~ Pergamon S0277-5387 (96)00200-8

Polyhedron Vol. 15, No. 24, pp. 4425M433, 1996 Copyright © 1996 Elsevier Science Ltd

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CHEMISTRY OF POLYFUNCTIONAL MOLECULES--123.1 REACTIONS OF BiBr3, SbI3 AND Asl3 WITH LiN(PPh2)2; X-RAY

STRUCTURE OF A CYCLOPHOSPHAZENE SALT CONTAINING ARSENIC(I)

MARTINA DOTZLER, ASTRID SCHMIDT, JOCHEN ELLERMANN,* FALK A. KNOCH and MATTHIAS MOLL

Institut ftir Anorganische Chemie der Universit~it Erlangen-Niirnberg, Egerlandstrasse 1, D-91058 Erlangen, Germany

and

WALTER BAUER

Institut ffir Organische Chemie der Universit~it Erlangen-N0rnberg, Henkestrasse 42, D-91054 Erlangen, Germany

(Received 26 March 1996 ; accepted 24 April 1996)

Abstract--BiBr3 or SbI3 react at 20°C with LiN(PPh2)2 (1) to give elementary Bi or Sb and the P- -P coupled phosphazene ligand Ph2P- -N- -PPh2- -PPh~N--PPh2 (2). The reaction of AsI3 with 1 at room temperature formed yellow needles of the eight-membered heterocycle i i

AsPPh2NPPh2AsPPh2NPPh2 (3), whereas AsI3 interacted at 80°C with 1 in the molar ratio of 1 : 3 to give elementary arsenic and 2. Treatment of AsI3 and 1 at 20°C in a 1 : 2 stoichiometry

i i

yielded the seven-membered, cyclic arsenium (I) salt [As'---' 'PPh2--N--PPhz--PPh~N--PPh2] I" 4THF (5" 4THF), which was characterized by elemental analysis, conductivity, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis. Copyright © 1996 Elsevier Science Ltd

Keywords : arsenic(I) ; X-ray structural analysis ; cyclophosphazene ; lithium-bis(diphenyl- phosphanyl)amide ; bismuth ; antimony.

In previous studies 2-4 we have described an unusual oxidative splitting of LiN(PPh2)2 (1) 5-5 in the pres- ence of excess MC12 (M = Co, Ni, Pd, Pt) in refluxing toluene, which led after partial frag- mentation and recombination to spiro-cyclic 2'3 and bicyclic 4 complexes, of the,,types M(Ph2PNPPh2

NPPh2)2 and Ph2PNPPhzMPhzPNPPh2NPPh2, which are all characterized by X-ray crystal- lography. 24 Recently, Braunstein et al . 9 have reported an oxidative eouplin9 of 1 with iodine to the diphosphazene 2 :

* Author to whom correspondence should be addressed.

2LiN(PPh2)2 + 12 ' 2LiI 1 + Ph2P--N--PPh2--PPh2---N--PPh2 (1)

2 At the same time compound 2 was obtained in

our group by the reaction of 1 with anhydrous iron(III)fluoride or copper(II)fluoride, l° respec- tively:

2FeF3 + 2LiN(PPh2)2 THF 2FeF2 + 2 L i F+ 2 (2) 1

CuF2 +2LiN(PPhz)z THF C u + 2 L i F + 2 (3)

The structure of 2 was determined by means of X-ray analysis in both groups as well. 9'1°

4425

4426

As a part of our studies of the chemical behaviour of lithium-bis (diphenylphosphanyl) amide (1) towards metal halides we now report reactions of 1 with BiBr3, SbI3 and AsI3. The chemistry of I with the non-metal halide PC13 has been studied by Braunstein e t al. 9

RESULTS AND DISCUSSION

Bismuth tribromide and antimony triiodide are reduced in toluene at 20°C by lithium diphos- phinoamide (1) in a 1:3 stoichiometry to the elements Bi and Sb :

2MX3 + 6LiN(PPh2)2 ' 6LiX+ 2M ° 1

+ 3Ph2 P--N--PPhz--PPh2 ~N--PPh2 2

(4)

M B@r Sb X I

Under the same conditions arsenic triiodide forms the tetraphosphadiazen 2 and the arsenic- (I)phosphazene 3, similar to the reaction of PC13 with 1:9

M. DOTZLER et al.

molar ratio of 1 : 3 affords mainly 2 and elemental arsenic in somewhat indefinite grey to red forms.ll

80°C 2AsI3 + 6LiN(PPh2)e > 6LiI + 2As

toluene 1

+ 3Ph2P--N~PPh2---PPh2zN--PPh2 (6) 2

Due to separation problems the yields of 2 are mostly small. Besides 2 is unstable in a few solvents such as C4D80, (CD3)2CO and CHC13 or CDC13, so it is impossible to characterize 2 by pure 31p [in] NMR or other solution spectra. Therefore, 2 was always identified by its solid state IR spectrum (Table 1), which agrees with that of 2, prepared by previously described methods) ° The best synthetic routes for the preparation of 2 are given by Eqs (1) and (2). 9'1°

The compound 3" 1/2THF has been charac- terized by elemental analysis, IR, 1H NMR, 13C [IH] NMR and 31p [iH] NMR spectra. The eight- membered ring of 3" 1/2THF has been confirmed by mass spectrometry and can also be formulated in a mesomeric form with conjugated double bonds by analogy with the phosphorus homologue 4.12

When the arsenic triiodide is allowed to react with 1 in the molar ratio of 1 : 2 in THF [Eq. (7)],

2 ASI a + 6 LiN(PPh=) 2

1

i) toluene 6 LiI + (5)

2) THF

2 Ph2P-N=PPh2-PPh2=N-PPh 2

2

Ph2p.L~-"~'-.~.pPh 2

3" I/2 THF

THF

The heterocycle 3 is isolated after extraction of the reaction residue with tetrahydrofuran and pre- cipitation with n-pentane.

Reduction of AsI3 with 1 in toluene at 80°C in the

the arsenic(I)-complex salt 5-4THF is formed. Thereby arsenic triiodide is reduced to the nitren analogon {As-I} [Eq. (7a)] and the anion of 1 is oxidized to 2 [Eq. (7b). Under elimination of iodide,

Chemistry of polyfunctional molecules

/ Ph 2 P As I

l As PPh2

Ph2

3 " 1/2 THF

I N p ph2

/ \

I P PPh 2

Ph2

4427

2 coordinates {As-I} in a following step to yield the yellow salt 5" 4THF. It is directly obtained as suitable crystals for X-ray analysis.

As--As single bonds (244 p m ) . 19 21 In spite of this double-bond character of the As - -P bonds, only a relative small P(1)--As(1)--P(3) angle for 5 +

ASI3 + 2 LiN(PPh2) 2

1

THF 2 LiI + (7)

As +

IN l~ll I-" 4 THF

\ /7 p Ph2

5-4 THF

AsI3 + 2 e - , 2 I - + { < A s - I } (7a)

2[N(PPh2)2]- ,

Ph2 P - - N ~ - P P h 2 - - P P h 2 ~ N - - P P h 2 + 2e- (7b) 2

Figure 1 shows the cationic structure of 5" 4THF ; selected bond lengths and angles are listed in Table 2. The compound contains four molecules of tet- rahydrofuran of crystallization per formula unit. The skeleton of the cation of 5 consists of a waved seven-membered AsN2P4 ring. The cation 5 + may be regarded as a tetraphosphadiazene complex of the As + ion, which is unknown as such. The arsenic(1) presents the rare coordination number twoJ 3-15 The short bond lengths As(1)--P(1) and As(1)--P(3) [225.3(2) and 226.0(2) pm] are remarkable. They exhibit a partial double-bond character of the As- -P bonds, because the expected mean value of As- -P single bonds is 234 pm, an average of P - - P single bonds (224 pm) 1~18 and

(97.06 ° ) is observed. This value agrees with the average angle (98 ° ) at doubly coordinated phos- phorus(l) in cyclic compounds, n In contrast to the small P(1)--As(1)--P(3) angle the P(2) - - N(1)--P(1) [139.1(4) °] and P(4) - -N(2) - -P(3) [136.0(4) °] angles are wide.

The P - - N distances (159___2 pm) can be inter- preted in terms of partial double-bond character 23 and are typical of cyclic phosphazenes. 24 The other bond lengths as well as the angles of 5 ÷ and T H F show no anomalies.

The vibrational spectra of 2 and arsenium-phos- phines as 5" 4THF have not been published so far in detail and are, therefore, compared in Table 1. The assignments of the P--C6H5 modes 6 are based on the Whiffen nomenclature 25 in the nowadays more used description of Maslowsky. 26 The v ( P z N ) modes of 5 + are shifted at about 80 cm-1 to higher wavenumbers compared with those of 2. Such shifts to higher wavenumbers are also observed, but in smaller amounts, for most of the

4428 M. DOTZLER et al.

Table 1. Characteristic IR and Raman spectroscopic data" (cm ~) for Ph2P- -N=PPh2- -PPhz=N--PPh2 (2) and i i

[Ph2P--N--PPh2"'" As :=-PPh2--N=PPh2] +I-" 4THF (5" 4THF)

2 5" 4THF

Assignments IR Raman IR Raman

v(CH),Ph 30653080WShw-m sh ~ 3080vw 3 0 8 9 w s h ~

3058 m 3059 m, br 3055 w 3052 m-s 3024 w 3020 vw 3008 w-m

v(CH2), THF

v(CC)k, Ph

v(CC)I, Ph

v(CC)m, Ph

v(CC)n, Ph

2 x 4~(CC), Ph v(CC)o, Ph

6 (CH)e, Ph

v(P--N) v(P--N) 6(CH)a, Ph 6(CH)c, Ph P~V--ph sens. q Pm--Ph sens. q 6(CH)d, Ph

6(CH)b, Ph 7 ring p, Ph 7(CH)j, Ph 7(CH)h, Ph 7(CH)i, Ph v(P--N) 7(Cn)g, ah v(P--N) v(P--N) v(P--N) 7(CH) f, Ph

PW--Ph sens.

Pm--Ph sens. ~(CC)v v(P--P) and ) , (P- -N--P) ~(CCC)s

7 ( P - - N = P ) v ( A s P )

2970 w 2860 w

1586m 1585m 1585m 1580 w-msh ~ 1568 w sh 1569 w 1570 w 1560 vw sh 1475m 1477m-s 1472 w sh ~ 1465 w - m s h b ~ 1460 sh 1460wsh 1433 s 1435 s 1420 w-msh ~ 1420 w-msh ~ 1390 w-m 1400 w sh 1315 w-m 1310msh - -

12801304msh 1

1285 s sh 1276m 1188 vs, br 1265 vs, br 1175 vs, br 1215msh a ~ 1182m 1160 sh 1165 w-m l l02m-s 1130 w-m 1093 s ~ 1094 w-m 1100 s 1075msh --J 1070 w sh 1069m 1065 w-m c _2 1028m 1027 w-m 1025m 1000m 999 s 998m 972 w 937 w 935 w sh - - ] 921 w-m 910 w -~

890m, br 855 w sh 860 sh

851 w-m 849 w-m

2874 w 1583 vs

1024 w-m 998 vs

1159 w s h - - ] l l 1 9 m 1099m

815m 765 w-m sh 752 w-m sh

-2 748 vs 748 S

720 s 720 m 715 s 715 w-m sh - 2 700 vs 693 vs 690 vs 663 m-s 671 w 670 m-s

620 w-m ~ 615 w-m 620 w 614 w-m 605 w sh _2

591 w-m 580 vw 580 w 555 m 540 m 539 w-m

Chemistry of polyfunctional molecules

Table 1. (Continued)

4429

Assignments IR

5" 4THF

Raman IR Raman

P - -Ph sens. y 519 s 509 vs 491 s

P - -Ph sens. t 459 s 442 m

7(CC)w 410 w 398 w-m

6 ( P - - N = P ) 383 m 371 m-s

P - -Ph sens. u 330 w and 320 w P - -Ph sens. x 305 w 6 ( N = P - - P ) ? 288 w-m, br

515 w, br 520 vs 492 w sh

-2 485 m-s 460 w-m 430 m 445 w 415 w-m 400 vw sh / 380 w-m 360 w-m 340 w 330w 320 w 305 w 285 w-m 272 w

227 w-m 230 m 171 w 190 w-m sh _2

IR measured as KBr discs and Raman measured as pure solid products ; vs = very strong, s = strong, m = me- dium, w = weak, vw = very weak, br = broad, sh = shoulder.

b From intensity arguments with di(CH2)THF. 'Wi th v(COC) THF. d Obscured by v(P--N).

-1'(3) '-~'J

N(1) @ I(1)

P(2)

Fig. I. Molecular structure of [5]+ (C bound H atoms omitted).

P- -C6Hs-sens i t ive absorp t ions . The character is t ic bond ings o f the t e t r ahydro fu rane are main ly h idden by those o f the ca t ion 5 +. Only the v(CH2) absorp - t ions are found. The I R spec t rum o f 5" 4 T H F exhi- bits two new and intense bonds at 540 and 555 cm-1, which are assigned to P"-~'As"--~-'P modes .

The mass spec t rum (e.i.) o f 5 " 4 T H F does no t show the peak o f the molecu la r ion 5 +. Af te r loss

o f As or AsI the intense peak o f 2 (m/z = 768) is observed.

Since 5" 4 T H F is uns table in T H F and ace tone solut ions, the c o m p o u n d is ma in ly charac te r ized by its X- ray crysta l s t ructure and solid state I R spec t rum (Table 1).

The react ions o f 5 ' 4 T H F in T H F and acetone are under invest igat ion. Dry ing o f 5" 4 T H F in vacuo results in the loss o f T H F . Therefore , all analyt ic da t a are ob ta ined f rom 5. The 1:1 e lectrolyte charac te r o f 5 " 4 T H F was de te rmined by con- duct ivi ty measurement s in acetone.

E X P E R I M E N T A L

Materials

All man ipu l a t i ons were carr ied out under an a tmosphe re o f prepur i f ied d ry d in i t rogen by using s t anda rd Schlenk techniques and vacuum-l ine . Sol- vents were dr ied and purif ied p r io r to use by con- vent iona l methods . Chemica ls o f the best avai lable commerc ia l grade were used, in general wi thou t fur ther pur i f ica t ion : n -bu ty l l i th ium (1.6 M solu t ion in n-hexane, Merck -Schucha rd ) , BiBr3 (Aldrich) . AsI3, 27 SbI327 and HN(PPh2)2 (7) 6,28 were prepa red

by l i tera ture methods . The mel t ing po in ts were

4430 M. DOTZLER et al.

Table 2. Selected bond lengths (pm) and angles (°) for 5" 4THF with esti- mated standard deviations in parentheses

As(1)--P(1) 225.3(2) P(I)--As(I)--P(3) 97.06(7) P(1)--N(1) 160.9(5) N(1)--P(1)--As(I) 117.5(2) P(2)--P(4) 224.1 (3) N(2)--P(3)--As(1) 119.2(2) P(4)--N(2) 158.3(5) P(4)--N(2)--P(3) 136.0(4) As(1)--P(3) 226.0(2) N(1)--P(Z)--P(4) 108.0(2) P(2)--N(1) 157.0(5) N(2)--P(4)--P(2) 105.5(2) P(3)--N(2) 161.2(5) P(2)--N(1)--P(1) 139.1(4) P(1)--C(10) 182.9(7) C(10)--P(1)--C(20) 106.0(5)

Table 3. Crystal data for 5" 4THF

Formula Formula weight, Mr (g mol-~) Temperature (K) Wavelength (pm) Crystal system Space group Unit-cell dimensions a (pm) b (pm) c (pm)

7 (°) Cell volume (nm 3) Z Density (calculated ; g cm- 3) Absorption coefficient (mm-~) r(000) Crystal size (ram) 0 range for data collection (°) Index ranges

Reflections collected Independent reflections Refinement method

Data/restraints/parameters Goodness-of-fit on F 2

Final R indices [I > 2tr(/)] R indices (all data) Largest difference peak and hole (e" nm -3)

C64H72AslN204P4 1258.94 173(2) 71.073 Triclinic ,Oi

1305.2(3) 1363.9(5) 2030.4(7) 73.90(3) 83.88(2) 60.94(3) 3.034(2) 2 1.378 1.222 1296 0.80 x 0.40 x 0.20 2.04-27.06 -16~<h~<9, -17~<k~< 15, -25~</~<25 15 158 13 261 (Rint = 0.1184) Full-matrix least-squares on F 2 13252/0/610 0.987 Ri = 0.0672, wR2 = 0.1803 Rj = 0.1238, w R 2 = 0.2324 1612 and - 1051

determined in sealed capillaries and are uncor- rected.

P h y s i c a l m e a s u r e m e n t s

The IR spectra were measured with a Perkin- Elmer model 983 and are accurate +3 cm-L The Raman spectra were recorded on a Dilor XY laser Raman spectrometer equipped with a Kr ÷ (exciting

line, 647.1 nm) or an Ar + laser (exciting line, 514.5 nm) from Spectra Physics Stabilite. JEOL JNM- GX-270 spectrometer were used to obtain the ~H N M R (269.60 MHz), 13C [~H] N M R (69.70 MHz) and 3tp [1H] N M R (109.40 MHz) spectra. Chemical shifts were recorded relative to deuterated solvent peaks, which are reported to tetramethylsilane. 3~p [~H] N M R : external standard 85% H3PO4. Positive shift to lower fields. Field desorption (f.d.) and

Chemistry of polyfunctional molecules 4431

electron impact (e.i.) mass spectra were measured with a Varian MAT 212 instrument [e.i. : IXE-5 source. 70 eV (ca 1.1 x 10-17 j), direct inlet method]. Conductivity measurements were carried out using a WTW LF 90 instrument (Weilheim Technische Werkst~tten, Germany). Microanalyses: Carlo Erba, models 1106 and 1108.

X-ray crystallography

Yellow needles of 5" 4THF were grown at room temperature from the filtered red reaction solution. The intensity data from a suitable crystal were mea- sured at 173 K on a Siemens P4 diffractometer equipped with Mo-K~ radiation (graphite mono- chromator, 2 = 71.073 pm) employing the 09-20 scan technique. Crystal data are listed in Table 3. The structure was solved by direct methods (SHELXTL-PLUS29). Non-hydrogen atoms were refined anisotropically, (SHELXTL-933°), H atoms were taken from difference-Fourier syntheses and fixed on these positions with common isotropic temperature factors.

Supplementary material submitted to the Cam- bridge Crystallographic Data Centre comprises atom coordinates, anisotropic displacement para- meters and remaining bond lengths and angles.

Synthesis

1,1,3,3,4,4,6,6- Octaphenyl-2, 5 -diaza- 1,6- (0"323 ) di- phospha-3,4-(cr425)diphospha-2,4-hexadiene (2). (a) From BiBr3 and LiN(PPh2)2 (1). A sample (5 cm 3, 7.97 mmol) of a 1.6 M solution of n-BuLi in n- hexane is added to a solution of HN(PPh2)2 (3.07 g, 7.97 mmol) in toluene (30 cm 3) and stirred for 30 min at ambient temperature. A suspension of BiBr3 (1.19 g, 2.66 mmol) in toluene (15 cm 3) is then transferred in portions to the stirred reaction mixture. Within 4 h the colour of the suspension changed from brown to dark-red. After 6 h of stir- ring grey-black elementary Bi deposits and the reaction is virtually complete. The residue is filtered off and the solution is layered with n-pentane (30 cm3). The solvent mixture is kept at room tem- perature for 2 days. A yellow microcrystalline pre- cipitate of 2 slowly appears, but precipitation is not complete for several days. It is filtered off, washed with cold n-pentane (10 cm 3) and dried in vacuo. Yield: 0.1 g (5%) 2. IR (KBr, cm-~) : 3050 m, 3020 w, 3002 w-m, 1585 m, 1565 w, 1472 m, 1431 s, 1387 w-m, 1305 w-m, 1275 w-m, 1185 vs [v(P~N)] , 1170 vs [v(P--N)], 1105 m-s [PW--Ph sens. q], 1090 s [Pm--Ph sens. q], 1025 m, 1000 w-m, 920 w-m [v(P--N)], 850 w-m [v(P--N)], 748 vs, 720 s, 715 s, 700 vs, 690 vs, 660 m-s, 617 w-m, 518 m-s, 505 s,

490 s, 455 m-s, 440 w-m, 397 w, 380 w-m, 370 m, 280 w-m.

(b) From SbI3 and LiN(PPh:)2 (1). To a stirred solution of HN(PPh2)2 (2.66 g, 6.9 mmol) in toluene (30 cm 3) at 20°C n-butyllithium (4.3 cm 3, 6.9 mmol ; 1.6 M in n-hexane) is added. After 30 rain of stirring at room temperature a suspension of SbI3 (1.16 g, 2.3 mmol) in toluene (15 cm 3) is added to the reac- tion mixture. Over a period of 4 h the colour chan- ged from pink to dark-red brown. The suspension is filtered off and the dark-red solution was layered with 50 cm 3 of n-pentane. After 3 days a very finely divided dark grey suspension of antimony metal can be observed, whereas yellow quaders of 2 crys- tallize at the same time. These are separated mech- anically from the antimony powder, washed with 10 cm 3 of cold n-pentane and dried in vacuo. Yield : 0.26 g (11.2%) 2. IR (KBr, cm ~) : 3053 m, 3022 vw, 3002 w, 1585 m, 1475 m, 1432 s, 1387 w, 1305 w-m, 1275 w-m, 1265 w-m, 1185 vs [v(P--N)], 1170 vs [v(P--N)], 1105 m-s sh [P~V--ph sens. q ]+ 1090 s [Pm--Ph sens. q], 1027 m, 1000 w-m, 920 w- m + 9 0 0 w-m [v(P--N)], 850 w+805 w-m [v(P--N)], 748 s, 720 m-s, 700 vs, 693 vs, 663 m, 620 w, 520 m-s, 508 s, 492 m-s, 485 m, 442 w-m, 398 w, 382 sh + 372 m.

(c) From AsI3 and LiN(PPh2)2 (1). A quantity of HN(PPh2)2 (2.67 g, 6.94 mmol) is dissolved in toluene (30 cm3). The solution is treated dropwise with n-BuLi (4.35 cm 3, 6.94 mmol ; 1.6 M solution in n-hexane) and stirred for 30 min at room tem- perature. Then a suspension of AsI3 (1.05 g, 2.31 mmol) in toluene (15 cm 3) is added in small portions. The reaction mixture is stirred and heated to 80°C. During 7 h the colour changed from white to yellow. The light-yellow residue of lithium iodide, arsenic and small amounts of unreacted LiN(PPh2)2 is filtered off. To the yellow solution n- pentane (50 cm 3) is added. On standing over 5 days bright yellow blocks of 2 crystallize. These are sep- arated by filtration, washed with cold n-pentane (10 cm 3) and dried in vacuo. Yield: 0.57 g (32.3%) 2. IR (KBr, cm-~) : 3052 m, 3012 vw, 3003 w, 1585 m, 1475 m, 1431 s, 1388 w, 1302 w-m, 1273 w-m, 1262 w-m, 1183 vs [v(P--N)], 1170 vs [v(P--N)], 1099 m sh [pIV--ph sens. q] + 1090 s [PHI--ph sens. q], 1025 m, 998 w-m, 920 w-m + 897 w-m [v(P--N)], 850 w+805 w-m [v(P--N)], 745 s, 720 m, 712 m, 692 vs, 662 m, 617 w, 520 m-s, 508 s. 490 m-s, 458 m, 442 w, 398 w, 373 m.

2,2,4,4,6,6,8,8-Octaphenyl- 1,5-diarsa-3,7-diaza-2, 4,6,8-tetraphosphacycloocta-l,3,5,7-tetraen tetra- hydrofurane (2/1) (3" 1/2 THF). A toluene solution (40 cm 3) of HN(PPh2)2 (2.54 g, 6.58 mmol) is com- bined with n-butyllithium (4.12 cm 3, 6.58 mmol; 1.6 M solution in n-hexane). After 30 min of stirring

4432 M. DOTZLER et al.

at room temperature a suspension of AsI3 (1.00 g, 2.19 mmol) in toluene (15 cm 3) is added. Within 5 h of stirring at 22'~C the colour of the suspension changed from white to yellow. The microcrystalline solid is filtered offand the solvent is removed under reduced pressure to dryness. The yellow residue is solved in T H F (35 cm 3) and layered with n-pentane (35 cm3). During 24 h at room temperature 3" 1/2THF deposits as thin yellow needles. The sol- vent is decanted and the needles are dried in vacuo. Yield: 0.57 g (28.5%), m.pt 132°C. Elemental analysis : Found : C, 62.91 ; H, 5.06 ; N, 2.59. Calc. for Cs0H44As2N2P4OI/2 (954.66 g mol-J ) : C, 62.90; H, 4.65 ; N, 2.93 %. EI-MS (70 eV, 180°C) : m/z : 918 (M +), 658 (M + - As~PPh2) , 567 (M + - AsPPh> - N P P h ) , 534 (AsPPhzNPPh2As), 474 (NPPh2 AsPPh2N), 459 (AsPPheNPPh2). 1H N M R (C6D6, 19.8C): 6 7.8 6.4 (m, 40H, C6H5), 3.27 (m, 2H, CH2- -O- -CH2, THF) , 1.10 (m, 2H, CH2--CH2, THF) ppm. ~3C [~H] N M R (C6D6, 25.1 :'C) : 6 134- 126 (m, C6H5), 61.75 (s, CHz- -O- -CH2 , THF) , 25.75 (s, CH2--CH2, THF) ppm. 3~p [~H] N M R (C6D6, 22.0~C) : 6 32.75 (s) ppm. IR (KBr, cm L) : 3070 w-m, 3050 m, 3005 w [v(CH), Ph], 2960 w, 2860 w [v(CH2), THF], 1587 w [v(CC) k, Ph], 1570 w [v(CC) 1, Ph], 1487 m-s [v(CC) m, Ph ]+ 1460 w sh [6 (CH2), THF], 1432 s [v(CC) n, Phi, 1385 w [2 x q~(CC) v, Phi, 1330 w, 1305 w-m [v(CC) o, Ph], 1265 m [6 (CH) e, Ph], 1205 vs, br [v(P=N)] , 1172 s [v(P--N) + 6 (CH) a, Ph], 1153 m [6 (CH) c, Ph], 1123 w-m, 1097 s [P- -Ph sens. q], 1065 m-s [6 (CH) d, P h + v ( C O C ) THF], 1027 m [6 (CH) b, Ph], 998 m [7 ring p, Ph], 975 w [7 (CH) j, Ph], 918 w sh [7 (CH) h, Ph i+905 w-m sh [7 (CH) i, Ph]+898 m [v(P--N)], 855 vw [t' (CH) g, Ph], 802 m, br Iv(P--N)], 775 w, 765 w, 740 s [7 (CH) f, Ph], 710 m [P- -Ph sens. r], 690 vs [q~ (CC) v, Ph] + 680 m-s sh [~' ( P - - N = P ) ] , 618 w, 600 vw [6 (CCC) s, Ph], 555 w-m, 540 m-s [v (As"" P)], 520 vs, 482 m [P- -Ph sens. y], 428 m, 387 m + 360 sh [P- -Ph sens. t + 6 ( r ' - - N = e ) ] .

[2,2,4,4,5,5,7,7-Octaphenyl- 1-arsenium-3,6-diaza- 2 ,4,5,7- tetraphosphacyclohepta-3,5-dien]iodid- tetrahydrofuran (1/4) (5"4 THF). A mixture of HN(PPh2)z (1.63 g, 4.22 mmol) dissolved in T H F (30 cm 3) and n-butyllithium (2.65 cm 3, 4.22 mmol ; 1.6 M solution in n-hexane) is stirred for ca 30 min at room temperature. Then a solution of Asl3 (0.96 g, 2.11 mmol) in T H F (20 cm 3) was added. After 15 rain of stirring an orange suspension is observed, which becomes yellow during 5 h. The residue is filtered off and the yellow solution is allowed to stand at room temperature. After 24 h yellow nee- dles crystallize. The solvent is decanted and the needles are dried in a current of dinitrogen. Yield : 0.89 g (ca 37%), m.pt 139°C. The conductivity of a

3.68 x 10 -3 mol dm -3 solution in acetone (22°C) was 147.6 S cm2 moi -~. Elemental analysis : Found : C, 57.75; H, 4.55; N, 2.65. Calc. for Cs2H48As- IN2OP4 (1042.70 g mol - i ) [5] + I • 1THF : C, 59.90 ; H, 4.64 ; N, 2.68%. EI-MS (70 eV, 200°C) : m/z 768 (Ph2P- -N=PPh2- -PPhz - -N- -PPh2) . IH N M R [(CD3)2CO, 22'~C] : 6 8.3-7.0 (m, 40H, C6Hs), 3.6 (m, 4H, CH2- -O- -CH2, THF). 1.75 (m, 4H, CH2- -CH> THF) ppm. '3C ['H] N M R [(CD3)2CO, 25.1'~C]: 6 136-128 (m, C6H5), 61.8 (s, C H 2 - - O - - C H z , THF) , 26.0 (s, CH2- -CH> THF) ppm. 3~p ['H] N M R [(CD3)2CO, 22.0°C] : 6 71.2 (s, 1P), 44.1 (s, 1P), 33.9 (s, 2P) ppm.

Acknowledyements--The authors gratefully acknowledge financial support from the Deutsche Forschungs- gemeinschaft and the Fonds der Chemischen Industrie. We thank the Hoechst AG, Frankfurt/Main for gifts of expensive chemicals. We also express our thanks to Professor Dr D. Sellmann for making available the facili- ties for X-ray analysis.

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