Quinoline-functionalized N-heterocyclic carbene complexes of iridium: Synthesis, structures and catalytic activities in transfer hydrogenation

Iridium complexes containing quinoline-functionalized N-heterocyclic carbene (NHC) ligands have been synthesized by the transmetalation route from silver carbene precursors. The silver complexes undergo a facile reaction with [Ir(COD)Cl]₂ (COD = 1,5-cyclooctadiene) to yield a series of carbene complexes [(NHC)Ir(COD)Cl] (NHC = 3-methyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2a); 3-n-butyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2b); 3-benzyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2c); 1,3-di(8-quinolylmethyl)imidazole-2-ylidene (2d). The coordinated COD was replaced by carbon monoxide to yield the corresponding carbonyl species [(NHC)Ir(CO)₂Cl] (3). Complexes 2 and 3 have been characterized by IR, ESI-MS, ¹H and ¹³C NMR and elemental analyses. The molecular structures of complexes 2b and 2c have been confirmed by single-crystal X-ray diffraction. Two analogous Ir(I) complexes 5 and 6 with naphthalene-containing NHC have also been synthesized and characterized. These Ir(I) complexes in the current work have been proved to be active catalysts in the transfer hydrogenation of ketones to alcohols using 2-propanol as the hydrogen source.     

Syntheses and coordination behaviour of 2-(ortho-phosphinophenyl)-functionalised 1,3-dioxolanes and 1,3-dioxanes towards a [(COD)Rh]-complex fragment - models for immobilised complexes

The syntheses are reported of the ether-phosphine ligands: 2-(ortho-diphenylphosphinophenyl)-1,3-dioxolane (1a), 2-(ortho-diisopropylphosphinophenyl)-1,3-dioxolane (1b), 2-(ortho-diphenylphosphinophenyl)-1,3-dioxane (1c), 2-(ortho-diisopropylphosphinophenyl)-1,3-dioxane (1d). Their reaction with [(COD)RhCl]₂ (COD: 1,5-cyclooctadiene) results in the formation of the mononuclear complexes: {chloro(COD)[2-(ortho-diphenylphosphinophenyl)-1,3-dioxolane]rhodium(I)} (2a), {chloro(COD)[2-(ortho-diisopropylphosphinophenyl)-1,3-dioxolane]rhodium(I)} (2b), {chloro(COD)[2-(ortho-diphenylphosphinophenyl)-1,3-dioxane]rhodium(I)} (2c), and {chloro(COD)[2-(ortho-diisopropylphosphinophenyl)-1,3-dioxane]rhodium(I)} (2d). The chloride ligands of compounds 2a and 2b were abstracted with TlPF₆, with accompanied insertion of an acetal oxygen atom of the ligands 1a and 1b into the coordination sphere of the metal centre, producing {(COD)[η²-P,O-2-(ortho-diphenylphosphinophenyl)-1,3-dioxolane]rhodium(I)}PF₆ (3a∗PF₆) and {(COD)[η²-P,O-2-(ortho-diisopropylphosphinophenyl)-1,3-dioxolane]rhodium(I)}PF₆ (3b∗PF₆). In contrast the dioxane analogues of 3, 3c∗BF₄ and 3d∗BF₄, were formed by reacting the ligands 1c, 1d with [Rh(COD)₂]BF₄. The ligands 1 and the complexes 2 serve as model compounds for their via acetalation to a polyvinylalcohol resin bound analogues. The complexes synthesised were employed as pre-catalysts in the hydroformylation reaction of 1-octene.     

Rhodium and iridium complexes of N-heterocyclic carbenes: Structural investigations and their catalytic properties in the borylation reaction

Bridged and unbridged N-heterocyclic carbene (NHC) ligands are metalated with [Ir/Rh(COD)₂Cl]₂ to give rhodium(I/III) and iridium(I) mono- and biscarbene substituted complexes. All complexes were characterized by spectroscopy, in addition [Ir(COD)(NHC)₂][Cl,I] [COD = 1,5-cyclooctadiene, NHC =  1,3-dimethyl- or 1,3-dicyclohexylimidazolin-2-ylidene] (1, 4), and the biscarbene chelate complexes 12 [(η⁴-1,5-cyclooctadiene)(1,1′-di-n-butyl-3,3′-ethylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] and 14 [(η⁴-1,5-cyclooctadiene)(1,1′-dimethyl-3,3′-o-xylylene-diimidazolin-2,2′-diylidene)iridium(I) bromide] were characterized by single crystal X-ray analysis. The relative σ-donor/π-acceptor qualities of various NHC ligands were examined and classified in monosubstituted NHC-Rh and NHC-Ir dicarbonyl complexes by means of IR spectroscopy. For the first time, bis(carbene) substituted iridium complexes were used as catalysts in the synthesis of arylboronic acids starting from pinacolborane and arene derivatives.     

Chromium(0)-rhodium(I) metal exchange: Synthesis and X-ray structure of new Fischer (NHC)carbene complexes of rhodium(I)

An easy approach to Fischer (NHC)carbene complexes of rhodium(I) 3 from methoxy- and aminocarbene complexes of chromium 1 and (NHC)(cod)RhCl (2) is described. The process involves the transfer of the carbene unit and a CO ligand from chromium to rhodium. The X-ray analysis is provided for 3d and the preliminary results on their thermal stability and reactivity toward alkynes and allenes are also reported.     

Influence of multidentate N-donor ligands on highly electrophilic zinc initiator for the ring-opening polymerization of epoxides

A set of multidentate ligands have been synthesized and used to stabilize the putative highly electrophilic zinc species initiating ring-opening polymerization (ROP) of cyclohexene oxide (CHO) and propylene oxide (PO). Reaction of the bidentate C₂-chiral bis(oxazoline) ligand (^R2,R3BOX: R₂ = (4S)-tBu, R₃ = H (a); R₂ = (4S)-Ph, R₃ = H (b); R₂ = (4R)-Ph, R₃ = (5S)-Ph (c)) with Zn(R₁)₂ (R₁ = Et (1), Me (2)) led to the heteroleptic three-coordinate complexes (^R2,R3BOX)ZnR₁, 1a-c and 2a, which were isolated in 92-96% yield. Next, two pyridinyl-functionalized N-heterocyclic carbene (NHC) ligands have been designed and synthesized: the 1,3-bis(2-pyridylmethyl)imidazolinium salt (d) and the protected NHC adduct 2-(2,3,4,5,6-pentafluorophenyl)-1,3-bis(2-pyridylmethyl)imidazolidine (e). The reaction of ligands d and e with ZnEt₂ led directly to the formation of (NHC)ZnEt(Cl) 3d complex with ethane elimination and the adduct (NHC-C₆F₅(H))ZnEt₂4e, respectively, in high yield. In situ combinations of selected complexes 1a-c, 3d and 4e with B(C₆F₅)₃ (1 or 2 equivalents) give active systems for ROP, with high productivity (3.3-5.9 10⁶ g_polym. mol_Zn⁻¹ h⁻¹) and high molecular weight (M_n up to 132 10³ g mol⁻¹) for CHO polymerization. Although the in situ B(C₆F₅)₃-activated zinc species were not isolated, the sterically demanding BOX ligands (1c > 1b > 1a) and functionalized NHC ligands seem to enhance the stability of highly electrophilic zinc complexes over ligand redistribution, allowing a better control of the cationic ROP as reflected particularly for 3d and 4e complexes by their respective efficiency (42-88%).     

Rhodium(I) complexes with κP coordinated ω-phosphinofunctionalized alkyl phenyl sulfide, sulfoxide and sulfone ligands and their reactions with sodium bis(trimethylsilyl)amide and Ag[BF4]

Reactions of ω-diphenylphosphinofunctionalized alkyl phenyl sulfides Ph₂P(CH₂)_nSPh (n = 1, 1a; 2, 2a; 3, 3a), sulfoxides Ph₂P(CH₂)_nS(O)Ph (n = 1, 1b; 2, 2b; 3, 3b) and sulfones Ph₂P(CH₂)_nS(O)₂Ph (n = 1, 1c; 2, 2c; 3, 3c) with dinuclear chlorido bridged rhodium(I) complexes [(RhL₂)₂(μ-Cl)₂] (L₂ = cycloocta-1.5-diene, cod, 4; bis(diphenylphosphino)ethane, dppe, 5) afforded mononuclear Rh(I) complexes of the type [RhCl{Ph₂P(CH₂)_nS(O)_xPh-κP}(cod)]¹ (n/x = 1/0, 6a; 1/1, 6b; 1/2, 6c; 2/0, 8a; 2/1, 8b; 2/2, 8c; 3/0, 10a; 3/1, 10b; 3/2, 10c) and [RhCl{Ph₂P(CH₂)_nS(O)_xPh-κP}(dppe)] (n/x = 1/0, 7a; 1/1, 7b; 1/2, 7c; 2/0, 9a; 2/1, 9b; 2/2, 9c; 3/0, 11a; 3/1, 11b; 3/2, 11c) having the P^S(O)_x ligands κP coordinated. Addition of Ag[BF₄] to complexes 6-11 in CH₂Cl₂ led with precipitation of AgCl to cationic rhodium complexes of the type [Rh{Ph₂P(CH₂)_nS(O)_xPh-κP,κS/O}L₂][BF₄] having bound the P^S(O)_x ligands bidentately in a κP,κS (13a-18a, 15b-18b) or a κP,κO (13b, 14b, 13c-18c) coordination mode. Unexpectedly, the addition of Ag[BF₄] to 6a in THF afforded the trinuclear cationic rhodium(I) complex [Rh₃(μ-Cl)(μ-Ph₂PCH₂SPh-κP:κS)₄][BF₄]₂·4THF (12·4THF) with a four-membered Rh₃Cl ring as basic framework. Addition of sodium bis(trimethylsilyl)amide to complexes 6-11 led to a selective deprotonation of the carbon atom neighbored to the S(O)_x group (α-C) yielding three different types of organorhodium complexes: a) Organorhodium intramolecular coordination compounds of the type [Rh{CH{S(O)_xPh}CH₂CH₂PPh₂-κC,κP}L₂] (22a-c, 23a-c), b) zwitterionic complexes [Rh{Ph₂PCHS(O)_xPh-κP,κS/O}L₂] having κP,κS (21a, 21b) and κP,κO (20b/c, 21c) coordinated anionic [Ph₂PCHS(O)_xPh] ligands, and c) the dinuclear rhodium(I) complex [{Rh{μ-CH(SPh)PPh₂-κC:κP}(cod)}₂] (19). All complexes were fully characterized spectroscopically and complexes 15b, 15c, 12·4THF and 19·THF additionally by X-ray diffraction analysis. DFT calculations of zwitterionic complexes gave insight into the coordination mode of the [Ph₂PCHS(O)Ph] ligand (κP,κS versus κP,κO).     

1,3-Diarylimidazolidin-2-ylidene (NHC) complexes of Pd(II): Electronic effects on cross-coupling reactions and thermal decompositions

The synthesis of 1,3-diarylimidazolidin-2-ylidene (NHC) precursor, 1,3-bis(2,4,6-trimethylphenyl)imidazolinium chloride, (3b) has been extended to the electronically and sterically modified NHC precursors 3a (X = H), 3c (X = Br) and 3e (X = Cl) in order to investigate the electronic effect of a p-substituent (X) on cross-coupling catalysts. Complexes of the type PdCl₂(NHC)₂ (5), PdCl₂(NHC)(PPh₃) (6) and [RhCl(NHC)(cod)] (7) were prepared from 3 or 4d (1,3-bis(2,4-dimethylphenyl)-2-trichloromethylimidazolidin). Initial decomposition temperatures of the complexes 5 and 6 were determined by TGA. In situ formed complexes from Pd(OAc)₂ and 3 as well as the preformed complexes 5 and 6 have been tested as catalysts in coupling of phenylboronic acid with 4-haloacetophenones. The electron donating ability of NHCs derived from 3 was assessed by measuring C-O frequencies in the respective [RhCl(NHC)(CO)₂] complex 8 which was prepared by replacement of cod ligand of 7 with CO. An interesting correlation between the electron-donating nature of the aryl substituent and catalytic activity and also initial decomposition temperature of the complexes 5 and 6 was observed.     

Coordination compounds of N,N′-olefin functionalized imidazolin-2-ylidenes

N-Heterocyclic carbene ligands (NHC) were metalated with Pd(OAc)₂ or [Ni(CH₃CN)₆](BF₄)₂ by in situ deprotonation of imidazolium salts to give the N-olefin functionalized biscarbene complexes [MX₂(NHC)₂] 3-7 (3: M = Pd, X = Br, NHC = 1,3-di(3-butenyl)imidazolin-2-ylidene; 4: M = Pd, X = Br, NHC = 1,3-di(4-pentenyl)imidazolin-2-ylidene; 5: M = Pd, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 6: M = Ni, X = I, NHC = 1,3-diallylimidazolin-2-ylidene; 7: M = Ni, X = I, NHC = 1-methyl-3-allylimidazolin-2-ylidene). Molecular structure determinations for 4-7 revealed that square-planar complexes with cis (5) or trans (4, 6, 7) coordination geometry at the metal center had been obtained. Reaction of nickelocene with imidazolium bromides afforded the η⁵-cyclopentadienyl (η⁵-Cp) monocarbene nickel complexes [NiBr(η⁵-Cp)(NHC)] 8 and 9 (8: NHC = 1-methyl-3-allylimidazolin-2-ylidene; 9: NHC = 1,3-diallylimidazolin-2-ylidene). The bromine abstraction in complexes 8 and 9 with silver tetrafluoroborate gave complexes [NiBr(η⁵-Cp)(η³-NHC)] 10 and 11. The X-ray structure analysis of 10 and 11 showed a trigonal-pyramidal coordination geometry at the nickel(II) center and coordination of one N-allyl substituent.     

Synthesis and photophysicochemical properties of novel mononuclear rhodium(III) phthalocyanines

Chloro axially-substituted octa(4-isopropylphenoxy)rhodium(III)phthalocyanine, (R)₈PcRhCl (3), was reacted with the nitrogenous bases pyridine (Py) and pyrazine (Pyz) to give the axially-disubstituted octa(4-isopropylphenoxy)rhodium(III)phthalocyanines [(R)₈PcRhCl(L)] (4) and (5), L = (Py) and (Pyz), respectively. In this study, the fluorescence quantum yield (Φ_F), the phosphorescence quantum yield (Φ_phos) and the photodegradation quantum yield (Φ_pd) values for the newly synthesized rhodium phthalocyanine complexes (RhPcs) 4 and 5 are reported. The complexes have also been fully characterized by elemental analysis, FD mass spectrometry, FT-IR and ¹H NMR spectroscopy.     

Trifluoroacetylacetonate rhodium(III) methyl complexes, cis-[Rh(TFA)(PPh3)2(CH3)(L)][BPh4] and cis-[Rh(TFA)(PPh3)2(CH3)(I)] (L = CH3CN, NH3, pyridine), in comparison with their acetylacetonate analogs

The oxidative addition of CH₃I to planar rhodium(I) complex [Rh(TFA)(PPh₃)₂] in acetonitrile (TFA is trifluoroacetylacetonate) leads to the formation of cationic, cis-[Rh(TFA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (1), or neutral, cis-[Rh(TFA)(PPh₃)₂(CH₃)(I)] (4), rhodium(III) methyl complexes depending on the reaction conditions. 1 reacts readily with NH₃ and pyridine to form cationic complexes, cis-[Rh(TFA)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (2) and cis-[Rh(TFA)(PPh₃)₂(CH₃)(Py)][BPh₄] (3), respectively. Acetylacetonate methyl complex of rhodium(III), cis-[Rh(Acac)(PPh₃)₂(CH₃)(I)] (5), was obtained by the action of NaI on cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] in acetone at −15 °C. Complexes 1-5 were characterized by elemental analysis, ³¹P{¹H}, ¹H and ¹⁹F NMR. For complexes 2, 3, 4 conductivity data in acetone solutions are reported. The crystal structures of 2 and 3 were determined. NMR parameters of 1-5 and related complexes are discussed from the viewpoint of their isomerism.     

New N-heterocyclic carbene mercury(II) complexes: Close mercury-arene interaction

Mononuclear mercury complexes (1, 2, and 3) bearing bis-N-heterocyclic carbene (NHC) ligands of the form [(NHC)₂-μ-Hg]⁺² have been prepared and structurally characterised. The complexes were derived from three bis-imidazolium salts as precursors to NHC; either 1,3-bis(N-methylimidazolium-1-ylmethyl)benzene bis(hexafluorophosphate) (I·2PF₆), 1,3-bis(N-butylimidazolium-1-ylmethyl)benzene bis(hexafluorophosphate) (II·2PF₆) or 3,5-bis(N-butylimidazolium-1-ylmethyl)toluene bis(hexafluorophosphate) (III·2PF₆) treated with mercury(II) acetate. Interestingly X-ray crystal structure analysis revealed a close interaction between the Hg metal centre with one carbon atom of the aryl linker in addition to coordination with two NHCs.     

Carbonyl complexes of manganese, rhenium and molybdenum with 2-pyridylimino acid ligands

[MBr(CO)₃{κ²(N,O)-pyca}] [M = Mn(1a), Re(1b), pyca = pyridine-2-carboxaldehyde] and [MoCl(η³-C₃H₄Me-2)(CO)₂{κ²(N,O)-pyca}] (1c) react with aminoacid β-alanine to give the corresponding iminopyridine complexes 2a-2c. The same method affords the iminopyridine derivatives from γ-aminobutyric acid (GABA) (3a-3c) and 3-aminobenzoic acid (4a-4c). For complexes 2a-2c, 3a, 3c and 4a, the solid state structures have been determined by X-ray crystallography, revealing interesting differences in their hydrogen-bonding patterns in solid state.     

Group 9 complexes of an N-heterocycle carbene bearing a pentafluorobenzyl substituent: attempted dehydrofluorinative coupling of cyclopentadienyl and N-heterocycle carbene ligands

Treatment of N-methylimidazole with pentafluorobenzyl bromide produces 1-pentafluorobenzyl-3-methylimidazolium bromide (1), which reacts with silver(I) oxide to give the N-heterocycle carbene (NHC) complex 1-pentafluorobenzyl-3-methylimidazolin-2-ylidene silver(I) bromide (2). Complex 2 acts as a carbene transfer reagent giving the complexes [(η⁵-C₅Me₅)MCl₂(NHC)] (3a, M = Rh; 3b M = Ir) on reaction with [(η⁵-C₅Me₅)MCl(μ-Cl)]₂. An attempt to use intramolecular dehydrofluorinative coupling methodology to link the carbene and the pentamethylcyclopentadienyl ligands of [(η⁵-C₅Me₅)RhCl(CN^tBu)(NHC)]BF₄ was unsuccessful.     

Optically active cyclopentadienyl and indenyl ligands obtained from lactic acid esters

Asymmetric cyclopentadienes and indenes are easily prepared by nucleophilic attack of LiCp or LiInd on tosylate or triflate of ethyl (S)-(−) lactate. The selectivity of the reaction depends on the nature of the leaving group. This is particularly true in the case of the reaction of LiCp with sulfonates of ethyl (S)-(−) lactate. Indeed, only the monosubstituted cyclopentadiene lactate 2 is obtained from the triflate 6, whereas from the tosylate 1, besides 2 (20%) a 1,3-disubstituted cyclopentadiene lactate 3 is isolated (16.5%). From cyclopentadiene and indene lactate 2 and 7, optically active β-hydroxycyclopentadiene 10 and β-hydroxyindene 11 are obtained by reduction with LiAlH₄. Two rhodium(I) complexes 14 and 15 have been synthesized from (R,S)-2-(cyclopentadienyl)N,N-dimethylpropanamide 12 and (S)-2-(cyclopentadiene)propan-1-ol 10, respectively. The molecular structure of these complexes has been determined. Analytical and preparative chiral HPLC have been used to determine the optical purity of the ligands and to isolate enantiopure cyclopentadienyl complexes from racemic or enantiomerically enriched rhodium(I) complexes.     

2-Morpholinoethyl-substituted <Emphasis Type="Italic">N</Emphasis>-heterocyclic carbene (NHC) precursors and their silver(I)NHC complexes: synthesis,crystal structure and in vitro anticancer properties

In this study, a series of unsymmetrically 2-morpholinoethyl-substituted benzimidazolium salts and their Ag(I)NHC complexes were synthesized. The 1,3-dialkylbenzimidazolium salts (1a–d) were synthesized in dimethylformamide at 80 °C temperature from the N-(2-morpholinoethyl)benzimidazole and alkyl halides. The Ag(I)NHC complexes (2a–d) were synthesized in dichloromethane at room temperature from the benzimidazolium salts and Ag₂O. All compounds were characterized by spectroscopic techniques (NMR and FT-IR) and elemental analyses. Also, the salt 1c and complex 2c were characterized by single-crystal X-ray crystallography. Anticancer activities of 2-morpholinoethyl-substituted benzimidazolium salts and Ag(I)NHC complexes were investigated against the MCF-7 breast cancer cell line, and the IC₃₀ and IC₅₀ values of these compounds were found to be in the range of 241–490 and 6–14 µM, respectively.     

Silver N-heterocyclic carbene complexes as initiators for bulk ring-opening polymerization (ROP) of l-lactides

Synthetic, structural and catalysis studies of two silver complexes namely, {[1-(2,4,6-trimethylphenyl)-3-(N-phenylacetamido)imidazol-2-ylidene]₂Ag}⁺Cl⁻1b, supported over an amido-functionalized N-heterocyclic carbene ligand, and [1-(i-propyl)-3-(benzyl)imidazol-2-ylidene]AgCl 2b, supported over a non-functionalized N-heterocyclic carbene ligand, are reported. Specifically, 1b, a cationic complex bearing 2:1 NHC ligand to metal ratio, was obtained from the reaction of 1-(2,4,6-trimethylphenyl)-3-(N-phenylacetamido)imidazolium chloride 1a with Ag₂O in 52% yield. The corresponding 1a was synthesized by the alkylation reaction of 1-(2,4,6-trimethylphenylimidazole) with N-phenyl chloroacetamide in 73% yield. The other silver complex 2b, a neutral complex bearing 1:1 NHC ligand to metal ratio, was obtained from the reaction of 1-(i-propyl)-3-(benzyl)imidazolium chloride 2a with Ag₂O in 42% yield. The 2a was synthesized by the alkylation reaction of 1-(i-propylimidazole) with benzyl chloride in 45% yield. The molecular structures of the imidazolium chloride, 1a, and the silver complexes, 1b and 2b, have been determined by X-ray diffraction studies. The silver complexes, 1b and 2b, successfully catalyze bulk ring-opening polymerization (ROP) of l-lactides at elevated temperatures under solvent-free melt conditions producing moderate to low molecular weight polylactide polymers having narrow molecular weight distributions.     

N-phosphanylamidine ligands and their catalytic activity in the hydroformylation of 1-octene and styrene

Pyridine-based N-phosphanylamidine ligands i-Pr₂N-C(pyr)N-PR₂ (R = Ph (3), i-Pr (4)) were synthesized and fully characterized by NMR spectroscopy and X-ray crystallography. Mononuclear rhodium complexes 7 and 8 were obtained in one step from the [RhCl(COD)]₂ dimer and the monodentate ligands 1 and 2. Their single-crystal X-ray diffraction studies revealed the structural adaptive behavior of the monodentate N-phosphanylamidine ligands 1 and 2 upon k¹-P coordination mode in rhodium(I) complexes with the imino nitrogen atom of the amidine function which behaves as a “universal joint”. Compounds 1-4 were evaluated as ligands in the 1-octene and styrene hydroformylation reactions. The results obtained are encouraging and represent the first report on the use of N-phosphanylamidine ligands of the type R″₂N-C(R′)N-PR₂ in catalytic reactions.     

The reactivity of TMSN3 with ruthenium cyclopropenyl complexes containing different ligands and different substituent at Cγ

Ruthenium vinylidene complexes 2a-2c containing indenyl and bidentate dppe ligands can be obtained in efficient yields. Treatment of the cationic ruthenium vinylidene complexes with n-Bu₄NOH in acetone yields the neutral cyclopropenyl products (η⁵-C₉H₇)(dppe)Ru-CC(Ph)CHR (3) (3a, R = Ph; 3b, R = CN; 3c, R = p-C₆H₄-CN) via the deprotonation reaction. Reaction of complexes 3a and 3c with Me₃SiN₃ (TMSN₃) the N-coordinated complexes 4a and 4c can be obtained as stable products. Complex 3b containing CN group at Cγ in the cyclopropenyl ring reacts with TMSN₃ yielded the tetrazolate complex 5b. Similar cyclopropenyl products containing indenyl and two triphenylphosphine ligands 3′ can also be synthesized. Reaction of complex 3b′ with TMSN₃ also yielded the tetrazolate complex as the major product. And the minor products are [Ru]-N₃ and organic compound 6b. Reaction of 3a′ and 3c′ with TMSN₃ yielded [Ru]-N₃. The corresponding organic products can also be obtained via the N₃⁻ attacking the metal center in the N-coordinated complexes 4a′ and 4c′.     

Heterospin single-molecule magnets with extra-large anisotropic barrier

The mixtures of Co(X-hfpip)₂; X = I and H, and bisdiazo-dipyridine ligands, D2py₂(TBA), in 1:1 ratios gave the discrete cobalt complexes, 1 and 2, respectively. The molecular structures for 1 and 2 revealed by X-ray crystallography were cyclic 2:2 cobalt complexes formulated as [(Co(X-hfpip)₂)₂(D2py₂(TBA))₂], in which the cobalt units were compressed octahedra. After irradiation of the microcrystalline samples, the resulting Co-carbene complexes, 1c and 2c, showed SMM behaviors exhibiting slow magnetic relaxations. In dc and ac magnetic susceptibility experiments, the activation barrier, U_eff, for reorientation of the magnetic moment were estimated to be 139 and 135 K for 1c and 2c, respectively, and the hysteresis loops of the magnetization (the coercive force, H_c, and 26 and 15 kOe at 1.9 K for 1c and 2c, respectively) were observed. In addition, the values of the quantum tunneling time, τ_Q, were determined to be 1.1 × 10⁵ and 5.4 × 10⁵ s (t_1/2 = 21 and 104 h) for 1c and 2c, respectively, below 2.5 K.     

Short-step syntheses and complexation properties of Z,Z-tribenzodidehydro- and all-Z-tribenzo[12]annulenes

Syntheses of all-Z-tribenzo[12]annulenes (1a-c) and Z,Z-tribenzodidehydro[12]annulenes (2a-c) by the reduction of the corresponding tribenzohexadehydro[12]annulenes 3a-c were carried out using a low valent titanium complex generated from Ti(O-i-Pr)₄ and i-PrMgCl. The unique structure of the first reduction products 2a-c as well as 1a-c was fully characterized. Complexation of these annulenes with silver(I) ions produces the corresponding silver complexes. Among them, the silver complexes of 2a-c exhibit interesting monomer-dimer equilibrium.