Probing Cyanocuprates by Electrospray Ionization Mass Spectrometry

Nov 24, 2010 - While all of these data seemed to support the presence of the suggested Cu(+2)-containing anions, their genesis remained unclear...
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Organometallics 2010, 29, 6841–6842

Probing Cyanocuprates by Electrospray Ionization Mass Spectrometry [Organometallics 2010, 29, 3593.DOI: 10.1021/ om100510w]. Aliaksei Putau and Konrad Koszinowski* In the original version of this article (pages 3597, 3599, and 3600), we reported the observation of the Cu(þ2)-containing cyanocuprates Cu3R3(CN)2- (m/z 412/414/416) and LiCu4R4(CN)3- (m/z 565/567/569) upon analysis of solutions of LinCuRn(CN), R = nBu, sBu, n e 1, in tetrahydrofuran (THF) by anion-mode electrospray ionization (ESI) mass spectrometry. The given assignments were based on the observed m/z ratios, the isotope patterns, and the fragmentation behavior of these species. While all of these data seemed to support the presence of the suggested Cu(þ2)-containing anions, their genesis remained unclear. In the meantime, we have found evidence that ordinary Cu(þ1) ate complexes can react with background water present in the employed ion trap mass spectrometer. We therefore considered the possibility that the alleged Cu(þ2)-containing species might rather correspond to partially hydrolyzed Cu(þ1) ate complexes resulting from unwanted gas-phase reactions of Li2Cu3R3(CN)3- and Li3Cu4R4(CN)4- with water (eqs 1 and 2, respectively). Li2 Cu3 R3 ðCNÞ3 - þ H2 O f Li2 Cu3 R2 ðOHÞðCNÞ3 - þ RH

ð1Þ

Li3 Cu4 R4 ðCNÞ4 - þ H2 O f Li3 Cu4 R3 ðOHÞðCNÞ4 - þ RH

ð2Þ n

s

As the R = Bu, Bu groups are isobaric with Li2(OH)(CN) and do not display marked differences in their isotopic patterns either, a distinction between the originally inferred Cu(þ2)-containing anions on the one hand and partially hydrolyzed Cu(þ1) ate complexes on the other is not possible on the basis of the simple ESI mass spectra alone. The reported fragmentation experiments do not permit an unambiguous distinction either (although the observed loss of Δm = 57 from the ions at m/z 412 and the apparent absence of smaller neutral fragments may seem to argue against the presence of Li2Cu3R2(OH)(CN)3-, for which one might expect the expulsion of LiOH and LiCN as separate entities). To obtain a definitive proof of the identity of the ions in question, we therefore turned to isotopic labeling and performed additional experiments on solutions of Li0.8CuR0.8(13CN), R = nBu, sBu, in THF. Anion-mode ESI mass spectrometric analysis showed the presence of ions at m/z 415/417/419 and 569/571/573, respectively (Figures S1-S4 in the Supporting Information). In comparison to the corresponding unlabeled ions, the labeled ions are shifted by Δm = 3 and 4, respectively. This means that the complexes in question must contain three and four cyanide moieties, respectively, thus establishing their identity as Li2Cu3R2(OH)(CN)3- and

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Organometallics, Vol. 29, No. 24, 2010

Putau and Koszinowski

Li3Cu4R3(OH)(CN)4-. Fragmentation experiments on the labeled ions are fully in line with these assignments (Figures S5-S8 in the Supporting Information and Tables 1 and 2). Table 1. Gas-Phase Fragmentation Reactions of the Mass-Selected n-Butylcuprate Ions in Question parent ion m/z

fragment ion

assignt

412

Li263Cu3nBu2(OH)(CN)3-

415

Li263Cu3nBu2(OH)(13CN)3-

565

Li363Cu4nBu3(OH)(CN)4-

569

Li363Cu4nBu3(OH)(13CN)4-

m/z

assignt

235 266 355 237 267 357 299 388 301 391

Cu2 Bu(CN)263 Cu2nBu2(CN)63 Cu3nBu2(CN)263 Cu2nBu(13CN)263 Cu2nBu2(13CN)63 Cu3nBu2(13CN)2Li63Cu2nBu2(CN)2Li63Cu3nBu2(CN)3Li63Cu2nBu2(13CN)2Li63Cu3nBu2(13CN)363

n

neutral fragment Δm 177 146 57 178 148 58 266 177 268 178

assignt 63

figure

n

Li2 Cu Bu(OH)(CN) Li263Cu(OH)(CN)2 Li2(OH)(CN) Li263CunBu(OH)(13CN) Li263Cu(OH)(13CN)2 Li2(OH)(13CN) Li263Cu2nBu(OH)(CN)2 Li263CunBu(OH)(CN) Li263Cu2nBu(OH)(13CN)2 Li263CunBu(OH)(13CN)

S5

S6

Table 2. Gas-Phase Fragmentation Reactions of the Mass-Selected s-Butylcuprate Ions in Question parent ion m/z

fragment ion

assignt

412

Li263Cu3sBu2(OH)(CN)3-

415

Li263Cu3sBu2(OH)(13CN)3-

565

Li363Cu4sBu3(OH)(CN)4-

569

Li363Cu4sBu3(OH)(13CN)4-

m/z

assignt

235 266 355 237 267 357 299 388 301 391

Cu2 Bu(CN)263 Cu2sBu2(CN)63 Cu3sBu2(CN)263 Cu2sBu(13CN)263 Cu2sBu2(13CN)63 Cu3sBu2(13CN)2Li63Cu2sBu2(CN)2Li63Cu3sBu2(CN)3Li63Cu2sBu2(13CN)2Li63Cu3sBu2(13CN)363

s

neutral fragment Δm 177 146 57 178 148 58 266 177 268 178

assignt

Supporting Information Available: Figures giving mass spectra of Li0.8Cun,sBu0.8(13CN) solutions and mass-selected Li2Cu3n,sBu2(OH)(13CN)3- and Li3Cu4n,sBu3(OH)(13CN)4anions and their fragment ions. This material is available free of charge via the Internet at http://pubs.acs.org.

figure

s

Li2 Cu Bu(OH)(CN) Li263Cu(OH)(CN)2 Li2(OH)(CN) Li263CusBu(OH)(13CN) Li263Cu(OH)(13CN)2 Li2(OH)(13CN) Li263Cu2sBu(OH)(CN)2 Li263CusBu(OH)(CN) Li263Cu2sBu(OH)(13CN)2 Li263CusBu(OH)(13CN)

In summary, the labeling experiments show that the ions in question correspond to the partially hydrolyzed Cu(þ1) ate complexes Li2Cu3R2(OH)(CN)3- and Li3Cu4R3(OH)(CN)4-, R = nBu, sBu, which presumably arise from gasphase reactions with background water (eqs 1 and 2). No evidence for the presence of the originally inferred isobaric Cu(þ2)-containing cuprate anions is found. Note that the original assignments given for all of the other ions are not affected and remain valid.

DOI: 10.1021/om101038t Published on Web 11/24/2010

63

S7

S8