Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Addition of excesses of N-heterocyclic carbenes (NHCs) IEt₂Me₂, IⁱPr₂Me₂ or ICy (IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; IⁱPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; ICy = 1,3-dicyclohexylimidazol-2-ylidene) to [HRh(PPh₃)₄] (1) affords an isomeric mixture of [HRh(NHC)(PPh₃)₂] (NHC = IEt₂Me₂ (cis-/trans-2), IⁱPr₂Me₂ (cis-/trans-3), ICy (cis-/trans-4) and [HRh(NHC)₂(PPh₃)] (IEt₂Me₂(cis-/trans-5), IⁱPr₂Me₂ (cis-/trans-6), ICy (cis-/trans-7)). Thermolysis of 1 with the aryl substituted NHC, 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (IMesH₂), affords the bridging hydrido phosphido dimer, [{(PPh₃)₂Rh}₂(μ-H)(μ-PPh₂)] (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [HRh(CO)(PPh₃)₃] (9) and treated with either IMes (=1,3-dimesitylimidazol-2-ylidene) or ICy, the bis-NHC complexes trans-[HRh(CO)(IMes)₂] (10) and trans-[HRh(CO)(ICy)₂] (11) were formed. In contrast, the reaction of 9 with IⁱPr₂Me₂ gave [HRh(CO)(IⁱPr₂Me₂)₂] (cis-/trans-12) and the unusual unsymmetrical dimer, [(PPh₃)₂Rh(μ-CO)₂Rh(IⁱPr₂Me₂)₂] (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised.     

The first synthesis and X-ray structures of polyfluorinated 1,2-, 2,3- and 2,4a-dihydro-1,3-diazafluorenes

Acetic acid-catalyzed condensation of 2-amino-3-(1-imino-2,2,2-trifluoroethyl)-1,1,4,5,6,7-hexafluoroindene (1b) with acetone and cyclopentanone gives 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-2,3-dihydro-1,3-diazafluorene (2a) and 5,6,7,8,9,9-hexafluoro-4-trifluoromethyl-2,3-dihydro-1,3-diazafluorene-2-spiro-1′-cyclopentane (3a) together with small amounts of 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-1,2-dihydro-1,3-diazafluorene (2b) and 5,6,7,8,9,9-hexafluoro-4-trifluoromethyl-1,2-dihydro-1,3-diazafluorene-2-spiro-1′-cyclopentane (3b), respectively. When acted upon by (CH₃)₂SO₄ compounds 2, 3 were converted into corresponding fluorine-containing 1-methyl-1,2-dihydro-1,3-diazafluorenes 6, 7. 4a-Chloro-5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-2,4a-dihydro-1,3-diazafluorene (8) has been synthesized by the interaction of compound 2 with SOCl₂. Solution of compound 2 as well as 8 in CF₃SO₃H-CD₂Cl₂ generated 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-1,2,3,4-tetrahydro-1,3-diazafluorene-4-yl cation (2c). The structures of compounds 2, 3, 6-8 have been determined by single crystal X-ray diffraction.     

Synthesis and molecular structures of dinuclear complexes with 1,2-dihydro-1,2-diphenyl-naphtho[1,8-c,d]1,2-diphosphole as a bridging ligand

A bisphosphine in which a PhP-PPh bond bridges 1,8-positions of naphthalene, 1,2-dihydro-1,2-diphenyl-naphtho[1,8-cd]-1,2-diphosphole (1), was used as a bridging ligand for the preparation of dinuclear group 6 metal complexes. Free trans-1, a more stable isomer having two phenyl groups on phosphorus centers mutually trans with respect to a naphthalene plane, was allowed to react with two equivalents of M(CO)₅(thf) (M = W, Mo, Cr) at room temperature to give dinuclear complexes (OC)₅M(μ-trans-1)M(CO)₅ (M = W (2a), Mo (2b), Cr (2c)). The preparation of the corresponding dinuclear complexes bridged by the cis isomer of 1 was also carried out starting from the free trans-1 in the following way. Mono-nuclear complexes M(trans-1)(CO)₅ (M = W (3a), Mo (3b), Cr (3c)) which had been prepared by a reaction of trans-1 with one equivalent of the corresponding M(CO)₅(thf) (M = W, Mo, Cr) complex, were heated in toluene, wherein a part of the trans-3a-c was converted to their respective cis isomer M(cis-1)(CO)₅. Each cis trans mixture of the mono-nuclear complexes 3a-c was treated with the corresponding M(CO)₅(thf) to give a cis trans mixture of the respective dinuclear complexes 2a-c. The cis isomer of the ditungsten complex 2a was isolated, and its molecular structure was confirmed by X-ray analysis, showing a shorter W?W distance of 5.1661(3) Å than that of 5.8317(2) Å in trans-2a.     

Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)

The reactions of trans-[MoO(ONO^Me)Cl₂] 1 (ONO^Me = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONO^tBu)Cl₂] 2 (ONO^tBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes trans-[Mo(NPh)(ONO^Me)Cl₂] 3 and trans-[Mo(NPh)(ONO^tBu)Cl₂] 4, respectively. As analogous oxotungsten starting materials did not show similar reactivity, corresponding imido tungsten complexes were prepared by the reaction between [W(NPh)Cl₄] with aminobis(phenol)s. These reactions yielded cis- and trans-isomers of dichloro complexes [W(NPh)(ONO^Me)Cl₂] 5 and [W(NPh)(ONO^tBu)Cl₂] 6, respectively. The molecular structures of 4, cis-6 and trans-6 were verified by X-ray crystallography. Organosubstituted imido tungsten(VI) complex cis-[W(NPh)(ONO^tBu)Me₂] 7 was prepared by the transmetallation reaction of 6 (either cis or trans isomer) with methyl magnesium iodide.     

Synthesis and structural characterisation of the palladium N-heterocyclic carbene cluster complexes [Pd3(μ-CO)3(NHC)3] and [Pd3(μ-SO2)3(NHC)3]

The reduction of trans-[Pd(NHC)₂Cl₂] (NHC = IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; IⁱPr₂ = 1,3-bis-isopropylimidazol-2-ylidene) with potassium graphite under an atmosphere of CO affords the palladium NHC carbonyl clusters [Pd₃(μ-CO)₃(NHC)₃] (NHC = IMes, 1; IⁱPr₂, 3). Treatment of 1 with SO₂ at room temperature yields the bridging SO₂ complex [Pd₃(μ-SO₂)₃(IMes)₃] (4) in quantitative yield. Complexes 1, 3 and 4 have been structurally characterised by X-ray crystallography.     

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.     

Synthesis of 1,4-disilacyclohexa-2,5-dienes

Title compounds of the type 2,3,5,6-tetraphenyl-1,4-di-X-1,4-di-Y-1,4-disilacyclohexa-2,5-diene wherein X=Y=NMe₂ (4); X=NMe₂, Y=Cl (cis, trans-5); X=NMe₂, Y=Me [(trans)-6] and X=t-Bu, Y=Cl (trans-8) were synthesized from Si₂(NMe₂)₅Cl, sym-Si₂(NMe₂)₄Cl₂, sym-Si₂(NMe₂)₄Me₂, and sym-Si₂Cl₄(t-Bu)₂, respectively, in the presence of diphenylacetylene at 200 °C. Similarly the analogous title compound from the combination of 1-phenyl-1-propyne and Si₂(NMe₂)₅Cl [X=Y=NMe₂ (cis and trans-7) was synthesized. In all cases where cis/trans diastereomers could arise from two different silicon substituents (5, 6, 8) the trans isomer was the sole or dominant product. Evidence for the intermediacy of the silylene Si(NMe₂)₂ in these reactions was gained from a trapping experiment. Compound 4 upon treatment with SiCl₄, SiBr₄ or PI₃ provided the corresponding 1,1,4,4-tetrahalo derivatives 9a-c, respectively. Treatment of 4 with MeOH or PhOH gave the 1,1,4,4-tetramethoxy and tetraphenoxy analogues 9d and 9e, respectively. The tetrachloro derivative 9a upon LAH reduction led to the corresponding tetrahydro compound 10, while the reaction of 9a with H₂O gave the tetrahydroxy derivative 11. Allowing (trans)-6 to react with SiCl₄ provided a ca. 1:1 cis/trans ratio of the derivative 12 in which X=Cl, Y=Me, and possible pathways that rationalize this loss of stereochemistry are proposed. Synthesis of trans-13 in which X=t-Bu, Y=H was achieved by LAH reduction of 8. All of the title compounds except 8 experience free phenyl rotation at room temperature. At −30 °C this rotation in 8 is essentially halted. The molecular structures of 4, 8, 9c, 9e, 10 and 13 were determined by X-ray crystallography.     

Acyclic tertiary diamines and 1,4,7,10-tetraazacyclododecane with fluorine-containing β-diketones: Leading to low melting ionic adducts

N,N,N′,N′-Tetramethylmethanediamine (1a), N,N,N′,N′-tetramethylethanediamine (1b), N,N,N′,N′-tetramethyl-1,3-propanediamine (1c), and N,N,N′,N′-tetramethyl-1,6-hexanediamine (1d) were reacted at 25 °C with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2a), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (2b), 2-thenoyltrifluoroacetone (2c), and 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (2d) to form the ionic adducts 3-18. 1,4,7,10-Tetraazacyclododecane (1e) reacted at 25 °C with β-diketones (2a-d) and 1,1,1-trifluoro-2,4-pentanedione (2e) to give ionic solids 19-23 in good yields. Some of the products are liquid at 25 °C and are thermally stable over long liquid ranges as determined by thermal gravimetric analyses. Single-crystal X-ray structure determinations show that compounds 9 and 21 crystallize in the monoclinic space groups P2(1)/c and P2(1)/n, respectively. All the new compounds were characterized by ¹H, ¹⁹F and ¹³C NMR, electrospray MS and/or elemental analyses.     

Pincer ligand coordination at a triosmium cluster: X-ray structures of 1,2-Os3(CO)10[4,6-bis(diphenylphosphinomethyl)-m-xylene] and 1,2-Os3(CO)10[1-diphenylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinomethyl)phenyl}-propan-2-ol]

The reaction between the triosmium cluster 1,2-Os₃(CO)₁₀(MeCN)₂ and the diphosphine pincer ligand 4,6-bis(diphenylphosphinomethyl)-m-xylene (dppx) has been examined and found to yield the pincer-bridged cluster 1,2-Os₃(CO)₁₀(dppx) (2) as the major product, in addition to the pincer-bridged cluster 1,2-Os₃(CO)₁₀[1-diphenylphosphino-1-{(2,4-dimethyl-5-diphenylphosphinomethyl)phenyl}-propan-2-ol] (3) in trace amounts (<2% yield). Both cluster products have been isolated and their molecular structures determined by crystallographic analyses. The structural highlights of compounds 2 and 3, which represent the first examples of pincer-ligated metal clusters, are discussed. The origin of the functionalized diphosphine ligand in 3 is traced to the ethanol solvent that was used in the recrystallization of the dppx ligand.     

Preparation of hydride complexes of ruthenium with bidentate phosphite ligands

Hydride complex RuH₂(PFFP)₂ (1) [PFFP = (CF₃CH₂O)₂PN(CH₃)N(CH₃)P(OCH₂CF₃)₂] was prepared by allowing the compound RuCl₄(bpy) · H₂O (bpy = 1,2-bipyridine) to react first with the phosphite PFFP and then with NaBH₄. Chloro-complex RuCl₂(PFFP)₂ (2) was also prepared, either by reacting RuCl₄(bpy) · H₂O with PFFP and zinc dust or by substituting triphenylphosphine with PFFP in the precursor complex RuCl₂(PPh₃)₃. Hydride derivative RuH₂(POOP)₂ (3) (POOP = Ph₂POCH₂CH₂OPPh₂) was prepared by reacting compound RuCl₃(AsPh₃)₂(CH₃OH) first with the phosphite POOP and then with NaBH₄. Depending on experimental conditions, treatment of carbonylated solutions of RuCl₃ · 3H₂O with POOP yields either the cis- or trans-RuCl₂(CO)(PHPh₂)(POOP) (4) derivative. Reaction of both cis- and trans-4 with LiAlH₄ in thf affords dihydride complex RuH₂(CO)(PHPh₂)(POOP) (5). Chloro-complex all-trans-RuCl₂(CO)₂(PPh₂OMe)₂ (6) was obtained by reacting carbonylated solutions of RuCl₃ · 3H₂O in methanol with POOP. Treatment of chloro-complex 6 with NaBH₄ in ethanol yielded hydride derivative all-trans-RuH₂(CO)₂(PPh₂OMe)₂ (7). The complexes were characterised spectroscopically and the X-ray crystal structures of complexes 1, 3, cis-4 and 6 were determined.     

Dimolybdenum complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine and N-(2-pyrimidinyl)formamide

The reactions of Mo₂(O₂CCH₃)₄ with different equivalents of N,N′-bis(pyrimidine-2-yl)formamidine (HL1) and N-(2-pyrimidinyl)formamide (HL2) afforded dimolybdenum complexes of the types Mo₂(O₂CCH₃)(L1)₂(L2) (1) trans-Mo₂(L1)₂(L2)₂ (2) cis-Mo₂(L1)₂(L2)₂ (3) and Mo₂(L2)₄ (4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1–3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1–4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo?N and Mo?O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo?O interactions.     

Highly efficient, multigram and enantiopure synthesis of (S)-2-(2,4′-bithiazol-2-yl)pyrrolidine

(S)-2-(4-Bromo-2,4′-bithiazole)-1-(tert-butoxycarbonyl)pyrrolidine ((S)-1) was obtained as a single enantiomer and in high yield by means of a two-step modified Hantzsch thiazole synthesis reaction when bromoketone 3 and thioamide (S)-4 were used. Further conversion of (S)-1 into trimethyltin derivative (S)-2 broadens the scope for further cross-coupling reactions.     

Dependence of the product on the P–P ligand in reactions of [RuCl3(NO)(P–P)] complexes (P–P = aromatic diphosphines) with 2-mercaptopyridine

This study presents the syntheses and characterization of 2-mercaptopyridine (pyS⁻) complexes containing ruthenium(II) with the following general formula [Ru(pyS)₂(P–P)], P–P = (c-dppen) = cis-1,2-bis(diphenylphosphino)ethylene) (1); (dppe) = 1,2-bis(diphenylphosphino)ethane (2); (dppp) = 1,3-bis(diphenylphosphino)propane (3) and (dppb) = 1,4-bis(diphenylphosphino)butane (4). The complexes were synthesized from the mer- or fac-[RuCl₃(NO)(P–P)] precursors in the presence of triethylamine in methanol solution with dependence of the product on the P–P ligand. The reaction of pyS⁻ with a ruthenium complex containing a bulky aromatic diphosphine dppb disclosed a major product with a dangling coordinated dppbO-P, the [Ru(pyS)₂(NO)(η¹-dppbO-P)]PF₆(5). In addition, this work also presents and discusses the spectroscopic and electrochemical behavior of 1–5, and report the X-ray structures for 1 and 5.     

Heterobimetallic [Ru(II)/Fe(II)] complexes: On the formation of trans- and cis-[RuCl2(dppf)(diimines)]

The synthesis and characterization of trans/cis-[RuCl₂(dppf)(diimines)], dppf = 1,1′-bis(diphenylphosphino)ferrocene; diimines = 2,2′-bipyridine (trans/cis-(1)), the new complexes with 4,4′-dimethyl-2,2′-bipyridine (trans/cis-(2)) and 1,10-phenanthroline (cis-(3)) are presented. The complexes were synthesized using two routes and the trans/cis-isomer formation is dependent upon conditions and the precursor applied. The trans-isomer (kinetic) readily isomerizes to the cis-isomer (thermodynamic) when exposed to light (fluorescent) and this process was followed by cyclic voltammetry and UV-vis. The electrochemical studies on these complexes reveal that Fe^(III)/Fe^(II) couples are insensitive to the isomer (trans/cis) formed, but the Ru^(III)/Ru^(II) couples are dependent on the isomer. Transfer-hydrogenation reactions for reduction of acetophenone were conducted using complexes cis-(1) and cis-(2) and the results are compared with that obtained for similar complexes. X-ray structure for cis-(3) are presented and discussed.     

Iron(0) and ruthenium(0) complexes with tridentate phosphonite ligands and their potential for ketene formation from methyl iodide, CO and a base

An efficient route to the novel tridentate phosphine ligands RP[CH₂CH₂CH₂P(OR′)₂]₂ (I: R = Ph; R′ = i-Pr; II: R = Cy; R′ = i-Pr; III: R = Ph; R′ = Me and IV: R = Cy; R′ = Me) has been developed. The corresponding ruthenium and iron dicarbonyl complexes M(triphos)(CO)₂ (1: M = Ru; triphos = I; 2: M = Ru; triphos = II; 3: M = Ru; triphos = III; 4: M = Ru; triphos = IV; 5: M = Fe; triphos = I; 6: M = Fe; triphos = II; 7: M = Fe; triphos = III and 8: M = Fe; triphos = IV) have been prepared and fully characterized. The structures of 1, 3 and 5 have been established by X-ray diffraction studies. The oxidative addition of MeI to 1-8 produces a mixture of the corresponding isomeric octahedral cationic complexes mer,trans-(13a-20a) and mer,cis-[M(Me)(triphos)(CO)₂]I (13b-20b) (M = Ru, Fe; triphos = I-IV). The structures of 13a and 20a (as the tetraphenylborate salt (21)) have been verified by X-ray diffraction studies. The oxidative addition of other alkyl iodides (EtI, i-PrI and n-PrI) to 1-8 did not afford the corresponding alkyl metal complexes and rather the cationic octahedral iodo complexes mer,cis-[M(I)(triphos)(CO)₂]I (22-29) (M = Ru, Fe; triphos = I-IV) were produced. Complexes 22-29 could also be obtained by the addition of a stoichiometric amount of I₂ to 1-8. The structure of 22 has been verified by an X-ray diffraction study. Reaction of 13a/b-20a/b with CO afforded the acetyl complexes mer,trans-[M(COMe)(triphos)(CO)₂]I, 30-37, respectively (M = Ru, Fe; triphos = I-IV). The ruthenium acetyl complexes 30-33 reacted slowly with 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) even in boiling acetonitrile. Under the same conditions, the deprotonation reactions of the iron acetyl complexes 34-37 were completed within 24-40 h to afford the corresponding zero valent complexes 5-8. It was not possible to observe the intermediate ketene complexes. Tracing of the released ketene was attempted by deprotonation studies on the labelled species mer,trans-[Fe(COCD₃)(triphos)(CO)₂]I (38) and mer,trans-[Fe(¹³COMe)(triphos)(CO)₂]I (39).     

Novel synthesis of 2,4-bis(2-pyridyl)-5-(pyridyl)imidazoles and formation of N-(3-(pyridyl)imidazo[1,5-a]pyridine)picolinamidines: nitrogen-rich ligands

Heating a neat 1:2 mixture of 2-picolylamine and 2-cyanopyridine followed by treatment of the resultant red gummy substance with aqueous KOH resulted in the isolation of 2,4,5-tris(2-pyridyl)imidazole (1a) as the major product and N-(3-(2-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2a) in small amounts. Similarly, by using 3-picolylamine, 2,4,-bis(2-pyridyl)-5-(3-pyridyl)imidazole (1b) and N-(3-(3-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2b) were isolated, and by using 4-picolylamine, 2,4,-bis(2-pyridyl)-5-(4-pyridyl)imidazole (1c) and N-(3-(4-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2c) were isolated. The plausible mechanism of the formation of 1a-c and 2a-c is delineated.     

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.     

Mono and dinuclear half-sandwich platinum group metal complexes bearing pyrazolyl-pyrimidine ligands: Syntheses and structural studies

Reactions of 0.5 eq. of the dinuclear complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ (arene = η⁶-C₆H₆, η⁶-p-ⁱPrC₆H₄Me) and [(Cp∗)M(μ-Cl)Cl]₂ (M = Rh, Ir; Cp∗ = η⁵-C₅Me₅) with 4,6-disubstituted pyrazolyl-pyrimidine ligands (L) viz. 4,6-bis(pyrazolyl)pyrimidine (L1), 4,6-bis(3-methyl-pyrazolyl)pyrimidine (L2), 4,6-bis(3,5-dimethyl-pyrazolyl)pyrimidine (L3) lead to the formation of the cationic mononuclear complexes [(η⁶-C₆H₆)Ru(L)Cl]⁺ (L = L1, 1; L2, 2; L3, 3), [(η⁶-p-ⁱPrC₆H₄Me)Ru(L)Cl]⁺ (L = L1, 4; L2, 5; L3, 6), [(Cp∗)Rh(L)Cl]⁺ (L = L1, 7; L2, 8; L3, 9) and [(Cp∗)Ir(L)Cl]⁺ (L = L1, 10; L2, 11; L3, 12), while reactions with 1.0 eq. of the dinuclear complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ and [(Cp∗)M(μ-Cl)Cl]₂ give rise to the dicationic dinuclear complexes [{(η⁶-C₆H₆)RuCl}₂(L)]²⁺ (L = L1, 13; L2, 14; L3, 15), [{(η⁶-p-ⁱPrC₆H₄Me)RuCl}₂(L)]²⁺ (L = L1, 16; L2, 17; L3, 18), [{(Cp∗)RhCl}₂(L)]²⁺ (L = L1, 19; L2, 20; L3, 21) and [{(Cp∗)IrCl}₂(L)]²⁺ (L = L1 22; L2, 23; L3 24). The molecular structures of [3]PF₆, [6]PF₆, [7]PF₆ and [18](PF₆)₂ have been established by single crystal X-ray structure analysis.     

Palladium(II) and platinum(II) saccharinate complexes containing pyridine and 3-acetylpyridine: Synthesis, crystal structures, fluorescence and thermal properties

New palladium(II) and platinum(II) complexes of saccharinate (sac), trans-[Pd(py)₂(sac)₂] (1), cis-[Pt(py)₂(sac)₂] (2), trans-[Pd(3-acpy)₂(sac)₂] (3) and cis-[Pt(3-acpy)₂(sac)₂] (4) (py = pyridine and 3-acpy = 3-acetylpyridine) have been synthesized. Elemental analysis, UV-Vis, IR, NMR and TG/DTA characterizations have been carried out. The structures of 1-4 were determined by X-ray diffraction. The palladium(II) and platinum(II) ions are coordinated by two N-bonded sac ligands, and two nitrogen atoms of py or 3-acpy, forming a distorted square-planar geometry. The palladium(II) complexes (1 and 3) are trans isomers, while the platinum(II) complexes (2 and 4) are cis isomers. The mononuclear species in the solid state are connected by weak intermolecular C-H?O hydrogen bonds, C-H?π and π?π stacking interactions. The platinum(II) complexes show significant fluorescence at the room temperature.     

Synthesis, X-ray crystal structure and cytotoxicity of a new tetranuclear ruthenium arene complex

The tetranuclear ruthenium arene compound [(cym)₄Ru₄(2)Cl₆]Cl₂ (3) (cym = η⁶-p-cymene, 2 = 1,2-bis(di-N-methylimidazol-2-ylphosphino)ethane) was prepared and characterised by one- and two-dimensional NMR techniques. Its cytotoxicity against four different cell lines was determined and, with an approximate IC₅₀ of >100 μM 3 can be regarded as non-toxic. Its partition coefficient in n-octanol/water (log D_7.4) was also determined. The structures of complex 3 as well as of the related compound [(cym)₂Ru₂(4)Cl₂]Cl₂ (5) (4 = 1,2-bis(di-N-methylimidazol-2-ylphosphino)ethane dioxide) were determined by single crystal structure analysis. Upon oxidation in protic solvents, ligand 2 shows P-C bond cleavage reactions to yield P,P′-bis(N-methylimidazol-2-yl)ethylene diphosphinic acid (6).