SE-77 NMR-STUDIES OF CYCLOPENTADIENYLCHROMIUM SELENIUM SPECIES - EVIDENCE OF CONFORMERS

Variable-temperature Se-77 NMR spectroscopic studies of the complexes [CpCr(CO)(2)](2)Se (1) and [CpCr(CO)(2)](2)Se-2 (2) have been carried out. A singlet Se-77 resonance is found for 1 at 213-296 K, but the br oadness at the higher temperatures suggests the existence of rotamers exchanging at an intermediate rate on the time scale of Delta delta(Se ). For 2, the observations point to the existence of two conformers ov er the range 213-330 K, with relative proportions varying from ca. 1:3 .4 at 320 K to ca. 1:6.4 at 213 K. This conclusion is supported by C-1 3 NMR spectra at 213 and 298 K. Also reported are Se-77 NMR data for C p2Cr2(CO)(5)Se-2 (3), produced in situ by thermolysis of 2 in solution , and solid-state CP-MAS C-13 and Se-77 NMR data for [CpCrSe](4) (4).