Chemistry of vinylidene complexes

Vinylidene carbonylation at a manganese–iron complex: A density functional study of mechanism

“…The IR spectrum of 3 shows eight CO bands (Table 2) instead of 6 CO bands as one may expect for a hexacarbonyl complex [12]. Several CO frequencies obviously are due to isomeric complexes.…”

“…Thereby we compared the two-step mechanism 1 / 2 / 3 via the intermediate complex 2 and the single-step mechanism 1 / 3 where species 3 forms directly from the reactants. The first mechanism seems reasonable as recent IR and NMR measurements showed that both m-vinylidene 2 and the TMM isomeric form 3 co-exist in solution [12]. As more than one form of m-vinylidene may occur, we modeled several isomers of the binuclear complexes 2 and 3.…”

“…1973 1966 1930 1941 1870 1849 2011 1987 1972 1980 1930 1932 2004 2012 2013 1979 1989 2014 2019 2020 2004 2000 2021 2036 2037 2020 2016 2074 2082 2082 2059 2056 Exp. b 2009, 1955 2087, 2060, 2034, 2001, 1987, 1977, 1928, 1854 a IR spectrum recorded in C 6 H 12 , NMR spectra in CD 2 Cl 2 [12]. The calculated 13 1.42 Å, which is elongated from 1.33 Å in 2.…”

“…However, the simultaneous presence in solution of 2 and 3 and their isomers prevents an unambiguous assignment of the IR CO bands. NMR spectroscopy permitted a separate characterization of complexes 2 and 3, but the assignment to specific isomers remained open [12]. Therefore, to assist with the interpretation of the various spectra, we calculated CO vibrational frequencies as well as 1 H and 13 C NMR chemical shifts for all complexes under study, 1, 1 0 , 2 and 3 (Table 2).…”

“…Therefore, their presence does not increase the number of CO bands in the experimental IR spectrum, but rather affects their widths [12], e.g. the band at 1987 cm À1 is a shoulder.…”