Preparation and characterization of dialkylcarbamato derivatives of niobium and tantalum

he mononuclear compounds M(O(2)CNR(2))(n) (M = Nb or Ta, R = Et, n = 5; M = Nb, R = Et or Pr-i, n = 4) have been prepared by treating the corresponding metal chlorides or their adducts, i,e. [NbCl4(thf)(2)](thf = tetrahydrofuran), with CO2-NHR(2) in toluene. The molecular structures of Ta(O(2)CNEt(2))(5) and Nb(O(2)CNEt(2))(4) have been solved by X-ray diffraction methods. The tantalum atom is eight-co-ordinated, being surrounded by three bi- and two mono-dentate diethylcarbamato groups, in a slightly distorted square-antiprismatic arrangement. The niobium compound consists of mononuclear units, where the niobium atom is dodecahedrally co-ordinated to eight oxygen atoms of four bidentate diethylcarbamate ligands. The reaction of [NbCl3(dme)] (dme = 1,2-dimethoxyethane) with CO2-NHR(2)(R = Et or Pr-i) gave the corresponding dialkylcarbamates; on the basis of spectroscopic and magnetic data these niobium(III) derivatives are suggested to be dinuclear with bridging and terminal carbamato groups. Improved yields of [M(2)(eta(6)-C(6)Me(6))(2)Cl-4] (M = Nb or Ta), which are the precursors to the dialkylcarbamates of niobium(II) and tantalum(II), have been obtained. The [M(2)(eta(6)-C(6)Me(6))(2)Cl-4]-CO2-NHPr2i system (M = Nb or Ta) in toluene gave metal(II) dialkylcarbamato complexes of analytical composition M(eta(6)-C(6)Me(6))(O2CNPr2i)(2): these substantially diamagnetic compounds are suggested to be dinuclear with bridging carbamato groups, a metal-metal bond and axially co-ordinated hexamethylbenzene

Titanium(IV) Surface Complexes Bearing Chelating Catecholato Ligands for Enhanced Band-Gap Reduction

Protonolysis reactions between dimethylamido titanium(IV) catecholate [Ti(CAT)(NMe2)2]2 and neopentanol or tris(tert-butoxy)silanol gave catecholato-bridged dimers [(Ti(CAT)(OCH2tBu)2)(HNMe2)]2 and [Ti(CAT){OSi(OtBu)3}2(HNMe2)2]2, respectively. Analogous reactions using the dimeric dimethylamido titanium(IV) (3,6-di-tert-butyl)catecholate [Ti(CATtBu2-3,6)(NMe2)2]2 yielded the monomeric Ti(CATtBu2-3,6)(OCH2tBu)2(HNMe2)2 and Ti(CATtBu2-3,6)[OSi(OtBu)3]2(HNMe2)2. The neopentoxide complex Ti(CATtBu2-3,6)(OCH2tBu)2(HNMe2)2 engaged in further protonolysis reactions with Si–OH groups and was consequentially used for grafting onto mesoporous silica KIT-6. Upon immobilization, the surface complex [Ti(CATtBu2-3,6)(OCH2tBu)2(HNMe2)2]@[KIT-6] retained the bidentate chelating geometry of the catecholato ligand. This convergent grafting strategy was compared with a sequential and an aqueous approach, which gave either a mixture of bidentate chelating species with a bipodally anchored Ti(IV) center along with other physisorbed surface species or not clearly identifiable surface species. Extension of the convergent and aqueous approaches to anatase mesoporous titania (m-TiO2) enabled optical and electronic investigations of the corresponding surface species, revealing that the band-gap reduction is more pronounced for the bidentate chelating species (convergent approach) than for that obtained via the aqueous approach. The applied methods include X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and solid-state UV/vis spectroscopy. The energy-level alignment for the surface species from the aqueous approach, calculated from experimental data, accounts for the well-known type II excitation mechanism, whereas the findings indicate a distinct excitation mechanism for the bidentate chelating surface species of the material [Ti(CATtBu2-3,6)(OCH2tBu)2(HNMe2)2]@[m-TiO2]

Partial pancreatoduodenectomy versus duodenum-preserving pancreatic head resection in chronic pancreatitis: the multicentre, randomised, controlled, double-blind ChroPac trial

Background There is substantial uncertainty regarding the optimal surgical treatment for chronic pancreatitis. Short-term outcomes have been found to be better after duodenum-preserving pancreatic head resection (DPPHR) than after partial pancreatoduodenectomy. Therefore, we designed the multicentre ChroPac trial to investigate the long-term outcomes of patients with chronic pancreatitis within 24 months after surgery. Methods This randomised, controlled, double-blind, parallel-group, superiority trial was done in 18 hospitals across Europe. Patients with chronic pancreatitis who were planned for elective surgical treatment were randomly assigned to DPPHR or partial pancreatoduodenectomy with a central web-based randomisation tool. The primary endpoint was mean quality of life within 24 months after surgery, measured with the physical functioning scale of the European Organisation for Research and Treatment of Cancer QLQ-C30 questionnaire. Primary analysis included all patients who underwent one of the assigned procedures; safety analysis included all patients who underwent surgical intervention (categorised into groups as treated). Patients and outcome assessors were masked to group assignment. The trial was registered, ISRCTN38973832. Recruitment was completed on Sept 3, 2013. Findings Between Sept 10, 2009, and Sept 3, 2013, 250 patients were randomly assigned to DPPHR (n=125) or partial pancreatoduodenectomy (n=125), of whom 226 patients (115 in the DPPHR group and 111 in the partial pancreatoduodenectomy group) were analysed. No difference in quality of life was seen between the groups within 24 months after surgery (75.3 [SD 16.4] for partial pancreatoduodenectomy vs 73.0 [16.4] for DPPHR; mean difference -2.3, 95% CI -6.6 to 2.0; p=0.284). The incidence and severity of serious adverse events did not differ between the groups. 70 (64%) of 109 patients in the DPPHR group and 61 (52%) of 117 patients in the partial pancreatoduodenectomy group had at least one serious adverse event, with the most common being reoperations (for reasons other than chronic pancreatitis), gastrointestinal problems, and other surgical morbidity. Interpretation No differences in quality of life after surgery for chronic pancreatitis were seen between the interventions. Results from single-centre trials showing superiority for DPPHR were not confirmed in the multicentre setting