Thomas Zahn

Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen: IX. Tellur-brücken in organometall-komplexen: Aufbau, protonierung und molekülgeometrie☆

Abstract Ligand-free tellurium acts as a bridging element in the novel chromium, molybdenum, and tungsten complexes of composition (μ-Te)[(η 5 -C 5 R 5 )M(CO) 3 ] 2 ( 2a–2e ; R = H, CH 3 ; M = Cr, Mo, W) which are accessible in 32–72% isolated yield on treatment of the ionic precursor species Na + (K + ) [(η 5 -C 5 R 5 )M(CO) 3 ] − ( 1a–1e ) with potassium tellurite in the presence of hydrochloric acid. The new compounds have been structurally characterized (X-ray diffraction, compound 2a ) and exhibit bent metal-tellurium-metal frameworks (e.g. Cr,Te,Cr 117.2(0)°). The comparably long chromium-tellurium distances recorded in the case of 2a (279.9(1), 281.4(1) pm) are interpreted as single bonds, thus being in agreement with the electronic requirements of the chromium centres. The tellurium bridge is considered to act as a two-electron ligand which stabilizes two (η-C 5 H 5 )Cr(CO) 3 fragments. Neither under thermal conditions nor upon photolysis do complexes 2a–2e undergo partial decarbonylation. Hence, they do not represent suitable precursors of the hitherto unknown derivatives of composition (μ-Te)[(η 5 -C 5 R 5 )M(CO) 2 ] 2 ; these latter compounds should contain linear multiple-bonded structures like those established for the stoichiometrically analogous sulfur and selenium derivatives. Protonation of 2a with ethereal tetrafluoroboric acid quantitatively yields the Bronsted-acidic ionic complex 3a of formula [(μ-TeH){(η-C 5 H 5 )Cr(CO) 3 } 2 ][BF 4 ]. which can be deprotonated by diethylamine in reverse to its formation.

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen. X: Aufbau einer tetraedrischen TeMnFe2-Clusterverbindung nach dem Isolobal-Prinzip

Abstract Treatment of the tellurium complex (μ-Te)[(η 5 -C 5 Me 5 )Mn(CO) 2 ] 2 ( 1 ; Me = CH 3 ) with enneacarbonyldiiron yields the tetranuclear cluster compound 2 of composition (η 5 -C 5 Me 5 )MnFe 2 Te(CO) 8 . From a structural point of view, this compound is considered to be a metallatetrahedral-type molecule, according to a single-crystal X-ray diffraction study, thus following the concept of isolobal connectivity (monoclinic, space group P 2 1 / n ; a 982.4(2), b 1483.6(3), c 1535.5(5) pm, β 97.22(2)°; R (iso) = 0.13, R (aniso) = 0.036, R w = 0.033).

Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen: XVIII. Heterometallische selenido-komplexe☆

Abstract The selenium bridge present in the iron complex (μ-Se)[(η5-C5H5)Fe(CO)2]2 (1) exhibits nucleophilic character and is thus prone to addition reactions with electrophilic reagents. Treatment of 1 with the coordinatively unsaturated fragment (η5-C5H5)Mn(CO)2 results in formation of the heteronuclear complex (η5- C5H5)3Fe2MnSe(CO)6 (2) which contains a flattened pyramidal Fe2MnSe core, with the selenium atom occupying the top of position of this framework. No FeMn and FeFe bonds are present in this molecule (single crystal X-ray diffraction study). Compound 2 is very light-sensitive in solution, thus giving the derivative (η5-C5H5)3Fe2MnSe(CO)5(3). According to a crystal structure determination, this latter compound once again exhibits a pyramidal Fe2MnSe core but with the iron atoms directly connected with each other via a single bond (266.7(1) pm).

Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen XXVIII. Cycloaddition von heterokumulenen an oxorhenium-halbsandwich-komplexe: Synthese neuartiger metallacyclen

Abstract The dinuclear oxorhenium complex (η 5 -C 5 Me 5 )Re 2 O 4 reacts with diphenylketene to give, via formal [2 + 2]-cycloaddition at the (hypothetical) fragment (η 5 -C 5 Me 5 )ReO 2 , the novel, four-membered metallacyclic compound (η 5 -C 5 Me 5 )Re(O)(η 2 - O 2 CCR 2 ) (R = C 6 H 5 ). Cleavage of the dinuclear Re 2 O 2 core with addition of the heterocumulene to a ReO group is also observed when phenyl isocyanate is used instead of diphenyl ketene. In this case, the cyclic derivative (η 5 -C 5 Me 5 )Re(O)(η 2 - O CO N R) (R = C 6 H 5 ) containing a O,N -coordinated ligand in the four-membered structure has been formed. In contrast, the mononuclear half-sandwich complex (η 5 -C 5 Me 5 ReO 3 reacts with diphenylketene according to a formal [3 + 2]-cycloaddition at a ReO 2 core to give the five-membered metallacycle (η 5 -C 5 Me 5 )Re(O)(η 2 - O 2 COCR 2 ) (R = C 6 H 5 ). The three cycloaddition products have been structurally characterized by means of X-ray diffraction techniques.

Übergangsmetall-methylen-komplexe: LXIV. Mehrfachbindungen zwischen verschiedenartigen übergangsmetallen: die elementkombinationen cobalt/iridium und rhodium/iridium sowie ihre organische und metalloganische “cyclopropanierung”

Abstract The metal combinations, cobalt/iridium and rhodium/iridium, exhibiting formal double bonds, are readily and cleanly obtained as the heterodinuclear organometallic compounds (η 5 -C 5 R 5 )M(η-CO) 2 M′(η 5 -C 5 R 5 ) ( 1–4 ; R = H, CH 3 ; M/M′ = Co/Ir and Rh/Ir, respectively). By the well-established cyclopropanation reaction with diazoalkenes, compounds 1–4 yield their μ-alkylidene derivatives 5, 6, 7 and 8a–e , of which the formal M/M′ bond order is reduced to 1. Sulfur dioxide and 4 analogously produce the cyclic RhIrS compound 9 . The heterotrinuclear complexes 10–12 are examples of 46e- and 48e-cluster molecules and result either from side-reactions in the synthesis of 1 and 4 , or from a straightforward synthesis. The structural details of the reported complexes 1 (metal combination Co/Ir), 5 (Co/Ir), 8a (Rh/Ir), 10 (Rh 2 /Ir) and 12 (Co 2 /Ir) have been determined.

Metal complexes of cyclophanes: VIII. The crystal and molecular structures of 5,13-dimethyl[2.2]metacyclophane and [3-8-η-5,13-dimethyl[2.2]metacyclophane(η5-cyclopentadienyl)iron]-hexafluorophosphate

Abstract The crystal structures of 5,13-dimethyl[2.2]metacyclophane and [3-8-η-5,13-dimethyl[2.2]metacyclophane(η 5 -cyclopentadienyl)iron]hexafluorophosphate have been determined in order to examine the effect of metal π-bonding to the geometry of the metacyclophane molecule.

Synthesis and characterization of the triethylphosphine adduct of bis(2,4-dimethylpentadienyl)tungsten, [W(2,4-C7H11)2(PEt3)], a complex with one η5-U and one η5-S pentadienyl ligand

Abstract The reaction of [WCl4(PEt3)2] with 4 equiv. of the 2,4-dimethylpentadienyl anion leads to the spontaneous reduction of the W(IV) complex by two of the dienyl anions, along with incorporation of the other two anions in the resulting W(II) complex [W(2,4-C7H11)2(PEt3)] (2,4-C7H11=2,4-dimethylpentadienyl). Spectroscopic data reveal a low symmetry structure, presumed to be analogous to that found for the molybdenum analogue, in which one dienyl ligand was bound in the usual η5-U conformation, the other in the uncommon η5-S (sickle) conformation. This has been confirmed through a single crystal X-ray diffraction study.