C---H bond activation by rhodium(I) and the mechanism of the olefin isomerization: new synthesis of β,γ-unsaturated ketones via η- or η-alkylallylrhodium(III) complexes by reductive elimination

Acylrhodium(III)-η³-1-ethylallyl complex (7) was prepared by the reaction of 8-quinolinecarboxaldehyde (3) and 1,4-pentadienerhodium(I) chloride (2) by C---H bond activation, followed by hydrometallation, and double bond migration. Higher concentrations of pyridine as coordinating ligand transforms η³-1-ethylallylrhodium(III) complexes (8a,8b) into η¹-pent-2-enylrhodium(III) complex (11a). Acylrhodium(III)-η³-syn,anti-1,3-dimethylallyl complex (14) was also prepared from 1,3-pentadienerhodium(I) chloride (16) and 3. The reductive elimination of acylrhodium(III)-η¹- and -η³-1-alkylallyl complexes by trimethylphosphite gives various β,γ-unsaturated ketones.     

Übergangsmetallketen-verbindungen : XXIX. Cyclopropylsubstituierte η- und η-Ketenylverbindungen des Wolframs; Elektronenstruktur und Bindungsverhältnisse in Carbonyl(η-cyclopentadienyl)(η-cyclopropylketenyl) (trimethylphosphin)wolfram

Synthesis and spectroscopic data of carbonyl(η⁵-cyclopentadienyl)(η²-cyclopropylketenyl) (trimethylphosphine)tungsten and dicarbonyl(η⁵-cyclopentadienyl)(η¹-cyclopropylketenyl) (trimethylphosphine)tungsten are reported. The electronic structure of, and types of bonding in carbonyl(η⁵-cyclopentadienyl)(η²-cyclopropylketenyl) (trimethylphosphine)tungsten are described.     

Stereoselectivity in nucleophilic addition to unsaturated ligands bound to molybdenum : Allylic alkylation of cyclohexanone

The stereochemistry and regiochemistry of nucleophilic addition to olefinic, allylic, or diene moieties can be controlled in reactions of molybdenum complexes. The synthesis of a wide range of -allylic cyclohexanones is feasible using (η⁵-cyclopentadienyl)Mo(CO)(NO)(allyl) cations. The stereoselective preparation of (RS,SR)-2-(1-methyl-2-butenyl)cyclohexanone from the reaction of 1-pyrrolidino-1-cyclohexene with [CpMo(CO)(NO)(η³-1,3-dimethylallyl)]BF₄ illustrates the methodology.     

Syntheses, X-ray structures, and reactions of ruthenium carbonyl complexes containing 1,1-dithiolates

Treatment of [Ru₂(CO)₄(MeCN)₆][BF₄]₂ or [Ru₂(CO)₄(μ-O₂CMe)₂(MeCN)₂] with uni-negative 1,1-dithiolate anions via potassium dimethyldithiocarbamate, sodium diethyldithiocarbamate, potassium tert-butylthioxanthate, and ammonium O,O′-diethylthiophosphate gives both monomeric and dimeric products of cis-[Ru(CO)₂(η²-(SS))₂] ((SS)⁻=Me₂NCS₂⁻ (1), Et₂NCS₂⁻ (2), ^tBuSCS₂⁻ (3), (EtO)₂PS₂⁻ (4)) and [Ru(CO)(η²-(Me₂NCS₂))(μ,η²-Me₂NCS₂)]₂ (5). The lightly stabilized MeCN ligands of [Ru₂(CO)₄(MeCN)₆][BF₄]₂ are replaced more readily than the bound acetate ligands of [Ru₂(CO)₄(μ-O₂CMe)₂(MeCN)₂] by thiolates to produce cis-[Ru(CO)₂(η²-(SS))₂] with less selectivity. Structures 1 and 5 were determined by X-ray crystallography. Although the two chelating dithiolates are cis to each other in 1, the dithiolates are trans to each other in each of the {Ru(CO)(η²-Me₂NCS₂)₂} fragment of 5. The dimeric product 5 can be prepared alternatively from the decarbonylation reaction of 1 with a suitable amount of Me₃NO in MeCN. However, the dimer [Ru(CO)(η²-Et₂NCS₂)(μ,η²-Et₂NCS₂)]₂ (6), prepared from the reaction of 2 with Me₃NO, has a structure different from 5. The spectral data of 6 probably indicate that the two chelating dithiolates are cis to each other in one {Ru(CO)(η²-Et₂NCS₂)₂}fragment but trans in the other. Both 5 and 6 react readily at ambient temperature with benzyl isocyanide to yield cis-[Ru(CO)(CNCH₂Ph)(η²-(SS))₂] ((SS)=Me₂NCS₂⁻ (7) and Et₂NCS₂⁻ (8)). A dimerization pathway for cis-[Ru(CO)₂(η²-(SS))₂] via decabonylation and isomerization is proposed.     

Photochemische reaktionen von übergangsmetall-organyl-komplexen mit Olefinen XII. Photochemisch induzierte [5 + 2, 3 + 2]-cycloadditionen von alkinen an tricarbonyl-η-cyclohexadienly-mangan

Upon UV irradiation in hexane at 243 K tricarbonyl-η⁵-cyclohexadienyl-manganese (1) and two equivalents of 2-butyne (2) or diphenylacetylene (4) yield in successive [5 + 2, 3 + 2] cycloadditions tricarbonyl-η^2:2:1-1,2,3,10-tetramethyl-tricyclo[5.2.1.0^4,9]-deca-2,5-dien-10-yl-manganese (6), or tricarbonyl-η^2:2:1-1,2,3,10-tetraphenyl-tricyclo[5.2.1.0^4,9]-deca-2,5-dien-10-yl-manganese (8), respectively. 3-Hexyne (3) reacts with 1 under the same conditions by successive [5 + 2, 3 + 2] cycloadditions and 1,4-H-shift to tricarbonyl-η^2:2:1-1,2,3-triethyl-10-ethylidene-tricyclo[5.2.1.0^4,9]dec-2-en-5-yl-manganse (7). Identical products are also obtained when 1 is first irradiated in THF at 208 K and the thermolabile intermediate, dicarbonyl-η⁵-cyclohexadienyl-tetrahydrofurane-manganese (11), is treated with an excess of the alkynes 2–4. In contrast, bis(trimethylsily)acetylene (5) substitutes photochemically in 1 only a CO ligand to yield dicarbonyl-η⁵-cyclohexadienyl-η²-bis(trimethylsily)Acetylene-manganese (9). The crystal and molecular structure of 7 was determined by an X-ray diffraction analysis. Complex 7 crystallizes in the triclinic space group , a = 822.6(2) pm, B = 882.5(2) pm, C = 1344.6(2) pm, = 92.36(2)°, β = 107.13(2)°, γ = 99.71(2)°, V = 0.9152(3) nm³, Z = 2. The complexes 6–9 were studied in solution by IR and NMR spectroscopy. The structures of 6,8 and 9 were elucidated from the NMR spectra. A possible formation mechanism for the complexes 6–9 will be discussed.     

Titanocene and zirconocene σ-alkynyl complexes in C---C single bond coupling and cleavage reactions

Group 4 metallocene mono- and bis-σ-alkynyl complexes of the type L₂M(σ-CCR) and L₂M(σ-CCR)₂ with M=titanium and zirconium in the oxidation states +3 and +4 and L=Cp (η⁵-cyclopentadienyl) and Cp^* (η⁵-pentamethylcyclopentadienyl) are important compounds for stoichiometric and catalytic C---C single bond coupling and cleavage reactions. Detailed investigations show five-membered metallacyclocumulenes L₂M(η⁴-1,2,3,4-RC₄R) as the key intermediates in both reactions of a C---C single bond cleavage of different 1,4-substituted 1,3-butadiynes RCC---CCR to alkynyl groups and the opposite reaction of C---C single bond formation starting from alkynyl groups under the formation of 1,4-substituted 1,3-butadiynes. Depending on different metals M and ligands L, coupling or cleavage is favoured. Combination of both reactions offered the first C---C single bond metathesis in homogeneous solution, which is photocatalyzed and titanocene-mediated. It proceeds via titanocene–mono-alkynyl complexes, which are interesting species also for other stoichiometric and catalytic C---C coupling reactions. Some similarities regarding the σ-to-π conversion exist between the coupling of the alkynyl groups at titano- and zirconocenes to complexed 1,3-butadiynes on one side and the coupling of phenyl groups at chromium to complexed diphenyl on the other side.     

Synthesis, structure and hydrogenation catalytic activity of [Ru3(μ3,η-ampy)(μ,η:η-PhC=CHPh)(CO)6(PPh3) (Hampy = 2-amino-6-methylpyridine)

The compound [RU₃(μ₃,η²- -ampy)(μ₃η¹:η²-PhC=CHPh)(CO)₆(PPh₃)₂] (1) (ampy = 2-amino-6-methylpyridinate) has been prepared by reaction of [RU₃(η-H)(μ₃,η²- ampy) (μ,η¹:η²-PhC=CHPh)(CO)₇(PPh₃)] with triphenylphosphine at room temperature. However, the reaction of [RU₃(μ-H)(μ₃, η² -ampy)(CO)₇(PPh₃)₂] with diphenylacetylene requires a higher temperature (110°C) and does not give complex 1 but the phenyl derivative [RU₃(μ₃,η²-ampy)(μ,η ¹:η² -PhC=CHPh)(μ,-PPh₂)(Ph)(CO)₅(PPh₃)] (2). The thermolysis of complex 1 (110°C) also gives complex 2 quantitatively. Both 1 and 2 have been characterized by0 X-ray diffraction methods. Complex 1 is a catalyst precursor for the homogeneous hydrogenation of diphenylacetylene to a mixture of cis- and trans -stilbene under mild conditions (80°C, 1 atm. of H₂), although progressive deactivation of the catalytic species is observed. The dihydride [RU₃(μ-H)₂(μ ₃,η²-ampy)(μ,η¹:η²- PhC=CHPh)(CO)₅(PPh₃)₂] (3), which has been characterized spectroscopically, is an intermediate in the catalytic hydrogenation reaction.     

Photochemische reaktionen von übergangsmetall-organyl-komplexen mit olefinen XI. Photochemisch induzierte C---C-verknüpfung von tricarbonyl-η-2,4-dimethyl-2,4-pentadien-1-yl-mangan mit 1-dimethylamino-2-propin—Synthese eines η-7-dimethylamino-N-2,4-heptadien-1-yl-chelatkomplexes

UV irradiation of tricarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-manganese (2) in THF at 208 K yields solvent-stabilized dicarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-tetrahydrofurane-manganese (3), which reacts in situ with two equivalents of 1-dimethylamino-2-propyne (4) to dicarbonyl-1–5-η-2,4-dimethyl-(6-dimethylaminomethyl-N)-10-dimethylamino-deca-2,4,6,8- tetraen-1-yl-manganese (5). The crystal and molecular structure was determined by an X-ray diffraction analysis. Complex 5 crystallizes in the monoclinic space group P2₁/c, A = 1109.9(2) pm, B = 836.0(2) pm, C = 2156.9(4) pm, β = 93.23(3)°, V = 1.9982(7) nm³, Z = 4. Complex 5 was also studied in solution by IR and NMR spectroscopy. A possible formation mechanism of 5 will be discussed.

Zusammenfassung

UV-Bestrahlung von Tricarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-mangan (2) in THF bei 208 K liefert solvenstabilisiertes Dicarbonyl-η⁵-2,4-dimethyl-2, 4-pentadien-1-yl-tetrahydrofuran-mangan (3), welches in situ mit zwei Äquivalenten 1-Dimethylamino-2-propin (4) zu Dicarbonyl-1–5-η-2,4-dimethyl-(6-dimethylaminomethyl-N)-10-dimethylamino-deca-2,4,6,8-tetraen-1-yl-mangan (5) reagiert. Seine Kristall- und Molekülstruktur wurde durch eine Röntgenbeugungsanalye bestimmt. Komplex 5 kristallisiert in der monoclinen Raumgruppe P2₁/c, A = 1109.9(2) pm, B = 836.0(2) pm, C = 2156.9(4) pm, β = 93.23(3)°, V = 1.9982(7)_ nm³, Z = 4. Komplex 5 wurde auch in Lösung IR- und NMR-spektroskopisch untersucht. Ein möglicher Bildungsmechanismus von 5 wird diskutiert.     

Versatile reactions of a para-bromophenylacetylide iron(II) derivative and X-ray structure of the fluoro analogue. Synthesis of new redox-active organoiron(II) synthons

The synthesis of the new (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,3-(C₆H₄X) (m-2a/2b; X=F/Br) and (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄I) (2c) complexes, as well as the solid-state structure of the known (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄F) (2a) complex are described. The catalytic coupling reactions of the bromo complexes with various alkynes were next investigated. Starting from the known (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄Br) complex (2b), the synthesis of the (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄)---CC---H complex (6d) and of the corresponding silyl-protected precursors (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄)CC---SiR₃ (6b/6c; R=ⁱPr/Me) are reported. By use of lithium---bromine exchange reactions on 2b, the silyl- (7a; E=Si; R=Me) and tin- (7b–7d; E=Sn; R=Me, Bu, Ph) substituted analogues (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄)ER₃ are also isolated. The spectroscopic and electrochemical characterisations of all these new Fe(II)/Fe(III) redox-active building blocks are presented and the electronic substituent parameters for the “(η²-dppe)(η⁵-C₅Me₅)Fe---CC” group are determined by means of ¹⁹F-NMR.     

Wasserstoff-wanderungen in organometall-verbindungen: Die thermisch induzierte isomerisierung des (η-cyclopentadienyl)(η-1,1-dimethylallyl)(η-isopren)-zirconiums

Treatment of CpZrCl₃ with 3-methylbutenyl-Grignard reagent yields thermally labile tris(1,1-dimethylallyl) ZrCp (6), which is slowly decomposed (5d) at −15°C to give (η-cyclopentadienyl)(η³-1,1-dimethylallyl)(η⁴-isoprene)zirconium (7), which is thermally unstable; with a half-live of 43 h at 20°C it rearranges to the η₃-1,2-dimethylallyl isomer and an (isoprene) zirconium hydride is proposed as the intermediate for this hydrogen-migration reaction.     

Synthesis of new N-substituted imidazolyl and 1H-1,2,4-triazolyl derivatives of (η-arene)(η-cyclopentadienyl)iron(II) salts

A series of new imidazolyl and 1H-1,2,4-triazolyl derivatives of (η⁶-arene)(η⁵cyclopentadienyl)iron(II) salts have been prepared by reaction of the corresponding chloroarene complexes with the sodium salts of the heterocycles. Good yields of N-substituted products were obtained in all cases under very mild conditions. In contrast to substitution by primary and secondary amines, both chlorines were displaced from [(η⁵-1,2-dichlorobenzene)(η⁵-Cp)Fe][PF₆], indicating electron withdrawal by the imidazolyl and triazolyl groups. Detailed ¹H and ¹³C NMR analysis confirmed this point. NOE difference spectra were used for ¹³C assignments, and evidence for conformational isomers in the 1,2-disubstituted complexes is presented.     

Ein beitrag zur darstellung und reaktivität der η-allyliridium-komplexe [Ir(η-2-RC3H4) (PPr3)2]

The η³-allyliridium complexes [Ir(η³-2-RC₃H₄)(PⁱPr₃)₂] (2, 3) have been prepared in a one-pot reaction from [IrCl(C₂H₄)₂]₂, 2-RC₃H₄Li and PⁱPr₃ in 70% yield. Compounds 2 and 3 react spontaneously with H₂ to give [IrH₅(PⁱPr₃)₂] (7) and with excess PhC=CH and MeCCH to give [Ir(CCPh)₃(PⁱPr₃)₂] (5) and [Ir(CCMe)₂(CMe=CH₂)(PⁱPr₃)₂] (6), respectively. From 2 (or 3) and two equivalents of PhCCH the complex [IrH(CCPh)₂(PⁱPr₃)₂] (4) has been obtained. Treatment of 2 or 3 with CF₃CO₂H does not lead to a cleavage of the allyl-metal bond but affords the allyl(hydrido)-iridium(III) complexes [IrH(η³-2-RC₃H₄)(η¹-P₂CCF₃)(PⁱPr₃)₂] (8, 9) in almost quantitative yield.     

Syntheses of dibenzo[b,e][1,4]dioxin derivatives via iron complexes, and further functionalizations via directed metallation

Double nucleophilic aromatic substitution reactions between (cyclopentadienyl)(η⁶-1,2-dichlorobenzene)iron(1 + ) salts and substituted 1,2benzenediols have been carried out under mild conditions to prepare [η⁶-dibenzo[b,e][1,4]dioxin]iron(1 + ) complexes functionalized in the 1- or 2-position with an alkyl, aldehyde, carboxylic acid, methoxycarbonyl, carboxamide, or hydroxy group. 3-Methyl- and 4-methyl-(η⁶-1,2-dichlorobenzene)iron complexes were treated with substituted 1,2-benzenediols to effect functionalization of both aromatic rings of the heterocycle. The dibenzodioxin ligands were liberated routinely by irradiation with ultraviolet light. Directed deprotonation of the free functionalized dibenzodioxins with an alkyllithium reagent followed by quenching with a variety of electrophiles yielded further derivatives, including two new isoindolone systems.     

Übergangsmetall—methylen-komplexe : XXXI. Primärkomplexierung von diazoalkanen an metall—metall-mehrfachbindungen; ein weiterer koordinationstyp

An unexpected novel coordination mode of diazoalkanes has been verified via addition of 2-diazopropane to the metal—metal triple bond of bis[dicarbonyl(η⁵-pentamethylcyclopentadienyl)molybdenum] (MoMo). The dinuclear 1:1 addition product isolated in nearly quantitative yield is structurally characterized by a bent, 4-electron type η¹:η²-diazoalkane ligand, with the terminal nitrogen atom symmetrically bridging the metal-metal “single bond” (d(MoMo) 305.0(2) pm; d(Mo---N(1)) 212.0(12) and 212.6(10) pm, respectively) and the second nitrogen atom being bonded to one molybdenum atom only (d(Mo---N(2)) 213.4(13) pm).     

具有螺旋结构的金属镍有机-无机配位聚合物的合成及表征

在水热体系中合成了3个中心金属为镍离子, 以六配位扭曲八面体构型形成的具有螺旋结构的配位聚合物{[Ni₂L₂(bib)₂·2H₂O]·5H₂O}_n(1), [Ni₂L₂(bpy)]_n(2)和{[Ni₂L₂(bibpip)₂·2H₂O]·6H₂O}_n(3)[H₂L=4,4'-三苯胺二甲酸; bib=1,3-二(咪唑基)苯; bpy=4,4-联吡啶; bibpip=1,4-二(4-咪唑苄基)哌嗪]. 通过单晶及粉末X射线衍射、 红外光谱、 元素分析和热重分析对这3种化合物进行了表征. 结果表明, 化合物1属于单斜晶系, C2/c空间群, 其骨架为具有{4²·6⁵·8}拓扑结构的二维层结构; 化合物2属于斜方晶系, Fdd2空间群, 其骨架为具有{4⁸·5⁴·6³}拓扑结构的三维超分子网络; 化合物3属于三斜晶系, P\begin{array}{c}\bar{1}\end{array}空间群, 为1个五重穿插的三维超分子网络, 其骨架具有{4⁴·6²}拓扑结构.     

Vitamin B12-catalyzed conversion of some γ- and δ-bromoalkanols to polyhydroxy alkanols

Vitamin B₁₂-catalyzed allylic dimerization of some γ- and δ-bromoalkanols with activated Zn-dust in mixture ethanol/water (1:1) has been studied. Investigated bromoalkanols were prepared from corresponding tertiary Δ⁴- and Δ⁵-alkenols by means of benzeneselenyl bromide and subjected to chemical reduction with vitamin B₁₂. All investigated bromoalkanols, after dehydrobromination, underwent to oxidative allylic coupling and hydratation in the presence of protic solvents to give predominantly polyhydroxy alkanols.     

Crystal and molecular structure of Δ-5,6-diphenyl-5-methoxy-1,2,4-triazacyclohexene-3-thione and Δ-4-methyl-5,6-diphenyl-5-ethoxy-1,2,4-triazacyclohexene-3-thione

Condensation of thiosemicarbazide or N(4)-ethylthiosemicarbazide with 1,2,8,9-tetraphenyl-3,7-diazanona-1,9-dione in the presence of copper(II) acetate in 96% ethanol leads to Δ⁶-5,6-diphenyl-5-methoxy-1,2,4-triazacyclohexene-3-thione, C₁₆H₁₅N₃OS, or Δ⁶-4-methyl-5,6-diphenyl-5-ethoxy-1,2,4-triazacyclohexene-3-thione, C₁₈H₁₉N₃OS. For C₁₆H₁₅N₃OS the crystal data are monoclinic, P2₁/c, a=9.7780(7), b=8.5120(3), c=18.2210(13) Å, β=100.958(3)°, V=1488.89(16) ų, and Z=4 in agreement with an earlier report. For C₁₈H₁₉N₃OS the crystal data are orthorhombic, P2₁2₁2₁, a=8.6940(3), b=12.9946(3), c=15.5139(5) Å, V=1752.68(9) ų, and Z=4.     

New ferrocenyl heterometallic complexes of 2,7-diethynylfluoren-9-one

A new series of rigid-rod alkynylferrocenyl precursors with central fluoren-9-one bridge, 2-bromo-7-(2-ferrocenylethynyl)fluoren-9-one (1b), 2-trimethylsilylethynyl-7-(2-ferrocenylethynyl)fluoren-9-one (2) and 2-ethynyl-7-(2-ferrocenylethynyl)fluoren-9-one (3), have been prepared in moderate to good yields. The ferrocenylacetylene complex 3 can provide a direct access to novel heterometallic complexes, trans-[(η⁵-C₅H₅)Fe(η⁵-C₅H₄)CCRCCPt(PEt₃)₂Ph] (4), trans-[(η⁵-C₅H₅)Fe(η⁵-C₅H₄)CCRCCPt(PBu₃)₂CCRCC(η⁵-C₅H₄)Fe(η⁵-C₅H₅)] (5), [(η⁵-C₅H₅)Fe(η⁵-C₅H₄)CCRCCAu(PPh₃)] (6) and [(η⁵-C₅H₅)Fe(η⁵-C₅H₄)CCRCCHgMe] (7) (R=fluoren-9-one-2,7-diyl), following the CuI-catalyzed dehydrohalogenation reactions with the appropriate metal chloride compounds. All the new complexes have been characterized by FTIR, ¹H-NMR and UV–vis spectroscopies and fast atom bombardment mass spectrometry. The solid state molecular structures of 3, 5, 6 and 7 have been established by X-ray crystallography. The redox chemistry of these mixed-metal species has been investigated by cyclic voltammetry and oxidation of the ferrocenyl moiety is facilitated by the presence of the heavy metal centre and increased conjugation in the chain through the ethynyl and fluorenone linkage units.     

Preparation and characterization of ruthenium(II), rhodium(III) and iridium(III) complexes of isocyanide bearing the azo group

Reactions of [(η⁶-arene)RuCl₂]₂ (1) (η⁶-arene=p-cymene (1a), 1,3,5-Me₃C₆H₃ (1b), 1,2,3-Me₃C₆H₃ (1c) 1,2,3,4-Me₄C₆H₂(1d), 1,2,3,5-Me₄C₆H₂ (1e) and C₆Me₆ (1f)) or [Cp*MCl₂]₂ (M=Rh (2), Ir (3); Cp*=C₅Me₅) with 4-isocyanoazobenzene (RNC) and 4,4′-diisocyanoazobenzene (CN–R–NC) gave mononuclear and dinuclear complexes, [(η⁶-arene)Ru(CNC₆H₄N=NC₆H₅)Cl₂] (4a–f), [Cp*M(CNC₆H₄N=NC₆H₅)Cl₂] (5: M=Rh; 6: M=Ir)_, [{(η⁶-arene)RuCl₂}₂{μ-CNC₆H₄N=NC₆H₄NC}] (8a–f) and [(Cp*MCl₂)₂(μ-CNC₆H₄N=NC₆H₄NC)}] (9: M=Rh; 10: M=Ir)_, respectively. It was confirmed by X-ray analyses of 4a and 5 that these complexes have trans-forms for the ---N=N--- moieties. Reaction of [Cp*Rh(dppf)(MeCN)](PF₆)₂ (dppf=1,1′-bis (diphenylphosphino)ferrocene) with 4-isocyanoazobenzene gave [Cp*Rh(dppf)(CNC₆H₄N=NC₆H₅)](PF₆)₂ (7), confirmed by X-ray analysis. Complex 8b reacted with Ag(CF₃SO₃), giving a rectangular tetranuclear complex 11b, [{(η⁶-1,3,5-Me₃C₆H₃)Ru(μ-Cl}₄(μ-CNC₆H₄N=NC₆H₄NC)₂](CF₃SO₃)₄ bridged by four Cl atoms and two μ-diisocyanoazobenzene ligands. Photochemical reactions of the ruthenium complexes (4 and 8) led to the decomposition of the complexes, whereas those of 5, 7, 9 and 10 underwent a trans-to-cis isomerization. In the electrochemical reactions the reductive waves about −1.50 V for 4 and −1.44 V for 8 are due to the reduction of azo group, [---N=N---]→[---N=N---]²⁻. The irreversible oxidative waves at ca. 0.87 V for the 4 and at ca. 0.85 V for 8 came from the oxidation of Ru(II)→Ru(III).     

Synthesis and structure of ansa-cyclopentadienyl pyrrolyl titanium complexes: [(η-C5H4)CH2(2-C4H3N)]Ti(NMe2)2 and [1,3-{CH2(2-C4H3N)}2(η-C5H3)]Ti(NMe2)

Reaction of ansa-cyclopentadienyl pyrrolyl ligand (C₅H₅)CH₂(2-C₄H₃NH) (2) with Ti(NMe₂)₄ affords bis(dimethylamido)titanium complex [(η⁵-C₅H₄)CH₂(2-C₄H₃N)]Ti(NMe₂)₂ (3) via amine elimination. A cyclopentadiene ligand with two pendant pyrrolyl arms, a mixture of 1,3- and 1,4-{CH₂(2-C₄H₃NH)}₂C₅H₄ (4), undergoes an analogous reaction with Ti(NMe₂)₄ to give [1,3-{CH₂(2-C₄H₃N)}₂(η⁵-C₅H₃)]Ti(NMe₂) (5). Molecular structures of 3 and 5 have been determined by single crystal X-ray diffraction studies.