Mass spectra of polyazamacrocycles containing pyridine or 2,2′-dipyridine subunits

ORGANIC MASS SPECTROMETRY, VOL. 23, 859-860 (1988)

New Mass Spectra Mass Speetra of Polyammacrocycles Containing Pyridine or 2,2'-Dipyridine Subunits

pounds. Although mass spectral studies of 2,6-pyridino-containing macrocyclic polyethers have been reported?' no relevant mass spectral data are currently available for the related azacrown analogues. While the EI mass spectra of their immediate N-tosyl precursors (R = Ts) are of little assistance for structural assignment, owing to the absence of a molecular ion even at low voltage, deprotected polyamino macrocycles 1-6 give goodquality EI mass spectra, which are analytically useful to establish firmly their ring sizes. The mass spectrum of N , N , N trimethyl-2,11,20-triaza[3.3.3](2,6)pyridinophane (4), typical of this series, is reported in Fig. 1. The general rationale for the EI-induced mass spectral fragmentation of 1-6 is shown in Scheme 1. Selected ions and their relative abundances are listed in Table 1. The majority of fragment ions present in the spectra of 1-6, whose formation involves the breaking of at least two bonds, have been interpreted by assuming an EI-induced skeletal rearrangement of the molecular ion to the open-chain aldimino structure, shown in Scheme 1, prior to fragmentation. This process may proceed via a six-membered cyclic transition state (McLafferty rearrangement) by a methylene hydrogen transfer to the adjacent pyridine or dipyridine nitrogen. The rearranged molecular ion might subsequently undergo fl and /?' fissions of the bridging chain(s) to produce the relatively intense fragment ions a-h. Ion h constitutes the base peak in 4, and occurs with good intensity in 2. The mass spectra of the compounds investigated are also characterized by the presence of prominent peaks, associated with structures i, j and k (only for m = 2), which may arise from the molecular ion in the open-chain form by hydrogentransfer mechanisms quite similar to that already described. Ion i attains the base peak in compounds 1, 2, 5 and 6, while ions j and k are among the most intense peaks in the spectra of 1-6 (Table 1 and Fig. 1). The low-resolution mass spectra were recorded on a Kratos MS 50 double-focusing mass spectrometer at 18 eV using the direct insertion technique at a source temperature of 250 "C.

Macrocycles 1-6, containing (2,6)-pyridino (n = 0) or (6,6)2,T-dipyridino (n = 1) subunits connected by CH,N(R)CH, linkages, have recently been synthesized as potential ligands for the complexation of both inorganic and organic cations.' In continuation of our studies on the mass spectra of acyclic and cyclic multidentate ligands incorporating N-heterocyclic subunit^,^.^ we took the opportunity to study the electron impact (EI) mass spectral fragmentation pattern of these com-

n

m

R

1

O

1

H

2

0

2

H

3

0

1

CH,

4

0

2

CH,

5

1

1

H

6

1

1

CH,

~~~

Table 1. Selected ions in the 18 eV EI mass spectra of compounds 1-6" Ion

M+' [M - R]+ a

b C

d e f g h I

i k a

2

3

4

360 (17) 359 (1) 254 (7) 106 (18) 239 (25) 121 (88) 225 (23) 134 (37) 119 (9) 241 (57) 107 (100) 120 (70) 227 (45)

268 (12) 253 (8) 162 (46) 106 (43) 133 (30)b 135 (58)

402 (13) 387 (2) 296 (6) 106 (28) 267 (4) 135 (81) 253 (16) 162 (36) 133 (16) 269 (100) 107 (52) 134 (82) 241 (84)

1

240 (88) 239 (35) 134 (47) 106 (34) 119 (20) 121 (60)

107 (100) 120 (89)

107 (57) 134 (66)

6

6

394 (12) 393 (1) 211 (17) 183 (18) 196 (7) 198 (29)

422 (43) 407 (10) 239 (55) 183 (28) 210 (13) 212 (39)

184 (100) 197 (43)

184 (100) 211 (66)

Relative intensities in parentheses. The loss of H from this fragment gives the ion at m/z 132, which is the base peak in the spectrum.

0030-493X/88/120859-02 $05.00 0 1988 by John Wiley & Sons, Ltd.

Received 14 March 1988 Accepted (revised) 6 M a y 1988

NEW MASS SPECTRA

860

H

k

H

Scheme 1

8

100

1

134

141

i l

107

80

I 269

120

160

200

240

280

320

360

400

m/z Figure 1. The 18 eV El mass spectrum of compound 4.

We are grateful to the Italian Ministry of Education for partial support of this work. FRANCESCO BOTTINO and SEBASTIANO PAPPALARDO Dipartjmanto di Scienze Chimiche, Universita di Catania, Viale A. Doria 8,95125 Catania, Italy.

ANTONINO MAMO Istituto Chimico, Facolta di Ingegneria, Universita di Catania, Viale A. Doria 6,95125 Catania, Italy.

References 1. F. Bottino, M . Di Grazia, P. Finocchiaro, F. R. Fronczek, A. Mamo and S. Pappalardo. J. Org. Chem., 53,3521 (1988). 2. G. R. Newkome, V. K. Gupta and S. Pappalardo, Org. Mass Specfrom. 19, 590 (1 984). 3. S. Pappalardo and S. Occhipinti, Org. Mass Spectrom. 22, 269 (1987). 4. R. R. Whitney and D. A. Jaeger, Org. Mass Spectrom. 15, 343 (1 980). 5. S. N. Chen, M. L. Wang, S. C. Chen, Z. 2. Jing, C. T. Wu, X. L. Wang and M . A. Baldwin, Org. Mass Spectrom. 22, 633 (1987).