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Mass spectrum and ion—molecule reactions of trimethylphosphine investigated by ion cyclotron resonance spectrometry
23 Inremarionai
.lournai of Mass
Specrronrrrry
and Ion P_?+sics. I 7 (I975) 73-X - Printed in The Netherkmds
c Ekcvicr Scientific Publishing Company. Amsterdam
MASS SPECTRUM THYL PHOSPHINE SPECTROMETRY*
KARL-PETER
received
AKD
wAsczEK*
lnrrirur ,Gr ph~x-ik&xhc (First
AND ION-MOLECULE REACTIONS INVESTIGATED BY ION CYCLOTRON
S August
Chemie 1974;
ZDEXEK-CHRISTIXX dcr Unircrsirti~r Fbankfiur,
OF -TRIMERESONANCE
PROFOUS Fmnh-fir
( IVcsr GcrnzanF)
in rcviscd form 21 November 1974)
Mass spectrum and ion-molecule reactions of trimethylphosphine have been studied by ion cyclotron resonance spectrometry- The product ions obtained can be classified as ions with two phosphorus atoms, P2R3*, P?R,-+* P,RSi and P,R,-* (R = CH, or H), phosphocium ions and ions with the same masses as primary ions resultirq from charge exchaqe and collision dissxiation reactions_ The dimeric mokcular ion Pz (CH,),-i and the tertiary ion P, (CH.),* are also detected_ The mechanism of several ion-molecule reactions is discussed_ Although 60 ion-molecule reactions h:ve ken detected, each primary ion shows onIy one or two predominating ion-mokcule reactions. The molecular ion undergoes a displacement reaction with the neutral molecule, with a rate constant of O-32 - lO-‘O cm3 molecule -’ s-I* to yield pratamethyldiphosphonium (1 +) product ion3 and forms the protonated molecule with a rate constant of O-10 - 1O-‘o cm3 molecule-’ s-I_ The P(CH,)= + ion reacts with the neutral to form the protonated molecule with a rate constant of 2.7 - IO-” cm’ molecule-’ s-‘_TheP(CH&* ionwhichhasprobablyacyclicstructureunder~oesaphosphorus cation transfer reaction to yield the P1(CH3)3* product ion with a rate constant of l-4 - lO-‘O cm3 molecule s-‘_ The structure of this product ion is discussed_
Until now, only a few mass sjxctrometrk investi-tions on trimethylFhosphine have been published [l-6]_ The mass spectra obtained by Halman P_], by Wada and Kiser [4] and by Kostyanovsky and Yakshin [S] differ substantially_ * Dcdicatcd10 PrckssorH- Hm on Ihe occasisn of his 6@b birtbdaye Author to u-horn corrcspondcnce should be addressed-
ft
24 The decompositions
of the metastable ions appcarin_e in the mass spectrum
by Gillis and Long [6]_ They * ion in the metztable decompositions which lead to fiagment ions of higher order_ They assigxd the ion with rplie = 41 and composition C,Hs* to a rearranement which joked the three of
trimethylphosphine
have
been
investigated
showed the importance of the P(CH3),CH,
seeante
methyl groups-
While
the mass spectrum and the ion-molecule
have already
ken
the relative McDaniel
proton
affinity
et al- [IO]_These
77 and m/c =
ICR spectrometry
studied by
of
[7] of
trimethylphosphine
authors
137 are formed
has been assigxd
reactions of phosphine
[S, 9]- only a determination
by ion-molecule
to the protonated
has
been
carried
out-by
that two product ions with m/e=
mentioned
reactions.
The
first production
trimethylphosphine.
In this paper a study of the ion chemistry of the positive ions of trimethylphosphine
is presented-
EXPERIMEXTAL Theexperiments V 5900, Vatian
were carried out with a standard ICR spectrometer (Varisn
Associates,
Palo Alto,
in the literature [I I]_ Therefore be given_ A flat ICR termination
Ca!if_)
which has aheady
only a brief description
been described
of the measurements
cell with three sections was used, thus allowing
of the spectra and rate constants
All ICR spectm were recorded
than a square
ICR
a .betterde-
cell [12]_
at an electron energy of 30 eV unless other-
wise stated, by the electron energy pulse technique.
Electron
trap currents were
typically in the region of IO- 7 A giving total ion currents in the range lo- “-IOA so that the space charge and ion trapping appearance
potentials
wil:
were determined
would
”
be relatively small [13]_ The
usin g the same technique
and also the
drift plates pulse technique_ The electron energy scale was calibrated
in the usual
way usin_e rare gases_ AlI
ions appearing
in the spectrum
\;_erc subjected
to double
resonance
experiments at several pressures and irradiatin_r field strengths- The results of the double resonance experiments were supponed Rate
constants
were
obtained
by pressure plots whenever possible-
by the approximation
method
of Goode
et al- [14]r ki
A*. i n15
=
nrz
1 -__
1
[Ml fi+Hfp
where ki is the rate constant of the formation of the ith secondary ion, A, and d,, i and t+ and ntsr are the sir&e resonance intensities and masses of the primary and the ith secondary ions, ri and rP are the times the ions spend in the
25 source
and analyzer regions, which were determined
the magnetic and electric field strengths, and [M] neutral species_ A plot of
versus pr-ure
$ves
a straight line with a slope proportional
The great number of ion-molecule makes it necessary
to determine
[15]_ The rate constant molecular ion
from the known values of is the number density of the
reactions
the rate constants
of the formation
to ki-
occurring
in
the spectrum
at several electron
of the protonated
molecule
entrgics from
the
and the neutral molecule xvas determined at 1OBOeV electron ener_qv to 10S4 torr simultaneously with the formation
and a pressure ranSinS from low5 rate constant encrsy,
of the pentamethyldiphosphonium
the first fragment
neutral molecule
ion_ At :2_00 eV electron
ion P(CH.),+ has appeared and reacts also with the P(CH3),H*_ P=(CH,),’ and PI(CH,),* with abun-
yieldin
dances sufficient to determine For calculation
(I+)
rate constants-
of the absolute
values of the rate constants
to know the exact values of the pressure in the ICR
it is necessary
cc11and the residence times
of the ions in the source and analyzer regions. This pressure was determined by measuring the pumping current of the ion pump (Varian Vaclon pump) and the residence times were caiculated
as mentioned
approximate
the absolute
values_ Therefore
above_ Both procedures rate constants
probably
yield only have
only an absolute accuracy of about 50 T’_ However the relative values of the rate con-
stants are more
accurately
known.
Their
relative accuracy
should
be approxi-
mateIy 10 % [16]_ Trimethylphosphine phine P *
[S, 9, 171. P+
ions
&iSnard
(X >
trap
ions appear
1) were
synthesis
composition
does not pyrolize
[IS]
only
not observed_
with smali abundance Trimethplphosphine
and precipitated
in a
as does
iodide complex
phos-
in the spectrum.
was prepared
as silver iodide complex_
of the trimethylphosphine-silver
distillation
at the hot filament
Thermal
by a de-
yields. by tnp-to-
vacuum system, a very pure product containing
no im-
purities detectable with the ICR spectrometer-
RESULTS
ICR
AXD
DISCUSSION
s_rlecrnnn of rrinierl?)rlplrosprxine
The ICR spectrum of trimethylphosphine
at a pressure of IO-’ tot-r, shown
in Fig_ 1, is relatively simple_ The mass corrected relative intensities are compared
26
76
’ fil Fig_ I_ ICR of 33 cv_ TABLE
I
miC
Ion
spectrum
15 16 34 35 4t 43
GHs+ PC*
44 45
PCH- + PCH2+
46 47 57 58 59 60 61 73 75 76
PCH,-+ HPCH, P(CH)=+ PC*H,-
of trimcthyiphcnphinc
Rdarire aLuvtdzurrcs -This work 7aIman [Z] -i2cv 3oeY
CH,‘ CH&-+ PH,- +
110
6.6
95
6 78.6 4.4
PI&’
73 113 209 112 780 108
+
WCH,),* PCzHs-+
P(CH&+
by HaImau
of Kostyanovsky
p]
show
and an &m-on
W-aai~amd Kihr [4 J 70CV
energy
Kox~~-amrsk_tad fsakdxitzis]
73.5 653 635 1000 45 191 653
1. The
[5]_ The
but without comments_
100 224
662 94
633
1000
loo0
200
200
782
800
results obtained
better agreement
and Yakshin
280
103 111 325 118
by Wada
and Kiser
with our measurements
dimethylpkosphiuium
peak in all spectra_ The ion m/e = 41 is to be found tained by Halman
torr
II 121 564
56-S 103 4x9
loo0 74 193 683
PU-I,L+ PGI-?5+ P(CH&CH,+
IO-=
8 7
67-4 2%
227 +
of
152
107
with literature values in Table and
at a ~rcs~urc
[4]
than those
ion is the base
only in the spectrum
ob-
27 If the pressure is raised, numerous An
ICR
spectrum recorded
assigned to PHI* in Fis
at IO-’
eons (x = 0, I, 2,3,4)
3 recorded at 5 - IO-’
the extraordinarily
spectrum
60
in the spectrum.
in Fi_g_ 2_ The new peaks are
and to hydrocarbon
ions_ The spectrum
torr in the mass range from 1,1/e= 40 to 140 shows
great number of product ions formed.
10
Fig- 2- ICR of 30 cv_
new peaks are observed
torr is shown
m/e-
60 I
of trimcthy-lphosphinc
80 mre -100
101
80
at a pressure
120
of IO-’
torr zmd an electron
energy
140
Fig. 3. ICR spectrum of trimcthylphosphincat a prcssurc of 5 - 10e5 torr and an electron energy of 30 ev_
,
potentials of the main primary ions and the three most The appearance abundant product ions are listed in Table 2_ These values do not compare weli those obtained by Fischler and Halman [3] and by Wada and Kiser [4]_ However, the value for the appearance potential of the molecular ion, 8_4&0_3 eV, is close to the value obtained ‘by Wada and Kiser, S_6Of:O_2 eV, while the value of Fisehlei and Hahnan
differs by +O_S eV- Our appearance
potentials of the fragment
the _eret differences cannot
are in general smaller thaa the cited values. however
potentials; ions are close to that of the molecular ion_ be rationalized-
APPfARAscE
The appearance
OF
POTEL.
THE
yxI_X
A_P_ (CL-)
rn+
1023
1% THE
of the three most
ICR
SPECTRUU
OF
abundant
I~-__c___._Fiscix~crundHdmm [;I
W-ah ad
41 45
14.1 14.3
17
16.1 fO.4
46
137
14.0 20.3
47
13.8
14.7 20.7,
57 59 61
12-S 13-o IO-9
73
92 8.6
76 77
s-4 9.0
107 137
9-o 8-7
x The unarrtinty
----
&I
product
TRIXEl-HYLPHOSPHI_SE
Thish-0&
75
ions
15 _I 11_8~02
16.7 20-3 14-O 202 II-7 2 02
I1_8&0.2
IO2 &O-S
92~0s
Kixrr[IJ
--
SA!iO_rO_~
of this data is 50.3 cV_
lotz-molecule reactions
Figures
4 and
5 show
the variation
tensities of the main primary and product 8 - 10-j
abundant
ion
stability of this ion is ah-eady well known
from
torr the trimethylphosphonium
in the spectrum_ The remarkable
with pressure of single resonance inions- At a pressure higher than about
ion
becomes
the
most
chemistry_ Only the proportions of the P-,(CH&* and P(CH,),CH2* ions show a comparable increase with pressure_ At high pressures the former ion reaches almost 10 o/0 of the total ion intensity, and the latter almost 20 y!_ The
soIution
proportion of z!l other product ions increases much more slowly with pressure. The abundance of ail primary ions, with the exception of the molecular ion. decreases stron.qIy if the pressure is raised- The proportion of the molecular ion
p(krr) Fig_ 1_ Mas-corrcctcd
rchtitr:
intensities
of the major
ions in the ICR spectrum of trimethb-t-
phosphinc as a function of the total pressure_
Fie 5_ Mllsz-corrcctcd reIativ~ intensities of the low abundant ions in the ICR spectrum of trimcthylphosphirre as ;L functiun of the total pressure-
increases with pressure; this results from charge exchange reactions becoming important at higher pressures_ Table 3 lists all ion-molecule reactions of the primary ions and Table 4 those of the secondary ions_ The reactions are numbered startins with the dimeric molecular ion formed from the molecular ion and the neutral mokcule. The neutral products being formed in the course of the ion-molecule reactions are not listed in the Tables.
30 TABLE
3
IOX-MOLECULE
Product ions
RUCCIOSS
Primary
OF THE
PRlBlARY
10s
OFTRI
MElHYLFHOSPHISE
IX
T-ME MASS
RASSE
FROM
m:C
ions +
PlCH,l,-
x0_
P(Cli,?-
+
X0_
P(Cff=)=
+
NO_
Diphosphine ions P2%- *
P,(CHdaP2(CH&H-’
P,R,*
*
3
PACHA9
PdCH,MCHA+ PAC&),(CW,+
4
P,(CH,),C=+?
6
P,R,-•
Phasphonium
P,KH,)s*
IS
P,(CH,MCH,L+
I9
P,(CH,),C,
20
P,(CH,),(CH,),+
31
5 l?
PACHAd%+
21
PACH,),Hz’
32
P,KH,ML+
22
PdCH,LH,+
33 33
Pz(CHlrP-H,’
7
PACHA-
8
PI(CHA-
9
P,(CH,),H-+
35 36
l
Pr(CH,),HP,R, +
I 2
*
PACH,),* P,(CH&H+
+
10
PACH,),‘,
23
P,(CH,),
I1
P2(CH&H+
24
PACH,hH*
12
HP(CHd>+
25
HPKH,),
13
P(CH,)ICH2
26
P(CHAC=Ha+ P(CH,)zCH= *
40
PC,H.*
41
14
P(CH,),CHz+
27
‘8
+
37
ions
HP(CHdx+
P(CH,)=CH= P(CH,),CH=+
+
+
*
3s 39
Colhsion d-fsmciarions
P(CH,L
+
is
P(Cr-r,), +
I6
P(CH&
P(CH)2 +
17
P(CH)z *
29
P(CH)z *
42
P(CH,k+
30
P(CHd,-+
43
+
chizrgc excIrangc
31
= 3orom;‘c
P(CH),
=
190
+
137 135 4-t
133
P,(CH,),C,*l
45
131
P~(Cli,)~H,+
46
P=(CH,),(CH):
l
109 P&H&H,
+
95
49
122
Pr(CHJ)T(CH)z*
118
47
10s
107 93
HP(C!i,),
*
P(CH,),C,H,+
53
117
P&He
5-l
75
77
50 +
103 75 73 P(CH,),CH,-
+
51
P(CH&CHz+
5’
90
61 59 57
WC&),-
+
a!?a
76
32 TABLE
4
IOXiMOIJXULE
REACTIOS
sccoRaitr_b-
OF
SECOSDARY
IO.SS
YIELDING
TERTIARY
IOX
ion ML
PdCHA’
Pz
x0-
(CH,), +
Dincciarion
58
P&H,),+ Merh_rfgrrup rmtqfcr P,(CH,L-+ P,(CH,k +
55 56
59 60
PACH3)6-+
P,U-Ll,+ Addiciiun * P,(CHh
57
All the reactions can be assigned to only a few reaction types already known
well
from chemistry: (I)
Reactions which yield product ions with two or more phosphorus
Ions with the compositions
P2R3*,
were detected_ The dimeric
P2R4-ir
molecular
P2R5*
and P,R,-*
atoms_
(R = CH,
ion and a tertiary ion
with
or H)
three phos-
phorus atoms were also observed(2) Reactions one phosphorus molecule-
which yield phosphonium
and quasi phosphonium
atom- The most important
the most abundant
(3) Collision
product
dissociation
ion in this group
ions with
is the protofiated
ion observed_
reactions are observed
at elevated pressures_
(4) At pressures greater than lob6 torr, charge exchange
reactions become
important_ Prodrtct ions with two or three pi~osphorus atom< The secondary reactiocs
ions with two phosphorus
of molecular
into four groups: phenium
atoms formed
2nd its fi-a_ment
trimetbylphosphine
(a) P,R,- * ions, (b) diphosphonium
ions P,R,-*
and (d)
diphosphinium
by ion-molecule
ions can be divided
ions P,R,*,
ions PZR3*,
(c) diphos-
where
R represents
either a hydrogen atom ur a methyl group- Ions having only methyl groups bonded to the phosphorus hydrosn two
atoms and methyl groups-
methy!
P-,(CH&H-’
reactions
groups
occur
in
and P,(CH,),H’
Most addition
atoms are much more abundant
of the product
reactions, which
Almost
all possible
spectrum:
mixed ions with at least
P2(CH,)rHS+,
P,(CH,),H1*,
were detected-
ions described
displacement
include
the
than the mixed ions containin
are formed
reactions,
rearrangements_
product ions with small abundances-
atom
The
by four types of reactions:
or ion transfer
reactions
last type of reaction
and
yields only
33 In all cases an electrophihc attack by the phosphorus atom cf the ion on the phosphorus atom of the neutral molecuIe must be assumed_ The phosphorus atom is we’ll known as a highly nuclcophilic centre from the chemistry of alkyl phosphines [IS, 191.The lifetime of the intermediate must be shorter than IO-* s in most of the observed reactions because it can be detected, by ion cyclotron double resonance experiments, only in a few cases as a precursor ion of the final products. Detection of the intermediate is howeverpossible for the reaction of the dimethylphosphinium ion which yields the ?1(CH3),+ product ion:
I
Fis
1
m 6_
209
300
kHz
Ion cyclotron double resonancespectrumof the P,(CH&+
im at a pressure of 1. 10es
IOft_
The corresponding
ion cyclotron
The other two formation detecred in this spectrumr
double
reactions
resonance
of the dimethyl
spectrum is shown diphosphenium
in FIN_ 6_
ion are also
34 Reactions
(10).
phosphorus
(23)
cation
and
transfer
reagent is the P(CH,),+ P(CH,)?’
(36)
reactions_
most powerful
phosphorus
as
transfer
ion and the fragment ions P(CH,)Z
addition
reactions
ion (1)
P,(CH,),’
+,
the neutral molecule
wi’h
(IIS), P,(CH,),(CH,),^
(44)
phosphorus
attack
by the phosphorus
atom
atom of the neutral is assumed,
structure results as tSe product of only small abundances,
ions_ The addition
normally dissociation
primary addition product occurs_ The most intense ion with phosphanium
ions and can be regarded
undergo
an electrophilic
nucleophilic
The
*
molecular
(31) and P,(CH,),(CH)I+ If however
PZ(CH,),
ion- The molecular
and P(CH)?’
and produce the dimeric
yield
(1 t ) ion, is mainly
two
ion
reactions yield product
rather than stabilization
phosphorus
formed
of the ion at the
a diphosphonium
atoms,
ions
of the
the pentamethyldi-
by ;1 displacement
reaction
of the
moJeeular ion_
(CH31,P‘-
C
PICH,),
-
_--
tCH,),P
PcH,l,
-\
-
-1%
,P-ycy
This reaction
is the main ion-molecute
Symme’ticaJJy substituted P2(CH,),’ It is easily formed
by alkylation
of the molecular
ion_ The
un-
ion has been known for a long time [20,21]_
of tetramethyldiphosphine
(CH,),P-P(CH,)LtCH,I The P-P
reaction
*
C%
-L4c
with methyliodide:
--+ (CH&P-P(CH&‘I-
bond in this ion is stabilized by the methyl _group+_ The bond is wakened
by eIectron-withdrawing trifluoromethyl
substituents at the phosphorus
groups_ The attempt to quartemize
or tetra-(trifluoromethyl)diphosphine
1231 results in dissociation
In the Iight of the results obtained the structure of the P&H,), bond are possible: rearrangement, and a PP(CH,),’ CH,P-P(CH
&
atoms such as phenyl or
tetraphenyldiphosphine of the P-P
bond_
for the pentame’-hyIdiphosphonium
ion,
* ion can he discussed_ Two
if the phosphorus
(221
structures with a P-P
cation transfer reactions take place without
the three methyl groups
remain
bonded
to one phosphorus
atom
torn will be formed; if rearrangement occurs, also the sttuctute * is possible- Although this question can only be decided finally
by a study of deuterated tioned that the ion-molecule and not P,(CH,),‘_
methylphosphines
which is planned,
reactions of the P(CH),+
it should
he men-
ion yield onlyP1(CH,)LH
*
35 This strongly indicates rearran_eement_ Therefore are believed
to occur-
Rearrangement
both structures of the Pz-(CH3)3i
ions with P-H
bonds
have already
been
mentioned_ The stabilization confirmed
in the case
mechanism
of the
via dissociation
fbrmation
of hydrogen
can also be observed during the course of secondary +
(CH)?P+ The formation
-
-!_
+P(CW,
V-W’*
ion formation:
PI(CHx),(CH,)z*
+
--, P,(CH,),(CH)z* --I -+ P,C,H,’
(CH,),P-*+P(CH,),
(H,+CH,-)
i-(2H,+CH,-)
(4) (5)
+(3H1+CH,-)
(6)
P~(CH&(CH,)=*+H2
p-c 1 5
H
+
+ P(CH,),
+3H,
+
9
P&H,*
of tertiary ions includes,
besides dissociation
tions. a further type of transfer reaction, namely methyl goup served in the case of secondary, At a pressure seater ion is formed
The
ion formation
than IO-’
by the following -
P,(CH,),’
P,(CH,),’
t- P(CH,),
-
PJCH&+
tiphosphines
of
are comparable
phine and methylphosphine
reac-
transfer, not ob-
4, reactions 55,59)_ (1 t)
two reactions:
+P(CH,),
reactions
(Table
and addition
tot-r the tertiary hexamethykriphosphonium
Pz(CH,L*
ion-molecule
molecules, EKin_g
reactions of higher order primary ions [6],
(57) -k&H,
(60)
trimethylphosphine
with the ion-molecule
yielding reactions
diphosphines
and
of dimethylphos-
[24 ]_ I-iowever, in the case of dimethylfluorophosphine
and methyldifiuorophosphine,
addition
product ions with two phosphorus
reactions
atoms
predominate
for formation
of
[3F]_
PJtospJxonium ions The most abundant Small contributions (3s) and P(CH)?+ Raction channel
product ion in the spectrum is the quasi phosphonium
which is mainly formed from the dimethylphosphinium
ion (CH,),PH*+,
come from the molecular
ion (25)_
ion (12) and from the P(CH,),*
(50) ions.
(12) can be a hydrogen
(13) being a hydrogen
H&H
atom or a proton transfer, the competin,o
atom transfer or a hydride
ion transfer
reaction:
36 The products of reactiow Two
corresponding
however
(12) and (13) differ only in the position of the charge-
channels occur in the case of the dimethylphosphinium
ion,
the neutral reaction products have one methyl group less_ Reaction
(25)
is a proton transfer, reaction (26), only a minor reaction channel, is a hydride ion transfer-
A rzzmarkable ion molecule reaction is tl,e addition nl/e = 41,
C3HS+, which yields also a phosph?nium
C,Hs+ +WH.),
reaction of the ion with
iocr
- (CH,M’GH,+
(53)
A second reaction channel of this ion is reaction 54 a further hydride ion transferNo tetramethyIphosphonium
ions have been detected (m/e = 91), ho\vever
an ion with RI/~ = 90 is formed durin, 0 the course of the ion-molecule
reactions
(14); (27), (51) and (52) These reactions can all be regarded as CHz- e ion transfer reactions leading to the molecular ion, (CHB),PCHI-‘,
of the simplest ylid. methylenetrimethylphosphor-
ane.
Several rate constants for the ion-molecuIe the dimethylphosphinium
ion and the P(CHt)?*
In general, quantitative undergoins
measurements
main ion-moL.uIe
methyldiphosphonlum
(I--)
(CH&P-*+P(CH&
reaction
ion,
ion have been determined-
show each of the main primaiy
mainly one characteristic ion-molecule
tion channels yield only small quantities The
reactions of the molecular
ions
reaction, while all other reac-
of product
ions_
of the mokcular
ion leads to the penta-
ion: --, (CH,)IP-P(CH,).+
with a rate constant, k,, 032 - 1O-‘o
+CH,-
cm3 molecule-’
s-‘_
(33) The rate constant of
the reaction:
(CWP*
+-PW-M,
has a value approximately cule-’
s-I_
molecular
f (CH&PCH,-
three times smalIer:
This rate constant
methylphosphine as from
--, (CH&PH*
is remarkably
k,Z = O-10 - IO-”
small- This
ion differs substantially
merhyldifiuarophosphine
(12)
from
cm3
mole-
behaviour
of the tri-
phosphine
[S] as bvell
and dimethylfluorophosphine
[S]
where
the
37 molecular
ions react to form the correspondins
protonated
tions having comparatively Parse rate constants_ The ion-molecule reaction of the P(CH.)=* 9s 7: of all product
ion formed
tion (25) with 3 rate constsnt the ion-mohxule
ion is the predominant which Fields the P,(CH,), rate constant
the reac-
ion which yields approximately
from this primary ion is the proton transfer reacof X-,, = 27 - IO-”
cm3 molecule-’
reaction with the largest rate constant
investi@ed_ While the P(CH,),
molecules,
* ion is the main proton phosphorus
transfer
observed
s-I_
This is
in the system
resent,
the P(CH,)?+
transfer reagent_ Its ion-molzcule
reaction,
9 ion arzd the ethylene molecule, has a surprisingy
if the pressxe
does not exceed
10m5 torrr kJ6 =
iar_p,-
1.4 - 1O-1o cm3
molecule- ’ s- ‘_ In the iitenture a cyclic structure of t5e P(CH?),* ion has been discussed [2, 51. The ease of the phosphorus transfer reaction supports this cyclic structure by the same arsumcnts distinguish
between c+ic
with ammonia_
already and
emphasized
linear
C,H,-*
by Gross
In fact. the dimethylphosphinium
structure, undersocs
oniy a minor phosphorus
We thank Professor
H_ Hartmann
the research facilities made available
and
McLafErty
ions with the aid
[X]
to
of their reactions
ion, which cannot
have a cyclic
transfer reaction.
for his encouraging
to Professor
Hartmann
support
and use of
by the Deutsche
Forschuws~emeinschaft_ We thank aIso Dr_ G--V_ Rlischenthaler, -5 fiir Anorganische Chemie der Technischen Universitst Braunschweig,
Lehrstuhf
B
for samples
of trimethylphosphine*,
REFFRESCES 1 Z 3 3 5
6 7 S 9
W- R- Cullcn and D C- Frosr, Cuu. /_ C-lrcnr..40 (1962) 390. M. Halman. J_ Chcnr_ SW_. Lan&n. (1962) 3270_ J_ Fischlcr and %I_ Halman, I_ C&m_ Sot__, London. (1964) 31_ Y- Wada and R- W- Kiscr. J_ Ph!x_ Chcnr.. 68 (1964) 2290. R_ G_ Rosr~~noxky and V_ V_ Y&shin. Ix_ Akud_ Nauk SSSR. Scr- Khim.. (1967) 2363R_ G- Gillis and G_ J_ Long. Org. Mass Sprclrunr., 2 (1969) 131% J- W- LonS and J_ L_ Franklin. I_ Amcr_ C&m. SOC., 96 (197-t) 2320_ J_ R_ Eyicr, Znorg_ Chcm.. 9 (I 970) 93 I _ D_ Holrz, J_ L Bczu~champand J_ R_ Eylcr. I_ Ann_ Chem_ Sot-, 91<1970) 7ML
* Now ad&d
38 10 D. H. McDzniel. N_ B_ Coffman and J_ M_ Strong. J_ .-her_ Cl;mr_ Srrc-. 92 (1970) 6697_ 11 H- Hartmann. K--H_ Lcbert and K--P_ Wancxk. Topics in Current Chemktry, 43 (1973) 57. II S_ E Butdl, Jr_, I_ Chern. P/rp_, 50 (1969) 4125. I3 G- C_ Goode_ h J_ Ferrer-Correia and K- R Jt~ing, Int- 1. Afau Spcrrrom. Ion P&x_, 5 (1970)
229_
R_ M_ O’~MaIfey. A_ J_ Ferrer-Correia. R_ J_ hlssey, K_ R. Jennings- J_ H. Fucrelt and P_ M_ l_ltudlyn. IM- /- Afuss Spccrrorn. Ion P&-s_. 5 (1970) 393_ 15 J_ L_ Franklin, J_ Chem_ l&c_, 40 (1963) 284_ 16 Tht aulho~ e?rpre~s tbit gratitude to a dcrec for his comments conccming the accuracy of 14 G_ C_ Goode.
the dctcrmination
of the c5te constants
17 T_ P_ FehIner_ f_ Anzrr_ ChemSac_. 89 (1967) 6477_ 18 cf_ L_ Maier in G- M_ Kosohpoff and L_ Maier (Eds). Organic Phovhorrur
19 20 II
22 23 lit 25 26 27
Compormds,
Vol. 1.
Wiley-lntuscien~ London. 1972_ Elsevier. Amsterdam, A_ J_ Kirby xd S_ G. Warren. 7Xc Orgatic Clkmktry of Phosphor-. X967_ H- NGth, Z- Ncmujimrt. B, I5 (1960) 337. K_ Isskib and \V- Se&l. C/rem &r-, 92 (1959) 2681. H- Hoffinann. R Griinevald and L_ Homer, C/&n. Ser_, 93 (1960) 861_ R. W_ Culkn. Colr f_ Chr~r. 39 (1960) 439_ K--P_ Wancze~ Z_ Nutm-forsch A. to bc published_ K--P- Wzuwzck ad G.-V- l&chcnthalcr, Dm_ lcloss Swcrrun~, Vol_ 4. to bc published_ M. L. Gross and F- \V_ Mcl_afkrty~ I_ Amu_ C-hem- Z&c_-. 93 (1971) 1267_ R_ M_ Stanley and I_ 1- Beauchamp, A Amcr_ Chcm_ Sot_, 96 (1974) 6252
.lournai of Mass
Specrronrrrry
and Ion P_?+sics. I 7 (I975) 73-X - Printed in The Netherkmds
c Ekcvicr Scientific Publishing Company. Amsterdam
MASS SPECTRUM THYL PHOSPHINE SPECTROMETRY*
KARL-PETER
received
AKD
wAsczEK*
lnrrirur ,Gr ph~x-ik&xhc (First
AND ION-MOLECULE REACTIONS INVESTIGATED BY ION CYCLOTRON
S August
Chemie 1974;
ZDEXEK-CHRISTIXX dcr Unircrsirti~r Fbankfiur,
OF -TRIMERESONANCE
PROFOUS Fmnh-fir
( IVcsr GcrnzanF)
in rcviscd form 21 November 1974)
Mass spectrum and ion-molecule reactions of trimethylphosphine have been studied by ion cyclotron resonance spectrometry- The product ions obtained can be classified as ions with two phosphorus atoms, P2R3*, P?R,-+* P,RSi and P,R,-* (R = CH, or H), phosphocium ions and ions with the same masses as primary ions resultirq from charge exchaqe and collision dissxiation reactions_ The dimeric mokcular ion Pz (CH,),-i and the tertiary ion P, (CH.),* are also detected_ The mechanism of several ion-molecule reactions is discussed_ Although 60 ion-molecule reactions h:ve ken detected, each primary ion shows onIy one or two predominating ion-mokcule reactions. The molecular ion undergoes a displacement reaction with the neutral molecule, with a rate constant of O-32 - lO-‘O cm3 molecule -’ s-I* to yield pratamethyldiphosphonium (1 +) product ion3 and forms the protonated molecule with a rate constant of O-10 - 1O-‘o cm3 molecule-’ s-I_ The P(CH,)= + ion reacts with the neutral to form the protonated molecule with a rate constant of 2.7 - IO-” cm’ molecule-’ s-‘_TheP(CH&* ionwhichhasprobablyacyclicstructureunder~oesaphosphorus cation transfer reaction to yield the P1(CH3)3* product ion with a rate constant of l-4 - lO-‘O cm3 molecule s-‘_ The structure of this product ion is discussed_
Until now, only a few mass sjxctrometrk investi-tions on trimethylFhosphine have been published [l-6]_ The mass spectra obtained by Halman P_], by Wada and Kiser [4] and by Kostyanovsky and Yakshin [S] differ substantially_ * Dcdicatcd10 PrckssorH- Hm on Ihe occasisn of his 6@b birtbdaye Author to u-horn corrcspondcnce should be addressed-
ft
24 The decompositions
of the metastable ions appcarin_e in the mass spectrum
by Gillis and Long [6]_ They * ion in the metztable decompositions which lead to fiagment ions of higher order_ They assigxd the ion with rplie = 41 and composition C,Hs* to a rearranement which joked the three of
trimethylphosphine
have
been
investigated
showed the importance of the P(CH3),CH,
seeante
methyl groups-
While
the mass spectrum and the ion-molecule
have already
ken
the relative McDaniel
proton
affinity
et al- [IO]_These
77 and m/c =
ICR spectrometry
studied by
of
[7] of
trimethylphosphine
authors
137 are formed
has been assigxd
reactions of phosphine
[S, 9]- only a determination
by ion-molecule
to the protonated
has
been
carried
out-by
that two product ions with m/e=
mentioned
reactions.
The
first production
trimethylphosphine.
In this paper a study of the ion chemistry of the positive ions of trimethylphosphine
is presented-
EXPERIMEXTAL Theexperiments V 5900, Vatian
were carried out with a standard ICR spectrometer (Varisn
Associates,
Palo Alto,
in the literature [I I]_ Therefore be given_ A flat ICR termination
Ca!if_)
which has aheady
only a brief description
been described
of the measurements
cell with three sections was used, thus allowing
of the spectra and rate constants
All ICR spectm were recorded
than a square
ICR
a .betterde-
cell [12]_
at an electron energy of 30 eV unless other-
wise stated, by the electron energy pulse technique.
Electron
trap currents were
typically in the region of IO- 7 A giving total ion currents in the range lo- “-IOA so that the space charge and ion trapping appearance
potentials
wil:
were determined
would
”
be relatively small [13]_ The
usin g the same technique
and also the
drift plates pulse technique_ The electron energy scale was calibrated
in the usual
way usin_e rare gases_ AlI
ions appearing
in the spectrum
\;_erc subjected
to double
resonance
experiments at several pressures and irradiatin_r field strengths- The results of the double resonance experiments were supponed Rate
constants
were
obtained
by pressure plots whenever possible-
by the approximation
method
of Goode
et al- [14]r ki
A*. i n15
=
nrz
1 -__
1
[Ml fi+Hfp
where ki is the rate constant of the formation of the ith secondary ion, A, and d,, i and t+ and ntsr are the sir&e resonance intensities and masses of the primary and the ith secondary ions, ri and rP are the times the ions spend in the
25 source
and analyzer regions, which were determined
the magnetic and electric field strengths, and [M] neutral species_ A plot of
versus pr-ure
$ves
a straight line with a slope proportional
The great number of ion-molecule makes it necessary
to determine
[15]_ The rate constant molecular ion
from the known values of is the number density of the
reactions
the rate constants
of the formation
to ki-
occurring
in
the spectrum
at several electron
of the protonated
molecule
entrgics from
the
and the neutral molecule xvas determined at 1OBOeV electron ener_qv to 10S4 torr simultaneously with the formation
and a pressure ranSinS from low5 rate constant encrsy,
of the pentamethyldiphosphonium
the first fragment
neutral molecule
ion_ At :2_00 eV electron
ion P(CH.),+ has appeared and reacts also with the P(CH3),H*_ P=(CH,),’ and PI(CH,),* with abun-
yieldin
dances sufficient to determine For calculation
(I+)
rate constants-
of the absolute
values of the rate constants
to know the exact values of the pressure in the ICR
it is necessary
cc11and the residence times
of the ions in the source and analyzer regions. This pressure was determined by measuring the pumping current of the ion pump (Varian Vaclon pump) and the residence times were caiculated
as mentioned
approximate
the absolute
values_ Therefore
above_ Both procedures rate constants
probably
yield only have
only an absolute accuracy of about 50 T’_ However the relative values of the rate con-
stants are more
accurately
known.
Their
relative accuracy
should
be approxi-
mateIy 10 % [16]_ Trimethylphosphine phine P *
[S, 9, 171. P+
ions
&iSnard
(X >
trap
ions appear
1) were
synthesis
composition
does not pyrolize
[IS]
only
not observed_
with smali abundance Trimethplphosphine
and precipitated
in a
as does
iodide complex
phos-
in the spectrum.
was prepared
as silver iodide complex_
of the trimethylphosphine-silver
distillation
at the hot filament
Thermal
by a de-
yields. by tnp-to-
vacuum system, a very pure product containing
no im-
purities detectable with the ICR spectrometer-
RESULTS
ICR
AXD
DISCUSSION
s_rlecrnnn of rrinierl?)rlplrosprxine
The ICR spectrum of trimethylphosphine
at a pressure of IO-’ tot-r, shown
in Fig_ 1, is relatively simple_ The mass corrected relative intensities are compared
26
76
’ fil Fig_ I_ ICR of 33 cv_ TABLE
I
miC
Ion
spectrum
15 16 34 35 4t 43
GHs+ PC*
44 45
PCH- + PCH2+
46 47 57 58 59 60 61 73 75 76
PCH,-+ HPCH, P(CH)=+ PC*H,-
of trimcthyiphcnphinc
Rdarire aLuvtdzurrcs -This work 7aIman [Z] -i2cv 3oeY
CH,‘ CH&-+ PH,- +
110
6.6
95
6 78.6 4.4
PI&’
73 113 209 112 780 108
+
WCH,),* PCzHs-+
P(CH&+
by HaImau
of Kostyanovsky
p]
show
and an &m-on
W-aai~amd Kihr [4 J 70CV
energy
Kox~~-amrsk_tad fsakdxitzis]
73.5 653 635 1000 45 191 653
1. The
[5]_ The
but without comments_
100 224
662 94
633
1000
loo0
200
200
782
800
results obtained
better agreement
and Yakshin
280
103 111 325 118
by Wada
and Kiser
with our measurements
dimethylpkosphiuium
peak in all spectra_ The ion m/e = 41 is to be found tained by Halman
torr
II 121 564
56-S 103 4x9
loo0 74 193 683
PU-I,L+ PGI-?5+ P(CH&CH,+
IO-=
8 7
67-4 2%
227 +
of
152
107
with literature values in Table and
at a ~rcs~urc
[4]
than those
ion is the base
only in the spectrum
ob-
27 If the pressure is raised, numerous An
ICR
spectrum recorded
assigned to PHI* in Fis
at IO-’
eons (x = 0, I, 2,3,4)
3 recorded at 5 - IO-’
the extraordinarily
spectrum
60
in the spectrum.
in Fi_g_ 2_ The new peaks are
and to hydrocarbon
ions_ The spectrum
torr in the mass range from 1,1/e= 40 to 140 shows
great number of product ions formed.
10
Fig- 2- ICR of 30 cv_
new peaks are observed
torr is shown
m/e-
60 I
of trimcthy-lphosphinc
80 mre -100
101
80
at a pressure
120
of IO-’
torr zmd an electron
energy
140
Fig. 3. ICR spectrum of trimcthylphosphincat a prcssurc of 5 - 10e5 torr and an electron energy of 30 ev_
,
potentials of the main primary ions and the three most The appearance abundant product ions are listed in Table 2_ These values do not compare weli those obtained by Fischler and Halman [3] and by Wada and Kiser [4]_ However, the value for the appearance potential of the molecular ion, 8_4&0_3 eV, is close to the value obtained ‘by Wada and Kiser, S_6Of:O_2 eV, while the value of Fisehlei and Hahnan
differs by +O_S eV- Our appearance
potentials of the fragment
the _eret differences cannot
are in general smaller thaa the cited values. however
potentials; ions are close to that of the molecular ion_ be rationalized-
APPfARAscE
The appearance
OF
POTEL.
THE
yxI_X
A_P_ (CL-)
rn+
1023
1% THE
of the three most
ICR
SPECTRUU
OF
abundant
I~-__c___._Fiscix~crundHdmm [;I
W-ah ad
41 45
14.1 14.3
17
16.1 fO.4
46
137
14.0 20.3
47
13.8
14.7 20.7,
57 59 61
12-S 13-o IO-9
73
92 8.6
76 77
s-4 9.0
107 137
9-o 8-7
x The unarrtinty
----
&I
product
TRIXEl-HYLPHOSPHI_SE
Thish-0&
75
ions
15 _I 11_8~02
16.7 20-3 14-O 202 II-7 2 02
I1_8&0.2
IO2 &O-S
92~0s
Kixrr[IJ
--
SA!iO_rO_~
of this data is 50.3 cV_
lotz-molecule reactions
Figures
4 and
5 show
the variation
tensities of the main primary and product 8 - 10-j
abundant
ion
stability of this ion is ah-eady well known
from
torr the trimethylphosphonium
in the spectrum_ The remarkable
with pressure of single resonance inions- At a pressure higher than about
ion
becomes
the
most
chemistry_ Only the proportions of the P-,(CH&* and P(CH,),CH2* ions show a comparable increase with pressure_ At high pressures the former ion reaches almost 10 o/0 of the total ion intensity, and the latter almost 20 y!_ The
soIution
proportion of z!l other product ions increases much more slowly with pressure. The abundance of ail primary ions, with the exception of the molecular ion. decreases stron.qIy if the pressure is raised- The proportion of the molecular ion
p(krr) Fig_ 1_ Mas-corrcctcd
rchtitr:
intensities
of the major
ions in the ICR spectrum of trimethb-t-
phosphinc as a function of the total pressure_
Fie 5_ Mllsz-corrcctcd reIativ~ intensities of the low abundant ions in the ICR spectrum of trimcthylphosphirre as ;L functiun of the total pressure-
increases with pressure; this results from charge exchange reactions becoming important at higher pressures_ Table 3 lists all ion-molecule reactions of the primary ions and Table 4 those of the secondary ions_ The reactions are numbered startins with the dimeric molecular ion formed from the molecular ion and the neutral mokcule. The neutral products being formed in the course of the ion-molecule reactions are not listed in the Tables.
30 TABLE
3
IOX-MOLECULE
Product ions
RUCCIOSS
Primary
OF THE
PRlBlARY
10s
OFTRI
MElHYLFHOSPHISE
IX
T-ME MASS
RASSE
FROM
m:C
ions +
PlCH,l,-
x0_
P(Cli,?-
+
X0_
P(Cff=)=
+
NO_
Diphosphine ions P2%- *
P,(CHdaP2(CH&H-’
P,R,*
*
3
PACHA9
PdCH,MCHA+ PAC&),(CW,+
4
P,(CH,),C=+?
6
P,R,-•
Phasphonium
P,KH,)s*
IS
P,(CH,MCH,L+
I9
P,(CH,),C,
20
P,(CH,),(CH,),+
31
5 l?
PACHAd%+
21
PACH,),Hz’
32
P,KH,ML+
22
PdCH,LH,+
33 33
Pz(CHlrP-H,’
7
PACHA-
8
PI(CHA-
9
P,(CH,),H-+
35 36
l
Pr(CH,),HP,R, +
I 2
*
PACH,),* P,(CH&H+
+
10
PACH,),‘,
23
P,(CH,),
I1
P2(CH&H+
24
PACH,hH*
12
HP(CHd>+
25
HPKH,),
13
P(CH,)ICH2
26
P(CHAC=Ha+ P(CH,)zCH= *
40
PC,H.*
41
14
P(CH,),CHz+
27
‘8
+
37
ions
HP(CHdx+
P(CH,)=CH= P(CH,),CH=+
+
+
*
3s 39
Colhsion d-fsmciarions
P(CH,L
+
is
P(Cr-r,), +
I6
P(CH&
P(CH)2 +
17
P(CH)z *
29
P(CH)z *
42
P(CH,k+
30
P(CHd,-+
43
+
chizrgc excIrangc
31
= 3orom;‘c
P(CH),
=
190
+
137 135 4-t
133
P,(CH,),C,*l
45
131
P~(Cli,)~H,+
46
P=(CH,),(CH):
l
109 P&H&H,
+
95
49
122
Pr(CHJ)T(CH)z*
118
47
10s
107 93
HP(C!i,),
*
P(CH,),C,H,+
53
117
P&He
5-l
75
77
50 +
103 75 73 P(CH,),CH,-
+
51
P(CH&CHz+
5’
90
61 59 57
WC&),-
+
a!?a
76
32 TABLE
4
IOXiMOIJXULE
REACTIOS
sccoRaitr_b-
OF
SECOSDARY
IO.SS
YIELDING
TERTIARY
IOX
ion ML
PdCHA’
Pz
x0-
(CH,), +
Dincciarion
58
P&H,),+ Merh_rfgrrup rmtqfcr P,(CH,L-+ P,(CH,k +
55 56
59 60
PACH3)6-+
P,U-Ll,+ Addiciiun * P,(CHh
57
All the reactions can be assigned to only a few reaction types already known
well
from chemistry: (I)
Reactions which yield product ions with two or more phosphorus
Ions with the compositions
P2R3*,
were detected_ The dimeric
P2R4-ir
molecular
P2R5*
and P,R,-*
atoms_
(R = CH,
ion and a tertiary ion
with
or H)
three phos-
phorus atoms were also observed(2) Reactions one phosphorus molecule-
which yield phosphonium
and quasi phosphonium
atom- The most important
the most abundant
(3) Collision
product
dissociation
ion in this group
ions with
is the protofiated
ion observed_
reactions are observed
at elevated pressures_
(4) At pressures greater than lob6 torr, charge exchange
reactions become
important_ Prodrtct ions with two or three pi~osphorus atom< The secondary reactiocs
ions with two phosphorus
of molecular
into four groups: phenium
atoms formed
2nd its fi-a_ment
trimetbylphosphine
(a) P,R,- * ions, (b) diphosphonium
ions P,R,-*
and (d)
diphosphinium
by ion-molecule
ions can be divided
ions P,R,*,
ions PZR3*,
(c) diphos-
where
R represents
either a hydrogen atom ur a methyl group- Ions having only methyl groups bonded to the phosphorus hydrosn two
atoms and methyl groups-
methy!
P-,(CH&H-’
reactions
groups
occur
in
and P,(CH,),H’
Most addition
atoms are much more abundant
of the product
reactions, which
Almost
all possible
spectrum:
mixed ions with at least
P2(CH,)rHS+,
P,(CH,),H1*,
were detected-
ions described
displacement
include
the
than the mixed ions containin
are formed
reactions,
rearrangements_
product ions with small abundances-
atom
The
by four types of reactions:
or ion transfer
reactions
last type of reaction
and
yields only
33 In all cases an electrophihc attack by the phosphorus atom cf the ion on the phosphorus atom of the neutral molecuIe must be assumed_ The phosphorus atom is we’ll known as a highly nuclcophilic centre from the chemistry of alkyl phosphines [IS, 191.The lifetime of the intermediate must be shorter than IO-* s in most of the observed reactions because it can be detected, by ion cyclotron double resonance experiments, only in a few cases as a precursor ion of the final products. Detection of the intermediate is howeverpossible for the reaction of the dimethylphosphinium ion which yields the ?1(CH3),+ product ion:
I
Fis
1
m 6_
209
300
kHz
Ion cyclotron double resonancespectrumof the P,(CH&+
im at a pressure of 1. 10es
IOft_
The corresponding
ion cyclotron
The other two formation detecred in this spectrumr
double
reactions
resonance
of the dimethyl
spectrum is shown diphosphenium
in FIN_ 6_
ion are also
34 Reactions
(10).
phosphorus
(23)
cation
and
transfer
reagent is the P(CH,),+ P(CH,)?’
(36)
reactions_
most powerful
phosphorus
as
transfer
ion and the fragment ions P(CH,)Z
addition
reactions
ion (1)
P,(CH,),’
+,
the neutral molecule
wi’h
(IIS), P,(CH,),(CH,),^
(44)
phosphorus
attack
by the phosphorus
atom
atom of the neutral is assumed,
structure results as tSe product of only small abundances,
ions_ The addition
normally dissociation
primary addition product occurs_ The most intense ion with phosphanium
ions and can be regarded
undergo
an electrophilic
nucleophilic
The
*
molecular
(31) and P,(CH,),(CH)I+ If however
PZ(CH,),
ion- The molecular
and P(CH)?’
and produce the dimeric
yield
(1 t ) ion, is mainly
two
ion
reactions yield product
rather than stabilization
phosphorus
formed
of the ion at the
a diphosphonium
atoms,
ions
of the
the pentamethyldi-
by ;1 displacement
reaction
of the
moJeeular ion_
(CH31,P‘-
C
PICH,),
-
_--
tCH,),P
PcH,l,
-\
-
-1%
,P-ycy
This reaction
is the main ion-molecute
Symme’ticaJJy substituted P2(CH,),’ It is easily formed
by alkylation
of the molecular
ion_ The
un-
ion has been known for a long time [20,21]_
of tetramethyldiphosphine
(CH,),P-P(CH,)LtCH,I The P-P
reaction
*
C%
-L4c
with methyliodide:
--+ (CH&P-P(CH&‘I-
bond in this ion is stabilized by the methyl _group+_ The bond is wakened
by eIectron-withdrawing trifluoromethyl
substituents at the phosphorus
groups_ The attempt to quartemize
or tetra-(trifluoromethyl)diphosphine
1231 results in dissociation
In the Iight of the results obtained the structure of the P&H,), bond are possible: rearrangement, and a PP(CH,),’ CH,P-P(CH
&
atoms such as phenyl or
tetraphenyldiphosphine of the P-P
bond_
for the pentame’-hyIdiphosphonium
ion,
* ion can he discussed_ Two
if the phosphorus
(221
structures with a P-P
cation transfer reactions take place without
the three methyl groups
remain
bonded
to one phosphorus
atom
torn will be formed; if rearrangement occurs, also the sttuctute * is possible- Although this question can only be decided finally
by a study of deuterated tioned that the ion-molecule and not P,(CH,),‘_
methylphosphines
which is planned,
reactions of the P(CH),+
it should
he men-
ion yield onlyP1(CH,)LH
*
35 This strongly indicates rearran_eement_ Therefore are believed
to occur-
Rearrangement
both structures of the Pz-(CH3)3i
ions with P-H
bonds
have already
been
mentioned_ The stabilization confirmed
in the case
mechanism
of the
via dissociation
fbrmation
of hydrogen
can also be observed during the course of secondary +
(CH)?P+ The formation
-
-!_
+P(CW,
V-W’*
ion formation:
PI(CHx),(CH,)z*
+
--, P,(CH,),(CH)z* --I -+ P,C,H,’
(CH,),P-*+P(CH,),
(H,+CH,-)
i-(2H,+CH,-)
(4) (5)
+(3H1+CH,-)
(6)
P~(CH&(CH,)=*+H2
p-c 1 5
H
+
+ P(CH,),
+3H,
+
9
P&H,*
of tertiary ions includes,
besides dissociation
tions. a further type of transfer reaction, namely methyl goup served in the case of secondary, At a pressure seater ion is formed
The
ion formation
than IO-’
by the following -
P,(CH,),’
P,(CH,),’
t- P(CH,),
-
PJCH&+
tiphosphines
of
are comparable
phine and methylphosphine
reac-
transfer, not ob-
4, reactions 55,59)_ (1 t)
two reactions:
+P(CH,),
reactions
(Table
and addition
tot-r the tertiary hexamethykriphosphonium
Pz(CH,L*
ion-molecule
molecules, EKin_g
reactions of higher order primary ions [6],
(57) -k&H,
(60)
trimethylphosphine
with the ion-molecule
yielding reactions
diphosphines
and
of dimethylphos-
[24 ]_ I-iowever, in the case of dimethylfluorophosphine
and methyldifiuorophosphine,
addition
product ions with two phosphorus
reactions
atoms
predominate
for formation
of
[3F]_
PJtospJxonium ions The most abundant Small contributions (3s) and P(CH)?+ Raction channel
product ion in the spectrum is the quasi phosphonium
which is mainly formed from the dimethylphosphinium
ion (CH,),PH*+,
come from the molecular
ion (25)_
ion (12) and from the P(CH,),*
(50) ions.
(12) can be a hydrogen
(13) being a hydrogen
H&H
atom or a proton transfer, the competin,o
atom transfer or a hydride
ion transfer
reaction:
36 The products of reactiow Two
corresponding
however
(12) and (13) differ only in the position of the charge-
channels occur in the case of the dimethylphosphinium
ion,
the neutral reaction products have one methyl group less_ Reaction
(25)
is a proton transfer, reaction (26), only a minor reaction channel, is a hydride ion transfer-
A rzzmarkable ion molecule reaction is tl,e addition nl/e = 41,
C3HS+, which yields also a phosph?nium
C,Hs+ +WH.),
reaction of the ion with
iocr
- (CH,M’GH,+
(53)
A second reaction channel of this ion is reaction 54 a further hydride ion transferNo tetramethyIphosphonium
ions have been detected (m/e = 91), ho\vever
an ion with RI/~ = 90 is formed durin, 0 the course of the ion-molecule
reactions
(14); (27), (51) and (52) These reactions can all be regarded as CHz- e ion transfer reactions leading to the molecular ion, (CHB),PCHI-‘,
of the simplest ylid. methylenetrimethylphosphor-
ane.
Several rate constants for the ion-molecuIe the dimethylphosphinium
ion and the P(CHt)?*
In general, quantitative undergoins
measurements
main ion-moL.uIe
methyldiphosphonlum
(I--)
(CH&P-*+P(CH&
reaction
ion,
ion have been determined-
show each of the main primaiy
mainly one characteristic ion-molecule
tion channels yield only small quantities The
reactions of the molecular
ions
reaction, while all other reac-
of product
ions_
of the mokcular
ion leads to the penta-
ion: --, (CH,)IP-P(CH,).+
with a rate constant, k,, 032 - 1O-‘o
+CH,-
cm3 molecule-’
s-‘_
(33) The rate constant of
the reaction:
(CWP*
+-PW-M,
has a value approximately cule-’
s-I_
molecular
f (CH&PCH,-
three times smalIer:
This rate constant
methylphosphine as from
--, (CH&PH*
is remarkably
k,Z = O-10 - IO-”
small- This
ion differs substantially
merhyldifiuarophosphine
(12)
from
cm3
mole-
behaviour
of the tri-
phosphine
[S] as bvell
and dimethylfluorophosphine
[S]
where
the
37 molecular
ions react to form the correspondins
protonated
tions having comparatively Parse rate constants_ The ion-molecule reaction of the P(CH.)=* 9s 7: of all product
ion formed
tion (25) with 3 rate constsnt the ion-mohxule
ion is the predominant which Fields the P,(CH,), rate constant
the reac-
ion which yields approximately
from this primary ion is the proton transfer reacof X-,, = 27 - IO-”
cm3 molecule-’
reaction with the largest rate constant
investi@ed_ While the P(CH,),
molecules,
* ion is the main proton phosphorus
transfer
observed
s-I_
This is
in the system
resent,
the P(CH,)?+
transfer reagent_ Its ion-molzcule
reaction,
9 ion arzd the ethylene molecule, has a surprisingy
if the pressxe
does not exceed
10m5 torrr kJ6 =
iar_p,-
1.4 - 1O-1o cm3
molecule- ’ s- ‘_ In the iitenture a cyclic structure of t5e P(CH?),* ion has been discussed [2, 51. The ease of the phosphorus transfer reaction supports this cyclic structure by the same arsumcnts distinguish
between c+ic
with ammonia_
already and
emphasized
linear
C,H,-*
by Gross
In fact. the dimethylphosphinium
structure, undersocs
oniy a minor phosphorus
We thank Professor
H_ Hartmann
the research facilities made available
and
McLafErty
ions with the aid
[X]
to
of their reactions
ion, which cannot
have a cyclic
transfer reaction.
for his encouraging
to Professor
Hartmann
support
and use of
by the Deutsche
Forschuws~emeinschaft_ We thank aIso Dr_ G--V_ Rlischenthaler, -5 fiir Anorganische Chemie der Technischen Universitst Braunschweig,
Lehrstuhf
B
for samples
of trimethylphosphine*,
REFFRESCES 1 Z 3 3 5
6 7 S 9
W- R- Cullcn and D C- Frosr, Cuu. /_ C-lrcnr..40 (1962) 390. M. Halman. J_ Chcnr_ SW_. Lan&n. (1962) 3270_ J_ Fischlcr and %I_ Halman, I_ C&m_ Sot__, London. (1964) 31_ Y- Wada and R- W- Kiscr. J_ Ph!x_ Chcnr.. 68 (1964) 2290. R_ G_ Rosr~~noxky and V_ V_ Y&shin. Ix_ Akud_ Nauk SSSR. Scr- Khim.. (1967) 2363R_ G- Gillis and G_ J_ Long. Org. Mass Sprclrunr., 2 (1969) 131% J- W- LonS and J_ L_ Franklin. I_ Amcr_ C&m. SOC., 96 (197-t) 2320_ J_ R_ Eyicr, Znorg_ Chcm.. 9 (I 970) 93 I _ D_ Holrz, J_ L Bczu~champand J_ R_ Eylcr. I_ Ann_ Chem_ Sot-, 91<1970) 7ML
* Now ad&d
38 10 D. H. McDzniel. N_ B_ Coffman and J_ M_ Strong. J_ .-her_ Cl;mr_ Srrc-. 92 (1970) 6697_ 11 H- Hartmann. K--H_ Lcbert and K--P_ Wancxk. Topics in Current Chemktry, 43 (1973) 57. II S_ E Butdl, Jr_, I_ Chern. P/rp_, 50 (1969) 4125. I3 G- C_ Goode_ h J_ Ferrer-Correia and K- R Jt~ing, Int- 1. Afau Spcrrrom. Ion P&x_, 5 (1970)
229_
R_ M_ O’~MaIfey. A_ J_ Ferrer-Correia. R_ J_ hlssey, K_ R. Jennings- J_ H. Fucrelt and P_ M_ l_ltudlyn. IM- /- Afuss Spccrrorn. Ion P&-s_. 5 (1970) 393_ 15 J_ L_ Franklin, J_ Chem_ l&c_, 40 (1963) 284_ 16 Tht aulho~ e?rpre~s tbit gratitude to a dcrec for his comments conccming the accuracy of 14 G_ C_ Goode.
the dctcrmination
of the c5te constants
17 T_ P_ FehIner_ f_ Anzrr_ ChemSac_. 89 (1967) 6477_ 18 cf_ L_ Maier in G- M_ Kosohpoff and L_ Maier (Eds). Organic Phovhorrur
19 20 II
22 23 lit 25 26 27
Compormds,
Vol. 1.
Wiley-lntuscien~ London. 1972_ Elsevier. Amsterdam, A_ J_ Kirby xd S_ G. Warren. 7Xc Orgatic Clkmktry of Phosphor-. X967_ H- NGth, Z- Ncmujimrt. B, I5 (1960) 337. K_ Isskib and \V- Se&l. C/rem &r-, 92 (1959) 2681. H- Hoffinann. R Griinevald and L_ Homer, C/&n. Ser_, 93 (1960) 861_ R. W_ Culkn. Colr f_ Chr~r. 39 (1960) 439_ K--P_ Wancze~ Z_ Nutm-forsch A. to bc published_ K--P- Wzuwzck ad G.-V- l&chcnthalcr, Dm_ lcloss Swcrrun~, Vol_ 4. to bc published_ M. L. Gross and F- \V_ Mcl_afkrty~ I_ Amu_ C-hem- Z&c_-. 93 (1971) 1267_ R_ M_ Stanley and I_ 1- Beauchamp, A Amcr_ Chcm_ Sot_, 96 (1974) 6252