Mass Spectrometric Study of Some Zirconocene and Hafnocene Dialcoholates Containing a Norbornane Moiety

Abstract

The electron ionization mass spectrometric behaviour of a new series of hafnocene and zirconocene dialcoholates is discussed. Deprotonized norborneol and 3-methyl-2-norbornanemethanol were used as lateral Ligands. These data are also compared to those of mass-analysed ion kinetic energy spectrometry. Fragmentation patterns of the complexes in question give relevant information on their gas-phase behaviour and on an influence of the ligand's structure on decomposition pathways as well.Development of co-ordination chemistry in the gas phase is one of the most promising methods for the solution of a number of problems related to modem techniques.' For example, deposition of inorganic films and powders by thermal decomposition of volatile co-ordination and organometallic compounds is of particular interest as a practical method in research in this area. Such processes, usually referred to as MOCVD processes, allow the generation of functional materials and coatings with a set of predetermined major properties, such as: corrosion, erosion and thermal protection, wear resistance, dielectricity and conductivity?Data about the pathways and mechanisms of thermal dissociation in the precursors used are needed for the further development of MOCVD technologies. In this case, mass spectrometry methods, in particular mass-analysed ion kinetic energy spectroscopy (MIKES), have proven to be the most informative methods and are widely used. They provide an opportunity to follow the rules of fragmentation as it function of the nature of both the central metal atom and the ligands.Organometallic compounds for use in MOCVD processes have to satisfy a set of suitability criteria with high voltatility together with enough thermal stability as principal riter ria.^ From this point of view, complexes of heavy transition metals with bulky mono-or polycyclic shielding ligands drew our special attention recently4 because of a particular interest in zirconium and hafnium oxides and carbides derived from precursors in the gas phase. The possibility of controlling both thermal decomposition passways and the chemical composition of the products obtained by changing the structure of the ligand or the organometallic molecule as a whole prompted us to undertake systematic studies of the mass spectrometric behaviour of a new family of zirconocene and hafnocene dialcoholates. Previously5 we have described the mass spectra of dicyclopentadienylhafnium derivatives, Cp,HfX,,where the X-ligands were deprotonated exo-and endonorborneols. Thus the investigation of analogous zirconium compounds and the related 3-methyl-2-norbornanemethanol derivatives of both Z r and Hf appeared to be expedient.

Fragmentation study of mixed-ligand zirconocene and hafnocene alcoholates of the type Cp2M(OR)Cl

“…A characteristic feature of mass spectra of the complexes under discussion is the presence of very intense peaks for their molecular ions, compared with those of similar dialcoholato derivatives 7,. 8 The relative intensities of these peaks decrease in the order O2Ad > O1Ad > OMAd ∼ OMNBM.…”

“…There is no evidence of M‐Cl bond cleavage at the primary fragmentation step. It is interesting to note that the elimination of the Cp ring is a dominant process for decomposition of the molecular ions of the corresponding dialcoholates 7. This fact could be explained as a result of strengthening of the M‐Cp bond due to electron density redistribution between σ‐and π‐bonded ligands at the central metal atom of the bent metallocene molecule, when chloro ligand substitutes the alcoxo one.…”

“…Previously,1,, 6–9 we have reported the use of sterically hindered shielding ligands as a promising way for tailoring advanced MOCVD precursors of Group 4 metals. A series of their metallocene dialcoholates was prepared and studied by means of mass spectrometry and MIKES.…”

“…Within the context of our search for new prospective MOCVD precursors we synthesised3 a series of zirconocene and hafnocene derivatives with mono‐, bi‐ and tricyclic alcoholato ligands, studied their structures and properties,4,, 5 investigated their fragmentation in the gaseous phase,6–9 and obtained HfO 2 films 10. As a continuation of the above research it was of interest to study several mixed‐ligand metallocene complexes, in which only one chloro ligand was replaced by the alcoholato species.…”