Real-time Fourier transform IR (FTIR) spectroscopy in organometallic chemistry: Mechanistic aspects of the fac to mer photoisomerization of fac-[Mn(Br)(CO)(3)(R-DAB)]

Real-time Fourier transform IR (RT/FTIR) spectroscopy was used to study the photoisomerization of fac-[Mn(Br)(CO)(3)(R-DAB)] (R-DAB, N,N'-di-R-1,4-diazabutadiene; R=Pr-i, Bu-t) to mer-[Mn(Br)(CO)(3)(R-DAB)]. The primary photoproduct [Mn(Br)(L)(CO)(2)(R-DAB)] could be detected at room temperature for L=MeCN and identified at 273 K as a cis-cis isomer for L=P(OMe)(3). RT/FTIR spectroscopy was also used to determine the thermodynamic parameters E-a, Delta H-double dagger and Delta S-double dagger of the thermal backreaction of this mer product to the parent fac isomer. For slow reactions, GC/FTIR software was used to provide a real-time screen display of the IR spectral changes. For fast reactions ( 10(-1) 1 s), the high speed collect (HSC) kinetic software was used to collect 12 spectra s(-1) at 2 cm(-1) resolution, recording one spectrum per scan.