Organometallics 1986,5, 113-117 from eq 7 and 8. Here the upper limit of C5 is 3 y5/ y6 = C5/C6
X
lo*
(7)
(8) C5 + c6 1 AA(t)/~5m(Mn2(Co)9)1 mol dm-3 and c6 is the molar concentration of Mn2(C0)& The equality relationship in (8)is satisfied when Mn2(CO)8 and other species such as Mn2(C0)7do not have absorptions at that wavelength. Inequality in (8) is due to any absorbance of these species. The optical path length (1) is 0.3 cm in this double-pulse experiment. The absorbance change, AA(t) (0.002),is shown in Figure 4a. The ratio Y 5 / Y 6is therefore estimated to be lower than 0.7. The yield for process 5, which was proposed by Coville et al.,l& is, therefore, concluded to be low even if it is present. The major process in Mn2(CO)gphotolysis is not the cleavage
113
of the metal-metal bond but of the Mn-CO bond (process 6). The steady-state irradiation at low temperature is in progress to clarify the products of the photoreaction of Mn2(CO)9. The recombination of Mn2(CO), with CO following the second flash has not been studied because of the complicated kinetics and the small absorbance change. Advanced studies will be published in another paper.
Acknowledgment. We wish to express thanks to Prof. A. Poe for his helpful discussions on the wavelength dependence. They also thank Mr. J. Iwai for his help in the early stage of the study. Registry No. Mnz(CO)lo,10170-69-1; Mn(C0)5, 54832-42-7; Mn2(CO)9, 86728-79-2; Mn(C0I4, 71518-80-4; CO, 630-08-0.
A New General Route to Diphosphenes via Germylated Compounds Claude Couret, Jean Escudie, Henri Ranaivonjatovo, and Jacques SatgQ" Laboratoire de Chimie des Organomin&aux, UA du CNRS No. 4 77, Universitg Paul Sabatier, 3 1062 Toulouse. France Received April 10, 1985
Several (trichlorogermy1)phosphinesRP(H)GeCl, (3) are prepared by two different routes: (i) from primary phosphines RPH2 and germanium tetrachloride and (ii) from dichlorophosphines RPClz and the dichlorogermylene-dioxane complex, GeC12.C4H802.Subsequent addition of 3 to an excess of DBU (1,5diazabicyclo[5.4.0]undec-5-ene)affords the corresponding diphosphenes RP=PR. This method appears conveniently and generally applicable to the synthesis of diphosphenes. This reaction involves formation of chlorophosphine intermediates RP(H)Cl (2). Stable diphosphenes IC, bis(2,4,6-tri-tert-butylphenyl)diphosphene, and le, bis[bis(trimethylsilyl)methyl]diphosphene, can be isolated in excellent yield. Unstable dienophilic diphosphenes were characterized by cycloaddition with 1,3-dienes. Cycloadduct 12d, obtained by reaction of di-tert-butyldiphosphenewith cyclopentadiene, is a clean precursor of di-tert-butyldiphosphene, Id.
Introduction Since the report by Yoshifuji et al. describing the synthesis and characterization of the first stable compound with a P=P bond, bis(2,4,6-tri-tert-butylphenyl)diphosphene,l this new class of unsaturated compounds has been of current interest.2-10 (1) (a) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotau, K.; Higuchi, T., J . Am. Chem. Soc. 1981,103,4587; (b) Ibid. 1982,104,6167. (2) For recent reviews see: Cowley, A. H. Polyhedron 1984,3,389-432. Cowley, A. H.; Kilduff, J. E.; Lasch, J. G.; Mehrotra, S. K.; Norman, N. C.; Pakulski, M.; Whittlesey, B. R.; Atwood, J. L.; Hunter, W. E. Inorg. Chem. 1984,23, 2582-2593. (3) Smit, C. N.; Van der Knaap, T. A.; Bickelhaupt, F. Tetrahedron Lett. 1983, 24, 2031. (4) Cowley, A. H.; Kilduff, J. E.; Newman, T. H.; Pakulski, M. J. Am. Chem. SOC.1982,104,5820. Cowley, A. H.; Kilduff, J. E.; Pakulski, M.; Stewart, C. A. Ibid. 1983, 105, 1655. (5) (a) Bertrand, G.; Couret, C.; EscudiB, J.; Majid, S.;Majoral, J. P. Tetrahedron. Lett. 1982,23, 3567. (b) Couret, C.; Escudi6, J.; Satg6, J. Ibid. 1982,23, 4941. Escudi6, J.; Couret, C.; Ranaivonjatovo, H.; Satg6, J.; Jaud, J. Phosphorus Sulfur 1983, 17, 221. Niecke, E.; Ruger, R. Angew. Chem. 1983,95,154; Angew. Chem., Int. Ed. Engl. 1983,22,155. Niecke, E.; Ruger, R.; Lysek, M.; Pohl, S.; Schoeller, W. Angew. Chem. 1983,95,495;Angew. Chem.,Int. Ed. Engl. 1983,22,486; Angew. Chem. Suppl. 1983, 639. Schmidt, H.; Wirkner, C.; Issleib, K. 2.Chem. 1983, 23,67. Cetinkaya, B.; Hudson, A.; Lappert, M. F.; Goldwhite, H. J. Chem. Soc., Chem. Commun. 1982, 609, 691.
Diphosphenes have been obtained by several routes from reactions of the corresponding dichlorophosphines with various reagents: magnesium,l*, odium,^ or lithium derivatives: bis(trimethylsiiyl)mercury,6divalent species of group IVA7 (14),30primary phosphines (dehydrochlorination in the presence of amines),8and silylphosphines (dechlorosilylation).3~9 However, although all these methods are convenient for the preparation of some kinds of diphosphenes, there is currently no generally applicable methodology for the preparation of all diphosphenes. In a preceding paper, we described the synthesis of bis[bis(trimethylsilyl)methyl]diphosphene via organogermanium compounds,1° which is presently the only existing route to this diphosphene. Herein, we describe the (6) Romanenko, V. D.;Klebalskii, E. 0.; Markovskii, L. N. Zh. Obshch. Khim. 1984,54, 465. (7) Veith, M.; Huch, V.; Majoral, J. P.; Bertrand, G.; Manuel, G. Tetrahedron Lett. 1983, 24, 4219. (8) (a) Cowley, A. H.; Kilduff, J. E.; Mehrotra, N. C.; Norman, N. C.; Pakulski, M. J. Chem. SOC., Chem. Commun. 1983, 528. (b) Yoshifuji, M.; Shibayama, K.; Inamoto, N.; Matsushita, T.; Nishimoto, K. J. Am. Chem. Soc. 1983,105, 2495. (9) EscudiB, J.; Couret, C.; Andriamizaka, J. D.; Satg6, J. J . Organomet. Chem. 1982,228 C76. (10) Escudi6, J.; Couret, C.; Ranaivonjatovo, H.; Satg6, J. J. Chem. Soc., Chem. Commun. 1984, 24, 1621.
0276-7333/86/2305-0113$01.50/00 1986 American Chemical Society
114 Organometallics, Val. 5, No. 1, 1986
Couret et al.
general applicability of this method to the synthesis of almost all diphosphenes including very hindered, but stable diphosphenes, as well as unhindered and reactive diphosphenes. The major focus of this new method is the use of readily available precursors: primary phosphines, commercially available germanium tetrachloride, and 1,5-diazabicyclo[5.4.0]undec-5-ene(DBU). Results and Discussion In our experiments, we have observed that chlorophosphines 2 afford almost quantitatively diphosphenes 1 by dehydrochlorination with DBU. This reaction is illustrated employing the relatively stable chlorophosphine 2c (eq 1). However, chlorophospines of type 2 are stable" only when bulky substituents are attached to phosphorus. Thus, it is necessary in other cases to use precursors of these compounds such as (trichlorogermy1)phosphines3, which also afford chlorophosphines 2 by reaction with DBU (eq 2) and thus can be used as in situ reagents for RP (H)C1.
plexes have been described in the literature,13and they are generally obtained simply by mixing a germylene with a phosphine. Complex 5, presumably would give the intermediate chloro(trichlorogermy1)phosphine 6, corresponding to an insertion of GeClz into the P-C1 bond of 5 (eq 6), consistent with the observation of Du Mont and Schumann of the reaction between di-tert-butylchlorophosphine and the dichlorogermylene-dioxane complex.'3d Under these experimental conditions, we suggest germylphosphine 6 is thermally labile and undergoes decomposition by a-elimination with formation of germanium tetrachloride and a phosphinidene, 8 (eq 7 ) . The latter then abstracts two hydrogen atoms from the solvent to afford phosphine 9, which then reacts with germanium tetrachloride according to the already described reaction i (vide supra). RPC12 t G e C 1 2 C 4 H e 0 2
4 CRPC12*GeCl21
-
RP-GeCI3
I
DBU
RP-CI
t DBU.GeC12
I
(2)
I
RP-GeC13
I
2
3
H
(Trichlorogermy1)phosphines 3 are themselves easily prepared in excellent yield by two different routes, i and ii. (i) The addition of germanium tetrachloride to primary phosphines gives, after spontaneous evolution of hydrogen chloride, trichlorogermylphosphinesin nearly quantitative yield (eq 3). This method appears especially convenient for the synthesis of (trichlorogermyl)phosphines, since these rapidly precipitate from the reaction mixture and can be easily isolated as the pure substances. (ii) Heating dioxane solution of dichlorogermylene-dioxane complex12 and a dichlorophosphine at reflux gives, unexpectedly, the same (trichlorogermy1)phosphines 3 in variable yield (20-95%), depending of the substituent R (see Experimental section) (eq 4). (01
€120)
-Hc,
-
9 a-e
RP-GeC13
I H
(3)
3
In the experimental conditions, primary phosphines 9 and GeC1, react immediately to give 3; but their formation is unambiguously proved by recent results (not yet published): in the reaction between RPC12and GeC12.C,H802 (R = 2,4-bis(trifluoromethyl)phenyl)quantitative formation of phosphine 9 and GeCl, have been observed because, in this case, reaction between these two derivatives is very difficult (heating at 110 "C for 24 h). Synthesis and Characterization of Diphosphenes The addition of (trichlorogermy1)phosphines 3, in benzene solution, t o an excess (100%) of DBU gives immediately the corresponding diphosphenes and a mixture of solid materials identified as the hydrochloride DBUeHC1 and the complex DBU.GeC1214(eq 8).
-
2RP(H)GeC13
3a-e
e
3
DBU
RP=PR 1
e , (Me3Si)zCH
a , R - P h : b . Mes: c , @ ; d , t - B u ;
C4H 80 2
RPC12 t G e C I 2 4 4 H s 0 2 (10.~RP-GeC13 4
CI
(61
6
H
H
C&Is
I
IC
I
R P H 2 t GeCI4
(5)
5
FY-GeCI;]
I
5
2c
CRPC12*GeC121
I H
(4)
3
The mechanism of formation of 3 by the latter route probably involves initial formation of the germylenephosphine complex 5 (eq 5). Germylene-phosphine com(11) Halophosphines RP(H)X are generally unstable and lose HX to afford the corresponding cyclopolyphosphines. The only exception was trifluoromethylhalophosphines CF,P(H)X Dobbie, R. C.; Gosling, P. D.; Straughan, B. P. J. Chem. SOC.,Dalton Trans. 1975, 2368. (12) Kolesnikov, S.P.; Shiryaev, V. I.; Nefedov, 0. M. Izu. Akad. Nauk SSSR, Ser. Khim. 1966, 584.
+ 2DBUsGeC1, + 2DBU.HC1
(8)
When R is a bulky substituent, monomeric diphosphenes are obtained: IC (R = 2,4,6-tri-tert-butylphenyl) and le (R = bis(trimethylsily1)methyl). With other substituents, oligomers [(RP),] la (R = phenyl, n = 5 ) , l b (R = 2,4,64rimethylphenyl, n = 3, 4), and Id (R = tert-butyl, n = 3, 4) are the major products. (a) Mechanism of Formation of Diphosphenes. Our mechanistic ideas on the formation of diphosphenes from (13) (a) King, R. B. Inorg. Chem. 1963,2,199. (b) Escudi6, J.; Couret, C.; RiviBre, P.; Satgb, J. J. Organomet. Chem. 1977,124, C45. (c) Schumann, H.; Du Mont, W. W. J. Organomet. Chem. 1975,85, C45. (d) Du Mont, W. W.; Neudert, B.; Rudolph, G.; Schumann, H. Angew. Chem. 1976, 88, 303;Angew. Chem., Int. Ed. Engl. 1976, 15, 308. (14) The complex DBUeGeCl, can be obtained by a direct synthesis from DBU and GeCIZ.E 0. It has been identified by mass spectroscopy (field desorption (74Ge,h1), m / e 296 (M+)).
Organometallics, Vol. 5, No. 1, 1986 115
A Route to Diphosphenes via Germylated Compounds
3 are derived specifically from the use of 3c (where R = 2,4,6-tri-tert-butylphenyl) owing to the stability of the intermediate 2c. Indeed, the first step of the reaction between (trichlorogermy1)phosphine 3c and DBU is the formation of the chlorophosphine 2c and the DBU.GeC1, complex. This process has been demonstrated by using a stoichiometric amount of DBU. Further addition of a 100% excess of DBU gives diphosphene IC in virtually quantitative yield (see eq 9, route a). DBU
RP-GeCl3
I H
-DBU*GeC12
e%-c1]
RP=PR
1
t-BuPCl2 t (Me3Si)2P-t-Bu
-
- 2 Moas i C I
t-Bu
12d
(9)
retro-Diels-Alder decomposition of 12d should afford Id. Evidence for such thermal decomposition of 12d with formation of Id was obtained by the novel *diene exchange". Thus, heating 12d in the presence of 2,3-dimethylbuta-173-dieneaffords l l d in good yields (85%) (eq 12). Small amounts of phosphine 9d (thermal decomposition of lOdZ9)and diphosphine 1Od (from diradical 13d) also were obtained in this reaction.
2
3
pentadiene as solvent gives 12d according to a procedure previously described for the synthesis of lld9 (eq 11). The
Soby RP-PR I H1 9 H
RPH2
12d
10
With other substituents, formation of diphosphenes 1 with minor quantities of phosphines 9 and diphosphines 10 are observed. For example, when R is the bis(trimethylsily1)methyl group, the product ratio of le/9e/ 10e is 55/25/20. Formation of these three compounds from 2 can be explained by pathways a and b (eq 9). Route a leads to the expected diphosphene via an intermolecular dehydrochlorination with formation of intermediate 14. Route b leads to 9 and 10 via an intramolecular dehydrochlorination giving the phosphinidene 8 which we postulate is the precursor of radical intermediate 15. Phosphine 9 and diphosphine 10 arise from intermediate 15 by hydrogen abstraction from the solvent or by dimerization, respectively. Dimerization of phosphinidene 8 to diphosphene 1 cannot be excluded. (b) Characterization of Diphosphenes. Stable diphosphenes IC and le have been isolated and unambiguously identified by their characteristic 6 (31P)NMR resonance at very low field; IC at +493 ppm;Ib l e at 517 ppm.1° Unstable diphosphenes la, lb, and Id have been characterized by trapping reactions with 2,3-dimethylbuta-1,3-diene or cyclopentadiene (eq 10).
+
[t-Bu-y-t-t-Bu]
13d
/ /I
lld
A
t BU-P-P-PBU H
I H
10d
When R is a mesityl group, the trapping reaction of dimesityldiphosphene (la) by cyclopentadiene gives the diphosphine 10b in quantitative yield. We rationalize this reaction by assuming that the low thermal stability of the cycloadduct 12b at room temperature results in formation of cyclopentadiene and 13b. 13b, which we write as a diradical, then abstracts two hydrogen atoms from the solvent (eq 13).
1 H
3b
L
Mes
12b LMesP-bMesl
J
SOIV
MesP-PMes
RP-PR
I
H
(13)
t
H
10b
7 0 11a. R = P h b. R = t-Bu
t-BuPhp
9d
13b
CRP=PRl
(12)
(10)
In summary, this organogermanium route to diphosphenes appears to be a general one; it has allowed in particular the synthesis of a very interesting diphosphene, bis[bis(trimethylsilyl)methyl]diphosphene which, while stable, also is reactive and was not accessible by other ways. This new diphosphene should allow an extensive investigation of the reactivity of the diphosphenes, which, until now, is only poorly developed.
R
1 2 d , R = t-Bu
Cycloadduct 12d has been isolated and characterized and has been prepared by an independent synthesis. For example, the reaction between tert-butyldichlorophosphine and tert-butylbis(trimethylsily1)phosphineusing cyclo-
Experimental Section General Comments. All syntheses were performed under an atmosphere of dry nitrogen using standard Schlenk or highvacuum line techniques. Solvents were dried by distillation from sodium benzophenone ketyl immediately prior to use. Commercial 2,3-dimethylbuta-l,3-diene, cyclopentadiene, and 1,5-diazabicy-
116 Organometallics, Vol. 5,No. 1, 1986 clo[5.4.0]undec-5-ene (DBU) were freshly distilled under nitrogen. GeC1, was purchased from Sogemet and PhPCl, from Fluka. The complex GeC12-C4H802 was prepared according to the method of Kolesnikov.12 Dichlorophosphines 4 were prepared by reaction of PCl, with Grignard or lithio compounds: 4b,15 4c,la 4d,16 4e.I7 Primary phosphines 9 were obtained by reduction of corresponding di, 9e.I0 ~ ~ chlorophosphines 4 by LiAlH,: 9a,18 9b," g ~9d,21 'H NMR spectra were recorded on a Varian EM 360 A at 60 MHz and Bruker WH 90 at 90 MHz. 31PNMR spectra were recorded on a Bruker WH 90 at 36.44 MHz. Chemical shifts are reported in parts per million from internal MelSi for 'H and from external 85% H3P04for 31P. Downfield shifts are noted positive in all cases. Infrared spectra were recorded on a Perkin-Elmer 457 grating spectrometer. Mass spectra were performed on a Varian MAT 311 A spectrometer (EI) and a Ribermag R 1010 spectrometer (desorption). For (trichlorogermyl)phosphines, experimental molecular peaks patterns were assigned after comparison with theoretical peaks patterns calculated on a Tektronics 4051. Melting points were determined on a Reichert apparatus and are uncorrected. Elemental analyses were done by the "Service Central de Microanalyse du CNRS", Vernaison, France. Synthesis of (Trichlorogermy1)phosphines3.2, (a) From Primary Phosphines 9 and Germanium Tetrachloride. The (trichlorogermy1)phosphines 3 (except 3c) were synthesized according to the experimental procedure which we describe in detail below for the case of 3a. The 100-mL three-necked flask used for the reaction was connected to a trap cooled to -196 "C. To a stirred solution of 9a (4.4 g, 40.0 mmol) in benzene (50 mL) was added slowly a large excess of GeC1, (25 g, 300% excess) at room temperature. A white precipitate appeared immediately. The reaction mixture was stirred for 30 min and then frozen to 0 "C. Hydrogen chloride then was eliminated in vacuo from the reaction mixture, trapped in a receiver cooled to -196 "C, and titrated with a 1 N solution of NaOH. Yield of HC1: 95%. The reaction mixture was allowed to warm to room temperature. Filtration afforded white crystals of 3a; yield 10.0 g (87%). In the case of 3c, 24-h stirring with periodical elimination of HCl from the solution, in vacuo, was necessary for completion of the reaction. 3a: mp 69-72 "C dec; 'H NMR (CsD6)6 4.66 (d, 'J(PH) = 198 NMR (C6D6)6 -67.8 IR (KBr) v(PH) 2290 Hz, 1 H, PH); 31P{1H) cm-'; mass spectrum (field desorption, %C1,'"e), m/e 288 (M')). Anal. Calcd for C&&13GeP: C. 25.21; H, 2.10 c1,36.93. Found: C,24.87; H, 2.01; C1, 37.12. 3b: mp 23-25 "C; 'H NMR (C6D6)6 1.96 (s, 3 H, p-Me), 2.23 (s, 6 H, o-Me), 4.65 (d, 'J(PH) = 210 Hz, 1 H, PH), 6.63 (br s, 2 H, aromatic H); 31P{1H)NMR (C&) 6 -94.8; IR (KBr) u(PH) 2320 cm-'; mass spectrum (desorption, 35Cl,74Ge),m/e 330 (M'). Anal. Calcd for C&I,,Cl,GeP: C, 32.76 H, 3.66; C1,32.22. Found: C, 33.01; H, 3.89; C1, 31.86. 3c: mp 150-155 "C dec; 'H NMR (Cd),) 6 1.23 (s, 9 H, p-t-Bu), 1.50 (s, 18 H, o-t-Bu), 5.90 (d, 'J(PH) = 212 Hz, 1 H, PH), 7.51 (br s, 2 H, aromatic H); 31P(1H}NMR (C6D6)6 -59.6; IR (KBr) v(PH) 2270 cm-'; mass spectrum (field desorption, %C1,74Ge),m / e 456 (M'). Anal. Calcd for C18H30C13GeP:C, 47.37; H, 6.63; C1, 23.31. Found: C, 47.41; H, 6.76; C1, 23.11. 3d: mp 49-52 "C dec; 'H NMR (C6D6)6 1.26 (d, 3J(PH) = 13.0 Hz, 9 H, t-Bu), 3.86 (d, 'J(PH) = 193 Hz, 1 H, PH); 31P(1H} NMR (C,D,) 6 -21.4; IR (KBr) u(PH) 2270 cm-l; mass spectrum (field (15) Brazier, J. L.; Mathis, F.; Wolf, R. C. R. Hebd. Acad. Sei., Ser. C 1966,262, 1393. (16) Voskuil, W.; Arens, J. F. Red. Trau. Chim. Pays-Bas 1963, 82, 302. (17) Gynane, M. J. S.;Hudson, A.; Lappert, M. F.; Power, P. P.; Goldwhite, H. J. Chem. SOC.,Dalton Trans. 1980, 2428. (18) Horvat, R. J.; Furst, A. J. Am. Chem. SOC.1952, 74, 562. (19) Kosolapoff, G. M.; Maier, L., Eds. "Organic Phosphorus Compounds";Wiley-Interscience: New York, 1972; Vol. 1, Chapter 1. (20) Issleib, K.; Schmidt, H.; Wirkner, C. Z.Anorg. Allg. Chem. 1982, 488,75. (21) Issleib, K.; Hoffmann, H. Chem. Ber. 1966, 99, 1320. (22) Tris(trimethylsilyl)methylphosphine, (Me3Si)3CPH,, does not react with germanium tetrachloride in refluxing benzene presumably for steric reasons.
Couret et al. desorption, 35Cl, 74Ge), m / e 456 (M+). Anal. Calcd for C4Hl0Cl3GeP:C, 17.92; H, 3.76; C1, 39.68. Found: C, 18.07; H, 3.97; C1, 39.92. 3e:" mp 46-49 "c dec; 'H NMR (C&) 6 0.15 (s, 18 H, Me3Si), 3.58 (d, 'J(PH) = 185 Hz, 'H, PH); 31P(1H)NMR (C&) 6 -72.5; IR (KBr) v(PH) 2268 cm-l; cryoscopy (C6H6)calcd 370.1, found 366. Anal. Calcd for CsHzoC13GePSiz:C, 22.70; H, 5.44; C1,28.72. Found: C, 23.02; H, 5.76; C1, 29.08. (b) From Dichlorophosphines 4 a n d t h e Dichlorogermylene-Dioxane Complex. All reactions were performed according to the same procedure. A solution of the alkyl- or aryldichlorophosphine 4 (10 mmol), dichlorogermylene-dioxane complex (10 mmol), and 1,4-dioxane (20 mL) was heated at 110 "C for 1 h. Analysis of the reaction mixture, performed by 'H and 31PNMR, showed the formation of the (trichlorogermy1)phosphines 3, previously prepared (see above). Dioxane was eliminated in vacuo and replaced by benzene. A white precipitate of 3 appeared immediately; filtration afforded pure 3. Other products were sometimes obtained in these reactions and were identified on the basis their literature data ('H and 31P NMR). Derivativesobtained from 4 and the dichlorogermylene-dioxane complex and yields calculated by NMR from 4a, 3a (20%), ( P h P ) t 3 (70%); from 4b, 3b (85%); from 4c, 3c (70%), 9c (20%);5a*20324 from 4d, 3d (40%),( ~ - B u P )(10%) , ~ ~ [31P11H]NMR (C&) 6 -581, other unidentified products; from 4e, 3e (85%). Synthesis of IC. (a)Characterization of Chlorophosphine 2c. To a suspension of 3c (3.50 g, 7.7 mmol) in 15 mL of C6Hs was slowly added a stoichiometric quantity of DBU (1.17 g, 7.7 mmol). The reaction mixture was stirred for 30 min at room temperature, and then benzene was evaporated in vacuo and replaced by pentane (10 mL). After elimination of complex DBU.GeC1, by centrifugation, 'H and 31PNMR analysis of the solution showed the nearly quantitative formation of chlorophosphine 2c: 31PNMR (C6D6)6 + 21.3 ('J(PH) = 216 Hz). 2c has recently been obtained by Cowley.26 (b) Preparation of IC. Addition of an excess of DBU (100%) to the mixture of chlorophosphine 2c and the DBU-GeC1, complex gives immediately a light yellow precipitate and an orange solution. Benzene was removed in vacuo, and 20 mL of pentane was added to allow complete precipitation of DBU.HC1 and DBU-GeC1,. After filtration, the orange solution was evaporated and the residue was chromatographedon silica gel with pentane (R, -0.7) to afford an orange solid (1.65 g, yield 78 %), identified as IC according to its physicochemical data,' particularly its very low-field 31P NMR chemical shift, +493 ppm.Ib ICcan also be obtained in one step by reaction of (trichlorogermy1)phosphine 3c with an excess of DBU. In this case, the same result was obtained by the addition of 3c to DBU or by the addition of DBU to 3c because of the stability of the chlorophosphine intermediate 2c. In the other cases, since chlorophosphines 2a, 2b, 2d, and 2e are not stable, better yields of diphosphenes were obtained by addition of the corresponding (trichlorogermy1)phosphines to an excess of DBU. Synthesis of le. A solution of 3e (2.88 g, 7.8 mmol) in benzene (20 mL) was added by syringe to a solution of DBU (4.72 g, 31.2 mmol, 100% excess) in benzene (10 mL) at room temperature. The reaction mixture was stirred for 30 min at room temperature; after elimination of benzene in vacuo and addition of pentane (20 mL), filtration gave an orange solution. A 31PNMR analysis showed the formation of three products in the relative percentages: le, 55%; 9e, 25%; 10e, 20%. These three products were identified on the basis of their literature data.'O le: 31PNMR (C&) 6 +517; mass spectrum (field desorption), m/e 380 (M+).
(23) Fluck, E.; Issleib, K. Chem. Ber. 1965, 98, 2674. (24) Zschunke, A.; Baver, E.; Schmidt, H.; Issleib, K. 2. Anorg. Allg. Chem. 1982,495, 115. (25) Issleib, K.; Hoffmann, M. Chem. Ber. 1966, 99, 1320. (26) Cowley, A. H.; Kilduff, J. E.; Norman, N. C.; Pakulski, M.; Atwood, J. L.; Hunter, W. E. J . Am. Chem. SOC.,1983, 105, 4845.
Organometallics, Vol. 5, No. 1, 1986 117
A Route to Diphosphenes via Germylated Compounds 9e: 31PNMR (cp6)6 -149 ('J(PH) = 188 Hz); 'H NMR ( C a d 6 0.07 (s,18 H, Me3%),2.67 (dd, 'J(PH) = 188 Hz) 3J(HH) = 8.0 Hz, 2 H, PH). 10e: two diastereoisomers; AA'XX' systems. As the low intensity bands have not been assigned with precision, the AA'XX' system has not been completely elucidated; only the sum of the two coupling constants 'J(PH) and 2J(PH)has been determined. 10'e (40%): 31PNMR (C6D6) 6 -90.0 ('J(PH) + 'J(PH) = 195 Hz). 10'e (60%): 31PNMR (C6D6)6 = -97.9 ('J(PH) + 2J(PH) = 183 Hz). No trace of [(Me3Si),CH- PI, (n = 3,4)was detected. A rapid distillation on a short column afforded a mixture of l e and 10e and a minor quantity of oligomers [(Me3Si),CH - PI, (n = 3,8e 4 31P(1H} NMR (C6D6) 6 -17.0 (9)) (10%). The latter were formed by heating diphosphene le during the distillation. Action of DBU on (Trichlorogermy1)phosphines 3a, 3b, and 3d without Trapping Reagent. Addition of a suspension of (trichlorogermy1)phosphines3a, 3b, or 3d (10 mmol) in pentane to DBU (50% excess) results immediately in the formation of a precipitate of DBU.GeC1, and DBU.HC1. Subsequent filtration gave a colorless solution. 31PNMR analysis showed, in every case, the formation in very good yield (more than 80%)of the oligomers (RP),, identified when R is a phenyl or a tert-butyl group by their literature data. R = Ph: (PhP)5,2331P(C6H6) 6 4-4.4. R = t-Bu: (t-BuP)S2' (80%),31P(1HJNMR (C&, AZB system) 6(A) - 71.0, 6(B) -69.6 (J(AB) = 201.1 Hz); ( ~ - B u P )(20%), ~ ' ~ 31P{1H} NMR (C6D6) 6 -58. When R is a mesityl group, the reaction mixture was filtered and excess DBU eliminated at 80 "C mmHg). The residue was crystallized from C6Hsto afford a mixture of (MesP), (75%) and ( M ~ S P(25%). )~ ( M ~ S P )31P{1H) ~: NMR (C&, A,B system) 6(A) -111.6,6(B) -145.8 (J(AB)= 179 Hz). (MesP),: 31P{1H]NMR (C&) 6 -45.4 (s). Mass spectrum (EI, 70 eV): m/e 600 (MesP)4, 450 ( M ~ S P ) ~ . Synthesis of 1 la. A suspension of (trichlorogermy1)phosphine 3a (3.18g, 11.0 mmol) in pentane (20 mL) was added to a solution (15 mL) of DBU (6.71g, 44.0 mmol) in 2,3-dimethylbuta-1,3-diene at room temperature. Immediate filtration of solid DBU-HC1and DBU-GeC1, afforded a colorless solution. 31PNMR analysis showed the formation of (PhP)523(see above) (50%), PhPH,lg (30%),and l l a (20%) characterized on the basis its literature data:28 31P(1HJ NMR (C6D6)6 -23 (9); mass spectrum (EI, 70 eV), mle 298 (M'). Synthesis of l l d . (a) From 3d and DBU. A solution of 3d (1.80 g, 6.7 mmol) in benzene (15 mL) was slowly added to a (27) Baudler, M.; Hahn, J.; Dietsch, H.; Furstenberg, G. 2.Nuturforsch., E : Anorg. Chem., Org. Chem. 1976, 31E, 1305. (28) Meriem, A.; Majoral, J. P.; Revel, M.; Navech, J. Tetrahedron Lett. 1983, 24, 1975.
solution of DBU (4.08 g, 26.8 mmol, 100% excess) in 2,3-dimethylbuta-1,3-diene(15 mL) at room temperature. A precipitate appeared immediately. After elimination of solvents (benzene and DMB) in vacuo, 20 mL of pentane was added, and the reaction mixture was filtered to remove DBU-GeC12 and DBU-HCl. Distillation gave pure l l d (0.60 g, 69%)identified by its literature data:9 bp 138-139 "c (2 mmHg); 'H NMR (C&) 6 1.23 (pseudotriplet, XdA'X'9 system, (3J(PH)+ 4J(PH) = 12.2 Hz, 18 H, t-Bu), 1.77 (s, 6 H, MeC), 2.07-2.40 (m, 4 H, CH2C);31PNMR (C6D6) 6 -11.4. (b) From 12d and 2,3-Dimethylbuta-1,3-diene. A mixture (5.15 of 12d (1.50 g, 6.2 mmol) and 2,3-dimethylbuta-1,3-diene g, large excess) was heated in a sealed tube at 120 "C for 15 h. 'H and 31PNMR analysis of the reaction mixture showed the formation of l l d , 9d, and 10d in the relative percentages of 85/10/5. No oligomers (t-BuP), were detected, demonstrating the efficient trapping of the diphosphene generated from 12d. 9d19and 10dB were unambiguously identified by their 31PNMR data. 9d: 31PNMR (C6D6) 6 -82. 10d: 31PNMR (C6D6, two diastereoisomers 10'd and 10"d, AA'XX' system) lO'd, 6 -62.0 (V(PP) = -206 Hz), 10"d, 6 -60.8 ('J(PP) = -162 Hz). Distillation of the reaction mixture gave pure l l d identified by its physicochemical datag (see above) (1.20 g, 75%). Synthesis of 12d. (a) By Me3SiCl Elimination. A mixture of tert-butyldichlorophosphine (8.54 g, 53.7 mmol), tert-butylbis(trimethylsily1)phosphine (12.57 g, 53.7 mmol), and cyclopentadiene (20 g, large excess) was heated in a sealed tube a t 90 "C for 72 h. A rapid distillation using a short column afforded 12d: yield 8.45 g (65%);bp 95 "C (0.02 mmHg); 'H NMR (C6D6) 6 0.90 (d, 3J(PH) = 13.4 Hz, 9 H, endo t-Bu), 1.13 (d, 3J(PH) = 12.4 Hz, 9 H, exo t-Bu); 31P(1H]NMR (CEDE)(AB system) 6 -1.8 and -6.1 ('J(PP) = 272 Hz). Anal. Calcd for C13H24P2: C, 64.44; H, 9.98. Found: C, 65.01; H, 10.22. (b) From 3d and DBU. A solution of 3d (2.11 g, 7.9 mmol) in benzene (15 mL) was added to a solution of DBU (4.78 g, 31.6 mmol) in cyclopentadiene (15 mL) at room temperature. The precipitate that appeared immediately was filtered. After evaporation of solvents from the filtrate in vacuo, the residue was extracted with pentane. Distillation of the extracts gave 12d (1.17 g, 61%) (see data above). (29) Baudler, M.; Gruner, C.; Tschabunin, H.; Hahn, J. Chem. Eer. 1982, 115, 1739.
(30) In this paper the periodic group notation is in accord with recent actions by IUPAC and ACS nomenclature committees. A and B notation is eliminated because of wide confusion. Groups IA and IIA become groups 1and 2. The d-transition elements comprise groups 3 through 12, and the p-block elements comprise groups 13 through 18. (Note that the former Raman number designation is preserved in the last digit of the new numbering: e.g., I11 3 and 13.)
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