Making the invisible visible: Improved electrospray ion formation of metalloporphyrins/-phthalocyanines by attachment of the formate anion (HCOO)

A protocol is developed for the coordination of the formate anion (HCOO(-)) to neutral metalloporphyrins (Pors) and -phthalocyanines (Pcs) containing divalent metals as a means to improve their ion formation in electrospray ionization (ESI). This method is particularly useful when the oxidation of the neutral metallomacrocycle fails. While focusing on Zn(II)Pors and Zn(II)Pcs, we show that formate is also readily attached to Mn(II), Mg(II) and Co(II)Pcs. However, for the Co(II)Pc secondary reactions can be observed. Upon collision-induced dissociation (CID), Zn(II)Por/Pc·formate supramolecular complexes can undergo the loss of CO2 in combination with transfer of a hydride anion (H(-)) to the zinc metal center. Further dissociation leads to electron transfer and hydrogen atom loss, generating a route to the radical anion of the Zn(II)Por/Pc without the need for electrochemical reduction, although the Zn(II)Por/Pc may have a too low electron affinity to allow electron transfer directly from the formate anion. In addition to single Por molecules, multi Por arrays were successfully analyzed by this method. In this case, multiple addition of formate occurs, giving rise to multiply charged species. In these multi Por arrays, complexation of the formate anion occurs by two surrounding Por units (sandwich). Therefore, the maximum attainment of formate anions in these arrays corresponds to the number of such sandwich complexes rather than the number of porphyrin moieties. The same bonding motif leads to dimers of the composition [(Zn(II)Por/Pc)2·HCOO](-). In these, the formate anion can act as a structural probe, allowing the distinction of isomeric ions with the formate bridging two macrocycles or being attached to a dimer of directly connected macrocycles.


Table of Contents
Pathways to the four different products (a product corresponds here to all molecules with the same mass).Each reactant can react with itself or with the corresponding partner.
The Co-mediated [2+2+2] cycloaddition of a diphenylacetylene leads to hexaphenylbenzene.If a diphenylbutadiyne is used, three acetylene units will remain as spacers.If the reaction mixture contains both, acetylene-and butadiyne-spaced biphenyl, a statistical mixture of all possible isomers will result.

Figure
Figure S2 Negative-ion ESI qTOF mass spectra of a) Mn(II)Pc 3, b) Co(II)Pc 4 and c) Mg(II)Pc 5 with sodium formate in DMF.

Figure S4
Figure S4 Positive-ion ESI MS of tetraphenyl Zn(II)Por 11 in acetonitrile recorded a) with the ESI ion trap (Esquire) and b) with the ESI qTOF (MicrOTOF-Q II) instrument, providing evidence of efficient radical cation formation (oxidation) in both cases.

Figure S5
Figure S5 Positive-ion ESI ion trap mass spectrum of Zn(II)Pc 2 in acetonitrile.The radical cation is is formed in only low abundances.Background signals are more intense than the signal due to the oxidation of 2.

Figure S6
Figure S6 Positive-ion ESI ion trap mass spectrum of the Zn(II)Pc 6 in acetonitrile.Analyte oxidation is absent.

Figure S7
Figure S7 Positive-ion ESI ion trap mass spectra of Zn(II)Por triad 14 (top) and pentad 15 (bottom) in acetonitrile.Only for 15, the formation of the radical cation can be observed in minute amounts.14 does not show any radical cation formation.

Figure S8
Figure S8 Poisitive-ion ESI ion trap mass spectrum of aldehyde-substituted Zn(II)Pc 9 in acetonitrile.Radical cation formation of 9 is not observed (no oxidation).Background signals are more intense than signals due to the analyte.

Figure S10
Figure S10 Negative-ion ESI qTOF mass spectra of a) Zn(II)Pc 2, b) Mn(II)Pc 3, c) Co(II)Pc 4 and d) Mg(II)Pc 5 with sodium formate in DMF.The adducts dissociate via loss of CO2The hydride containing fragment undergoes charge transfer and loss of a neutral hydrogen atom.Only the Mg-phthalocyanine shows an additional signal [5•O2] − , the origin of which has not been examined here.

Figure
Figure S11 CID (MS²) of the oxygen-bridged dimer [3•O•3•HCOO] − , depicting its fragmentation studied with the ion trap and the qTOF instrument.With the ESI ion trap (Esquire), the major dissociation channel is the loss of CO2, accompanied/ followed by the dissociation into monomeric species.Whereas with the ESI qTOF (MicrOTOF-Q II), the major fragment is [3•HCOO] − .