Fast‐atom bombardment mass spectrometry of 2,4‐diketonate complexes of transition metals [V(III), Cr(III), Mn(III), Fe(III), Co(III), Ru(III) and Os(III)]

Abstract

The tris(acety1acetonate) (LJ and tris( l,l,l-trifluoromethyl-2,4-pentanedionate) (Li) complexes of transition metals V, Cr, Mn, Fe, Co, Ru and 0 s in their +3 oxidation states were studied under fast-atom bombardment (FAB) conditions using 3-nitrobenzyl alcohol as a matrix. All complexes showed the formation of molecular ion and protonated molecules [ML2]+ and [ML;]' are the most abundant ions in the spectra of all the metal acetylacetonates (L) and trifluoroacetylacetonates (L') studied. Interaction of matrix with metal complexes and polynuclear metal complexes led to the formation of polynuclear species with significant abundance especially for manganese and iron complexes. Formation of these metal ions was observed with relative intensities from 3-30%. Ions corresponding to ligand-exchange reactions were observed with moderate to high abundance in all metal complexes studied except those of ruthenium and osmium. Experiments carried out with a split FAB probe tip suggested ligand-ligand exchange reactions were not due to gas-phase reactions but only due to solutionphase exchanges. Osmium and ruthenium complexes do not yield polynuclear species or ions due to matrix clustering. Instead they show neutral ligand losses and formation of acetyl ion.Due to their high solubility in organic solvents and their volatile nature, metal P-diketonates have been the focus of attention of various groups.'-3 Metal acetylacetonates are used in industries such as ceramic,2 rubber4 and polymer.'^^ These compounds can also, due to their unsaturation, quench triplet states of benzophenone.' The volatile nature of these compounds attracted mass spectrometrists to study the gas-phase properties of these metal acetyla~etonates.~. '-19 A number of reports on electron ionization of metal complexes in the gas phase due to their thermal stability and ease of preparation.' These studies are useful for structure elucidation and also allow us to compare the effect of metals of different oxidation states and different electronegativities on the stability of the metal complexes towards fragmentation of the molecular ion, and on the formation of polynuclear ions. A few reports are available on the soft ionization mass spectrometry of these metal c o m p l e~e s .~~-~~ High pressure mass spectra of 16 bis-and tris-acetylacetonates and hexafluoroacetylacetonates of transition metals showed the formation of positive ions containing two or more metal atoms with significant abundance which could be produced from an iodneutral molecule reaction.20 The formation of bimetallic polymer ions was also reported for chromium acetylacetonate under electron ionization due either to the vaporization of a neutral dimer or to the high pressure which caused ion/molecule reactions in the electron ionization (EI) source itself." The polynuclear ion concentration was sample dependent, but this work was never followed up.Similar formation of polynuclear ions (two or more metal ions) was observed in the ammonia and methane chemical ionization mass spectra of Cu(II), ...

Analysis of transition‐metal acetylacetonate complexes by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

“…14,23 However, some fragmentation was observed, in the form of the [M À acac] þ species, which is often the base peak in EI spectra. Radical molecular ions have been reported previously for all five complexes by FAB, 18 and were also observed for Fe(acac) 3 and Co(acac) 3 by CI, for Mn(acac) 3 by ESI, and for V(acac) 3 , Cr(acac) 3 and Co(acac) 3 by LSIMS, in our laboratory. Higher mass multimetallic cluster ions were observed by MALDI, as has been noted for other techniques in our own laboratory and by others, 14,15,17,18,21 and again the nature of the clusters varies greatly between complexes.…”

“…12,13 However, neutral metal complexes without strong chromophores have not been studied systematically. The acetylacetonate ligand (acac; also known as bdiketonate) can be regarded as a weak chromophore, and metal acac complexes have been characterized previously by electron ionization (EI), 14 chemical ionization (CI), 15,16 secondary ion (SIMS) and laser desorption/ionization (LDI) mass spectrometry, 17 fast-atom bombardment (FAB), 18 and electrospray (ESI) 19 techniques. In this study, various first row transition-metal acac complexes were chosen as model compounds, and analyzed by MALDI-TOFMS using DCTB matrix.…”

Gas‐phase ligand exchange of select transition‐metal acetylacetonate and hexafluoroacetylacetonate complexes

“…Transition‐metal acetylacetonate complexes and select derivatives of each have been previously characterized by different MS techniques including matrix‐assisted laser desorption/ionization (MALDI),7 fast‐atom bombardment (FAB),8 electrospray ionization (ESI),9 secondary ion (SI),10, 11 chemical ionization (CI),12 and electron ionization (EI). Each technique provides a different glimpse into the chemistry of various metal β ‐diketonates where the overall collection of results from these species is quite substantial 5, 6, 13.…”

The gas‐phase ligand exchange of copper and nickel acetylacetonate, hexafluoroacetylacetonate and trifluorotrimethylacetylacetonate complexes

“…The more recent applications of these bis‐ or tris‐coordinated compounds likely stem from their ease of preparation, volatile nature, thermal stability, and ligand tunability in that many substituents are possible for the β ‐diketonate ligands 1, 2. Several metal β ‐diketonate complexes have been previously investigated using mass spectrometry,3–17 where the fragmentation patterns of numerous species are well established 4, 5 . β ‐Diketonate complexes have also been observed to form high mass clusters6 as well as undergo partial and complete gas‐phase ligand exchange (i.e., the exchange of one ligand versus the exchange of two) 7, 8…”

“…The mass spectra obtained from these investigations expose the rich chemistry of this class of compounds and illustrate unique characteristics, such as metal center influence, ligand stability, as well as subsequent reactivity. While ligand exchange has been observed to occur on a limited extent under matrix support,12, 13 ligand‐exchange processes have been reported to clearly ensue in the gas phase 7, 8. The results presented herein further establish the propensity of gas‐phase ligand‐exchange processes occurring with the 2,4‐pentadionato and 1,1,1,5,5,5‐hexafluoro‐2,4‐pentadionato ligands, and now, for the first time, exchange processes involving 1,1,1‐trifluoro‐5,5‐dimethylhexane‐2,4‐dionato ligands.…”