Effect of bulky ligands on one-dimensional platinum compounds

Summary Diaminedithiocyanatoplatinum(II) complexes react with iodine in ethanolic suspension to yield diamagnetic compounds of empirical formula Pt(diamine)(SCN)₂I, which exhibit properties characteristic of one-dimensional materials. Incorporation of bulky substituents in the diamine ligand does not prevent the extended z-axis interaction responsible for these properties, in contrast to the effect of large ligands upon cooperative phenomena in Magnus' Green Salt analogues.Reprintsof this article are not available.The phase cooperative phenomena refers to magnetic and electronic properties that arise form the interaction between neihbouring metal in the solid state.     

Chemistry of platinum hydrides : XXV. Preparation and characterization of platinum(II) hydridotin complexes containing bulky phosphines

Platinum(II) hydridotin complexes containing bulky phosphine ligands, trans-Pt(H)L₂(SnR₃) have been prepared from: (i) the equimolar reaction between corresponding platinum(II) dihydride complexes and HSnR₃ (Cy = cyclohexyl), P-i-Pr₃, P-t-BuPh₂, P-t-Bu₂Me; R = Ph), (ii) the oxidative addition of the corresponding zerovalent complexes, Pt⁰L₂, with HSnR₃ (L = P-i-Pr₃, P-t-BuPh₂; R = Ph), (iii) the reaction of the corresponding platinum(II) dihydride complexes with ClSnR₃ in the presence of pyridine in benzene (L = P-i-Pr₃, P-t-BuPh₂; R = CH₃, n-Bu), (iv) the sodium borohydride reduction of the corresponding hydridochloride complexes Pt(H)Cl(PR₃)₂ with ClSnR₃ in THF (L = PCy₃; R = Ph), these compounds have been characterized by their elemental analysis, infrared, ¹H and ³¹P NMR spectral data.     

Metathesis reactions of allylsilanes containing bulky aromatic substituents

Bulky substituents, such as -naphthyl and ferrocenyl groups, do not inhibit the metathesis of allylsilanes on a Re₂O₇/Al₂O₃-SnBu₄, catalyst system. Metathesis represents a preparative synthetic method for the synthesis of 1,4-bis(-napthyl-dimethylsilyl)- and 1,4-bis(ferrocenyldimethylsilyl)but-2-enes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1207–1209, May, 1991.     

Asymmetric anionic polymerization of maleimides bearing bulky substituents

Asymmetric anionic homopolymerizations of N‐substituted maleimide (RMI) bearing bulky substituents [R = benzyl, diphenylmethyl (DPhMI), 9‐fluorenyl (9‐FlMI), triphenylmethyl, (diphenylmethyloxycarbonyl)methyl, (9‐fluorenyloxycarbonyl)methyl] were carried out with complexes of organometal compounds (alkyllithium, diethylzinc) with six chiral ligands to obtain optically active polymers. The chiroptical properties of the polymers were affected strongly by the substituents on nitrogen in the maleimide ring, the organometal and chiral ligands. Poly(DPhMI) initiated by an n‐butyllithium/(−)‐sparteine (Sp) complex showed a positive specific rotation ([α] +60.3°). Poly(9‐FlMI) prepared with a florenyllithium/Sp complex exhibited the highest specific rotation (+65.7°). The specific rotations of the poly(RMI) obtained were attributed to different contents between the stereogenic centers (S,S) and (R,R) based on threo‐diisotactic structures of the main chain. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 310–320, 2000     

Synthesis and phosphorescent properties of two novel iridium (Ⅲ) complexes bearing bulky tert-butyl substituents

The synthesis and phosphorescence properties of two novel Ir(Ⅲ)complexes bearing tert-butyl substituents,bis(4-tert-butyl-2- phenylbenzothiozolato-N,C~(2′))iridium(Ⅲ)(acetylacetonate)[(tbt)_2Ir(acac)]and bis(4-tert-butyl-1-phenyl-1H-benzimidazolato- N,C~(2′))iridium(Ⅲ)(acetylacetonate)[(tpbi)_2Ir(acac)],are reported,their molecular structures are confirmed by~1H NMR,ESI-MS and elementary analysis.Photoluminescence(PL)studies revealed that they can emit strong green and orange phosphorescence in high quantum yields.Compared to their prototypes lacking of tert-butyl substituents,the two novel iridium(Ⅲ)complexes both have shorter lifetimes and improved or nearly similar PL quantum efficiencies,implying that the exciton quenching is inhibited effectively when molecular steric hindrance increases.The two chelates have great potential to be used as electrophosphorescent materials.     

The anti-neoplastic activity of ethylamine-carboxyborane and triphenylphosphine-carboxyborane in L-1210 lymphoid leukemia cells

Studies on the mode of action of two boroncontaining anti-neoplastic agents, ethylamine-carboxyborane and triphenylphosphine-carboxyborane, are reported. The major site of inhibition was in the pyrimidine de nove synthetic pathway at orotidine monophosphate decarboxylase activity. Additional sites which may facilitate the inhibition of cell growth were IMP dehydrogenase, thymidine kinase, TMP kinase and TDP kinase, m-RNA, r-RNA and t-RNA polymerase activities as well as topoisomerase II activity. The reduction in enzyme activities led to sufficient reduction of d(NTP) levels to suppress DNA synthesis and cell growth. DNA strand scission was evident in the presence of drug. Multiple modes of action are common with amine-carboxyboranes. Acute toxicity studies in mice showed that both agents were safe in their therapeutic range based on organ weights, histological tissue sections, clinical chemistry values and hematopoietic parameters.     

Versatile method for introduction of bulky substituents to alkoxychlorosilanes

The reactions of various alkoxytrichlorosilanes prepared in situ from tetrachlorosilane and alcohols, with Grignard reagents bearing a bulky substituent such as the isopropyl, sec-butyl, and cyclohexyl group afforded triisopropyl-, tri(sec-butyl)-, and tricyclohexylalkoxysilane in high yields. The reactions of n-butoxytrichlorosilane with these Grignard reagents produced triisopropyl-, tri(sec-butyl)-, and tricyclohexyl(n-butoxy)silane in 94%, 96%, and 92% yields, respectively. Methoxymethyldichlorosilane reacted with the same Grignard reagents to give diisopropyl-, di(sec-butyl)-, and dicyclohexylmethoxymethylsilane in 84%, 83%, and 83% yields. Treatment of methoxydimethylchlorosilane with the Grignard reagents readily afforded isopropyl-, sec-butyl-, and cyclohexylmethoxydimethylsilane in excellent yields. Similar treatment of methoxydimethylchlorosilane with tert-butylmagnesium chloride gave tert-butylmethoxydimethylsilane in 62% yield.     

Synthesis and characterization of soluble seco-porphyrazines with bulky substituents

By cyclotetramerization of 3,4-bis(4-tert-butylphenyl)pyrroline-2,5-diimine in the presence of magnesium butanolate, magnesium porphyrazinate with eight (4-tert-butylphenyl) units on the periphery has been synthesized. Its demetalation by the treatment with trifluoroacetic acid resulted in a partially oxidized product, namely, octakis(4-tert-butylphenyl)-2-seco-porphyrazine-2,3-dione. Further reaction of this product with copper(II) acetate, zinc(II) acetate, and cobalt(II) acetate led to the metallo derivatives, [octakis(4-tert-butylphenyl)-2-seco-2, 3-dioxoporphyrazinato]M(II) (M = Cu, Zn, Co). These soluble complexes have been characterized by elemental analysis, FT-IR, ¹H NMR, UV-Vis, and mass spectral data.     

Synthesis and EPR studies of porphyrazines with bulky substituents

Magnesium porphyrazinate substituted with eight 4-tert-butylphenylthio-groups on the peripheral positions has been synthesized by cyclotetramerization of 1,2-bis(4-tert-butylphenylthio)maleonitrile in the presence of magnesium butanolate. The metal-free derivative was obtained by its treatment with trifluoroacetic acid and further reaction of this product with copper(II) acetate, zinc(II) acetate and cobalt(II) acetate led to the metal porphyrazinates (M = Cu, Zn, Co). These new compounds have been characterized by elemental analysis, together with FT-IR, ¹H NMR, UV–Vis spectral data. By using EPR technique, room temperature paramagnetic properties of Cu(II) doped porphyrazine sample as powder and solution forms were measured. The first-derivative EPR signals taken from as powder and solution forms shows that the sample is axially symmetric. The trend g_∥ > g_⊥ > 2 indicates that the unpaired electron is located mainly in the _dx2-y2${\mathrm{d}}_{x^2-y^2}$ orbital (²B₁ as ground state).     

The effect of substituents of immobilized Rh complexes on the asymmetric hydrogenation of acetophenone derivatives

Using a modified Augustine’s method variously substituted Rh complexes were anchored on Al₂O₃ support. The prepared catalysts were characterized by spectroscopic methods and were applied in the hydrogenation of several acetophenone derivatives (p-CF₃-acetophenone, acetophenone, p-NH₂-acetophenone). Enantioselective C=O hydrogenations were observed with reasonable activity and selectivity on all heterogenized complexes, e.e. up to 80%. At the same time the immobilized samples showed the advantages of the heterogeneous systems: easy handling and recyclability.      

1,1′-Binaphthyl ligands with bulky 3,3′-tertiaryalkyl substituents for the asymmetric alkyne addition to aromatic aldehydes

The BINOL ligand (R)-2 that contains bulky 3,3′-tertiaryalkyl groups shows improved catalytic properties over the previously reported 3,3′-substituted BINOL ligands in the asymmetric alkyne addition to aromatic aldehydes. It catalyzes the phenylacetylene addition to aromatic aldehydes with high enantioselectivity (86-94% ee) and good yields without using Ti(OⁱPr)₄ and a Lewis base additive. The catalytic properties of several analogs of (R)-2 in the asymmetric alkyne addition to aldehydes have also been studied.     

Tuning photophysics and nonlinear absorption of bipyridyl platinum(II) bisstilbenylacetylide complexes by auxiliary substituents

The photophysics of six bipyridyl platinum(II) bisstilbenylacetylide complexes with different auxiliary substituents are reported. These photophysical properties have been investigated in detail by UV-vis, photoluminescence (both at room temperature and at 77 K) and transient absorption (nanosecond and femtosecond) spectroscopies, as well as by linear response time-dependent density functional theory (TD-DFT) calculations. The photophysics of the complexes are found to be dominated by the singlet and triplet π,π* transitions localized at the stilbenylacetylide ligands with strong admixture of the metal-to-ligand (MLCT) and ligand-to-ligand (LLCT) charge-transfer characters. The interplay between the π,π* and MLCT/LLCT states depends on the electron-withdrawing or -donating properties of the substituents on the stilbenylacetylide ligands. All complexes exhibit remarkable reverse saturable absorption (RSA) at 532 nm for nanosecond laser pulses, with the complex that contains the NPh(2) substituent giving the strongest RSA and the complex with NO(2) substituent showing the weakest RSA.     

Inhibiting deactivation of iridium catalysts with bulky substituents on coordination atoms

Introducing bulky groups on the coordination phosphorus atoms can effectively block the formation of inactive dimer species and improve the activity of the iridium catalysts. Results of ESI-MS analysis gave strong evidence. This strategy was successfully applied to the asymmetric hydrogenation of quinolines with up to 93% ee on S/C ratio of 25,000.     

N(4)-tolyl-2-benzoylpyridine-derived thiosemicarbazones and their palladium(II) and platinum(II) complexes: Cytotoxicity against human solid tumor cells

Complexes [Pt(2Bz4oT)Cl], [Pt(2Bz4mT)Cl], and [Pt(2Bz4pT)Cl] were prepared with N(4)-ortho-(H2Bz4oT), N(4)-meta-(H2Bz4mT), and N(4)-para-(H2Bz4pT) tolyl-2-benzoylpyridine-derived thiosemicarbazones. The thiosemicarbazones exhibited moderate anti-proliferative activity against HepG2 (hepatoma) and UACC-62 (melanoma) cancer cell lines, but showed high anti-proliferative effect against A431 (epithelial carcinoma) cancer cell lines. Upon coordination to platinum(II) the anti-proliferative activity decreases in all cases. The cytotoxicity of the previously prepared palladium(II) analogues [Pd(2Bz4oT)Cl], [Pd(2Bz4mT)Cl], and [Pd(2Bz4pT)Cl] was also investigated. As in the case of the platinum(II) complexes, coordination to palladium(II) did not lead to activity improvement. Investigations on the mechanism of cytotoxic action against A431 cells revealed that [Pd(2Bz4oT)Cl] induced DNA fragmentation and apoptosis while H2Bz4oT did not present this effect. The high anti-proliferative effect of the thiosemicarbazones and [Pd(2Bz4oT)Cl] against A431 cells, together with the pro-apoptotic effect of [Pd(2Bz4oT)Cl] suggests that these compounds have potential as chemotherapeutic drug candidates.