Search

Bis(alkyl)nickel(II) complexes [(tmeda)NiR2] (R = CH2SiMe3 (1a), CH2CMe3 (1b), CH2CMe2Ph (1c)) can be prepared from [(tmeda)Ni(acac)2] and MgR2. This approach is equivalent to and, in some cases, e...

A series of Co(I), Co(II), and Ni(II) compounds were prepared by employing the open pentadienyl 2,4-(Me3C)2C5H5 (Pdl′) and some edge-bridged variants (ePdl) such as 6,6′-dimethylcyclohexadienyl (dm...

Four- and five-coordinate high-spin (S = 2) Fe(II) complexes bearing the pyrrolyl-derived tBuPNP pincer ligand [tBuPNP = 2,5-(tBu2PCH2)2(C4H2N)] have been prepared. All three complexes were characterized by X-ray diffraction, zero-field 57Fe Mossbauer spectroscopy and solid-state magnetic susceptibility studies. Furthermore, the experimentally determined Mossbauer parameters of compounds 4–6 can be modeled satisfactorily by density functional theory (DFT) computations at the B97D level of theory. Introduction of the sterically demanding bis(trimethylsilyl)amido moiety induces significant distortions from ideal tetrahedral geometry in [(tBuPNP)FeN(SiMe3)2] (4), featuring an Fe(II) high-spin state with large negative axial zero-field splitting and slow paramagnetic relaxation at low temperature, as evidenced by measurements of the solid-state magnetic susceptibility and zero-field 57Fe Mossbauer spectroscopy. Replacing the chlorido ligand in [(tBuPNP)FeCl] (3) by the bidentate acetylacetonato (acac) ligand enforces a trigonal–bipyramidal structure in [(tBuPNP)Fe(acac)] (5), in which the Fe(II) atom also adopts a high-spin configuration. Reaction of 3 with adamantyl azide allowed us to confirm the inherent lability of the phosphine coordination, since the azide inserts into the Fe P bond to form [(tBuPNPN3Adamantyl)FeCl] (6), in which the tBuPNP ligand is transformed to a phosphino-pyrrolyl-phosphazide ligand framework (tBuPNPN3Adamantyl). This motif can be considered as a trapped Staudinger intermediate along the reaction pathway of free phosphines with organic azides to form phosphinimines. Bidentate binding of the phosphazide sidearm in κN:κN-fashion to the Fe(II) atom enforces an s-anti coordination of the P1–N2–N3–N4 moiety, which raises the barrier for the thermodynamically favorable N2 elimination and allows this intermediate to be trapped. Complex 6 contains a high-spin Fe(II) atom with a square-pyramidal structure.

The half-sandwich complex [Cp′Fe(μ-I)]2 (1; Cp′ = η5-1,2,4-(Me3C)3C5H2) is cleaved when heated in toluene to form a cation–anion pair [{Cp′Fe(η6-toluene)}+{Cp′FeI2}−] (2), in which the two Fe(II) atoms adopt different spin states, i.e., a low-spin (S = 0) and a high-spin (S = 2) configuration. Upon oxidation of 1 with C2H4I2, the thermally stable 15VE species [Cp′FeI2] (3) can be isolated, in which the Fe(III) atom adopts an intermediate spin (S = 3/2) configuration. Complex 3 is an excellent starting material for further functionalizations and it reacts with Mg(CH2SiMe3)2 to form the unprecedented Fe(III) (S = 3/2) bis(alkyl) complex [Cp′Fe(CH2SiMe3)2] (4). The respective spin states of complexes 2–4 are confirmed by single-crystal X-ray crystallography, zero-field 57Fe Mossbauer spectroscopy, and solid-state magnetic susceptibility measurements. In contrast to the related 14VE high-spin (S = 2) Fe(II) alkyl species [Cp′FeCH(SiMe3)2], which resists the reaction with H2 as a consequence of a spin-induced reaction barrier, complex 4 reacts cleanly with H2 (8 bar) in cyclohexane to yield iron hydrides [{Cp′Fe}2(μ-H)3] (5) and [Cp′Fe(μ-H)2]2 (6) in a 1 : 4 ratio. However, when the hydrogenation of 4 is carried out in benzene, a green 19VE [Cp′Fe(η6-C6H6)] (A) intermediate is formed, which dimerizes to the bis(cyclohexadienyl)-bridged product [(Cp′Fe)2(μ2–η5:η5-C12H12)] (7). Further evidence for the intermediacy of [Cp′Fe(η6-C6H6)] (A) was gathered by X-band EPR and UV/vis spectroscopy. Interestingly, attempts to oxidize 7 with AgSbF6 proceeded via C–C bond cleavage instead of metal oxidation to form [Cp′Fe(C6H6)][SbF6] (8).

The reaction of the cycloheptatrienyl-cyclopentadienyl (Cht-Cp) titanium sandwich complexes [(η7-C7H7)Ti(η5-C5R5)] (R = H, Me) with n-BuLi followed by treatment with the chlorophosphanes ClPR'2 (R' = Cy, tBu) afforded the Cht-substituted phosphanes [(η7-C7H6PR'2)Ti(η5-C5R5)] (R = H, Me; R' = Cy, tBu). Together with their previously reported Cp-substituted analogues [(η7-C7H7)Ti(η5-C5H4PR2)] (R = Cy, tBu), these complexes were employed as ancillary phosphane ligands in palladium-catalyzed Suzuki-Miyaura coupling between sterically encumbered aryl bromides and aryl boronic acids. The unusually short reaction times indicated rapid generation of catalytically active Pd(0) species, and the reaction of palladium(II) acetate, Pd(OAc)2, with an excess of of the phosphorus ligands afforded linear diphosphane palladium(0) complexes. These reactions gave no indication of phosphane oxide formation, and it is supposed that the Cht-Cp titanium sandwich moiety serves as an integrated reducing agent. Accordingly, the reaction of [(η7-C7H7)Ti(η5-C5M5)] with Pd(OAc)2 or Ag(OAc) resulted in a three-electron redox reaction with formation of the half-sandwich complex [(η5-C5Me5)Ti(OAc)3] together with 7,7'-bi-1,3,5-cycloheptatriene (ditropyl) and elemental Pd or Ag metal. Upon reaction with silver(I) trifluoromethanesulfonate, Ag(OTf), a four-electron redox process was observed which furnished the tropylium titanate complex [C7H7][(η5-C5Me5)Ti(OTf)4].

Half-sandwich complexes of the N-heterocyclic carbene-phosphinidene adduct [(IPr)PH] (1, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by its reaction with dimeric complexes of the type [LMCl2]2, which afforded the three-legged piano-stool complexes [LMCl2{HP(IPr)}] (9a/9b: M = Ru/Os, L = η6-p-cymene; 10a/10b: M = Rh/Ir, L = η5-C5Me5). Their conversion into the corresponding carbene-phosphinidenide complexes [LMCl{P(IPr)}] (11a/11b: M = Ru/Os; 12a/12b: M = Rh/Ir) with a two-legged piano stool geometry was studied by NMR spectroscopy in the presence of the strong base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Alternatively, the complexes 11 and 12 were isolated in high yields from the reactions of the carbene-phosphinidene adduct [(IPr)PTMS] (2) with [LMCl2]2, whereby formation of the metal-phosphorus bonds was accompanied by elimination of trimethylsilyl chloride (Me3SiCl). Theoretical calculations reveal a strong polarization of the phosphorus ligands upon metal complexation, wh...

The pyrrolyl-based iron pincer compounds [(tBuPNP)FeCl] (1), [(tBuPNP)FeN2] (2), and [(tBuPNP)Fe(CO)2] (3) were prepared and structurally characterized. In addition, their electronic ground states were probed by various techniques including solid-state magnetic susceptibility and zero-field 57Fe Mossbauer and X-band electron paramagnetic resonance spectroscopy. While the iron(II) starting material 1 adopts an intermediate-spin (S = 1) state, the iron(I) reduction products 2 and 3 exhibit a low-spin (S = 1/2) ground state. Consistent with an intermediate-spin configuration for 1, the zero-field 57Fe Mossbauer spectrum shows a characteristically large quadrupole splitting (ΔEQ ≈ 3.7 mm s–1), and the solid-state magnetic susceptibility data show pronounced zero-field splitting (|D| ≈ 37 cm–1). The effective magnetic moments observed for the iron(I) species 2 and 3 are larger than expected from the spin-only value and indicate an incompletely quenched orbital angular momentum and the presence of spin–orbit co...

The enantiomerically pure pentadienyl (Pdl*) ligand derived from the natural product (1R)-(−)-myrtenal forms with MCl3 (M = La, Ce, Pr, and Nd) the corresponding homoleptic [(η5-U-Pdl*)3M compounds (1-M). These complexes were fully characterised by 1H NMR spectroscopy, elemental analyses and X-ray diffraction. They exhibit in solution and solid state idealized C3 symmetry, and their molecular structures also reveal that the Pdl* ligand adopts a U-conformation and coordinates exclusively with its less sterically encumbered face to the rare-earth metal atom. For the paramagnetic representatives an assignment of the 1H NMR resonances based on a simple dipolar model gave satisfactory results.

The reactions of the molybdenum alkylidyne complex [MesCMo{OCMe(CF3)2}3] (1) with the diaminoacetylenes R2NCCNR2 (2, NR2 = 4-methylpiperidinyl; 3, NR2 = NEt2; Mes = 2,4,6-trimethylphenyl) afforded the metallacyclobutadiene (MCBD) complexes 4 and 5. In contrast to all other MCBD complexes, 4 and 5 are paramagnetic and best described as Mo(IV) species containing an anionic diaminodicarbene of the type [(R2N)CC(Mes)C(NR2)]−.

The reaction of the ferrocene-bridged bis(imidazolin-2-imine) ligand N,N′-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,1′-ferrocenediamine [fc(NIm)2] with MCl2 salts furnished the complexes [{fc(NIm)2}MCl2] (M = Mn, Fe, Co, Ni, Cu, Zn), which were structurally and spectroscopically characterized. The iron complex was oxidized by reaction with ferrocenium hexafluoroantimonate, and both compounds, [{fc(NIm)2}FeCl2] and [{fc(NIm)2}FeCl2]SbF6, were further studied by means of Mossbauer spectroscopy, SQUID magnetometry, and single-crystal X-ray diffraction, revealing that oxidation occurred at the tetrahedral FeN2Cl2 moiety. The CuX (X = Cl, Br, I) complexes of fc(NIm)2 were synthesized, affording dimeric (X = Cl, Br) or polymeric (X = I) structures. In addition, the ligand bis(N,N,N′,N′-tetraisopropyl-2,3-diaminocyclopropen-1-ylidene)-1,1′-ferrocenediamine [fc(NCyp)2], was prepared and the trimetallic complex [{fc(NCyp)2}Pd2Cl4] was synthesized and structurally characterized. The attempted synthesis of the corresponding nickel complex furnished single crystals of the composition [{fc(NHCyp)2}Cl(NiCl3)]; X-ray diffraction analysis afforded the first crystal structure of the [Ni2Cl6]2– anion.

The synthesis of the frustrated carbene-borane 4-(9-borabicyclo[3.3.1]nona-9-yl)-1,3-di-tert-butylimidazolin-2-ylidene (6) was accomplished by deprotonation of the N-heterocyclic carbene (NHC) 1,3-di-tert-butylimidazolin-2-ylidene (1) at the 4-position with n-butyllithium, followed by addition of 9-chloro-9-borabicyclo[3.3.1]nonane (BBN-Cl). The abnormal carbene-borane adduct 5, with the BBN-Cl moiety at the 4-position, was obtained from the reaction of 1 with BBN-Cl; however, its conversion into 6 by treatment with K[N(SiMe3)2] (potassium hexamethyldisilazide, KHMDS) was not achieved. The reactions of 6 with the rhodium(I) complexes [Rh(COD)Cl]2 (COD = 1,4-cyclooctadiene) and [Rh(CO)2Cl]2 afforded the complexes cis-[(6)Rh(COD)Cl] (7) and cis-[(6)Rh(CO)2Cl] (8), with the latter allowing assessment of the σ-donor/π-acceptor properties of 6 by IR spectroscopy. The reactivity of 6 towards carbon dioxide, phenylacetylene and acetonitrile was studied, affording the labile adduct 6·CO2 (9), whereas irreversible deprotonation and formation of the imidazolium phenylalkynylborate 10 and the imidazolium cyanomethylborate 11 was observed for PhCCH and CH3CN. The molecular structures of 5, 7, 8, 10, and 11 were established by X-ray diffraction analyses.

Sterically encumbered ferrocenium salts with four, five, or six tert-butyl substituents and a variety of counteranions ([BF4]–, [SbF6]–, and [PF6]–) were prepared. The electronic structures of these materials were investigated by various physical techniques including electron paramagnetic resonance (EPR) and Mossbauer spectroscopy and solid-state magnetic susceptibility measurements. Spin–orbit coupling and low-symmetry distortions split the electronic ground states (2E2g) in these compounds into two Kramers doublet states (Ψa and Ψb); the energy difference between these states was evaluated by EPR spectroscopy and magnetic susceptibility measurements and decreases with increasing steric demand at the ferrocenium moiety. Further information on the first excited state (2A1g) was obtained by solid-state magnetic susceptibility measurements, which also indicated that an increasing steric bulk resulted in a decreasing energy gap between the 2E2g(Ψa) and 2A1g states. The Mossbauer spectra revealed temperature-dependent line shapes attributed to unusually slow paramagnetic relaxation on the 57Fe Mossbauer time scale. The pertinent spin–spin and spin–lattice (Orbach and Raman) relaxation parameters were determined for these materials and further substantiate the trends observed by our EPR spectroscopic and solid-state magnetic susceptibility studies.

Addition of N-heterocyclic carbenes [L = 1, 3-di-tert-butylimidazolin-2-ylidene (ItBu), 1, 3-diisopropyl-4, 5-dimethylimidazolin-2-yildene (IiPrMe2), 1, 3-di-mesitylimidazolin-2-yildene (IMes), and 1, 3-bis(2, 6-diisopropylphenyl)imidazolin-2-yildene (IPr)] to manganocene [(C5H5)2Mn] forms the neutral Lewis base adducts [(C5H5)2Mn(L)] (2–5) in moderate yields. Complexes 2–4 were structurally characterized and their solid-state magnetism was investigated between T = 2.6–300 K. In contrast to literature reports, these materials exclusively adopt a high-spin (S = 5/2) ground state.

This work presents the synthesis, characterization, and application of several new metal(I) complexes with trifluoromethylpyridine-containing N-heterocyclic carbene (NHC) ligands. The metal of choice was gold(I) for compounds 7 – 10, rhodium(I) for 11 – 12, and iridium(I) for 13 – 14, respectively. The trifluoromethylpyridine moiety was incorporated, along with other biologically active moieties, with the intention of modifying the lipophilicity of the complexes, so that the transport of the active units (M–NHC) through the cell wall barrier is facilitated. The biological activity of the complexes was investigated. In vitro assessment of antitumor activity in a panel of 12 human tumor cell lines by a monolayer assay revealed good potency (mean IC50 12.6 μm) and tumor selectivity for one compound. The solid-state structures of two solvates of compound 7, one with MeOH and one with THF, were determined by X-ray diffraction analysis.

The first preparations of half-open and open manganocenes were accomplished. Treatment of KPdl′ (Pdl′ = 2,4-(Me3C)2C5H5)) with [{(η5-Cp”)Mn(thf)(μ-I)}2] (Cp″ = 1,2,4-(Me3C)3C5H2) and MnI2(thf)2 resulted in the formation of [(η5-Cp″)Mn(Pdl′)] (2) and [(Pdl′)2Mn] (4), respectively. Both compounds adopt a high-spin (S = 5/2) ground state. Maximum spin states are rather unusual for pentadienyl complexes, since these ligands generally stabilize transition metal complexes in their low-spin state. In addition, the electronic structure of 2 was compared to its closed analogue [(η5-Cp″)Mn(η5-Cp′)] (Cp′ = 1,3-(Me3C)2C5H3), which also adopts the high-spin configuration because of steric hindrance destabilizing the electronically more favorable low-spin state. Reaction of KPdl′ with [(C5H5)2Mn] yields the trimetallic compound [{(η5-Pdl′)Mn(η5-C5H5)]}2Mn] (5) concomitant with the formation of 2,4,7,9-tetra-tert-butyl-1,3,7,9-decatetraene (Pdl′2), indicating reduction of two Mn atoms. Solid-state magnetic susceptibilit...

A series of (allyl)palladium(II) complexes of anionic N-heterocyclic carbenes that contain a weakly coordinating borate moiety (WCA-NHC) were prepared by deprotonation of the carbene IPr with n-butyllithium in the 4-position, which was followed by addition of B(C6F5)3 and reaction of the resulting lithium carbene–borate with [(η3-allyl)Pd(μ-Cl)]2 (allyl = 2-propenyl, 2-butenyl, 2-methyl-2-propenyl, 1-phenyl-2-propenyl). In polar solvents such as tetrahydrofuran, chloropalladate complexes of the type [Li(THF)3][(WCA-NHC)PdCl(η3-allyl)] were formed, whereas the reactions in toluene afforded neutral complexes of the type [(WCA-NHC)Pd(η3-allyl)], which exhibit an intramolecular interaction with the N-aryl groups of the carbene ligands. The allyl-palladium complexes were employed as catalysts for the Buchwald–Hartwig amination of various aryl halides with morpholine.

A series of Au(I) complexes (12, 13, 14, 15, 16) and Ag(I) complexes (17, 18, 19, 20) derived from imidazo[1,5-a]pyridin-3-ylidenes were synthesized from AuCl(SMe2) or by reacting silver(I) acetate with 2,5-dimethylimidazo[1,5-a]pyridin-2-ium iodide or imidazo[1,5-a]pyridin-2-ium salts, and were characterized using NMR spectroscopy, mass spectrometry and elemental analyses. In addition, the Au(I) complex 13 and the Ag(I) complex 19 were characterized using single-crystal X-ray diffraction. Using paclitaxel as a standard, all Au(I) and Ag(I) N-heterocyclic carbene complexes were evaluated for their in vitro anti-tumour activity against 12 cell lines using a monolayer cell survival and proliferation assay. The highest anticancer activity was found for complexes 15, 13 and 14 with mean IC50 values of 10.09, 10.42 and 12.28 μM, respectively. Copyright © 2016 John Wiley & Sons, Ltd.

Deprotonation of 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (IDipp) with n-butyllithium at the 4-position and addition of B(C6F5)3 afforded the lithium-carbene borate complex [(WCA-NHC)Li(toluene)] with a weakly coordinating anionic (WCA) moiety. The reaction of the lithiocarbene with the dimeric allyl complex [(η3-C3H5)Ni(μ-Cl)]2 in tetrahydrofuran (THF) afforded the chloronickelate complex [Li(THF)n][(WCA-IDipp)NiCl(η3-C3H5)] (1 ≤ n ≤ 3), which was used to generate the complex [(WCA-IDipp)Ni(η3-C3H5)], which is expected to achieve stabilization through an intramolecular arene-metal interaction (“π-face donation”) involving the N-aryl groups of the carbene ligand, by elimination of LiCl in toluene solution. The labile complex [(WCA-IDipp)Ni(η3-C3H5)], which undergoes decomposition by C–H activation and/or reductive elimination, can be stabilized by addition of carbon monoxide or phosphines to form novel neutral complexes of the type [(WCA-IDipp)NiL(η3-C3H5)] (L = CO, PMe3, PMe2Ph, PMePh2).

International audience; The molybdenum and tungsten 2,4,6-trimethylbenzylidynes [MesC M{OC(CF3)(2)Ph}(3)] (12a, M = Mo; 12b, M = W) were prepared and structurally characterized as related complexes to already known [MesC M{OC(CF3)(2)Me}(3)] (MoF6, M = Mo; WF6, M = W). While treatment of 12a with 3-hexyne yielded the propylidyne complex [EtC Mo{OC(CF3)(2)Ph}(3)] (13), the tungsten congener 12b formed isolable metallacyclobutadiene (MCBD) species 14-16 by reaction with 3-hexyne, 1-phenyl-1-propyne, and 2,4-hexadiyne, which can be correlated with the higher electrophilicity of the tungsten complex. Furthermore, the labile MCBD [(C3Et3 )Mo{OC(CF3)(2)Me}(3)] (17) was isolated at low temperature from the reaction of the highly active MoF6 catalyst with 3-hexyne and could be characterized by X-ray diffraction analysis. At room temperature, the same reaction afforded [EtC Mo{OC(CF3)(2)Me}(3)] (18), and the equilibrium reaction with 3-hexyne to form 17 was additionally studied by variable temperature NMR spectroscopy, which allowed determining Delta H degrees and Delta S degrees for the formation of MCBD 17. The experimental thermodynamic data were used to set the benchmark for DFT calculations. Moreover, the deprotiometallacyclobutadiene complex (DPMCBD) [C-3(Mes)(Ph)}Mo{OC(CF3)(3)}(2)] (19), prepared from [MesC Mo{OC(CF3)(3)}(3)] (MoF9) and phenylacetylene, was isolated and structurally characterized as a decomposition product of terminal alkyne metathesis and employed in the polymerization of phenylacetylenes.

The coordination chemistry of the sterically encumbered pentadienyl ligand pdl' (pdl' = 2,4-(Me3C)2C5H5) towards a series of rare-earth metals was systematically explored and the resulting metal complexes were fully characterized by several techniques including X-ray diffraction, elemental analysis, NMR spectroscopy and solid-state magnetic susceptibility studies. Three different reaction products were isolated depending on the redox-potentials and ionic radii of the metal atoms. They can be classified as (a) salt-metathesis, (b) metal reduction-ligand oxidation and (c) ligand deprotonation products. While for the larger and difficult to reduce metal ions, M = La, Ce, Pr and Nd, trivalent compounds [(η5-pdl')3M] (1-M) were isolated, for the more readily reduced metal ions the corresponding divalent compounds [[(η5-pdl')2M(thf)n] (2-M; with M = Sm (n = 2); Eu, Yb (n = 1)) were formed. A more complex structural motif was observed for the smaller and also difficult to reduce metal ions, M = Sc, Y, Gd, Tb, Dy, Ho, Er, Tm and Lu, which yielded the bimetallic complexes of the type [(pdl')(pdl'-1H)(pdl'-2H)M2(thf)2] (3-M). In these dimeric complexes the pdl' ligand acts as a result of deprotonation reactions not only as a monoanionic [pdl']-, but also as a dianionic [pdl'-1H]2- and a trianionic [pdl'-2H]3- ligand scaffold, which form unusual structural motifs including a six-membered metallacycle. Solid-state magnetic susceptibility studies revealed the expected free-ion magnetic moments at T = 300 K for all investigated compounds, whereas at lower temperatures crystal-field effects dominate. Furthermore, for 3-Gd, 3-Tb, 3-Dy and 3-Er weak ferromagnetic exchange interactions were observed at low temperature.

Two new Pt(II) complexes with imidazolin-2-imines as ancillary ligands, [Pt(DMEAImiPr)Cl2] and [Pt(DPENImiPr)Cl2], were synthesized and characterized. Substitution reactions of these complexes with nucleophiles – thiourea (TU), L-methionine (L-Met), L-histidine (L-His) and guanosine-5′-monophosphate (5′-GMP) – were carried out in 25 mM Hepes buffer in the presence of 30 mM NaCl. The reactions were monitored using variable-temperature UV-Vis spectrophotometry and were followed under pseudo-first-order conditions with a large excess of nucleophiles. A slightly higher reactivity was found for [Pt(DMEAImiPr)Cl2], while the reactivity of the nucleophiles decreased in the order TU > L-Met > L-His > 5′-GMP. The negative values reported for the entropy of activation confirmed an associative substitution mode. Spectrophotometric acid–base titrations were performed to determine the pKa values of the coordinated water molecules in the diaqua complexes [Pt(DMEAImiPr)(H2O)2]2+ and [Pt(DPENImiPr)(H2O)2]2+. Solubility measurements revealed good solubility of the studied imidazolin-2-imine complexes in water. The crystal structure of [Pt(DMEAImiPr)Cl2] was determined by X-ray diffraction analysis. The coordination geometries around the platinum atoms are distorted square-planar; the [Pt(DMEAImiPr)Cl2] complex displays Pt–N distances of 2.0162(19) and 2.0663(19) A. Attempts to coordinate Au(III) ions to different imidazolin-2-imine ligands did not result in the formation of coordination complexes, but rather in the reduction of the Au(III) precursor. This was evidenced by the X-ray crystal structure of [(DACH(ImiPrH)2)(AuCl2)2], which formed during the reaction of KAuCl4 with the ligand DACH(ImiPr)2.

Addition of N-heterocyclic carbenes (L = 1,3-di-tert-butylimidazol-2-ylidene (ItBu), 1,3-di-iso-propyl-4,5-dimethylimidazol-2-yildene (IiPr2Me2), 1,3-mesitylimidazol-2-yildene (IMes) and 1,3-di-(2,6-di-isopropylphenyl)imidazol-2-yildene (IPr)) to the iron half-sandwich complex [Cp′FeI]2 (Cp′ = η5-1,2,4-(Me3C)3C5H2, 1) forms the neutral, 16VE adducts [Cp′FeI(L)] (2–5) in moderate to excellent yields. These complexes were structurally characterised. The NHC ligand binds strongly to the Fe(II) atom, so that no exchange is observed on the NMR and chemical time scale. Fe(II) atoms in the starting material 1 adopt a high-spin configuration (S = 2) and are weakly antiferromagnetically coupled at low temperatures. Furthermore, in contrast to previous reports on related [(η5-C5Me5)FeCl(NHC)] systems, in which the Fe(II) atoms assume an intermediate spin (S = 1), no spin state change occurs upon coordination of the NHC ligand; the Fe(II) atoms in complexes 2–5 retain their high-spin state (S = 2) as shown by solid state magnetic susceptibility and zero-field 57Fe Mossbauer spectroscopy investigations. Density functional theory (DFT) studies at the B3LYP level of theory also agree with a well separated S = 2 ground state for compounds 2–5. Surprisingly for Fe(II) high-spin systems, compounds 1–5 exhibit slow paramagnetic relaxation in their Mossbauer spectra; this can be traced to spin–spin and spin–lattice relaxation processes with unusually large spin–lattice relaxation barriers. A structural model is proposed that associates these processes with crystal packing effects.

The bis(imidazolin-2-imine) ligand N,N'-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,1'-ferrocenediamine, fc(NIm)2 (1) was prepared. Its reaction with [NiCl2(dme)] (dme = 1,2-dimethoxyethane) or [PdCl2(MeCN)2] afforded the tetrahedral, paramagnetic complex [(1-κ(2)N,N')NiCl2] (6a) or the diamagnetic, square-planar complex [(1-κ(2)N,N')PdCl2] (6b), respectively. For the latter, slow rearrangement to the ionic complex [(1-κFe,κ(2)N,N')PdCl]Cl, [7]Cl, was observed, which was followed by (1)H NMR and UV/vis spectroscopy. Treatment of [7]Cl with NaBF4 afforded [7]BF4; the palladium atoms in both cations adopt square-planar environments with short Fe-Pd bonds (ca. 2.65 Å). In addition, a series of dicationic complexes of the type [(1-κFe,κ(2)N,N')ML](BF4)2 (8a: M = Ni, L = MeCN; 8b: M = Pd, L = MeCN; 9a: M = Ni, L = PMe3; 9b: M = Pd, L = PMe3) was prepared from 6a (M = Ni) or [7]BF4 by chloride abstraction with NaBF4 or AgBF4 in the presence of acetonitrile or trimethylphosphine, respectively. In the presence of triphenylphosphine, the palladium(II) complex [(1-κFe,κ(2)N,N')Pd(PPh3)](BF4)2 (10) was isolated. Iron-nickel and iron-palladium bonding in these complexes was studied experimentally by NMR, UV/vis, and Mössbauer spectroscopy and by cyclic voltammetry. Detailed DFT calculations were carried out for the cations [(1-κFe,κ(2)N,N')M(MeCN)](2+) in the 8a/8b couple, with Bader's atoms in molecules theory revealing the presence of noncovalent, closed-shell metal-metal interactions. Potential energy surface scans with successive elongation of the Fe-M bonds allow an estimation of the iron-metal bond dissociation energies (BDE) as BDE(Fe-Ni) = 11.3 kcal mol(-1) and BDE(Fe-Pd) = 24.3 kcal mol(-1).

Reaction of NaPyrtBu2 [PyrtBu2 = 2, 5-(Me3C)2C4H2N] and KPyrtBu2Me2 [PyrtBu2Me2 = 2, 5-(Me3C)2-3, 4-Me2C4N] with MnI2(thf)3 resulted in the isolation of the first bis(pyrrolyl)manganese(II) complexes. However, different coordination modes are realized depending on the identity of the Pyr-ligand. For example, the MnII atom is κN coordinate in [(κN-PyrtBu2)2Mn] (1-Mn), whereas several different species were isolated with the more bulky PyrtBu2Me2 ligand. Depending on the reaction conditions the κN-coordinate complex [(κN-PyrtBu2Me2)2Mn] (2-Mn′) is initially formed, but converts on sublimation to the η3 coordinate isomer [(η3-PyrtBu2Me2)2Mn] (2-Mn′). In some cases we could also identify a THF adduct of 2-Mn to give [(κN-PyrtBu2Me2)(η2-PyrtBu2Me2)Mn(thf)] [2-Mn(thf)], in which one PyrtBu2Me2 ligand binds in a κN coordination mode, while the other is best described as η2-PyrtBu2Me2. These complexes were characterized by elemental analyses and X-ray diffraction studies. Density functional theory (DFT) computations confirm that the potential energy surface between the different hapticities is rather flat for these MnII high-spin species (S = 5/2).

The reaction of the N-heterocyclic carbene 1,3-di-tert-butyl-4,5-dimethylimidazolin-2-ylidene (1b) with trimethylsilyl iodide, triflate and triflimidate [Me3SiX, X = I, CF3SO3 (OTf), (CF3SO2)2N (NTf2)] by mixing the neat, liquid starting materials afforded the corresponding 2-(trimethylsilyl)imidazolium salts [(1b)SiMe3]X as highly reactive, white crystalline solids. Only the triflimidate (X = NTf2) proved to be stable in solution and could be characterized by means of NMR spectroscopy (in C6D5Br) and X-ray diffraction analysis, whereas dissociation into free 1b and Me3SiOTf was observed for the triflate system, in agreement with the trend derived by DFT calculations; the iodide was too insoluble for characterization. The compounds [(1b)SiMe3]X showed the reactivity expected for frustrated carbene–silylium pairs, and treatment with carbon dioxide, tert-butyl isocyanate and diphenylbutadiyne gave the 1,2-addition products [(1b)CO2SiMe3]X (X = I, OTf, NTf2), [(1b)C(NtBu)OSiMe3]OTf and [(1b)C(Ph)C(SiMe3)CCPh]OTf, respectively. Upon reaction with [AuCl(PPh3)], metal–chloride bond activation was observed, with formation of the cationic gold(I) complexes [(1b)Au(PPh3)]X (X = OTf, NTf2).

The synthesis of C2 symmetric enantiomerically pure open Ca and Sr metallocenes, [(η(5)-pdl*)2Ca(thf)] (1) and [(η(5)-pdl*)2Sr(thf)2] (2) (pdl* = dimethylnopadienyl) is described and these complexes were fully characterized. The solid state structures confirm that the pdl* ligands coordinate exclusively with the less sterically demanding site to the Ca and Sr atoms. These complexes are active catalysts for the controlled ring opening polymerization (ROP) of rac-lactide to give heterotactically enriched polylactides (PL) with narrow polydispersities (PDI = 1.29-1.31) and without adding further activators.

Deprotonation of the N-heterocyclic carbene 1,3-di-tert-butylimidazolin-2-ylidene (1) with n-butyl lithium in the 4-position, followed by addition of bis(2,4,6-trimethylphenyl)boronfluoride, Mes2BF, afforded 4-[bis(2,4,6-trimethylphenyl)boryl]-1,3-di-tert-butylimidazolin-2-ylidene (6), which contains non-interacting carbene and borane moieties and can thus be regarded as a potential intramolecular frustrated Lewis pair (FLP). Alternatively, 6 can be conveniently prepared from 1 by reaction with Mes2BF via the abnormal carbene–borane adduct 7, which could be converted into 6 by treatment with potassium hexamethyldisilazide, K(HMDS). The reactions of 6 with the rhodium(I) complexes [Rh(COD)Cl]2 and [Rh(CO)2Cl]2 furnished [(6)Rh(COD)Cl] (8) and [(6)Rh(CO)2Cl] (9), with the latter allowing an assessment of the donor properties of 6 by IR spectroscopy. 6 reacted with carbon dioxide and tert-butyl isocyanate to form the adducts 6·CO2 (11) and 6·tBuNCO (12), which proved unstable in solution, with partial dissociation into the starting materials. The X-ray crystal structures of 6, 7, 8·2CH2Cl2 and 12 are reported.

A series of novel Pd(ii) complexes with chelating mono(imidazolin-2-imine) and bis(imidazolin-2-imine) ligands were synthesized. The crystal structures of [Pd(DMEAIm(iPr))Cl2] and [Pd(DPENIm(iPr))Cl2] were determined by X-ray diffraction analysis. The reactivity of the six Pd(ii) complexes, namely, [Pd(en)Cl2], [Pd(EAIm(iPr))Cl2], [Pd(DMEAIm(iPr))Cl2], [Pd(DPENIm(iPr))Cl2], [Pd(BL(iPr))Cl2] and [Pd(DACH(Im(iPr))2)Cl2], were investigated. Spectrophotometric acid-base titrations were performed to determine the pKa values of the coordinated water molecules in [Pd(en)(H2O)2](2+), [Pd(EAIm(iPr))(H2O)2](2+), [Pd(DMEAIm(iPr))(H2O)2](2+), [Pd(DPENIm(iPr))(H2O)2](2+), [Pd(BL(iPr))(H2O)2](2+) and [Pd(DACH(Im(iPr))2)(H2O)2](2+). The substitution of the chloride ligands in these complexes by TU, l-Met, l-His and Gly was studied under pseudo-first-order conditions as a function of the nucleophile concentration and temperature using stopped-flow techniques; the sulfur-donor nucleophiles have shown better reactivity than nitrogen-donor nucleophiles. The obtained results indicate that there is a clear correlation between the nature of the imidazolin-2-imine ligands and the acid-base characteristics and reactivity of the resulting Pd(ii) complexes; the order of reactivity of the investigated Pd(ii) complexes is: [Pd(en)Cl2] > [Pd(EAIm(iPr))Cl2] > [Pd(DMEAIm(iPr))Cl2] > [Pd(DPENIm(iPr))Cl2] > [Pd(BL(iPr))Cl2] > [Pd(DACH(Im(iPr))2)Cl2]. The solubility measurements revealed good solubility of the studied imidazolin-2-imine complexes in water, despite the fact that these Pd(ii) complexes are neutral complexes. Based on the performed studies, three unusual features of the novel imidazolin-2-imine Pd(ii) complexes are observed, that is, good solubility in water, very low reactivity and high pKa values. The coordination geometries around the palladium atoms are distorted square-planar; the [Pd(DMEAIm(iPr))Cl2] complex displays Pd-N distances of 2.013(2) and 2.076(2) A, while the [Pd(DPENIm(iPr))Cl2] complex displays similar Pd-N distances of 2.034(4) and 2.038(3) A. The studied systems are of interest because little is known about the substitution behavior of imidazolin-2-imine Pd(ii) complexes with bio-molecules under physiological conditions.

A series of enantiomerically pure −SiMe2NR2 (R = Me, Et) substituted pentadienyl ligands were prepared starting from the natural product (1R)-(−)-myrtenal. Deprotonation with a Schlosser superbase yields the corresponding potassium salts, which were characterized by various spectroscopic techniques. In solution these neutral N-donor-substituted pentadienyl systems predominantly adopt a U conformation, but in two cases the rare S conformation was also observed as a minor component in solution. Addition of 18-crown-6 allowed the molecular structures of two of these potassium pentadienyls to be determined by X-ray diffraction. Interestingly, η5 and κN coordination of the pentadienyl system to the [K(18-crown-6)]+ cation was observed. Furthermore, these ligand systems also coordinate to transition metals and form an open titanocene, open vanadocenes, open chromocenes, and half-open trozircenes with [TiCl3(thf)3], [VCl3(thf)3], CrCl2, and [(η7-C7H7)ZrCl(tmeda)], respectively. These complexes were characterized...

The coordination chemistry of the previously neglected 2,4-di(tert-butyl)pentadienyl (Pdl′) ligand with transition metals is explored. Several open metallocenes [(η5-Pdl′)2M] (M = Ti (3), V (4) and Cr (5)) were prepared and characterized by various spectroscopic techniques and X-ray diffraction. Attempts to prepare the open ferrocene [(η5-Pdl′)2Fe] were hampered by its high thermal instability, which leads to the formation of iron metal and 2,4,7,9-tetra-tert-butyl-1,3,7,9-decatetraene (2). Nevertheless, the half-open ferrocene [(η5-Pdl′)Fe(η5-Cp″)] (Cp″ = 1,2,4-(Me3C)3C5H2, 6) and mono(pentadienyl) iridium complex [(η5-Pdl′)Ir(η4-cod)] (9) were successfully synthesized. The electronic and molecular structures of the half-open ferrocene [(η5-Pdl′)Fe(η5-Cp″)] (6) and its closed analogue [(η5-Cp′)Fe(η5-Cp″)] (7, Cp′ = 1,3-(Me3C)2C5H3) were compared. Complex 6 is significantly more encumbered than 7, as shown by the short Pdl′cent–Fe distance. Clean oxidation of 6 and 7 can be accomplished electrochemically and chemically to give the half-open ferrocenium 6+ and closed ferrocenium 7+, respectively, and in both cases steric strain is released upon oxidation. On heating of 6+ to 152 °C in the solid state H2 and isobutene is eliminated to give [(η5-Cp′)2Fe]+ (8).

With the natural product (1R)-(−)-myrtenal as the starting material, a series of chiral pentadienes (Pdl*) such as dimethylnopadiene (2a), methylphenylnopadiene (2b), and methylnopadiene (2c) have been prepared by Wittig reactions. Deprotonation with the Schlosser base gives the corresponding potassium pentadienides 3a-K–3c-K, whose structures were investigated by NMR spectroscopy and X-ray diffraction studies. In all cases a “U” conformation was observed. Furthermore, the coordination chemistry and electronic properties of these new pentadienyl systems were explored in several half-open trozircene complexes [(η7-C7H7)Zr(η5-Pdl*)] and their PMe3 and tBuNC adducts. Density functional theory (DFT) computations are consistent with the experimentally observed face selectivity upon metal coordination: namely, that the metal coordinates exclusively from the sterically less encumbered side.

Salt elimination reactions between dilithiotroticene [(η7–C7H6Li)Ti(η5–C5H4Li)]∙pmdta (1) (pmdta = N,N′,N′,N″,N″-pentamethyldiethylenetriamine) and siloxane dichlorides ClMe2Si-(OSiMe2)m-Cl (m = 1–3) at low temperature allowed the synthesis and isolation of the siloxane-bridged [n]troticenophanes [(η7–C7H6)Ti(η5–C5H4)](OSiMe2)m(SiMe2) (2, m = 1; 3, m = 2; 4, m = 3) as blue crystalline solids in moderate yield. The compounds were characterized by 1H, 13C and 29Si NMR spectroscopy, elemental and single-crystal X-ray diffraction analyses. The molecular structures of 2 and 3 showed a low degree of strain indicated by the dihedral (α = 4.8° for 2; 4.9/3.7° for 3) and distortion (δ = 176.2° for 2; 174.3/176.3° for 3) angles between the two rings. The structure of 4 was severely disordered. Compounds 2–4 are thermally resistant to ring-opening polymerization, as revealed by differential scanning calorimetry studies, with 2 exhibiting the higher melting temperature. Moreover, the observation of two endotherms in the DSC spectrum of 2 suggests a solid state transition as a result of polymorphism. The reactions of 2–4 with basic initiators such as potassium siloxanolate, ammonium siloxanolate or n-BuLi and analysis of the product distribution by electron ionization mass spectrometry revealed the formation of oligotroticenylsiloxanes incorporating one or more troticenyl units, ring-opened troticenes and ring-expanded troticenophanes [(η7–C7H6)Ti(η5–C5H4)](OSiMe2)r(SiMe2) (r > m). Similar cleavage and extension of the ring were observed by treatment of 2–4 with the acidic initiator Purolite CT-175, and ring-opened troticenes having mixed terminal –OH and –SiMe3 groups were detected. Attempts to copolymerize 2–4 and cyclotrisiloxane with n-BuLi afforded essentially the monomeric and polymeric siloxanes [Me2SiO]w (w = 7, 8), Me2(nBu)Si[OSiMe2]yOSiMe2 (y = 3–6) and Me2(n-Bu)Si[OSiMe2]zOH (z = 1–7), together with the ring-opened and ring-expanded products mentioned above.

The new bulky cyclopentadienyl anions 1,2,4-tri(cyclopentyl)cyclopentadienide and 2,3-diisopropyl-1,4-dimethyl-5-trimethylsilyl-cyclopentadienide were prepared. These and the already known 1,2,4-tri(cyclohexyl)-, 1,2,4-tri(isopropyl)-, 2,3-diisopropyl-1,4-dimethyl-, 1,3,4-triisopropyl-2,5-dimethyl-, pentaphenyl-, and p-butylphenyl-tetraphenyl-cyclopentadienide as well as tert-butylindenide were coordinated to the cycloheptatrienylzirconium fragment [(CHT)ZrCl(tmeda)]. The nine zirconium complexes of the [(CHT)Zr(Cp)] type were characterized by elemental analysis and NMR spectroscopy. For five of the sandwich complexes X-ray crystal structure determination could be carried out; structures of the four others were obtained by DFT calculations. The data serve as a basis for cone angle measurements of cyclopentadienyl ligands to evaluate the steric demand of these ligands.

The redox reaction between the cycloheptatrienyl-cyclopentadienyl zirconium sandwich complexes [(η7-C7H7)Zr(η5-C5R5)] [R = H (2a), R = Me (2b)] and three equivalents of silver(I) acetate, Ag(OAc), afforded [(η5-C5R5)Zr(OAc)3] [R = H (6a), R = Me (6b)] together with elemental silver and 7,7′-bi-1,3,5-cycloheptatriene (5). The molecular structures of 6a and 6b were established by X-ray diffraction analyses, revealing the presence of monomeric half-sandwich complexes with three acetato-κ2O,O′ ligands.

Bulky pyrrolyl ligands have been used for the synthesis of diazaferrocenes, which have been characterized by various spectroscopic techniques, including X-ray diffraction for rac-[{η5-2,3,5-(Me3C)3...

Efficient and simple methods for the large-scale preparation of 1,1′-ferrocenedicarboxylic acid, fc(COOH)2, involving the sodium salts of cyclopentadienecarboxylic methyl and ethyl esters, Na(C5H4COOR) (R = Me, Et), are presented. With fc(COOH)2 at hand, the syntheses of various 1,1′-disubstituted compounds of the type fcX2 (X = CH2OH, COCl, CON3, NCO, NHCOOMe, NHBoc, NH2) were optimized and scaled up. The X-ray crystal structures of fc(COOEt)2, fc(NCO)2·1/2C6H6, and fc(NHCOOMe)2·MeOH are reported.

bibtex: ISI:000400553000098 bibtex\location:'THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND',publisher:'ROYAL SOC CHEMISTRY',type:'Article',affiliation:'Walter, MD (Reprint Author), Tech Univ Carolo Wilhelmina Braunschweig, Inst Anorgan & Analyt Chem, Hagenring 30, D-38106 Braunschweig, Germany. Maron, L (Reprint Author), Univ Toulouse, INSA UPS LPCNO, CNRS LPCNO, 135 Ave Rangueil, F-31077 Toulouse, France. Reiners, Matthias; Maekawa, Miyuki; Daniliuc, Constantin G.; Freytag, Matthias; Jones, Peter G.; Walter, Marc D., Tech Univ Carolo Wilhelmina Braunschweig, Inst Anorgan & Analyt Chem, Hagenring 30, D-38106 Braunschweig, Germany. White, Peter S., Univ N Carolina, Dept Chem, CB 3290, Chapel Hill, NC 27599 USA. Hohenberger, Johannes; Sutter, Joerg; Meyer, Karsten, Univ Erlangen Nurnberg, Dept Chem & Pharm, Inorgan Chem, Egerlandstr 1, D-91058 Erlangen, Germany. Maron, Laurent, Univ Toulouse, INSA UPS LPCNO, CNRS LPCNO, 135 Ave Rangueil, F-31077 Toulouse, France.','author-email':'laurent.maron@irsamc.ups-tlse.fr mwalter@tu-bs.de',da:'2018-12-05','doc-delivery-number':'ET8MH',eissn:'2041-6539','funding-acknowledgement':'Alexander von Humboldt Foundation; NSF [CHE-0615704]; Emmy Noether and Heisenberg program [WA 2513/2, WA 2513/6]; Humboldt Foundation','funding-text':'We thank the Alexander von Humboldt Foundation for a Feodor-Lynen Fellowship (M. D. W.) and Prof. Maurice Brookhart for providing financial support (through NSF Grant CHE-0615704) and laboratory facilities (M. D. W.) during the initial phase of this research program. Deutsche Forschungsgemeinschaft (DFG) is acknowledged for generous funding by the Emmy Noether and Heisenberg program (WA 2513/2 and WA 2513/6, respectively). LM is grateful to the Humboldt Foundation for a grant of experienced researcher and the Chinese Academy of Science. CalMip is also gratefully acknowledged for a generous computational grant.','journal-iso':'Chem. Sci.','keywords-plus':'FE2O2 DIAMOND CORE; STRUCTURAL-CHARACTERIZATION; DINITROGEN ACTIVATION; SULFUR CLUSTERS; SOLVENT PURIFICATION; MOLECULAR-STRUCTURES; ELECTRON-TRANSFER; 2FE-2S CLUSTERS; DOUBLE-BOND; FE-IVN','number-of-cited-references':'106',oa:'DOAJ Gold','orcid-numbers':'Meyer, Karsten/0000-0002-7844-2998 Daniliuc, Constantin G./0000-0002-6709-3673','research-areas':'Chemistry','researcherid-numbers':'Meyer, Karsten/G-2570-2012 Walter, Marc/E-4479-2012','times-cited':'4','unique-id':'ISI:000400553000098','usage-count-last-180-days':'4','usage-count-since-2013':'20','web-of-science-categories':'Chemistry, Multidisciplinary'\; International audience; The iron half-sandwich [Cp'Fe(mu-I)](2) (Cp' = 1,2,4-(Me3C)(3)C5H2, 1) reacts with the pseudohalides NCO-, SCN-, SeCN- and N-3(-) to give [Cp'Fe(mu-NCO)](2) (2), [Cp'Fe(mu-S)](2) (3), [Cp'Fe(mu-Se-2)](2) (4) and [Cp'Fe(mu-N)](2) (5), respectively. Various spectroscopic techniques including X-ray diffraction, solid-state magnetic susceptibility studies and Fe-57 Mossbauer spectroscopy were employed in the characterization of these species. Mossbauer spectroscopy shows a decreasing isomer shift with increasing formal oxidation state, ranging from Fe(II) to Fe(IV), in complexes 1 to 5. The sulfido-bridged dimer 3 exhibits strong antiferromagnetic coupling between the Fe(III) centers. This leads to temperature-independent paramagnetism (TIP) at low temperature, from which the energy gap between the ground and the excited state can be estimated to be 2J = ca. 700 cm(-1). The iron(IV) nitrido complex [Cp'Fe(mu-N)](2) (5) shows no reactivity towards H-2 (10 atm), but undergoes clean reactions with CO (5 bar) and XylNC (Xyl = 2,6-Me2C6H3) to form the diamagnetic isocyanate and carbodiimide complexes [Cp'Fe(CO)(2)(NCO)] (7) and [Cp'Fe(CNXyl)(2)(NCNXyl)] (8), respectively. All compounds were fully characterized, and density functional theory (DFT) computations provide useful insights into their formation and the electronic structures of complexes 3 and 5.

The coordination chemistry of the enantiomerically pure dimethylnopadienyl ligand (Pdl*) with early to late transition metals is presented. Dimethylnopadiene is prepared by a Wittig reaction from (1R)-(−)-myrtenal, which is readily available from the chiral pool. Deprotonation of dimethylnopadiene with a Schlosser base gives K(Pdl*), which is a good starting material for the preparation of the early- to late-transition-metal open metallocenes [M(η5-Pdl*)2] (M = Ti, V, Cr, Fe) and mono(pentadienyl) complexes [(η5-Cp′)Fe(η5-Pdl*)] (Cp′ = 1,2,4-(Me3C)3C5H2), [(η7-C7H7)Zr(η5-Pdl*)], and [(η4-COD)Ir(η5-Pdl*)]. These complexes have been fully characterized by several spectroscopic techniques, elemental analysis, and X-ray crystallography. In all of these cases the Pdl* ligand exhibits excellent face selectivity upon metal coordination, because it coordinates exclusively from the sterically less hindered site of the bicyclic ligand framework. Within the series of open metallocenes [M(η5-Pdl*)2] (M = Ti, V, Cr, F...

An improved synthesis of 2,5-di(tert-butyl)-3,4-dimethylpyrrole (2-H, HPyr(tBu(2)Me(2))) and a subsequent reaction with KH yield K(Pyr(tBu(2)Me(2))) (2-K) in multi-gram quantities. Four different pyrrolyl (Pyr) and imidazolyl (Im) ligands were used in salt metathesis reactions with [(η(7)-C(7)H(7))ZrCl(tmeda)] (7) to afford a series of azatrozircenes: [(η(7)-C(7)H(7))Zr(η(5)-Pyr(tBu(2)))] (1-Zr), [(η(7)-C(7)H(7))Zr(η(5)-Pyr(tBu(2)Me(2)))] (2-Zr), [(η(7)-C(7)H(7))Zr(η(5)-Pyr(tBu(3)))] (3-Zr) and [(η(7)-C(7)H(7))Zr(η(5)-Im(tBu(3)))] (4-Zr), which were characterized by NMR spectroscopy and elemental analysis. In addition, the molecular structures of 2-H, 2-K·18-crown-6, 1-Zr, 2-Zr and 4-Zr were determined by X-ray diffraction analysis, revealing η(5)- rather than κ(1)-N-coordination of the N-heterocyclic ligands. Cone angle measurements on the sandwich complexes 1-Zr–4-Zr showed that their nitrogencontaining ligands belong to the class of very sterically encumbered π-ligands, but DFT calculations suggest lower stabilities compared to their all-carbon analogues.

[FeI2(thf)2] was sequentially treated with Li(C5Me5) and the potassium salt of the phenylmethallyl (“open indenyl”) ligand oIndMe, leading to selective formation of the half-open ferrocene [(η5-C5Me5)Fe(η5-oIndMe)] (1). A variable-temperature NMR study revealed a barrier of ca. 12 kcal mol–1 for the rotation of the phenyl group. The apparent lability and susceptibility of the oIndMe ligand in 1 to undergo η5–η3 interconversion allowed the preparation of the complexes [(η5-C5Me5)Fe(η3-oIndMe)(L)] (2, L = CO; 3, L = IMe; 4, L = PMe3) by addition of carbon monoxide, 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe), and trimethylphosphine, respectively. The η3-bound phenylmethallyl ligand in these complexes initially adopts an anti orientation with regard to the relative positions of the phenyl and methyl substituents, followed by anti-to-syn isomerization. For L = CO, both isomers could be isolated, and the conversion of anti-2 into syn-2 was monitored by NMR spectroscopy at 35, 50, 65, and 80 °C, affording an ...

3,4,5,6-Tetrachlorobenzo-3-(2,4,6-tri-tert-butylphenyl)-1,3,2-dioxaphospholane (2) and benzo-3-(2,4,6-tri-tert-butylphenyl)-1,3,2-dioxaphospholane (4), in which the reactive PIII-center lies close to the sterically demanding Mes* group (Mes* = 2,4,6-tri-tert-butylphenyl), were prepared from Mes*–Br and the corresponding P-chloro-phospholane. Compounds 2 and 4 reacted with various oxidants, azides, MeSO3CF3 or [(tht)AuCl] (tht = tetrahydrothiophene) to give the expected products. All crystal structures of the products display a strongly distorted Mes* system with a boat conformation of the phenyl ring and appreciable out-of-plane deviations of phosphorus and the ortho-tert-butyl groups to opposite sides of the ring. Quantum chemical calculations at the DFT (density functional theory) level of theory were used in order to discriminate between intra- and intermolecular forces, which are responsible for these distortions.

According to a protocol for the synthesis of phosphaallenes we recently established, 3-cyclopropyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphallene was obtained from (Z)-2-bromo-3-cyclopropyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphapropene. A novel bidentate ligand, 1,2-bis(cyclopropyl)-3,4-bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidenecyclobutene, was prepared by oxidative homocoupling of 3-cyclopropyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaallene in the presence of butyllithium, together with the generation of hydrogen gas. The 1,2-bis(cyclopropyl)-3,4-diphosphinidenecyclobutene was allowed to react with (tht)AuCl (tht = tetrahydrothiophene) to afford the corresponding digold(I) complex of a six-membered metallacycle containing the P=C-C=P skeleton. The molecular structures of the 2-bromo-3-cyclopropyl-1-phosphapropene, 1,2-bis(cyclopropyl)-3,4-diphosphinidenecyclobutene and the digold complex were unambiguously determined by X-ray crystallography and are discussed from the point of view of the cyclopropyl conjugation.

The reaction of the symmetric diphosphene 2, 4, 6-(CF3)3-C6H2-P=P-C6H2-2, 4, 6-(CF3)34 with Ru3(CO)12 led to the 50-electron Ru3P2nido-cluster Ru3(CO)9[μ-P-C6H2-2, 4, 6-(CF3)3]25, which in solution at room temperature displays hindered rotation of the aromatic rings about the C(aryl)—P bonds. The structure of 5 was determined by X-ray crystal structure analysis; its Ru3P2 centre forms a distorted square pyramid with one ruthenium atom at the apex. One of the two C6H2(CF3)3 groups is also appreciably distorted. Temperature-dependent 19F NMR studies of the [A3M3X]2 spin system (A = M = CF3, X = 31P) of 5 indicated a rotational barrier ΔG≠ of 82.3 kJ mol-1 at 141 °C. The same Ru3P2 core was obtained by the reaction of the unsymmetric diphosphene Mes*-P=P-Mes 11 with Ru3(CO)12; hindered rotation about the C(aryl)—P bonds was also observed, in this case. Reaktionen von Ru3(CO)12 mit Diphosphenen — Ein neuer Weg zu 50-Elektronen Ru3P2nido-Clustern Die Umsetzung des symmetrischen Diphosphens 2, 4, 6-(CF3)3-C6H2-P=P-C6H2-2, 4, 6-(CF3)34 mit Ru3(CO)12 fuhrte zu dem 50-Elektronen Ru3P2nido-Cluster Ru3(CO)9[μ-P-C6H2-2, 4, 6-(CF3)3]25. Dieser zeigt in Losung bei Raumtemperatur Rotationsbehinderung der aromatischen Ringe um die C(Aryl)-P-Bindungen. Die Struktur von 5 wurde durch Rontgenbeugung ermittelt. Das Ru3P2-Zentrum bildet eine verzerrte quadratische Pyramide mit einem Rutheniumatom in der apikalen Position. Eine der zwei C6H2(CF3)3-Gruppen ist ebenfalls betrachtlich verzerrt. Temperaturabhangige 19F-NMR-Studien des [A3M3X]2 Spinsystems (A = M = CF3, X = 31P) in 5 ergaben eine Rotationsbarriere ΔG≠ von 82.3 kJ mol-1 bei 141 °C. Das gleiche Ru3P2-Zentrum wurde bei der Umsetzung des unsymmetrischen Diphosphens Mes6ast;-P=P-Mes 11 mit Ru3(CO)12 erhalten. Auch in diesem Fall wurde eine Hinderung der Rotation um die C(Aryl)-P-Bindungen beobachtet.