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Gold Complexes of a P-Coordinate Cyclotriphosphazene [1,2]

K. C. Dash+, A. Schmidpeter++, und H. Schmidbaur+* •Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstraße 4, D-8046 Garching, und +Institut für Anorganische Chemie der Universität München, Meiserstraße 1, D-8000 München 2 Z. Naturforsch. 35b, 1286-1288 (1980); eingegangen am 9. Juni 1980

Gold Complexes, Cyclotriphosphazenes, N/P-Ambidentate System, Tautomerism

Contrary to the reports on the coordination oi copper (I) to N/P-ambidentate cyclotri-phosphazenes, gold (I), gold (III) and dimethylgoldf 111) chloride are found to become exclusively P-coordinated to the prototype ligand 2-methyl-4,4,6,6-tetraphenylcyclotri-phosphazene (1). The P-H proton is transferred to an adjacent nitrogen atom of the heterocycle. According to temperature dependent NMR spectra, the AuCl and the AuClß complexes are fluxional molecules or ions, resp., with a rapid proton transfer between P-NH-P and P = N-P functions. The behaviour is similar to that of related palladium and platinum complexes, reported previously.

Cyclophosphazenes are an unusual class of po-tential ligand molecules, the coordination chemistry of which was developed only recently after many years of neglection [3, 4]. The currently increasing interest is caused by certain aspects of possible usage in chemotherapy [4], While the classical cyclotriphosphazenes A with six electronegative or organosubstituents can only function as nitrogen donors, the novel class of PH-functional cyclotri-phosphazenes B [5, 6] is offering an additional co-ordination site at phosphorus in a tautomeric NH-form. These ambivalent donor properties may lead to selective complexation of metals depending e.g. on their hard/soft acceptor character and on the kind of substituents at phosphorus.

PR2 R2P R2P PR2

A B

Whereas in earlier work by Allcock et al. [6] on copper(I) complexes the metal coordination was deduced to occur at nitrogen, a more recent work by Schmidpeter et al. have shown the palladium and platinum(II) complexes to be solely phosphorus-bonded [7]. As part of a continuing investigation on potential gold drugs with various nitrogen and phosphorus ligands [8, 9] a study of gold(I) com-plexes of cyclotriphosphazenes was therefore ini-tiated. From previous results on the acceptor prop-

* Reprint requests to Prof. Dr. H . Schmidbaur. 0340-5087/80/1000-1286/$ 01.00/0

erties of gold [10,11] a behaviour similar to platinum could be expected, which would thus differ from the reports on the copper homologue.

Gold(I), gold(III) and dimethylgold(III) chlo-ride [11] were selected as representative gold ac-ceptor components for a screening of the coordi-nation properties, and 2-methyl-4,4,6,6-tetraphen-ylcyclotriphosphazene 1 was chosen as a ligand molecule [5].

Results and Discussion The reaction of the ligand 1 with (CO)AuCl, as a

soluble source [11] of AuCl, in dichloromethane causes an instantaneous evolution of gaseous CO, and from the clear solution a colourless crystalline product 2 can be obtained in high yield:

r V * (CO)AuCI Ph2P^N>Ph2 Ph2P"'NxPPh2

-co N^ ^NH P A / \ / \

H CH3 Au CHo c/

Au CH3 C l ' -

1 2a 2b

In the IR-spectrum of the complex, the v(PH) absorptions of the free ligand 1 (2310 and 2360 cm - 1 ) have disappeared and are replaced by weak v(NH) absorptions at 3160 cm-1. The 31P NMR signal of P-2 is strongly shifted to low field, d = 66.8 com-pared to 6.9 in 1. These results clearly indicate P-bonding of the metal. v(PAuCl) appears at 372 and 320 cm-1 .

The conclusion is supported by the findings in temperature dependent NMR spectroscopy. The 1 H NMR spectrum exhibits a PCH3 doublet reso-nance at 6 = 2.75 (2J(PH) = 10.5 Hz), which is

K . C. Dash et al. • Gold Complexes of a P-Coordinate Cyclotriphosphazene 1287

independent of temperature, and a complex CÖHS multiplet. The 13C{1H} NMR spectrum shows a cor-responding PCH3 doublet at <5 = 31.25 (iJ(PC) = 46.9 Hz) at 30 °C, with little change at —60 °C. (The multiplet of the phenyl carbons has not been assigned.) The 31P{!H} NMR spectrum is clearly temperature dependent, however, and contains a triplet/doublet AX 2 pattern at 30 °C, which changes to an A X Y spin system at —80 °C. At 30 °C the two (C6H5)2P phosphorus atoms are thus equivalent on the NMR time scale, but become non-equivalent below—40 °C (in CDCI3 or CD2C12). This observation can be explained through a tautomerism as repre-sented by the formulae 2a/b. There is precedence for such a process in the analogous palladium and platinum complex [7].

The reaction of ligand 1 with anhydrous AuClß in CH2C12 also yields a 1 : 1 complex in high yield, whose conductivity and spectroscopy data indicate an ionic structure 3:

[AUCI3]2 2x1

H CH, N"^ r, \ I N Cl\ X ' vV P P h 2

CI ^ ) CH3 N P

H Ph2

AUCI4'

The greatly reduced solubility has precluded i3C NMR measurements, but both XH and 31P NMR as well as IR spectra resemble those of 2, and those of the isoelectronic Pt(II) chloride complex. The structure of the Pd(II) analogue was confirmed by an X-ray diffraction analysis [7]. With the oxidation of Au(I) in 2 to Au(III) in 3 the 3 iP-C-*H coupling increases characteristicly [12] (from 10.5 to 17.0 Hz).

Direct proof for a P-coordination of gold (III) is available from a closely related (CH3)2AUC1 com-plex 4, which is again obtained from 1 and [(CH3)2AUC1]2 in CH2C12 at —20 °C (73% yield):

Ph NPPh2

[(CH3)2AuCl]2 • 2x1 c A^ NH \ / \ Au CH3

ch/ \ l

4 is a non-electrolyte in acetone according to conductivity measurements. In the XH NMR spec-tra of this complex two doublet signals of CH3AU groups are evidence for the eis-configuration at the

metal center and for a xH-C-Au3 1P coupling through the AuP linkage. Coupling constants are in the range of data for other (CH3)2AuCl complexes with phosphines [11]. 31P decoupling experiments con-firm the assignments. The 31C NMR spectra com-plement the iH data through the appearance of two CH3AU signals with rather different eis- and trans-1 3C-Au-3 1P coupling, J = 4.9 Hz [eis), 157.2 Hz (trans). The 31P NMR spectra are unexpected in that the non-equivalence of the (CßHs^P groups is obvious already at room temperature in CD2C12. The A X Y pattern shows the proton exchange (of the type 2 a ±5: 2 b) to be much slower in 4 than it is in 2 or 3. Details of the spectral data are given in the Experimental Section.

In summary the results in gold complexes of the pentaorganocyclotriphosphazene show a clear pref-erence for P-coordination, similar to findings with the neighbouring element platinum, and to palla-dium, where additional proof is available from X-ray studies [7]. The discrepancy with the sug-gestions for the copper coordination [6] is remark-able and makes further investigations highly desir-able.

Experimental Chloro[2-methyl-4,4,6,6-tetraphenylcyclotriphos-phazenejgold(l) (2)

To a suspension of 0.15 g (0.57 mmol) (CO)AuCl in 5 ml CH2C12 is added a solution of 0.27 g (0.57 mmol) of the ligand 1 in 3 ml CH2C12. The suspension clears with evolution of CO gas, and after prolonged stirring for 5 h the resulting solution is concentrated to 3 ml. Addition of 8 ml diethylether and cooling to —78 °C affords a white precipitate, which is collected on a frit and dried in vacuo. 0.32 g (80%) yield, m.p. 165 °C (dec.). /1M = 3.15 Q ' 1 cm2 in acetone at 20 °C (c = 3.12 • IO-3 M). IR spectrum (Nujol): 3160, »(NH); 372, 320, v(PAuCl). NMR spectrum (CDCla): <5 = 2.75, d, CH3, 2J(PH) = 10.5 Hz. 13C NMR spectrum (CDCI3) at 30 °C: <5 = 31.3, d, CH3P, !J(PC) = 46.9 Hz; at —60 °C: <5 = 30.5, J = 44.0 Hz. siP NMR spectrum (CDCI3) at 30 °C: 6 = 16.8, d, PC6H5, 2J(PP) = 20.9 Hz; a = 66.8, t, PCH3 ; at —60 °C: <5 = 18.6, 20.3 and 86.9 constitute an A X Y spectrum. The values for CD2C12 solution are similar, at 30 °C: <5 = 16.0 and 66.6, J = 21.2 Hz; at —80 °C: A X Y spectrum, interpreted in first order approximation, 6 = 13.5, d, PC6H5, 2J(PP) = 36.6 Hz; 6 = 14.9, d, PC6H5, 2J(PP) = 15.3 Hz; Ö = 64.2, dd, PCH3. C25H24AUC1N3P3 (691.9)

Found C 43.47 H 3.62 N 6.40 P 13.78, Calcd C 43.35 H 3.47 N 6.07 P 13.44.

1288 K . C. Dash et al. • Gold Complexes of a P-Coordinate Cyclotriphosphazene 1288

cis-Dichloro-bis[2-methyl-4,4,6,6-tetraphenylcyclo-triphosphazene]gold(III) tetrachlor oauratefl II) (3)

To a red suspension of 0.34 g (1.12 mmol) AUC13

in 20 ml CH2C12 0.52 g are added at —10 °C (1.13 mmol) 1 in 10 ml CH2C12. The colour of the suspen-sion fades and a clear light yellow solution is obtained, which is stirred for 6 h at 20 °C. Concen-tration in vacuo to 10 ml followed by addition of 15 ml ether and cooling to —60 °C affords a lemon yellow precipitate. After standing for 12 h at 20 °C the product is filtered, washed with ether and dried. 0.65 g (76%) yield, m.p. 125 °C (dec.). /1M = 168.1 .Q-i cm2 in acetone at 20 °C (c = 1.22 • 10-3 M). IR spectrum (Nujol): v(NH) not observed; v(P2AuCl2) 359, 335 cm - 1 . W NMR spectrum (CD2C12): <5 = 2.39, d, CH3P, 2J(PH) = 17.0 Hz; sip NMR spec-trum ( C H A / C e D e ) : <5 = 23.1, d, PC6H5, 2J(PP) = 11.8 Hz; Ö = 38.7, t, PCH3.

Cso^sAuaCleNePe (1525.0) Found C 38.54 H 3.24 N 5.50 P 12.27, Calcd C 39.37 H 3.14 N 5.50 P 12.18.

cis-Chlorodimethyl[2-methyl-4,4,6,6-tetraphenyl-cyclotriphosphazene]gold(III) (4)

A solution of 0.15 g (CH3)2AUC1 and 0.26 g of the ligand 1 (0.57 mmol each) in 9 ml CH2C12 is prep-ared at — 2 0 °C and stirred for 4 h. Concentration

in vacuo and addition of ether again affords a pre-cipitate, which is filtered, washed with ether and dried. Colourless crystals, 0.3 g (73%) yield, m.p. 151 °C (dec.). Am = 1.76 cm2 in acetone at 20 °C (c = 1.76 • IO-3 M). IR spectrum (Nujol): 3120, v(NH); 1220 and 1230, <5CH3AU; V(AUC2) masked by ligand absorption. 1H NMR spectrum (CD2C12): 6 = 1.40, d, CH3P, 2J(PH) = 12.0 Hz; Ö = 2 .00 , d , trans-CH3AU, 3J(PH) == 9 .0 HZ ; 6 = 2.27, d, cw-CHsAu, 3J(PH) = 7.5 Hz. p P } gives three singlets. 13C NMR spectrum (CD2C12): <5 = 26.5, d, CH3P, iJ(PC) = 22.5 Hz; 0 = 1 1 . 6 , dt, trans-CH3Au, 2J(PC) = 157.2 Hz, 5 / (PC) = 2.4Hz ; 6 = 8.0, d, eis-CH3Au, 2J(PC) = 4.9 Hz. siP NMR spectrum (CDC13) at 30 °C: A X Y spectrum, inter-preted in first order approximation, 6 = 15.7, d, PC6H5, 2J(PP) = 43.1 Hz; <5 = 20.0, d, PC6H5, 2J(PP) = 20.9 Hz ; <5 = 94.7, dd, PCH3. C27H30AUC1N3P3 (721.5)

Found C 45.3 H 4.30 N 5.71 P 12.63, Calcd C 44.9 H 3.74 N 5.82 P 12.88.

One of the authors (K. C. D.) thanks the A. v. Humboldt Foundation for a fellowship and Utkal University for leave of absence. Support from Degussa A.G., through the donation of chemicals, is also gratefully acknowledged.

[1] Organogold Chemistry: For a preceding paper in the series see H. Schmidbaur and A. A. M. Aly, Angew. Chem. 92, 66 (1980); Angew. Chem. Int. Ed. Engl. 19, 71 (1980).

[2] Phosphazenes, LXXIV. - Part LXXIII : A. Schmidpeter and H. Tautz, Z. Naturforsch., in press.

[3] H. R. Allcock, Phosphorus-Nitrogen Compounds, Academic Press, New York and London 1972.

[4] R. W. Allen, J. P. O'Brien, and H. R. Allcock, J. Am. Chem. Soc. 99, 3987 (1977) and literature cited therein.

[5] A. Schmidpeter, J. Ebeling, H. Stary, and C. Weingand, Z. Anorg. Allg. Chem. 394, 171 (1972).

[6] H. R. Allcock and P. J. Harris, J. Am. Chem. Soc. 101, 6221 (1979); J. Chem. Soc., Chem.

Commun. 1979, 714. For a P-bonded iron complex see P. P. Griegger and H. R. Allcock, J. Am. Chem. Soc. 101, 2492 (1979).

[7] A. Schmidpeter, K. Blanck, H. Hess, and H. Rif-fel, Angew. Chem. 92, 655 (1980); Angew. Chem. Int. Ed. Engl. 19, 650 (1980).

[8] K. C. Dash, H. Schmidbaur, and A. Schmidpeter, Inorg. Chim. Acta 41, 167 (1980).

[9] H. Schmidbaur, J. R. Mandl, A. Wohlleben-Hammer, and A. Fügner, Z. Naturforsch. 33b, 1325 (1978).

[10] R. J. Puddephatt, The Chemistry of Gold, Else-vier, Amsterdam 1978.

[11] Gmelin Handbuch der Anorg. Chemie, 8. Aufl., "Organogold Compounds", Springer, Berlin 1980.

[12] J. Högel and A. Schmidpeter, Z. Anorg. Allg. Chem. 458, 168 (1979).