Tandem radical cyclization-based strategy for the synthesis of oxa- and aza-cages: a case of fragmentation versus cyclization

A new strategy for the synthesis of oxa- and aza-cage compounds based on tandem radical cyclizations is described. The iodides 1 lead to oxa-cages 3 after two tandem radical cyclizations. The ester 10aa on reaction with n-Bu₃SnH and AIBN gives rise to the oxa-cage 12aa after two tandem 5-exo-trig cyclizations. On the other hand, reaction of the ketones 17aa and 21 under similar conditions furnished the oxa-cages 20aa and 23, respectively, via a double 5-exo-trig tandem radical cyclization followed by fragmentation.     

Intramolecular nucleophilic capture of radical cations by tethered hydroxy functions

A range of systems bearing hydroxy functions tethered to the molecular framework gives rise to a family of interesting radical cations, 5⁺-11⁺, upon electron transfer to photo-excited cyanoaromatics. Geraniol (5), nerol (6), citronellol (7), chrysanthemol (8), homochrysanthemol (9), trans-1-o-hydroxyphenyl-2-phenylcyclopropane (10), and endo-5-hydroxymethylnorbornene (11), generate a series of mono-, bi-, or tricyclic ethers via a series of four- to seven-membered transition states. Two of the radical cations, 5⁺ and 6⁺, undergo tandem cyclizations where 1,5- and/or 1,6-C-C cyclizations precede nucleophilic capture.     

Application and details of photoinduced oxidative cyclization of 5-(4′,9′-methanocycloundeca-2′,4′,6′,8′,10′-pentaenylidene)pyrimidine-2,4,6(1,3,5H)-triones and related compounds

As novel methodology for synthesizing the furan ring, a photoinduced oxidative cyclization of 5-(4′,9′-methanocycloundeca-2′,4′,6′,8′,10′-pentaenylidene)pyrimidine-2,4,6(1,3,5H)-triones (7a-c) and related compounds 9a-c was accomplished to give 5,10-methanocycloundeca[4,5]furo[2,3-d]pyrimidine-2,4(1,3H)-dionylium tetrafluoroborates (8a-c⁺·BF₄⁻) and related compounds 2a-c⁺·BF₄⁻, respectively. In the photoinduced oxidative cyclization, the molecular oxygen in air is used as oxidant and the reaction proceeds under mild conditions to give desired products without byproducts, and thus, it is interesting from the viewpoint of the green chemistry. On the reactions of the mono-substituted derivatives 7d,e and 9e,f, the selectivity of the photoinduced cyclizations were reversed as compared with those of the DDQ-promoted oxidative cyclizations. By the NMR monitoring of the reactions of 7a and deuterated compound 7a-D₂ under degassed conditions, the details of the reaction pathway were clarified and rationalized on the basis of the MO calculation by the 6-31G^∗ basis set of the MP2 levels as well.     

Synthesis of a tetraoxy-bis-nortaxadiene, en route to taxol, using a cascade radical cyclisation sequence

Concise syntheses of the substituted enynediones 28a, 33b and 36 starting from the cyclohexenealdehyde 18, corresponding to ring A in the taxanes, and the vinylstannane 24, are described. Treatment of 36 with Bu₃SnH-AIBN did not lead to the oxy-substituted taxadiene 37 expected from a tandem radical macrocyclisation-radical transannulation sequence; instead, a mixture of unidentified products resulted. When the PMB ether 33b corresponding to the alcohol 36 was treated with Bu₃SnH-AIBN under similar conditions, p-anisaldehyde was isolated, as a major by-product, but no evidence for the formation of a taxadiene could be observed. In contrast, the iododienynedione 41, i.e., deoxy 36, underwent a tandem radical macrocyclisation-transannulation sequence, when treated with Bu₃SnH-AIBN, leading to the tetraoxy-bis-nortaxadiene 42 in 44% yield. Attempts to synthesise the alcohol 28b from the silyl ether 28a en route to the iodide 28c instead gave the substituted tetrahydrofuran 29 via an intramolecular oxy-Michael reaction.     

Hydro- and chloro-substituted silyl- and silyl-η-amido-η-tetramethylcyclopentadienyl titanium complexes

Chlorosilyl-cyclopentadienyl titanium precursors [Ti(η⁵-C₅Me₄SiMeXCl)Cl₃] (X=H 2, Cl 3) were prepared by reaction of TiCl₄ with the trimethylsilyl derivatives of the corresponding cyclopentadienes. Methylation of these compounds with MgClMe under appropriate conditions afforded the methyl complexes [Ti(η⁵-C₅Me₄SiMe₂R)XMe₂] (R=H, X=Cl 5, Me 6; R=X=Me 7). Reactions of 2 and 3 with two equivalents of LiNH^tBu afforded the ansa-silyl-η-amido compounds [Ti{η⁵-C₅Me₄SiMeX(η¹-N^tBu)}Cl₂] (X=H 8, Cl 9). Methylation of 8 gave [Ti{η⁵-C₅Me₄SiMeH(η¹-N^tBu)}Me₂] 10. Complex 9 was also obtained by reaction of 8 with BCl₃, whereas the same reaction using alternative chlorinating agents (TiCl₄, HCl) resulted in deamidation to give 2, which was also converted into 3 by reaction with BCl₃. All of the new compounds were characterized by NMR spectroscopy and the molecular structures of 2 and 4 were determined by X-ray diffraction methods.     

Synthesis and characterization of half-sandwich Rh, Ir complexes containing mono-thiolate-ortho-carborane ligand

Two binuclear complexes [Cp^∗M(Cl)Carb^S]₂ (Cp^∗ = η⁵-C₅Me₅, M = Rh (1a), Carb^S = SC₂(H)B₁₀H₁₀, Ir (1b)) were synthesized by the reaction of LiCarb^S with the dimeric metal complexes [Cp^∗MCl(μ-Cl)]₂ (M = Rh, Ir). Four mononuclear complexes Cp^∗M(Cl)(L)Carb^S (L = BuⁿPPh₂, M = Rh (2a), Ir (2b); L = PPh₃, M = Rh (4a), Ir (4b)) were synthesized by reactions of 1a or 1b with L (L = BuⁿPPh₂ (2); PPh₃ (4)) in moderate yields, respectively. Complexes 3a, 3b, 5a, 5b were obtained by treatment of 2a, 2b, 4a, 4b with AgPF₆ in high yields, respectively. All of these compounds were fully characterized by IR, NMR, and elemental analysis, and the crystal structures of 1a, 1b, 2a, 2b, 4a, 4b were also confirmed by X-ray crystallography. Their structures showed 3a, 3b and 5a, 5b could be expected as good candidates for heterolytic dihydrogen activation. Preliminary experiments on the dihydrogen activation driven by these half-sandwich Rh, Ir complexes were done under mild conditions.     

Photoreactions of 1,2,4,5-benzenetetracarbonitrile with arylethenes—photo- olefin dimerization-aromatic substitution reactions

Irradiation of 1,2,4,5-tetracyanobenzene (TCNB) with styrene derivatives 1-4, respectively, leads to a photochemical olefin dimerization-aromatic substitution reaction to give the corresponding (2,4,5-tricyanophenyl)tetralin derivative (8, 12, 16, 17, and 20) as the main product. Further irradiation of the primary product with alkene results in substitution of the meta-CN group by another phenyltetralinyl to give the corresponding 4:1 (alkene-TCNB) product. According to the effect of the codonor (biphenyl) and salt (magnesium perchlorate) on reaction rate, the result of photoinduced reactions of TCNB with tetralin (6) and 1-phenyltetralin (7) and analysis of the known kinetic data for relevant processes in the cyanoarene-alkene reactions, the mechanism for the formation of the olefin dimerization-aromatic substitution products (such as 8) is proposed to involve radical pair combination of the alkene cyclodimer radical (the corresponding 4-phenyl-1-tetralinyl radical) with TCNB⁻ followed by expulsion of a CN⁻. Photoreactions of TCNB with the alkene photocyclodimer (1-phenyltetralin) may also make minor contributions. Photoinduced reaction of TCNB with 1-phenylcyclohexene (5) takes a different pathway from 1-4 to afford the 1:1 (5-TCNB) primary product 21 by deprotonation of 5⁺ and radical pair combination with TCNB⁻ followed by elimination of HCN.     

Half-sandwich η-benzene Ru(II) complexes of phenolate-based pyridylalkylamine/alkylamine ligands: Synthesis, structure, and stabilization of one-electron oxidized species

Four half-sandwich ruthenium(II) complexes [(η⁶-C₆H₆)Ru(L¹-O)][PF₆] (1), [(η⁶-C₆H₆)Ru(L²-O)][PF₆] (2), [(η⁶-C₆H₆)Ru(L³-O)][PF₆] (3), [(η⁶-C₆H₆)Ru(L⁴-O)][PF₆] (4a), and [(η⁶-C₆H₆)Ru(L⁴-O)][BPh₄] (4b) [L¹-OH, 4-nitro-6-{[(2′-(pyridin-2-yl)ethyl)methylamino]methyl}-phenol; L²-OH, 2,4-di-tert-butyl-6-{[(2′-(pyridin-2-yl)ethyl)methylamino]methyl}-phenol; L³-OH, 2,4-di-tert-butyl-6-{[2′-((pyridin-2-yl)benzylamino)methyl}-phenol; L⁴-OH, 2,4-di-tert-butyl-6-{[(2′-imethylaminoethyl)methylamino]methyl}-phenol (L⁴-OH)], supported by a systematically varied series of tridentate phenolate-based pyridylalkylamine and alkylamine ligands are reported. The molecular structures of 1-3, 4a, and 4b have been elucidated in solution using ¹H NMR spectroscopy and of 1, 3, and 4b in the solid state by X-ray crystallography. Notably, due to coordination by the ligands the Ru center assumes a chiral center and in turn the central amine nitrogen also becomes chiral. The ¹H NMR spectra exhibit only one set of signals, suggesting that the reaction is completely diastereoselective [1: S_Ru,S_N/R_Ru,R_N; 2: R_Ru,R_N/S_Ru,S_N; 3: S_Ru,R_N/R_Ru,S_N; 4b: S_Ru,R_N/R_Ru,S_N]. The crystal packing in 1 and 3 is stabilized by C-H^…O interactions, in 4b no meaningful secondary interactions are observed. From the standpoint of generating phenoxyl radical, as investigated by cyclic voltammetry (CV), complex 1 is redox-inactive in MeCN solution. However, 2, 3, and 4a generate a one-electron oxidized phenoxyl radical coordinated species [2]²⁺, [3]²⁺, and [4a]²⁺, respectively. The radical species are characterized by CV, UV-Vis, and EPR spectroscopy. The stability of the radical species has been determined by measuring the decay constant (UV-Vis spectroscopy).     

Reactions of P4S10 and pyPS2Cl with N,N′-diphenylurea and N,N′-diphenylthiourea

The reaction of P₄S₁₀ (1) with N,N′-diphenylurea (PhNH)₂CO (2) results in new heterocyclic compounds: the pyridinium salt of 1,3-diphenyl-2-sulfido-2-thioxo-1,3-diaza-2λ⁵-phosphetidine (3) (with a P–N–C–N cycle) and the pyridinium salt of 1,4-diphenyl-2,5-disulfido-2,5-dithioxo-1,4-dithiadiaza-2λ⁵,5λ⁵-diphosphinane (4), containing the (P–S–N)₂ cycle and the cyclic thiophosphates [pyH]₂[P₂S₈] (5), [pyH]₂[P₂S₇] (6) and [pyH]₃[P₃S₉] (7). A similar reaction, but carried out with N,N′-diphenylthiourea (PhNH)₂CS (8), leads to the formation of 4 and 6. pyPS₂Cl (9), used as an alternative starting material, also yields compounds 3, 4, 5, and further [pyH][PS₂Cl₂] (10) and S₈ after reaction with 2. Compound 3 reacts with Pd(CH₃COO)₂, with the formation of the complex [Pd(Ph₂N₂COPS₂)₂] (11). The crystal structures of 3 and 7 were determined by single-crystal X-ray diffraction.     

Syntheses and structures of iron carbonyl complexes derived from N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine and N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine

The reaction of N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine (1) with Fe₂(CO)₉ in refluxing acetonitrile yielded di-(μ₃-thia)nonacarbonyltriiron (2), μ-[N-(5-methyl-2-thienylmethyl)-η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido]hexacarbonyldiiron (3), and N-(5-methyl-2-thienylmethylidene)amine (4). If the reaction was carried out at 45 °C, di-μ-[N-(5-methyl-2-thienylmethylidene)-η¹(N);η¹(S)-2-thiolethylamino]-μ-carbonyl-tetracarbonyldiiron (5) and trace amount of 4 were obtained. Stirring 5 in refluxing acetonitrile led to the thermal decomposition of 5, and ligand 1 was recovered quantitatively. However, in the presence of excess amount of Fe₂(CO)₉ in refluxing acetonitrile, complex 5 was converted into 2-4. On the other hand, the reaction of N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine (6) with Fe₂(CO)₉ in refluxing acetonitrile produced 2, μ-[N-(6-methyl-2-pyridylmethyl)-η¹ (N_py);η¹:η¹(N); η¹:η¹(S)-2-thiolatoethylamido]pentacarbonyldiiron (7), and μ-[N-(6-methyl-2-pyridylmethylidene)-η²(C,N);η¹:η¹(S)-2- thiolethylamino]hexacarbonyldiiron (8). Reactions of both complex 7 and 8 with NOBF₄ gave μ-[(6-methyl-2-pyridylmethyl)-η¹(N_py);η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido](acetonitrile)tricarbonylnitrosyldiiron (9). These reaction products were well characterized spectrally. The molecular structures of complexes 3, 7-9 have been determined by means of X-ray diffraction. Intramolecular 1,5-hydrogen shift from the thiol to the methine carbon was observed in complexes 3, 7, and 9.     

Microwave-assisted synthesis and characterization of a new soluble metal-free and metallophthalocyanines peripherally fused to four 18-membered tetrathiadiaza macrocycles

Preparation of some novel symmetrically tetrasubstituted metal-free phthalocyanine (6) and metallophthalocyanines (7-10) containing four 18-membered tetrathiadiaza macrocycles moieties on peripheral positions has been achieved by cyclotetramerization reaction of phthalonitrile derivative (5) in a multi-step reaction sequence. Metal-free phthalocyanine (6) was synthesized by microwave irradiation of 13,24-bis[(4-methylphenyl)sulfonyl]-6,7,14,15,23,24-hexahydro-13H,22H-tribenzo[b,h,n][1,4,10,13,7,16]tetrathiadiazacyclo-octadecine-18,19-dicarbonitrile (5) in 2-(dimethylamino)ethanol. The metallophthalocyanines (7-10) were prepared by the reaction of the phthalonitrile compound (5) with NiCl₂, Zn(CH₃COO)₂, CoCl₂, CuCl₂ salts, respectively, by microwave irradiation in 2-(dimethylamino)ethanol for at 175 °C, 350 W. The new compounds were characterized by IR, ¹H NMR, ¹³C NMR, UV-Vis, elemental analysis and MS spectra data.     

Ring transformation of cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium ion to the corresponding pyrrole derivatives via troponeimine intermediates: photo-induced autorecycling oxidizing reactions of some amines

Ring transformation of 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]furan- 8(7H),10(9H)-dionylium tetrafluoroborate 4⁺·BF₄⁻ to 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrrole-8(7H),10(9H)-dionylium tetrafluoroborate 6a-d⁺·BF₄⁻ consists of the reaction of 4⁺·BF₄⁻ with amines and subsequent exchange of the counter-ion using aq. HBF₄. Reactions of 4⁺·BF₄⁻ with aniline and 4-substituted anilines afforded the corresponding pyrrole derivatives 6a-c⁺·BF₄⁻ directly in good yields. On the other hand, reaction of 4⁺·BF₄⁻ with benzylamine gave the troponeimine intermediate 9, which was not converted to 6d⁺·BF₄⁻ and reverted to 4⁺·BF₄⁻ by adding HBF₄; however, it was converted to 6d⁺·BF₄⁻ upon treatment with (COCl)₂ or SOCl₂, followed by exchange of the counter-ion. In a search for the characteristics of 9, inspection and comparison of the X-ray crystal analyses, NMR and UV-vis spectra, and CV measurement of 9 and N,N-disubstituted troponeimine derivatives 12 were carried out to suggest the remarkable structure of 12 having ionic C-O bonding between the imine-carbon atom and the oxygen atom of the barbituric acid moiety in the solid state. Thus, characteristics of 9 were ascribed to the sterically hindered and favorable conformation of N-protonated troponeimine intermediates. Furthermore, novel photo-induced oxidation reactions of a series of 4⁺·BF₄⁻, 5⁺·BF₄⁻, and 6a,e⁺·BF₄⁻ towards some amines under aerobic conditions were carried out to give the corresponding imines in 455-8362% yields [based on compounds 4⁺, 5⁺, and 6a,e⁺], suggesting the oxidation reaction occurs in an autorecycling process. Mechanistic aspects of the amine-oxidation reaction are also postulated.     

Regiochemistry in the reductive opening of phthalan derivatives

The lithiation of phthalan derivatives 4, 9 and 12 with an excess of lithium in the presence of a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB) in THF at −78 °C gives dianionic intermediates 5, 10 and 13, respectively, which by reaction with different electrophiles [H₂O, t-BuCHO, Me₂CO, (EtO)₂CO] at the same temperature, followed by hydrolysis, leads to regioselective functionalised naphthalenes 7, and biphenyls 11 and 14. The reductive opening takes place with high or total regioselectivity and can be explained considering the electron density in the dianion or in the radical anion, which are formed previous to the carbon-oxygen bond excision. The lithiation of the dihydrofurophthalan derivative 18 with the same reaction mixture but at higher temperature (0 °C) leads to intermediates 19 and 20, resulting from a single and a double reductive cleavage, respectively, which after addition of H₂O and benzaldehyde as electrophiles gives a mixture of compounds 21 and 22.     

Syntheses,characterizations and crystal structures of monomeric or macrocyclic compounds of di- or triorganotin (IV) moieties with 4,4′-thiodibenzenethiol

Six organotin compounds with 4,4′-thiodibenzenethiol (LH₂) of the type R_nSnL_4−nSnR_n (n = 3: R = Me 1, Ph 2, PhCH₂3, n = 2: R = Me 4, Ph 5, PhCH₂6) have been synthesized. All compounds were characterized by elemental analysis, IR and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectra. The structures of compounds 1, 2, 4, 5 and 6 were also determined by X-ray diffraction analysis, which revealed that compounds 1 and 2 were monomeric structures, compounds 4, 5 and 6 were centrosymmetric dinuclear macrocyclic structures, and all the tin(IV) atoms are four-coordinated. Furthermore, supramolecular structures were also found in compounds 1, 2, 4, 5 and 6, which exhibit one-dimensional chains, two-dimensional networks or three-dimensional structures through intermolecular C–H?S weak hydrogen bonds (WHBs), non-bonded Sn?S interactions or C–H?π interactions.     

Synthesis and characterization of aluminum complexes of 2-pyrazol-1-yl-ethenolate ligands

The synthesis and the characterization of some new aluminum complexes with bidentate 2-pyrazol-1-yl-ethenolate ligands are described. 2-(3,5-Disubstituted pyrazol-1-yl)-1-phenylethanones, 1-PhC(O)CH₂-3,5-R₂C₃HN₂ (1a, R = Me; 1b, R = Bu^t), were prepared by solventless reaction of 3,5-dimethyl pyrazole or 3,5-di-tert-butyl pyrazole with PhC(O)CH₂Br. Reaction of 1a or 1b with (R¹ = Me, Et) yielded N,O-chelate alkylaluminum complexes (2a, R = R¹ = Me; 2b, R = Bu^t, R¹ = Me; 2c, R = Me, R¹ = Et). Compound 1a was readily lithiated with LiBuⁿ in thf or toluene to give lithiated species 3. Treatment of 3 with 0.5 equiv of MeAlCl₂ or AlCl₃ yielded five-coordinated aluminum complexes [XAl(OC(Ph)CH{(3,5-Me₂C₃HN₂)-1})₂] (4, X = Me; 5, X = Cl). Reaction of 5 with an equiv of LiHBEt₃ generated [Al(OC(Ph)CH{(3,5-Me₂C₃HN₂)-1})₃] (6). Complex 6 was also obtained by reaction of 3 with 1/3 equiv of AlCl₃. Treatment of 5 with 2 equiv of AlMe₃ yielded complex 2a, whereas with an equiv of AlMe₃ afforded a mixture of 2a and [Me(Cl)AlOC(Ph)CH{(3,5-Me₂C₃HN₂)-1}] (7). Compounds 1a, 1b, 2a-2c and 4-6 were characterized by elemental analyses, NMR and IR (for 1a and 1b) spectroscopy. The structures of complexes 2a and 5 were determined by single crystal X-ray diffraction techniques. Both 2a and 5 are monomeric in the solid state. The coordination geometries of the aluminum atoms are a distorted tetrahedron for 2a or a distorted trigonal bipyramid for 5.     

Endo and exo cyclometallated iron carbonyl complexes derived from N-(N′-methyl-2-pyrrolylmethylidene)-2-thienylmethylamine

The reaction of N-(N′-methyl-2-pyrrolylmethylidene)-2-thienylmethylamine (1) with Fe₂(CO)₉ in refluxing toluene gives endo cyclometallated iron carbonyl complexes 2 and 5, exo cyclometallated iron carbonyl complex 3, and unexpected iron carbonyl complex 4. Complexes 2, 3, and 5 are geometric isomers. Complex 5 differs from complex 2 in the switch of the original substituent from α to β position of the pyrrolyl ring, and the pyrrolyl ring bridges to the diiron centers in μ-(3,2-η¹:η²) coordination mode in stead of μ-(2,3-η¹:η²). In complex 4, the pyrrolyl moiety of the original ligand 1 has been displaced by a thienyl group, which comes from the same ligand. Single crystals of 2, 3, and 5 were subjected to the X-ray diffraction analysis. The major product 2 undergoes: (i) thermolysis to recover the original ligand 1; (ii) reduction to form a hydrogenation product, 6, of the original ligand; (iii) substitution to form a monophosphine-substituted complex 7; (iv) chemical as well as electrochemical oxidation to produce a carbonylation product, γ-butyrolactam 8.     

Syntheses, crystal structures and coordination modes of tri- and di-organotin derivatives with 2-mercapto-4-methylpyrimidine

The organotin (IV) derivatives of 2-mercapto-4-methylpyrimidine (Hmpymt) R₃SnL (R = Ph 1, PhCH₂2, n-Bu 3), R₂SnCl_mL_n (m = 1, n = 1, R = CH₃4, Ph 5, n-Bu 6, PhCH₂7; m = 0, n = 2, R = CH₃8, n-Bu 9, Ph 10, PhCH₂11) were obtained by the reaction of the organotin(IV) chlorides R₃SnCl or R₂SnCl₂ with 2-mercapto-4-methylpyrimidine hydrochloride (HCl · Hmpymt) in 1:1 or 1:2 molar ratio. All complexes 1-11 were characterized by elemental analyses, IR, ¹H, ¹³C and temperature-dependent ¹¹⁹Sn NMR spectra. Except for complexes 3 and 6, the structures of complexes 1, 2, 4, 5, 7, 8-11 were confirmed by X-ray crystallography. Including tin-nitrogen intramolecular interaction, the tin atoms of complexes 1-7 are all five-coordinated and their geometries are distorted trigonal bipyramidal. While the tin atoms of complexes 8-11 are six-coordinated and their geometries are distorted octahedral. Besides, the ligand adopts the different coordination modes to bond to tin atom between the complexes 1, 6, 7 and 2, 3, 4, 5, 8-11. Furthermore, intermolecular Sn?N or Sn?S interactions were recognized in crystal structures of complexes 4, 7 and 11, respectively.     

From bis(silylamino)tin dichlorides via di(1-alkynyl)-bis(silylamino)tin to new heterocycles by 1,1-organoboration

Bis(silylamino)tin dichlorides 1 [X₂SnCl₂ with X=N(Me₃Si)₂ (a), N(9-BBN)SiMe₃ (b), N(^tBu)SiMe₃ (c), and N(SiMe₂CH₂)₂ (d)] were prepared from the reaction of two equivalents of the respective lithium amides (Li-a-d) with tin tetrachloride, SnCl₄, or from the 1:1 reaction of the respective bis(amino)stannylene with SnCl₄. The compounds 1 react with two equivalents of lithium alkynides LiCCR¹ to give the di(1-alkynyl)-bis(silylamino)tin compounds X₂Sn(CCR¹)₂, 2 (R¹=Me), 3 (R¹=^tBu), and 4 (R¹=SiMe₃). Problems were encountered, mainly with LiCC^tBu as well as with 1b, since side reactions also led to the formation of 1-alkynyl-bis(silylamino)tin chlorides 5-7 and tri(1-alkynyl)(silylamino)tin compounds 8 and 9. 1,1-Ethylboration of compounds 2-4 led to stannoles 10, 11, and in the case of propynides, also to 1,4-stannabora-2,5-cyclohexadiene derivatives 12. The molecular structure of the stannole 11b (R¹=SiMe₃) was determined by X-ray analysis. The reaction of 2a and d with triallylborane afforded novel heterocycles, the 1,3-stannabora-2-ethylidene-4-cyclopentenes 14. These reactions proceed via intermolecular 1,1-allylboration, followed by an intramolecular 1,2-allylboration to give 14, and a second intramolecular 1,2-allylboration leads to the bicyclic compounds 15.     

Synthesis, coordination studies and redox properties of a novel ditertiary phosphine bearing two ferrocenyl groups

The new ferrocenyl substituted ditertiary phosphine {FcCH₂N(CH₂PPh₂)CH₂}₂ [Fc = (η⁵-C₅H₄)Fe(η⁵-C₅H₅)] (1) was prepared, in 72% yield, by Mannich based condensation of the known bis secondary amine {FcCH₂N(H)CH₂}₂ with 2 equiv. of Ph₂PCH₂OH in CH₃OH. Phosphine 1 readily coordinates to various transition-metal centres including Mo⁰, Ru^II, Rh^I, Pd^II, Pt^II and Au^I to afford the heterometallic complexes {RuCl₂(p-cym)}₂(1) (2), (AuCl)₂(1) (3), cis-PtCl₂(1) (4), cis-PdCl₂(1) (5), cis-Mo(CO)₄(1) (6), trans,trans-{Pd(CH₃)Cl(1)}₂ (7) and trans,trans-{Rh(CO)Cl(1)}₂ (8). In complexes 2, 3, 7 and 8 ligand 1 displays a P,P′-bridging mode whilst for 4-6 a P,P′-chelating mode is observed. All new compounds have been fully characterised by spectroscopic and analytical methods. Furthermore the structures of 1, 2 · 2CH₂Cl₂, 3 · CH₂Cl₂, 4 · CH₂Cl₂, 6 · 0.5CHCl₃ and 8 have been elucidated by single crystal X-ray crystallography. Electrochemical measurements have been undertaken, and their redox chemistry discussed, on both noncomplexed ligand 1 and representative compounds containing this new ditertiary phosphine.     

Syntheses, characterization and crystal structures of di- and triorganotin (IV) derivatives with 6-amino-1,3,5-triazine-2,4-dithiol

A series of organotin (IV) complexes with 6-amino-1,3,5-triazine-2,4-dithiol of the type [(R_nSnCl_4−n)₂ (C₃H₂N₄S₂)] (n = 3: R = Me 1, n-Bu 2, PhCH₂3, Ph 4; n = 2: R = Me 5, n-Bu 6, PhCH₂7, Ph 8) have been synthesized. All the complexes 1-8 have been characterized by elemental analysis, IR, ¹H and ¹³C NMR spectra. Among them complexes 1, 4, 5 and 8 have also been characterized by X-ray crystallography diffraction analyses, which revealed that the tin atoms of complexes 1, 4, 5 and 8 are all five-coordinated with distorted trigonal bipyramid geometries.