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CYCLO ADDITION REACTIONS OF AZIDO METAL COMPLEXES 7 4 5
[2 + 3] Cycloaddition Reactions of Azido Metal Complexes and
Crystal Structure of the Cycloadduct of (Ph3P)2Pd(N3)2
with Benzonitrile P . KREUTZER, CH. WEIS, H . BOEHME, T .
KEMMERICH, a n d W . BECK
Institut für Anorganische Chemie, Universität München
and
C . SPENCER * a n d R . MASON
School of Molecular Sciences, University of Sussex, Brighton
(Z. Naturforsch. 27 b, 745—747 [1972] ; received April 17,
1972)
Cycloaddition reactions of ( R 3 P ) 2 M ( N 3 ) 2 (M = Pd, Pt)
with organic nitriles, thiocyanates, isothiocyanates,
dimethylacetylenedicarboxylate and carbon disulphide are described;
an X-ray analysis of the crystal structure of bis
(5-phenyltetrazolato)-bis (triphenylphosphine) palladium (II) is
summarised and related to isomerism of the complex in solution.
Recently, a number of [2 + 3 ] cycloadditions of nitriles and
isonitriles to the coordinated azide group, yielding metal nitrogen
or metal carbon bonded tetrazolato complexes, have been de-scribed
2 . Similarly the dipolarophile CS2 adds to the azide ligand to
give thiatriazolthionato com-plexes which easily decompose to
isothiocyanate compounds 3 .
W e report here some new cycloaddition reactions of ( P h 3 P )
2 M ( N 3 ) 2 (M = Pd, Pt ) . The azido pla-tinum (II) complexes
have been prepared by dif-ferent routes
(RjP)2PtClj
[P«N3)4]2 PR HJO/C2H5OH' c/s-tRjPbPtlNj)
(Ph3P)2Pt' \>0 X0/ C6HS
and proved to be the cis-isomers (high dipole moments, ju 13 D
in benzene; Pt-P coupling con-stants 4 = 3300 - 3500 Hz ) .
The observed cyclo addition reactions of ( R 3 P ) 2 M ( N 3 ) 2
with Örganic nitriles, thiocyanates, isothiocyanates, dimethyl
acetylendicarboxylate and carbon disulfide are summarised in the
following scheme:
Requests for reprints should be sent to Prof. Dr. W. BECK,
Institut für Anorganische Chemie, Universität München, D-8000
München 2, Meiserstr. 1, or to Prof. R. MASON, School of Molecular
Sciences, University of Sussex, Brighton BN 1 9QJ.
* Present address: H. 0 . C. Division, Imperial Chemical
Industries Ltd.
RCN (M=Pt,R-olkyl,aryl) * ^ ^ h ^ ^ h RSCN / - N
T r ^ T ( P W - N V - 2 C >' (M=Pd) * (Ph3P>JPd(CN)2 N nSR
R R-CN
(Ph3P)2M(Nj)2 R
RNCS /̂ ^N M=Pd, R=CH3,CtH5"(Ph^Pd(-N I )2 C R II "
S
(R=CH3)* "Ph3P)2M(-N̂ jJ ),]tB^c/s-{Ph,P),M(NC0),
6
- j ^ f T I ( P H , P ) , P T ( " N \ ] J ' 2 l " S l N ? *
C/S-(Ph3P)2Pt(NCS)2
The rate of reaction of c i s - ( R 3 P ) 2 P t ( N 3 ) 2 with
p-substituted benzonitriles, RC6H4CN, increases with increasing
electron withdrawing effect of the group R (R = - N 0 2 > - C 0
2 E t > C l > H > C H 3 > OCH3) and with increasing
o-donor strength of the phosphine ligands ( (n-C4H9 ) 3 P >
(n-C4H9) 2PhP > (n-C4H9) Ph2P > Ph 3 P) .
Cycloaddition is facilitated therefore by electron-poor nitriles
and by electron-rich azide groups, a similar situation to that
found for 1.3-dipolar cyclo-additions of organic compounds 5 . The
kinetic para-meters for the reaction of ( R 3 P ) 2 P t ( N 3 ) 2
with benzonitrile (zf/7+ ~ 15 kcal/Mole, AS* ~ 3 5 e . u . /
-
7 4 6 P. KREUTZER, CH. WEIS, H. BOEHME, T. KEMMERICH, AND W.
BECK
Mol) are also similar to those observed for cyclo-additions of
organic 1.3 dipoles 5 .
An X-ray structural determination of
bis(5-phe-nyltetrazolato)-bis(triphenylphosphin)palladium1 has
defined the mode of attachment of the tetrazolate ligand.
Colourless crystals of the complex were picked out of the mother
liquor (solution in CH2C12) and sealed in L i n d e m a n n tubes
but they disintegrated after only a few hours of ex-posure to an
X-ray beam; surrounding the crystals by glycerol in sealed L i n d
e m a n n tubes gave satisfactory experimental conditions. The
crystals
are triclinic and contain one molecule of solvated CH2C12 per
palladium atom, the data being col-lected in terms of an F-centred
unit cell with a — 21.89, b = 14.08, c = 18.12 Ä, a = 108.93° , ß =
107 .48° , y = 89 .32° . 2675 reflections with /obs ^ 5.0 o were
obtained by automatic four-circle diffractometer methods (MoKa) and
the structure determination and refinement has proceeded to the
point where the discrepancy index for these re-flections is 0.041.
The molecular streochemistry and some important bond lengths are
shown in the Figure; the complex has Q symmetry in the crystal.
Structure of Bis (5-phenyltetrazolato) -bis (triphenylphosphine)
palladium.
The phenyltetrazolate ligand is essentially planar, the angle
between the five-membered ring and phe-nyl group being only 3 . 9 °
; the ligand is however virtually orthogonal to the coordination
plane de-fined by the palladium, phosphorus and coordinated
nitrogen atoms, the angle between the tetrazolate ring and this
plane being 83 .4 ° . The metal-ligand bond lengths are close to
expected values. In trans-(Me2PhP) 2PdI2 6 , 7i-MeC3H4 - PdPPh3Cl 7
and 7i-C3H5PdPPh3SnCl3 8 , the palladium-phosphorus distances
average 2.33 Ä while palladium-nitrogen distances in complexes of
palladium (II) with saturated N-donor ligands average 2.03 + 0 . 0
2 Ä (see for example, reference 9 ) . Little ^-bonding be-tween the
metal and phenyltetrazolate is evident or, indeed, would have been
expected. By contrast, both the conformation and the inter-ring
bond lengths, which are very close to those in other tetrazole
com-pounds (e. g. sodium-tetrazolate10), are consistent with
extensive delocalisation in the tetrazolate ligand.
Whereas the cycloaddition of organic azides with nitriles yields
1.5-tetrazoles, the structural analysis confirms earlier
suggestions 1 that it is the 2.5-tetra-
zole which is formed from the metal coordinated azide. However,
the p.m.r. spectra of solutions of 5-methyltetrazolate complexes,
(Ph 3P) 2M (N4CCH3)2 , clearly show the presence of isomers (M =
Pt: TCH, = 7.79, 8 . 0 5 ; M = P d : r C H j = 8.13, 8.18, 8.50
in
CDC13) which are assigned to c is - (M = Pt) and cis-and
Jrans-complexes (M = Pd) respectively with N1 and N2 bonded
tetrazolate ligands. From the ob-served crystallographic
conformation of the tetra-zolate rings the syn- and anit-isomers
(two 5-ring substituents anti-or syn-related to each other) could
arise *. Actually from 1H-nmr data JONASSEN et al.1 1 demonstrated
the existence of various iso-mers of (Ph 3 P) 2 Pd(N 4 C — CH 3 ) 2
, obtained from P d ( P P h 3 ) 4 and 5-methyltetrazole, which were
as-signed to the czs-complex with N1-, N1-(syn and and), N1-, N2 -
and N2-, N2-bonded tetrazolyl rings.
It has been found that the methyl NMR signals of eis- [ (n-C4H9)
3 P] 2Pt (N4CCH3) 2 (rC H l = 7,64, 7.87 in CDC13 at 3 8 ° )
collapse at higher tempera-
* The presence of syn- and arUi-isomers however seems to be
questionable since such isomers should be detectable also for
metal-carbon bonded 1-methyl tetrazolate complexes (see also the
x-ray analysis of [Au(CN 4 i -C 3 H 7 ) 4 ] " 1 2) .
-
CYCLOADDITION REACTIONS OF AZIDO METAL COMPLEXES 7 4 7
tures (TCH, = 7.72 in 1.2-dichlorobenzene at 160° ) which is
consistent with a fluctuation of N ^ N 2 bonded tetrazolate rings
11.
N1- and N2-bonded linkage isomers have to be assumed also in
solutions of the tetrazolate com-plexes, (Ph3P) 2Ir (CO) N4C — CH3
, [ W ( C O ) 5 ( N 4 C - S C H 3 ) ] - and ( P h 3 P ) 2 P t ( N 4
C - S C H 3 ) 2 which
have been prepared from the corresponding azido compounds and
CH3CN or CH3SCN respectively, each complex showing two methyl NMR
signals. By contrast no linkage isomers could be detected from 19F
NMR spectra in the 5-trifluoromethyl-tetrazolato-complexes, (Ph3P)
2Ir (CO) (N4C — CF 3 ) , trans- (Ph3P) 2Pt (N4 — CF3) 2 and [ W ( C
O ) 5 N 4 C -c f 3 ] - .
Another triazolato complex has been obtained from
azido-bis(dimethylglyoximate) cobalt (III) 12,
N 3 C O ( D H ) 2 L ( L = PR 3 , pyridine or other bases), and
dimethylacetylendicarboxylate. The appearance of only one 1 H nmr
signal for the two OCH3 groups indicates the symmetrical N2-bonded
tri-azolate14. It appears that such easily accessible azido-chelate
complexes provide a suitable platform for carrying out reactions of
the coordinated azide group, the rate of cycloaddition being
strongly influenced by the nature of the trans-ligand L (L = P P h
3 > P ( C 6 H 1 1 ) 3 > pyridine).
J R= .—C=C—R
R R \ / C - C
N ^ C O N CH3C00
Vm^ I L
1 W . BECK and W . P. FEHLHAMMER, Angew. Chem. internat. E d i t
. 6 , 1 6 9 [ 1 9 6 7 ] ; W . BECK, W . P . FEHLHAMMER, H . BOCK, a
n d M . BAUDER, C h e m . B e r . 1 0 2 , 3 6 3 7 [ 1 9 6 9 ] ; W .
BECK, K . BURGER, a n d W . P . FEHLHAMMER, C h e m . B e r . 1 0 4
, 1 8 1 6 [ 1 9 7 1 ] .
2 R . F . Z IOLO, A . P . GAUGHAN, Z . D O R I , C . G .
PIERPONT, a n d R . EISENBERG, I n o r g . C h e m . 1 0 , 1 2 8 9
[ 1 9 7 1 ] .
3 R . F . ZIOLO a n d Z . DORI , J . A m e r . d i e m . S o c .
9 0 , 6 5 6 0 [ 1 9 6 8 ] .
4 Trans complexes show lower /p t -p constants: S. 0 . GRIM, R .
L . KEITER, a n d W . M C F A R L A N E , I n o r g . C h e m . 6 ,
1 1 3 3 [ 1 9 6 7 ] .
5 R . HUISGEN, A n g e w . C h e m . 7 5 , 6 0 4 , 7 4 2 [ 1 9 6
3 ] ; R . HUISGEN, G . SZEIMIS, a n d L . MÖBIUS, C h e m . B e r .
1 0 0 , 2 4 9 4 [ 1 9 6 7 ] ,
6 N . A . BAILEY a n d R . M A S O N , J . d i e m . S o c . A [
L o n d o n ] 1 9 6 8 , 2 5 9 4 .
7 R . M A S O N a n d D . R . RUSSELL, C h e m . C o m m u n . 1
9 6 6 , 2 6 . 8 R . M A S O N a n d P . O . WHIMP, J . c h e m . S
o c . A [ L o n d o n ]
1 9 6 9 , 2 7 0 9 . M J . R . WIESNER a n d E . C . LINGAFELTER,
I n o r g . C h e m . 5 ,
1 7 7 0 [ 1 9 6 6 ] . 10 G. J. PALENEK, Acta Crystallogr. 16,
596 [1963 ] . 1 1 J . H . NELSON, D . L . SCHMITT, R . A . HENRY, D
. W . M O O R E ,
a n d H . B . JONASSEN, I n o r g . C h e m . 9 , 2 6 7 8 [ 1 9
7 0 ] . 1 2 W . P . FEHLHAMMER a n d L . F . D A H L , J . A m e r
. c h e m . S o c .
1972, in press. 13 G. N. SCHRAUZER, Inorg. Synthesis 1968, XI ,
62. 14 The cycloaddition of (CH 3 ) 3 SiN 3 with acetylenes
also
yields 2-silylsubstituted triazoles (L. BIRKOFER and P. WEGNER,
Chem. Ber. 99, 2512 [ 1 9 6 6 ] ) .