摘要:

Halogenogermenes: evidence for the formation of the chloro- or fluoro-germenes (Me5C5)(X)Ge=CR2 (CR, = fluorenylidene)IMarie-Anne Chaubon, Jean EscudiC, Henri Ranaivonjatovo and Jacques SatgCHPtProchimie Fondamentale et Appliquke, URA 477 du CNRS, UniversitP P. Sabatier,31062 Toulouse Cedex, FranceThe reaction of tert-butyllithium with dichloro- or difluoro-(pentamethylcyclopentadienyl)(fluorenyl)germaneled to the corresponding stable lithio compounds which were characterized by reactions with various halides,trimethylsilyltriflate and methanol. The germenes (Me,C,)(X)GdR, (X = F or C1, CR, = fluorenylidene)were obtained by the thermal defluorosilylation of Ge(C,Me,)F(X)[C(SiMe3)R2] and trapped in excellentyields by methanol, water or chloroform.Since the first stabilization of a silene by Brook et a/.in 1981,’many other stable compounds with a S i x double b ~ n d , ~ . ~ andmore recently with a Ge=C4y5 or a Sn=C 6 3 7 double bond, havebeen synthesized and isolated. However, none of these stablemetallaalkenes was substituted on a metal or on carbon byfunctional groups (the existence of only transient chlorosileneshas been proved by trapping8). Thus it seemed interesting, inorder to widen their synthetic utility, to prepare functionalmetalIaalkenes.Among all the possibilities of functionalization of suchdoubly bonded compounds, we have chosen to substitute themetal by a halogen. Moreover, the presence of chlorine orfluorine on the metal should shorten the double bond andconsequently stabilize it better, according to calculations onS i x compounds bearing a fluorine on the silicon atom.We aimed to prepare a stable halogenogermene of the typeR’(X)Ge=CR,. As bulky groups are necessary to preventoligomerization, we substituted the germanium with thepentamethylcyclopentadienyl group, which is very efficient instabilizing low co-ordinated species, lo and included the carbonin the fluorenylidene group previously used for germenesR‘R”Ge=CR,.Sc-fResults and DiscussionSynthesis of precursors 2 and 4As previously a good route to germenes is thedehydrochlorination or the dehydrofluorination of a chloro- orfluoro-germane by a lithio compound (Scheme 1).Thus, we first synthesized the dichloropentamethylcyclo-pentadienyl(fluoreny1)germane 2 by addition of fluorenyl-lithium to the corresponding trichlorogermane 1 l 1 prepared byreaction of pentamethylcyclopentadienyllithium with germa-nium tetrachloride (Scheme 2); addition of methanol andtriethylamine, followed by treatment with an aqueous solutionof hydrofluoric acid, led to 4 via the dimethoxygermane 3.Thegermanes 2 and 4 were obtained in good yields and were easilyrecrystallized from Et,O due to their relatively low solubility.Attempted synthesis of the germenes 9 and 10 from thegermanes 2 and 4Addition of tert-butyllithium to a solution of the germane 2 (or4) in tetrahydrofuran (thf) at low temperature (between -78and -5OOC) afforded an orange solution of the lithiocompound 5 or 6 (Scheme 3). Unfortunately both compounds 5and 6 are very stable and elimination of lithium halide did notoccur: thus the Ge=C double bond could not be formed by this\-LiX /LiBu’-Et,O \ \/ I I -78°CGe-CR2 - Ge-CR2 - Ge=c&I? Ci X HScheme 1 X = C1 or FCIGec14 LiH(CR2) I MeOH-NE1Li(C5Me5) - Ge(C5Me5)CI3 - (Me5C5)Ge-CHR2 a 1CI1 2OMeIIOMe3FI HF-HzOF(Me5C5)Ge-CHR2 - (Me5C5)Ge-CHR2 - I4 7= 9Scheme 2route.This result is in agreement with previous observationsreported on similar compounds in which silicon or germaniumis substituted by alkyl group^.^^,'^ Thus it seems that thesubstituents on the metal play a major role in the formation ofthe double bond since the lithium halide elimination occurseasily when silicon or germanium is substituted by at least onearomatic one of the driving forces in this reactioncould be the conjugation between the aromatic ring and thegermanium-or silicon-carbon double bond [such a conjugationthrough the germanium should occur since recent calculationshave shown that it was observed even through two germaniumatoms in H,C==Ge(H)-Ge(H)=CH,’3]. In compounds 5 and 6the - I effect of the halogen on germanium does not favour theexpected elimination of lithium halide, as do aromatic groups.However, Wiberg et a/.l4 found that Me,XSi-CLi(SiMe,),species readily eliminated LiX even if there was no aromaticgroup present. Thus, other factors unambiguously contribute;in our case, the difference from the derivatives of Wiberg is thevery large steric hindrance of the substituents which probablyplay a major role in the non-elimination of LiX.The lithio compounds 5 and 6 have been characterized byquenching with methanol and alkyl halides (EtBr or BuBr)leading respectively to 7,8, 14 and 15; note that with methanol,J.Chem. SOC., Dalton Trans., 1996, Pages 893-897 89X=CI2 orF 4HeatCl16tX X XII IX H(Me5C5)Ge- C R2Li( OMe) 1MeOH-Li(OMe) -X=CI 9 orFlOX=CI 5 x i i orF 6 \tX CI x'I II IIX SiMea(Me5C5)Ge-CR2 (Me5C5)Ge - C R2 (Me5C5)Ge-CR2I I I tCI R' Me0 HX=CI7or F 8 R'=Et 14 or Bu 15 X,x'=CI,CI 11,F,F 12 or CI, F 13Scheme 35 and 6 behave as synthetic equivalents of the halogenogermenes9 and 10 since the same compounds would be obtained byaddition of methanol to the Ge==C double bond.We also treated compound 5 with mercury(I1) chloride in thehope of forming 9 by elimination of HgCl, from compound 16.Unfortunately, heating of 16 affords exclusively 2 due to ahomolytic cleavage of the C-Hg bond.As our first attempts to obtain halogenogermenes usinglithio compounds or mercury(1r) chloride failed, a new strategywas employed which took advantage of the lability of thefluorenyl-silicon bond and the great energy of the silicon-halogen bond', to eliminate SiMe,X from 11-13; 11 and12 have been obtained by quenching the lithio compounds 5and 6 with chlorotrimethylsilane or trimethylsilyltriflate. In thereaction between 6 and SiMe,Cl, 12 was the major compoundas expected, but small amounts of Ge(C,Me,)F(Cl)[C(SiMe,)-R,] 13 were obtained probably due to a fluorine-chlorineexchange between 12 and LiCI.Synthesis of halogenogermenes by dehalogenosilylationAs expected, the germenes 9 and 10 could be obtained bythermal dehalogenosilylation from 12 or 13 generally at 100 "Cand characterized by trapping with an excess of methanol,chloroform or water (Scheme 4).In the case of chloroform, it is likely that 2 and 17 arise from18 and 19 which are not stable at the decompositiontemperature (1 00 "C) and undergo elimination of dichloro-carbene.Such an addition of chloroform to a germanium-nitrogen double bond has recently been observed.' Withwater, only the formation of 21 was observed, in the form oftwo diastereoisomers. The first step of this reaction, as in thehydrolysis of the germene (2,4,6-Me,H,C6)2Ge=CR2, ' ' isprobably the formation of the germanol20 which reacts furtherwith a second equivalent of 10 to give 21.The addition of small amounts (0.1 equivalent) of a base suchas triethylamine is necessary to induce the nucleophilicelimination of trimethylsilylhalide.In contrast, when we heated12 or 13 with an excess of methanol, NEt, was not necessary,the methanol acting as both the base and the trapping agent.The formation of trimethylfluorosilane is the first step ofthese reactions both from 12 and 13; in the latter, the selectiveelimination of SiMe,F is observed and never, at thistemperature, of SiMe,CI. Thus, the formation of the adducts 2,7, 8, 17 and 21 arises unambiguously from the addition ofreagents onto the Ge=C double bond of the chlorogermene 9 orof the fluorogermene 10.Attempts to isolate these halogenogermenes by performingthe reaction without a trapping agent have been unsuccessful: aNMR spectroscopic analysis showed the formation of manyunidentified products with some C,Me,H.It has beenimpossible to determine what happened in this case:rearrangement of the monomer, head-to-head or head-to-taildimerization or some other type of dimerization followed byrearrangements and cleavage of the Ge-(C,Me,) bond? Thusthe best solution for the use of 9 and 10 in organometallicsynthesis is their in situ trapping.NMR dataAll the products were characterized by NMR spectroscopy(Tables 1 and 2) and mass spectrometry.In the 'H and 13CNMR spectra, the methyls of the pentamethylcyclopentadienylgroup appeared as a broad singlet, particularly so in the 13CNMR. This is of course due to the well known fluxionalityoccurring in this group." A low-temperature (-60 "C) 13CNMR spectrum of compound 2 displays, as expected,completely different signals: 6 11.27 and 1 1.55 ( M e M ) , 14.08(MeCGe), 64.64 (CGe), 132.77 (C=CCGe) and 140.67 (CCGe).The great magnetic anisotropy of the fluorenyl group isclearly evident in the 'H NMR spectrum for the ethyl and n-butyl group bonded to the fluorenyl: in derivative 14, the CH,of the ethyl group is largely deshielded (6 2.64) whereas the CH,group is shielded at F 0.05. In 15, the same phenomenon isobserved with the CH, (bonded to CR,) at 6 2.58 and the CH,in the p position at 6 0.27.In the I3C NMR spectrum, the CH,of the ethyl group in 14 is also shielded (6 5.94).Various trapping reactions from these new halogenatedgermenes and functionalization of germanium are now inprogress.894 J. Chem. SOC., Dalton Trans., 1996, Pages 893-89'r' Heat.NEt3I I SiMe3FF SiMe3(Me5C5)Ge-CR2 -X = F 12 OT CI 13iX=CI18 Or F l 9 X=CI 2 Or F17CHC13 IX = F 10 OT CI 9 X=CI 7 Or F 87 (Me&)Ge - C R2I IO HI410 1 r f (M~~CS)G,~-$A~~ - 5Experiment a1The reactions were performed using vacuum-line techniquesand carefully dried and deoxygenated solvents [usually Et20,tetrahydrofuran (thf) and pentane] which must be freshlydistilled over sodium benzophenone.Proton NMR spectrawere recorded on Bruker AC 80 and AC 250 instrumentsrespectively at 80.13 and 250.13 MHz, 13C NMR spectra onBruker AC 200 and AC 250 instruments respectively at 50.32and 62.89 MHz and "F NMR spectra on a Bruker AC 80 at75.39 MHz. Mass spectra were measured on a Hewlett-Packard5989 A spectrometer by electron-impact ionization (EI) at 70 eV(ca. 1.12 x J) and referenced to 74Ge. Melting pointswere determined on a Leitz microscope heating stage 250.Elemental analyses were performed by the Service deMicroanalyse de 1'Ecole de Chimie de Toulouse.Synthesis of Ge(C5Me5)CI,(CHR3 2To a solution of GeCl,(C,Me,) (6.03 g, 19.20 mmol) in Et,O(50 cm3) cooled at -30°C was added 1 equivalent offluorenyllithium LiH(CR2) prepared from fluorene (3.19 g,19.20 mmol) in Et20 and LiBu" (12 cm3, 1.6 mol dmP3 inhexane).The red colouration of LiH(CR,) disappearedimmediately. The resulting light yellow mixture was stirred for30 min at room temperature and then hydrolysed; after additionof thf in order to dissolve the precipitate in the organic layer,extraction with Et20 and drying over Na2S04, recrystallizationfrom Et20 gave pure 2 (4.58 g, 53%), m.p. 191-192°C. EImass spectrum: m/z 444 (M', 17%) (Found: C, 62.4; H, 5.5.C2,H,,C12Ge requires C, 62.2; H, 5.45%).Synthesis of Ge(C,Me,)F,(CHR,) 4To a solution of the germane 2 (3.00 g, 6.76 mmol) in thf (20cm3) was added NEt, (2.8 cm3) and an excess of MeOH (0.8cm3). The reaction mixture was refluxed for 30 min and thenHF (1 cm3, 40% in H,O) was added.After stirring at roomtemperature for 10 min the solution was washed with water,extracted with Et20 and dried over Na2S0,. Removal of Et20afforded crude 4 which was recrystallized from thf-pentane(30: 70) (white crystals, 2.60 g, 9373, m.p. 129 "C. EI massHO H20 21Scheme 4spectrum: m/z 412 (M', 24%) (Found: C, 66.9; H, 6.0. C23-H2,F2Ge requires C, 67.2; H, 5.9%).General procedure for the synthesis of 7,11,14 and 15To a solution of the germane 2 (0.50 g, 1.13 mmol) in thf(10 cm3) cooled to -50 "C was added a solution of tert-butyllithium (1.5 mol drn-,) in pentane (0.75 cm3, 1.13 mmol).The reaction mixture turned yellow, then orange duringwarming to room temperature, One equivalent of MeOH, EtBr,Bu"Br, CF,SO,SiMe, or SiMe,Cl as appropriate was thenadded leading to a light yellow solution (in the case oftrimethylchlorosilane a 10 min reflux was necessary for thecompletion of the reaction), then the solvents were eliminated invacuo and replaced by pentane.After filtration of LiCl,recrystallization from pentane afforded pure white crystals of7 (0.35 g, 71%), m.p. 113 "C, m/z 440 ( M ' , 4%) (Found: C,65.9; H, 6.25. C2,H2,C1GeO requires C, 65.6; H, 6.2%), 14(0.43 g, 8l%), m.p. 7&71 "C, m/z 472 (M', 2%) (Found: C,63.65; H, 5.9. C,,H,,Cl,Ge requires C, 63.6; H, 6.0%) or 15(0.45 g, 81%), m.p. 110-111 "C, m/z 500 (M', 1%) (Found:C, 65.1; H, 6.6. C2,H,,C12Ge requires C, 64.85; H, 6.45%);recrystallization from Et,O-pentane (30 : 70) afforded purecolourless crystals of 11 (0.52 g, 89%), m.p.213 "C, m/z 516(M', 16%) (Found: C, 60.35; H, 6.20. C2,H,,C12GeSi requiresC, 62.5; H, 6.25%).Synthesis of Ge(C5Me,)(F)(OMe)(CHR2) 8Compound 8 was obtained by a similar procedure as that usedfor 7 from 0.50 g of4.8 (0.36 g, 70%), white crystals, m.p. 91 "C,m/z 424 (M', 13%) (Found: C, 67.9; H, 6.25. C2,H2,FGe0requires C, 68.1; H, 6.4%).Synthesis of Ge(C,Me,)F(X)(C(SiMe,)R,) (X = F 12 or C1 13)As previously described for 11, 1 equivalent of SiMe,Cl wasadded to a thf solution of 6 prepared from 4 (0.50 g, 1.22 mmol)and 1 equivalent of LiBu' (1.5 mol dm-, in pentane) at - 50 "C.The reaction mixture was stirred at room temperature thenhydrolysed, extracted with Et20 and dried over Na,SO,.Afterremoval of Et20, a NMR spectroscopic analysis showed theJ. Chem. SOC., Dalton Trans., 1996, Pages 893-897 894Table 1 Proton NMR data"3 Ts 2 4' 7 8' 11 12d 13 14J 159CH,(C,Me,) 1.31 (s) 1.29 (s) 1.30 (s) 1.31 (s) 1.22 (s) 1.21 (s) 1.23 (br)CHR, 4.30 (s) 4.18 (br s) 4.13 (s) 4.1 1 (s)CR, 7.18-7.44 (m), 7.20-7.46 (m), 7.16-7.92 (m) 7.14-7.29 (m) 7.2Cb7.45 (m), 7.25-7.37 (m), 7.267.38 (m), 7.18-7.46 (m), 7.3C7.377.64-7.96 (m) 7.57-7.92 (m) 7.70-8.00 (m) 7.61-7.75 (m), 7.67-7.90 (m) 7.62-7.87 (m) 7.72-1.29 1.29 (s)7.79-7.91 (m)OMe or SiMe, 3.85 (s) 3.89 (s) -0.15 (s) -0.15 -0.14(t, ,JHF = 0.55) (d, 5JHF = 0.60)a Measured in CDCI,, chemical shifts (6) in ppm, coupling constants ( J ) in Hz. 6(19F) - 79.1. 6(19F) -94.9.6(19F) -74.2. 6(19F) -73.0. 6Y) "SCH,CH,). At 250 MHz. 6 0.21-0.32 (m, 2 H, CH,CH,CH,CH,), 0.62 (t, 3 H, ,JHH = 7.3, CH,CH,CH,CH,), 1.05 (sxt, 2 H, ,JHH = 7.3, CH,CH,-75.0 (21a), -74.8 (21b).Table 2 Carbon-13 NMR data"2 4 7 8 11 12 13 141 1.65 (br) 1 1.0648.46 42.501 19.82 119.92(t, 2JcF = 6.4)11.41 (br)43.1311.31 (br)40.21(d, 2JCF = 8.9)1 19.70119.74124.27124.66(d, 4JCF = 2.3)126.47126.5311.00d1 1.06 (br)d10.96 (br)d1 1.34 (br)57.93119.65119.69124.34124.62119.63 119.71 119.71119.76124.59(d, "JCF = 2.9)124.70125.92125.95126.09126.31139.64140.02142.42(d, ,JCF = 5.1)143.96(SiMe,)-2.15119.76c1c8 124.79 124.40 125.17 124.26 124.52126.66 126.83127.18 127.08126.45126.64126.1 1 125.79126.15126.6 1127.54140.58 140.57 140.39140.75141.88142.47140.62 140.04143.26139.72142.91141.24143.97141.35 140.70 141.81(d, 3JcF = 4.4)142.0652.99(d, ,JCF = 3.3,OMe)OMe or SiMe, 53.29 - 1.72(SiMe,)- 2.66(SiMe,)a Measured in CDCI,, chemical shifts (6) in ppm, coupling constants ( J ) in Hz. ' 6 26.77 (CHzCH3) and 5.94 (CHzCH3).6 33.22 (CH,CR,), 23.42 andcarbons bonded to a germanium and a silicon or a mercury atom have not been observedformation of 12 as the major product (about SO%), with a minoramount of 13. Crystallization from thf-pentane (40: 60)afforded pure 13 (0.09 g, 1573, m.p. 220 "C, m/z 500 (M' , 12%)(Found: C, 64.95; H, 6.9. C,,H,,F,GeSi requires C, 64.6; H,6.7%) and then colourless crystals of 12 (0.49 g, 83%), m.p.142OC, m/z 484 ( M ' , 17%) (Found: C, 62.8; H, 6.5.C&,,-ClFGeSi requires C, 62.5; H, 6.5%).Reaction of 5 with HgCl,To a solution of 5 prepared from the germane 2 (0.38 g, 0.85mmol) in thf was added at - 50 "C a solution of HgCl, (0.1 1 g,0.5 equivalent) in thf (7 cm3).The reaction was performed in thedark. After stirring at room temperature for 20 min andremoval of solvents in uacuo, pentane ( 5 cm3) was added and theprecipitate eliminated by filtration. Cooling of the solutionafforded 16 (0.36 g, 78%). The strong peak at m/z 444 ( M -Ge(C,Me,)CI,CR, - Hg + 1, 11%) indicated homolysis ofthe Hg-C bond. Heating 16 in refluxing thf for 2 h led to amixture of the starting material 16 (40%) and its decompositionproducts (mercury and 2) in 60% yield.Reaction of 12 or 13 with excess of methanolCompound 12 or 13 (100 mg) dissolved in methanol (3 cm3)was heated at 100°C (12) or 140°C (13) overnight. Afterelimination of trimethylfluorosilane and methanol in uacuo, theNMR spectra showed the formation of 7 and 8, previouslyobtained from 5 or 6 and methanol, in nearly quantitativeyields.Reaction of 12 or 13 with chloroformCompound 12 or 13 (200 mg), 0.1 equivalent of triethylamineand a large excess of chloroform were heated in a sealed tube at100 "C for 15 h.After removal of NEt,, CHCI, and SiMe,F inuacuo, the NMR spectra showed the formation of 2 or 17.Compound 17 could not be isolated in pure form but wasunambiguously characterized by 'H, 13C and "F NMRspectroscopy and mass spectrometry.Synthesis of digerrnoxane 21Compound 12 (200 mg), 0.5 equivalent of water and 1equivalent of triethylamine were heated in a sealed tube at100 "C overnight. The 'H NMR spectrum showed theformation of 21 as a mixture of two diastereoisomers in theratio 55:45.Only 21a (0.35 g, 36%) was isolated byrecrystallization from Et,O. EI mass spectrum: m/z 800 (M',2%).References1 A. G. Brook, F. Abdesaken, B. Gutekunst, G. Gutekunst andR. K. Kallury, J. Chem. SOC., Chem. Commun., 1981, 191.2 G. Raabe and J. Michl, Chem. Rev., 1985,85,419; A. G. Brook andK. M. Baines, Ado. Organomet. Chem., 1986, 25, 1; G. L. Larson,J. Organomet. Chem., 1989,374, 1; 1991,416, 1.3 (a) A. G. Brook, A.Baumegger and A. J. Lough, Organometallics,1992, 11, 3088; (6) N. Wiberg, G. Wagner and G. Muller, Angew.Chem., Int. Ed. Engl., 1985, 24, 229; (c) N. Wiberg, G. Wagner,J. Riede and G. Muller, Organometallics, 1987,6,32; ( d ) G. Delpon-Lacaze and C. Couret, J. Organomet. Chem., 1994,480, C14.4 J. Barrau, J. Escudie and J. Satge, Chem. Rev., 1990,90,283; J. Satge,J. Organomet. Chem., 1990, 400, 121; J. Escudie, C. Couret,H. Ranaivonjatovo and J. Satgt, Coord. Chem. Rev., 1994,130,427;T. Tsumuraya, S. A. Batcheller and S. Masamune, Angew. Chem.,Int. Ed. Engl., 1991,30,902.5 (a) H. Meyer, G. Baum, W. Massa and A. Berndt, Angew. Chem.,Int. Ed. Engl., 1987, 26, 798; (b) A. Berndt, H. Meyer, G. Baum,W. Massa and S. Berger, Pure Appl. Chem., 1987, 59, 101 1; (c)C.Couret, J. Escudie, J. Satge and M. Lazraq, J. Am. Chern. SOC.,1987, 109, 4411; ( d ) M. Lazraq, J. Escudie, C. Couret, J. Satge,M. Drager and R. Dammel, Angew. Chem., Int. Ed. Engl., 1988,27, 828; (e) G. Anselme, J. Escudie, C. Couret and J. Satge,J. Organomet. Chem., 1991, 403, 93; (f) M. Lazraq, C. Couret,J. Escudie, J. Satge and M. Soufiaoui, Polyhedron, 1991, 10,1153; (8) C. Couret, J. Escudie, G. Delpon-Lacaze and J. Satge,Organometallics, 1992, 1 1, 3 1 76.6 H. Meyer, C. Baum, W. Massa, S. Berger and A. Berndt, Angew.Chem., Int. Ed. Engl., 1987, 26, 546.7 G. Anselme, H. Ranaivonjatovo, J. Escudie, C. Couret and J. Satge,Organometallics, 1992, 11,2748.8 W. Ziche, C. Seidenschwarz, N. Auner, E. Herdtweck andN. Sewald, Angew. Chem., Int. Ed. Engl., 1994, 33, 77 and refs.therein.9 C. E. Allison and T. B. McMahon, J. Am. Chem. Soc., 1990, 112,1672.10 P. Jutzi, Adv. Organomet. Chem., 1986, 26, 217; P. Jutzi andU. Meyer, J. Organomet. Chem., 1987,326, C6; P. Jutzi, U. Meyer,B. Krebs and M. Dartmann, Angew. Chem., Int. Ed. Engl., 1986,25,919.11 P. Jutzi, H. Saleske, D. Buhl and H. Grobe, J. Organomet. Chem.,1983, 252, 29.12 C. Couret, J. Escudie, G. Delpon-Lacaze and J. Satge, J. Organomet.Chem., 1992,440,233.13 C. Jouany, S. Mathieu, M. A. Chaubon-Deredempt andG. Trinquier, J. Am. Chem. Soc., 1994, 116,3973.14 N. Wiberg, G. Preiner, 0. Schieda and G. Fischer, Chew. Ber., 1981,114,3505.15 D. A. Armitage, Comprehensive Organometallic Chemistry, 1982, 2,1; J. Dunogues, Actual. Chim., 1986, 3, 11.16 M. Riviere-Baudet, A. Khallaayoun and J. Satge, J. Organomet.Chem., 1993,462,89.17 M. Lazraq, C. Couret, J. Escudie, J. Satge and M. Drager,Organometallics, 199 1, 10, 1 77 1.Received 14th July 1995; Paper 5/04643BJ. Chem. SOC., Dalton Trans., 1996, Pages893497 89

ISSN:1477-9226    

DOI:10.1039/DT9960000893

出版商:RSC    

年代:1996

数据来源: RSC