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Isomerization with Methyl Migration in Trimethyl Phosphite-Arsenido and -Antimonido Complexes of Transition Metals.

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Trapping of Unstable a-Pyrone/Singlet Oxygen
Adduct by Reduction with Diazene[**]
By Waldemar Adam and Ihsan Erden"]
Unstable endoperoxides such as the singlet oxygen adducts
of cyclopentadiene['"I, fulvenes''bl, and furans['Clcan be conveniently and selectively reduced to their respective dihydroendoperoxides, thus preserving the bicyclic structure without
severing the peroxide bond. This reductive trapping technique
has now been extended to the hitherto unknown and unstable
endoperoxide of a-pyrone (2). Presently we report on the
chemistry of these unusual bicyclic endoperoxides.
On photo-oxygenation of a-pyrone ( 1 ) in CHzClz at 0°C
using tetraphenylporphyrin as sensitizer and a General Electric
400 W sodium lamp resulted in slow consumption of the a-pyrone as monitored by subambient 'H-NMR spectroscopy. After
12 h essentially all the a-pyrone had been consumed and the
characteristic multiplets at 6=5.9%6.3 and 7.0-7.5 of the 1,3diene were replaced by broad singlets at 6=6.80 (olefinic
H) and 5.02 and 6.25 (bridgehead H). When allowed to warm
up to 30"C, carbon dioxide was rapidly evolved and the
above proton resonances were replaced by two multiplets
at 6 = 10.25 (aldehydic H) and 6.48 (olefinic H) corresponding
to the signals of malealdehyde ( 4 ) as confirmed by an authentic
sample[2'. These results suggested intervention of the novel
and thermally labile cyclic peroxide (2) as an intermediate
in the singlet oxygenation of ( 1 ) . We decided to isolate and
purify it and confirm its structure.
Low temperature chromatography of the photo-oxygenated
a-pyrone reaction mixture on silica gel at -40°C and elution
with CHzCl2 afforded pure (2)['1. Efforts to recrystallize it
at low temperature failed. Reduction of (2) with excess diimide
in CHzClzat - 78 "C['a341followedby column chromatography
on silica gel at -20°C and eluting with CHzClz gave the
saturated cyclic peroxide (3)"l. This new compound is thermally considerably more stable than its unsaturated precursor
(2); decarboxylation of (3) to succinaldehyde on heating
at 140°C was confirmed by IR and 'H-NMR spectroscopy
on an authentic sample.
An interesting feature of (3) was its emission of light during
decarboxylation to succinaldehyde[6? Thus, either ( 3 ) stores
sufficient energy so that simultaneous peroxide bond fission
and decarboxylation leads to electronically excited succinaldehyde directly or the intermediary bicyclic dioxetane (6) is
first formed on decarboxylation of (3). Subsequent ring opening of the dioxetane (6) would be expected to afford electronically excited s~ccinaldehyde[~!
Received: January 23, 1978 [Z 912b IE]
German version: Angew. Chem. YO. 223 (1978)
CAS Registry numbers:
( I ) , 504-31-4; ( 2 ) . 65651-81-2; ( 3 ) , 65651-82-3; ( 4 ) , 3675-13-6; (6), 3769327-9; diazene, 3618-05-1
[I] a) W Adam, H . J . Eggelte, J. Org. Chem. 42, 3987 (1977); b) W Adam,
I . Erden, Angew. Chem. YO, 223 (1978); Angew. Chem. lnt. Ed. Engl.
17, 210 (1978); c ) W Adam, H . J . Eggelte, A . Rodrlguez, unpublished.
121 K . Alder, H . Betsing, K . Heimbach, Justus Liebigs Ann. Chem. 638,
198 (1960).
[3] Colorless liquid, yield 85%; 'H-NMR (CCI4, TMS): 6=5.02 (br. s,
IH), 6.25 (br. s, IH), 6.80 (br. s , 2H); 1R (CCL): 1810, 1325, 1265,
1030,960 c m - ' ; MS: m/e=128.
r41 W Adam. H . Eaaelte. Annew. Chem. 89, 762 (1977); Angew. Chem.
Int. Ed. Engl. 16, 713 (1977).
r51 Colorless solid, m. p. 30°C. yield 25 %; 'H-NMR (CC14, TMS): 6 = 1.852.60 (m, 4H), 4.45 (m, IH), 5.78 (m, 1H); IR (CC14): 2950, 1800, 1340,
1300, 1180, 1050, 970 c m - l ; MS: m/e=130.
[6] W Adam, Angew. Chem. 86, 683 (1974); Angew. Chem. Int. Ed. Engl.
13, 619 (1974).
171 W Adam, Adv. Heterocycl. Chem. 21, 437 (1977).
L
A
L
_
I"
Isomerization with Methyl Migration in Trimethyl
Phosphite-Arsenido and -Antimonido Complexes of
Transition Metals"]
By Wolfgang Malisch and Reinhard Junta[*]
The E atom in complexes of the type CP(CO)~(PR~)ME(CH3)2(M=Mo, W; E=As, Sb; R=CH3) is a center of
unusually high basic activity which is manifested in a
pronounced tendency to react with electrophiles[21.The electron rich state of the E atoms is also responsible for the
irreversible isomerization with a methyl shift from the R3P
ligand to the arsenido or antimonido function which we have
observed in derivatives with R=OCH3.
The isomerizing complexes (2) are accessible by reaction
of the tricarbonyl precursors ( 1 )C31 in benzene with equimolar
amounts of trimethyl phosphite at 25 "C [ ( 1 a)] or 50°C [ ( 1 b )
and ( 1 c)]. Under these conditions only the CO group in
the trans position relative to the o-bonded (CH3)2Egroup
is replaced[4!
+
FYOCHh
CP(CO)~M-E(CH~)Z
( l a ) , M = Mo, E = A s
( I b ) , M = W , E = As
( I c ) , M = W , E = Sb
~-
[*I Prof. Dr. W. Adam ( N I H Career Development Awardee, 1975-1980),
Dr. I. Erden
Department of Chemistry
University of Puerto Rico
Rio Piedras, PR 00931 (USA)
[**I Cyclic Peroxides, Part 65. This work was supported by the Petroleum
Research Fund (Grant 8341-AC-1,4), administered by the American Chemical
Society, the National Science Foundation (Grant CHE-72-04956-A-04) and
the National Institutes of Health (Grants GM-22119-02, GM-00141-02, and
RR-8102-04). We thank Prof. Dr. A . de Meijere, Gottingen, for supplying
the a-pyrone. -Part 64:[I b].
Angew. Chem. Int. Ed. Engl. 1 7 (1978) N o . 3
( W :m . p .
68-70°C
(26): m . p . 80-82OC
(3a): m . p . 152-154OC
(3b)decomp. above 1 6 7 O C
( 2 C ) : m . p . 87°C
(3c): m . p . 177-178°C
[*] Priv.-Doz. Dr. W. Malisch, Dipl.-Chem. R. Janta
Institut fur Anorganische Chemie der Universitat
Am Hubland, D-8700 Wurzburg (Germany)
211
The rearrangement (2)+ (3) which is readily observed by
'H-NMR spectroscopy sets in at room temperature in the
presence or absence of solvent, can be thermally accelerated,
and proceeds with retention at the transition metalL4]. It is
complete within 7d in the case of ( 2 a ) in CHCI3 ( 0 . 4 6 ~
solution, 25 "C). Rate-determining factors are not only the
concentration of the trimethyl phosphite complex but also
the nature of its E and M atoms and the solvent polarity
[k,,, (CHCI3, 25°C) for As:Sb=2:1, Mo:W=1:1.5;
CHC13:C&= 350: I]. These observations and the fact that
an equimolar mixture of ( 2 n ) and ( 2 6 ) rearranges just as
fast as pure ( 2 b ) [catalytic action of ( 2 b ) l unequivocally
indicate intermolecular site exchange of the methyl group.
The composition and structure of the crystalline, deep and
pale yellow complexes ( 2 ) and (31, respectively, have been
confirmed by elemental analysis and mass, IR, and NMR
('H, 13C, 31P)spectra. Compounds of the same isomeric type
exhibit almost identical 6(3'P) and J(3'PL83W)
These
data are therefore very suitable for rapid identification of
the isomers which differ especiallyin their solubility properties.
Unlike ( 2 ) , the thermally stable rearrangement product is
soluble only in polar solvents (CHC13,CH3CN).
The O+As(Sb) methyl shift presented in this communication transforms a phosphite into a phosphonate ligand (with
concomitant formation of a trimethylarsane(-stibane) ligand)c6]
without assistance by alkyl halides as is generally required['!
Compared with the few known examples of direct P-0 bond
formation as a result of methyl migration['], the reaction
proceeds under astonishingly mild conditions. It therefore
follows that the donor strength of transition metal units
endows 5B atoms with a striking ability to take over methyl
groups.
In accord with this interpretation, the bismetallostibanes
( 5 ) accessible from trimethyl phosphite and dinuclear complexes (4)C91 by double trans-CO substitution isomerize even
more readily than the systems in the monometal series, since
the basic acceptor center is now exposed to the influence of
two metal donor ligands. In the case of ( 5 b), the antimony
bridge is methylated so quickly that ( 5 6 ) itself can only
be detected as an intermediate by spectroscopy.
I
Experimental
( 5 a ) :P(OCH3)3(295 mg, 2.37 mmol) is added to a solution
of [C5H5(C0)3Mo]2SbCH3[9]
(505 mg, 0.79 mmol) in benzene
(30ml) and the mixture is stirred at room temperature for 2 h
(evolution of CO!). Addition of pentane (20ml) to the filtered
solution which has been evaporated down to half its volume
precipitates a solid which is washed with cold pentane (5 ml)
and dried in an oil-pump vacuum; yield 756mg (91%) of
(5 0 ) .
( 6 a ) : Compound (5a) (371 mg, 0.45 mmol) is heated in
benzene (20ml) to 60°C for 6 h. Insoluble products are filtered
off, the solvent is removed under vacuum, and the solid residue
washed with pentane (4 ml); yield 302 mg (81 %) of ( 6 a ) .
'H-NMR (TMS int.): ( S a ) in C6D6: 8C5H55.11 (d, 10H),
3 J ~ c 1.2;
~ p 6CH30P 3.4 (d, 18H), 3 J ~ c o p11.6; GCH3Sb 2.4
(s, 3H). ( 6 a ) in CDCI3: 6C5H5 5.19 (d, 5H), 3 J H C M p 1.2;
6CH30P 3.29 (d, 9H), 3JHc0p
12.0; 6C5H5* 5.23 (d, 5H),
3 J ~ c 0.8;
~ p 6CH30P 3.95 (d, 6H), 3JHc0p
10.8; 6CH3Sb 1.65
(s, 6H).-3'P{1H}-NMR (C6D6, H3P04 ext.): ( 5 a ) 6= 197;
(6~6
) 4 8 7 , 120*.-IR (Vcoin C6H6): ( 5 U ) 1919 (S), 1898
(s), 1848 (vs), 1840 (Sh), 1810 (vs) cm-'; ( 6 a ) 1940 (Sh)*,
1929 (s), 1876 (s)*, 1855 (Sh) cm-l (*absorptions of the
Cp(C0)2M-P(O)[OMe]2 group).
Received: January 16, 1978 [Z 914 IE]
German version: Angew. Chem. 90,221 (1978)
Transition Metal Substituted 5 B Element Systems, Part 20. This work
was supported by the Deutsche Forschungsgemeinschaft.Part 19: W
Malisch, P . Punster, Chem. Ber., in press.
W Malisch, H . Rossner, K . Keller, R. Janta, J. Organomet. Chem. 133,
c 2 1 (1977).
W. Malisch, M . Kuhn, Angew. Chem. 86, 51 (1974); Angew. Chem. Int.
Ed. Engl. J3, 85 (1974).
The trans configuration of the complexes ( 2 ) and ( 3 ) is confirmed
by the intensity ratio vCO,,,/vCO.,,,
(> 1) and the appearance of a single
CO resonance with 'JCMp=25-37 Hz in the "C{'H}-NMR spectra.
S(31P)/J(31P183W)
[rel. H 3 P 0 4 ext./Hz]: phosphite complexes (C6D6)
( 2 b ) 160/460, ( 2 c ) 159/480, ( 5 b ) 159/430; phosphonate complexes
(CDCI3)(3b) 84/317, ( 3 ~82/325,(66)
)
90/347 [149/419 (CH30)JP-q.
Isomerization is accompanied by formal exchange of donor properties
of the two 5B element atoms towards the metallic center:
As(Sb)
one-electron donor ~====2
two-electron donor.
P
R. F . Hudson: Structure and Mechanism in Organo-Phosphorus Chemistry Academic Press, New York 1965; concerning CH31-assisted transformations of metal-coordinated trimethyl phosphite, cf. H . Werner, H .
Neukomm, W Kliiui, Helv. Chim. Acta 60, 326 (1977).
B. W Fitzsimmons, C . Hewlett, R. A. Shaw, J. Chem. SOC.1965, 7432;
I . M . Filatova, E. L. Zaitseva, A. P. Simanov, A. Ya. Yakubovich, J.
Gen. Chem. USSR 38, 1256 (1968).
W Malisch, P . Panster, Chem. Ber. 108, 700 (1975).
Tetraphenylphosphonium
Tetrakis(difluorooxosulfimidato)borate[**]
(5a): m . p . 5 6 ° C ( d e c o m p . )
(561
-
( 6 ~ ) m: . p . 145OC ( d e c o m p . )
( 6 6 ) : m . p . 194OC ( d e c o m p . )
According to the v C 0 absorption bands, the bridged complexes ( 5 ) exist in solution as a mixture of several conformers.
212
By Rainer Eisenbarth and Wolfgang Sundermeyer"]
We wish to report the synthesis of the tetraphenylphosphonium salt of tetrakis(difluorooxosu1fimidato)borate ( 3 ) ,
the first coordination compound containing only NSOF2
groups as ligands. Along with Li[B(N3)4][11 and
Li[B(NCS)4][21,(3) constitutes a further example of a tetra-
[*] Prof. Dr. W. Sundermeyer, Dip1.-Chem. R. Eisenbarth
Anorganisch-chemisches Institut der Universitat
im Neuenheimer Feld 270, D-6900 Heidelberg (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie. We thank Dr. G. Heckmann, Stuttgart, for recording and interpreting the "B-NMR spectrum.
Angew. Chem. Int. Ed. Engl. 17 (1978) No. 3
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methyl, trimethyl, metali, migration, phosphite, isomerization, arsenide, antimonid, transitional, complexes
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