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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 ] ) .