The structure of bis(trialkyltin) carbonates: Evidence for two non-equivalent tin sites

Bis(tributyltin) oxide or trimethyltin hydroxide react with carbon dioxide to afford the bis(trialkyltin) carbonates, (R₃SnO)₂CO; ¹¹⁹Sn NMR (in the case of R = Bu) or ^119mSn Mössbauer spectroscopy show that these compounds contain 4- and 5-coordinate tin atom sites.     

A new procedure for exact ring closure

An algorithm is presented that very efficiently generates all feasible values for the six torsions constrained by the condition of ring closure. Furthermore, the algorithm is straightforward to implement, thus providing an alternative to the more common and less efficient conformational search technique of breaking the ring and rejecting trial conformers with an unacceptable length for the broken bond. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 870–881, 2000     

Two different copper sites in hexakis(1-methyltetrazole)copper(II) bis(tetrafluoroborate)

An electron spin resonance study at temperatures between 300 and 4 K demonstrates that the two crystallographically inequivalent Cu(II) sites in the title compound are subject to different Jahn-Teller behaviour. It is shown that this is not induced by cooperative interactions between the Jahn-Teller sites but arises from the different lattice symmetries of the two sites.     

Crystal structures of two polymeric bis(triphenyltin) malonates

In an attempt to prepare potassium/sodium salts of malonato-triphenylstannate, two bis(triphenyltin) malonates were obtained instead, [(C₆H₅)₃Sn]₃[O₂CCH₂CO₂]_1.5 (1) and {[(C₆H₅)₃SnO₂CCH₂CO₂Sn(C₆H₅)₃]H₂O}CH₃CH₂OH (2). This provides an excellent example of structural diversity in triorganotin carboxylates. In both complexes, the dicarboxylate was connected to the triphenyltin groups forming a linear infinite polymeric chain. Both complexes have a trans-trigonal bipyramidal geometry with the three phenyl groups occupying the equatorial plane and two oxygens at axial positions. Both short and long tin–oxygen distances were observed in 1 and 2. In 1, all carboxylates functioned as bridging bidentate ligands, resulting in an infinite 3-D polymer network propagating along all three axes. In 2, Sn1 is bonded to a carboxylate and a water molecule (Sn1–O1 2.145(3)?Å, Sn1–O3 2.341(3)?Å, O1–Sn1–O3 173.97(12)°). Only one carboxylate acts as a bidentate ligand allowing the carbonyl group to be axially coordinated to the adjacent tin, Sn2. Also, Sn2 is covalently bonded to the other carboxylate group in the malonate ligand (Sn2–O4 2.163(3)?Å, Sn2–O5 2.353(3)?Å, O4–Sn2–O5 173.47(12)°). There is a water molecule included in the crystal lattice hydrogen bonded to the uncoordinated carbonyl in malonate.     

Chelate ring closure kinetics in the reaction of a platinum(II) complex with diphosphines

The reactions of PPh2(CH2)nPPh2 (n=1–4, P-P) and PPh3 with cis- [PtPh2(CO)(SEt2)] have been studied in chloroform-d by 1H- and 31P{1H}-n.m.r. When n=2 or3 the first product observed is [PtPh2(P-P)], where the diphosphine is acting as a chelate, and ring closure is fast compared to the rate of entry of the phosphine into the complex. When n=1 or 4 the first observed product is [PtPh2(CO)(P-P)], with P-P acting as monodentate, and the second observable stage of reaction is ring closure. The rate constants and activation parameters kc at 298K (s–1), H (kJmol–1), S (JK–1mol–1) for the dppm and dppb complexes are 0.0198, 88±1, +17±3; and 0.00273, 38±2, –169±6, respectively. The formation of the large seven-membered ring is a strainless process, comparable to the intermolecular process. The increase in the enthalpy of activation as ring size decreases is due to ring strain and inter-atomic repulsions associated to the conformation of the four-membered chelate ring.     

A force-field study of alkenyl radical ring closure

In accord with stereoelectronic considerations there is a good correlation between the relative rates, regiochemistry, and stereochemistry of ring closure of ω-alkenyl radicals, and the strain energies of transition structures determined by force field calculations.     

Interaction of bis(ethylene)tin(bis(salicylidene)ethylenediamine) with DNA.

The fluorescence spectral characteristics and interaction of bis(ethylene)tin(bis(salicylidene)ethylenediamine) [Et2Sn(salen)] with DNA are described. The polarity of the solvent has a strong effect on the fluorescence characteristics of Et2Sn(salen). Et2Sn(salen) bound to DNA showed a marked decrease in the fluorescence intensity with a bathochromic shift of the excitation and emission peaks. A hypochromism in the UV absorption spectra was also observed. KI quenching and competitive binding to DNA between Et2Sn(salen) and ethidium bromide (EB) were studied in connection with other experimental observations to show that the interactive model between Et2Sn(salen) and DNA is an intercalative one. The pH and salt effect on the fluorescence properties was also investigated. The intrinsic binding constant was estimated to be 1.071 x 10(5) mol L(-1) in base pairs and the binding site number is 1.98, respectively. A linear relationship between F/F0 and the concentration of calf thymus DNA covers 5.1 x 10(-6) - 2.41 x 10(-4) mol L(-1), which can be utilized for determining traces of calf thymus DNA with a detection limit of 1.1 x 10(-7) mol L(-1) in base pairs.     

The reaction of bis(phenyldimethylphosphine)bis(diphenylsilyl)platinum(II) with acetylenes

The synthesis and the reactions of cationic complexes of rhodium(I) and iridium(I) of the type [M(NN′)(COD)]⁺ and [M(NN′)(CO)₂]⁺ (NN′  Schiff bases of pyridine-2-aldehyde; COD  cis,cis-1,5-cyclooctadiene) are reported.     

A novel synthesis of reactive polymers with pendant halomethyl groups by the polyaddition reaction of bis(epoxide)s with bis(chloroacetoxy)esters or bis(bromoacetoxy)esters

New reactive polymers with pendant halomethyl groups were successfully synthesized by polyaddition reactions of bis(epoxide)s with bis(chloroacetoxy)ester such as 1,4-bis [(chloroacetoxy)methyl]benzene (BCAMB) or 1,4-bis[(bromoacetoxy)methyl]benzene (BBAMB) using quaternary onium salts or crown ether complexes as catalysts. The polyaddition reaction of diglycidyl ether of bisphenol A (DGEBA) with BCAMB proceeded very smoothly with high yields (83–96%) by the addition of quaternary onium salts such as tetrabutylphosphonium bromide (TBPB) or crown ether complexes such as 18-crown-6/KBr as catalysts to produce high molecular weight polymers, although the reaction occurred without any catalyst to give low molecular weight polymer in low yield at 90°C for 48 h. It was also found that the reaction proceeded smoothly in aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc) to produce high molecular weight polymers. Polyaddition reactions of DGEBA or digylcidyl ether of ethylene glycol (DGEEG) with BBAMB, other bis(chloroacetoxy)esters or bis(bromoacetoxy)esters using TBPB in DMAc also proceeded smoothly to give the corresponding polymers. The resulting poly(ether-ester)s contain reactive halomethyl groups as side chains, which were introduced during main chain formation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3791–3799, 1997     

A novel synthesis of polyethers with pendant hydroxyl groups by polyaddition of bis(oxetane)s with bis(phenol)s

The polyaddition of 1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene (BEOB) with 3,3′,5,5′-tetrachlorobisphenol A (TCBPA) was examined with or without catalysts. High molecular weight polymer (polymers 1) (M_n = 13,600) with pendant primary hydroxyl groups was obtained in a 99% yield without any gel products when the reaction was performed with 5 mol % of tetraphenylphosphonium bromide as a catalyst in NMP at 160°C for 96 h. However, when the reaction was carried out without a catalyst under the same conditions, a low molecular weight polymer (M_n = 3200) was obtained in a 51% yield. The structure of the resulting polymer was confirmed by IR, ¹H-NMR, and ¹³C-NMR spectra. In this reaction system, it was also found that tetraphenylphosphonium iodide and crown ether complexes such as 18-crown-6 (18-C-6)/KBr and 18-C-6/KI have high catalytic activity. Polyadditions of 1,4-bis[(3-methyl-3-oxetanyl)methoxymethyl]benzene with TCBPA and BEOB with 3,3′,5,5′-tetrabromobisphenol-S were also examined, and corresponding polymers (polymers 2 and 3) were obtained in good yields. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2781–2790, 1999     

Carbenoid type base induced ring expansion of the adducts of cyclic ketones with bis(phenylthio)methyllithium

In another application of the principle that metallo derivatives of bis(phenylthio)acetals behave as carbenoids when present in the same molecule with another anionic group, the adducts of cyclic ketones with bis(phenylthio)methyllithium react with an alkyllithium to yield the ring expanded α-(phenylthio) ketones.     

Comparison of the bis(ferrocenylethynyl)phenylmethylium cation with bis(ferrocenylethenyl)methylium analogues

Several new ferrocenylethynyl derivatives, (FcCC)₂CHOH, (FcCC)₂CH₂, (FcCC)₂CPhOH have been synthesised from ethynylferrocene. Attempts to synthesise the corresponding bis(ferrocenylethynyl)-stabilised carbocations by hydroxyl or hydride abstraction from the bridging group was unsuccessful for (FcCC)₂CHOH and (FcCC)₂CH₂, respectively. In the case of (FcCC)₂CPhOH, the [(FcCC)₂CPh]⁺ cation could be observed by ¹H and ¹³C NMR, and by UV-Vis-NIR spectroscopy, but was too unstable for isolation or prolonged study in solution. The UV-Vis-NIR spectrum of [(FcCC)₂CPh]⁺ is compared to that of the considerably more stable cations, [Fc(CHCH)₂CH]⁺ and [(FcCHCH)₂CPh]⁺.     

Isolation and crystal structures of two singlet bis(triarylamine) dications with nonquinoidal geometries

We report the first structural data for bis(diarylamine) "bipolarons": we have isolated and crystallographically characterized salts of the dications obtained by two-electron oxidation of E-4,4'-bis[di(p-anisyl)amino]stilbene and E,E-2,5-bis{4-[di(p-anisyl)amino]styryl}-3,4-di(n-butoxy)thiophene, [1](2+) and [2](2+) respectively. ESR, NMR, and magnetometry suggest both species have singlet ground states. X-ray structures, together with (1)H NMR coupling constants for [2](2+), indicate geometries in which the bond lengths are shifted toward a quinoidal pattern relative to that in the neutral species, but not to a fully quinoidal extent. In particular, the bond-length alternations across the vinylene bridging groups approach zero. DFT calculations with closed-shell singlet configurations reproduce the observed structures well. Our results indicate that singlet species for which one might expect quinoidal geometries (with differences of ca. 0.1 A between formally single and double bonds) on the basis of a limiting valence-bond representation of the structure can, in fact, show structures with significantly different patterns of bond lengths.