Niobium Complexes Supported by Chalcogen-Bridged [OEO]-Type Bis(phenolate) Ligands (E = S, Se): Synthesis, Characterization, and Phenylacetylene Polymerization.

Trichloro niobium(V) complexes 3 and 4 with the sulfur- or selenium-bridged [OEO]-type bis(phenolate) ligands (E = S, Se) were synthesized and fully characterized on the basis of their NMR spectroscopic data and X-ray crystallographic analysis. In the crystalline state of 4, the [OSeO]-core of the ligand was coordinated to the niobium center in a fac-fashion. The corresponding tribenzyl niobium(V) complexes 5 and 6 were also prepared by the reactions of 3 and 4 with 3 equivalents of PhCH2MgCl in toluene. The X-ray diffraction analysis of 6 revealed that the distorted six-coordinated niobium center incorporated in the [OSeO]-type ligand took a mer-fashion, and one benzyl ligand was coordinated to the niobium center by η2-fashion. Complexes 5 and 6 were tested for the phenylacetylene polymerization that produced poly(phenylacetylene)s (PPAs), oligomers, and triphenylbenzenes (TPBs) depending on the chalcogen atom in the [OEO]-type ligand.

Iminophosphonamido-Supported Plumbylenes and Plumbyliumylidenes: Synthesis and Properties.

A series of low-valent lead(II) species, i.e., plumbylenes and plumbyliumylidenes supported by an N,N'-di-tert-butyliminophosphonamide ligand, have been synthesized. Chloroplumbylene [Ph2P(NtBu)2PbCl] (1) was readily prepared by the reaction of the corresponding lithium iminophosphonamide and PbCl2 in THF. The substitution reaction of 1 with KN(SiMe3)2 in THF afforded the corresponding aminoplumbylene [Ph2P(NtBu)2PbN(SiMe3)2] (2) in the form of colorless crystals. The structures of these plumbylenes in the solid state and in solution were exhaustively characterized using multinuclear NMR spectroscopy and X-ray diffraction analysis. In the crystalline state, 1 adopts a nearly linear polymeric structure in the direction of the c axis via Pb-Cl bonds, with alternating four-membered PbN2P rings. The chloride-abstraction reaction of 1 using Na[B(C6F5)4] in fluorobenzene proceeded efficiently at ambient temperature to furnish plumbyliumylidene [Ph2P(NtBu)2Pb:]+ (3+), which was isolated as the air-sensitive yellow borate salt 3[B(C6F5)4]. Plumbyliumylidene 3[B(C6F5)4] acts as a Lewis acid catalyst for the hydroboration of benzophenone and benzaldehyde at catalyst loadings of as low as 0.1 mol % under ambient conditions. Furthermore, the details of the reaction mechanism are discussed on the basis of the results of DFT calculations.

Halogen-Exchange Reactions of Iminophosphonamido-Chlorosilylenes with Alkali Halides: Convenient Synthesis of Heavier Halosilylenes.

Halogen-substituted silylenes are an important building block for synthesizing silicon-based low-valent and multiple-bond species. However, the number of reports on heavier halosilylenes that contain bromine and iodine is still limited. Here, we present a convenient synthesis for bromo- and iodosilylenes supported by an iminophosphonamide ligand. The heavier halosilylenes [Ph2P(tBuN)2]SiX (2: X = Br, 3: X = I) were successfully synthesized via the halogen-exchange reaction of chlorosilylene 1 with alkali halides in THF. As a demonstration of the reactivity of 2 and 3, oxidative addition reactions of 2 and 3 with elemental selenium in C6D6 afforded the corresponding bromo- (5) or iodosilylene-selone (6) as colorless crystals. The molecular structures of 2, 3, 5, and 6 were fully characterized by spectroscopic means and single-crystal X-ray diffraction analysis. Furthermore, the effects of the halogen atom on the electronic state of halosilylenes 1-3 and halosilylene-selones 4-6 were investigated using density functional theory (DFT) calculations.

An Iminophosphonamido-Chlorosilylene as a Strong σ-Donating NHSi Ligand: Synthesis and Coordination Chemistry.

The N-heterocyclic silylene (NHSi) [Ph2 P(t BuN)2 ]SiCl (1), supported by an iminophosphonamide ligand, was obtained from the dehydrochlorination of [Ph2 P(t BuN)2 ]SiHCl2 (2) with LiN(SiMe3 )2 . NHSi 1 contains an extremely high-energy HOMO level and consequently displays unique coordination behavior toward RhI complexes. When 1 was treated with 1/4 of an equivalent of [RhCl(cod)]2 (cod=1,5-cyclooctadiene), the 14-electron Y-shaped bis(chlorosilylene) RhI complex 5 was obtained as dark purple crystals. The reaction of 1 with 1/6 of an equivalent of [RhCl(cod)]2 yielded the cationic tris(silylene)-RhI complex [6]+ ⋅Cl- as red crystals, wherein a two-coordinated silylene ligand engages in a Si=Rh double bond. A structural analysis of 5 and [6]+ ⋅Cl- revealed that the central rhodium atoms adopt trigonal and square-planar coordination geometries, respectively, with considerably shortened Si-Rh bonds [5: 2.1605(5) Å; [6]+ : 2.133(1) Å].

Highly Isospecific Polymerization of Silyl-Protected ω-Alkenols Using an [OSSO]-Type Bis(phenolato) Dichloro Zirconium(IV) Precatalyst.

The coordination polymerization of silyl-protected ω-alkenols such as ω-alken-α-oxytriisopropylsilanes 1 provides poly(ω-alkenyl-α-oxytriisopropylsilalne)s with a highly isospecific microstructure ([mmmm] > 95%) when a combination of [OSSO]-type bis(phenolato) dichloro zirconium(IV) complex 2 and dried methylaluminoxane is used as the precatalyst and activator, respectively. The resulting siloxy-substituted polymers could be efficiently transformed into the corresponding functionalized polyolefins, which contained up to 90% acetyl groups and ≈7% hydroxy groups in the terminal side chains.

Macromol. Rapid Commun. 12/2016.

Back Cover: Highly isospecific polymerization of silyl-protected ω-alkenols, using a combination of [OSSO]-type bis(phenolato) dichloro zirconium(IV) complex and dMAO as the precatalyst and the activator, respectively, is established. This method represents the first example for a stereoselective polymerization of polar functional α-olefins ([mmmm] > 95%). Subsequently, the obtained terminal siloxy-substituted isotactic polymer could be readily transformed by a macromolecular desilylation/acetylation reaction sequence to afford the corresponding terminal acetyl-enriched polymer. Further details can be found in the article by Y. Saito, N. Nakata,* and A. Ishii* on page 969.

Enantio- and Stereoselective Cyclopolymerization of Hexa-1,5-diene Catalyzed by Zirconium Complexes Possessing Optically Active Bis(phenolato) Ligands.

Enantio- and stereoselective cyclopolymerization of hexa-1,5-diene was achieved by enantiomerically pure dichloro zirconium(IV) pre-catalysts 2 possessing chiral [OSSO]-type bis(phenolate) ligands (-)-1 and (+)-1 in combination with dried methylaluminoxane (dMAO) as an activator. The corresponding activities were recorded with quite high values up to 1,960 g mmol(2)-1 h-1 , which are extremely larger than those of the related complexes. The microstructure analysis for the PMCPs furnished by pre-catalysts (Λ,S,S)-2 and (Δ,R,R)-2 showed good isotacticity factors (α = 75-78%) and relatively high proportions of trans-cyclopentane rings (σ = 14-21%). These enantiomeric PMCPs exhibited large specific optical rotations ([α]D = +28 to +32° from (Λ,S,S)-2, -26 to -34° from (Δ,R,R)-2).

Red and Near-Infrared Photoluminescence of D-π-A-Type Compounds Based on a 1,4-Diaryl-1-thio-1,3-butadiene Conjugated System in a Dibenzobarrelene Skeleton.

1,4-Diaryl-1-thio-1,3-butadiene derivatives having a π-donor dimethylamino group and several π-acceptor substituents at both terminals of the conjugated system were synthesized by intramolecular [4 + 2] cycloaddition of 1-thio-enynes and subsequent chemical transformations. They displayed largely red-shifted absorption and emission spectra in solution, the powder state, and in polymer films. The derivatives with a 2,2-dicyanoethenyl group as the π-acceptor exhibited inverted solvatochromism in both optical absorption and fluorescence spectroscopies.

Synthesis of 4-chalcogeno-1-aza-1,3-butadiene derivatives by intramolecular cyano-Diels-Alder reaction and borane-coordination-induced fluorescence enhancement.

4-Thio-1-aza-1,3-butadiene derivatives 3 incorporating a rigid dibenzobarrelene skeleton were synthesized by the intramolecular cyano-Diels-Alder reaction of 9-anthryl cyanoethenyl sulfides 6. The thermal reaction of 6 afforded an equilibrium mixture of 3 and 6, but the cyclization was effectively promoted by the addition of BF3·Et2O or B(C6F5)3 to yield imine-borane adducts 8 and 9. The imine-borane adducts emit intense blue fluorescence both in solution and in the crystalline state. This is in stark contrast to free imines 3, which are weakly fluorescent. Selenium analogue 4 and N-oxide 12 of 3a were synthesized, along with their B(C6F5)3 adducts.

Syntheses of Iminophosphomamido Chlorogermylenes and Their Complexation with a Rhodium(I) Complex.

Three-coordinated chlorogermylenes of the type [Ph2 P(RN)2 ]GeCl (3: R=t Bu; 4: R=Dip=2,6-i Pr2 C6 H3 ), which bear an N,N-substituted iminophosphonamide ligand, were synthesized. The coordination behavior of 3 and 4 toward rhodium(I) complex was investigated. When 3 was treated with 1/2 of an equivalent of [RhCl(cod)]2 (cod=1,5-cyclooctadiene), the corresponding chlorogermylene-Rh(I) complex 5 was obtained as orange crystals. In contrast, the reaction of 4 with a half equivalent of [RhCl(cod)]2 under a CO atmosphere resulted in the formation of a five-membered germarhodacycle 7. Compounds 3, 4, 5, and 7 were characterized using NMR spectroscopies and single-crystal X-ray diffraction. Complex 5 can be employed as a catalyst for the hydrosilylation and hydroboration reactions of diphenylacetylene, thus demonstrating the utility of germylene ligands comparable to those of NHCs in the major transition metal catalytic processes.

Synthesis of a homoleptic tris(silylene)-palladium(0) complex and a silylyne-bridged tetranuclear palladium cluster.

We report the reactions of an iminophosphonamido-silylene (1) with different palladium complexes. The reaction of 1 with [Pd(PPh3)4] furnished a homoleptic tris(silylene)-palladium(0) complex. In contrast, treatment of 1 with [PdMe2(tmeda)] led to the unprecedented formation of a non-planar µ3-silylyne-bridged tetranuclear palladium cluster that contains palladium atoms in different oxidation states.

Titanium complexes supported by an [OSSO]-type bis(phenolato) ligand based on a trans-cyclooctanediyl platform: synthesis, structures, and 1-hexene polymerization.

trans-Cyclooctanediyl-bridged [OSSO]-type ligand 4 reacts with TiCl(4)(thf)(2) in toluene to produce the corresponding titanium(IV) dichloro complexes as an inseparable mixture of cis-α isomer 6a and cis-ß isomer 6b in a ratio of 2:1, whereas treatment of dilithio salt of 4 with TiCl(3)(thf)(3) in Et(2)O afforded chloride-bridged dimeric titanium(III) complex 8, which indicated the antiferromagnetic character in a nonpolar solvent solution. Di(isopropoxy) titanium(IV) complex 10 having a C(2)-symmetric cis-α configuration was synthesized by the reaction of 4 with Ti(O(i)Pr)(4) in toluene as yellow crystals. Moreover, the reaction of 4 with Ti(NEt(2))(4) in toluene resulted in the unexpected formation of [OSSO]-type bis(phenolato)-bridged dinuclear diamido titanium(IV) complex 11, which adopted a distorted tetrahedral geometry on the titanium center. These titanium complexes were characterized on the basis of their NMR spectroscopic data, and the molecular structures of complexes 8, 10, and 11 were established by single crystal X-ray diffraction. The titanium(IV) and (III) complexes 6 and 8 upon activation with a cocatalyst in toluene polymerized 1-hexene isospecifically to produce poly(1-hexene) having high molecular weight (M(w) = 22,000-52,000 g mol(-1)) and relatively narrow polydispersity (M(w)/M(n) = 1.7-1.8), albeit with low activity [0.27-1.0 g mmol(cat)(-1) h(-1)].

Novel [FeFe]-Hydrogenase Mimics: Unexpected Course of the Reaction of Ferrocenyl α-Thienyl Thioketone with Fe3(CO)12.

The influence of the substitution pattern in ferrocenyl α-thienyl thioketone used as a proligand in complexation reactions with Fe3(CO)12 was investigated. As a result, two new sulfur-iron complexes, considered [FeFe]-hydrogenase mimics, were obtained and characterized by spectroscopic techniques (1H, 13C{1H} NMR, IR, MS), as well as by elemental analysis and X-ray single crystal diffraction methods. The electrochemical properties of both complexes were studied and compared using cyclic voltammetry in the absence and in presence of acetic acid as a proton source. The performed measurements demonstrated that both complexes can catalyze the reduction of protons to molecular hydrogen H2. Moreover, the obtained results showed that the presence of the ferrocene moiety at the backbone of the linker of both complexes improved the stability of the reduced species.

Confluent two-balloon technique: an alternative method for subintimal recanalization of peripheral arterial occlusion.

The present report describes a technique of simultaneous confluent balloon inflation in cases in which conventional subintimal angioplasty failed. Eight patients with peripheral vascular occlusive disease (n = 4 each with iliac arterial lesions and superficial femoral arterial lesions) of clinical category 3-5 received treatment with the confluent two-balloon technique. Recanalization was successfully completed with this technique in all eight patients, without any major complications. All patients with claudication and rest pain were relieved of their symptoms, and both patients with ulcers showed improvement.

Formation of silaimines from a sterically demanding iminophosphonamido chlorosilylene via intramolecular N-P bond cleavage.

The sterically demanding iminophosphonamido chlorosilylene [Ph2P(DipN)2]SiCl (Dip = 2,6-diisopropylphenyl) was synthesized and fully characterized using NMR spectroscopy and X-ray crystallography. Substitution reactions of [Ph2P(DipN)2]SiCl with N- and Fe-nucleophiles led to the unexpected formation of the corresponding silaimine derivatives. This process involves the ring-opening rearrangement of three-coordinated silylene intermediates that proceeds via intramolecular N-P bond cleavage.

Interconversion between a silaimine and an aminosilylene supported by an iminophosphonamide ligand.

The reaction of a chlorosilylene, supported by an iminophosphonamide ligand, with KN(SiMe3)2 resulted in the formation of a silaimine instead of the expected aminosilylene. However, this silaimine exists in equilibrium with the corresponding aminosilylene, which was experimentally demonstrated using variable-temperature NMR spectroscopy and a trapping reaction with elemental selenium to give a silaselenourea.

Hydroboration of carbonyls and imines by an iminophosphonamido tin(II) precatalyst.

A novel three-coordinated tin(II) chloride [Ph2P(NtBu)2]SnCl (1) supported by an N,N'-di-tert-butyliminophosphonamide having two phenyl groups on the phosphorus atom was synthesized by the reaction of the starting lithium iminophosphonamide [Ph2P(NtBu)2]Li with SnCl2·(dioxane) in toluene. The molecular structure of 1 was established by X-ray diffraction analysis. Tin(II) chloride 1 can act as an efficient precatalyst for the hydroboration of a wide variety of aldehydes, ketones, and imines at -10 °C. DFT calculations propose that hydroboration involves hydride transfer from the corresponding tin(II) hydride intermediate [Ph2P(NtBu)2]SnH (10) to the carbonyl substrates via four-membered transition states (TS-12), affording three-coordinated tin(II) alkoxide intermediates [Ph2P(NtBu)2]SnOR (13), followed by the stepwise reaction of 13 with HBpin (pin = pinacolate) to release the boronate esters and regenerate the tin(II) hydride 10. The stoichiometric reaction of the in site-generated 10 with benzophenone 2a at -10 °C led to the formation of 13. Moreover, 13 also stoichiometrically reacted with HBpin at -10 °C, forming the corresponding boronate ester 3a and 10 based on the 1H NMR spectrum of the reaction mixture.

Syntheses of selenolato-bridged dinuclear hydridoplatinum complexes [Pt2H2(mu-Se(t)Bu)2(PPh3)2] and [Pt2H(Se(t)Bu)(mu-Se(t)Bu)2(PPh3)2]: unusual thermal reaction of hydrido(1,1-dimethylethaneselenolato) platinum complex cis-[PtH(Se(t)Bu)(PPh3)2].

Novel selenolato-bridged dinuclear hydridoplatinum complexes, cis-[Pt(2)H(2)(mu-Se(t)Bu)(2)(PPh(3))(2)] (2) and cis-[Pt(2)H(Se(t)Bu)(mu-Se(t)Bu)(2)(PPh(3))(2)] (3) were synthesized in 30% and 57% yields, respectively, by the thermolysis of hydrido(1,1-dimethylethaneselenolato) Pt(II) complex cis-[PtH(Se(t)Bu)(PPh(3))(2)] (1) in toluene at 80 degrees C for 3 h. The structures of dinuclear complexes 2 and 3 were fully characterized on the basis of their NMR and IR spectroscopic data and X-ray crystallography. The two distorted square planar Pt atoms in 2 and 3 are held together by two bridged selenolato ligands, (t)Bu groups of which adopt a trans configuration with respect to the four-membered Pt(2)Se(2) ring. Each central Pt(2)Se(2) ring in 2 and 3 has a hinged arrangement due to the steric repulsion among the two PPh(3) ligands and the (t)Bu group lying between them.

Zirconium complex of an [OSSO]-type diphenolate ligand bearing trans-1,2-cyclooctanediylbis(thio) core: synthesis, structure, and isospecific 1-hexene polymerization.

Six-coordinated dibenzyl Zr complex bearing an [OSSO]-type tetradentate ligand was synthesized, and the structure was fully characterized by NMR spectroscopy and X-ray crystallography. The zirconium complex has C(2) symmetry in solution. Owing to an effect of the cyclooctane ring structure, the combination of the zirconium complex and B(C(6)F(5))(3) or (Ph(3)C)[B(C(6)F(5))(4)] as the activator exhibited high activity toward polymerization of 1-hexene to yield highly isotactic poly(1-hexene).

Combined stent placement and high dose PGE1 drip infusion for chronic occlusion of the superficial femoral artery as a modality to salvage chronic critical limb ischemia.

PURPOSE: To assess the initial effect, short-term patency, and limb salvage rates of combined stent placement and high-dose prostaglandin E-1 (PGE1) drip infusion for chronic occlusion of the superficial femoral artery (SFA). MATERIALS AND METHODS: A total of 15 arteriosclerotic occlusive lesions of the SFA were treated in 11 consecutive patients (mean age: 78.4 years old). All cases were of category 4 or 5, based on the criteria of the Society of Vascular Surgery and Intermittent Society for Cardiovascular Surgery (SVC/ISCVS). In all cases a self-expandable stainless steel stent was implanted. PGE1 treatment was started 3-5 days before stent placement and continued for 7-10 days after the intervention. The technical success, limb salvage outcomes, patency rates, and complications were examined. RESULTS: In all cases, the technical success rate of the procedure was 100%. After stent implantation, the clinical status of all cases was improved by at least +2, and major amputation was not required in any cases. The 12-month primary, secondary patency rates, and limb salvage rate were 57%, 100%, and 100%, respectively. CONCLUSION: Combined stent placement and high-dose PGE1 drip infusion is a treatment of choice for salvaging the lower limb of a patient with chronic critical ischemia.