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Steric and electronic effects in the mass spectra of Schiff base complexes
International
.TournaCof Mass
Spectrometry
and Zon Physics
63
Elsevier Publishing Company, Amsterdam. Printed in the Netherlands
STERIC
AND
SCHIFF
BASE COMPLEXES
F.
3.
ELECTRONIC
EFFECTS
THE
MASS
SPECTRA
OF
PRESTON**
Imtiitlte for Atomic Research,
Iowa State
Unirersity,
W.
KNOX,
1.
T.
FLANNIGAN,
Unkersity AND
IN
FL
University
G.
of Strathciyde, I.
R.
Glasgow
P.
Ames,
Zowa 5OOZO (U.S.A.)
PAUSON
(Scotland)
REED
of Glasgow
(Scotlonri)
(Received February IZth, 1969; in revised form April 17th, 1969)
ABSTRACT
-Mass spectrometric
stl-ldies of complexes
formed
by the reaction
of Schiff
bases of aromatic aldehydes and ketones with enneacarbonyldi-iron show characteristic fragmentation patterns. Changes in the mass spectra as a result of varying substituents at specific positions on the organic ligand are discussed in terms of their steric and electronic origins.
INTRODUCTION
In a previous communication’ a report was given on the structural features of complexes (I) (Fig. I) formed by the reaction of enneacarbonyldi-iron with the SchiZ bases of arcmatic aldehydes and ketones, and a discussion of the features of the mass spectrum of I(a). In general under electron impact all complexes of structural type (I) show stepwise elimination of all six carbonyl units from the parent ion (P’). Further fragmentation of the (P-KO) ion is characterized by loss of either a benzene molecule or 2.n iron atom followed by a benzene or hydrogen cyanide molecule. IabelIing experiments’ show that the aromatic ring involved in the elimination of * Work was performed in part in the Ames Laboratory of the U. S. Atomic EnergyComxnis-
sion. Contribution No. 2X%
** To whom all ccrrrespondence should be zddressed. Znr. .T. _MzssSpecrrom. Ion Phys., 3 (1969) 63-63
F. J. PRESTON
64
et al.
I
R,=h
,R2=H
*
‘13 m =c&
%,-II
.Rz=He
.
R3 - W-
Rt
-
H
RI
.
ct.
a) ‘0’ -e-k.
=il-n
R3 = c&
R2 = C&.
it2 - ‘!
. 33 - C&
Rt-H
*
R,
-
Fi,
. Rz -
RI
-
H
. R2’n
R3 - w.5
.Rj-CgW?~
-112-q
H
. “3
-
‘#+s
,R;=tk
Fig. I. Structuresof Schiff base compIexes.
ion is the N-phenyI ring with concomitant benzene (R,H) from ithe (PACO)’ removal of one hydrogen atom from the methylene bridge. The similar process from ‘Se (P-KO-Fe)” ion, however, involves the aromatic ring directly bonded to iron, i.e. elimination of R,C,& a fact more in keeping with the B-bond fission occurring with compounds of ten&e& nitrogen’. The general framentation scheme for compIexes (I) is given in Fi g. 2. It is now our purpose to discus further studies on com?Iexes Teefated to these previously discussed’, but having varying substituents in position R, , R,, and R,.
(P-6CO)*
I
-R&N
Fig. 2. Gend
fhgmentzttion scheme for S&X
base uxnpIexs.
MASS
SPECTRA
OF SCHIFF
BASE
65
COMPLEXES
DISCUSSION
Substitution of one methylene hydrogen at R, by methyl (I(b)) leaves the two main fragmentation routes from the (P-SCO)’ ion unchanged, hydrogen cyanide elimination being replaced, of course, by that of methyl cyanide (see Fig. 2). In addition, hcwever, precise mass masurement of the ion at nz/c 281 shows it to arise by loss of an acetylene molecule from the (P-6CO)’ ion. In order to clarify this process the complex I(R, = H, R, = CD,, R3 = CsHs) was synthesized with the intention of differentiating between acetylene abstraction from the bridge system and that from one of the aromatic rings. Benzene loses acetylene from a butadienyl acetylene type parent ion3, and a similar possibility existed here. The labelled complex could not be prepared in very high isotopic purity (R,: CH, = 32 %, CH,D = 33 %, CHD, = 23 %_ CD, = 12 %) but was considered sticient for the experiment. The deuterium isotope incorporation was verified by low voltage mass spectrometry. That negligible scrambling of deuterium had occurred was also verified by him in the methyl region of the spectrum. Calculations made on the basis of these isotopic concentrations and making no allowances for isotopic effects showed that the expected ratios of abundances of nzje 281:282 : 283 should be 2.00 : 1.20 : 1 if acetylene were eliminated entirely from the methlyene group and its substituent R2 with concomitant transfer of 2H, DH or Dz to the remaining daughter ion as in Fig. 3. Experimental measurements, making corrections for 13C, 5”Fe, and 57Fe contributions give values of 1.99 : 1.25 : 1 in extremely good agreement with the theoretical values, and define the fragmentation route as given in Fig. 3. Such a rearrangement could result in formation of a G-X complex ion, a structure which has already been shown to be very stable in similar systemr?. It has been stated previously
ASJNLYLNCE
m/e
203
m/e
262
that the methylene
m!e
bridge hydrogens
of I(a)
261
THEORETICAL
1.0
1.20
2.00
EXPERIMENTAL
I.0
1.25
I.99
-CH*CH
CP-6COl* m/e
307
Fig. 3. Mechanism of acetylene
m/e
261
abstraction front (P-KO)+. IlIt. J. Mass Spectrom. ion Phys., 3 (1969) 63-69
66
F. 3. PRESTON
et ai.
play a large r&e in eiimination of benzene from the (P-6CO)’ ion. In I(t), however, the closer proximity of methyl hydrogens to the N-phenyl ring allow a similar rearrangement to occur by means of a five membered transition state as shown in Fig. 4. Calculations based on the assumption that all hydrogen trans-
Fig. 4. Mode of knzene
eIimination of (PdCO)’
of I@).
ferred originates in the methyl group predicted that the ratio m/e 229 :m/e 230 be 1.53: I for the labelled compIex_ The experimental value of 1.59: 1 is in good agreement and leaves little doubt that this is the major process occurring. In contrast, substitution by the much Iarger phenyl group [R, = phenyl I(c)] causes two major observed effects. First, the base peak in the spectrum is m/e 369 second, elimination of phenyl occurs from the (P-6CO)* ion compared (P-WO)‘, with the more normal benzene elimination. The loss of benzene has already been
shown to involve the N-phenyl ring and it must be assumed that the large phenyl group of the bridge system prevents hydrogen migration by steric interaction. The (P-6CO-Fe)i, however, does demonstrate elimination of neutral benzene due to the change in stereochemistry around the nitrogen atom. It may be concluded from these observations that changes in the mass spectrum resulting from substitution at Rz are primarily steric in nature. This feature, however, is not necessarily true for substituents on other parts of the &and. Electron donating or withdrawing groups on the aromatic ring directly bonded to iron may have a considerabie affect on metal-&and bonding. Indeed, attempts to synthesize similar complexes from nitro-substituted benzylidene-anilines have proved unsuccessf-‘~. Similarly in the mass spectra of those compiexes which
-6C
t? -6CO)* jfc32?
soE (COI,
KOl,
Pi m/e
-X0 495
i
1%liL*SE (P-zco)*
SIUULTANEOGSLY I
-203 SIuuLTAKEoujLY
I [P-4=0’
Fig- 5 Fragmentatior. pattern of I(d). I/XL I_ MISS Spectrom fan Phyx, 3 (1969) 63-69
&MASS SPECTRA
OF SCHIFF
BASE
COMPLEXES
67
have been synthesized with various substituents in R,, electronic effects in the nature of the decompcsition may be noted. A prime example of these effects may be seen in the spectrum of I(d) (Fig. 5). The system’uic srepwise fragmentation of car-bony1 groups from the parent ion is modified somewhat as there is evidence (M* = 334.1 and m* = 279.2) for simultaneous elimination of two carbonyl groups from the (P-2CO)’ and (P-4CO)’ ions. We have more commonly observed multiple elimination of carbon monoxide from manganese carbonyl complexes’ than any other metal carbonyl system and it may be that the influence of ch!oro substitution reduces the effective electron fiow to iron from the aromatic ring causing one iron to become deficient in electrons and to behave more like manganese*. This tendency to “weaken” the ring-metal bond may aIso be seen in the formation of m/e 236 (Fig. 5). Mass measurement and metastable ion observations show this ion to originate by elimination of FeCi from the (P-6CO)’ ion. This is possible if we assume homolysis of the bond between iron and the chloro-substituted ring. followed by rotation about the bond as shown in Fig. 6. /..
c+ _&-s
Cl
H
,H
=I!--
”
I
‘N--PP
-
-
i
!- FCC1 m/e
236
Fig. 6. Elimination of FeCl from the cpdCO)+
ion ofI(
An accurate three dimensional model of the complex using X-ray data from the corresponding benzalaniline complex6 and a carbon-chlorine bond distance of 1.73 A shows iron-chlorine overlap to be unavoidable if such rotation occurs. Beynon et al.‘, who have studied the mass spectra of various mono and dibasic aromatic acids have shown that deutero-benzoic acid exhibits both OH” and OD” elimination accounted fcr by an intermediate rotational state which produces an equilibrium exchange of hydrogen between the ortho position and the carbonyl. That such rotational intermediates have been shown to exist is good evidence in support of the mechanism of elimination of FeCl from the complex. Further evidence in the spectrnm is found at m/e 91 which precise mass measurement has shown to be (FeCi)+. This rearrangement is doubly interesting as it demonstrates * Current work 21 these laboratories has conf%med that increasing the B-d donor ability in complexes of the type L2Fe2(CO& increases the b(Fe-CO) value whilst electron wiihdrawiug substituents on the ligand cause a corresponding decrease in the BtFe-CO) energy. In?. J. Mass Speczrcm. Ion Phys., 3 (1969) 63-69
F. J. PRESTON
68
et a].
the combination of the electronic effect and stcric effect in ion decomposition. In general, it is found that aryl substituents at Rs behave in a fashion similar to I(a), thus I(f) shows eiimination of toluene rather than benzene from the (PG~ZO)~ ion. AK--l sub~tituents at RX, however, behave somewhat differently, e.g. in I(h) preliminary iors of benzene from the (P--6CO)* ion observed in I(a) is not paralleled by a loss of methane nor is there any such elimination from the (P-CO-Fe) + ion. Similarities do occur, however, in elimination of hydrogen cyanide from both the (P-KO)+ and (P-6CO-Fe)+ ions.
It can be concluded that the mass spectral decompositions of the compiexes I(a)-(h) depend upon the nature of the subsfituents R, , Rz, and R, . Rearrangement ions from the (P-603) t ions involving efimination of benzene are afkted ma&y by the size and geometry of the substituent at Rz, whereas elimination of benzene from the (P-6CO-Fe+) ion is dependent upon the co-ordination state of the nitrogen atom. These effects are, therefore, primariiy steric in character. Substituents in the aroma& ring R, , however, effect the decomposition process primarily by electronic effects upon the metal-ligaod bonding and are prominent in orz!zo-substituted complexes. Variations in the mass spectrum caused by R3 axe very small and cannot be attributed to either of the above effects.
The mass spectra were obtained with an A.E.I. MS9 double focussing mass spectrometer at a source temperature of 180 “C and an ionizing voltage of 70 eVA direct irser!ion system was used to introduce samp!es. Precise mass measurements were made at a resolution of approximately 10,000 based upon the 10 % valley definition. AU samples were prepared by standard methods’. Methods used for synthzsin of labelfed compounds are listed below. (a)
a,a,~-T~~utero-acerophc’none
Five exchanges according to the method of Noyce, Woodward and Jorgenson* gave 97.6 ‘A r,z,z-tricdeuterc-acetophenone by low-voltage mass spectromen-y-
2.4 g (O-02 moIe) of acetophenone-D3 and 2.74 g (0.025 mole) of formamide acetal bydrcchlorideg were stirred in ethanol (7.5 ml) for 4 days giving 97 % yield of D,-acetophenone ciiethyl ketak 2.5 g of the ketal were then stirred hr.
x
M-ass
S_Dectrom.ran Phys., 3 (1969) 63-69
MASS
SPECTRA
OF
SCHIFF
BASE
69
COMPLEXES
with aniline-D2 (1.2 g), the ethanol removed by distillation and a,r,cr-trideuteroacetophenoce anii was obtained in a 25 7; yield (0.72 g). Isotopic purity CDs (12 %), CD,H
(23 %), CDH~ (33 %), CH,
(33 %)-
The authors would like to express their gratitude to S.R.C. Petroleum for research grants during the course of this work.
and Institute
of
REFERE-NCES I M. M. BAGGA, W. T. FLA~XGAN,
2 3 4 5 6 7 8 9
G. R. Knox, P. L. PAU:ON, F. J. P-ON AND R. I. REED, J. Chem. sue, (C), (1968) 36. R. S. GOHLZ;E tiD F. W. IMcL.~~R~, Anal. Chern., 34 (1962) 1281. J. Mo\ff~hi, L. BRAXEERAND L. D’OR, BulL Chzsse Sci. Acad. Roy. Belg., 48 (1962) 1002. F. J. PREST0Nxm R. I. REED, Org. Mass Spec., 1 (1968) 71. M. AH!sIED,G. R. KNOX, F. J. WN em R. I. ReD, Chem. Commun., (1967) 138. P. E. BNUKIE.kXD 0. S. m, C&m. Common., (1966) 70i. J. H. BEYXOS, B. E. JOB AND A. E. W~LIAMS, 2. Natur-rsch., 20a (1965) 883. D. S. NOY(Z, G. L. WWDWARD ,ts M. I. JORGEP~SON, J. Am. Chem. Sue., 83 (1961) 1162. HOUBES-WEYL, Afethoden der Organ&hen Chemie, VoI. 8, p. 698.
int. J. A4as.s Spectrom Zon Phys., 3 (1969) 63-69
.TournaCof Mass
Spectrometry
and Zon Physics
63
Elsevier Publishing Company, Amsterdam. Printed in the Netherlands
STERIC
AND
SCHIFF
BASE COMPLEXES
F.
3.
ELECTRONIC
EFFECTS
THE
MASS
SPECTRA
OF
PRESTON**
Imtiitlte for Atomic Research,
Iowa State
Unirersity,
W.
KNOX,
1.
T.
FLANNIGAN,
Unkersity AND
IN
FL
University
G.
of Strathciyde, I.
R.
Glasgow
P.
Ames,
Zowa 5OOZO (U.S.A.)
PAUSON
(Scotland)
REED
of Glasgow
(Scotlonri)
(Received February IZth, 1969; in revised form April 17th, 1969)
ABSTRACT
-Mass spectrometric
stl-ldies of complexes
formed
by the reaction
of Schiff
bases of aromatic aldehydes and ketones with enneacarbonyldi-iron show characteristic fragmentation patterns. Changes in the mass spectra as a result of varying substituents at specific positions on the organic ligand are discussed in terms of their steric and electronic origins.
INTRODUCTION
In a previous communication’ a report was given on the structural features of complexes (I) (Fig. I) formed by the reaction of enneacarbonyldi-iron with the SchiZ bases of arcmatic aldehydes and ketones, and a discussion of the features of the mass spectrum of I(a). In general under electron impact all complexes of structural type (I) show stepwise elimination of all six carbonyl units from the parent ion (P’). Further fragmentation of the (P-KO) ion is characterized by loss of either a benzene molecule or 2.n iron atom followed by a benzene or hydrogen cyanide molecule. IabelIing experiments’ show that the aromatic ring involved in the elimination of * Work was performed in part in the Ames Laboratory of the U. S. Atomic EnergyComxnis-
sion. Contribution No. 2X%
** To whom all ccrrrespondence should be zddressed. Znr. .T. _MzssSpecrrom. Ion Phys., 3 (1969) 63-63
F. J. PRESTON
64
et al.
I
R,=h
,R2=H
*
‘13 m =c&
%,-II
.Rz=He
.
R3 - W-
Rt
-
H
RI
.
ct.
a) ‘0’ -e-k.
=il-n
R3 = c&
R2 = C&.
it2 - ‘!
. 33 - C&
Rt-H
*
R,
-
Fi,
. Rz -
RI
-
H
. R2’n
R3 - w.5
.Rj-CgW?~
-112-q
H
. “3
-
‘#+s
,R;=tk
Fig. I. Structuresof Schiff base compIexes.
ion is the N-phenyI ring with concomitant benzene (R,H) from ithe (PACO)’ removal of one hydrogen atom from the methylene bridge. The similar process from ‘Se (P-KO-Fe)” ion, however, involves the aromatic ring directly bonded to iron, i.e. elimination of R,C,& a fact more in keeping with the B-bond fission occurring with compounds of ten&e& nitrogen’. The general framentation scheme for compIexes (I) is given in Fi g. 2. It is now our purpose to discus further studies on com?Iexes Teefated to these previously discussed’, but having varying substituents in position R, , R,, and R,.
(P-6CO)*
I
-R&N
Fig. 2. Gend
fhgmentzttion scheme for S&X
base uxnpIexs.
MASS
SPECTRA
OF SCHIFF
BASE
65
COMPLEXES
DISCUSSION
Substitution of one methylene hydrogen at R, by methyl (I(b)) leaves the two main fragmentation routes from the (P-SCO)’ ion unchanged, hydrogen cyanide elimination being replaced, of course, by that of methyl cyanide (see Fig. 2). In addition, hcwever, precise mass masurement of the ion at nz/c 281 shows it to arise by loss of an acetylene molecule from the (P-6CO)’ ion. In order to clarify this process the complex I(R, = H, R, = CD,, R3 = CsHs) was synthesized with the intention of differentiating between acetylene abstraction from the bridge system and that from one of the aromatic rings. Benzene loses acetylene from a butadienyl acetylene type parent ion3, and a similar possibility existed here. The labelled complex could not be prepared in very high isotopic purity (R,: CH, = 32 %, CH,D = 33 %, CHD, = 23 %_ CD, = 12 %) but was considered sticient for the experiment. The deuterium isotope incorporation was verified by low voltage mass spectrometry. That negligible scrambling of deuterium had occurred was also verified by him in the methyl region of the spectrum. Calculations made on the basis of these isotopic concentrations and making no allowances for isotopic effects showed that the expected ratios of abundances of nzje 281:282 : 283 should be 2.00 : 1.20 : 1 if acetylene were eliminated entirely from the methlyene group and its substituent R2 with concomitant transfer of 2H, DH or Dz to the remaining daughter ion as in Fig. 3. Experimental measurements, making corrections for 13C, 5”Fe, and 57Fe contributions give values of 1.99 : 1.25 : 1 in extremely good agreement with the theoretical values, and define the fragmentation route as given in Fig. 3. Such a rearrangement could result in formation of a G-X complex ion, a structure which has already been shown to be very stable in similar systemr?. It has been stated previously
ASJNLYLNCE
m/e
203
m/e
262
that the methylene
m!e
bridge hydrogens
of I(a)
261
THEORETICAL
1.0
1.20
2.00
EXPERIMENTAL
I.0
1.25
I.99
-CH*CH
CP-6COl* m/e
307
Fig. 3. Mechanism of acetylene
m/e
261
abstraction front (P-KO)+. IlIt. J. Mass Spectrom. ion Phys., 3 (1969) 63-69
66
F. 3. PRESTON
et ai.
play a large r&e in eiimination of benzene from the (P-6CO)’ ion. In I(t), however, the closer proximity of methyl hydrogens to the N-phenyl ring allow a similar rearrangement to occur by means of a five membered transition state as shown in Fig. 4. Calculations based on the assumption that all hydrogen trans-
Fig. 4. Mode of knzene
eIimination of (PdCO)’
of I@).
ferred originates in the methyl group predicted that the ratio m/e 229 :m/e 230 be 1.53: I for the labelled compIex_ The experimental value of 1.59: 1 is in good agreement and leaves little doubt that this is the major process occurring. In contrast, substitution by the much Iarger phenyl group [R, = phenyl I(c)] causes two major observed effects. First, the base peak in the spectrum is m/e 369 second, elimination of phenyl occurs from the (P-6CO)* ion compared (P-WO)‘, with the more normal benzene elimination. The loss of benzene has already been
shown to involve the N-phenyl ring and it must be assumed that the large phenyl group of the bridge system prevents hydrogen migration by steric interaction. The (P-6CO-Fe)i, however, does demonstrate elimination of neutral benzene due to the change in stereochemistry around the nitrogen atom. It may be concluded from these observations that changes in the mass spectrum resulting from substitution at Rz are primarily steric in nature. This feature, however, is not necessarily true for substituents on other parts of the &and. Electron donating or withdrawing groups on the aromatic ring directly bonded to iron may have a considerabie affect on metal-&and bonding. Indeed, attempts to synthesize similar complexes from nitro-substituted benzylidene-anilines have proved unsuccessf-‘~. Similarly in the mass spectra of those compiexes which
-6C
t? -6CO)* jfc32?
soE (COI,
KOl,
Pi m/e
-X0 495
i
1%liL*SE (P-zco)*
SIUULTANEOGSLY I
-203 SIuuLTAKEoujLY
I [P-4=0’
Fig- 5 Fragmentatior. pattern of I(d). I/XL I_ MISS Spectrom fan Phyx, 3 (1969) 63-69
&MASS SPECTRA
OF SCHIFF
BASE
COMPLEXES
67
have been synthesized with various substituents in R,, electronic effects in the nature of the decompcsition may be noted. A prime example of these effects may be seen in the spectrum of I(d) (Fig. 5). The system’uic srepwise fragmentation of car-bony1 groups from the parent ion is modified somewhat as there is evidence (M* = 334.1 and m* = 279.2) for simultaneous elimination of two carbonyl groups from the (P-2CO)’ and (P-4CO)’ ions. We have more commonly observed multiple elimination of carbon monoxide from manganese carbonyl complexes’ than any other metal carbonyl system and it may be that the influence of ch!oro substitution reduces the effective electron fiow to iron from the aromatic ring causing one iron to become deficient in electrons and to behave more like manganese*. This tendency to “weaken” the ring-metal bond may aIso be seen in the formation of m/e 236 (Fig. 5). Mass measurement and metastable ion observations show this ion to originate by elimination of FeCi from the (P-6CO)’ ion. This is possible if we assume homolysis of the bond between iron and the chloro-substituted ring. followed by rotation about the bond as shown in Fig. 6. /..
c+ _&-s
Cl
H
,H
=I!--
”
I
‘N--PP
-
-
i
!- FCC1 m/e
236
Fig. 6. Elimination of FeCl from the cpdCO)+
ion ofI(
An accurate three dimensional model of the complex using X-ray data from the corresponding benzalaniline complex6 and a carbon-chlorine bond distance of 1.73 A shows iron-chlorine overlap to be unavoidable if such rotation occurs. Beynon et al.‘, who have studied the mass spectra of various mono and dibasic aromatic acids have shown that deutero-benzoic acid exhibits both OH” and OD” elimination accounted fcr by an intermediate rotational state which produces an equilibrium exchange of hydrogen between the ortho position and the carbonyl. That such rotational intermediates have been shown to exist is good evidence in support of the mechanism of elimination of FeCl from the complex. Further evidence in the spectrnm is found at m/e 91 which precise mass measurement has shown to be (FeCi)+. This rearrangement is doubly interesting as it demonstrates * Current work 21 these laboratories has conf%med that increasing the B-d donor ability in complexes of the type L2Fe2(CO& increases the b(Fe-CO) value whilst electron wiihdrawiug substituents on the ligand cause a corresponding decrease in the BtFe-CO) energy. In?. J. Mass Speczrcm. Ion Phys., 3 (1969) 63-69
F. J. PRESTON
68
et a].
the combination of the electronic effect and stcric effect in ion decomposition. In general, it is found that aryl substituents at Rs behave in a fashion similar to I(a), thus I(f) shows eiimination of toluene rather than benzene from the (PG~ZO)~ ion. AK--l sub~tituents at RX, however, behave somewhat differently, e.g. in I(h) preliminary iors of benzene from the (P--6CO)* ion observed in I(a) is not paralleled by a loss of methane nor is there any such elimination from the (P-CO-Fe) + ion. Similarities do occur, however, in elimination of hydrogen cyanide from both the (P-KO)+ and (P-6CO-Fe)+ ions.
It can be concluded that the mass spectral decompositions of the compiexes I(a)-(h) depend upon the nature of the subsfituents R, , Rz, and R, . Rearrangement ions from the (P-603) t ions involving efimination of benzene are afkted ma&y by the size and geometry of the substituent at Rz, whereas elimination of benzene from the (P-6CO-Fe+) ion is dependent upon the co-ordination state of the nitrogen atom. These effects are, therefore, primariiy steric in character. Substituents in the aroma& ring R, , however, effect the decomposition process primarily by electronic effects upon the metal-ligaod bonding and are prominent in orz!zo-substituted complexes. Variations in the mass spectrum caused by R3 axe very small and cannot be attributed to either of the above effects.
The mass spectra were obtained with an A.E.I. MS9 double focussing mass spectrometer at a source temperature of 180 “C and an ionizing voltage of 70 eVA direct irser!ion system was used to introduce samp!es. Precise mass measurements were made at a resolution of approximately 10,000 based upon the 10 % valley definition. AU samples were prepared by standard methods’. Methods used for synthzsin of labelfed compounds are listed below. (a)
a,a,~-T~~utero-acerophc’none
Five exchanges according to the method of Noyce, Woodward and Jorgenson* gave 97.6 ‘A r,z,z-tricdeuterc-acetophenone by low-voltage mass spectromen-y-
2.4 g (O-02 moIe) of acetophenone-D3 and 2.74 g (0.025 mole) of formamide acetal bydrcchlorideg were stirred in ethanol (7.5 ml) for 4 days giving 97 % yield of D,-acetophenone ciiethyl ketak 2.5 g of the ketal were then stirred hr.
x
M-ass
S_Dectrom.ran Phys., 3 (1969) 63-69
MASS
SPECTRA
OF
SCHIFF
BASE
69
COMPLEXES
with aniline-D2 (1.2 g), the ethanol removed by distillation and a,r,cr-trideuteroacetophenoce anii was obtained in a 25 7; yield (0.72 g). Isotopic purity CDs (12 %), CD,H
(23 %), CDH~ (33 %), CH,
(33 %)-
The authors would like to express their gratitude to S.R.C. Petroleum for research grants during the course of this work.
and Institute
of
REFERE-NCES I M. M. BAGGA, W. T. FLA~XGAN,
2 3 4 5 6 7 8 9
G. R. Knox, P. L. PAU:ON, F. J. P-ON AND R. I. REED, J. Chem. sue, (C), (1968) 36. R. S. GOHLZ;E tiD F. W. IMcL.~~R~, Anal. Chern., 34 (1962) 1281. J. Mo\ff~hi, L. BRAXEERAND L. D’OR, BulL Chzsse Sci. Acad. Roy. Belg., 48 (1962) 1002. F. J. PREST0Nxm R. I. REED, Org. Mass Spec., 1 (1968) 71. M. AH!sIED,G. R. KNOX, F. J. WN em R. I. ReD, Chem. Commun., (1967) 138. P. E. BNUKIE.kXD 0. S. m, C&m. Common., (1966) 70i. J. H. BEYXOS, B. E. JOB AND A. E. W~LIAMS, 2. Natur-rsch., 20a (1965) 883. D. S. NOY(Z, G. L. WWDWARD ,ts M. I. JORGEP~SON, J. Am. Chem. Sue., 83 (1961) 1162. HOUBES-WEYL, Afethoden der Organ&hen Chemie, VoI. 8, p. 698.
int. J. A4as.s Spectrom Zon Phys., 3 (1969) 63-69