Large Spin‐Relaxation Barriers for the Low‐Symmetry Organolanthanide Complexes [Cp*2Ln(BPh4)] (Cp*=pentamethylcyclopentadienyl; Ln=Tb,Dy)

Single‐molecule magnets comprising one spin center represent a fundamental size limit for spin‐based information storage. Such an application hinges upon the realization of molecules possessing substantial barriers to spin inversion. Axially symmetric complexes of lanthanides hold the most promise for this due to their inherently high magnetic anisotropies and low tunneling probabilities. Herein, we demonstrate that strikingly large spin reversal barriers of 216 and 331 cm^?1 can also be realized in low‐symmetry lanthanide tetraphenylborate complexes of the type [Cp*₂Ln(BPh₄)] (Cp*=pentamethylcyclopentadienyl; Ln=Tb ( 1 ) and Dy ( 2 )). The dysprosium congener showed hysteretic magnetization data up to 5.3 K. Further studies of the magnetic relaxation processes of 1 and 2 under applied dc fields and upon dilution within a matrix of [Cp*₂Y(BPh₄)] revealed considerable suppression of the tunneling pathway, emphasizing the strong influence of dipolar interactions on the low‐temperature magnetization dynamics in these systems.     

Facile Access to Transition‐Metal–Carbonyl Complexes with an Amidinate‐Stabilized Chlorosilylene Ligand

Three transition‐metal–carbonyl complexes [V( L )(CO)₃(Cp)] ( 1 ), [Co( L )(CO)(Cp)] ( 2 ), and [Co( L₂ )(CO)₃]⁺[CoCO)₄]^? ( 3 ), each containing stable N‐heterocyclic‐chlorosilylene ligands ( L ; L =PhC(NtBu)₂SiCl) were synthesized from [V(CO)₄(Cp)], [Co(CO)₂(Cp)], and Co₂(CO)₈, respectively. Complexes 1 , 2 , 3 were characterized by NMR and IR spectroscopy, EI‐MS spectrometry, and elemental analysis. The molecular structures of compounds 1 , 2 , 3 were determined by single‐crystal X‐ray diffraction.     

Dysprosiacarboranes as Organometallic Single‐Molecule Magnets

The dicarbollide ion, nido‐C₂B₉H₁₁^2? is isoelectronic with cyclopentadienyl. Herein, we make dysprosiacarboranes, namely [(C₂B₉H₁₁)₂Ln(THF)₂][Na(THF)₅] (Ln=Dy, 1Dy ) and [(THF)₃(μ‐H)₃Li]₂[{η⁵‐C₆H₄(CH₂)₂C₂B₉H₉}Dy{η²:η⁵‐C₆H₄(CH₂)₂C₂B₉H₉}₂Li] 3Dy and show that dicarbollide ligands impose strong magnetic axiality on the central Dy^III ion. The effective energy barrier (U_eff) for the loss of magnetization can be varied by the substitution pattern on the dicarbollide. This finding is demonstrated by comparing complexes of nido‐C₂B₉H₁₁^2? and nido‐[o‐xylylene‐C₂B₉H₉]^2?, which show a U_eff of 430(5) K and 804(7) K, respectively. The blocking temperature defined by the open hysteresis temperature of 3Dy reaches 6.8 K. Moreover, the linear complex [Dy(C₂B₉H₁₁)₂]^? is predicted to have comparable properties with the linear [Dy(Cp^Me3)₂]⁺ complex. As such, carboranyl ligands and their derivatives may provide a new type of organometallic ligand for high‐performance single‐molecule magnets.     

Structures and magnetic relaxation properties of cyclopentadienyl/β-diketonate/trispyrazolylborate hybridized dysprosium single-molecule magnets

The combination of cyclopentadiene, β-diketonate and tripyrazoylborate ligands with dysprosium ion afforded five mononuclear compounds: [(Cp)₂Dy(Tp*)] (1Dy), [(Cp)Dy(Tp*)Cl(THF)] (2Dy), [(Cp)Dy(Tp)Cl(THF)] (3Dy), [(DBM)Dy(Tp)Cl(THF)] (4Dy), [{(Tp)Dy(DBM)₂(H₂O)}·THF] (5Dy) (Cp = cyclopentadiene; Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; Tp = hydrotris(1-pyrazolyl)borate; DBM = dibenzoylmethanoate). Magnetic study revealed that 1Dy and 3Dy exhibited typical butterfly-type hysteresis. AC susceptibility study combined with ab initio calculations indicated that the magnetic relaxation behaviors of 1Dy–4Dy were governed by the Orbach and Raman processes under applied DC field. Moreover, 3Dy showed two-step magnetic relaxation, which was attributed to the static disordering of the coordinated THF molecule. Magnetic anisotropy analysis indicated that it was the relative strength of the interactions between Dy^III and surrounding ligands that determined the orientation of the magnetic easy axis.     

Synthesis and characterization of ethylthioethylcyclopentadienyl organolanthanide complexes: CpLnCl (Ln=Gd,Dy), Cp2LnCpTh (Ln=Yb,Sm, Dy,Y) and CpThErCl2·2THF

Six new ethylthioethylcyclopentadienyl containing organolanthanide complexes CpLnCl [Ln=Gd (1), Dy (2)] and Cp₂LnCp^Th [Cp=C₅H₅, Ln=Yb (3), Sm (4), Dy (5), Y (6)] were synthesized by the reaction of ethylthioethyl‐cyclopentadienyl (Cp^Th) sodium salt with LnCl₃ or Cp₂LnCl in THF. Complexes 1–6 were characterized by elemental analyses, infrared and mass spectroscopies. The molecular structures of complexes 1–3 were also determined by the X‐ray single crystal diffraction. The results show that the side‐chain sulfur atom on the ethylthioethylcyclopentadienyl ring can form intramolecular chelating coordination to the central lanthanide ion, improving the stability of organolanthanide complexes and reducing the number of coordinated THF molecules.     

Chalkogen‐Derivate der Halbsandwich‐Wolfram(V)‐Komplexe Cp*WCl4 und Cp*WCl4(PMe3). Röntgen‐Kristallstrukturanalysen von anti‐[Cp*W(Se)(μ‐Se)]2 und Cp*W(S)2(OMe)

Chalcogen Derivatives of the Halfsandwich Tungsten(V) Complexes Cp*WCl₄ and Cp*WCl₄(PMe₃). X‐Ray Crystal Structure Analyses of anti ‐[Cp*W(Se)(μ‐Se)]₂ and Cp*W(S)₂(OMe) The chalcogenation of Cp*WCl₄ ( 1 ) by E(SiMe₃)₂ (E = S, Se) and Te(SiMe₂^tBu)₂ in chloroform solution leads to dimeric products of the type anti‐[Cp*W(E)(μ‐E)]₂ (E = S ( 3 a ), Se ( 3 b ) and Te ( 3 c )). An X‐ray structure determination of 3 b indicates a centrosymmetric molecule containing a planar W(μ‐Se)₂W ring, the W–W distance (297.9(1) pm) corresponds to a single bond. In the presence of air the two terminal chalcogenido ligands (E) in 3 a – c are stepwise replaced by oxido ligands (O) to give [Cp*W(O)(μ‐E)]₂ (E = S ( 5 a ), Se ( 5 b ) and Te ( 5 c )) in quantitative yields. The reaction of Cp*WCl₄ with H₂S or ammonium polysulfide, (NH₄)₂S_x (x ∼ 10), leads to Cp*W(S)₂Cl ( 6 a ); the corresponding methoxy derivative, Cp*W(S)₂OCH₃ ( 9 a ), has been characterized by an X‐ray structure analysis. On the other hand, the reaction of Cp*WCl₄(PMe₃) ( 2 ) with sodium tetrasulfide, Na₂S₄, in dimethylformamide solution gives a mixture of mononuclear Cp*W(S)(S₂)Cl ( 8 a ), dinuclear [Cp*W(S)(μ‐S)]₂ ( 3 a ) and a trinuclear side‐product of composition Cp*₂W₃S₇ ( 13 a ). Terminal sulfido ligands are replaced by terminal oxido ligands in solution in the presence of oxygen. Thus, 6 a is stepwise converted into Cp*W(O)(S)Cl ( 10 a ) and CpW(O)₂Cl ( 12 a ), whereas 8 a gives Cp*W(O)(S₂)Cl ( 11 a ) and 13 a leads to Cp*₂W₃(O)S₆ ( 14 a ). The disulfido complexes 8 a and 11 a are desulfurized by triphenylphosphane to give 6 a and 10 a . The new complexes have been characterized by their IR and NMR spectra and by mass spectrometry.     

Versatile reactivity of half-sandwich Ir and Rh complexes toward carboranylamidinates and their derivatives: synthesis, structure, and catalytic activity for norbornene polymerization

Synthesis, structure, and reactivity of carboranylamidinate‐based half‐sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ‐Cl)Cl}₂] (M=Ir, Rh; Cp*=η⁵‐C₅Me₅) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18‐electron complexes [Cp*IrCl(Cab^N‐DIC)] ( 1 a ; Cab^N‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHiPr)]), [Cp*RhCl(Cab^N‐DIC)] ( 1 b ), and [Cp*RhCl(Cab^N‐DCC)] ( 1 c ; Cab^N‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHCy)]). A series of 16‐electron half‐sandwich Ir and Rh complexes [Cp*Ir(Cab^N′‐DIC)] ( 2 a ; Cab^N′‐DIC=[iPrN?C(closo‐1,2‐C₂B₁₀H₁₀)(NiPr)]), [Cp*Ir(Cab^N′‐DCC)] ( 2 b , Cab^N′‐DCC=[CyN?C(closo‐1,2‐C₂B₁₀H₁₀)(NCy)]), and [Cp*Rh(Cab^N′‐DIC)] ( 2 c ) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab^N,S‐DIC)], [Cp*M(Cab^N,S‐DCC)] (M=Ir 3 a , 3 b ; Rh 3 c , 3 d ), formed through BH activation, are obtained by reaction of [{Cp*MCl₂}₂] with carboranylamidinate sulfides [RN?C(closo‐1,2‐C₂B₁₀H₁₀)(NHR)]S^? (R=iPr, Cy), which can be prepared by inserting sulfur into the C? Li bond of lithium carboranylamidinates. Iridium complex 1 a shows catalytic activities of up to 2.69×10⁶ g_PNB ${{\rm{mol}}_{{\rm{Ir}}}^{ - {\rm{1}}} }Synthesis, structure, and reactivity of carboranylamidinate-based half-sandwich iridium and rhodium complexes are reported for the first time. Treatment of dimeric metal complexes [{Cp*M(μ-Cl)Cl}(2)] (M = Ir, Rh; Cp* = η(5)-C(5)Me(5)) with a solution of one equivalent of nBuLi and a carboranylamidine produces 18-electron complexes [Cp*IrCl(Cab(N)-DIC)] (1?a; Cab(N)-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NHiPr)]), [Cp*RhCl(Cab(N)-DIC)] (1?b), and [Cp*RhCl(Cab(N)-DCC)] (1?c; Cab(N)-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10))(NHCy)]). A series of 16-electron half-sandwich Ir and Rh complexes [Cp*Ir(Cab(N')-DIC)] (2?a; Cab(N')-DIC = [iPrN=C(closo-1,2-C(2)B(10)H(10))(NiPr)]), [Cp*Ir(Cab(N')-DCC)] (2?b, Cab(N')-DCC = [CyN=C(closo-1,2-C(2)B(10)H(10)(NCy)]), and [Cp*Rh(Cab(N')-DIC)] (2?c) is also obtained when an excess of nBuLi is used. The unexpected products [Cp*M(Cab(N,S)-DIC)], [Cp*M(Cab(N,S)-DCC)] (M = Ir 3?a, 3?b; Rh 3?c, 3?d), formed through BH activation, are obtained by reaction of [{Cp*MCl(2)}(2)] with carboranylamidinate sulfides [RN=C(closo-1,2-C(2)B(10)H(10))(NHR)]S(-) (R = iPr, Cy), which can be prepared by inserting sulfur into the C-Li bond of lithium carboranylamidinates. Iridium complex 1?a shows catalytic activities of up to 2.69×10(6) g(PNB) mol(Ir)(-1) h(-1) for the polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst. Catalytic activities and the molecular weight of polynorbornene (PNB) were investigated under various reaction conditions. All complexes were fully characterized by elemental analysis and IR and NMR spectroscopy; the structures of 1?a-c, 2?a, b; and 3?a, b, d were further confirmed by single crystal X-ray diffraction.     

Chemistry of Diruthenium and Dirhodium Analogues of Pentaborane(9): Synthesis and Characterization of Metal N,S‐Heterocyclic Carbene and B‐Agostic Complexes

Building upon our earlier results on the synthesis of electron‐precise transition‐metal–boron complexes, we continue to investigate the reactivity of pentaborane(9) and tetraborane(10) analogues of ruthenium and rhodium towards thiazolyl and oxazolyl ligands. Thus, mild thermolysis of nido‐[(Cp*RuH)₂B₃H₇] ( 1 ) with 2‐mercaptobenzothiazole (2‐mbtz) and 2‐mercaptobenzoxazole (2‐mboz) led to the isolation of Cp*‐based (Cp*=η⁵‐C₅Me₅) borate complexes 5 a , b [Cp*RuBH₃L] ( 5 a : L=C₇H₄NS₂; 5 b : L=C₇H₄NOS)) and agostic complexes 7 a , b [Cp*RuBH₂(L)₂], ( 7 a : L=C₇H₄NS₂; 7 b : L=C₇H₄NOS). In a similar fashion, a rhodium analogue of pentaborane(9), nido‐[(Cp*Rh)₂B₃H₇] ( 2 ) yielded rhodaboratrane [Cp*RhBH(L)₂], 10 (L=C₇H₄NS₂). Interestingly, when the reaction was performed with an excess of 2‐mbtz, it led to the formation of the first structurally characterized N,S‐heterocyclic rhodium‐carbene complex [(Cp*Rh)(L₂)(1‐benzothiazol‐2‐ylidene)] ( 11 ) (L=C₇H₄NS₂). Furthermore, to evaluate the scope of this new route, we extended this chemistry towards the diruthenium analogue of tetraborane(10), arachno‐[(Cp*RuCO)₂B₂H₆] ( 3 ), in which the metal center possesses different ancillary ligands.     

Reactions of 2‐Substituted Pyridines with Titanocenes and Zirconocenes: Coupling versus Dearomatisation

Reactions of group 4 metallocene sources with 2‐substituted pyridines were investigated to evaluate their coordination type between innocent and reductive dearomatisation as well as to probe the possibility for couplings. A dependence on the cyclopentadienyl ligands (Cp, Cp*), the metals (Ti, Zr), and the substrates (2‐phenyl‐, 2‐acetyl‐, and 2‐iminopyridine) was observed. While 2‐phenylpyridine is barely reactive, 2‐acetylpyridine reacts vigorously with the Cp‐substituted complexes and selectively with their Cp* analogues. With 2‐iminopyridine, in all cases selective reactions were observed. In the isolated [Cp₂Ti], [Cp₂Zr], and [Cp*₂Zr] compounds the substrate coordinates by its pyridyl ring and the unsaturated side‐chain. Subsequently, the pyridine was dearomatised, which is most pronounced in the [Cp*₂Zr] compounds. Using [Cp*₂Ti] leads to the unexpected paramagnetic complexes [Cp*₂Ti^III(N,O‐acpy)] and [Cp*₂Ti^III(N,N′‐impy)]. This highlights the non‐innocent character of the pyridyl substrates.     

Half‐Sandwich Iridium Complexes Bearing a Diprotic Glyoxime Ligand: Structural Diversity Induced by Reversible Deprotonation

Synthesis and deprotonation reactions of half‐sandwich iridium complexes bearing a vicinal dioxime ligand were studied. Treatment of [{Cp*IrCl(μ‐Cl)}₂] (Cp*=η⁵‐C₅Me₅) with dimethylglyoxime (LH₂) at an Ir:LH₂ ratio of 1:1 afforded the cationic dioxime iridium complex [Cp*IrCl(LH₂)]Cl ( 1 ). The chlorido complex 1 undergoes stepwise and reversible deprotonation with potassium carbonate to give the oxime–oximato complex [Cp*IrCl(LH)] ( 2 ) and the anionic dioximato(2?) complex K[Cp*IrCl(L)] ( 3 ) sequentially. Meanwhile, twofold deprotonation of the sulfato complex [Cp*Ir(SO₄)(LH₂)] ( 4 ) resulted in the formation of the oximato‐bridged dinuclear complex [{Cp*Ir(μ‐L)}₂] ( 5 ). X‐ray analyses disclosed their supramolecular structures with one‐dimensional infinite chain ( 1 and 2 ), hexagonal open channels ( 3 ), and a tetrameric rhomboid ( 4 ) featuring multiple intermolecular hydrogen bonds and electrostatic interactions.     

Pentamethylcyclopentadienyl Halfsandwich Complexes of Vanadium and Tantalum with Amido‐, Imido‐ Nitrido‐ and Azido Ligands

Lithium bis(trimethylsilyl)amide, LiN(SiMe₃)₂, reacts with Cp*V(O)Cl₂ and Cp*TaCl₄ to give trimethylsilylimido complexes such as [Cp*V(NSiMe₃)(μ‐NSiMe₃)]₂ ( 7 ) and Cp*Ta(Cl)(NSiMe₃)[N(SiMe₃)₂] ( 19 ), respectively. Substitution of the chloro ligand in 19 by anionic groups leads to complexes with 3 different N‐containing ligands, Cp*Ta(X)(NSiMe₃)[N(SiMe₃)₂] (X = N₃ ( 20 ) or NPEt₃ ( 21 )). Complex 7 is air‐ and moisture‐sensitive, and several derivatives containing oxo and trimethylsiloxy ligands have been identified. Trimethylsilyl azide, Me₃Si‐N₃, is able to replace the oxygen‐containing ligands for azido ligands. The two complete series of bis(azido)‐bridged complexes, [Cp*VCl_n(N₃)_2‐n(μ‐N₃)]₂ (n = 2, 1, 0) and [Cp*TaCl_n(N₃)_3‐n(μ‐N₃)]₂(n = 3, 2, 1, 0), are accessible from the reactions of Cp*VCl₃ and Cp*TaCl₄, respectively, with trimethylsilyl azide. A bis(nitrido)‐bridged azido‐vanadium complex, [Cp*V(N₃)(μ‐N)]₂ ( 18 ), has also been obtained and structurally characterized.     

Zur Reaktivität von Titanocenkomplexen [Ti(Cp′)2(η2‐Me3SiC≡CSiMe3)] (Cp′ = Cp,Cp*) gegenüber Benzoldicarbonsäuren

On the Reactivity of Titanocene Complexes [Ti(Cp′)₂(η²‐Me₃SiC≡CSiMe₃)] (Cp′ = Cp, Cp*) towards Benzenedicarboxylic Acids Titanocene complexes [Ti(Cp′)₂(BTMSA)] ( 1a , Cp′ = Cp = η⁵‐C₅H₅; 1b , Cp′ = Cp* = η⁵‐C₅Me₅; BTMSA = Me₃SiC≡CSiMe₃) were found to react with iodine and methyl iodide yielding [Ti(Cp′)₂(μ‐I)₂] ( 2a / b ; a refers to Cp′ = Cp and b to Cp′ = Cp*), [Ti(Cp′)₂I₂] ( 3a / b ) and [Ti(Cp′)₂(Me)I] ( 4a / b ), respectively. In contrast to 2a , complex 2b proved to be highly moisture sensitive yielding with cleavage of HCp* [{Ti(Cp*)I}₂(μ‐O)] ( 7 ). The corresponding reactions of 1a / b with p‐cresol and thiophenol resulted in the formation of [Ti(Cp′)₂{O(p‐Tol)}₂] ( 5a / b ) and [Ti(Cp′)₂(SPh)₂] ( 6a / b ), respectively. Reactions of 1a and 1b with 1,n‐benzenedicarboxylic acids (n = 2–4) resulted in the formation of dinuclear titanium(III) complexes of the type [{Ti(Cp′)₂}₂{μ‐1,n‐(O₂C)₂C₆H₄}] (n = 2, 8a / b ; n = 3, 9a / b ; n = 4, 10a / b ). All complexes were fully characterized analytically and spectroscopically. Furthermore, complexes 7 , 8b , 9a ·THF, 10a / b were also be characterized by single‐crystal X‐ray diffraction analyses.     

2‐(2′‐Pyridyl)‐4,6‐diphenylphosphinine versus 2‐(2′‐Pyridyl)‐4,6‐diphenylpyridine: Synthesis,Characterization, and Reactivity of Cationic RhIII and IrIII Complexes Based on Aromatic Phosphorus Heterocycles

The bidentate P,N hybrid ligand 1 allows access for the first time to novel cationic phosphinine‐based Rh^III and Ir^III complexes, broadening significantly the scope of low‐coordinate aromatic phosphorus heterocycles for potential applications. The coordination chemistry of 1 towards Rh^III and Ir^III was investigated and compared with the analogous 2,2′‐bipyridine derivative, 2‐(2′‐pyridyl)‐4,6‐diphenylpyridine ( 2 ), which showed significant differences. The molecular structures of [RhCl(Cp*)( 1 )]Cl and [IrCl(Cp*)( 1 )]Cl (Cp*=pentamethylcyclopentadienyl) were determined by means of X‐ray diffraction and confirm the mononuclear nature of the λ³‐phosphinine–Rh^III and Ir^III complexes. In contrast, a different reactivity and coordination behavior was found for the nitrogen analogue 2 , especially towards Rh^III as a bimetallic ion pair [RhCl(Cp*)( 2 )]⁺[RhCl₃(Cp*)]^? is formed rather than a mononuclear coordination compound. [RhCl(Cp*)( 1 )]Cl and [IrCl(Cp*)( 1 )]Cl react with water regio‐ and diastereoselectively at the external P?C double bond, leading exclusively to the anti‐addition products [MCl(Cp*)( 1 H ? OH)]Cl as confirmed by X‐ray crystal‐structure determination.     

A Trinuclear Radical‐Bridged Lanthanide Single‐Molecule Magnet

Assembly of the triangular, organic radical‐bridged complexes Cp*₆Ln₃(μ₃‐HAN) (Cp*=pentamethylcyclopentadienyl; Ln=Gd, Tb, Dy; HAN=hexaazatrinaphthylene) proceeds through the reaction of Cp*₂Ln(BPh₄) with HAN under strongly reducing conditions. Significantly, magnetic susceptibility measurements of these complexes support effective magnetic coupling of all three Ln^III centers through the HAN^3−. radical ligand. Thorough investigation of the Dy^III congener through both ac susceptibility and dc magnetic relaxation measurements reveals slow relaxation of the magnetization, with an effective thermal relaxation barrier of U_eff=51 cm⁻¹. Magnetic coupling in the Dy^III complex enables a large remnant magnetization at temperatures up to 3.0 K in the magnetic hysteresis measurements and hysteresis loops that are open at zero‐field up to 3.5 K.     

Umsetzungen von Cp*NbCl4 und Cp*TaCl4 mit Trimethylsilyl‐azid,Me3Si‐N3. Molekülstrukturen der bis(azido)‐oxo‐verbrückten Komplexe [Cp*NbCl(N3)(μ‐N3)]2(μ‐O) und [Cp*TaCl2(μ‐N3)]2(μ‐O) (Cp* = Pentamethylcyclopentadienyl)

Reactions of Cp*NbCl₄ and Cp*TaCl₄ with Trimethylsilyl‐azide, Me₃Si‐N₃. Molecular Structures of the Bis(azido)‐Oxo‐Bridged Complexes [Cp*NbCl(N₃)(μ‐N₃)]₂(μ‐O) and [Cp*TaCl₂(μ‐N₃)]₂(μ‐O) (Cp* = Pentamethylcyclopentadienyl) The chloro ligands in Cp*TaCl₄ (1c) can be stepwise substituted for azido ligands by reactions with trimethylsilyl azide, Me₃Si‐N₃ (A) , to generate the complete series of the bis(azido)‐bridged dimers [Cp*TaCl_3‐n(N₃)_n(μ‐N₃)]₂ ( n = 0 (2c) , n = 1 (3c) , n = 2 (4c) and n = 3 (5c) ). If the solvent CH₂Cl₂ contains traces of water, an additional oxo bridge is incorporated to give [Cp*‐TaCl₂(μ‐N₃)]₂(μ‐O) (6c) or [Cp*TaCl(N₃)(μ‐N₃)]₂(μ‐O) (7c) , respectively. Both 6c and 7c are also formed in stoichiometric reactions from [Cp*TaCl₂(μ‐OH)]₂(μ‐O) (8c) and A . Analogous reactions of Cp*NbCl₄ (1b) with A were used to prepare the azide‐rich dinuclear products [Cp*NbCl_3‐n(N₃)_n(μ‐N₃)]₂ (n = 2 (4b) , and n = 3 (5b) ), and [Cp*NbCl(N₃)(μ‐N₃)]₂(μ‐O) (7b) . The mononuclear complex Cp*Ta(N₃)Me₃ (10c) is obtained from Cp*Ta(Cl)Me₃ and A . All azido complexes were characterised by their IR as well as their ¹H and ¹³C NMR spectra; X‐ray crystal structure analyses are available for 6c and 7b .     

On Approaching the Limit of Molecular Magnetic Anisotropy: A Near‐Perfect Pentagonal Bipyramidal Dysprosium(III) Single‐Molecule Magnet

We report a monometallic dysprosium complex, [Dy(O^tBu)₂(py)₅][BPh₄] ( 5 ), that shows the largest effective energy barrier to magnetic relaxation of U_eff=1815(1) K. The massive magnetic anisotropy is due to bis‐trans‐disposed tert‐butoxide ligands with weak equatorial pyridine donors, approaching proposed schemes for high‐temperature single‐molecule magnets (SMMs). The blocking temperature, T_B , is 14 K, defined by zero‐field‐cooled magnetization experiments, and is the largest for any monometallic complex and equal with the current record for [Tb₂N₂{N(SiMe₃)₂}₄(THF)₂].     

Iodination of cyclo‐E5‐Complexes (E=P,As)

In a high‐yield one‐pot synthesis, the reactions of [Cp*M(η⁵‐P₅)] (M=Fe ( 1 ), Ru ( 2 )) with I₂ resulted in the selective formation of [Cp*MP₆I₆]⁺ salts ( 3 , 4 ). The products comprise unprecedented all‐cis tripodal triphosphino‐cyclotriphosphine ligands. The iodination of [Cp*Fe(η⁵‐As₅)] ( 6 ) gave, in addition to [Fe(CH₃CN)₆]²⁺ salts of the rare [As₆I₈]^2? (in 7 ) and [As₄I₁₄]^2? (in 8 ) anions, the first di‐cationic Fe‐As triple decker complex [(Cp*Fe)₂(μ,η^5:5‐As₅)][As₆I₈] ( 9 ). In contrast, the iodination of [Cp*Ru(η⁵‐As₅)] ( 10 ) did not result in the full cleavage of the M?As bonds. Instead, a number of dinuclear complexes were obtained: [(Cp*Ru)₂(μ,η^5:5‐As₅)][As₆I₈]_0.5 ( 11 ) represents the first Ru‐As₅ triple decker complex, thus completing the series of monocationic complexes [(Cp^RM)₂(μ,η^5:5‐E₅)]⁺ (M=Fe, Ru; E=P, As). [(Cp*Ru)₂As₈I₆] ( 12 ) crystallizes as a racemic mixture of both enantiomers, while [(Cp*Ru)₂As₄I₄] ( 13 ) crystallizes as a symmetric and an asymmetric isomer and features a unique tetramer of {AsI} arsinidene units as a middle deck.     

Reactions of Group 4 Metallocene Complexes with Mono‐ and Diphenylacetonitrile: Formation of Unusual Four‐ and Six‐Membered Metallacycles

Reactions of Group 4 metallocene alkyne complexes [Cp′₂M(η²‐Me₃SiC₂SiMe₃)] ( 1 : M=Zr, Cp′=Cp*=η⁵‐pentamethylcyclopentadienyl; 2 a : M=Ti, Cp′=Cp*, and 2 b : M=Ti, Cp′₂=rac‐(ebthi)=rac‐1,2‐ethylene‐1,1′‐bis(η⁵‐tetrahydroindenyl)) with diphenylacetonitrile (Ph₂CHCN) and of the seven‐membered zirconacyclocumulene 3 with phenylacetonitrile (PhCH₂CN) were investigated. Different compounds were obtained depending on the metal, the cyclopentadienyl ligand and the reaction temperature. In the first step, Ph₂CHCN coordinated to 1 to form [Cp*₂Zr(η²‐Me₃SiC₂SiMe₃)(NCCHPh₂)] ( 4 ). Higher temperatures led to elimination of the alkyne, coordination of a second Ph₂CHCN and transformation of the nitriles to a keteniminate and an imine ligand in [Cp*₂Zr(NC₂Ph₂)(NCHCHPh₂)] ( 5 ). The conversion of 4 to 5 was monitored by using ¹H NMR spectroscopy. The analogue titanocene complex 2 a eliminated the alkyne first, which led directly to [Cp*₂Ti(NC₂Ph₂)₂] ( 6 ) with two keteniminate ligands. In contrast, the reaction of 2 b with diphenylacetonitrile involved a formal coupling of the nitriles to obtain the unusual four‐membered titanacycle 7 . An unexpected six‐membered fused zirconaheterocycle ( 8 ) resulted from the reaction of 3 with PhCH₂CN. The molecular structures of complexes 4 , 5 , 6 , 7 and 8 were determined by X‐ray crystallography.     

Binuclear CpV,Cp*V,and Cp*Ta Complexes containing Organochalcogenolato Bridges, μ‐ER (E = Sulfur,Selenium, Tellurium; R = Methyl,Phenyl, and Ferrocenyl)

Photolysis of the halfsandwich tetracarbonylmetal complexes CpV(CO)₄, Cp*V(CO)₄ and Cp*Ta(CO)₄ in solution in the presence of di(organyl)dichalcogenides E₂R₂ (E = S, Se, Te; R = Me, Ph, Fc) leads to diamagnetic doubly organochalcogenolato‐bridged compounds, [Cp⁽⁾M(CO)₂(μ‐ER)]₂. According to the X‐ray structure determinations carried out for [CpV(CO)₂(μ‐TeMe)]₂, [Cp*V(CO)₂(μ‐TePh)]₂ and [Cp*Ta(CO)₂(μ‐SPh)]₂, the molecular framework consists of a folded M₂(μ‐ER)₂ ring with the cyclopentadienyl ligands in cis‐configuration and the organyl substituents R in a syn‐equatorial arrangement, thus forming a bowl‐shaped molecule with the four terminal CO ligands protruding into the inner sphere. The M…M distances (in the range between 305 and 330 pm) are not considered to indicate direct bonding interactions. The vanadium complexes [Cp⁽⁾V(CO)₂(μ‐ER)]₂ are completely decarbonylated in the presence of an excess of E₂R₂ in boiling toluene, and in many cases the paramagnetic quadruply‐bridged products, [CpV(μ‐ER)₂]₂, can be isolated.     

Chemistry of N,S‐Heterocyclic Carbene and Metallaboratrane Complexes: A New η3‐BCC‐Borataallyl Complex

A high‐yielding synthetic route for the preparation of group 9 metallaboratrane complexes [Cp*MBH(L)₂], 1 and 2 ( 1 , M=Rh, 2 , M=Ir; L=C₇H₄NS₂) has been developed using [{Cp*MCl₂}₂] as precursor. This method also permitted the synthesis of an Rh–N,S‐heterocyclic carbene complex, [(Cp*Rh)(L₂)(1‐benzothiazol‐2‐ylidene)] ( 3 ; L=C₇H₄NS₂) in good yield. The reaction of compound 3 with neutral borane reagents led to the isolation of a novel borataallyl complex [Cp*Rh(L)₂B{CH₂C(CO₂Me)}] ( 4 ; L=C₇H₄NS₂). Compound 4 features a rare η³‐interaction between rhodium and the B‐C‐C unit of a vinylborane moiety. Furthermore, with the objective of generating metallaboratranes of other early and late transition metals through a transmetallation approach, reactions of rhoda‐ and irida‐boratrane complexes with metal carbonyl compounds were carried out. Although the objective of isolating such complexes was not achieved, several interesting mixed‐metal complexes [{Cp*Rh}{Re(CO)₃}(C₇H₄NS₂)₃] ( 5 ), [Cp*Rh{Fe₂(CO)₆}(μ‐CO)S] ( 6 ), and [Cp*RhBH(L)₂W(CO)₅] ( 7 ; L=C₇H₄NS₂) have been isolated. All of the new compounds have been characterized in solution by mass spectrometry, IR spectroscopy, and ¹H, ¹¹B, and ¹³C NMR spectroscopies, and the structural types of 4 – 7 have been unequivocally established by crystallographic analysis.