Roger Kanitz

Comparison of electrospray mass spectrometry with other soft ionization techniques for the characterisation of cationic π-hydrocarbon organometallic complexes

Abstract Electrospray (ES) mass spectrometry provides a convenient method for the characterisation of a wide range of π-hydrocarbon complex salts of the general types [FeCp(η-arene)]BF 4 , [M(CO) 3 (η-C 7 H 7 )BF 4 (MCr, Mo, W), [Fe(CO) 2 L ( η 5 -dienyl)]BF 4 L  CO or PPh 3 ; dienyl  C 6 H 7 , 2-MeOC 6 H 6 , or C 7 H 9 ), [CpFe(CO) 3 ] PF 6 and [CpFe(CO) 2 ( η -C 2 H 4 )]BF 4 . At low skimmer voltages (20 V), principal (molecular) ions are generally the only observed species. For the arene complexes, [FeCp( η -arene)]BF 4 , high skimmer voltages (80–135 V) are required before fragmentation is observed. However, for the carbonyl containing cations, moderate skimmer voltages (40–55 V) also give rise to [MCO] + ,[M2CO] + and [M3CO] + ions. Very similar behaviour is observed with phosphonium and imidazolium adducts of the type [Fe(CO) 3 (η 4 -diene. Nuc)] + ( diene  C 6 H 7 or C 7 H 9 ; Nuc PPh 3 or Im) and [CpFe(CO) 2 ( η 1 -C 2 H 4 ·PPh 3 )] + . comparison with fast atom bombardment (FAB) and field desorption (FD) mass spectra for the same complex salts indicates that fragmentation decreases along the series FAB > ES > FD, and that ES mass spectrometry is the most convenient and informative of the three soft ionization techniques.

Synthetic and kinetic studies of the reaction of amino acid esters with tricarbonyl(dienyl)iron cations

Abstract Amino acid esters add rapidly and reversibly to the dienyl iron cations [Fe(CO) 3 (2-XC 6 H 6 )] + ( Ia , X  MeO; Ib , X  H) to give first the cation adducts II and then the neutral adducts III , as follows: [Fe(CO) 3 (XC 6 H 6 )] + ( I ) + H 2 NCH(R)CO 2 ,Et K 1 K −1[Fe(CO) 3 XC 6 H 6 ·NH 2 CH( R)CO 2 Et)] + ( II ) K 1 K − [Fe(CO) 3 XC 6 H 6 · NHCH(R)(CO 2 Et)] ( III ). Results of 1 H NMR spectral studies confirm that the addition of the amino acid esters to the dienyl rings of ( I ) is exo. With the chiral substrate Ia , moderate chiral discrimination occurs in the attack of ( R )-amino acid esters, providing a new route to optically active Ia . Kinetic studies of the reactions reveal the general rate law, Rate = k [Fe][RNH 2 ]; this observation may be rationalized in terms of a mechanism involving the steady-state formation of the intermediate II . Since k 2 [RNH 2 ] can be expected to be >> k −1 (and k −2 negligible), the second-order rate constants k equate with k 1 for the initial ring addition step. The large negative entropies of activation support such a bimolecular process. The data permit amino acid esters to be placed in a quantitative order of nucleophility with some 40 other nucleophiles towards cation Ib .

Electrospray mass spectrometry of neutral π-hydrocarbon organometallic complexes

Electrospray mass spectrometry (ESMS) provides a convenient new technique for the characterisation of neutral [(π-hydrocarbon) M(CO)3] species and related eneone and eneimine complexes which have protonatable sites on their hydrocarbon ligands: At low skimmer voltages (20V) strong [M + H]+ ions are generally observed, even for adducts known to be relatively labile. Progressively higher skimmer voltages cause fragmentation of the parent ions, including sequential loss of the CO ligands. Ferrocene derivatives with protonatable substituents behave similarly. However, ferrocenen and [Cp Fe(C5H4Ph)] instead it [M]−+ base peaks in their ESMS, presumably arising from oxidation to the associated ferricenium cations in the ion source. In contrast, ESMS is not generally useful as a technique for characterising neutral binary metal carbonyls and clusters, except for complexes such as [Fe(CO)5−x(PPh3)x] x = 1,2) containing ligands which provide a site for protonation.

Determination of the relative stabilities of metal-antibiotic and metal-cryptand complexes by electrospray ionisation mass spectrometry

Electrospray ionisation mass spectrometry (ESI-MS) has been used to characterise alkali metal and alkaline earth metal complexes formed in methanol solutions containing one of several synthetic cryptand ligands, or the naturally occurring ionophore valinomycin. The spectra are very simple and easily interpreted, reflecting the gentle nature of the electrospray ionisation process. Mass spectra were also obtained for solutions containing equimolar concentrations of each of the alkali metal ions or alkaline earths, with valinomycin or the cryptands. In each case the intensities of peaks due to metal complexes correlated well with the expected composition of the solution predicted from stability constants obtained by other techniques. These results suggest that ESI-MS will not only prove to be of great benefit for assisting determination of the composition of metal complexes formed in systems of these types, but will also be valuable as a tool for rapidly establishing the metal ion selectivity of new ligands.

Organometallic complexes as reagents in peptide synthesis and modification The masking of peptide bonds by the [Fe(CO)3(C6H7]+ (Fed) group

Abstract The [Fe(CO) 3 (C 6 H 7 ] + (Fed) species provides a novel masking group for peptide bonds in peptide synthesis. Significant advantages include the rapid one-step mode of attachment, and the facile release and quantitative recovery of the Fed masking group.

COMPARISON OF THE REACTIVITY OF CIS-RUCL2(DMSO)4 AND TRANS-RUCL2(DMSO)4 TOWARDS NUCLEOSIDES

Abstract Electrospray ionization mass spectrometry and 1H NMR spectroscopy were used to examine the reactions of cis[RuCl2(DMSO)4] and trans-[RuCl2(DMSO)4] with deoxynucleosides. Both complexes react with 2′-deoxyguanosine to give identical products, two diastereoisomers containing a single nucleoside coordinated to ruthenium, and a bis adduct containing two coordinated nucleosides. Coordination of the nucleoside to ruthenium is via the N-7 atom in each complex. Trans-[RuCl2(DMSO)4] reacts with 2′-deoxyadenosine to give a pair of diastereoisomers in which the nucleosides are coordinated via their N-1 atoms. Cis-[RuCl2(DMSO)4] reacts less extensivley with 2′-deoxyadenosine to give a mixture of products, each of which contains a single 2′-deoxyadenosine ligand coordinate to the metal through the N-1 atom. Trans-[RuCl2(DMSO)4] was found to react only to a small extent with 2′-deoxycytidine under conditions similar to those used for 2′-deoxyguanosine and 2′-deoxyadenosine, and not at all with thymidine, even after prolonged periods. The implications of these results for the mechanisms of antitumour activity of these two complexes are discussed.

Mechanisms of nucleophilic attack at coordinated carbon monoxide: II. Iodide addition to a carbon monoxide ligand in [Fe(CO3 (1–5-η-dienyl)]+ cations (dienyl = C6H7, C7H9, 2-MeOC6H6)

Abstract Nucleophilic addition to a carbonyl ligand has been shown to compete with attack at the metal or dienyl ring in the reactions of [Fe(CO) 3 (1–5-η-dienyl)] + cations with iodide ion. Thus, the novel acyl iodide complex [Fe(CO) 2 (COI)(1–5-η-C 6 H 7 )] is found to be a major product from the reaction of [Fe(CO) 3 (1–5-η-C 6 H 7 )] + with I − in nitromethane or acetone solvents. The other major initial product is the ring adduct [Fe(CO) 3 (1–4-η-IC 6 H 7 )]. Exposure of the acyl iodide species to light causes its rapid decomposition. Analogous behaviour towards I − is shown by the related [Fe(CO) 3 (1–5-η-C 7 H 9 )] + and [Fe(CO) 3 (1–5-η-2-MeOC 6 H 6 )] + cations.

Kinetics of nucleophilic attack on coordinated organic moieties: XXIV. A carbon basicity scale based on the cation [CpFe(CO)2(C2H4)]+☆

Kinetic and equilibrium studies have been carried out for the addition of a wide range of pyridine and phosphorus nucleophiles to the ethene ligand of the cation [CpFe(CO)2(C2H4)]+. Equilibrium constants determined for these reversible processes are proposed as the basis for a general carbon basicity (pKc) scale.

Ether formation on the tridentate Schiff base ligands of copper(II) complexes

A series of copper(II) complexes, CuL·imidazole, where L2− are tridentate Schiff base ligands formed by condensation of salicylaldehyde with a series of amino acids, have been synthesized. Visible spectral data indicate that copper(II) in these complexes are five coordinate in the solid state and in solution. Electrospray mass spectrometry has been used to show how these complexes react in alcohol/NaOH solutions with and without the presence of d-galactose. In the absence of d-galactose where the amino acid in the ligand is serine, the alcohol group on the ligand is converted to its alkyl ether after sonication of the solution for up to 4 h. In the presence of d-galactose, an alkoxy group is added to the ligands except for the ligand containing serine after sonication of the solutions for up to 4 h. At the same time, d-galactose is oxidized to its aldehyde. Where the ligand contains methionine, oxygen is also added to the ligand, most likely to the thioether sulfur. Graphical Abstract

KINETICS OF NUCLEOPHILIC ATTACK ON COORDINATED ORGANIC MOIETIES. PART 31 ADDITION OF IMIDAZOLES TO [Fe(CO)3(1-5-η-DIENYL)]+ CATIONS

Abstract Synthetic and spectroscopic studies show that imidazole, 2-methylimidazole, and 4-methylimidazole (BH) react with the dienyl cations [Fe(CO)3(1-5-η-dienyl)]+ (Ia-Ic; dienyl = C6H7, 2-MeOC6H6, or C7H9) in CH3CN or acetone solvent via the two-step sequence shown below. With N-methylimidazole, which contains no ring N-H group, reaction stops at the monocationic adduct (III). In all cases the rate law, kobs = k1 [amine] is obeyed. This may be rationalised in terms of rate-determining addition (k1) at the dienyl ring to yield (III), followed where applicable by rapid deprotonation (k2) to yield the final neutral adduct (IV). For attack by imidazole, the rate trend is C6H7 > 2-MeOC6H6 > C7H9 (relative rates: 47:4:1), revealing a previous k1 value for cation (Ib) to be erroneous. This rate trend, together with the exo-configuration established for adducts (III), support direct addition (k1) of imidazole from above the dienyl ring. The reactivity order 2-methylimidazole > 4-methylimidazole > N-methylimid...