Manganese propane and manganese butane complexes derived from CpMn(CO) 3 were generated photochemically at 130-136 K with the alkane as solvent and characterized by FTIR spectroscopy and by 1H NMR spectroscopy with in situ laser photolysis. Time-resolved IR spectroscopic measurements were performed at room temperature with the same laser wavelength. The ν(CO) bands in the IR spectra of the photoproducts in propane are shifted to low frequency with respect to CpMn(CO)3, consistent with formation of CpMn(CO)2(propane). The 1H NMR spectra conform to the criteria for alkane complexes: a high-field resonance for the η2-CH protons that shifts substantially on partial deuteration of the alkane and exhibits a coupling constant JC-H on 13C-labeling of ca. 120 Hz. The NMR spectrum of each system exhibits two diagnostic product resonances in the high-field region for the η2-CH protons, corresponding to CpMn(CO)2(η 2-C1-alkane) and CpMn(CO)2(η2-C2-alkane) isomers. Partial deuteration of the alkane at C1 results in characteristic strong isotopic perturbation of equilibrium of the η2-CH resonance of CpMn(CO)2(η2-C1-alkane). With propane-13C1, the η2-CH resonance of CpMn(CO)2(η2-C1-alkane) isomer exhibits 13C satellites with JC-H = 119 Hz. The corresponding resonance of CpMn(CO)2(η2-C2-alkane) is identified by use of propane-2,2-d2. The lifetimes of the (η2-C1-alkane) isomers of the manganese complexes were determined by NMR spectroscopy as 22 ± 2 min at 134 K (propane) and 5.5 min at 136 K (butane). The corresponding spectra and lifetimes of the CpRe(CO)2(alkane) complexes were measured for reference (CpRe(CO)2(propane) lifetime ca. 60 min at 161 K; CpRe(CO)2(butane) 13 min at 171 K). The lifetimes determined by IR spectroscopy were similar to those determined by NMR spectroscopy, thereby supporting the assignments. These measurements extend the range of alkane complexes characterized by NMR spectroscopy from rhenium and rhodium derivatives to include less stable manganese derivatives.
ASJC Scopus subject areas
- Chemistry (all)
- Colloid and Surface Chemistry