First experimental evidence for a bis-ethene chromium(I) complex forming from an activated ethene oligomerization catalyst.

A bis-ethene chromium(I) species, which is the postulated key intermediate in the widely accepted metallacyclic mechanism for ethene oligomerization, is experimentally observed. This catalytic transformation is an important commercial route to linear α-olefins (primarily, 1-hexene and 1-octene), which act as comonomers for the production of polyethene. Here, electron paramagnetic resonance studies of a catalytic system based on [Cr(CO)4(PNP)][Al(OC(CF3)3)4] [PNP = Ph2PN(iPr)PPh2] activated with Et6Al2 provide the first unequivocal evidence for a chromium(I) bis-ethene complex. The concentration of this species is enhanced under ethene and isotope labeling studies that confirm its composition as containing [Cr(C2H4)2(CO)2(PNP)]+ These observations open a new route to mechanistic studies of selective ethene oligomerization.

Causes of enucleation in Northern India (1995-2005).

PURPOSE: There are limited data concerning the reasons for surgical removal of eyeball. The present retrospective study was undertaken to evaluate the frequency of diseases requiring surgical removal of eyeball and to study the histopathologic changes in these specimens. METHODS: Forty-eight surgical eyeball specimens received between January 1999 and June 2005 were included in the study. Age, sex, and clinical diagnoses were recorded in each case. Specimens were classified on the basis of surgical procedure. Gross and microscopic findings were noted for all the specimens. RESULTS: Between January 1995 and June 2005, there were 139,092 outpatients, 6,574 hospital admissions, 12,044 ophthalmic operations, and a total of 48 enucleations in 47 patients. Of these 47 patients, 24 were male and 23 female with almost equal male:female ratio. Right eye was involved in 29 cases while left was involved in 17 cases. Bilateral eye involvement was seen in one case. Surgical specimens included enucleation (28 cases, 58.3%), exenteration (12 cases, 25%), and evisceration (8 cases, 16.6%). On histopathologic examination, the lesions were categorized into two broad groups: neoplastic (8 cases, 16.6%) and non-neoplastic (40 cases, 83.4%). Both groups were further subcategorized and correlated with clinical diagnosis. CONCLUSIONS: In our setting, non-neoplastic lesions are the main cause of eyeball surgery, as compared to the West, where trauma followed by neoplasms constitute important causes. Pathologic examination of eyeballs is a must for proper postoperative management of the patient.