Why is such a dramatic increase in complex stability ob- served in the case of vanadium? This selectivity must be connected with the special arrangement of the ligands around the vanadium. However, the structure assumed so far, 3, cannot provide an explanation.

date. Nitrogen-containing ligands in naturally occurring vanadium complexes are of growing interest because of the recent report of a vanadium nitrogenase.[*']

Received: December 18, 1986 [Z 2017 IE] German version: Angew. Chem. 99 (1987) 568

Table 2. Complex formation constants K , . ([ML,I/[ML,- ,][L]) for various amino and N-hydroxyamino acid metal complexes (T= 25°C. I=O.l (KNO,)).

Ligand vo' 0 CU'O

IgK, lgKi IgKz IgKt k K >

HIN-O-CHi-COOH n,,,,, i 0.15 5.02 [a] H?N-CH2-CHZ-COOH < 7.5 7.10 [b] 5.40 [b] HO-NH-CH?-COOH 6.4 6.2 5.1 CuZQ reduction H'N-CHI-COOH i 6.6 8.46 [b] 6.83 [b] HO-N(CH2)-CHZ-COOH 6 5 4 CuZo reduction H3C-NH-CH2-COOH i 7.5 7.94 [c] 6.65 [c]

HOOC-CHZ-CH(NH2)-COOH 9.2 8.57 [d] 6.78 [dl HOOC-CH?-CH(NH0H)-COOH 7.24 5.4 6.54 4.3

HON(CH2CH2COOH)2 5.8 4.2 7.3

[a] From 1231. [b] From [24]. [c] From 1251. [d] From [26]

Synthesis of substances for comparison and investiga- tion of their complex formation with V 0 2 @ were used to establish which elements of structure are essential for the vanadium selectivity. These compounds, together with the stability constants for the V 0 2 @ and Cu2@ complexes, are collected in Table 2. The complex stability of amavadin is not even approached with any of these ligands. We there- fore conclude that, in addition to the NOH group, the two carboxyl groups are also necessary for the vanadium selec- tivity. On the basis of our results, we propose the new, symmetrical structure 4 as the true structure of amavadin. The absence of a VO group, as found in structure 3, can be concluded from the following observations. The ESR spec- tra provide no evidence for the binding of additional l i - gands,['61 as is often observed to be the case for vanadyl c ~ r n p l e x e s . ~ ' ~ ~ The IR band at 980 cm- ' exhibited by amavadin and assigned to the VO vibration is not observed for the vanadium(rv) complex of N-hydroxyiminodiacetic acid, even though this complex exhibits a stability similar to that of amavadin. Therefore, the band at 980 cm- ' can- not be assigned to the vanadyl group. Furthermore, re- cently performed large-angle X-ray scattering (LAXS) ex- periments show that the djhortest metal-ligand distance is probably larger than 1 .? The V - 0 distance of a vana- dyl group is 1.57- I .65 A. The acidity of amavadin, pK, = 0, moreover, does not support the presence of free carboxyl groups. A side-on binding of the anion of the NOH group, as postulated in structure 4, has been observed for vana- dium(v) hydroxylamine c o m p l e ~ e s . ~ ' ~ ~ ~ ~ ~

The vanadium compound of fly agaric, amavadin, repre- sents the most stable vanadium(~v) complex known to

'CH \

4 CH3

546 0 V C H Verlaysgesel/.icha/, mbH. 0-6940 Weinheim. 1987

[ I ] E. Bayer, Experientio 12 (1956) 365. [Z] H. J . Bielig, E. Bayer, L. Califano, L. Wirth, Pubbl. Sfn. 2001. Napoli 25

[3] M. Henze, Hoppe-Seylerk 2. Physiol. Chem. 72 (191 I ) 494. 141 E. D. Goldberg, W. McBlair, K. M. Taylor, Brol. Bull. Woods Hole,

[ S ] H. Ter Meulen, Red. Trav. Chim. Poys-Bas 50 (193 I) 491 [6] D. Bertrand, Bull. Am. Mus. Nut. Hut. 94 (1950) 409. [7] K. Kustin, G. C. McLeod, T. R. Gilbert, L. B. R. Briggs, Srruct. Bonding

B e r h 53 (1983) 139. [8] H. J. Bielig, E. Bayer, H. D. Dell, G . Rohns, H. Molllnger, W. Riidiger in

H. Peelers: Protides of the Bioloyicol Fhiids. Elsevier, Amsterdam 1967. [9] a ) H. Kneifel, E. Bayer, Angew. Chem. 85 (1973) 542; Angew. Chem. In,.

Ed. Engl. 12 (1973) 508; b) J. Am. Chem. SOC. I08 (1986) 3075. [ lo] E. Koch, H. Kneifel, E. Bayer, 2. Naturforsch. B41 (1985) 359. [ l I] E. Bayer, H. Kneifel, 2. Naturforsch. 8 2 7 (1972) 207. 1121 G. Anderegg, E. Koch, E. Bayer, XXlV Int. Congr. Coord. Chem..

Athens, August 1986; Inorg. Chim. Acta. in press. [I31 G . Anderegg, Helu. Chim. Acta 44 (1961) 1673; 46 (1963) 2471. [I41 G. Schwarzenbach, E. Freitag, Helu. Chim. Acta 34 (1951) 1147. [IS] J . Felcman, M. Candida, T. A. Vaz, J . J. R. Frausto da Silva, Inorg.

1161 P. Krauss, E. Bayer, H. Kneifel, 2. Naturforsch. 8 3 9 (1984) 829. 1171 C . M. Guzy, J. B. Raynor, M. C. R. Symons, J . Chem. SOC. A 1969.

118) T. Vogt, E. Koch, G. Folkers, E. Bayer, unpublished results. [I91 L. Saussine. H. Mimoun, A. Mitschler, J. Fisher, Now. J. Chrm. 4 (1980)

235. 1201 K. Wieghardt, U. Quilitzsch, B. Nuber, J. Weiss, Anyew. Chem. 90 (1978)

381; Angew. Chem. Int. Ed. Enyl. 17 (1978) 351. 1211 R. L. Robson, R. R. Eady, T. H. Richardson, R. W. Miller, M. Hawkins,

J. R. Postgate, Nature 322 (1986) 388. [22] L. G. Sillen, A. E. Martell (Stability Constants .f Metal-Ion Complexes)

7he Chemrcal Society. London, Special Publications 17 ( 1964); 25 ( I97 I).

(1955) 26.

Mass. I01 (1951) 84.

Chrm. Acta 93 ( 1984) I0 I .

279 I .

1231 Z. Warnke. C. Trojanoska, A. Liwo, J. Coord. Chem. 14 (1985) 31. [24] V. S. Sharma, H. B. Mathur, P. S. Kilharni. Ind. J Chem 3 (1965) 146,

(251 F. Basolo. Y . T. Chen. J . Am Chem. Soc. 76 (1954) 953. I261 S. Chabarek, Jr.. A. E. Martell, J Am. Chem. Soc. 74 (1952) 6021

475.

A Stable Stannaethene** By Harald Meyer. Gerhard Baum, Werner Massa, Stefan Berger, and Armin Berndt*

Silaethenes 1 have been completely characterized['.21 and germaethenes 2 have been identified by trapping reac- t i o n ~ ; [ ~ ] I ,I-dimethylstannaethene 3a has been generated in the gas phase.[41 Calculations have been carried out for the basic structures 1-3.['] We now describe the synthesis, spectroscopic characterization, and crystal structure of the stable stannaethene 3b.

\ / \ / \ / C=Si /C=Ge C=Sn

/ \ \ / \ 1 2 3

The boranediylborirane 4, which, according to calcula- tions,['l has the nonclassical structure shown in Scheme 1,

[*] Prof. Dr. A. Berndt, H. Meyer, G. Baum, Priv.-Doz. Dr. W. Massa, Priv.-Doz. Dr. S . Berger Fachbereich Chemie der Universitat Hans-Meerwein-Strasse, D-3550 Marburg (FRG)

the Fonds der Chemischen Industrie. [**I This work was supported by the Deutsche Forschungsgemeinschaft and

05 70-0833/8 7/0606-0546 !3 02.50/0 Angew. Chem. Int. Ed. Engl. 26 11987) No. 6

behaves toward suitable reagents as if it were the carbene 5.[ ' - ' ] This observation prompted us to carry out the reac- tion of 4 with the stannanediyl 6.I"l Reaction in pentane at room temperature led to formation of the stannaethene 3b in quantitative yield as shown by I3C-NMR spectrosco- PY.

4 1 fi2 1

5

R2 I

Scheme I

Compound 3b crystallizes from pentane at -30°C as Indian red cubes, which slowly lose their color (over 2 h) upon exposure to air. They melt a t 133"C, undergoing par- tial decomposition to give 6 and the 1,3-dihydro-1,3-dibor- ete 7.17] Compound 3b reacts with HCI to give the color- less 1,3-diboretane 8 (m.p. = 178°C) in quantitative yield according to I3C-NMR spectroscopy.

The structures of 3b and 8 were established from the IH-, I3C-, "B-, and "9Sn-NMR spectra (Table 1). Decisive

Table 1. N M R spectroscopic data for 3b and 8 [a].

3b: 'H-NMR: 6 = 1.40 ( s , 2 H; SnCH), 1.27 ( s , 18 H; BC(CH&), 0.20 (s, 18 H; BCSi(CH,),), 0.0 (s, 36H; HCSi(CH,)3); "C-NMR: 6 = 142.0 (br. s, 1 C; C=Sn), 34.9 (d, 2C: SnCH), 32.4 (q, 6C: BC(CH,),), 29.1 (br. s, 1 C; BCSi), 24.2 (br. s, 2C; BC(CH,),), 5.8 (4. 6C: BCSi(CH,)3), 4.5 (4, 12C: SnCSi(CH,),): "B-NMR: 6=64; "'Sn-NMR: 6=835 8: 'H-NMR: 6= 1.36 (s, 1 H; BCHSn), 1.28 (s, 18H; BC(CH,),, 0.51 (s, 2 H ; SnCHSi), 0.39 and 0.35 ( s , each 18H; SnCSi(CH,)I), 0.29 and 0.21 (s, each 9 H ; BCSi(CH,),): "C-NMR: 6=56.7 (br. s, 1C; BCSi), 53.1 (br. d, IC; BCSn), 30.5 (9, 6C: BC(CH,),), 27.5 (br. s, 2C; BC(CH&), 16.2 (d, 'J(' 'C'' 'Sn)= 183 Hz. 2C; SnCSi), 7.1 and 5.6(q,each 3C; BCSi(CH,),), 5.2 and 5.1 (4, each 6C: SnCSi(CH+); "B-NMR: 6 = 8 3 : ""Sn-NMR: 6=75

[a] Solvent C,,D,,

proof for the presence of tricoordinated tin in 3b is pro- vided by the very high-frequency position of the "'Sn- N M R signal at 6=835 (cf. 6 = 7 5 for 8, both values relative to G(Sn(CH,),) = 0). Chemical shifts of 6( ' "Sn)= 427.3""I and 658.3['" were found for the tricoordinated Sn atoms in 9 and 10, respectively.

Aryl, ,Aryl Ary( , R3 ,Sn=Sn P=Sn

R3 \ \

A W Aryl 9 10

propylphenyl butylphenyl Aryl = 2, 4, G-triiso- Aryl' = 2, 4, 6-tri-tert-

R 3 = CH(Si(CHJ3)2

A typical chemical shift (6( I3C) = 142) for a tricoordi- nated C atom is observed for the C atom of the C=Sn bond. The shift of the "B-NMR signal of 3b to lower fre- quencies (6(' 'B) = 64) compared with the signals of 8 (6(11B)=83) reveals negative n charge on the B atoms and therefore a strong polarization of the C=Sn bond corre- sponding to the ylide form B.

An X-ray structure analysis"21 of 3b gave a length of 2.025(4) A for the bond between the Sn atom and the tri- coordinated C2 atom and lengths of 2.152(5) and 2.172(4) A for the bonds to the tetracoordinated C atoms C19 and C20 (Fig. 1). The torsion angles BI-C2-Sn-C19 and B3-C2-Sn-C20 (Fig. 2) are 40 and 82", respectively;

Fig. I. ORTEP plot of a molecule of 3b in the crystal (ellipsoid\ 0 1 thermal vibration at 30% probability level: view onto the plane C2,C19,C20; H atoms not shown). Important bond lengths [Al, bond angles and torsion angles I"]: Sn-C2 2.025(4), Sn-C19 2.152(5), Sn-C20 2.172(4), BLC2 1.510(6), BI-C4

Si1 1.868(4), C4-Si2 1.872(5), BI . . .B3 1.994(8), C3. . -C4 2.393(5); C2-Sn- C19 129.2(2), C2-Sn-C20 125.6(2), C19-Sn-C2O 104.8(2), Sn-C2-BI 139.2(4), Sn-C2-B3 132.9(4), BI-C2-B3 83.2(4), C2-BI-C4 99.5, BI-C4-83 75-00), C4- B3-C2 98.9(4), Sil-C4-Si2 113.3(3); BI-C2-Sn-C19 40.2(6), BI-C2-Sn-C20 - 132.2(4), B3-CZ-Sn-CI9 - 106.1(5), B3-C2-Sn-C20 8135). Sn-C2-BI-C4 - 170.5(4), Sn-C2-B3-C4 I72.9(4).

1.624(8), BI-C5 1.601(9), B3-C2 1.494(7), B3-C4 1.653(6), B3-C9 1.603(8), C4-

the average twist angle around the C=Sn bond is therefore 61 O . The angles between the line joining C2 and Sn and the planes C19,Sn,C20 and BI,C2,B3 are 5 and 16", respec- tively; i.e., the Sn atom is slightly pyramidalized and the

c19

$+? ; v

Fig. 2. Stereoprojection along the C2=Sn bond. c20

Angew. Cheni. In! Ed Engl 26 11987) No. 6 0 VCH Verlagsyesellschafr mbH, 0-6940 Wernheim. 1987 0570-0833/87/0606-0547 S 02.50/0 547

C2 atom is significantly pyramidalized. Despite these dis- tortions, the C=Sn distance (2.025 A) is in good agreement with that calculated for HZC=SnH2 (1.982 A).[51 The short distances B I-C2 (1.5 10(6)) and B3-C2 (1.494(7) A)-which are practically identical with the corresponding distances in the 1,3-dihydro-l,3-diborete (7 with R2= N(CH,),) syn- thesized by Siebert et al.'"'-confirm the importance of the ylide resonance form B, which was concluded from the "B-NMR chemical shift data. This resonance form also helps to explain the extremely high-frequency It9Sn-NMR signal.

Received: December 29, 1986: supplemented: March II, 1987 [ Z 2032 I€]

German version: Angew Chem. 99 (1987) 559

CAS Registry numbers: 3b, 107940-89-6; 4, 87556-27-2; 6, 41823-72-7: 7, 90028-93-6; 8, 107940-90-9.

ences in their chemical behavior. Finally, in some cases, compounds 5 may act as masked 1,4-diphosphabuta- d iene~. [~I In spite of these interesting aspects, however, the chemistry of 1,2-dihydro-1,2-diphosphetes 5 is presently very poorly developed, undoubtedly because of the lack of a simple and general synthesis of this ring. The initial high- temperature route [(RP), + R'C=CR"][2.'.5.hl yields compli- cated mixtures of products and can only provide an access to thermally stable 1,2-dihydro- I ,2-diphosphetes 5. The only other practical route [RP(SiMe& +CICO-COC1]141 has a limited generality since the two carbons of the ring necessarily bear MezSiO substituents.

Fortunately, the recent discovery in our laboratory of a new and simple access to tervalent phosphirenes[" has al- lowed US to conceive a new and versatile synthesis of the title compounds. It relies on the formal insertion of a phos- phanediyl into a phosphirene C-P bond.

[ I ] A. G. Brook, S. C. Nyburg, F. Abdesaken, B. Gutekunst, G. Gutekunst, R. K. M. R. Kallury, Y . C. Poon, Y.-M. Chang, W. Wong-Ng, J Am. Chem. SOC. 104 (1982) 5667.

[2] N. Wiberg, G. Wagner, Chem. Eer. 119 (1986) 1467, and references cited therein.

[3] J . Satge, Adc. Orgonomet. Chem. 21 (1982) 241: N. Wiberg, C.-K. Kim, Chem. Ber. I19 (1986) 2966,2980.

[4j W. J. Pietro, W. J. Hehre, J Am. Chem. Sor. I04 (1982) 4329. [ S ] K . D. Dobbs, W. J. Hehre, Organometollics 5 (1986) 2057, and references

cited therein. [6] a ) P. H. M. Budzelaar, P. von R. Schleyer, K. Krogh-Jespersen, Angew.

Chem. 96 (1984) 809; Angew. Chem. In!. Ed. Engl. 23 (1984) 825: b) G. Frenking, H. F. Schaefer 111, Chem. Phyr. Left. 109 (1984) 521.

[7] R. Wehrmann, H. Klusik, A. Berndt, Angew. Chem. 96 (1984) 810: An- gen. Chem. Int. Ed. Engl. 23 (1984) 826.

[XI According to calculations performed on model systems for 4 and 5 (with SiH3 instead of Si(CH& and CH, instead of C(CH,),, the carbene is only about 10.2 kcal/mol higher in energy than the nonclassical boranediylborirane [6a].

[9] R. J. Davidson, D. H. Harris, M. F Lappert, J . Chem. SOC. Dalton Trans. 1976. 2268.

[lo] S. Masamune, L. R. Sita, J . Am. Chem. SOC. 107(1985) 6390. [ 1 I ] C. Couret, J. Escudie, J. Satge, J . Am Chem SOC. 107 (1985) 8280 1121 3b: space group PT, 2 = 2 , n=10.123(1), h=13.113(3), c=17689(3).&,

n=97.63(2), fi=91.87(1), y = 107.65(1)O. 4822 unique reflections with F,,>3o(F,,) measured at 294 K on a four-circle diffractometer (CAD4, Enraf-Nonius) with MoK.. radiation. Refinement of the heavier atoms with anisotropic temperature factors: the boron atoms refined with iso- tropic temperature factors; H atoms localized by means of difference Fourier syntheses, but put on calculated positions (d(C-H)=0.95 A, rid- ing model) with fixed isotropic temperature factors. R,, = 0.036 (weights w'= I/o'(fi,), 392 parameters, goodness of fit S=2.288. Further details of the crystal structure investigation may be obtained from the Fachin- formationszentrum Energie, Physik, Mathematik GmbH, D-7514 Eggen- stein-Leopoldshafen 2 (FRG), on quoting the depository number CSD- 52451, the names of the authors, and the journal citation.

[I31 M. Hildenbrand, H. Pritzkow, U. Zenneck, W. Siebert, Angew. Chem. 96 (1984) 371: Angew. Chem. Int. Ed. Engl 23 (1984) 371.

A New Low-Temperature Synthesis of 1,2-Dihydro-1,2-diphosphetes By Louis Ricard, Nicole Maigror, Claude Charrier, and Francois Mathey*

Among carbon-phosphorus heterocycles, 1 Jdihydro- 1,2-diphosphetes 5 deserve special attention. In some in- stances, their chemistry can be controlled by their poten- tially aromatic x-electron sextet.L'.21 On the other hand, the cyclic strain within the ring varies widely according to the substitution pattern,".31 thus inducing significant differ-

[*] Prof. F. Mathey, Dr. L. Ricard, Dr. N. Maigrot, Dr. C . Charrier Ldboratoire de Chimie du Phosphore et des Metaux de Transition, DCPH, Ecole Polytechnique F-91 128 Palaiseau C'edex (France)

R2PCl, R 2

I 6 R' - 30°C

1

R CL 0 b\ MR

P-P -C l R2' ' R'

4

R - 30°C

HR + [Bu3PCL]@ CLQ f- P-P

5 R2' ' R'

Table I . Substituents of 1 and 3-5: yields [ 'W, ] of 5

BU3P

I 3-5 5 R R R R' R" Yield ['!4l

a b

C'

d e f f' g g' h

C

Ph Ph Ph Ph Ph Ph Me Ph Ph Me Ph I B U Ph Ph tBu

Ph I B U Ph Et Ph Ph Me Me Et Me Et Ph Ph Et tBu Et Ph Me

Et Me Ph Et Ph tBu Et tBu Ph Et rBu Me

80 60 la1 20 15 70 50 15 la1 la1 30

[a] Unsatisfactory yields.

In the first step, a dichlorophosphane, 2, is allowed to react with a phosphirene, 1 . The reaction probably pro- ceeds through a transient phosphirenium salt, 3. In the presence of AICI,, 3a has been characterized by ,'P-NMR spectroscopy: AB system with &("P)= - 102.9 (Pa) and +67.6 ppm (PCI), 'J(PP)=503 Hz. Without AICI,, 3 im- mediately rearranges to give a dihydrodiphosphetium salt, 4, which is reduced in situ by Bu3P to give 5 (for yields see Table I) .

The rearrangement to 4 probably involves the nucleo- philic attack of C1' on Po inducing the opening of the ring. The carbanion thus formed reacts with the P-CI bond of the exocyclic phosphino group. Except for 5a and 5e,'31 all the 1,2-dihydro-l,2-diphosphetes 5 thus produced are new and have been fully characterized (Table 2). The ring expansion sometimes fails when bulky R ' or R2 groups are used (Sc, g, g').

548 0 V C H Verlagsge.~ellsrliafr mbH. 0-6940 Weinheim, 1987 0570-0833/87/0606-0548 $ 02.50/0 Angew. Chem. Int. Ed. Engl. 26 (1987) No. 6