Electrospray mass spectrometry of metal carbonyl complexes †

Abstract

Methods are described for characterising neutral metal carbonyl complexes using electrospray mass spectrometry, by converting them into ions with suitable reagents. Ionisation techniques included addition of OMe Ϫ generating [M ϩ OMe] Ϫ species, addition of Ag ϩ or Na ϩ ions giving the appropriate positive ion, abstraction of acidic hydrogen forming [M Ϫ H] Ϫ ions, or (in rare cases) oxidation giving radical cations [M] ϩ . The methods can be used on pure compounds or on mixtures. Fragmentation in the mass spectrometer can be minimised so that identification of parent species is unambiguous. Applications are demonstrated with a wide range of compounds including mononuclear and polynuclear binary carbonyls, and with derivatives containing phosphine, cyclopentadienyl, π-arene, σ-aryl and other ligands.Characterisation of metal carbonyl compounds, particularly the higher-nuclearity cluster compounds, has traditionally relied heavily on single-crystal X-ray crystallography. This is because microanalytical data are usually not particularly informative, 13 C NMR data are often limited by low sensitivity and fluxional processes, while structure assignment based on the interpretation of infrared spectra is limited to smaller molecules. The strong reliance on X-ray methods has a corollary; only compounds that form suitable single crystals become fully characterised. There is therefore a need for alternative means of investigating metal cluster compounds.Mass spectrometry has been applied to organometallic chemistry for many years, but the traditional electron impact method of ionisation is limited to thermally robust, neutral compounds of low molecular mass since appreciable vapour pressure is necessary at temperatures below the decomposition point. 1The development of FAB (fast-atom bombardment) methods extended the mass spectral technique to non-volatile compounds, but it is a rather violent means of ionisation so extensive fragmentation and recombination processes can make interpretation complicated.2 An alternative, developing technique based on laser desorption has been applied to organometallic systems, 3 but again aggregation processes complicate interpretation.In the past decade a new method of sample ionisation has been developed: electrospray mass spectrometry (ESMS).4 This involves spraying samples in solution from a charged outlet into an atmospheric-pressure source and then rapidly evaporating the solvent, leaving ions in the gas phase which are then transferred to a mass analyser. The process is gentle so that fragile samples can be examined, and fragmentation processes are minimised so that clean parent ions are usually found (although fragmentation can be induced by altering the conditions if further information is needed). It can also be applied directly to ionic species since solubility rather than volatility is the key factor. The new method has been extensively developed by those interested in biological systems since it enables mass spectrometry to be applied to high mass, fragile biomolecule...

Ruthenium and osmium carbonyl clusters incorporating stannylene and stannyl ligands

“…16 The m/z values reported are the strongest in the isotope envelope, and formulations were confirmed by matching isotope patterns with simulated ones generated with ISOTOPE. 30 Fast atom bombardment mass spectra were obtained on a JEOL SX-102 spectrometer using 3-nitrobenzyl alcohol as matrix and CsI as calibrant.…”

“…16,21 Both of these ions were remarkably robust, undergoing CO loss only at high cone voltages, >60 V, and in contrast to the very ready loss of Ph 3 Sn + from 1, there was no indication at all of a similar process for 5.…”

Alkynyl and poly-ynyl derivatives of carbon-tricobalt clusters

“…Chemical aids to ionisation were used. 34 Elemental analyses were by CMAS, Belmont, Vic., Australia.…”

A Hypothetical Model for the Formation of Transition Metal Carbonyl Clusters Based upon 4n Series Skeletal Numbers

“…The corresponding cluster k values of the fragment should be on the increase. Very interesting extensive work on the metal carbonyls that involves stripping off the CO ligands has been done by several research groups (Butcher, et al, 2002(Butcher, et al, , 2003Crawford, et al, 2006;Critchley, et al, 1999;Dyson, et al, 2001;Henderson, et al, 1998Henderson, et al, , 2009 Table 7). Although the series and the skeletal numbers predict that each of the Re skeletal atoms except one should have a hydrogen atom, the structural determination indicates all the hydrogen atoms are bridging (Miessler, et al, 2014) as observed in borane clusters.…”