F. Di Bianca

6-Thiopurine complexes of organotin(IV) moieties. Synthesis and structural characterization by infrared and Mössbauer spectroscopy

Abstract The novel complexes Me3Sn(6-TP−1) and Bun2Sn(6-TP−1)2, where 6-TP−1 is the mono-anion of 6-thiopurine, have been synthesized. The sites of stannylation of 6-TP have been inferred from the known directions of electrophilic substitution reactions of 6-TP itself. The compounds have been characterized by infrared and Mossbauer spectroscopy. A solid state polymeric structure has been proposed for Me3Sn(6-TP−1), where planar SnC3 skeletons are bridged by 6-TP−1 (thione tautomer) axially bound to Sn through N(3) and N(1) atoms. For Bun2Sn(6-TP−1)2, a molecular structure has been advanced, with the ‘aromatic’ ligand anions chelating Sn by S-N(7) atoms.

119Sn Mössbauer spectroscopic studies of the products of the reaction of triorganotin(IV) derivatives with 6-thiopurine

Abstract A structural study of the products of the reaction of R 3 Sn IV derivatives (R = Me, Bu n , Ph) with 6-thiopurine, 6-TPH 2 , and its sodium salt, 6-TPHNa, has been undertaken using Mossbauer spectroscopy and the point-charge model rationalization of the Mossbauer parameter nuclear quadrupole splitting. The synthetic reactions have been carried out at ca . 0 °C, 20 °C and 50 °C. The Mossbauer spectra of the complexes AlK 3 Sn(6-TPH) are consistent with the occurrence of two distinct tin(IV) sites in samples prepared at the lower temperature, while one only site appears by increasing the temperature of the reaction. Two tin sites constantly occur in the products of the reactions involving the Ph 3 Sn IV moiety; the stoichiometry is assumed to be (Ph 3 Sn) 3 (6-TPH)(6-TP) for the uniquely-formed complex. Solid state polymeric structures with trigonal bipyramidal environments of the tin atoms and planar SnC 3 skeletons have been proposed. The apical ligand atoms have been assumed to be N, S and N, N in the samples showing two individual tin(IV) sites, and N, N when a single site was present.

Organometallic nucleophiles. A mechanistic study of halide displacement at saturated carbon by 2- and 4-pyridyl complexes of palladium(II) and platinum(II)

Abstract The reactions of the 2- and 4-pyridyl complexes [MX(C 5 H 4 N C n )(dppe)] and trans -[MX(C 5 H 4 N C n )(PPh 3 ) 2 ] (M  Pd, Pt; X  Cl, Br; n = 2, 4)- involving halide displacement from the organic halides XCH 2 R (X  Cl, Br; R  CN, Ph, CH  CH 2 ) by the pyridyl nitrogen have been studied kinetically by conductivity in acetone or acetonitrile at 25°C. The kinetic data fit the second-order rate law rate k 2 [XCH 2 R][complex], in agreement with an S N 2 process at saturated carbon. The higher rates are displayed by the 2-pyridylplatinum derivatives with X  Br in both the metal complex and the organic halide. The higher nucleophilic power of the 2-pyridyl complexes compared with their 4-pyridyl analogs is paralleled by a higher basicity, as reflected by a higher p K a value. In any case, the metal-containing substituent enhances considerably the reactivity and basicity of the pyridine nitrogen. The rates are scarcely influenced by the coordination geometry around the metal.

Solvent and temperature effects in the mechanism of allyl amination of the α-diimine complex [Pd(η3-C3H5)-(C5H4N-2-CHNC6H4OMe-4)]+ by piperidine and morpholine

Abstract A study is reported of the solvent and temperature effects on the equilibrium of α-diimine displacement from [Pd( η 3 -C 3 H 5 (NN′)] + (NN′N′C 5 H 4 N-2-CHNC 6 H 4 OMe-4) by piperidine and morpholine and on the rates of allyl amination by these amines in the presence of activated olefins (ol) leading to [Pd( η 2 -ol)(NN′)] in either chloroform or methanol. The larger extent of α-diimine displacement in chloroform is essentially governed by entropy factors. ΔH ° and ΔS ° values for the equilibrium are discussed. The activation parameters for the slow amination reaction indicate that the reactivity differences observed are determined mainly by the entropic factor, as far as the solvent effect is concerned.

Equilibrium studies of α-diimine displacement in cationic allylpalladium(II) complexes by monodentate N-donors and the mechanism of allyl amination by triethylamine and pyridine

In the cationic complexes [Pd(η3-allyl)(L–L)]ClO4[L–L = 1,2-bis(imino)ethanes or 2-(iminomethyl)-pyridines] the chelated α-diimine was rapidly and reversibly displaced by secondary amines (N-methylaniline, morpholine or piperidine), triethylamine and 4-substituted pyridines. The observed equilibrium constants Ke, increased with increasing basicity and decreasing steric requirements of the entering N-donor. They strongly depend on the α-diimine and decrease in the order RNCHCHNR RNC(Me)C(Me)NR ≈ NC5H4(CHNR)-2 (R = C6HaOMe-4). The cationic complex [Pd(η3-C3H5){NC5H4(CHNC6H4OMe-4)-2}]+ underwent a slow allyl amination by triethylamine or pyridine (L′) in the presence of fumaronitrile (fn), yielding [Pd(η2-fn){NC5H4(CHNC6H4OMe-4)-2}] and Et3[graphic omitted]CH2CHCH2 or C5H5[graphic omitted]CH2CHCH2. Kinetic studies showed that the pseudo-first-order rate constants for amination (kobs) are given by kobs=k2[L′], suggesting a direct bimolecular attack of L′ on the η3-allyl ligand. Amination hardly proceeds in the presence of the less-activated olefin dimethyl fumarate (dmf). The π-accepting properties of the olefinic ligands play an important role also in the reaction of Et3[graphic omitted]CH2CHCH2 or C5H5[graphic omitted]CH2CHCH2 with [Pd(η2-olefin){NC5H4(CHNC5H4OMe-4)-2}](olefin = fn or dmf), i.e. the reverse of the amination reaction.

Antimony-121 mössbauer and infrared spectral study on halophenylantimonate(III) Compounds

Abstract The synthesis and the 121 Sb Mossbauer and infrared spectra of halophenylantimonates(III) M[PhSbX 3 ] (M  Me 4 N, Ph 4 As;X  Cl, Br, I) are reported, and the spectral data are discussed and compared with those of SbX 4 and other related systems. The results are in accord with the participation of the antimony 5s electrons in the SbPh bond. In the interpretation of the electric field gradient, the contributions to V zz from both the lone pair and the SbPh bond electron densities are assumed to be dominant.

Organometallic nucleophiles. Mechanism of halide displacement at saturated carbon by 2-pyridyl and 4-Pyridyl complexes [M(dmtc)(C5H4N-Cn)(L)] (M Pd, Pt; dmtc dimethyldithiocarbamate; n 2,4; L

Abstract A mechanistic study is reported of nucleophilic halide substitution by pyridyl complexes [M(dmtc)C 5 H 4 N- C 2 )(L)] (M  Pd or Pt; L  PMe 3 , PEt 3 or PPh 3 ) and [Pd(dmtc)C 5 H 4 N- C 4 )(L)] (L  PMe 3 or PPh 3 ) on organic halides XCH 2 R (X  Cl or Br; R  CHCH 2 , COMe, Ph, or CN) in various solvents, yielding the pyridylium derivatives [M(dmtc)1-CH 2 R)C 5 H 4 N- C 2 (L)] + and [Pd(dmtc)(1-CH 2 R)(C 5 H 4 N- C 4 (L)] + , respectively. The kinetics obey a second-order rate law: rate  k 2 [XCH 2 R][Complex]. A similar rate law is observed for the analogous reactions involving 4-dimethyl-aminopyridine (4-dmapy) as the nucleophile. The effects of solvent and leaving group, and the largely negative activation entropies, are in line with S N 2 substitution at saturated carbon. Tle nucleophilic power ( k 2 ) generally increases with increasing basicity (p K a ) of the pyridine nitrogen. Both these parameters depend on the position and nature of the substituent in the pyridine ring, in the order 2-M(dmtc)(L) > 4-NMe 2 > 4-Pd(dmtc)(L). The electron-release of the metal-containing groups appears to be essentially inductive.

A powerful organometallic nucleophile the 2-pyridyl group in (dimethyldithio-carbamate) (2-pyridyl)(triphenyl-phosphine)platinum(II)

Kinetic study of the reactions of DMAP and [Pt(dmctc)(2-C 5 H 5 N)(PPH 3 )] with chloroacetonitrile or 3-bromopropene in actonitrile.

STUDIES ON SOME ANTIMONY(III) COMPLEXES WITH TRIDENTATE SCHIFF BASE LIGANDS

Abstract The antimony(III) complexes FSb(Sab), ClSb(Sab) and ClSb(Sat) containing dianonic, potentially tridentate Schiff-base ligands with ONO(Sab 2− ) and ONS(Sat 2− ) donor atoms have been prepared and characterized. The mass spectra of these derivatives are reported. The occurrence of chelation by the tridentate ligand is inferred from the infrared data. The antimony-121 Mossbauer parameters at 4.2 K are reported. The magnitudes and the positive sign of eQV zz suggest a consistent p-character of the antimony lone-pair orbital. Observed differencies in the isomer shift and eQV zz values are discussed on the basis of the likely distribution of electron density around antimony.

Infrared and Mössbauer studies on adducts R3SnOH · R3MX (M = Sn, Pb; X = Pseudohalide)

Abstract The synthesis of the solid adducts Me3SnOH · Me3 SnNCO, Me3SnOH · Me3SnNCS, Me3SnOH · Me3PbN3, Ph3SnOH · Ph3SnN3 is reported. The compounds have been investigated by infrared and Mossbauer spectroscopy. Their structure probably consists of polymeric OH-R3Sn-X-R3Sn(Pb) chains in which hydroxyl and pseudohalide (X) groups are bridging pentacoordinate tin atoms. In contrast to the triphenyl compound, the trimethyl derivatives show evidence of hydrogen bonding between adjacent chains.