Syntheses and structure of dimeric yttrium tris [bis(trimethylsilyl) phosphanide]; X-ray structures of [(thf)LiCl·(thf)2LiPtBu2]2 and Y[CH(SiMe3)2]3

Isolation and Electronic Structures of Lanthanide(II) Bis(trimethylsilyl)phosphide Complexes

While lanthanide (Ln) silylamide chemistry is mature, the corresponding silylphosphide chemistry is underdeveloped, with [Sm{P(SiMe3)2}{μ-P(SiMe3)2}3Sm(THF)3] being the sole example of a structurally authenticated Ln(II) silylphosphide complex. Here, we expand the Ln(II) {P(SiMe3)2} chemistry through the synthesis and characterization of nine complexes. The dinuclear "ate" salt-occluded complexes [{Ln[P(SiMe3)2]3(THF)}2(μ-I)K3(THF)] (1-Ln; Ln = Sm, Eu) and polymeric "ate" complex [KYb{P(SiMe3)2}3{μ-K[P(SiMe3)2]}2]∞ (2-Yb) were prepared by the respective salt metathesis reactions of parent [LnI2(THF)2] (Ln = Sm, Eu, Yb) with 2 or 3 equiv of K{P(SiMe3)2} in diethyl ether. The separate treatment of these complexes with either pyridine or 18-crown-6 led to the formation of the mononuclear solvated adducts trans-[Ln{P(SiMe3)2}2(py)4] (3-Ln; Ln = Sm, Eu, Yb) and [Ln{P(SiMe3)2}2(18-crown-6)] (4-Ln; Ln = Sm, Eu, Yb), with concomitant loss of K{P(SiMe3)2}. The complexes were characterized by a combination of NMR, electron paramagnetic resonance (EPR), attenuated total reflectance infrared (ATR-IR), electronic absorption and emission spectroscopies, elemental analysis, SQUID magnetometry, and single crystal X-ray diffraction. We find that these complexes contrast with those of related Ln(II) bis(silyl)amide complexes due to differences in ligand donor atom hardness and ligand steric requirements from Ln-P bonds being longer than Ln-N bonds. This leads to higher coordination numbers, shorter luminescence lifetimes, and smaller easy-axis magnetic anisotropy parameters.

In situ generation of organocalcium compounds for a calcium-based Grignard-type chemistry

Organocalcium compounds are highly reactive reagents whereas the alkaline-earth metal itself is a weak reductant. This discrepancy hampered a straightforward development of an organocalcium chemistry. The in situ generation of the highly reactive organocalcium reagent and immediate metalation of a H-acidic compound (iGMM) or addition onto a polar π-system (iGAM) offers not only a loophole to organocalcium reagents but opens the entry to a rich organic chemistry of this non-toxic and globally abundant alkaline-earth metal, being competitive to the organolithium chemistry.

Scandium bis(trimethylsilyl)methyl complexes revisited: extending the 45Sc NMR chemical shift range and a new structural motif of Li[CH(SiMe3)2]

Depending on the molar ratio employed, the reaction of ScCl₃(thf)₃ with Li[CH(SiMe₃)₂] afforded the bis and tris(alkyl) ate complexes [Sc{CH(SiMe₃)₂}₂(μ-Cl)₂Li(thf)₂]₂ and Sc[CH(SiMe₃)₂]₃(μ-Cl)Li(thf)₃, respectively, in moderate yields. Treatment of these mixed alkyl/chlorido complexes with MeLi gave the mixed alkyl complexes [Sc{CH(SiMe₃)₂}₂(μ-Me)₂Li(thf)₂]₂ and Sc[CH(SiMe₃)₂]₃(μ-Me)Li(thf)₃. Aiming at homoleptic {Sc[CH(SiMe₃)₂]₃} both of the mixed [CH(SiMe₃)₂]/Me complexes were treated with AlMe₃. Although LiAlMe₄ separation occurred, aluminium complex Al[CH(SiMe₃)₂]Me₂(thf) was the only isolable crystalline complex. Ate complexes [Sc{CH(SiMe₃)₂}₂(μ-Me)₂Li(thf)₂]₂ and [Sc(CH₂SiMe₃)₄][Li(thf)₄] revealed the maximum downfield ⁴⁵Sc NMR chemical shifts of 888.0 and 933.4 ppm, respectively, reported to date. The synthesis of putative {Sc[CH(SiMe₃)₂]₃} was also attempted via the aryloxide route applying complexes Sc(OC₆H₂tBu₂-2,6-Me-4)₃ and [Sc(OC₆H₃iPr₂-2,6)₃]₂ along with Li[CH(SiMe₃)₂] but the outcome was inconclusive. Instead, a cyclic octamer was found for Li[CH(SiMe₃)₂] in the solid state.

Recent developments in the field of organic heterobimetallic compounds of the alkaline-earth metals

Heterobimetallic compounds of the alkaline-earth metals show a wide structural variety with strongly differing reactivity patterns. The combination of magnesium and alkali metal amides yields cyclic molecules with an extreme high reactivity which often are considered as "inverse crowns" with the metal atoms as coordination sites for Lewis bases. In other metallates of the alkaline-earth metals an activation of alkyl groups succeeds. In alkaline-earth metal zincates an inverse coordination of the type M(2)[(mu-R)(2)ZnR](2) is observed and the alkyl groups are in bridging positions between zinc and the s-block metals thus forming a very reactive M-C-Zn three-center-two-electron bond. Furthermore, the metals of the carbon group form alkaline-earth metal-silicon, -germanium and -tin bonds or, in the presence of very strong Lewis bases, even solvent-separated ion pairs. For electronegative substituents at tin an inverse coordination mode such as M[(mu-R)(2)SnR](2) is observed.

Cationic Rare-Earth Metal Trimethylsilylmethyl Complexes Supported by THF and 12-Crown-4 Ligands: Synthesis and Structural Characterization

To expand the limited range of rare-earth metal cationic alkyl complexes known, a series of mono- and dicationic trimethylsilylmethyl complexes supported by THF and 12-crown-4 ligands with [BPh4]-, [BPh3(CH2SiMe3)]-, [B(C6F5)4]-, [B(C6F5)3(CH2SiMe3)]-, and [Al(CH2SiMe3)4]- anions were prepared from corresponding neutral precursors [Ln(CH2SiMe3)3Ln] (Ln = Sc, Y, Lu; L = THF, n = 2 or 3; L = 12-crown-4, n = 1) as solvent-separated ion pairs. The syntheses of the monocationic derivatives [Ln(CH2SiMe3)2(12-crown-4)n(THF)m]+[A]- are all high yielding and proceed rapidly in THF solution at room temperature. A "one pot" procedure using the neutral species directly for the syntheses of a number of lutetium and yttrium dicationic derivatives [Ln(CH2SiMe3)(12-crown-4)n(THF)m]2+[A]-2 with a variety of different anions, a class of compounds previously limited to just a few examples, is presented. When BPh3 is used to generate the ion triple, the presence of 12-crown-4 is required for complete conversion. Addition of a second equiv of 12-crown-4 and a third equiv of [NMe2PhH]+[B(C6F5)4]- abstracts a third alkyl group from [Ln(CH2SiMe3)(12-crown-4)2(THF)x]2+[B(C6F5)4]-2 (Ln = Y, Lu). X-ray crystallography and variable-temperature (VT) NMR spectroscopy reveal a structural diversity within the known series of neutral 12-crown-4 supported tris(trimethylsilylmethyl) complexes [Ln(CH2SiMe3)3(12-crown-4)] (Ln = Sc, Y, Sm, Gd-Lu) in the solid and solution states. The X-ray structure of [Sc(CH2SiMe3)3(12-crown-4)] exhibits incomplete 12-crown-4 coordination. VT NMR spectroscopy indicates fluxional 12-crown-4 coordination on the NMR time scale. X-ray crystallography of only the second structurally characterized dicationic rare-earth metal alkyl complex [Y(CH2SiMe3)(12-crown-4)(THF)3]2+[BPh4]-2 shows exocyclic 12-crown-4 coordination at the 8-coordinate metal center with well separated counteranions. 11B and 19F NMR spectroscopy of all mono- and dicationic rare-earth metal complexes reported demonstrate that the anions are symmetrical and noncoordinating on the NMR time scale. A series of trends within the 1H and 13C{1H} NMR resonances arising from the Ln-CH2 groups and, in the case of yttrium, the 1JYC coupling constants at the Y-CH2 group and the 89Y chemical shift values are discussed.

Synthetic and structural experiments on yttrium, cerium and magnesium trimethylsilylmethyls and their reaction products with nitriles; with a note on two cerium beta-diketiminates

The yttrium, cerium and magnesium bis(trimethylsilyl)methyls [Ln[CH(SiMe3)2]3][Ln = Y (1), Ce (2)], and the known compound Mg[[CH(SiMe3)2]2 (C) and [Mg(mu-Br)[CH(SiMe3)2](OEt2)]2 (D) formed the crystalline nitrile adducts [1(NCBut)2] (5), [2(NCPh)] (6), [C(NCR)2][R = But (8), Ph (9), C6H3Me2-2,6 (10)] and [Mg(mu-Br)[CH(SiMe3)2](NCR)]2 [R = But (11), Ph (12), C6H3Me2-2,6 (13)], rather than beta-diketiminato-metal insertion products. The beta-diketiminato-cerium complex [Ce[(N(SiMe3)C(C6H4But-4))2CH][N(SiMe3)2]2] (16) was obtained from [Ce[N(SiMe3)2]3] and the beta-diketimine H[[N(SiMe3)C(C6H4But-4)]2CH]]. The cerium alkyl 2 and [Ln[CH(SiMe3)(SiMe2OMe)]3][Ln = Y (3), Ce (4)] were obtained from the appropriate lithium alkyl precursor and [Ce(OC6H2But2-2,6-Me-4)3] or LnCl3, respectively. Heating complex 3 with benzonitrile in toluene afforded 2,2-dimethyl-4,6-diphenyl-5-trimethylsilyl-1,3-diaza-2-silahexa-1,3-diene (7), a member of a new class of heterocycles. The X-ray structures of the crystalline compounds, D, [Mg[CH(SiMe3)2]2(OEt2)2], the known [Ce(Cl)[(N(SiMe3)C(Ph))2CH]2] (E) and 16 are reported. The cerium alkyl (like 1) has one close Ce...C contact for each ligand, attributed to a gamma-C-Ce agostic interaction. The Ln alkyls and have a trigonal prismatic arrangement of the chelating ligands (each of the same chirality at Calpha) around the metal. In an arene solution at 313 K exists as two isomers, as evident from detailed NMR spectroscopic experiments.