Andreas Behrendt

Metall-Komplexe von Heteroarenen. VI: Hexakis (η1-phosphinin)chrom : Synthese, Struktur und Redoxverhalten

Two alternative pathways, metal-atom ligand-vapor cocondensation and ligand substitution at bis(2,4-dimethyl-η5-pentadienyl)chromium, lead to hexakis(η1-phosphinine)chromium(0), 10. According to an X-ray crystal structure determination the CrP6 core represents an almost ideal octahedron, the bond lengths d(Crue5f8P) 226.5 pm being particularly short. Whereas the intraligand bond-lengths experience only minor changes upon η1-coordination of phosphinine, the changes in the 1H-, 13C- and 31P parameters are substantial. Compared with hexakis(η1-phenylisocyanide)chromium, the UV/VIS spectrum of 10 displays a bathochromic shift in the MLCT region which attests to a stronger π-acceptor character of phosphinine. The attendant propensity of this ligand to stabilize the oxidation state Cr 0 manifests itself in the redox potentials for the couples CrL6+/0 which are increasingly anodic according to the sequence Cr(bpy)3 < Cr(PhNC)6 < Cr(C5H5P)6 < Cr(CO)6.

Metal π-complexes of benzene derivatives XLVIII. Dimethylphosphano derivatives of bis(benzene) chromium as monodentate and chelating ligands at μ-ethylidyne-nona(carbonyl)-tri(cobalt). Synthesis via ETC-autocatalysis, crystal structure determination and redox behavior of [(Me2P-η6-C6H5)(η6-C6H6)Cr[(μ-MeC)Co3(CO)8], [(Me2P-η6-C6H5)2Cr][(μ-MeC) Co3(CO)8]2 and [(Me2P-η6-C6H5)2Cr][μ,-MeC)Co3(CO)7]

Abstract Reaction of μ-ethylidyne-nona(carbonyl)-tri(cobalt) (3) with (Me2P-η7-C6H5)(η6-C6H6)Cr (1) and (Me2P-η6-C6H5)2Cr (2), respectively, at ambient temperature affords the substitution products [(Me2P-η6-C6H6)(η6-C6H6)Cr[(μ-MeC)Co3(CO)5] (5), [(Me2P-η16-C6H5)2Cr][(μ-MeC)Co3(CO)8]2 (6) and [Me2P-η6-C6H5Cr][(μ-MeC)Co3(CO)7] (7). The surprisingly mild conditions under which these reactions proceed are a consequence of an electron-transfer chain (ETC) autocatalysis which operates due to the close proximity of the redox potentials 1+/0, 2+/0 and 30/− as determined by cyclic voltammetry. In the case of 6, reduction of the two CCo3 carbonyl cluster units does not feature redox splitting, i.e. δE 1 2 P 1 , a = 862.5(4) pm, b = 1005.7(5) pm, c = 1282.7(3) pm, α = 106.54(3)°, β = 94.86(3)°, γ = 93.52(4)°, Z = 1, wR = 0.073 for 2419 reflections with F > 4σ-(F). 7: triclinic; P 1 , a = 1047.4(2) pm, b = 1068.0(1) pm, c = 1442.4(2) pm, α = 90.36(1)°, β = 110.34(1)°, γ = 113.32(1)°, Z = 2, R = 0.0435 for 2241 reflections with F > 4σ(F).

Metal π complexes of benzene derivatives: XLIII. Intramolecular interactions between bis(benzene) chromium and cymantrene units in di- and tri-nuclear species containing PMe2 spacers, as studied by CV and EPR

Abstract Taking advantage of the ability of R2P-substituted derivatives of bis(benzene)chromium and bis(benzene)vanadium to act as organometallic ligands, we have prepared the di- and tri-nuclear complexes [(η)6-C6H6)(Me2P-η6-C6H5)Cr](η5-MeC5H4)(CO)2Mn) (3), μ(Me2P-η6-C6H5)2CrI(η5-MeC5H4)(CO)2Mn]2 (7), [(Me2P-η6-C6H5)2Cr](η5-MeC5H4)(CO)Mn (9) and [(Me2P-η6-C6H5)2V] (η5-MeC5H4)(CO)Mn (10). The structures of 7 and 9 were determined by X-ray diffraction studies. Intermetallic communication in the binuclear complexes is reflected in small shifts of their redox potentials relative to those of the corresponding mononuclear component. Redox splitting for the oxidation of the terminal MeCpMn(CO)2 units of 7+. is not resolved. The EPR spectra of 3+., 7+. and 9+. show, in addition to strong 53Cr hyperfine coupling, a small interaction caused by 55Mn. Whereas the monoradical monocations 3+., 7+. and 9+. can be isolated as hexafluorophosphates, the dications 3+.+. and 9+.+. and the trication 7+.+.+.; although formed reversibly as indicated by cyclic voltammetry, could not be isolated on a preparative scale. In the case of 9+.+. the biradical character was demonstrated by the observation of a ΔMs = 2 transition in the EPR spectrum. Detailed analysis of the ΔMs = 1 region was hampered by substantial decomposition of the dication even at low temperature.

Metallkomplexe von Heteroarenen, VII: Bis(2,3,5,6-tetramethyl-η6-pyrazin)vanadium, der erste Bis(aren)metall-Komplex mit vier N-Atomen in der Koordinationssphäre / Metal Complexes of Heteroarenes, VII: Bis(2,3,5,6-tetramethyl-η6-pyrazine)vanadium, the First Bis(arene)metal Complex with Four N Atoms in the Coordination Sphere

Cocondensation of 2,3,5,6-tetramethyl-pyrazine with vanadium atoms affords [2,3,5,6-(CH3)4-η6-1,4-C4N2]2V (6) which has been studied by X-ray crystallography, EPR-spectro-scopy and cyclic voltammetry. As shown by unequal metal ring-atom distances (V—C = 219.6, V—N = 210.9 pm) the ligand in 6 is folded along the N—N axis (dihedral angle 13.6°). The conformation adopted by the cyclic ligands in the crystal has a torsional angle of 44.2° which comes close to the angle of 45° expected for maximum back-bonding, the filled vanadium orbitals 3 dx2-γ2and 3 dxy interacting separately with unoccupied b3u(π*) orbitals of the individual pyrazine rings. The hyperfine coupling constant a(51V) = 4.45 mT attests to comparatively small spin density at the metal nucleus. It is proposed, that substantial transfer of spin density is effected by V 3dz2→ag(σn+) overlap, the latter function representing the in-phase combination of the nitrogen “lone pair” orbitals. Contrary to bis(η6-phosphinine)vanadium 8, for the pyrazine complex 6 only the anion 6⁻ is formed reversibly in cyclovoltammetry, oxidation to 6+ being irreversible. However, in common with 8, the redox potentials for 6 show pronounced anodic shifts. Attempts towards η6-coordination of 2,4,6-trimethyl-1,3,5-triazine failed. Apparently, the 1:1 ratio of CH3/N is insufficient to furnish the triazine ring with the appropriate combination of π-donor and δ-acceptor properties essential for synergetic bond formation.

Phosphaniminato-Cluster des Kupfers. Synthese und Kristallstrukturen von [Cu6Cl6(NPMe3)4]Cl[Me3SiNPMe3] · CH2Cl2 und [Cu6Cl6(NPMe3)4][Cu(Me3SiNPMe3)2]Cl2 / Phosphoraneim inato Clusters of Copper. Syntheses and Crystal Structures of [Cu6Cl6(NPMe3)4]Cl[Me3SiNPMe3] · CH2Cl2 and [Cu6Cl6(NPMe3)4][Cu(Me3SiNPMe3)2]Cl2

Abstract The title compounds have been prepared as black-blue crystals with metallic lustre by the reaction of CuCl2 and CuCl, respectively, with Me3SiNPMe3 in CH2Cl2 suspensions. The complexes have been characterized by cyclic voltammetry and by crystal structure determinations. [Cu6Cl6(NPMe3)4]Cl[Me3SiNPMe3] · CH2Cl2: Space group P212121, Z = 4, structure solution with 4407 unique observed reflections, R = 0.057. Lattice dimensions at -70 °C: a -1159.3(8), b = 2027.1(14), c = 2063.3(12) pm. The compound consists of cluster ions [Cu6Cl6(NPMe3)4]+, in which the copper atoms form a regular octahedron. Four planes of the octahedra are capped by μ3-nitrogen atoms of the (NPMe3)- groups. Each of the Cu atoms is connected with a terminal chlorine atom . Another chloride ion serves for charge compensation; this ion occupies another Cu3 plane of the octahedron. Without bonding interaction one Me3SiNPMe3 molecule and one CH2Cl2 molecule are included in the lattice. [Cu6Cl6(NPMe3)4][Cu(Me3SiNPMe3)2]Cl2: Space group Pna21, Z = 4, structure solution with 5676 unique observed reflections, R = 0.071. Lattice dimensions at -70 °C: a = 3117.2(21), b = 1927.4(11), c = 1002.7(8) pm. The compound consists of cluster ions [Cu6Cl6(NPMe3)4]+, the complex ion [Cu(Me3SiNPMe3)2]+, and chloride ions. In the cation [Cu(Me3SiNPMe3)2]+ the copper atom is linearly coordinated by the nitrogen atoms of the phosphaneimine molecules.