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Hammett Constants of Phosphorus-containing Groups Determined from Nuclear Magnetic Resonance Spectra of para-Phosphorus-substituted Toluenes.

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butyl ether and, after decomposition of the excess of hydride
with sulfuric acid, the product (5) was distilled off together
with some solvent. By extraction with conc. sulfuric acid and
distillation over sodium we obtained a 37% yield of the
= -7.8 O (c =- 2.5, in
hydrocarbon (5)' b.p. 87 "C and [a]?,"
chloroform), which had a faint smell of petrol.
In comparison with the rotation [a]2$=-11.4' given by
Freudenberg 131 for the optically pure hydrocarbon our value
indicates a n optical activity of 68 %. The purity of (5) was
proved by its mass spectrum: M' = 100, (M-l5)+, (M-29).+,
Received: May 31, 1968
[ Z 793 IE]
German version: Angew. Chem. 80, 562 (1968)
[*I Dr. H. Brockmann jr. and D. Miiller-Enoch
Institut fur Molekulare Biologie, Biochemie und Biophysik
3301 Stockheim iiber Braunschweig, Mascheroder Weg 1
and Institut fur Organische Chemie
der Technischen Universitat
33 Braunschweig, Schleinitzstr. (Germany)
[l] Substituted Succinic Acids, Part 1.
[2] H. Brockmann j r . , Angew. Chem. 80, 234 (1968); Angew.
Chem. internat. Edit. 7, 222 (1968). Inadvertently an incorrect
value was given in this paper for the [a18 value of bis(p-bromophenacyl) (+)-threo-2-ethyl-3-methyIsucc1nate.The correct rotations at various wavelengths are: [a]'::= -36.5 % 3 ', [a]$', =
= -49.5 + 3 ', [ ~ r ] & = -87 & 4
(C = 1.3,
-38.5 i 3
in chloroform).
[3] K. Freudenberg and W . Lwowski, Liebigs Ann. Chem. 587,
213 (1954).
oxane molecules (cf. free dioxaner31: 1451, 1366, 1292, 1255,
1124, 1085, 1049, and 879 cm-1). The presence of C4Hs02
ligands is also proved by the mass spectrum [41.
In the N M R spectrum of ( I ) (in deuterioacetone) a sharp
signal is observed at r = 6.45 (referred to tetramethylsilane
as internal standard), which is hardly shifted in comparison
with that for free dioxane (T = 6.44). However, in this connection a very rapid exchange between solvent molecules and
the dioxane ligands in solution cannot be excluded; this would
explain why it has not yet been possible to recover the dioxane complex from its solution in acetone or deuterioacetone; moreover, on addition of acetonitrile to ( I ) an
extremely rapid exchange of ligands occurs, with quantitative
formation of (CH3CN)3Cr(CO)3.
The binuclear nature of the complex is shown by elemental
analysis and determination of the molecular weight, and on
the basis of the above results we assume structure ( I ) with
three dioxane molecules as bridging ligands. The weak donor
character of the ether oxygen atoms is probably mainly
responsible for the low stability of the compound. On the
other hand, its extreme reactivity, shown in the synthesis of the
hexaalkylborazole-tricarbonylchromiumcompounds,makes it
predestined as a starting material for the preparation of other
Cr(CO)3 complexes. In this connection it may be noted that
very recently tris(dimethy1amino)borane-tricarbonyltungsten
was obtained by reaction of (CH3CN)3W(C0)3 with
B[N(CH&], in dioxane [51. I t can be assumed that here also
a carbonyldioxanetungsten complex analogous to ( I ) is
formed as intermediate and that this then reacts rapidly with
the tris(dimethy1amino)borane by ligand exchange.
A Binuclear Chromium Complex with Dioxane as
Bridging Ligand
By H. Werner and E. Deckelmann I*]
Recently we reported the synthesis of hexaalkylborazoletricarbonylchromium compounds, the first representatives
of borazole-transition metal complexes. These are most
profitably obtained by starting with (CH3CN)3Cr(CO)3 or
analogous compounds of the type cis-AjCr(CO)3 (A =
amine)[l.21. The choice of solvent is decisive for success in
this method of preparation; dioxane has so far proved most
suitable for this purpose. Measurements of absorption in the
visible region indicated a t once that in the reaction of tris(amine)tricarbonylchromium compounds with hexaalkylborazoles the dioxane clearly acts, not merely as solvent, but
also as coordination partner.
We have now confirmed this assumption by isolating the binuclear complex (C4Hs02)3Cr2(C0)6 ( I ) . This orange, diamagnetic substance is extremely sensitive to air and glows o n
exposure to even traces of oxygen; as expected, it does not
sublime and it decomposes slowly even at room temperature.
Darkening is observed from 90°C if the material is heated
rapidly under nitrogen in a sealed tube. In the region of the
CO stretching vibrations, the I R spectrum (in KBr) shows
two strong bands of relative intensities 1 : 2 at 1919 and 1763
cm-1, thus confirming the existence of a Cr(C0)3 group. Absorptions at 1455, 1370, 1289, 1252, 1119, 1103, 1047, 879,
and 866cm-1 are ascribed to the coordinately bonded di-
1 g of (CH3CN)3Cr(C0)3 was treated with two successive
portions, each 50 ml, of dioxane in a two-necked flask under
nitrogen, and the solution was evaporated almost to dryness
in vacuum at a bath temperature of ca. 15 'C. The resulting
crystalline mass was made into a slurry with a little dioxane
and filtered rapidly through a G 3 fritted filter. The orange
solid thus isolated was washed several times with a few ml of
cold dioxane, then with ether, and was finally dried under a
high vacuum. The yield was 75 "/,.
Received: May 31, 1968
[ Z 795 IE]
German version: Angew. Chem. 80, 564 (1968)
[*I Prof. Dr. H. Werner and Dip1.-Chem. E. Deckelmann
Anorganisch-Chemisches Laboratorium
der Technischen Hochschule, Miinchen (Germany)
New address:
Anorganisch-ChemischesInstitut der Universitat Zurich
CH-8001 Zurich, Ramistr. 76 (Switzerland)
[ l] R. Prim and H . Werner, Angew. Chem. 79,63 (1967); Angew.
Chem. internat. Edit. 6, 91 (1967).
121 H . Werner, R. Prinz, and E. Deckelmann, Chem. Ber. 101
(1968), in press.
[3] 0. D. Shreve, M . R . Heether, H. B. Knight, and D. Swern,
Analytic. Chem. 23, 277 (1951).
[4] Measured on an Atlas mass spectrometer CH 4; we thank
Dr. J . MuNer, Technische Hochschule, Miinchen, for this
[5] G. Schmid, H. Noth, and J . Deberitz, Angew. Chem. 80, 282
(1968); Angew. Chem. internat. Edit. 7, 293 (1968).
Hammett Constants of Phosphorus-containing
Groups Determined from Nuclear Magnetic
Resonance Spectra of para-Phosphorus-substituted
By G. P. Schiemenz [*I
Earlier121 we found Hammett constants of ca. +1 for subCD
stituents -PRAr2 o n the aromatic ring. Onium-phosphorus
is thus disclosed as a stronger electron acceptor than positive
nitrogen[3.41. In view of the electronegativity series N > P
Angew. Chem. internat. Edit. 1 Vol. 7 (1968) / N o . 7
this finding could not be explained as an inductive effect
By proton magnetic resonance spectroscopy of anilinium
salts Fraenkel[sl showed that the inductive effect of the
’onium atom is almost wholly abolished by ion-pair formation. We found, also by nuclear magnetic resonance spectroscopy, that triarylmethylphosphonium salts in chloroform
associate t o contact ion pairs, in which the anionic charge is
localized on the phosphorus [61. Thus, Hammett constants,
determined in the same medium and by the same method,
should provide information about the non-inductive portions
of the electronic effect of ’onium phosphorus.
For compounds X-C6H4-Y-H
the position of the nuclear
resonance signal of -Y-H is often linearly dependent o n the
Hammett constants cs of X (-Y-H
CHOI71, OH[8l, or
NH2[9J). so that cs values for new substituents X can be
determined from 8 (-Y-H). I n this way we obtained “satisfactory” [31 correlation for para-substituted toluenes (-Y-H
= CH3) in CDCI, between 8 and 0[31 of groups X that
contain n o free electron pair [X = N 0 2 , S02CH3, CN,
COOC2H5, COCH,, COCsHs, CHO. C6H5, H , Si(CH3)3,
CH(CH3)z. CH3, C(CH3)3; equation (l)][lo). The experimental points for 1 6 toluenes whose substituents X d o carry a free
electron pair all iie below the best straight line [X = F, C1, Br,
I. NH2, NHCH3. N(CH&,
NHCOC6H5, OH, OCH3, OC2H5. OC6HS. SH. SCH3I [lo].
Thus new substituent constants can be calculated from
equation (l), although for groups with free electron pairs
these are only minimal values.
- 0.142.0 + 2.332
r = 0.960, for
8 s = 10.016 ppm, for cr s = i O . 1 1 cs unit
In this way we determined cspuru values for 28 groups X that
contain phosphorus or, for comparison, sulfur or nitrogen
(Table 1). For all phosphonium groups cspuru is again about
1; cspuru is larger when electron-donating methyl groups are
replaced by electron-attracting aryl groups. The three sulfurTable 1. Chemical shifts 6 (ppm) of the N M R signals of the CHI
protons in p-X-CsH4CHs [cu. 0.9 mole ofp-CH3CaH4 group/1000 g of
CDCI,; (CHI)& as internal standard] and Hammett constants of the
substituents X.
... -.
[*I Priv.-Doz. Dr. G. P. Schiemenz
Institut fur Organische Chemie der Universitlt
23 Kiel, Olshausenstrasse 40-60 (Germany)
[ l ] Read at the International Symposium on Valence and Reactivity, Oxford, on January 11, 1968.
[2] G. P. Schiemenz, Angew. Chem. 78,605 (1966); Angew. Chern.
internat. Edit. 5, 595 (1966).
131 H. H. Jafl, Chem. Reviews 53, 191 (1953).
141 J. D. Roberts, R . A . Clement, and J. J. Drysdale, J. Arner.
chem. SOC.73, 2181 (1951)
151 G. Fraenkel, J. chem. Physics 39, 1614 (1963).
[6] G. P. Schiemenz, Lectures at Kiei (November 2, 1967) and
Hamburg (April 5, 1968).
[7] R. E. Klinck and J. B. Stothers, Canad. J. Chem. 40,1071
(1962); G. P. Schiernenz, Angew. Chem. 77, 1089 (1965); 79, 1016
(1967); Angew. Chem. internat. Edit. 4,1093 (1965); 6,996 (1967).
[8] J. G. Traynham and G. A . Knesel. J. org. Chemistry 31, 3350
[9] B. M. Lynch, B. C. Macdonald, and J. G. K. Webb, Tetrahedron 24, 3595 (1968).
[lo] G. P. Schiemenz, Lecture at Berlin (September 22, 1967);
Angew. Chem. 79, 1016 (1967); Angew. Chem. internat. Edit. 6,
996 (1967).
1111 D. J . Marfin and C. E. Griffin, J. org. Chemistry 30, 4034
[12] R. W. Taftjr. in M. S . Newman: Steric Effects in Organic
Chemistry. Wiley, New York 1956, p. 556ff., p. 594ff.
We found [21 phosphorus Hammett constants o > 1 for para0
Received: May 7, 1968
[Z 784a 1El
German version: Angew. Chem. 80, 559 (1968)
By G . P. Schiemenz [*I
Hammett Constants of Phosphorus-containing
Groups Determined from Nuclear Magnetic
Resonance Spectra of meta- and ortho-Phosphorussubstituted Toluenes111
containing groups also have Hammett constants near 1,
whereas, in agreement with earlier results 121, phosphinyland thiophosphinyl-phosphorus usually behaves as a moderately strong electron-acceptor (in two cases spur= does not
differ significantly from 0).
Martin and Griffin[ I 11 determined Taft constants a* of some
phosphorus-containing groups, some of which are so similar
t o our substituents that the inductive portion cq of their
Hammett constants can be determined from o* by Tuft’s
(see Table 1). Using the relation cs == 01 OM
then affords for phosphonium-phosphorus a mesomeric
contribution ISM that greatly exceeds that of the ethoxycarbonyl group (csLooC>”S
=- +0.20 1121).
’Onium-phosphorus thus behaves as a strong (-M)-substituent, whereas
in the chalcogenides phosphorus gives n o indication of a
+O 71
+ O 47
[a] Multivalent groups carry a corresponding number of p-CH3C6H4
groups. [b] Third decimal place estimated. [c] Calculated according
to eq. (1). [dl Approximate values.
Angew. Chem. inrernat. Edit. J Vol. 7 (1968) J No. 7
tolyl-substituted phosphonium salts A Q P ( C H ~ ) C ~ H ~ C H ~ - ~
10 although, because of formation of contact ion pairs, there
should be n o good grounds for an inductive effect. We
wished t o use the same method t o test applicability of this
remarkable finding to the metu- and ortho-isomers.
Exner’s equation 131
apuru - dmeta
should apply to the meta-compounds, i.e. ometuof ’onium
phosphorus should be somewhat smaller than rrpuru but still
around + l . Eleven phosphorus-free meta-substituted toluenes m-X-C6&CH3 without an electron pair o n X [ X =
CH=CH-C6H5, H, CH3, or C(CH3)3] gave a markedly
poorer correlation in the plot of 8(CH3),’ametuof X than did
the para-compounds; the best linear relation [equation (l)].
with r = 0.850, is according to Jaflh[41 less than “satisfactory”
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group, constantin, toluene, containing, para, nuclear, determiners, magnetic, hammett, resonance, substituted, spectral, phosphorus
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