Accessing Cationic α-Silylated and α-Germylated Phosphorus Ylides

The synthesis and full characterization of α-silylated (α-SiCPs; 1–7) and α-germylated (α-GeCPs; 11–13) phosphorus ylides bearing one chloride substituent R$_{3}$PC(R$^{1}$)E(Cl)R$^{2}$$_{2}$ (R=Ph; R$^{1}$=Me, Et, Ph; R$^{2}$=Me, Et, iPr, Mes; E=Si, Ge) is presented. The molecular structures were determined by X-ray diffraction studies. The title compounds were applied in halide abstraction studies in order to access cationic species. The reaction of Ph$^{3}$PC(Me)Si(Cl)Me$^{2}$ (1) with Na[B(C$^{6}$F$^{5}$)$^{4}$] furnished the dimeric phosphonium-like dication [Ph$^{3}$PC(Me)SiMe$^{2}$]$^{2}$[B(C$^{6}$F$^{5}$)$^{4}$]$^{2}$ (8). The highly reactive, mesityl- or iPr-substituted cationic species [Ph$^{3}$PC(Me)SiMes$^{2}$][B(C$^{6}$F$^{5}$)$^{4}$] (9) and [Ph$^{3}$PC(Et)SiiPr$^{2}$][B(C$^{6}$F$^{5}$)$^{4}$] (10) could be characterized by NMR spectroscopy. Carrying out the halide abstraction reaction in the sterically demanding ether iPr$^{2}$O afforded the protonated α-SiCP [Ph$^{3}$PCH(Et)Si(Cl)iPr$^{2}$][B(C$^{6}$F$^{5}$)$^{4}$] (6 dec) by sodium-mediated basic ether decomposition, whereas successfully synthesized [Ph$^{3}$PC(Et)SiiPr$^{2}$][B(C$^{6}$F$^{5}$)$^{4}$] (10) readily cleaves the F−C bond in fluorobenzene. Thus, the ambiphilic character of α-SiCPs is clearly demonstrated. The less reactive germanium analogue [Ph$^{3}$PC(Me)GeMes$^{2}$][B{3,5-(CF$^{3}$)$^{2}$C$^{6}$H$^{3}$}$^{4}$] (14) was obtained by treating 11 with Na[B{3,5-(CF$^{3}$)$^{2}$C$^{6}$H$^{3}$}$^{4}$] and fully characterized including by X-ray diffraction analysis. Structural parameters indicate a strong C$^{Ylide}$−Ge interaction with high double bond character, and consequently the C−E (E=Si, Ge) bonds in 9, 10 and 14 were analyzed with NBO and AIM methods

A Method of Drusen Measurement Based on the Geometry of Fundus Reflectance

BACKGROUND: The hallmarks of age-related macular degeneration, the leading cause of blindness in the developed world, are the subretinal deposits known as drusen. Drusen identification and measurement play a key role in clinical studies of this disease. Current manual methods of drusen measurement are laborious and subjective. Our purpose was to expedite clinical research with an accurate, reliable digital method. METHODS: An interactive semi-automated procedure was developed to level the macular background reflectance for the purpose of morphometric analysis of drusen. 12 color fundus photographs of patients with age-related macular degeneration and drusen were analyzed. After digitizing the photographs, the underlying background pattern in the green channel was leveled by an algorithm based on the elliptically concentric geometry of the reflectance in the normal macula: the gray scale values of all structures within defined elliptical boundaries were raised sequentially until a uniform background was obtained. Segmentation of drusen and area measurements in the central and middle subfields (1000 μm and 3000 μm diameters) were performed by uniform thresholds. Two observers using this interactive semi-automated software measured each image digitally. The mean digital measurements were compared to independent stereo fundus gradings by two expert graders (stereo Grader 1 estimated the drusen percentage in each of the 24 regions as falling into one of four standard broad ranges; stereo Grader 2 estimated drusen percentages in 1% to 5% intervals). RESULTS: The mean digital area measurements had a median standard deviation of 1.9%. The mean digital area measurements agreed with stereo Grader 1 in 22/24 cases. The 95% limits of agreement between the mean digital area measurements and the more precise stereo gradings of Grader 2 were -6.4 % to +6.8 % in the central subfield and -6.0 % to +4.5 % in the middle subfield. The mean absolute differences between the digital and stereo gradings 2 were 2.8 +/- 3.4% in the central subfield and 2.2 +/- 2.7% in the middle subfield. CONCLUSIONS: Semi-automated, supervised drusen measurements may be done reproducibly and accurately with adaptations of commercial software. This technique for macular image analysis has potential for use in clinical research

High-Resolution Imaging of the Retinal Nerve Fiber Layer in Normal Eyes Using Adaptive Optics Scanning Laser Ophthalmoscopy

To conduct high-resolution imaging of the retinal nerve fiber layer (RNFL) in normal eyes using adaptive optics scanning laser ophthalmoscopy (AO-SLO).AO-SLO images were obtained in 20 normal eyes at multiple locations in the posterior polar area and a circular path with a 3-4-mm diameter around the optic disc. For each eye, images focused on the RNFL were recorded and a montage of AO-SLO images was created.AO-SLO images for all eyes showed many hyperreflective bundles in the RNFL. Hyperreflective bundles above or below the fovea were seen in an arch from the temporal periphery on either side of a horizontal dividing line to the optic disc. The dark lines among the hyperreflective bundles were narrower around the optic disc compared with those in the temporal raphe. The hyperreflective bundles corresponded with the direction of the striations on SLO red-free images. The resolution and contrast of the bundles were much higher in AO-SLO images than in red-free fundus photography or SLO red-free images. The mean hyperreflective bundle width around the optic disc had a double-humped shape; the bundles at the temporal and nasal sides of the optic disc were narrower than those above and below the optic disc (P<0.001). RNFL thickness obtained by optical coherence tomography correlated with the hyperreflective bundle widths on AO-SLO (P<0.001)AO-SLO revealed hyperreflective bundles and dark lines in the RNFL, believed to be retinal nerve fiber bundles and Müller cell septa. The widths of the nerve fiber bundles appear to be proportional to the RNFL thickness at equivalent distances from the optic disc

Lewis Base Mediated β-Elimination and Lewis Acid Mediated Insertion Reactions of Disilazido Zirconium Compounds

The reactivity of a series of disilazido zirconocene complexes is dominated by the migration of anionic groups (hydrogen, alkyl, halide, OTf) between the zirconium and silicon centers. The direction of these migrations is controlled by the addition of two-electron donors (Lewis bases) or two-electron acceptors (Lewis acids). The cationic nonclassical [Cp2ZrN(SiHMe2)2]+ ([2]+) is prepared from Cp2Zr{N(SiHMe2)2}H (1) and B(C6F5)3 or [Ph3C][B(C6F5)4], while reactions of B(C6F5)3 and Cp2Zr{N(SiHMe2)2}R (R = Me (3), Et (5), n-C3H7 (7), CH═CHSiMe3 (9)) provide a mixture of [2]+ and [Cp2ZrN(SiHMe2)(SiRMe2)]+. The latter products are formed through B(C6F5)3 abstraction of a β-H and R group migration from Zr to the β-Si center. Related β-hydrogen abstraction and X group migration reactions are observed for Cp2Zr{N(SiHMe2)2}X (X = OTf (11), Cl (13), OMe (15), O-i-C3H7 (16)). Alternatively, addition of DMAP (DMAP = 4-(dimethylamino)pyridine) to [2]+ results in coordination to a Si center and hydrogen migration to zirconium, giving the cationic complex [Cp2Zr{N(SiHMe2)(SiMe2DMAP)}H]+ ([19]+). Related hydrogen migration occurs from [Cp2ZrN(SiHMe2)(SiMe2OCHMe2)]+ ([18]+) to give [Cp2Zr{N(SiMe2DMAP)(SiMe2OCHMe2)}H]+ ([22]+), whereas X group migration is observed upon addition of DMAP to [Cp2ZrN(SiHMe2)(SiMe2X)]+ (X = OTf ([12]+), Cl ([14]+)) to give [Cp2Zr{N(SiHMe2)(SiMe2DMAP)}X]+ (X = OTf ([26]+), Cl ([20]+)). The species involved in these transformations are described by resonance structures that suggest β-elimination. Notably, such pathways are previously unknown in early metal amide chemistry. Finally, these migrations facilitate direct Si–H addition to carbonyls, which is proposed to occur through a pathway that previously had been reserved for later transition metal compounds