Published: November 08, 2011 r2011 American Chemical Society 14325 dx.doi.org/10.1021/jp2066265 | J. Phys. Chem. A 2011, 115, 14325–14330 ARTICLE pubs.acs.org/JPCA Sensitive Fluorescent Detection and Lewis Basicity of Aliphatic Amines Ivan Pietro Oliveri and Santo Di Bella* Dipartimento di Scienze Chimiche, Universit a di Catania, I-95125 Catania, Italy b S Supporting Information ’ INTRODUCTION Aliphatic amines are widespread compounds in nature. 1 They are also involved in many organic syntheses and catalysis. 2 In this view, the molecular recognition and sensitive optical detection of low-molecular-weight amines 3 is critical in the medical field, in environmental science, in food safety, and in organic chemistry. 4 The most important property of amines is certainly related to their intrinsic Brønsted or Lewis basicity. However, the evalua- tion of basicity in solution is of most importance for their actual properties in solvent media. In particular, the Lewis basicity represents the relevant parameter to predict and rationalize, in terms of basicity, the chemical behavior of amines. 5,6 Tetracoordinated Schiff base Zn II complexes are Lewis acidic species capable of saturating their coordination sphere by coor- dinating a large variety of neutral substrates including nitrogen- based donor Lewis bases, 7 or in their absence, they can be stabilized through intermolecular Zn 333 O axial coordination involving Lewis basic atoms of the ligand framework. 8 Moreover, they possess variegate fluorescent features, related to the struc- ture of the Schiff base template 9 and the axial coordination. 7,10 We have recently demonstrated that some amphiphilic Zn II Schiff base complexes in solution of dichloromethane (DCM) exhibit substantial optical variations and a dramatic enhancement of the fluorescence emission upon addition of a coordinating species. 11 As this process occurs because of the axial coordination to the acidic Zn II ion, it is expected to be selective and sensitive to the Lewis basicity of the coordinating species. In this contribution, we report on the sensitive properties of the Zn II complex, 1, with respect a series of primary, secondary and tertiary aliphatic amines, by changing the steric hindrance of N-alkyl substituents (Scheme 1), through the study of optical absorption and fluorescence changes upon amine coordination to the Lewis acidic Zn II metal center. Various chromogenic 12 and fluorogenic 13 approaches are repor- ted in the literature for the selective detection of aliphatic amines. These approaches are generally based on either Brønsted basicity of amines or formation of guesthost adducts. In our case, detection of investigated amines is based on their actual Lewis basicity in the low-polarity, nonprotogenic, noncoordinating sol- vent medium such as DCM, hence avoiding relevant specific solvation effects. Thus, the calculated binding constants of 1 3 amine adducts can properly be related to the relative Lewis basicity of involved amines. 5,14 ’ EXPERIMENTAL SECTION Materials and General Procedures. The Zn II complex, 1, was synthesized and fully characterized as previously reported. 11 Received: July 12, 2011 Revised: November 8, 2011 ABSTRACT: In this contribution is reported the sensitive properties of the Zn II Schiff base complex, 1, in dichloromethane with respect a series of primary, secondary, and tertiary aliphatic amines through the study of fluorescence enhancement upon amine coordination to the Lewis acidic Zn II metal center with formation of 1:1 adducts. It is found that complex 1 exhibits selectivity and nanomolar sensitivity for primary and alicyclic amines. A distinct selectivity is also observed along the series of secondary or tertiary amines, paralleling the increasing steric hindrance at the nitrogen atom. The binding interaction can be related to the Lewis basicity of the coordinating amine; thus, complex 1 represents a suitable reference Lewis acid, and estimated binding constants within the investigated amine series can be related to their relative Lewis basicity. A relative order of the Lewis basicity can be established for acyclic amines, primary > secondary > tertiary, while an inverted order, tertiary > secondary ≈ primary (acyclic), is found in the case of alicyclic amines. The present approach represents a simple, suitable method to ranking the relative Lewis basicity of aliphatic amines in low-polarity, nonprotogenic solvents.
Transcript
Published: November 08, 2011
r 2011 American Chemical Society 14325 dx.doi.org/10.1021/jp2066265 | J. Phys. Chem. A 2011, 115, 14325–14330
ARTICLE
pubs.acs.org/JPCA
Sensitive Fluorescent Detection and Lewis Basicity of Aliphatic AminesIvan Pietro Oliveri and Santo Di Bella*
Dipartimento di Scienze Chimiche, Universit�a di Catania, I-95125 Catania, Italy
bS Supporting Information
’ INTRODUCTION
Aliphatic amines are widespread compounds in nature.1 Theyare also involved in many organic syntheses and catalysis.2 In thisview, the molecular recognition and sensitive optical detection oflow-molecular-weight amines3 is critical in the medical field, inenvironmental science, in food safety, and in organic chemistry.4
The most important property of amines is certainly related totheir intrinsic Brønsted or Lewis basicity. However, the evalua-tion of basicity in solution is of most importance for their actualproperties in solvent media. In particular, the Lewis basicityrepresents the relevant parameter to predict and rationalize, interms of basicity, the chemical behavior of amines.5,6
Tetracoordinated Schiff base ZnII complexes are Lewis acidicspecies capable of saturating their coordination sphere by coor-dinating a large variety of neutral substrates including nitrogen-based donor Lewis bases,7 or in their absence, they can bestabilized through intermolecular Zn 3 3 3O axial coordinationinvolving Lewis basic atoms of the ligand framework.8 Moreover,they possess variegate fluorescent features, related to the struc-ture of the Schiff base template9 and the axial coordination.7,10
We have recently demonstrated that some amphiphilic ZnII
Schiff base complexes in solution of dichloromethane (DCM)exhibit substantial optical variations and a dramatic enhancementof the fluorescence emission upon addition of a coordinatingspecies.11 As this process occurs because of the axial coordinationto the acidic ZnII ion, it is expected to be selective and sensitive tothe Lewis basicity of the coordinating species.
In this contribution, we report on the sensitive properties ofthe ZnII complex, 1, with respect a series of primary, secondaryand tertiary aliphatic amines, by changing the steric hindrance of
N-alkyl substituents (Scheme 1), through the study of opticalabsorption and fluorescence changes upon amine coordinationto the Lewis acidic ZnII metal center.
Various chromogenic12 and fluorogenic13 approaches are repor-ted in the literature for the selective detection of aliphatic amines.These approaches are generally based on either Brønsted basicityof amines or formation of guest�host adducts. In our case,detection of investigated amines is based on their actual Lewisbasicity in the low-polarity, nonprotogenic, noncoordinating sol-vent medium such as DCM, hence avoiding relevant specificsolvation effects. Thus, the calculated binding constants of 1 3 amineadducts can properly be related to the relative Lewis basicity ofinvolved amines.5,14
’EXPERIMENTAL SECTION
Materials andGeneral Procedures.The ZnII complex, 1, wassynthesized and fully characterized as previously reported.11
Received: July 12, 2011Revised: November 8, 2011
ABSTRACT: In this contribution is reported the sensitive properties of the ZnII
Schiff base complex, 1, in dichloromethane with respect a series of primary,secondary, and tertiary aliphatic amines through the study of fluorescenceenhancement upon amine coordination to the Lewis acidic ZnII metal centerwith formation of 1:1 adducts. It is found that complex 1 exhibits selectivity andnanomolar sensitivity for primary and alicyclic amines. A distinct selectivity isalso observed along the series of secondary or tertiary amines, paralleling theincreasing steric hindrance at the nitrogen atom. The binding interaction can berelated to the Lewis basicity of the coordinating amine; thus, complex 1represents a suitable reference Lewis acid, and estimated binding constantswithin the investigated amine series can be related to their relative Lewis basicity.A relative order of the Lewis basicity can be established for acyclic amines,primary > secondary > tertiary, while an inverted order, tertiary > secondary ≈primary (acyclic), is found in the case of alicyclic amines. The present approach represents a simple, suitable method to ranking therelative Lewis basicity of aliphatic amines in low-polarity, nonprotogenic solvents.
14326 dx.doi.org/10.1021/jp2066265 |J. Phys. Chem. A 2011, 115, 14325–14330
The Journal of Physical Chemistry A ARTICLE
Amines 2�15 (Aldrich) were used without further purifications.Dichloromethane (Aldrich) stabilized with amylene was used toprepare solutions of 1. Fresh prepared DCM solutions of 1,obtained from 1.0 � 10�3 M stock solutions, were used forspectrophotometric and fluorimetric measurements.Measurements. Optical absorption spectra were recorded at
25 �Cwith a Varian Cary 500UV�vis�NIR spectrophotometer.Fluorescence spectra were recorded at 25 �C with a Fluorolog-3(Jobin Yvon Horiba) spectrofluorimeter. Spectrophotometric andfluorimetric titrations were performed with a 1 cm path cell usingDCMsolutions of1. Involved amines inDCMsolutionswere addedto the solution of the complex 1 via a 25 μL Hamilton syringe. Atleast three replicate titrations were performed for each amine. Ineach fluorimetric titration, the wavelength of excitation was chosenin an isosbestic point.Calculation of the Binding Constants.The 1 3 amine binding
constants, K, were calculated from fluorescence titration data bythe nonlinear curve fitting analysis of F versus cp in eq 115
F ¼ F0 þ Flim � F02c0
½c0 þ cp þ 1=K � ½ðc0 þ cp þ 1=KÞ2 � 4c0cp�1=2� ð1Þwhere F0 is the initial fluorescence of the solution having aconcentration c0, F is the fluorescence intensity after addition of agiven amount of amine at a concentration cp, and Flim is thelimiting fluorescence reached in the presence of an excess ofamine (see Supporting Information for further details).Calculation of the Limit of Detection. The LOD was cal-
culated from fluorescence data, according to IUPAC recommenda-tions.16 In particular, it was calculated using eq 2
LOD ¼ K � Sb=S ð2ÞwhereK= 3, Sb is the standard deviation of the blank solution, and Sis the slope of the calibration curve. In our case, because the DCMsolution of 1 gives a fluorescence signal without the presence of theamine, this signal is taken as the blank. Fifteen blank replicates wereconsidered. The calibration curve was obtained from plots of thefluorescence intensity of 1 versus the concentration of the amineadded. Each point is related to themean value obtained from at leastthree replicate measurements (see Supporting Information forfurther details).
’RESULTS AND DISCUSSION
The amphiphilic complex 1 represents a Lewis acidic systemcapable of axially coordinating donor Lewis bases.11 In particular,
the binding interaction between 1 and the involved aminesalways implies formation of 1:1 adducts, as established by Job’splot analysis, 1H NMR spectroscopy, and ESI mass spectrometry(see Supporting Information). Because this process is accom-panied by appreciable optical variations, it can be investigated ona quantitative ground simply by means of spectrophotometricand spectrofluorimetric titrations.
Spectrophotometric and spectrofluorimetric titrations of 10 μMDCM solutions of 1were performed using DCM solutions of theamines 2�15 as titrants. As a representative example, the titra-tion with propylamine, 2, is reported in Figure 1.
Optical absorption spectra upon titration indicate someabsorbance changes in the UV�vis region with the existence ofmultiple isosbestic points and an appreciable increase of theabsorbance (λmax = 557 nm) in the region between 530 and600 nm. Spectrophotometric titrations of all investigated amines(see Supporting Information) show almost identical opticalchanges in the region >330 nm, in terms of intensity, λmax values(Table 1), and isosbestic points, thus indicating that coordina-tion of the amine to the ZnII atom similarly affects the low-lyingelectronic states of 1. Moreover, the existence of multiple isos-bestic points in optical absorption spectra upon titration is inagreement with the formation of defined adducts.
Titration with propylamine is accompanied by an enhance-ment of the fluorescence emission, almost an order of magnitudelarger. Spectrofluorimetric titrations of all investigated amines
Scheme 1. Structure of the Investigated Amines
Figure 1. UV�vis absorption (top) and fluorescence (bottom) (λexc =467 nm) titration curves of 1 (10 μM solution in DCM) with theaddition of propylamine. The concentration of propylamine addedvaried from 0 to 12.0 μM. (Inset) Variation of the fluorescence intensityat 600 nm as a function of the concentration of propylamine added. Thesolid line represents the curve fitting analysis with eq 1.
14327 dx.doi.org/10.1021/jp2066265 |J. Phys. Chem. A 2011, 115, 14325–14330
The Journal of Physical Chemistry A ARTICLE
(see Supporting Information) involve rather constant fluores-cence emission λmax values (Table 1), independent from theexcitation wavelength, and almost the same fluorescence en-hancement upon reaching of the saturation point. Analogously tooptical absorption data, the almost constant fluorescence λmax
values upon formation of 1 3 amine adducts indicate that the sameexcited electronic state is involved for all of the investigatedaliphatic amines.
Although both optical absorption and fluorescence emissionchanges can be easily detected upon titration of 1 with theinvolved amines, we have chosen the latter observable because ofthe higher sensitivity of detection.17 Thus, fluorescence titrationdata are used to calculate the limit of detection16 (LOD) of 1 forthe investigated aliphatic amines and, eventually, to explore itsselective sensing. Moreover, as we are interested to variations of1 3 amine binding constants along the considered series, ratherthan in their absolute values, we have estimated them from
fluorescence titration data by the nonlinear curve fitting analysisof fluorescence intensity versus amine concentration.15 Relevantoptical absorption and fluorescence emission data, calculatedbinding constants, and LODs are collected in Table 1.
On the basis of above considerations, formation of defined 1:1Lewis acid�base adducts whose optical properties are almostindependent by the nature of the base complex 1 represents asuitable reference Lewis acid, and the observed variations ofestimated binding constants within the investigated amine seriescan be properly related to their relative Lewis basicity.5,14 Thecalculated binding constants for 1 3 amine adducts span overseveral orders of magnitude (Table 1, Figure 2). In particular,while binding constants are almost invariable along primaryamines, exhibiting the largest values among the consideredacyclic species, they show a distinct decrease along the series ofsecondary or tertiary amines, strictly related to the increasingsteric hindrance at the nitrogen amine atom. In line with thisview, the alicyclic piperidine, 10, having a low steric hindrancewithin the series of secondary amines, possesses a binding con-stant comparable to that of the ethylmethylamine, 6, the latterof which is the least sterically encumbered species within theseries secondary acyclic amines. Analogously, quinuclidine, 15,representing the least sterically encumbered tertiary amine,18
exhibits the largest binding constant value, even with respectprimary amines (Table 1). Moreover, from calculated bindingconstants, a relative order, primary > secondary > tertiary, isfound for amines having an analogous N-alkyl chain, especiallyfor those with more branched N-alkyls (e.g., 5, 9, 14), whilea leveling effect is observed for amines with linear N-alkyls(e.g., 2, 6, 11).
Overall, these data indicate a relative order of the Lewisbasicity for acyclic amines, primary > secondary > tertiary, ac-cording to the relative enthalpies of formation for amineboraneadducts with a series of primary, secondary, and tertiary amines19
or to the relative basicity deduced by competition experimentsusing B(Me)3 as a reference acid,
20 although gas-phase basicitiesindicate the opposite.21,22 This order is however inverted, tertiary> secondary ≈ primary (acyclic), in the case of alicyclic amines.Thus, it turns out that the Lewis basicity of aliphatic amines withrespect to the reference Lewis acid 1 is dominated by steric effectsand can be attributed to poorer overlap of orbitals because of theadditional steric constraints in the case of more encumberedspecies.23 In fact, the less sterically crowded primary amines showthe highest, almost unchanging, binding constants. Alicyclicamines, possessing a reduced sterical hindrance, exhibit the largerbinding constant values.
Unfortunately, the relevant Lewis basicity scales reported inthe literature5,6 include just very few aliphatic amines, thusprecluding any useful comparison with present data. A possibilityof comparison is, however, offered by a scale of hydrogen bondbasicity, involving 4-fluorophenol as a reference acid, developedby Graton et al.,24 which includes most of the present investi-gated aliphatic amines, although the resulting hydrogen-bondedcomplexes can be considered as a special case of Lewis acid�baseinteractions.5 The comparison of the present Gibbs energy forthe 1 3 amine adducts with that for hydrogen-bonded complexesis reported in Figure 3. It shows a roughly linear correlation, withthe Gibbs energy for the 1 3 amine adducts approximately twicethan that found for hydrogen-bonded complexes, thus indicatinga stronger acid�base interaction in the former case. A divergenceof this rough linearity is observed in the case of diisopropylamine,8, representing one of the most encumbered species among the
Table 1. Optical Absorption and Fluorescence EmissionMaxima, Binding Constants, and Limits of Detection forthe 1 3Amine Adducts
15, quinuclidine 558 600 6.9 ( 0.3 0.19 (21)aValues in parentheses refer to LOD values in (μg L�1).
Figure 2. Profile of the calculated binding constants for the investigatedamines.
14328 dx.doi.org/10.1021/jp2066265 |J. Phys. Chem. A 2011, 115, 14325–14330
The Journal of Physical Chemistry A ARTICLE
amines involved in this comparison. This further indicates themajor role of the steric hindrance on the stability of 1 3 amineadducts and, hence, on the relative Lewis basicity.
Present results are in full agreement with the relative Lewisbasicities of aliphatic amines deduced from spectrophotometrictitrations using complex 1 as a reference acid and a least-squaresnonlinear regression of multiwavelength spectrophotometricdata.14
The plots of the relative fluorescence change versus the amineconcentration, in the micromolar range, can be related to theselectivity of 1 with respect to the investigated amines. Asexpected, 1 is not selective within primary amines, according tothe aforementioned almost identical estimated binding con-stants. In contrast, a distinct selectivity is observed along theseries of secondary or tertiary amines and parallels the increasingsteric hindrance at the nitrogen atom (Figures 4 and 5).
Thus, among the secondary amines 6�10, piperidine andethylmethylamine can selectively be detected with respect to theremaining amine series. This can be easily verified by competitiveexperiments. For example, fluorimetric titrations of 1 with piper-idine performed with and without the presence of an equimolarconcentration of diisopropylamine indicate negligible variationsof fluorescence intensity (see Supporting Information, FigureS8). To observe an analogous fluorescence response to that ofpiperidine, it needs a concentration of diisopropylamine morethan 2 orders of magnitude larger (see Supporting Information,Figure S9). Analogously, quinuclidine and dimethylethylaminecan selectively be detected with respect to any other moresterically encumbered tertiary amine, as can be also easily verified bycompetitive titration experiments. Again, to observe an analogousfluorescence response to that of quinuclidine or dimethylethylamine,
it needs, for example, a concentration of triisopropylamine about600 times larger, while for triethylamine, a concentration 50times larger is required.
Selectivity of 1 becomes also evident upon comparing thefluorescence response, again in the micromolar range, of primaryversus secondary and tertiary acyclic amines having an analogousN-alkyl chain (Figure 6).
For example, within the amines 4, 8, and 13, to observe ananalogous fluorescence response to that of isopropylamine, itneeds a concentration of diisopropylamine more than 1 order ofmagnitude larger, while for triisopropylamine, a concentrationalmost 2 orders of magnitude larger is required. Therefore,except for the secondary and tertiary linear N-alkyl amines, 6and 11, primary amines can selectively be detected over acyclicsecondary and tertiary amines, especially those with branchedN-alkyl chains.
The limit of detection of a 10 μM DCM solution of 1,calculated according to IUPAC recommendations,16 indicatesvery low values for the series of investigated amines, falling intothe nanomolar range for primary and alicyclic amines (Table 1).Thus, complex 1 is useful for fast detection in solutions of low-polarity solvents of primary and alicyclic amines in the range oftrace amounts (μg L�1). For secondary and tertiary amines, evenif LOD values are definitely higher, they again evidence anappreciable sensitivity of 1 for all involved amines.
The sensitivity of complex 1 for primary and alicyclic aminesexceeds that reported in the literature for the selective chro-mogenic12a,b,f or fluorogenic13a�c,h detection of aliphatic amines,rivaling that reported for fluorescent sensors of aliphatic aminesin traces.25
Figure 3. Comparison of the Lewis basicity for 1 3 amine adductsand the 4-fluorophenol Lewis basicity. 4-Fluorophenol data in CCl4are from ref 24.
Figure 4. Plots of the relative fluorescence changes versus the concen-tration of the secondary amines 6�10 in DCM added to 1 (10 μMsolution in DCM), monitored at 600 nm.
Figure 5. Plots of the relative fluorescence changes versus the concen-tration of the tertiary amines 11�15 in DCM added to 1 (10 μMsolution in DCM), monitored at 600 nm.
Figure 6. Plots of the relative fluorescence changes versus the concen-tration of the amines 4, 8, and 13 in DCM added to 1 (10 μMsolution inDCM), monitored at 600 nm.
14329 dx.doi.org/10.1021/jp2066265 |J. Phys. Chem. A 2011, 115, 14325–14330
The Journal of Physical Chemistry A ARTICLE
Preliminary data suggest that complex 1 can potentially beapplied for the detection of amines even in aqueous solutions.However, given the insolubility of 1 in water, a two-phase(DCM/H2O) system should be used. Thus, the addition ofdefined amounts of amine in aqueous solution to a DCM solu-tion of 1 produces a fluorescence response that can be com-pared to that achieved for addition of the same mole amounts ofamine in DCM (see Supporting Information, Figure S10).
’CONCLUSIONS
In this contribution, we have successfully developed a sensitivefluorescent probe for aliphatic amines, which exhibits fluores-cence enhancement upon formation of 1:1 supramolecular ad-ducts. It is found that complex 1 shows selectivity and nanomolarsensitivity for primary and alicyclic amines. Moreover, a distinctselectivity is also observed along the series of secondary ortertiary amines, paralleling the increasing steric hindrance atthe nitrogen atom.
Because complex 1 represents a suitable reference Lewis acid,the observed variations of estimated binding constants within theinvestigated amine series can be properly related to their relativeLewis basicity. Thus, present results indicate a relative order ofthe Lewis base strength for acyclic amines, primary > secondary >tertiary. This order is however inverted, tertiary > secondary ≈primary (acyclic), in the case of alicyclic amines, thus indicating amajor role of the steric hindrance on the stability of 1 3 amineadducts and, hence, on the relative Lewis basicity. These findingsare in agreement with available literature data. Therefore, thepresent approach represents a simple, suitable method to rankingthe relative Lewis basicity of aliphatic amines in low-polarity,nonprotogenic solvents.
’ASSOCIATED CONTENT
bS Supporting Information. Job’s plot analysis, ESI massspectrometry, and 1H NMR data for 1 3 amine adducts. Addi-tional spectrophotometric and spectrofluorimetric titrations.Calculation of the binding constants and the detection limits.Preliminary studies in DCM/H2O. This material is available freeof charge via the Internet at http://pubs.acs.org.
We gratefully thank Prof. G. Maccarrone (Universit�a diCatania) for useful comments and suggestions. This researchwas supported by the MIUR and PRA (Progetti di Ricerca diAteneo).
’REFERENCES
(1) See, for example:Lawrence, S. A. Amines: Synthesis, Properties andApplications; University Press: Cambridge, U.K., 2004.(2) See, for example: (a) Song, C. E. Cinchona Alkaloids in Synthesis
& Catalysis: Ligands, Immobilization and Organocatalysis; Wiley-VCH:Weinheim, Germany, 2009. (b) Nugent, T. C. Chiral Amine Synthesis;Wiley-VCH: Weinheim, Germany, 2010. (c) France, S.; Guerin, D. J.;Miller, S. J.; Lectka, T. Chem. Rev. 2003, 103, 2985–3012.
(3) Selected general reviews:(a) Mohr, G. J. Anal. Bioanal. Chem.2006, 386, 1201–1214. (b) Wright, A. T.; Anslyn, E. V. Chem. Soc. Rev.2006, 35, 14–28.
(4) Selected general reviews:(a) Al Bulushi, I.; Poole, S.; Deeth,H. C.; Dykes, G. A.Crit. Rev. Food Sci. Nutr. 2009, 49, 369–377. (b) Silva,P. J.; Erupe, M. E.; Price, D.; Elias, J.; Malloy, Q. G. J.; Li, Q.; Warren, B.;Cocker,D.R., III.Environ. Sci. Technol.2008,42, 4689–4696. (c)Ruiz-Capillas,C.; Jimenez-Colmenero, F. Crit. Rev. Food Sci. Nutr. 2004, 44, 489–499.(d) Schipper, R. G.; Penning, L. C.; Verhofstad, A. A. J. Semin. Cancer Biol.2000, 10, 55–68. (e) Greim, H.; Bury, D.; Klimisch, H.-J.; Oeben-Negele, M.;Ziegler-Skylakakis, K. Chemosphere 1998, 36, 271–295.
(5) (a) Laurence, C.; Gal, J.-F. Lewis Basicity and Affinity Scale: Dataand Measurements; Wiley: Chichester, U.K., 2010. (b) Laurence, C.;Graton, J.; Gal, J.-F. J. Chem. Educ. 2011, 88, 1651.
(6) (a) Maria, P. C.; Gal, J.-F. J. Phys. Chem. 1985, 89, 1296–1304.(b) Laurence, C.; Queignec-Cabanetos, M.; Dziembowska, T.; Queignec,R.; Wojtkowiak, B. J. Am. Chem. Soc. 1981, 103, 2567–2573. (c) Jensen,W. B. Chem. Rev. 1978, 78, 1–22.
(7) (a) Escudero-Ad�an, E. C.; Benet-Buchholz, J.; Kleij, A. W. Inorg.Chem. 2008, 47, 4256–4263. (b) Germain, M. E.; Knapp, M. J. J. Am.Chem. Soc. 2008, 130, 5422–5423. (c) Germain, M. E.; Vargo, T. R.;Khalifah, G. P.; Knapp, M. J. Inorg. Chem. 2007, 46, 4422–4429. (d)Dalla Cort, A.; Mandolini, L.; Pasquini, C.; Rissanen, K.; Russo, L.;Schiaffino, L. New J. Chem. 2007, 31, 1633–1638. (e) Ma, C. T. L.;MacLachlan, M. J. Angew. Chem., Int. Ed. 2005, 44, 4178–4182. (f)Consiglio, G.; Failla, S.; Finocchiaro, P.; Oliveri, I. P.; Di Bella, S. DaltonTrans. 2011, DOI: 10.1039/C1DT11295C.
(8) A recent general review:Kleij, A. W. Dalton Trans. 2009,4635–4639.
(9) (a) Liuzzo, V.; Oberhauser, W.; Pucci, A. Inorg. Chem. Commun.2010, 13, 686–688. (b) Bhattacharjee, C. R.; Das, G.; Mondal, P.; Rao,N. V. S. Polyhedron 2010, 29, 3089–3096. (c) Kuo, K.-L.; Huang, C.-C.;Lin, Y.-C. Dalton Trans. 2008, 3889–3898. (d) Son, H.-J.; Han, W.-S.;Chun, J.-Y.; Kang, B.-K.; Kwon, S.-N.; Ko, J.; Han, S. J.; Lee, C.; Kim,S. J.; Kang, S. O. Inorg. Chem. 2008, 47, 5666–5676. (e) Lin, H.-C.;Huang, C.-C.; Shi, C.-H.; Liao, Y.-H.; Chen, C.-C.; Lin, Y.-C.; Liu, Y.-H.Dalton Trans. 2007, 781–791. (f) Di Bella, S.; Leonardi, N.; Consiglio,G.; Sortino, S.; Fragal�a, I. Eur. J. Inorg. Chem. 2004, 4561–4565. (g) Ma,C.; Lo, A.; Abdolmaleki, A.; MacLachlan, M. J. Org. Lett. 2004,6, 3841–3844. (h) Chang, K.-H.; Huang, C.-C.; Liu, Y.-H.; Hu, Y.-H.;Chou, P.-T.; Lin, Y.-C.Dalton Trans. 2004, 1731–1738. (i) La Deda, M.;Ghedini, M.; Aiello, I.; Grisolia, A. Chem. Lett. 2004, 33, 1060–1061.(j) Wang, P.; Hong, Z.; Xie, Z.; Tong, S.; Wong, O.; Lee, C.-C.; Wong,N.; Hung, L.; Lee, S. Chem. Commun. 2003, 1664–1665.
(10) (a) Di Bella, S.; Consiglio, G.; Sortino, S.; Giancane, G.; Valli, L.Eur. J. Inorg. Chem. 2008, 5228–5234. (b) Di Bella, S.; Consiglio, G.;La Spina, G.; Oliva, C.; Cricenti, A. J. Chem. Phys. 2008, 129, 114704.(c) Oliveri, I. P.; Failla, S.; Malandrino, G.; Di Bella, S. New J. Chem.2011, 35, 2826–2831.
(11) (a) Consiglio, G.; Failla, S.; Finocchiaro, P.; Oliveri, I. P.;Purrello, R.; Di Bella, S. Inorg. Chem. 2010, 49, 5134–5142. (b) Consiglio,G.; Failla, S.; Oliveri, I. P.; Purrello, R.; Di Bella, S. Dalton Trans.2009, 10426–10428.
(12) Selected recent examples:(a)Ajayakumar,M.R.;Mukhopadhyay,P. Chem. Commun. 2009, 3702–3704. (b) Montes-Navajas, P.; Baumes,L. A.; Corma, A.; Garcia, H. Tetrahedron Lett. 2009, 50, 2301–2304. (c) Reinert, S.; Mohr, G. J. Chem. Commun. 2008, 2272–2274.(d) Jung, J. H.; Lee, H. Y.; Jung, S. H.; Lee, S. J.; Sakata, Y.; Kaneda, T.Tetrahedron 2008, 64, 6705–6710. (e) Kim, J. S.; Lee, S. J.; Jung,J. H; Hwang, I.-C.; Singh, N. J.; Kim, S. K.; Lee, S. H.; Kim, H. J.; Keum,C. S.; Lee, J. W.; Kim, K. S. Chem.—Eur. J. 2007, 13, 3082–3088.(f) Nelson, T. L.; O’Sullivan, C.; Greene, N. T.; Maynor, M. S.;Lavigne, J. J. J. Am. Chem. Soc. 2006, 128, 5640–5641. (g) Basurto,S.; Torroba, T.; Comes, M.; Martínez-M�a�nez, R.; Sancen�on, F.;Villaescusa, L.; Amor�os, P.Org. Lett. 2005, 7, 5469–5472. (h) Comes,M.; Marcos, M. D.; Martínez-M�a�nez, R.; Sancen�on, F.; Soto, J.;Villaescusa, L. A.; Amor�os, P.; Beltr�an, D. Adv. Mater. 2004, 16,1773–1786.
14330 dx.doi.org/10.1021/jp2066265 |J. Phys. Chem. A 2011, 115, 14325–14330
The Journal of Physical Chemistry A ARTICLE
(13) (a) C€orstern, S.; Morh, G. J. Chem.—Eur. J. 2011, 17, 969–975.(b) McGrier, P. L.; Solntsev, K. M.; Miao, S.; Tolbert, L. M.; Miranda,O. R.; Rotello, V. M.; Bunz, U. H. F. Chem.—Eur. J. 2008, 14, 4503–4510. (c) García-Acosta, B.; Comes, M.; Bricks, J. L.; Kudinova, M. A.;Kurdyukov, V. V.; Tolmachev, A. I.; Descalzo, A. B.; Marcos, M. D.;Martínez-M�a�nez, R.; Moreno, A.; Sancen�on, F.; Soto, J.; Villaescusa,L. A.; Rurack, K.; Barat, J. M.; Escriche, I.; Amor�os, P. Chem. Commun.2006, 2239–2241. (d) Lu, G.; Grossman, J. E.; Lambert, J. B. J. Org.Chem. 2006, 71, 1769–1776. (e) Chung, Y. M.; Raman, B.; Ahn, K. H.Tetrahedron 2006, 62, 11645–11651. (f) Secor, K.; Plante, J.; Avetta, C.;Glass, T. J. Mater. Chem. 2005, 15, 4073–4077. (g) Secor, K. E.; Glass,T. E. Org. Lett. 2004, 6, 3727–3730. (h) Fabbrizzi, L.; Francese, G.;Licchelli, M.; Perotti, A.; Taglietti, A. Chem. Commun. 1997, 581–582.(14) Oliveri, I. P.; Maccarrone, G.; Di Bella, S. J. Org. Chem. 2011,
76, 8879–8884.(15) Bourson, J.; Pouget, J.; Valeur, B. J. Phys. Chem. 1993, 97,
4552–4557.(16) See, for example:(a) Currie, L. A. Anal. Chim. Acta 1999,
D. N.; Crego-Calama, M. Chem. Soc. Rev. 2007, 36, 993–1017. (b) Bell,T. W.; Hext, N. M. Chem. Soc. Rev. 2004, 33, 589–598.(18) Wann, D. A.; Blockhuys, F.; Van Alsenoy, C.; Robertson, H. E.;
Himmel, H.-J.; Tang, C. Y.; Cowley, A. R; Downs, A. J.; Rankin, D.W. H.Dalton Trans. 2007, 1687–1696.(19) Flores-Segura, H.; Torres, L. A. Struct. Chem. 1997, 8, 227–232.(20) Brown, H. C. J. Am. Chem. Soc. 1945, 67, 1452–1455.(21) As can be deduced by the first ionization energy22 or by the
proton affinity5 of relevant aliphatic amines.(22) (a) Noffsinger, J. B.; Danielson, N. D. Anal. Chem. 1987,
59, 865–868. (b) Campbell, S.; Beauchamp, J, L.; Rembe,M.; Lichtenberger,D. L. Int. J. Mass Spectrom. Ion Processes 1992, 117, 83–99.(23) Staubitz, A.; Robertson, A. P. M.; Sloan, M. E.; Manners, I.
Chem. Rev. 2010, 110, 4023–4078.(24) Graton, J.; Berthelot, M.; Besseau, F.; Laurence, C. J. Org. Chem.
2005, 70, 7892–7901.(25) See, for example:(a) Takagai, Y.; Nojiri, Y.; Takase, T.; Hinze,
W. L.; Butsugan, M.; Igarashi, S. Analyst 2010, 135, 1417–1425. (b) Bao,B.; Yuwen, L.; Zheng, X.; Weng, L.; Zhu, X.; Zhan, X.; Wang, L. J. Mater.Chem. 2010, 20, 9628–9634.
