Dominance of Cyclobutadienyl Over Cyclopentadienyl in the Crystal Field Splitting in Dysprosium Single-Molecule Magnets.

Replacing a monoanionic cyclopentadienyl (Cp) ligand in dysprosium single-molecule magnets (SMMs) with a dianionic cyclobutadienyl (Cb) ligand in the sandwich complexes [(η -Cb'''')Dy(η -C Me Bu)(BH )] (1), [(η -Cb'''')Dy(η -Pn )K(THF)] (2) and [(η -Cb'''')Dy(η -Pn )] (3) leads to larger energy barriers to magnetization reversal (Cb''''=C (SiMe ) , Pn =1,4-di(tri-isopropylsilyl)pentalenyl). Short distances to the Cb'''' ligands and longer distances to the Cp ligands in 1-3 are consistent with the crystal field splitting being dominated by the former. Theoretical analysis shows that the magnetic axes in the ground Kramers doublets of 1-3 are oriented towards the Cb'''' ligands.

Magnetic hysteresis up to 80 kelvin in a dysprosium metallocene single-molecule magnet.

Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(Cp )Dy(Cp*)] (Cp , penta-iso-propylcyclopentadienyl; Cp pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures.

Rare-Earth Cyclobutadienyl Sandwich Complexes: Synthesis, Structure and Dynamic Magnetic Properties.

The potassium cyclobutadienyl [K {η -C (SiMe ) }] (1) reacts with MCl (THF) (M=Y, Dy) to give the first rare-earth cyclobutadienyl complexes, that is, the complex anions [M{η -C (SiMe ) }{η -C (SiMe ) -κ-(CH SiMe }] , (2 ), as their dipotassium salts. The tuck-in alkyl ligand in 2 is thought to form through deprotonation of the "squarocene" complexes [M{η -C (SiMe ) } ] by 1. Complex 2 is a single-molecule magnet, but with prominent quantum tunneling.

Cyclopentadienyl Ligands in Lanthanide Single-Molecule Magnets: One Ring To Rule Them All?

The discovery of materials capable of storing magnetic information at the level of single molecules and even single atoms has fueled renewed interest in the slow magnetic relaxation properties of single-molecule magnets (SMMs). The lanthanide elements, especially dysprosium, continue to play a pivotal role in the development of potential nanoscale applications of SMMs, including, for example, in molecular spintronics and quantum computing. Aside from their fundamentally fascinating physics, the realization of functional materials based on SMMs requires significant scientific and technical challenges to be overcome.

Single-molecule magnet properties of a monometallic dysprosium pentalene complex.

The pentalene-ligated dysprosium complex [(η8-Pn†)Dy(Cp*)] (1Dy) (Pn† = [1,4-(iPr3Si)2C8H4]2-) and its magnetically dilute analogue are single-molecule magnets, with energy barriers of 245 cm-1. Whilst the [Cp*]- ligand in 1Dy provides a strong axial crystal field, the overall axiality of this system is attenuated by the unusual folded structure of the [Pn†]2- ligand.

Activation of C-H bonds by rare-earth metallocene-butyl complexes.

The stable metallocene-butyl complexes [(Cp)M(Bu)] (M = Y, Dy) were synthesized and their reactivity towards to ferrocene and bulky N-heterocyclic carbenes investigated. Selective mono-deprotonation of ferrocene and a benzylic methyl group of IMes were observed, whereas a control reaction of (Cp)M with IMes resulted in a normal-to-abnormal NHC rearrangement.

A Dysprosium Metallocene Single-Molecule Magnet Functioning at the Axial Limit.

Abstraction of a chloride ligand from the dysprosium metallocene [(Cp ) DyCl] (1 Cp =1,2,4-tri(tert-butyl)cyclopentadienide) by the triethylsilylium cation produces the first base-free rare-earth metallocenium cation [(Cp ) Dy] (2 ) as a salt of the non-coordinating [B(C F ) ] anion. Magnetic measurements reveal that [2 ][B(C F ) ] is an SMM with a record anisotropy barrier up to 1277 cm (1837 K) in zero field and a record magnetic blocking temperature of 60 K, including hysteresis with coercivity. The exceptional magnetic axiality of 2 is further highlighted by computational studies, which reveal this system to be the first lanthanide SMM in which all low-lying Kramers doublets correspond to a well-defined M value, with no significant mixing even in the higher doublets.

A three-coordinate iron-silylene complex stabilized by ligand-ligand dispersion forces.

The structural and bonding properties of a three-coordinate N-heterocyclic silyene (NHSi) complex of the iron(ii) amide [Fe{N(SiMe3)2}2] are reported. Computational studies reveal that dispersion forces between the amido SiMe3 substituents and the isopropyl substituents on the NHSi ligand significantly enhance the stability of the complex, along with Fe-to-Si π-backbonding.

Strong Exchange Coupling in a Trimetallic Radical-Bridged Cobalt(II)-Hexaazatrinaphthylene Complex.

Reducing hexaazatrinaphthylene (HAN) with potassium in the presence of 18-c-6 produces [{K(18-c-6)}HAN], which contains the S=1/2 radical [HAN](.-) . The [HAN](.

Iron- and Cobalt-Catalyzed Synthesis of Carbene Phosphinidenes.

In the presence of stoichiometric or catalytic amounts of [M{N(SiMe3 )2 }2 ] (M=Fe, Co), N-heterocyclic carbenes (NHCs) react with primary phosphines to give a series of carbene phosphinidenes of the type (NHC)⋅PAr. The formation of (IMe4 )⋅PMes (Mes=mesityl) is also catalyzed by the phosphinidene-bridged complex [(IMe4 )2 Fe(μ-PMes)]2 , which provides evidence for metal-catalyzed phosphinidene transfer.

Open-shell doublet character in a hexaazatrinaphthylene trianion complex.

Three-electron reduction of hexaazatrinaphthylene (HAN) with a magnesium(I) reagent leads to [(HAN){Mg(nacnac)}3] (1), containing a [HAN](3-) ligand with a spin of S = 1/2. Ab initio calculations reveal that the [HAN](3-) ligand in 1 has a ground-state wave function with multiconfigurational properties, and can be described as a triradicaloid species with a small amount of open-shell doublet character.

Molecular and electronic structures of donor-functionalized dysprosium pentadienyl complexes.

Two dysprosium complexes, [(C5H4Me)2Dy(L(1))] (3) and [(L(1))Dy(μ-Cl)3{Li(tmeda)}]2 (4), with amino-functionalized pentadienyl ligands L(1) are described. Crystallographic studies of 3 and 4 show that the pendant amino group influences the pentadienyl conformation and the ligand hapticity. Electronic structure calculations reveal that L(1) has a strong influence on the orientation of the main magnetic axis of the ground Kramers doublets in 3 and 4.

Carbene rearrangements in three-coordinate N-heterocyclic carbene complexes of cobalt(II) bis(trimethylsilyl)amide.

The synthesis and molecular structures of the cobalt(II) N-heterocyclic carbene (NHC) complexes [(NHC)Co{N(SiMe3)2}2], where NHC = 1,3-bis(diisopropylphenyl)imidazolylidene (IPr) (6), 1,3-bis(mesityl)imidazolylidene (IMes) (7), and 1,3-bis(tert-butyl)imidazol-2-ylidene (I(t)Bu) (8), are reported. Complexes 6-8 are rare examples of three-coordinate cobalt NHC complexes. The steric congestion within the coordination environments of the cobalt(II) centers in 6 and 7 results in the longest Co-C(NHC) distances currently known.

Catalytic bond forming reactions promoted by amidinate, guanidinate and phosphaguanidinate compounds of magnesium.

The synthesis and catalytic properties of a series of magnesium compounds consisting of monoanionic, N,N'-chelating ligands (N∩N = amidinates, guanidinates, phosphaguanidinates) is reported. The compounds were synthesized by (i) insertion of a carbodiimide into an existing Mg-C or Mg-N bond, or (ii) protonolysis of an organomagnesium compound by a neutral pre-ligand. Structural analyses of mono- or bis-(chelate) compounds with general formula Mg(N∩N)X(L)n and Mg(N∩N)2(L)n (X = halide, aryloxide, amide; L = Et2O, THF; n = 0, 1 or 2) have been performed and the influence that the ligand substituent patterns have on the solid-state structures has been probed.

Low-coordinate bismuth cations.

Chloride abstraction from the diamido-bismuth compound Bi(Me2Si{NAr}2)Cl (1, Ar = 2,6-i-Pr2C6H3) using MCl3 (M = Al, Ga) is a facile route to cationic species. Stoichiometric reactions afford the tetrachlorometallate salts [Bi(Me2Si{NAr}2)][MCl4] (2a, M = Al; 3a, M = Ga), whereas reaction with 0.5 equiv of the group 13 reagent gives the μ-chlorido bridged cations [{Bi(Me2Si{NAr}2)}2(μ-Cl)][MCl4] (2b, M = Al; 3b, M = Ga).

Normal-to-abnormal rearrangement and NHC activation in three-coordinate iron(II) carbene complexes.

The 'normal' three-coordinate iron-NHC complex [(IPr)Fe(N'')2] (N″ = N(SiMe3)2) rearranges to its abnormal NHC analogue [(aIPr)Fe(N″)2] (6) on heating, providing a rare abnormal iron-aNHC complex, and the first such three-coordinate complex. The tert-butyl-substituted complex [(I(t)Bu)Fe(N″)2] (4) undergoes a thermal decomposition that has not previously been observed in iron-NHC chemistry, resulting in the bis(imidazole) complex [((t)BuIm)2Fe(N″)2] (7). A mechanism that involves consecutive C-H and C-N activation is proposed to account for the formation of 7.

Synthetic and catalytic intermediates in a magnesium promoted Tishchenko reaction.

Magnesium-aryloxide and -amide compounds supported by amidinate ligands are accessible in two-steps from a suitable Grignard reagent. Both species are active for the dimerization of benzaldehyde. The slower initiation by the aryloxide was exploited in the isolation of a bis-mesitylaldehyde adduct.

Hydroformylation by Pt-Sn compounds from N-heterocyclic stannylenes.

[(Me(2)Si{NAr}(2))-κ(2)N,N']Sn, reacts with PtCl(2)(L(2)) and [PtCl(μ-Cl)(L)](2) to afford products containing Pt-Sn bonds. In the absence of supporting ligands L, coordination of the stannylene and rearrangement to a structurally unique PtSn(2)N(2)Si metallacycle occurs. The hydroformylation activity of a representative Pt-Sn compound is investigated.

Bicyclic guanidinate compounds of magnesium and their activity as pre-catalysts in the Tishchenko reaction.

A synthetic route to magnesium guanidinate compounds that avoids ligand redistribution is reported; selected derivatives are active pre-catalysts in the dimerization of aldehydes.