ISSN:
0947-6539
Schlagwort(e):
alkenes
;
chromium
;
cis-divacant octahedral geometry
;
polymerizations
;
tris(pyrazolyl)borate complexes
;
Chemistry
;
General Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
Reaction of CrCl2 with TptBu, MeK yielded [TptBu, MeCr(3-tBu, 5-MepzH)Cl] (1) and [TptBu, MeCrCl] (2), while the same reaction in the presence of pyridine gave 1 and [TptBu, MeCr(py)Cl] (3). Alkylation of 3 with Grignard reagents produced the chromium(II) alkyls [TptBu, MeCrR] (4, R = Et; 5, R = Ph; 6, R = CH2SiMe3), which reversibly added to pyridine to form the five-coordinate adducts [TptBu, MeCr(py)R] (7, R = Et; 8, R = Ph; 9, R = CH2SiMe3). 1, 2, 4, and 5 were structurally characterized by X-ray diffraction. The four-coordinate molecules 2, 4, and 5 adopt a highly unusual cis-divacant octahedral coordination geometry, while 1 is the first five-coordinate TptBu, Me-complex of a first-row transition metal. Despite their coordinative unsaturation, chromium alkyls 4-6 do not polymerize ethylene, or even react with it. This observation is inconsistent with the catalytic activity commonly ascribed to divalent chromium in heterogeneous polymerization catalysts. Attempts to oxidize 4-6 (e.g., with [Cp2Fe]BPh4) to cationic chromium(II) alkyls failed, yielding [TptBu, MeCr(thf)][BPh4] (10) instead.
Zusätzliches Material:
3 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/chem.19970031016
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