Synthesis and characterization of ether-derivatized aminophosphines and their application in C-C coupling reactions

Four new bis(phosphino)amine ligands (Ph₂P)₂N-C₆H₃-R, where R = 3,5-OMe (1), 2,5-OMe (2), 2,4-OMe (3) or 3,4-OMe (4), were prepared via aminolysis of the corresponding dimethoxyanilines with 2 equiv. of diphenylphosphine chloride in the presence of triethyl amine. Oxidation of these ligands with aqueous H₂O₂, elemental S₈ or Se powder afforded the corresponding chalcogen oxides 1a-4a, sulfides 1b-4b and selenides 1c-4c in good yields. Reaction of 1-4 with [MCl₂(cod)] (M = Pt, Pd; cod = cycloocta-1,5-diene) in equimolar ratios afforded cis-[MCl₂{(Ph₂P)₂N-C₆H₃-R}] (M = Pt; R = 3,5-OMe 1d, R = 2,5-OMe 2d, R = 2,4-OMe 3d, and R = 3,4-OMe 4d. M = Pd; R = 3,5-OMe 1e, R = 2,5-OMe 2e, R = 2,4-OMe 3e, and R = 3,4-OMe 4e). Similarly, reaction of [Cu(CH₃CN)₄]PF₆ with the 1-4 in 1:2 ratio gave [Cu{(Ph₂P)₂N-C₆H₃-R}₂]PF₆ (R = 3,5-OMe 1f, 2,5-OMe 2f, 2,4-OMe 3f and 3,4-OMe 4f). All new compounds were fully characterized by spectroscopy and elemental analysis and the molecular structures of seven representative compounds were determined by single-crystal X-ray crystallography. In addition, the palladium complexes were investigated as pre-catalysts in C-C coupling reactions.     

A new series of iodocarbonyl ruthenium (II) complexes with unsymmetrical phosphine-phosphine sulfide ligands of the type Ph2P(CH2)nP(S)Ph2, n = 1-4: Isolation and structural investigation

Hexa-coordinated chelate complex cis-[Ru(CO)₂I₂(P∩S)] (1a) {P∩S = η²-(P,S)-coordinated} and penta-coordinated non-chelate complexes cis-[Ru(CO)₂I₂(P∼S)] (1b-d) {P∼S = η¹-(P)-coordinated} are produced by the reaction of polymeric [Ru(CO)₂I₂]_n with equimolar quantity of the ligands Ph₂P(CH₂)_nP(S)Ph₂ {n = 1(a), 2(b), 3(c), 4(d)} in dichloromethane at room temperature. The bidentate nature of the ligand a in the complex 1a leads to the formation of five-membered chelate ring which confers extra stability to the complex. On the other hand, 1:2 (Ru:L) molar ratio reaction affords the hexa-coordinated non-chelate complexes cis,cis,trans-[Ru(CO)₂I₂(P∼S)₂] (2a-d) irrespective of the ligands. All the complexes show two equally intense terminal ν(CO) bands in the range 2028-2103 cm⁻¹. The ν(PS) band of complex 1a occurs 23 cm⁻¹ lower region compared to the corresponding free ligand suggesting chelation via metal-sulfur bond formation. X-ray crystallography reveals that the Ru(II) atom occupies the center of a slightly distorted octahedral geometry. The complexes have also been characterized by elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopy.     

Synthesis and electrochemical aspects of group 14 iron complexes of the type (η-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2; E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (η⁵-C₅H₅)Fe(L)₂ER₃ (L₂ = (CO)₂ (a), (Ph₂P)₂CH₂ (b); ER₃ = CH₃ (1a/b); SiMe₃ (2a/b), GeMe₃ (3a/b), SnMe₃ (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a-4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b-4b were reversible. The E_ox values found for the series 1a-4a were in the narrow range 1.3-1.5 V and in the order Si > Sn ≈ Ge > C; those for 1b-4b (involving replacement of the excellent retrodative π-accepting CO ligands by the superior σ-donor and poorer π-accepting phosphines) have much lower oxidation potentials in the sequence Sn > Si ≈ Ge > C. This latter oxidation potential pattern relates directly to the solution ³¹P NMR chemical shift data illustrating that stronger donation lowers the E_ox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems.     

Platinum(II) diphosphine complexes as catalysts for the Baeyer-Villiger oxidation of ketones: Is it possible to increase the concentration of the active species?

The synthesis and characterization of new bis-aquo platinum(II) complexes of the type [Pt(H₂O)(P-P)][OTf]₂ (OTf = triflate anion), in which the diphosphine P-P is a series of 1,n-bis-diphenyphosphinoalkanes (1a-d, with n = 1-4), 1,2-bis-(di-n-fluorophenylphosphino)ethanes (2a-c, with n = 2, 4-5) and 1,2-bis-dialkylphosphinoethanes (3a-e), where the alkyl substituents at phosphorus have been systematically changed (dmpe) (3a), (depe) (3b), (dippe) (3c), (dcype) (3d) are reported. These complexes were used as catalysts in the Baeyer-Villiger oxidation of 2-methylcyclohexanone, 2-methylcyclopentanone and cyclobutanone with 35% hydrogen peroxide as an environmentally friendly oxidant. The reactions were performed at 25 °C in a chlorinated solvent/H₂O two-phase system. All the investigated catalysts performed better than the corresponding dimeric complexes of general formula [Pt(μ-OH)(P-P)]₂[BF₄]₂ as a consequence of the positive effect imparted by the triflate counter-anion on catalysts speciation.     

Synthesis, reactivities and catalytic carbonylation of rhodium(I) carbonyl complexes containing isomeric acetylpyridine ligands

[Rh(CO)₂Cl]₂ reacts with two mole equivalent of 2-acetylpyridine (a), 3-acetylpyridine (b) and 4-acetylpyridine (c) to afford chelate [Rh(CO)Cl(η²-N∩O)] (1a) and non-chelate [Rh(CO)₂Cl(η¹-N∼O)] (1b, 1c) complexes, where, N∩O = a, N∼O = b, c. Oxidative addition (OA) of 1a-1c with CH₃I and C₂H₅I yields penta coordinate rhodium(III) complexes, [Rh(COR)ClI(η²-N∩O)] {R = -CH₃ (2a); -C₂H₅ (3a)} and [Rh(COR)(CO)ClI(η¹-N∼O)] {R = -CH₃ (2b, 2c); -C₂H₅ (3b, 3c)}. Kinetic study for the reaction of 1a-1c with CH₃I indicates a pseudo-first order reaction. The catalytic activity of 1a-1c for the carbonylation of methanol to acetic acid and its ester was evaluated at different initial CO pressures 5, 10 and 20 bar at ∼25 °C and higher turn over numbers (TON = 1581-1654) were obtained compared to commercial Monsanto’s species [Rh(CO)₂I₂]⁻ (TON = 1000) under the reaction conditions: temperature = 130 ± 1 °C, pressure = 15-32 bar, rpm = 450, time = 1 h and catalyst: substrate = 1: 1900.     

Synthesis and evaluation of chromenyl barbiturates and thiobarbiturates as potential antitubercular agents

A novel series of barbiturate and thiobarbiturate analogs of 2-benzoyl-3-methyl-5-oxo-5H-furo[3,2-g]chromene-6-carbaldehydes (3a-g and 4a-d, respectively) and 6-methyl-4,8-dioxo-4,8-dihydropyrano[3,2-g]chromenes (7a-c), were synthesized and evaluated for their antitubercular activities against Mycobacterium tuberculosis H37RV, and cytotoxicity (CC₅₀) in the VERO cell MABA assay. The results indicate that the furanochromene series of compounds (3a-g and 4a-d) showed only weak to moderate antitubercular activity. However, the pyranochromene analog 7b showed good antitubercular activity (IC₉₀: 5.9 μg/mL) and cytotoxicity (CC₅₀: 14.27 μg/mL). The antitubercular activity of 7b was superior to the antituberculosis drug, pyrazinamide (PZA; IC₉₀: >20 μg/mL). Analog 7b was considered to be a lead compound for subsequent structural optimization.     

Bis(pyrazolyl) palladium(II), platinum(II) and gold(III) complexes: Syntheses, molecular structures and substitution reactions with l-cysteine

A series of pyrazolyl palladium(II), platinum(II) and gold(III) complexes, [PdCl₂(3,5-R₂bpza)] {R = H (1), R = Me (2), bpza = bis-pyrazolyl acetic acid}, [PtCl₂(3,5-R₂bpza)] {R = H (3a), R = Me (4)}, [AuCl₂(3,5-R₂bpza)]Cl {R = H (5a), R = Me (6a)} and [PdCl₂(3,5-R₂bpzate)] {R = Me (7)} have been synthesised and structurally characterised. Single crystal X-ray crystallography showed that the pyrazolyl ligands exhibit N^N-coordination with the metals. Anticancer activities of six complexes 1-6a were investigated against CHO cells and were found to have low activities. Substitution reactions of selected complexes 1, 2, 3a and 5a with l-cysteine show that the low anticancer activities compounds and that the rate of substitution with sulfur-containing compounds is not the cause of the low anticancer activities.     

The syntheses, structures and redox properties of phosphine-gold(I) and triruthenium-carbonyl cluster derivatives of tolans

The syntheses of several ethynyl-gold(I)phosphine substituted tolans (1,2-diaryl acetylenes) of general form [Au(CCC₆H₄CCC₆H₄X)(PPh₃)] are described [X = Me (2a), OMe (2b), CO₂Me (2c), NO₂ (2d), CN (2e)]. These complexes react readily with [Ru₃(CO)₁₀(μ-dppm)] to give the heterometallic clusters [Ru₃(μ-AuPPh₃)(μ-η¹,η²-C₂C₆H₄CCC₆H₄X)(CO)₇(μ-dppm)] (3a-e). The crystallographically determined molecular structures of 2b, 2d, 2e and 3a-e are reported here, that of 2a having been described on a previous occasion. Structural, spectroscopic and electrochemical studies were conducted and have revealed little electronic interaction between the remote substituent and the organometallic end-caps.     

Lewis acidity of platinum(II)-based Baeyer-Villiger catalysts: An electrochemical approach

The electrochemical behavior of the Pt(II)-based Baeyer-Villiger catalysts of the general formulae [Pt(μ-OH)(P^∩P)]₂(BF₄)₂ (P^∩P = dppe (1a), 2Fdppe (1 b), 4Fdppe (1c), dfppe (1d), dmpe (1e), depe (1f), dippe (1g), dtbpe (1h)) and [Pt(OH₂)₂(P^∩P)](OTf)₂ (P^∩P = dppe (2a), 2Fdppe (2b), 4Fdppe (2c), dfppe (2d)) is reported. They exhibit irreversible reduction processes whose potentials reflect the Lewis acidity of the metal centres, showing (for the aromatic diphosphine complexes) overall relations with the number of fluorine atoms, with J_Pt-P, with the ν(CN) coordination shift of a ligand isocyanide probe and with the catalytic activity. Single-crystal X-ray diffraction analyses were carried out for [Pt(μ-OH)(4Fdppe)]₂(BF₄)₂ (1c) and [Pt(μ-OH) (dippe)]₂(BF₄)₂ (1g).     

Diiron and diruthenium aminocarbyne complexes containing pseudohalides: stereochemistry and reactivity

Acetonitrile is easily displaced from [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(MeCN)(Cp)₂][SO₃CF₃] (R = 2,6-Me₂C₆H₃ (Xyl) (1a); Me (1b)) upon stirring in THF at room temperature in the presence of [NBu₄][SCN]. The resulting complexes trans-[Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCS)(Cp)₂] (R = Xyl (trans-2a); Me (trans-2b)) are completely isomerised to cis-[Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCS)(Cp)₂] (R = Xyl (cis-2a); Me (cis-2b)) when heated at reflux temperature. Similarly, the complexes cis-[M₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCO)(Cp)₂] (M = Fe, R = Me (4a); M = Ru, R = Xyl (4b); M = Ru, R = Me (4c)) and cis-[M₂{μ-CN(Me)(R)}(μ-CO)(CO)(N₃)(Cp)₂] (M = Fe, R = Xyl (5a); M = Fe, R = Me (5b); M = Ru, R = Xyl (5c)) can be obtained by heating at reflux temperature a THF solution of [M₂{μ-CN(Me)(R)}(μ-CO)(CO)(MeCN)(Cp)₂][SO₃CF₃] (M = Fe, R = Xyl (1a); M = Fe, Me (1b); M = Ru, R = Xyl (1c); M = Ru, R = Me (1d)) in the presence of NaNCO and NaN₃, respectively. The reactions of 5 with MeO₂CCCCO₂Me, HCCCO₂Me and (NC)(H)CC(H)(CN) afford the triazolato complexes [M₂{μ-CN(Me)(R)}(μ-CO)(CO){N₃C₂(CO₂Me)₂}(Cp)₂] (M = Fe, R = Xyl (6a); M = Fe, R = Me (6b); M = Ru, R = Xyl (6c)), [M₂{μ-CN(Me)(R)}(μ- CO)(CO){N₃C₂(H)(CO₂Me)}(Cp)₂] (M = Fe, R = Me (7a); M = Ru, R = Xyl (7b)) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃C₂(H)(CN)}(Cp)₂] (8), respectively. The asymmetrically substituted triazolato complexes 7-8 are obtained as mixtures of N(1) and N(2) bonded isomers, whereas 6 exists only in the N(2) form. Methylation of 6-8 results in the formation of the triazole complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃(Me)C₂(CO₂Me)₂}(Cp)₂][CF₃SO₃] (9), [M₂{μ-CN(Me)(R)}(μ-CO)(CO){N₃(Me)C₂(H)(CO₂Me)}(Cp)₂][CF₃SO₃] (M = Fe, R = Me (10a); M = Ru, R = Xyl (10b)) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃(Me)C₂(H)(CN)}(Cp)₂][CF₃SO₃], 11. The crystal structures of trans-2b, 4b · CH₂Cl₂, 5a, 6b · 0.5CH₂Cl₂ and 8 · CH₂Cl₂ have been determined.     

Synthesis and evaluation of antioxidant and antibacterial activities of new substituted bis(1,3,4-oxadiazoles), 3,5-bis(substituted) pyrazoles and isoxazoles

Two series of five membered heterocyclic bis(1,3,4-oxadiazole) derivatives 2(a-h) and 3,5-bis(substituted)pyrazoles, isoxazoles 3(a,b,d-i), 4(a-c) were synthesized via oxidative cyclization of some diaroylhydrazones using chloramine-T and cyclocondensation reaction with hydrazine hydrate and hydroxylamine hydrochloride, respectively. The newly synthesized compounds were screened for antioxidant and anti-microbial activities. Compounds 2(b), 3(b), and 4(a) showed higher antioxidant activity at 10 μg/ml while compounds 2(a), 3(a), 3(f), and 4(a) exhibited better anti-microbial activity at 100 μg/ml compared with standard vitamin C and ciprofloxacin, respectively. Structures of newly synthesized compounds were confirmed by elemental analysis and spectral IR, ¹H NMR, and ¹³C NMR data.     

Half-sandwich ruthenium thiocarbonate complexes: Structures of CpRu(PPh3)2SCO2Bu, CpRu(dppe)SCO2Bu and CpRu(PPh3)(CO)SCO2Bu

Thiocarbonate ruthenium complexes of the form CpRu(L)(L′)SCO₂R (L = L′ = PPh₃ (1), 1/2 dppe (2), L = PPh₃, L′ = CO (3); R = Et (a), Buⁿ (b), C₆H₅ (c), 4-C₆H₄NO₂ (d)) have been synthesized by the reaction of the corresponding sulfhydryl complexes, CpRu(L)(L′)SH, with chloroformates, ROCOCl, at low temperature. The bis(triphenylphosphine) complexes 1 can be converted to 3 under CO atmosphere. The crystal structures of CpRu(PPh₃)₂SCO₂Buⁿ (1b), CpRu(dppe)SCO₂Buⁿ (2b), and CpRu(PPh₃)(CO)SCO₂Buⁿ (3b) are reported.     

Diheteroarylmethyl substituted titanocenes: A novel class of possible anti-cancer drugs

From the reaction of tert-butyl lithium or n-butyl lithium with N-methylpyrrole (1a), furan (1b) or 2-bromo-thiophen (1c), 2-N-methylpyrrolyl lithium (2a), 2-furyl lithium (2b) or 2-thiophenyl lithium (2c), respectively, was obtained. When reacted with 6-(2-N-methylpyrrolyl) fulvene (3a), 6-(2-furyl) fulvene (3b) or 6-(2-thiophenyl) fulvene (3c), the corresponding lithiated intermediates were formed (4a-c). Titanocenes (5a-c) were obtained through transmetallation with titanium tetrachloride. When these titanocenes were tested against pig kidney epithelial (LLC-PK) cells, inhibitory concentrations (IC₅₀) of 32 μM, 140 μM, and 240 μM, respectively, were observed. These values represent improved cytotoxicity against LLC-PK, compared to their ansa-analogues.     

Modification of aminoallenylidene complexes of chromium via exchange of the C3-bound amino group

The aminoallenylidene(pentacarbonyl)chromium complexes [(CO)₅CrCCC(NR¹R²)Ph] (1a-c) react with dimethylamine by addition of the amine to the C1C2 bond of the allenylidene ligand to give alkenyl(amino)carbene complexes [(CO)₅CrC(NMe₂)CHC(NR¹R²)Ph] (2a-c) (R¹ = Me: R² = Me (a), Ph (b); R¹ = Et: R² = Ph (c)). In contrast, addition of a large excess (usually 20 equivalents) of ammonia or primary amines, H₂NR, to solutions of [(CO)₅CrCCC(NMe₂)Ph] (1a) affords the aminoallenylidene complexes [(CO)₅CrCCC(NHR)Ph] (1d-w) in which the dimethylamino group is replaced by NH₂ or NHR, respectively. In addition to simple amines such as methylamine, butylamine, and aniline, amines carrying a functional group (allylamine, propargylamine) and amino acid esters as well as amino terpenes and amino sugars can be used to displace the NMe₂ substituent. Usually the Z isomer (with respect to the partial C3-N double bond) is formed exclusively. Products derived from addition of H₂NR to the C1C2 bond of 1a are not observed. The amino group in 1d-w is rapidly deprotonated by excess of amine to form iminium alkynyl chromates [1d-w]⁻, thus protecting 1d-w from addition of free amine to either C3 or across the C1C2 bond. The iminium alkynyl chromates are readily reprotonated by acids or by chromatography on wet SiO₂ to reform 1d-w.     

Neighbouring metal induced oxidative addition at the iron centre amongst the iron-arylpyridylphosphine complexes

Complexes of the type (η⁴-BuC₅H₅)Fe(CO)₂(P) (P = PPh₂Py 3, PPhPy₂4, PPy₃5; Py = 2-pyridyl) were satisfactorily prepared. Upon treatment of 3 with M(CO)₃(EtCN)₃ (M = Mo, 6a; W, 6b), the pyridyl N-atom could be coordinated to the metal M, which then eliminates a CO ligand from the Fe-centre and induced an oxidative addition of the endo-C-H of (η⁴-BuC₅H₅). This results in a bridged hydrido heterodimetallic complex [(η⁵-BuC₅H₄)Fe(CO)(μ-P,N-PPh₂Py)(μ-H)M(CO)₄] (M = Mo, 7a, 81%; W, 7b, 76%). The reaction of 4 or 5 with 6a,b did not give the induced oxidative addition, although these complexes contain more than one pyridyl N-atom. The reaction of 4 with M(CO)₄(EtCN)₂ (M = Mo, 9a; W, 9b) produced heterodimetallic complexes [(η⁴-BuC₅H₅)Fe(CO)₂(μ-P:N,N′-PPhPy₂)M(CO)₄] (M = Mo, 10a, 81%; W, 10b, 83%). Treatment of 5 with 6a,b gave [(η⁴-BuC₅H₅)Fe(CO)₂(μ-P:N,N′,N″-PPy₃)M(CO)₃] (M = Mo, 12a, 96%; W, 12b, 78%).     

Synthesis and characterization of cyclopentadienyltricarbonyl tungsten selenocarboxylate and selenosulfonate complexes

Cyclopentadienyltricarbonyl tungsten selenocarboxylate complexes CpW(CO)₃SeCOR (1) (R = C₆H₅ (a), 3,5-C₆H₃(NO₂)₂ (b), 3-C₆H₄NO₂ (c), 4-C₆H₄NO₂ (d), CH₃ (e)) and cyclopentadienyltricarbonyl tungsten selenosulfonate complexes CpW(CO)₃SeSO₂R (2) (R = C₆H₅ (a), 4-C₆H₄CH₃ (b), 4-C₆H₄OCH₃ (c), 4-C₆H₄Cl (d), CH₃ (e)) have been prepared from the tungsten anion [CpW(CO)₃Se]⁻ and acid- or sulfonyl chlorides respectively. The new complexes (1 and 2) have been characterized by IR, ¹H NMR spectroscopies as well as elemental analysis. The crystal structure of CpW(CO)₃SeCO-3-C₆H₄NO₂ (1c) was determined.     

Properties of homo- and heteronuclear mixed biscarbene complexes with conjugated bithiophene units

The syntheses and structures of homo- and heteronuclear biscarbene complexes with bithiophene spacers were investigated. The complexes were synthesized by lithiation of bithiophene followed by metallation using combinations of the metal precursors MnMeCp(CO)₃, W(CO)₆, Mo(CO)₆ and Cr(CO)₆, after which the reaction was quenched with triethyloxonium tetrafluoroborate. This classical Fischer method yielded monocarbene complexes, [ML_nC(OEt)C₄H₂S-C₄H₃S], ([ML_n] = Cr(CO)₅1a, W(CO)₅2a or MnMeCp(CO)₂3a), homonuclear biscarbene complexes, [ML_nC(OEt)C₄H₂S-C₄H₂SC(OEt)ML_n], ([ML_n] = Cr(CO)₅1b, W(CO)₅2b or MnMeCp(CO)₂3b) and heteronuclear biscarbene complexes, [ML_nC(OEt)C₄H₂S-C₄H₂SC(OEt)M′L_n] (1d: [ML_n] = Cr(CO)₅ and [M′L_n] = W(CO)₅; 1e: [ML_n] = MnMeCp(CO)₂ and [M′L_n] = Cr(CO)₅; 1f: [ML_n] = Cr(CO)₅ and [M′] = Mo(CO)₅); 2d: [ML_n] = MnMeCp(CO)₂ and [M′L_n] = W(CO)₅; 3c: [ML_n] = MnMeCp(CO)₂ and [M′L_n] = Mo(CO)₅). Electron density calculations with the gaussian03 software package of 1e revealed a polar rod with the negative pole towards the chromium carbene side, whereas the biscarbenes 1d and 1b showed very little polarity. By-products resulting from activation of the carbene moieties in homonuclear biscarbene complexes included (i) ester-type complexes of the form [ML_nC(OEt)C₄H₂S-C₄H₂SC(O)OEt], ([ML_n] = Cr(CO)₅1c or W(CO)₅2c), formed in situ in the reaction of 1b and 2b, (ii) the organic bis-ester compound [EtOC(O)C₄H₂S-C₄H₂SC(O)OEt] 4, where both metal moieties had been substituted by oxygen and (iii) the carbon-carbon coupled dimeric bithienyl compound [C₄H₃S-C₄H₂SC(O)C(O)C₄H₂S-C₄H₃S] 5. By-products obtained from heteronuclear biscarbene reactions contain the former diketo compound (or a derivative) as spacer between two metal carbonyl fragments and have the general formula [ML_nC(OEt)C₄H₂S-C₄H₂SCR-CR′C₄H₂S-C₄H₂SC(OEt)ML_n] (5a: [M] = Cr(CO)₅, R = OH, R′ = OEt; 5b: [M] = W(CO)₅, R = R′ = O; 5c: [M] = Mo(CO)₅, R = R′ = O). Reaction of 1d, 1e and 1f with hex-3-yne resulted in the formation of benzannulated products 6a, 6b and 6c. All novel complexes were fully characterized using various spectroscopic techniques. The crystal structures of 1b, 2a and 5 are reported.     

1,3-Dipolar cycloaddition to the FeSC fragment 20. Preparation and properties of carbonyliron complexes of di-thiooxamide. Reactivity of the mononuclear (di-thiooxamide)Fe(CO)3 towards dimethyl acetylenedicarboxylate

Reaction of Fe₂(CO)₉ at room temperature in THF with the di-thiooxamides (L), SC{N(R,R′)}C{(R,R′)N}S [R=Me, R′-R′=(CH₂)₂ (a); R=H, R′=ⁱPr (b); R=H, R′=iPr (c), R=H, R′=benzyl (d); R=H, R′=H (e)], results for ligands a-d initially in the formation of the mononuclear σ-S, σ-S′ chelate complexes Fe(CO)₃(L) (7a-d), which could be isolated in case of 7a and 7d. Under the reaction conditions, complexes 7a-d react further with [Fe(CO)₄] fragments to give three types of Fe₂(CO)₆(L) complexes (8a-d) in high yields, depending on the di-thiooxamide ligand used together with traces of the known complex S₂Fe₃(CO)₉ (14). The molecular structures of these complexes have been established by the single crystal X-ray diffraction determinations of 8a, 8b and 8d. In the reaction with ligand e the corresponding complex 7e was not detected and the well-known complexes 14 and S₂Fe₃(CO)₉ (15) were isolated in low yield. In situ prepared 7a reacts in a slow reaction with 1 equiv. of dimethyl acetylene dicarboxylate in a 1,3-dipolar cycloaddition reaction to give the stable initial ferra [2.2.1] bicyclic complex 10a in 60% yield. In complex 10a an additional Fe(CO)₄ fragment is coordinated to the sulfido sulfur atom of the cycloadded FeSC fragment. When a toluene solution of 10a is heated to 50 °C it loses two terminal CO ligands to give the binuclear FeFe bonded complex 11a in almost quantitative yield. The molecular structures of 10a and 11a have been confirmed by single crystal X-ray diffraction. Reaction of 7d at room temperature with 2 equiv. of dimethyl acetylene dicarboxylate results in the mononuclear complex 12d in 5% yield. The molecular structure of 12b has been established by single crystal X-ray diffraction and comprises a tetra dentate ligand with two ferra-sulpha cyclobutene, and a ferra-disulpha cyclopentene moiety. When the reaction is performed at 60 °C a low yield of 2,3,4,5-thiophene tetramethyl tertracarboxylate is obtained besides complex 12d.     

Hydrogen-halide versus alkyl-halide oxidative addition in dimethyl platinum(II) complexes: Crystal structure of [PtBr2(bpy)]

Dimethyl platinum(II) complexes [PtMe₂(NN)] {NN = bu₂bpy (4,4′-di-tert-butyl-2,2′-bipyridine) (1a), bpy (2,2′-bipyridine) (1b), phen (1,10-phenanthroline) (1c)} reacted with commercial 3-bromo-1-propanol in the presence of 1,3-propylene oxide to afford cis, trans- [PtBrMe₂{(CH₂)₃OH}(NN)] (NN = bu₂bpy (2a), bpy (2b), phen (2c)). On the other hand, [PtMe₂(NN)] (1a)-(1b) reacted with the trace of HBr in commercial 3-bromo-1-propanol to give [PtBr₂(NN)] (NN = bu₂bpy (3a), bpy (3b)). The reaction pathways were monitored by ¹H NMR at various temperatures. Treatment of 1a-1b with a large excess of 3-bromo-1-propanol at −80 °C gave the corresponding methyl(hydrido)platinum(IV) complexes [PtBr(H)Me₂(NN)] (NN = bu₂bpy (4a), bpy (4b)) via the oxidative addition of dimethyl platinum(II) complexes with HBr. The complexes [PtBr(H)Me₂(NN)] decomposed by reductive elimination of methane above −20 °C for bu₂bpy and from −20 to 0 °C for bpy analogue to give methane and platinum(II) complexes [PtBrMe(NN)] (5a)-(5b) and then decomposed at about 0 °C to yield [PtBr₂(NN)] and methane. When the reactions were performed at a molar ratio of Pt:RX/1:10, the corresponding complexes [PtBrMe(NN)] (5a)-(5b) were also obtained. The crystal structure of the complex 3b shows that platinum adopts square planar geometry with a twofold axis through the platinum atom. The Pt…Pt distance (5.164 Å) is considerably larger than the interplanar spacing (3.400 Å) and there is no platinum-platinum interaction.     

An efficient route to substituted 1-silacyclopent-2-enes and 1-silacyclohex-2-enes via consecutive 1,2-hydroboration and 1,1-organoboration

The reaction of alkyn-1-yl(vinyl)silanes R₂Si(CCR¹)CHCH₂ [R = Me (1), Ph (2); R¹ = ^tBu (a), Ph (b), SiMe₃ (c)] with 9-borabicyclo[3.3.1]nonane in a 1:1 ratio affords the 1-silacyclopent-2-ene derivatives 4a-c (R = Me) and 5a-c (R = Ph) as a result of selective intermolecular 1,2-hydroboration of the vinyl group, followed by intramolecular 1,1-organoboration of the alkynyl substituent. The analogous reaction sequence converts the alkyn-1-yl(allyl)dimethylsilanes 3a,c into the 1-silacyclohex-2-ene derivatives 7a,c. All reactions were monitored by ²⁹Si NMR spectroscopy and the structural assignment of the final products was based on multinuclear magnetic resonance data (¹H, ¹¹B, ¹³C and ²⁹Si NMR). The molecular structure of 6a was determined by X-ray analysis.