Charged tags as probes for analyzing organometallic intermediates and monitoring cross-coupling reactions by electrospray-ionization mass spectrometry.
Organic iodides bearing a cationic quaternary ammonium group at a remote position react with zerovalent Pd complexes, Zn, or In leading to a C-I bond insertion. The resulting charge-tagged organometallics can be detected by electrospray-ionization mass spectrometry, which provides detailed information on their stoichiometry, oxidation state, and coordination sphere. The properties of the observed organopalladium and -zinc intermediates largely agree with previous findings, whereas the organoindium species show a surprisingly high tendency to form ate complexes. Magnesium also undergoes insertion into the C-I bond of the charge-tagged organic iodides, but instead of the expected organomagnesium intermediates only the corresponding hydrolysis products could be detected in the diluted solutions. Electrospray-ionization mass spectrometry can also be used to study the reactivity of the charge-tagged species, as was demonstrated for a Pd-catalyzed Negishi cross-coupling reaction. The presented approach permits a straightforward identification of the rate-limiting step and the determination of the corresponding second-order rate constant.
Schade
Matthias A
MA
Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München, Germany.
Fleckenstein
Julia E
JE
Knochel
Paul
P
Koszinowski
Konrad
K
D007462:Iodobenzenes / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
D007462:Iodobenzenes; D009942:Organometallic Compounds; D000644:Quaternary Ammonium Compounds; D010165:Palladium