{ Abstract } { page one } { page two } { page three } { page four }

MALDI-TOF Mass Spectrometry of Cationic Complexes


The Results

CpRe(CO)2(h3-allyl)+ is a known, well-characterized cationic organometallic complex. We chose it as a suitable starting point to gauge the usefulness of MALDI-TOF for cationic organometallic chemicals.

With ATT matrix
...click to see spectrum full-size... 		Cyclopentadienyl rhenium dicarbonyl h3-allyl cation.
 No matrix
...click to see spectrum full-size...
In this experiment, we observed the parent peak (calcd 347.02, obsd 347.33) in cation detection mode. No fragmentation was observed -- the two lower mass peaks are from the ATT matrix and its dimer.
The experiment was repeated without any matrix. Since cyclopentadienyl rhenium complexes absorb light over a wide range of energy, it seemed reasonable that they could be ejected from the surface in the same way that standard matrices are. The laser power required to see signal was slightly higher without the ATT matrix, but the result (right spectrum above) cleanly showed the parent ion only.

CpRe(CO)2[h3-HC(CH3)-CH-CH2]+ is an analogous compound, with an extra methyl group on the pi-allyl unit.

With ATT matrix
...click to see spectrum full-size... 		Cyclopentadienyl rhenium dicarbonyl h3-(1-methyl)allyl cation.
 No matrix
...click to see spectrum full-size...
The ATT-matrix spectrum showed the parent ion (calcd 361.04, obsd 361.35) in cation detection mode, plus the signals from the ATT matrix and its dimer.
Again, the experiment was repeated without any matrix. As with the unsubstituted allyl complex, the parent ion (right spectrum above) was cleanly observed.

Cp*Re(CO)2(h3-tBu-C C-CH2)+ is a pi-propargyl complex .

With ATT matrix
...click to see spectrum full-size... 		Cyclopentadienyl rhenium dicarbonyl (h3-tBu-C C-CH2) cation.
 No matrix
...click to see spectrum full-size...
Pi-propargyl complexes are more reactive than pi-allyl complexes, and it was difficult for us to observe the parent ions of these complexes using LSIMS, where reaction with water or the liquid matrix rapidly decomposed the analyte. Using solid ATT as a matrix, we were able to observe the parent ion (calcd 471.15, obsd 471.43).
Ideally, we would likt to remove all possiblity of reaction with the matrix by not using any. As was the case with the allyl complexes, the parent ion (right spectrum above) was cleanly observed.

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{ Abstract } { page one } { page two } { page three } { page four }
Send comments and questions to John R. Nash.