Werner Massa

Phosphoraneiminato complexes of transition metals

Abstract A review on syntheses, chemical reactions, structure and bonding of phorphoraneiminato complexes of transition metals (TM) is given. The ligand group [NPR3]−, not known as a discrete ion, is isoelectronic with, amongst others, [OSiMe3]−, and is capable of a versatile coordination chemistry. Apart from terminal functions [M]≡N–PR3 with a close to linear M–N–P axis (A) and bent axis (B), complexes with μ2-N-bridges forming symmetrical (D) or unsymmetrical (C) four-membered M2N2 rings are as well known as those of the μ3-N-type (E) leading to heterocubane M4N4 structures. The coordination type preferred is primarily dependent on the oxidation state (OS) of the TM, but also on the ligand sphere of the TM and on the steric and electronic properties of the substituents at phosphorus (R=organic group, NR′2, halogen). Types A and B are predominantly realized in complexes of metals in high OS. Electron-rich metals prefer type E, and in mediate OS bonding modes C and D prevail.

1,1′-Bis(N,N-dimethylamino)ferrocene,1,1′-bis(N,N-dimethylamino) cobaltocenium hexafluorophosphate and 1,1′-bis(N,N-dimethylamino)titanocene dichloride. Crystal structure of 1,1′-bis(N,N-dimethylamino)titanocene dichloride

Abstract A general method for the preparation of 1,1′-bis( N,N -dimethylamino)metallocenes is described, involving the reaction of N,N -dimethylamino-cyclopentadienyllithium ( 1 -Li) with metal chlorides. 1,1′-Bis( N,N -dimethylamino)ferrocene ( 2 ), 1,1′-bis( N,N -dimethylamino)cobaltocenium hexafluorophosphate ( 3 + PF 6 − ) and 1,1′-bis( N,N -dimethylamino)titanocene dichloride ( 4 ) have been synthesized in this way. The influence of the dimethylamino donor substituent has been studied by means of cyclic voltammetry. 1,1′-Bis( N,N -dimethylamino)ferrocene ( 2 ), e.g., has the most negative redox potential ( E o −0.23 V (SCE)) so far reported for a ferrocene derivative. The structure of 1,1-bis( N,N -dimethylamino)titanocene dichloride ( 4 ) has been determined by X-ray crystallography. It crystallizes in hexagonal plates with the space group C2/c ( Z = 4, a 1301.4, b 647.2, c 1828.5 pm, β 98.81°). The titanium atom does not lie exactly above the centres of the cyclopentadienyl rings, and the CN bond from the cyclopentadienyl ring carbon atom C(1) to the nitrogen atom of the dimethylamino group is very short (134.7 pm).

Synthesis and structural, spectroscopic and magnetic characterization of iron(II) and iron(III) complexes of N-2-pyridinylcarbonyl-2-pyridinecarboximidate

Abstract One iron(II) complex of N -2-pyridinylcarbonyl-2-pyridinecarboximidate monoanion (bpca), [Fe(bpca) 2 ]·H 2 O ( 1 ), and three iron(III) complexes, [Fe(bpca)Cl 2 (H 2 O)]·(CH 3 ) 2 CO ( 2 ), [Fe(bpca) 2 ](NO 3 )·1.67H 2 O ( 3 ), [Fe(bpca) 2 ](ClO 4 ) ( 4 ), have been prepared and characterized by means of IR, UV-Vis and EPR spectroscopy and magnetic susceptibility measurements, where appropriate. The crystal structures of 1 – 3 have been determined from single crystal X-ray data, showing that the metallic ions are surrounded in all cases by distorted octahedral coordination spheres. From magnetic measurements it is evident that compounds 1 and 3 are practically in the low-spin state at room temperature, compound 2 is in the high-spin state in all the range of measured temperatures and compound 4 shows spin-crossover behaviour. Crystal data for 1 : space group P 2 1 / c , a =8.827(1), b =8.941(2), c =28.957(4) A, β=95.90(1)°, Z =4; for 2 : space group P 2 1 / c , a =8.293(2), b =13.779(2), c =15.884(4) A, β=98.22(1)°, Z =4; for 3 : space group P 1 , a =8.840(1), b =10.713(1), c =14.989(1) A, α=71.16(1), β=73.43(1), γ=82.67(1)°, Z =2.

Stable germa- and stannaethenes

Stable germaand stannaethenes have been synthesized by addition of germylenes and stannylenes to a kryptodiborylcarbene. Extreme nmr-deshielding of tin is decisive proof for tricoordinated tin atoms in the stannaethenes. Considerable ylid character of germaand stannaethenes is deduced from nmr-shielding of boron atoms adjacent to the tricoordinated carbon atom. X-ray analysis of a germaand a stannaethene revealed strong distortion from planarity at the C=Ge and C5n bond: twisting of 36* and 61* and pyramidalization at carbon of 5* and 16 as measured by the fold angle. The distances from germanium and tin to the tncoordinated carbon (182.7(4) and 202.5(4) pm) are distinctly shorter (8.4 and 6.4%) than to tetracoordinated carbon atoms.

Controlling the Assembly of Chalcogenide Anions in Ionic Liquids: From Binary Ge/Se through Ternary Ge/Sn/Se to Binary Sn/Se Frameworks

Seven compounds with binary or ternary Ge/Se, Ge/Sn/Se, or Sn/Se anionic substructures crystallized upon the ionothermal reactions of [K(4)(H(2)O)(3)][Ge(4)Se(10)] with SnCl(4)·5H(2)O or SnCl(2) in [BMMIm][BF(4)] or [BMIm][BF(4)] (BMMIm=1-butyl-2,3-dimethyl-imidazolium, BMIm=1-butyl-3-methyl-imidazolium). The products were obtained by subtly varying the reaction conditions; the nature and amount of an additional amine was the most important parameter in the product selection and in determining the Sn/Ge ratio in the isolated products. The crystal structures of these chalcogenides were based on complex anions with unprecedented topologies that varied from discrete clusters (0D) through 1D chain structures or 2D layers to 3D frameworks. The architecture and composition of the title compounds were well reflected by their optical absorption behavior. Herein, we report a convenient approach for the generation of chalcogenidometallate phases with fine-tunable electronic properties in ionic liquids, which have been inaccessible by traditional methods.

Intrachain exchange energies in 1-dimensional magnetic fluoromanganates(III) as a function of MnFMn bridge angle and crystal structure of Li2MnF5

Seven pentafluoromanganates(III) AI2MnF5 (A = Li, Na, NH4), AI2MnF5 · H2O (A = Rb, Cs), and AIIMnF5 · H2O (A = Sr, Ba) with linear chain structures of trans-connected [MnF6] octahedra have been used as model compounds for investigating the correlation of one-dimensional antiferromagnetic exchange energy and bridge angle. The crystal structure of Li2MnF5 was determined by X-ray diffraction (space group C2c, Z = 4, a = 10.016(1), b = 4.948(1), c = 7.408(1), A, β = 112.19(1)°, Rw = 0.019 for 605 reflections). The bridge angle MnFMn is dependent upon the cation and varies between 121.5° in this Li compound and 180° in Cs2MnF5 · H2O. The magnetic properties have been analyzed by use of both high- and low-temperature theoretical methods. Above 10 K, the susceptibility is essentially that of a system with weak antiferromagnetic coupling by nearest-neighbor Heisenberg exchange interaction within an extended linear chain. The absolute value of the intrachain exchange energy Jk depends to a marked extent upon the MnFMn bridge angle β rather than on the MnMn or MnF distances. With decreasing angle β, the antiferromagnetic interactions obviously decrease as cos2(β) owing to a decrease in the σ-overlap of the dz2 and pz orbitals involved in a superexchange mechanism.

Cycloadditions of vinylindoles with chiral carbodienophiles: the first asymmetric Diels-Alder reactions in the vinylhetarane series

Abstract The first asymmetric Diels-Alder reactions of some 3- and 2-vinylindoles with ( N -propenoyl)bornane-10,2-sultam are described. With one exception, the experimental results are indicative of a high π-facial diastereoselectivity. Following a related procedure, 3-vinylindoles were also allowed to react with a racemic bis(naphthylsulfonyl)-dienophile to furnish tetrahydrocarbazoles with endo -diastereoselectivity.

Changes in the structural dimensionality of selenidostannates in ionic liquids: formation, structures, stability, and photoconductivity.

In situ transformations of selenidostannate frameworks in ionic liquids (ILs) were initiated by treatment of the starting phase K2[Sn2Se5] and the consecutive reaction products by means of temperature increase and/or amine addition. Along the reaction pathway, the framework dimensionalities of the five involved selenidostannate anions develop from 3D to 1D and back, both in top-down and bottom-up style. Addition of ethane-1,2-diamine (en) led to the reversion of the 2D→1D step from 2D-{[Sn24Se56](16-)} to 1D-{[Sn6Se14](4-)}. As rationalized by DFT investigations, the 2D anion is thermodynamically favored. Photoconductivity measurements reveal that all samples show Schottky contact behavior with absolute thresholds below 10 V. One of the samples exhibits conductive states within the energy range of visible photons.

Unusual 14-Electron Fragments [Pd(η3-Bi3−xPbx)](x+1)− as Pseudo Lead Atoms in closo-[Pd@Pd2Pb10Bi6]4−†

How to simplify a complex thing: A salt of the heaviest intermetalloid cluster known to date, [K([2.2.2]crypt)]4 [Pd@Pd2 Pb10 Bi6 ]⋅2 en, resulted from a reaction of [Pd(PPh3 )4 ] with [K([2.2.2]crypt)]2 (Pb2 Bi2 )⋅2 en in ethane-1,2-diamine (en). The electron number of the ternary intermetalloid anion accords with Wade-Mingos rules, as the [Pd(η(3) -Bi3-x Pbx )]((x+1)-) (x=0, 1) 14-electron fragments formed in situ are isolobal with Pb atoms.

Alcoholysis of Aluminum Alkyls Supported by Bulky Phenoxide Ligands: Synthesis, Characterization, and ε-Caprolactone Polymerization Activity of Two Dimeric Aluminum Isopropoxides

Reaction of trialkylaluminum Al2R6 (R = Me, Et) with 2,2′-methylenebis(6-tert-butyl-4-methylphenol) (mbmpH2) gives the dimeric mono(alkyl) complex [Al(mbmp)R]2 with bridging oxygen atoms. Reaction of [Al(mbmp)R]2 with one equiv. of 2-propanol results in the formation of the dimeric isopropoxide [Al(mbmp)(μ-OiPr)]2. Single-crystal X-ray analysis shows a C2h-symmetric structure with a planar Al2O2 core. Monomeric methylbis(2,6-di-tert-butyl-4-methylphenolato)aluminum, AlMe(OC6H2-2,6-tBu2-4-Me)2 (MAD), was found to react with one equiv. of 2-propanol to give a dimeric isopropoxide [AlMe(OC6H2-2,6-tBu2-4-Me)(μ-OiPr)]2 in which the bulky phenolate, instead of the methyl group, has been displaced. According to the single-crystal X-ray structure analysis, the molecule contains a similar Al2O2 core, but the two 2,6-di-tert-butyl-4-methylphenolato ligands are cis- and orthogonally arranged to each other. ϵ-Caprolactone is polymerized at 50 °C in toluene in a controlled manner by [Al(mbmp)(μ-OiPr)]2, to give poly(ϵ-caprolactone) with high molecular weights and narrow molecular weight distributions (Mw/Mn < 1.50). The low efficiency values (number of polymer chains initiated per aluminum atom) imply that [Al(mbmp)(μ-OiPr)]2 exists in a monomer–dimer equilibrium. The polymerization of ϵ-caprolactone by [AlMe(OC6H2-2,6-tBu2-4-Me)(μ-OiPr)]2 is faster, but somewhat less controlled.