Rare-earth-metallocene alkylaluminates trigger distinct tetrahydrofuran activation.

Thermal treatment of Cp*2YMe(thf) (Cp* = C5Me5), obtained from Cp*2Y(AlMe4) via donor-induced AlMe3 cleavage, in THF resulted in the concomitant formation of vinyl oxide Cp*2Y(OC2H3)(thf) and 2-ethylene-tetrahydrofuranyl complex Cp*2Y(2-C2H4-OC4H7) via the release of methane. In stark contrast, dissolving Cp*2La(AlMe4) in THF/n-hexane led to the quantitative formation of AlMe3-stabilized 2-tetrahydrofuranyl complex Cp*2La(2-AlMe3-OC4H7), with methane elimination.

Nanoscale Organolanthanum Clusters: Nuclearity-Directing Role of Cyclopentadienyl and Halogenido Ligands.

Tetramethylaluminato/halogenido(X) ligand exchange reactions in half-sandwich complexes [CpR La(AlMe4 )2 ] are feasible in non-coordinating solvents and provide access to large coordination clusters of the type [CpR LaX2 ]x . Incomplete exchange reactions generate the hexalanthanum clusters [CpR 6 La6 X8 (AlMe4 )4 ] (CpR =Cp*=C5 Me5 , X=I; CpR =Cp'=C5 H4 SiMe3 , X=Br, I). Treatment of [Cp*La(AlMe4 )2 ] with two equivalents Me3 SiI gave the nonalanthanum cluster [Cp*LaI2 ]9 , while the exhaustive reaction of [Cp'La(AlMe4 )2 ] with the halogenido transfer reagents Me3 GeX and Me3 SiX (X=I, Br, Cl) produced a series of monocyclopentadienyl rare-earth-metal clusters with distinct nuclearity. Depending on the halogenido ion size the homometallic clusters [Cp'LaCl2 ]10 and [Cp'LaX2 ]12 (X=Br, I) could be isolated, whereas different crystallization techniques led to the aggregation of clusters of distinct structural motifs, including the desilylated cyclopentadienyl-bridged cluster [(µ-Cp)2 Cp'8 La8 I14 ] and the heteroaluminato derivative [Cp'10 La10 Br18 (AlBr2 Me2 )2 ]. The use of the Cp' ancillary ligand facilitates cluster characterization by means of NMR spectroscopy.

Potential Precursors for Terminal Methylidene Rare-Earth-Metal Complexes Supported by a Superbulky Tris(pyrazolyl)borato Ligand.

A series of solvent-free heteroleptic terminal rare-earth-metal alkyl complexes stabilized by a superbulky tris(pyrazolyl)borato ligand with the general formula [TptBu,Me LnMeR] have been synthesized and fully characterized. Treatment of the heterobimetallic mixed methyl/tetramethylaluminate compounds [TptBu,Me LnMe(AlMe4 )] (Ln=Y, Lu) with two equivalents of the mild halogenido transfer reagents SiMe3 X (X=Cl, I) gave [TptBu,Me LnX2 ] in high yields. The addition of only one equivalent of SiMe3 Cl to [TptBu,Me LuMe(AlMe4 )] selectively afforded the desired mixed methyl/chloride complex [TptBu,Me LuMeCl]. Further reactivity studies of [TptBu,Me LuMeCl] with LiR or KR (R=CH2 Ph, CH2 SiMe3 ) through salt metathesis led to the monomeric mixed-alkyl derivatives [TptBu,Me LuMe(CH2 SiMe3 )] and [TptBu,Me LuMe(CH2 Ph)], respectively, in good yields. The SiMe4 elimination protocols were also applicable when using SiMe3 X featuring more weakly coordinating moieties (here X=OTf, NTf2 ). X-ray structure analyses of this diverse set of new [TptBu,Me LnMeR/X] compounds were performed to reveal any electronic and steric effects of the varying monoanionic ligands R and X, including exact cone-angle calculations of the tridentate tris(pyrazolyl)borato ligand. Deeper insights into the reactivity of these potential precursors for terminal alkylidene rare-earth-metal complexes were gained through NMR spectroscopic studies.

Donor-stabilised molecular Mg/Al-bimetallic hydrides.

Treatment of dimethylmagnesium with dimethylaluminum hydride in common ethereal solvents led to the bimetallic monomagnesium addition compounds [(do)xMg{(µ2-H)(AlMe3)}2] (do = thf, x = 4, do = Et2O, x = 3; do = dme, x = 2). Utilization of methyl tert-butyl ether (mtbe) resulted in alkyl/hydrido overexchange and formation of an 8-membered ring structure of composition [(mtbe)2Mg{(µ2-H)(AlMe3)(µ2-H)(µ2-H)(AlMe2)}]2. Salt metathesis of [(thf)4Mg{(µ2-H)(AlMe3)}2] with potassium 1,2,3,4,5-pentamethyl-cyclopentadienide (KCp*) gave [Cp*Mg{(µ2-H)(AlMe3)}(thf)2] featuring a rare isolable magnesium half-sandwich hydride complex. Furthermore, magnesium hydride-inherent reactivity was proven for [(thf)4Mg{(µ2-H)(AlMe3)}2] by the selective reduction of pyridine to 1,4-dihydropyridide (1,4-DHP) at ambient temperature and the hydromagnesiation of 1-hexene in the absence of any transition metal catalyst (low conversion).

Lewis-Acid Stabilized Organoimide Complexes of Divalent Samarium, Europium, and Ytterbium.

Discrete organoimide complexes of the divalent rare-earth metals samarium, europium, and ytterbium are reported. Tandem salt metathesis-protonolysis reactions using LnII bis(tetramethylaluminate) precursors [Ln(AlMe4 )2 ]n and monopotassium salts of 2,6-diisopropylaniline (H2 NDipp) and triphenylsilylamine prove viable and efficient protocols. Depending on the ionic radius of the LnII metal centers and the steric demand of the imido carbon backbone, mono- and dilanthanide arrangements of general composition [(thf)x Ln(NR)(AlMe3 )]y (Ln=Sm, Eu, Yb; R=Dipp, SiPh3 ) are found in the solid state. Complex formation and stabilization is achieved by coordination of the Lewis acid AlMe3 , which also prevents formation of higher aggregated species. The feasibility of redox chemistry is shown with the plumbocene derivative Cp*2 Pb, providing access to the corresponding monomeric LnIII half-sandwich complexes [Cp*Ln(NR)(AlMe3 )(thf)2 ] (Ln=Sm, Yb).

Magnesium Stung by Nonclassical Scorpionate Ligands: Synthesis and Cone-Angle Calculations.

A series of tris(pyrazolyl)alkane (RCTp) scorpionate ligands of the type RCTp3-R' (R=Me, nBu, SiMe3 ; R'=H, Me, Ph, iPr, tBu) were synthesized and their ability to coordinate methylmagnesium moieties was examined. The reaction of Mg(AlMe4 )2 with neutral proligands HCTp3-Ph or Me3 SiCTp3-Me , containing a non-innocent backbone methine moiety, led to deprotonation/rearrangement and SiMe3 /AlMe3 exchange to afford [(Me3 AlCTp3-Ph )2 Mg] and [(Me3 AlCTp3-Me )Mg(AlMe4 )], respectively, with monoanionic tripodal ligands. Treatment of sterically less demanding RCTp3-R' with Mg(AlMe4 )2 produced isostructural dicationic "metal-in-a-box" complexes of the type [(RCTp3-R' )2 Mg][AlMe4 ]2 (R=Me, nBu; R'=H, Me). Utilization of the superbulky ligands MeCTp3-Ph and MeCTp3-tBu gave monocationic complexes [(MeCTp3-Ph )MgMe][AlMe4 ] and [(MeCTp3-tBu )MgMe][Al2 Me7 ] as separated ion pairs. The reaction of Mg(AlMe4 )2 with nBuCTp3-Ph led to the formation of the dimagnesium complex [{(nBuCTp3-Ph )Mg(AlMe4 )}2 (µ-CH3 )], which features a bridging methyl moiety and terminal η1 -coordinated tetramethylaluminato ligands. Isopropyl-substituted ligand MeCTp3-iPr emerged from further fine-tuning of the steric and electronic parameters and, upon reaction with Mg(AlMe4 )2 , gave (MeCTp3-iPr )Mg(AlMe4 )2 ; this represents the first example of a magnesium bis(alkyl) complex with an intact RCTp3-R' ligand. The exact ligand cone angles Θ° of all magnesium complexes were determined according to the mathematical analysis developed by Allen et al. [J. Comput. Chem. 2013, 34, 1189-1197].

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.

Dimethylmagnesium revisited.

A compilation of solvent-free homometallic methyl compounds of the type MMex (x = 1-6) is provided and categorised according to their method of characterisation (powder or single crystal X-ray diffraction, gas electron diffraction (GED), reactivity, unconfirmed). Recrystallisation of polymeric [MgMe2]n from excess GaMe3 led to the formation of highly pure [MgMe2]n suitable for single crystal X-ray crystallographic studies. Transient Mg(GaMe4)2 could be detected in excess GaMe3 by NMR spectroscopy, but its isolation as Mg(GaMe4)2 failed. On one occasion tetrameric [Mg(GaMe4)(OMe)]4 could be isolated as a minor co-product. The formation of single-crystalline [MgMe2]n from a saturated ethereal solution could be reproduced as reported earlier by Coates et al. Assessing the reactivity of potassium methoxide methanol adduct toward Mg(AlMe4)2, the protonolysis reaction with MeOH gave unprecedented [Mg(AlMe4){Al(OMe)2Me2}]2 featuring one 8-membered [MgOAlO]2 metalloxane ring and two 4-membered metallacycles.

Dimethylcalcium.

The salt metathesis reaction between homoleptic calcium bis(trimethylsilyl)amide [Ca{N(SiMe3)2}2]2 and "halide-free" methyllithium allowed for the isolation of X-ray-amorphous dimethylcalcium [CaMe2]n in good yields and purities. The formation of [CaMe2]n was proven by microanalysis and NMR/FTIR spectroscopic methods as well as a series of derivatization reactions. Despite slowly decomposing thf, [CaMe2]n could be crystallized from chilled thf solutions as the heptametallic adduct [(thf)10Ca7Me14]. Reaction of [CaMe2]n with CaI2 in thf led to the dimeric complex [(thf)3Ca(Me)(I)]2, whereas in tetrahydropyran (thp) the trinuclear complex [(thp)5Ca3(Me)5(I)] was obtained, both representing the first crystallographically characterized heavy-Grignard compounds with methyl groups as the hydrocarbyl ligand. While protonolysis of [CaMe2]n with the superbulky proligand HTptBu,Me in nonpolar solvents gave homoleptic (TptBu,Me)2Ca, reaction in donor solvents (thf, thp) afforded the monomeric complexes [(TptBu,Me)Ca(Me)(thf)] and [(TptBu,Me)Ca(Me)(thp)], which are the first examples bearing terminal Ca-CH3 functionalities. Grignard-type nucleophilic methyl-group transfer to hexamethylacetone gave access to the dimeric alkoxide complexes [(thf)Ca(OCtBu2Me)2]2 and [(tBu2CO)Ca(µ2-OCtBu2Me)3Ca(OCtBu2Me)]. Finally, addition of the Lewis acid GaMe3 to [CaMe2]n led to the corresponding tetramethylgallate compound [Ca(GaMe4)2]n.