摘要:
1972 1943Bonding Studies of Compounds of Boron and the Group IV Elements.Part VIII.1 Heats of Hydrolysis and Bond Energies for Some Trimethyl-metalyl Derivatives Me,M-X (M = Si, Ge, and Sn)By J. C. Baldwin, M. F. Lappert, J. B. Pedley,' and J. S. Poland, School of Molecular Sciences, University ofThe heats of hydrolysis, in aqueous 1 M-hydrochloric acid, of one silicon, five germanium, and eight tin(lv) com-pounds of type (Me,M),X (where M = Si, Ge, or Sn, n = 1-3, and X is a univalent ligand in which the donoratom adjacent t o M i s N, 0, S, CI. Br, or I) to give (Me,Si),O, (Me,Ge),O, and (Me,SnOH), have been measured.From these, standard heats of formation have been calculated as follows: AH," (Me,Si*OEt), I = -1 26.4 f 0.7;AH; [(Me,Ge),O], I = -136.0 f 4-0; AH; (Me,GeCI), :I = -71.6 f 2.1 ; AH; (Me,GeBr).I = -62.1 f 2.1 ;AH," (Me,Ge-OEt), I = -95.8 f 2.2; AHt" (Me,Ge*SBu"). I = -64.7 f 2.1 ; AH,' (Me,Ge*NMe,), I = -37.1 f2.2; AHfo (Me,SnCI), c = -58.4 f 1.2; AH; (Me,SnBr), c = -48.8 f 1.3; AH; (Me,Snl), I = -31.2 f 1.1 ;AH,' (Me,SnOH), c = -90.8 f 1.2; AHto (Me,Sn.OEt), I = -73.1 f 1.5; AH: (Me,Sn*SBu"). I = -47.1 f1.6; AH,' (Me,Sn.NMe,), I = -13.3 f 1.4; AH," [(Me,Sn),NMe], I = -31.5 f 2.5; AH," [(Me,Sn),N].c = -29.2 f 3.6 kcal mol-l. Gas-phase enthalpies of formation of these compounds and thermochemical bondenergy terms E(M-X) have been calculated. Group trends show that, for constant X, E(C-X) < E(Si-X) >E(Ge-X) > E(Sn-X), whereas €(C-Y) > E(Si-Y) (Y = H or Me). Another conclusion i s that the ' softness '(in terms of AH of reactions) of the acids Me,M+ increase in the order C < Si < Ge < Sn ; several chemical reactiontypes are examined in this light.Sussex, Brighton BN1 QQJIN Part I we described calorimetric experiments whichfurnished heats of hydrolysis of some compounds ofgeneral formula (Me,Si),X, namely those in which92.= 1, with X = C1, Br, OH, OBun, NHMe, andNMe,; n = 2, with X = NH or NMe; and n = 3,with X = N.2 We now report extensions of this workto n = 1, with X = OEt, and n = 2, with X = 0, aswell as to some germanium and tin(1v) analogues ofthese silicon compounds. The two papers should inmany ways be seen as a single whole. The work isalso related to (i) mass spectrometric studies on thecompounds Me,M1 and Me3M1-M2Me3 (M1 and M2 = C,Si, Ge, Sn, and Pb), which yielded gas-phase enthalpiesof formation [AH,' (g)] of these two classes of compoundPart VII, B.S. Iseard, J. B. Pedley, and J. A. Treverton,J . Chem. Soc. ( A ) , 1971, 3095.* Part I, J. C. Baldwin, M. F. Lappert, J. B. Pedley, andJ. A. Treverton, J . Chem. SOC. ( A ) , 1967, 1980.Part VI, M. F. Lappert, J. B. Pedley, J. Simpson, andT. R. Spalding, J . Organometallic Chem., 1971, 29, 195.and of radicals and ions derived from them; (ii)rotating bomb calorimetric studies on Et,Si and Me,Si,;and (iii) other thermochemical data on Group IVcorn pound^.^^^The compounds studied are (Me,M),X, where M = Si,Ge, or Sn, and X is a univalent ligand in which the atomadjacent to M has one or more formally non-bondingelectron pairs (Le., N, 0, S, Hal).Spectroscopy(lH n.m.r.) revealed that, under calorimetric conditions,acid hydrolysis was rapid and quantitative to afford(Me,Si) 20, ( Me,Ge) ,O, and (Me,Sn*OH) ,, respectively .For simplicity, thermochemical data for (Me,SnOH),refer to the monomer formula: strictly, they thereforerelate to g.f.w.-l, (gram-formula weight)-l, rather thanJ. D. Cox and G. Pilcher, ' Thermochemistry of Organicand Organometallic Compounds,' Academic Press, London-New 'York, 1970.Selected Values of Chemical Thermodynamic Properties',Nat. Bur. Stand. Tech. Note 270-3, U.S. Government PrintingOffice, Washington D.C., 19681944 J.C.S. Daltonmol-l. The compounds Me,SiF and Me3SnF were alsoexamined: the silicon compound (b.p.17 "C) provedinacceptably volatile for use in the calorimeter, whilethe tin fluoride did not react. In the hope of obtainingE(Si-Hg), the reaction of (Me,Si),Hg with oxygen inbenzene was investigated but was found to be non-stoicheiometric.From subsidiary data,4j5 heats of hydrolysis thusprovide standard enthalpies of formation AH: (c or 1)which, with literature or calculated heats of vaporisationAHvap, lead to AH," (g). From AH," (g), thermo-chemical bond energy terms E(M-X) become available.Apart from obtaining basic thermochemical data,our primary objectives were to examine in a thermo-chemical context (i) the concept of p,,-d, (N-Si) bonding,(ii) group trends, and (iii) the relative ' softness' orclass ' b ' behaviour of the cations Me,M+.As for (i),we found that E(Si-N) was rather insensitive (76.6 -j=2.5 kcal mol-l) to environment in the five compounds(see above) studied, and hence concluded that x-bondingfor SIN was not thermochemically important .z Problems(ii) and (iii) are discussed in this paper.EXPERIMENTALPreparation of Organornetallic Compounds.-These, withthree exceptions, were made by standard procedures anddetails are in Table 1. Compounds were shown to be pure,after rigorous fractional distillation, by g.1.c. Details for thethree exceptions follow.Chlorotrimethylgermane was made by the method brieflydescribed by Mironov and Kravchenko.7 A suspensionof aluminium trichloride (0.3 g) in 2-chloropropane (12.0 g)was added dropwise to tetramethylgermane 8 (20.0 g) a t0 "C, whereafter the mixture was gradually (18 h) warmedto 90 "C.Distillation afforded chlorotrimethylgermane(19.0 g, 82%).Attempts to prepare ethoxytrimethylgermane by a similarmethod to that used for the silicon analogue (see Table 1)failed, owing to formation of an amine complex. Thefollowing route was therefore devised. Bromotrimethyl-germane (15.0 g, 1 mol) was added to ethanol-free sodiumethoxide (6-1 g, 1.27 mol) in diethyl ether (60 ml), where-after the mixture was heated (12 h) under reflux. Dis-tillation afforded ethoxytrirnethylgerrnane (6.3 g, 51 yo)(Found: C, 34.5; H, 8.75. C,H,,GeO requires C, 39.9;H, 8.65%); urnax. (cap. film): 2987vs, 2925s, 2880s, 1410w,1380s, 1240s, 111Os, 1070s, 830vsb, 660w, and 612s cm-l;lH n.m.r.(T): 9.71 (singlet, Me,Ge), 8.83 (triplet, Me), and6-35 (quartet, CH,).Chlorotrimethylgermane (10.0 g, 2.2 mol) in diethyl ether(10 ml) was slowly added to di-n-butylthioplumbane (8.8 g,1 mol) in the same solvent (10 ml), whereafter the mixturewas heated (24 h) under reflux. The colour changed fromyellow to white. The mixture was filtered and the pre-cipitate was washed with ether (2 x 10 ml). Distillation ofthe combined filtrate and washings afforded n-butylthiotri-methylgermane (4.34 g, 470/,) (Found: C, 41.2; H, 8.75.C,H18GeS requires C, 40-6; H, 8.75%); urnax. (cap. film):2978s, 2940s, 2885m, 1462m, 1405w, 1290w, 1255s, 830vsb,598s, and 560m cm-l; lH n.m.r. ( 7 ) : 9-55 (singlet, Me,Ge),S.Ahrland, J. Chatt, and N. R. Davies, Quart. Rev., 1958,12, 265.9.08 (multiplet, Me), 8-47 (multiplet, p- and y-CH,), 7-48(multiplet, a-CH,).The Stoicheiornetry of the Hydro1yses.-This was estab-lished [equations (1) and (2)] by 1H n.m.r. spectroscopicexamination of (a) pure starting materials, (b) all possibleTABLE 1Preparation of compoundsCompound Reagents B.p./("C/mmHg) Ref.Me,Si*OEt Me,SiCl-EtOH-Et,N 76/760 aMe,GeBr Me,Ge-Br, 113*7/760 bMe,Ge*OEt Me,GeBr-EtONa 101-lO2/750 SeeMe,Ge.SBun Me,GeCl-Pb(SBu*) , 6616 SeeMe,Ge.NMe, Me,GeCl-LiNMe, 103/760 cMe,SnCl Me,Sn-SnC1, 1541760 dMe,GeCl Me,GeC1-Me2CHC1-A1C1, 981750 7texttextMe,SnBr Me,Sn-Br, 164-165/750 eMe,SnI Me,Sn-I, 641 10 fMe,Sn*OEt Me,Sn*NMe,-EtOH SOjO.1 gMe,Sn*SBun Me,SnOH-BunSH 4410.05 hMe,Sn*NMe, Me,SnCl-LiNMe, 1261760 i(Me,Sn) ,NMe Me,SnCI-MeNH,-LiBun 6413 i(Me,Sn) ,N (Me,Sn) ,NMe-NH, 7012 ia R.0. Sauer, J . Amer. Chem. SOC., 1944, 66, 1707.6 L. M. Dennis and W. I. Patnode, J . Amer. Chem. SOC.,1930, 52, 2779, c J. Sat& and M. Baudet, Compt. rend.,1966, 263, C, 435. d K. A. Kocheshkov, Ber., 1929, 62, 996.C. A. Kraus and W. V. Sessions, J . Amer. Chem. SOC., 1925,47, 2361. f S. N. Naumov and 2. M. Manulkin, Zhtur. obskcheiKhim., 1935, 5, 281. B J. Lorberth and M. R. Kula, C h e wBey., 1964, 97, 3444. h E, W. Abel and D. B. Brady, J .Chem. SOC., 1965, 1192. K. Jones and M. F. Lappert,J . CJaem. SOC., 1965, 1944.hydrolysis products (pure), and (G) actual calorimetric(hydrolysis) products in aqueous IM-HC~.In each case(c), there was no evidence for either unchanged startingmaterials or unexpected products.(Me,M),X(l) + n H20 (in IM-HCL soln.) ---t[: (Me,M),O + XH, IM-HCl (1)11 = Si or Ge 1(Me,M),X(l or c) + ?zH20 (in 13r-HCl soln.) --+(Me,Sn.OH), + XH, IM-HCl (2) 1 &'I = SnCaZoriwzetry.-The heats of hydrolysis in lM-hydrochloricacid were measured with the calorimeter described in ref. 2.The values of AHobs in Table 2 are the mean of a t least sixseparate measurements, the uncertainties being twice thestandard deviation of the mean.RESULTSEnthalpies of Fovtnafioiz.-Equation (3) corresponds tothe hydrolysis process and was used to determine thestandard enthalpies of formation of the compoundsMe,Si.OEt and Me,GeX (X = Cl, Br, OEt, and SBun).Me,MX(l) + +H,O(l) &(Me,M),O(l) +HX(56H20) (3)V.F. Mironov and A. L. Kravchenko, Izvest. Akad. NaukD. F. van de Vondel, J . Organometallic Chem., 1965, 3, 400.S.S.S.R. Ser. khim., 1965, 6, 1026The use of equation (3) was justified because the enthalpiesof mixing of (Me,Si),O(l) and (Me,Ge),O(l) with lM-hydro-chloric acid were found to be less than 0.1 kcal mol-l,and the enthalpies of mixing the molar HX solutionswith the molar HCl solution is negligible. For Me,Ge*-NMe,(l), equation (4) is appropriate.hSe,Ge*NMe,(l) + &H,0(1) + HC1(55H2O) ---t+(Me,Ge),O(l) + Me2NH*HC1(55H,O) (4)The standard enthalpy of formation of Me,Si*OEt wasdetermined from the subsidiary data in Table 3.Un-fortunately, none of the germanium compounds studiedwas assumed to be ca. -136 kcal mol-l. By use of datafrom refs. 4 and 5, the enthalpy change for reaction (5) is-9 kcal mol-l (M = Si, X = Cl), -8 kcal mol-l (M = Si,X = Br), - 13 kcal mol-l (M = Sn, X = CI), and - 13kcal mol-l (M = Sn, X = Br). A value of ca. -10 kcalgMe4M(I) + aMX4(l) -w Me,MX(I) (5)mol-1 seemed appropriate for M = Ge and X = C1 or Brand, with use of values for Me,Ge(l) (-41 kcal m~l-'),~GeC1,(1) (- 127 kcal mol-l),S and GeBr,(l) (-83 kcal m0l-1),5gives values of -72 and -62 kcal mol-1 for AHf" of Me,-GeCl(1) and Me,GeBr(l), respectively. Use of the appro-Compound(Me3Si)20(!)Me,SiC1(1)Me,Si*OEt (1)Me,GeC1(1)Me,GeBr(l)Me,Ge*OEt (1)Me,Ge.SBun( 1)Me,Ge*NMe,( 1)Me,Sn*OH (c)Me,SnCl(c)Me,SnBr(c)Me,SnI(l)Me,Sn.OEt (1)Me,Sn.SBun( 1)Me,Sn*NMe, (1)(Me,Sn) ,NMe(l)(Me3Ge)20(1)(Me3Sn) ,N(c)TABLE 2Enthalpies of formation and bond energies (all values in kcal mol-l)-AHobs AHf" (c or 1) AHvapQ AHt" (g)- -194.7 f 1.3' 8.9 e - 185.8- -91.8 f 0.7 7.2 e - 84.65-7 +.0.1 -126.4 f 0.7 8 - 118.4- - 136.0 f 4.0 d 9 - 127.01.7 f 0.1 -71.6 f 2.1 8 - 63.60.5 & 0-1 -62.1 & 2.1 9 -53.16.9 & 0.2 -95.8 f 2.2 8 - 87.825.8 f 0.2 -37.1 f 2.2 8 - 29.1-1.1 f 0.1 -64.7 f 2.1 10 - 54.7-3.3 &- 0.12.4 f. 0.24-2 f 0.118-3 f 0.45.1 f 0.238-2 f 0.343.6 f 0.370.2 f 0.3-90.8 f 1.2-58.4 f 1.2-48.8 f 1.3-31.2 & 1.1 C-73.1 f 1.5-47.1 f 1.6-13.3 f 1.4-31.5 f 2.5-29.2 f 3.6151214 e11.5101091215- 75.8- 46.4- 34.8- 19.7-63.1- 37.1- 4.3- 19.5- 14.2E10596 e1038281 e68795855777561456652414842BondSi-0Si-ClSi-0Ge-0Ge-C1Ge-BrGe-0Ge-SGe-NSn-0Sn-C1Sn-BrSn-ISn-0Sn-SSn-NSn-NSn-N0 All values, except those specified, caIcuIated from b.p.s by use of a Trouton's constant of 22 cal mol-l K-l.Where the condensedstate is crystalline a heat of fusion of 3 kcal mol-1 has been assumed. The error limits on AH,,, are of order 2 to 3 kcal mol-1.b Data from ref. 2, included to enable calculation of E values for Si compounds. J. D. Cox and G. Pilcher, ' Thermochemistry ofOrganic and Organometallic Compounds,' Academic Press, New York, 1970. e Valuescalculated from enthalpies of formation of tetrahalides (see Table 4) and assumed appropriate for the inetal-chlorine bonds inMe,M-Cl.See text for a discussion of this value.here had an accurately known enthalpy of formation fromwhich to derive the enthalpies of formation of the remainingcompounds [cf.(Me,Si),O for Me,Si*OEt and other com-pounds in ref. 21. However, the ethalpy of formation ofTABLE 3 aSubsidiary AHf" for calculation of AHf" (c or 1) (allvalues in kcal mol-l)Compound AHI' Compound- 68.32 Bu"SH(1)gtgk)(aq.) - 68-9 Me,NH, HC1( 55H20)HC1(55H20) - 39.55 MeNH2,HC1(55H20)HBr(55H20) -28.72 (Me,Si),O(l)HI(55H20) - 12.96 (Me,Ge),O(l)HCl(53HZO) - 39.54 NH,C1(55HZO)Me,SnI (1)AHt'-29.72'- 68.57- 69.65- 71.48-194.7'- 136.0 e- 31.2 b0 All values, except those specified, taken from ref.5.b J. D. Cox and G. Pilcher, ' Thermochemistry of Organicand Organometallic Compounds, Academic Press, New York,1970. An extrapolated value from other experimentaldata: see text.(Me,Ge) ,0(1) can be estimated reasonably accurately asfollows.The enthalpy of formation of Et,Ge,O(I) is -148 kcalm0l-1.~ The increment in AHf" on changing from an ethylgroup to a methyl group is ca. 2 kcal mol-l for most organo-metallic compound^,^ whence the value for (Me,Ge) 20(1)priate enthalpies of hydrolysis for equation (3) gives valuesof - 136.8 and - 135.8 kcal mol-l for AHf" [(Me,Ge),O(l)].A value of -136.0 & 4 kcal mol-l therefore seemed ap-propriate for (Me,Ge),O(l), and with subsidiary data fromTable 3 yields the enthalpies of formation of the Ge com-pounds listed in Table 2.[The enthalpy of solution ofBunSH(l) in IM-HCl was found to be less than 0.1 kcalrnol-l] .The enthalpy of solution of Me,Sn*OH(c) in lr\f-HCl wasmeasured and found to be less than 0-1 kcal mol-l, so theenthalpies of hydrolysis of the Me,SnX compounds arerepresented to within 0.1 kcal mol-l by equation (6). Forthe amido-compounds, equation (7) is appropriate. TheMe,SnX(l or c) + H,0(1) +(Me,Sn),NMe,-n(l or c) + nH,O(l) + HC1(55H20) ---+enthalpy of formation of Me,SnI(l) quoted in Table 3 wasused to calculate AH," [Me,SnOH(c)], whence the enthalpiesof formation of the Sn compounds in Table 2 are derived.The values for crystalline Me,SnCI and Me,SnBr are con-sistent with the literature values of -50.9 & 2.5 and-44.3 & 1.0 kcal mol-l for the corresponding Eiquidphases, since enthalpies of fusion in the range 3-5 kcalmol-l would probably be appropriate for these compounds.Me,Sn*OH(c) + HX(55H20) (6)nMe,Sn*OH(c) f Me3-,NH,*HCI(55H,O) (71946 J.C.S.DaltonBond Energies.-The chemical significance of the thermo-chemical data is best described by the energies of ap-propriate bonds in the molecules. The derivation of bondenergies automatically involves drastic approximationssuch as assuming that the contribution of the Me,M groupto the enthalpy of formation of Me,MX is independentof the nature of X. Thus, the absolute values of E listedin Table 2 may not be significant, but the relative valuesprobably have chemical relevance.The bond energieswere derived from the gaseous enthalpies of formation byuse of equation (8).*1n - (Me3M)nWg) + HCW ----t Me,MCW + 5 H,zX(g)1 1n nAH" = AHf" [Me,MCl(g)] + - AHf" [HnX(g)] - - AH,"[(Me,M)nX(g)l - AHf" [HCWl= E(M-X) + E(H-Cl) - E(M-Cl) - E(H-X) (8)As a basis for calculation, E(M-Cl) was taken to have thevalue in the corresponding tetrachloride (see Table 4).This was an arbitrary choice and the alternative of calculat-ing E(M-Cl) in Me,MCl from M-CH, bond energies from,TABLE 4 aSubsidiary AH," and bond energies for calculation ofE values in Table 2 (all values in kcal mol-1)Compound AHf" (g) I? Atomb AH*" (8)HC1 -22.062 103.2 H 52.095HBr - 8.70 87.5 0 59.553C 171.291HI 6.33 71-3 C1 29-082-57.796 110.8 Br 26.741-66.19 I 25.535- 4-93 87.9 S 66.636- 20.98 N 112.979 BunSH c- 11.02 93.4 Si 108.9- 5-49 Ge 90.0 MeNH,Me,NH - 4.41 Sn 72.2SiC1, - 157.03 95.6GeCl, -118.5 81.2Q All values, except that for BunSH, taken from ref.5.b AHf: of atoms required for calculation of bond energies, E.C J. D. Cox and G. Pilcher, ' Thermochemistry of Organic andOrganometallic Compounds,' Academic Press, New York, 1970.3:HH2SNH3CCI, c - 26.2 78.2SnCl, - 112.7 75.3for example, the tetramethyl compounds, would lead tosignificantly different values for all the bond energies.However, the relative values would remain unchangedand the discussion in the following section depends oneither their relative values or the orders of magnitude ofthe bond energies.DISCUSSIONComparison with Published Data.-Our results (Table2) can in a few cases be compared with earlier data(for comments on Me,SnCl and Me,SnBr, see p.1945).* Values for carbon bonds were calculated from appropriateenthalpies of formation from ref. 4, some of the compounds beingslightly different from those given in equation (8) (Tee legend toFigure 1).T. L. Cottrell, 'The Strengths of Chemical Bonds,' 2ndedn., Butterworths, London, 1958.lo J. B. Pedley, H. A. Skinner, and C . L. Chernick, Trans.Faraday SOC., 1957, 53, 1612.The value of E(Si-0) of 103-105 kcal mol-l agreesreasonably with other estimate^,^ and that of E(Ge-Br)of 68 kcal mol-l is close to the mean value based onGeBr,, E(Ge-Br) = 66 kcal m ~ l - ~ .~The values for E(Sn-Br) and E(Sn-I) of 61 and 45kcal mol-l, which are relative to jT(Sn-Cl) for SnCl,,differ appreciably from those lo calculated on the basis of,!?(Sn-C) in Me,Sn. However, the ratios of E(Sn-Br) :E(Sn-I) agree well.Groztp Trends.-The Group IV trends for mean bonddissociation energies D(M-R) in MR, and D(M-H)reveal (data of refs. 9 and 11) a monotonic decreasewith increasing atomic number of M (i.e., C > Si >Ge > Sn > Pb). Likewise, a similar trend is observedfor E(M-Me) and E(M-H) for the compounds Me,MX(X = Me In contrast, for the tetrahalides(data of refs. 5, 9, and 13), there is an enhancementor H 12).------- ---- - -- -- \-L - - -I - -- -----I IC Si Ge SnM-\20 ITrends in mean bond energy terms I?(M-X)for E(5-X) (i.e., C < Si > Ge > Sn > Pb).Similartrends are observed for E(M-X) values taken from Table2, as shown in the Figure. It is tempting to attributethe enhancement of ,!?(Si-X) when X is in principlelone-pair possessing to p,,-d, (Si-X) bonding, and tosuch x-bonding being more effective for Si than for Ge,Sn, or Pb analogues.The Relative Softness of the Me,M+ Ions.-The car-bonium ion has been described as a ' borderline ' acid.14This concept can now be considered in terms of AHin a quantitative sense in relation to the other Me&+ions. Three ideal systems could be taken. Theseare the F-C1, OR-SR, and NR2-PR, exchanges, asexemplified by equation (9); from Table 2 and ref.5,l1 H. A. Skinner, Adv. Organometallic Chem., 1964, 2, 49;A. E. Pope and H. A. Skinner, Trans. Faraday SOG., 1964, 60,1404; J. V. Davis, ,4. E. Pope, and H. A. Skinner, ibid., 1963,59, 2233.l2 S. R. Gunn and L. Green, J . Phys. Chem., 1964, 68, 946.l3 D. F. Evans and R. E. Richards, J . Chem. SOL, 1952, 1292.l4 R. B. Pearson, J . Amer. Chem. SOC., 1963,85,3533; Chem. i nBritain, 1967, 3, 1031972 1947enthalpies AHiaeal for reaction (9) are +2.0 (Si), -2.2(Ge), and -9.4 (Sn) kcal mol-l.Me,M*OR(g) + RSH(g)+Me,M*SR(g) + R W g ) (9)From these data, it is clear that the degree of 'soft-ness' for the species Me,M+, based on AH, increaseswith increasing atomic number of M, and we predictthat this is the probable trend for other Groups of thePeriodic Table. The terms ' hard ' and 'soft ' are seenas providing an essentially phenomenological descriptionrather than a rationalisation.Features such as polaris-ing power or x-bonding may contribute significantly,but their relative value is unknown, and to some degreeis irrelevant t o the above conclusion.Some Chemical and Thermochemical Coyyelatiouts.-From the AHf' data of Table 2 and elsewhereJs it ispossible to comment on the significance of thermo-chemical information in relation to chemical differencesamong the Group IV elements.It is established that reactions of equation (9), butfor compounds in their standard states, proceed fromleft-to-right for M = Sn or Pb, but conversely forM = Si or Ge.15 This is consistent with trends inAHlkcal mol-l for reaction (10) : -1.3 (Si), -5.6 (Ge),Me,M*OEt(l) + BunSH(l) .--tMe,M-SBun(l) + EtOH(1) '(10)and -10.7 (Sn).Similar trends show that it is notunreasonable that alkylthio-derivatives may be formedCf. E. W. Abel and D. A. Armitage, Adv. OrganometallicChem., 1967, 5, 1; H. Schumann, I. Schymann-Ruidisch, andM. Schmidt, in 'Organotin Compounds, ed. A. K. Sawyer,Marcel Dekker, New York, 1971, vol. 2, p. 297.from aqueous solutions for Sn [e.g. (Me,SnOH), orMe,SnOR + RSH in H,O] but not Si or Ge.Another difference between the Group IV elements isthat chlorides M%MC1 can be converted into Me,MBrby heating under reflux with BBr,, for M = Sn butnot M = Si.16 Consistent with this, the Sn reaction ismore exothermic: AH for the condensed-phase re-action = -1.0 (Si) and -5.3 (Sn) kcal mol-l.Finally, aminostannanes cannot generally be obtainedfrom corresponding halides and amines. Reactionsbetween such compounds leads to 1, l-adduct formation[e.g., reaction (lla)], whereas for Si or Ge analoguesequation (llb) is appropriate, although initial formationof an adduct is probab1e.l'Me3MC1(1 or c) +(4 7 Me,MCl.Me,NH(c) + Me,NH(l)k Me,M*NMe,(l) + Me,NH,Cl(c)Me,NH(l)- (11)Trends in A.H/kcal mol-l for reaction (llb) are: -22.3(Si), -13.0 (Ge), and -2.4 (Sn). It is clear that equa-tion (llb) is thermochemically much more favourablefor M = Si than for M = Sn; the enthalpy of adductformation [equation (lla)] is likely to be ca. -10kcal mol-l.We thank Dr. J. A. Treverton for data on (Me,Sn),N,and the D.S.I.R. (Studentship to J. C . B.) and the U.S.Air Force Office of Scientific Research for support.[2/550 Received, 9th March, 19721l6 P. M. Druce and M. F. Lappert, J . Chem. Soc. ( A ) , 1971,l7 K. Jones and M. F. Lappert, J . Chem. Soc., 1965, 1944.3595
ISSN:1477-9226
DOI:10.1039/DT9720001943
出版商:RSC
年代:1972
数据来源: RSC