2 (E = Al, Ga) successfully promote carbonyl methylenation reactions upon addition of ketone.

Yttrocene derivatives [Cp* 2 Y(MMe 4 )] (Cp* = C 5 Me 5 ; M = Al, Ga) and Cp* 2 Y[Me 3 Al{B(NDippCH) 2 }] (Dipp = C 6 H 3 i Pr 2 -2,6) deprotonate benzene at elevated temperatures via the release of methane. The formation of [Cp* 2 Y(Me 2 MPh 2 )] (M = Al, Ga), Cp* 2 Y(MPh 4 ) (M = Al, Ga), Cp* 2 Y[Me 2 AlPh{B(NDippCH) 2 }], and Cp* 2 Y[AlPh 3 {B(NDippCH) 2 }] can be controlled via the temperature applied. The activation temperature and formation of the coordinatively unsaturated "reactive" [Cp* 2 YMe] strongly depend on the coordination strength of the displaceable Lewis acids [AlMe 3 ] 2 , GaMe 3 , and [Me 2 Al{B(NDippCH) 2 }] 2 . Hence, [Cp* 2 Y(AlMe 4 )] requires temperatures above 100 °C to metalate benzene, while Cp* 2 Y[AlMe 3 {B(NDippCH) 2 }] undergoes C-H-bond activation even at ambient temperatures. A kinetic deuterium isotope effect was observed for the reactions in C 6 D 6 solutions. Distinct differences in the stabilities of the bulky Group 13 anions ([Me 2 MPh 2 ] - , [MPh 4 ] - , [Me 3 Al{B(NDippCH) 2 }] - , [Me 2 AlPh{B(NDippCH) 2 }] - , and [AlPh 3 {B(NDippCH) 2 }] - ) are assessed by detailed studies of the coordination chemistry with tetrahydrofuran (THF) and by variable-temperature 1 H NMR spectroscopy. Thus, increased steric bulk or a reduced Lewis acidity of the Group 13 metal center promote temperature-sensitive dissociation of trivalent Group 13 alkyl entities. Consequently, compound Cp* 2 Y[AlPh 3 {B(NDippCH) 2 }] was found to engage in a dissociation equilibrium with [Cp* 2 YPh] and AlPh 2 {B(NDippCH) 2 } in a C 6 D 6 solution at ambient temperature. The reaction of Cp* 2 Y[AlPh 3 {B(NDippCH) 2 }] with THF results in the concomitant formation of monometallic Cp* 2 YPh(THF) and the solvent-separated ion pair [Cp* 2 Y(THF) 2 ][AlPh 3 {B(NDippCH) 2 }].

The cerium(IV) pyrazolate complexes [Ce(Me 2 pz) 4 ] 2 and [Ce(Me 2 pz) 4 (thf)] initiate β-hydride abstraction of the bis(dimethylsilyl)amido moiety, to afford a heteroleptic cerium(IV) species containing a dimethylpyrazolyl-substituted silylamido ligand, namely [Ce(Me 2 pz) 3 (bpsa)] (bpsa=bis((3,5-dimethylpyrazol-1-yl)dimethylsilyl)amido; Me 2 pz =3,5-dimethylpyrazolato), along with some cerium(III) species. Remarkably, the nucleophilic attack of the pyrazolyl at the silicon atom and concomitant Si-H-bond cleavage is restricted to the tetravalent cerium oxidation state and appears to proceed via the formation of a transient cerium(IV) hydride, which engages in immediate redox chemistry. When [Ce(Me 2 pz) 4 ] 2 is treated with [Li{N(SiMe 3 ) 2 }], that is, in the absence of the SiH functionality, any redox chemistry did not occur. Instead, the ceric ate complex [LiCe 2 (Me 2 pz) 9 ] and the stable mixed-ligand ceric species [Ce(Me 2 pz) 2 {N(SiMe 3 ) 2 } 2 ] were obtained., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Trinuclear rare-earth metal methylidene complexes with a Ln3(μ3-CH2)(μ3-Me)(μ2-Me)3 structural motif were synthesized by applying three protocols. Polymeric [LuMe3]n (1-Lu) reacts with the sterically demanding amine H[NSiMe3(Ar)] (Ar = C6H3iPr2-2,6) in tetrahydrofuran via methane elimination to afford isolable monomeric [NSiMe3(Ar)]LuMe2(thf)2 (4-Lu). The formation of trinuclear rare-earth metal tetramethyl methylidene complexes [NSiMe3(Ar)]3Ln3(μ3-CH2)(μ3-Me)(μ2-Me)3(thf)3 (7-Ln; Ln = Y, Ho, Lu) via reaction of [LnMe3]n (1-Ln; Ln = Y, Ho, Lu) with H[NSiMe3(Ar)] is proposed to occur via an "intermediate" species of the type [NSiMe3(Ar)]LnMe2(thf)x and subsequent C-H bond activation. Applying Lappert's concept of Lewis base-induced methylaluminate cleavage, compounds [NSiMe3(Ar)]Ln(AlMe4)2 (5-Ln; Ln = Y, La, Nd, Ho) were converted into methylidene complexes 7-Ln (Ln = Y, Nd, Ho) in the presence of tetrahydrofuran. Similarly, tetramethylgallate complex [NSiMe3(Ar)]Y(GaMe4)2 (6-Y) could be employed as a synthesis precursor for 7-Y. The molecular composition of complexes 4-Ln, 5-Ln, 6-Y and 7-Ln was confirmed by elemental analyses, FTIR spectroscopy, (1)H and (13)C NMR spectroscopy (except for holmium derivatives) and single-crystal X-ray diffraction. The Tebbe-like reactivity of methylidene complex 7-Nd with 9-fluorenone was assessed affording oxo complex [NSiMe3(Ar)]3Nd3(μ3-O)(μ2-Me)4(thf)3 (8-Nd). The synthesis of 5-Ln yielded [NSiMe3(Ar)]2Ln(AlMe4) (9-Ln; Ln = La, Nd) as minor side-products, which could be obtained in moderate yields when homoleptic Ln(AlMe4)3 were treated with two equivalents of K[NSiMe3(Ar)].