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Regiospecific metallation in palladium–hydrazone complexes |
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Dalton Transactions,
Volume 1,
Issue 8,
1983,
Page 1483-1487
Beatrice Galli,
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J. CHEM. SOC. DALTON TRANS. 1983 1483Reg iospecif ic M eta1 lat ion in Pal lad ium-Hydrazone ComplexesBeatrice Galli and Francesco Gasparrinilstituto di Chimica Organica, Universita di Roma, ItalyLuciana Marescalstituto di Chimica Generale ed lnorganica, Universita di Venezia, ItalyGiovanni NatileCattedra di Chimica Generale ed lnorganica, Universitd di Bari, ItalyGianni PalmieriDipartimento di Scienze Chimiche, Universita di Camerino, ItalyThe dimethylhydrazone of pinacolone, ButMeC=N1 N2Me2, reacts with [PdCI,(NCR),] (R = Me or Ph)to give the complexes [PdCI2( B u ' M ~ C = N N M ~ ~ ) ~ ] and [ ( P ~ C I , ( B U ~ M ~ C = N N M ~ ~ ) } ~ ] , in which theligands co-ordinate preferentially through the aminic nitrogen, N2. Both species, in solution,carbopalladate regiospecifically on the Me group to give [(P~[CH,C(=NNM~,)BU~]CI}~]. In contrast,ButMeC=N1 N2MePh reacts with palladium to give only the 1 : 1 adduct [(PdCI,( Bu'MeC=NNMePh)),]in which the ligand co-ordinates preferentially through the iminic nitrogen, N'.This complex is fairlystable in benzene or dichloromethane solution where it slowly decomposes to give only a small amount,of the methylpalladated complex [{ Pd[CH,C(=NNMePh) But]CI},] ; however, in methanol solution andin the presence of a base, NaO,CMe, it carbopalladates regiospecifically on the Bu' group to give[{Pd[CH2C(CH,),C(=dlNMePh)Me]CI}2]. The reason for different regioselectivity and the relative rate ofcarbopalladation on the Me and But group (for N2- and N1 -co-ordinated hydrazones respectively) arediscussed.The metallation of co-ordinated hydrazones has been the topicof quite a number of studies in the past fewThe most recent report on this subject described the carbo-palladation of the dimethylhydrazone of pinacolone, Bu'Me-C=NN Me2, and format ion of [ { Pd [ CH2C(=NN Me2)Bu '1 C1)2]in which the ligand co-ordinates to the metal through theaminic nitrogen, N2, and metallation occurs on the Me groupof the ketiminyl resid~e.~ This is in contrast to the generallypreferred N' co-ordination of the hydrazone ligands whichwould have led to metallation on the But group.Pursuing our current studies on the hydrazone complexesof ~alladium,~-~ we gained some insight into the reactionstudied by Shaw and co-workers5 which clarifies the reasonfor its regiospecificity.The results of this investigation arereported in this paper.-Experiment a1Starting Matevials.-The ligands, ButMeC=NNMez (L')and Bu'MeC=NNMePh (L'), were prepared by reaction ofBu'MeC=O, with the appropriate hydrazine (H2NNMe2 orH2NNMePh respectively)." Their purity was checked by g.l.c.,t.l.c., elemental analysis, and 'H n.m.r. spectra. The com-plexes tr~ns-[PdCl~(NCR)~] (R = Me or Ph) were preparedfrom PdCl, and NCR according to the method of Kharaschet al."Complexes with L'.-[PdC12(L')2]. This complex was pre-pared by reaction of tran~-[PdCl~(NCMe)~] (0.44 g, 1.7 mmol)with twice the stoicheiometric amount of L' (0.48 g, 3.4mmol) in benzene containing 10% v/v of hexane, at 0 "C.After stirring for 3 h the reaction mixture was filtered, con-centrated to a small volume under vacuum, and treated with anexcess of pentane to give a yellow solid. The crude productwas purified by passing it through a chromatographic columnof acetylated cellulose (acetyl content 40%) using benzene aseluant, yield ca.55% {Found: C, 41.3; H, 7.3; C1, 16.1; N,12.1. [PdC12(CsH18N2)2] requires C, 41.6; H, 7.9; CI, 15.4;N, 12.1%).[(PdC12L1)J. This complex was prepared by reaction oftran~-[PdCl~(NCMe)~] (0.44 g, 1.7 mmol) with the stoicheio-metric amount of L' (0.24 g, 1.7 mmol) in benzene at 5 "C.After stirring for 3 h the solution was filtered, taken to drynessunder vacuum, and the residue treated with pentane to give abrown solid, yield ca.50% {Found: C, 30.3; H, 5.7; Cl, 22.2;N, 8.5. [PdC12(C8HlsN2)]2 requires C, 30.1; H, 5.7; CI, 22.2;N, 8.8%).[{Pd[ CH2C(=NNMe2)Bu']Cl}2]. This compound was firstobtained by Shaw et aL5 by reaction of Na2[PdCLJ, L1, andNaOzCMe in methanol at room temperature. We preparedthe same compound, starting from the substitution productsprepared above according to the following procedures. (i)A methanolic solution of either [PdC12(L1)2] or [(PdC12L')2]was treated with twice the stoicheiometric amount of sodiumacetate. After 1 d at room temperature a yellow precipitateseparated out, this was collected by filtration of the mother-liquor, dried, and crystallized from dichloromethane-hexane.The yield referred to palladium was ca. 90% in both cases{Found: C, 33.8; H, 6.0; C1, 12.6; N, 9.7.[PdCl(C8H17N2)l2requires C, 33.9; H, 6.0; Cl, 12.5; N, 9.9%). (ii) The samecompound could be obtained directly from either [PdC12-(L')2] or [(PdC12L1)2] without the use of a base. In a typicalexperiment a solution of [PdC12(L1),] in benzene was leftstanding at room temperature for 2 d, a red solid separatedout while the solution became orange-yellow. The precipitate,separated by filtration of the mother-liqvor, was washed withbenzene and shown to be the salt [HLL],[PdCl4] [Found: C,35.6; H, 7.1; C1, 26.8; N, 10.4. (CsH19N2)2(PdC14) requiresC, 35.9; H, 7.2; C1, 26.5; N, 10.5%]. The solution wasevaporated to dryness under vacuum and the residue, crystal-lized from dichloromethane-hexane, afforded the desiredcomplex, [(Pd[ CH2C(=mMe2)But] C1)4Complexes with L2.-[(PdC12L2)2].Only the 1 : 1 adduct1484 J. CHEM. SOC. DALTON TRANS. 1983Table. Proton chemical shifts (6/p.p.m., downfield from SiMe,) of free and complexed hydrazones (R'R2C=NNR3R4)ButMeC"NMe2ButMeC=NNMe2H+[ PdC12(ButMeC=NNMe2)21[ (PdC12(Bu'MeC=NNMe2)}21i I[{ Pd [CH2C(=NNMe2)But] Cl},]Bu'MeC"NMePhBu'MeC=NNMePhH+[{PdC12(But MeC=NNMePh)}21[ { Pd [ CH2C(=NNMePh)Bu'] Cl},][{$d [CH2C(CH3)2C(=hMePh)Mel Cl},]-Isomer ~1 = ~~t R2 = Me R3R4 = Mez R4 = Ph1.06 1.88 2.351.15 2.43 3.171.12 3.04 2.812.902.281.08 2.892.761.863.3 =3.32.323.11 1.121.23 1.951.40 2.40{ ;:::{;:he1.1--zz-d1.26 3.35 {;:% 1.852.852.922.742.822.922.82.82.812.893.45 7.2-7.53.4-3.8 7.4-7.83.55 7.4-7.82.93 6.7-7.33.13 6.7-7.5All spectra were recorded in CD2C12 solution at 10 "C unless otherwise stated.3J(HH) = 5 Hz. The assignment of the NMe resonancesto the two sets of signals is only tentative. Tentative assignment.g PdCH2. Spectrum recorded in CDC13 solution at 34 "C. ' Complex resonance band. C(CH3)z.Spectrum recorded in C,D, solution at 10 "C. ' Broad resonance.[(PdC1zL2)z], could be obtained by reaction of trans-[PdCl2-(NCR),] with Lz even when a large excess of ligand was used.In a typical experiment tran~-[PdCl~(NCPh)~] (0.58 g, 1.5mmol) and L2 (0.31 g, 1.5 mmol) were allowed to react inbenzene at room temperature for 1.5 h. The resulting dark redsolution was filtered to separate a small amount of brownprecipitate, concentrated to small volume (3-4 cm3) andpassed through a chromatographic column of acetylatedcellulose (acetyl content 40%) using hexane containing 30%v/v of ethyl acetate as eluant.The chromatographed solutionwas taken t o dryness under vacuum and the solid residuecrystallized from dichloromethane-hexane {Found : C, 41.3 ;H, 5.4; C1, 18.9; N, 7.0. [PdC12(C13H20NZ)]2 requires C, 40.9;H, 5.3; C1, 18.6; N, 7.3%}.[ {Pd[CH2C(=NNMePh)Bu t]Cl}z]. Performing the react ionbetween trans-[PdCl,(NCR),] (R = Me or Ph) and L2 asreported above but using a longer reaction time (3-4 d),in addition to [(PdClzL2)z], a small amount of the methyl-palladated compound was formed. (i) In a typical experiment amixture of ~dClZ(NCPh),] and L2 (ratio 1 : 1) in benzene wasleft at room temperature under stirring for 7 d.The resultingsolution was filtered, to separate a black decomposition pro-duct, concentrated to small volume, and passed through achromatographic column of acetylated cellulose (acetylcontent 40%) using hexane containing 30% v/v of ethyl acetateas eluant. Two distinct fractions were collected, these weretaken to dryness and the solid residues crystallized fromdichloromethanehexane. The former fraction afforded yellowcrystals of the metallated species (Found: C, 45.5; H, 5.5;C1, 10.2; N, 8.2. [PdC1(C13H19NZ)]2 requires C, 45.2; H, 5.5;Cl, 10.3; N, 8.1%). The second fraction afforded the simplesubstitution product [(PdC12L2)J. (ii) The same products wereobtained when a mixture of trans-[PdClz(NCPh)z] and Lz(ratio 1 : 2) in dichloromethane was left at room temperature,under stirring, for 1 d.The resulting solution, filtered andconcentrated to small volume afforded by treatment withexcess diethyl ether, a brown precipitate of [(PdC1zL2)z]. Themother-liquor, treated with an excess of pentane, affordedthe metallated species.-[($d[CH2C(CH,),C(=NNMePh)Me]CI),1. (i) This specieswas obtained by performing the reaction between trans-[PdCl,(NCPh),] and L2 in the presence of a base (NaOz-CMe) (ratio 1 : 1 : 1.2) in methanol and leaving the mixtureunder stirring at room temperature for 1 d. The product,quite insoluble in methanol, was separated by filtrationof the solution and crystallized from dichloromethane-hexane, yield ca.50% (Found: C, 45.8; H, 5.2; C1, 10.4; N,8.3. [PdC1(C13H19N2)]2 requires C, 45.3; H, 5.5; Cl, 10.3; N,S.l%}. (ii) The same product was obtained by treating thesimple substitution product, [(PdCIzL2)2], with sodium acetate(a slight excess) in methanol. (iii) The t-butylmetallated com-plex was also obtained by performing the reaction under theconditions reported by Shaw and co-~orkers.~ A mixture ofNaz[PdCI4], Lz, and NaOzCMe (mol ratio 1 : 1 : 1.2) in meth-anol, left under stirring at room temperature for 1 d, affordeda brown precipitate which, when separated by filtration of themother-liquor and crystallized from dichloromethane-hexane,gave the desired product.Apparatus.-Infrared spectra in the range 4 000-250 cm-'were recorded as KBr pellets on a Perkin-Elmer 457 spectro-photometer.Proton n.m.r. spectra were obtained with aVarian EM 390 spectrometer. Separations by liquid chrom-atography were performed on a Waters model ALC/GPC-202chromatograph equipped with U6-K universal injector, modelM6000 solvent-delivery system, and model 440 differential U.V.detector (254 and 405 nm).Results and DiscussionIn order to understand the reason for the regioselectivityobserved in the carbopalladation reaction of the dimethyl-hydrazone of pinacolone, we investigated the nature of thesimple substitution products. The hydrazones of aliphaticketones, R1R2C=N1N2R3R4 (L) (R'R' = Me2, Et,, BunMe, orPr'Me etc.; R3R4 = Me2 or MePh), react with trans-[PdClz-(NCPh),] to give two types of complexes : trans-[PdCI,(L),]and tran~-[(PdCI~L)~], depending upon the metal to ligandratio.In both types of complexes the hydrazones co-ordinateexclusively through the iminic nitrogen, N', in spite of the factthat this type of co-ordination is very sterically demandinJ. CHEM. SOC. DALTON TRANS. 1983 1485and leads to hindered rotation about the Pd-N1 b ~ n d . ~ - ~ * ' ~In this context it is to be noted that the free ligands are syn-thesized as the geometrical isomer with the bulkier substituentof the ketiminyl residue (But in the case of pinacolone) cis tothe lone pair of electrons of N1.13By reaction of trans-[PdCl~(NCMe)~] with twice the stoiche-iometric amount of Bu'MeC=NNMe, (L1) in benzene at 5 "Cthe expected 2 : 1 adduct [PdClz(L1)2] was obtained.The n.m.r.spectrum of a freshly prepared solution of this compoundexhibited one set of signals (see Table) with resonances ofCBd, CMe, and NMe shifted to lower field, with respect tothose of the free ligand, by 0.06, 1.16, and 0.46 p.p.m.respectively. The large deshielding effect suffered by the CMegroup clearly indicates that this radical is cis to the metal 'and therefore the ligand is N2-co-ordinated to the metal[structure (lc)]. The n.m.r. spectrum changed,ButR3 R 4Me-C. .CI \ /But'C-Me 4"with time and,R3 R4,C' \ 1,Pd - N:in addition to the original set of signals, two new sets ofresonances of increasing intensity appeared. It was possibleto show by high pressure liquid chromatography experi-ments * that both of the new sets of signals belonged to thesame compound which, presumably, has the same stoicheio-metry, but where the ligands are unsymmetrically bonded tothe metal [structure (lb)]. In fact, while one set of resonancesexhibited downfield shifts comparable to those of the initialcompound (0.07, 1.02, and 0.5-0.6 p.p.m.for the CBu',CMe, and NMe groups respectively), the second set of reson-ances exhibited a much bigger downfield shift for the CBu'group (0.84 p.p.m.) than for the CMe group (0.40 p.p.nt.)therefore indicating that the former radical is now cis topalladium and the ligand is N1-co-ordinated.It is to be noted that neither the initial compound, type (lc),nor species type (1 b) showed the presence of rotational isomerswhich were observed in all complexes of hydrazones havingstructure of type (la).'p9 The explanation is that in complexesof type (la) there is the possibility of having two isomers dif-fering in the mutual orientation of the two ligands [symmetricin one case (syn isomer) and antisymmetric in the other (antiisomer)] because, being both N1-co-ordinated to the metal,they are not free to rotate about the Pd-N1 bonds.This is not*Column, LiChrosorb DTOL 10 pm, 25 x 0.45 em internaldiameter; mobile phase, n-hexane-dichloromethane (90 : 10 v/v) ;flow rate 1.5 cm3 min-'; at room temperature.possible in the complexes having structure type (lb) or (lc)where at least one ligand, being N2-co-ordinated to the metaland hence less sterically demanding, is free to rotate about thePd-N2 axis.The species having structure (1 b) reached a maximumconcentration corresponding to ca.50% of the total substrateafter ca. 5 h at 10°C. For a longer reaction time the metal-lation reaction took place according to the stoicheiometry ofequation (i) and the n.m.r. spectrum showed, in addition3[PdC12(L1)2] *[(PdCl(L' - H)}2] + [PdCl4Iz- + 2[HL1]+ 3- 2L' (i)to the previous resonances, those of the cyclopalladated com-plex [{~d[CHZC(=NNMe2)But]C1)Z1 and of partially proton-ated ligand. It is to be noted that the equilibrium between thesymmetrically bonded (lc) and unsymmetrically bonded[PdC12(L1)2] complexes (1 b) was maintained until the metal-lation reaction was complete.An experiment was performed in which trans-[PdClZ-(NCPh),] and L1 (mol ratio 1 : 2) were mixed in deuteriodi-chloromethane at 10 "C and the n.m.r.spectrum recordedimmediately. In this case, also, the first species to be formedwas (lc), which then isomerized partially to (lb), and for alonger reaction time gave rise to the formation of cyclo-palladated species. This experiment showed conclusively thatL1 co-ordinates first through the aminic nitrogen, NZ, andsubsequently part of it isomerizes to the "-bonded species.Moreover, only the hydrazone co-ordinated through theaminic nitrogen could undergo the metallation reaction whichoccurred exclusively on the CMe group.By reaction of tr~ns-[PdCl,(NCMe)~] with the stoicheio-metric amount of L1, in benzene at 5 "C, the expected 1 : 1adduct [(PdC1zL1)2] was obtained.The n.m.r. spectrumshowed three unresolved resonances centred at S 1.10, 3.30,and 2.78 p.p.m. of relative intensity 3 : 1 : 2. The downfieldshifts, with respect to those of the free ligand, were 0.04, 1.42,and 0.43 p.p.m. for CBu', CMe, and NMe protons respectivelyand were indicative of NZ co-ordination of the ligands[structure (2c)l. Tn addition to the above resonances a furtherset of signals, of weaker intensity, at 6 2.01, 2.32, and 2.81p.p.m. were observed which could be assigned to a "-bondedhydrazone (downfield shifts, with respect to the free ligand,were 0.95, 0.44, and 0.46 p.p.m. for CBu', CMe, and NMeprotons respectively). Performing the reaction between trans-[PdC12(NCMe)2] and L1 (ratio 1 : 1) directly in the n.m.r.sample tube and monitoring the spectrum immediately weobserved that the set of signals belonging to the "-bondedligand was initially weaker and increased with time reaching amaximum value corresponding to ca.20% of the total.Therefore in the dimeric 1 : 1 species [(PdClzL')2] also, theligand co-ordinates initially through the aminic nitrogen, N2,giving rise to structure (2c) and subsequently part of itisomerizes giving rise to structure (2b). It is to be noted that,owing to the dimeric nature of this adduct which brings thetwo hydrazones much farther apart than in the monomeric 2 : 1adduct, the resonances of the N2-bonded hydrazones in bothcomplexes (2c) and (2b) overlap and this could be one reasonfor the broadening of the corresponding signals.Anotheradditional cause could be the presence of geometrical isomerssuch as cis- and tran~-[(PdCl~L~)~].The dimeric 1 : 1 adduct (as with the monomeric 2 : 1complex) in solution undergoes a metallation reactionaccording to the stoicheiometry of equation (ii), giving2[(PdC1zL1)2] +[{PdCl(L1 - H)M + [Pd2C16l2- + 2[HL1]+ (ii1486 J. CHEM. SOC. DALTON TRANS. 1983But"1 4 Me-Crise to the formation of the cyclopalladated complex[{Pd[CH2C(=NNMe2)But]C1}2]. Therefore in this case alsoonly the N2-bonded hydrazone is capable of undergoinga metallation reaction on the CMe group.The metallation reaction which occurs spontaneously inboth the 2 : 1 and 1 : 1 adducts can be accelerated by theaddition of a base (Na02CMe); it can also be performed bydirect mixing of Na2[PdC14], L1, and Na02CMe in methanol asdescribed by Shaw and co-workers? In all cases the cyclo-palladation occurs on the CMe group giving rise to structureI - - l(3a).R3 R4R3 R4There is another report in the literature in which, becauseof steric interaction between the ligand substituents and thesix-co-ordinate metal core, the hydrazones have adopted theN2 co-ordination, i.e.in [Ru(M~~C=N~N~H~)~(P(OM~)~}.&[BPhr]2.'4 In the present case, however, the complexes arefour-co-ordinate and the shift from N' to N2 co-ordinationmust be caused exclusively by the steric hindrance of the Butgroup; in fact it is sufficient to substitute the But group withthe slightly smaller Pr' radical to revert back to N' co-ordin-ation.To investigate how strong this effect is, it would benecessary to reduce the basicity, and hence the co-ordinationability, of N2 and see how this affects the co-ordination modeof the hydrazone; we therefore decided to investigate thereactivity of the methylphenylhydrazone of pinacolone, But-MeGNNMePh (L'), towards palladium.Performing the reaction between tvans-[PdC12(NCPh)2]and L2, even in the presence of a very large excess of theligand, we were unable to isolate the 2 : 1 adduct but, instead,we always obtained the dimeric 1 : 1 complex [(PdC12L2)2].The n.m.r. spectrum of this compound was characterizedby resonances in the ranges S 1.9-2.3 and 3.4-3.8 of relativeintensity 4 : 1.Since no bands were observed at 6 lower than1.9 p.p.m., it was clear that the resonances of the But protonshad been shifted to lower field (with respect to those of thefree ligand) by no less than 0.7 p.p.m. This result is indicativeof a cis position of the But group with respect to palladiumand hence of a N' co-ordination of the hydrazone; as a conse-quence, the CMe group, trans to palladium, should not sufferits deshielding effect and resonate at a field not far from thatof the free ligand. Therefore we can confidently assign theresonances in the range S 1.9-2.3 to the CBu' and CMeprotons and those in the range 6 3.4-3.8 to the NMe protons.The reason why we observed several resonances, instead ofone or two lines, for each type of equivalent protons, can beascribed to different causes: (i) the presence of rotationalisomers which were always observed in bis-hydrazone com-plexes, even dimers, having both Iigands Nko-ordinated tothe metal; (ii) the presence of geometrical isomers such as cis-and tran~-[(PdCl~L~)~].Therefore the presence of a phenyl group on N2 has loweredthe basicity, and hence the co-ordination ability of this atom,to such an extent that N' has become the preferred co-ordin-ation site of L2 in spite of the serious steric interaction whichis built up between the But group and the metal core.More-over, only the l : l adduct is obtained in this case probablybecause of the dimeric nature of this complex which allows thetwo hydrazones to be farther apart one from the other andthe cis chlorines to be slightly bent outwards from the organicligands.12The complex [(PdC12L2)2] in solution (either benzene ordichloromethane) slowly decomposes to give a black solid,which is insoluble in most common solvents and has not beenidentified, and leaving in solution, in addition to the originalsubstrate, a small amount of the cyclopalladated species[{P~[CH,C(=NNM~P~)BU']CI)~] in which the hydrazone isco-ordinated through N2 and metallation has occurred on theCMe group [structure (3a)l.The metallation reaction occurs much more readily inmethanol in the presence of a base (Na02CMe).Under thesecircumstances, however, a change in regioselectivity is observedand the new cyclopalladated complex which is formed,I I[{Pd[CH2C(CH3)2C(=NNMePh)Me]C1}2], has the hydrazoneN'-co-ordinated to the metal and metallation has occurred onthe But group [structure (3b)l.The same product is obtainedif the reaction is carried out under the conditions of Shaw andco-workersS (i.e. from [PdC14], L2, and Na02CMe in meth-anol). The structures of the two stereoisomers (3a) and (3b),which were initially assigned on the basis of n.m.r. data insolution (see Table), have been confirmed by preliminary X-ray data.The peculiar behaviour of [(PdC12L2)2] which gives dif-ferent cyclopalIadated species under different experimentalconditions can be tentatively explained on the basis that themetallation on the CMe group, for a N2-co-ordinated hydra-zone, occurs much more readily than that on the But group,for a N'-co-ordinated ligand. Therefore although the [(PdC12-L2)J complex has the hydrazone ligands N'-co-ordinated tothe metal, we cannot exclude that an undetectable part of it isNz-bonded to palladium and that, in a very inert solvent suchas benzene or dichloromethane and in the absence of a base,this is capable of undergoing metallation reaction.In contrast,in a different solvent such as methanol and in the presence of abase, the bulk of the ligand, N1-co-ordinated to palladium,undergoes metallation reaction on the But group. This hypoJ . CHEM. SOC. DALTON TRANS. 1983 1487thesis is supported by the observation that in the complexeswith L1, although both types of co-ordination were present(through N' and N2), only the N2-bonded hydrazone gavecyclopalladation on the Me group.Also in accord with thishypothesis, the downfield shifts of the Me and But groups (ofN2- and N'-co-ordinated hydrazones respectively) were biggerfor the former than for the latter group.In conclusion we can confirm that the hydrazones co-ordinate to palladium preferentially through the iminicnitrogen (N') and that only in extreme cases [i.e. when N1is shielded by a very bulky group such as But and the aminicnitrogen (N2) is activated by two methyl substituents] canco-ordination occur through N2. Moreover, the different regio-specific metallation observed in normal conditions for L' andL2 originates from a different co-ordination mode, the formerco-ordinates preferentially through N2 and metallates on theMe group, the second co-ordinates preferentially through N1and metallates on the But group.We can recall at this pointthat the metallation on But observed in the reaction of theoxime of pinacolone (Bu'MeGNOH) with palladium andinvestigated by Shaw and co-workersS stems from the Nco-ordination of this ligand which brings the But group cisto the metal. Finally, it appears that metallation on the Megroup of a N2-bonded hydrazone occurs more readily thanthat on the But group of a "-bonded ligand.AcknowledgementsThe authors are grateful to Consiglio Nazionale delleRicerche (C.N.R.), Roma, for financial support.References1 B. N. Cockburn, D. V. Howe, T. Keating, B. F. G. Johnson,and J. Lewis, J. Chem. SOC., Dalton Trans., 1973, 404.2 P. Braunstein, J. Dehand, and M. Pfeffer, Inorg. Nucl. Chem.Lett., 1974, 10, 521.3 G. Bombieri, L. Caglioti, L. Cattalini, E. Forsellini, F. Gaspar-rini, R. Graziani, and P. A. Vigato, Chem. Commun., 1971,1415.4 L. Maresca, G. Natile, L. Cattalini, and F. Gasparrini, J.Chem. SOC., Dalton Trans., 1975, 1 6 0 1 .5 A. G. Constable, W. S. McDonald, L. C. Sawkins, and B. L.Shaw, J. Chem. SOC., Chem. Commun., 1978,1061 ; J . Chem. SOC.,Dalton Trans., 1980, 1992.6 G. Natile, L. Cattalini, and F. Gasparrini, J. Chem. SOC.,Chem. Commun., 1977,89.7 G. Natile, F. Gasparrini, D. Misiti, and G. Perego, J. Chem.SOC., Dalton Trans., 1977, 1747.8 G. Natile, L. Cattalini, F. Gasparrini, and L. Caglioti, J. Am.Chem. SOC., 1979,101,498.9 G. Natile, L. Cattalini, F. Gasparrini, L. Caglioti, B. Galli,and D. Misiti, J. Chem. Soc., Dalton Trans., 1979, 1262.10 E. Enders, in ' Die Methoden der Organischen Chemie,' 4thedn., Thiene Verlag, Stuttgart, 1976, vol. 12, p. 171.11 M. S. Kharasch, R. C. Seyler, and F. F. Mayo, J. Am. Chem.SOC., 1938, 60, 882.12 M. Biagini Cingi, G. Natile, A. Tiripicchio, and F. Gasparrini,J. Chem. Res., 1979, ( S ) 98, ( M ) 1319.13 G. J. Karabatsos, R. A. Taller, and F. M. Vane, TetrahedronLett., 1964, 18, 1081.14 W. J. Nolte and E. Singleton, J. Chem. SOC., Dalton Trans.,1974,2406.Received 21st July 1982; Paper 2/124
ISSN:1477-9226
DOI:10.1039/DT9830001483
出版商:RSC
年代:1983
数据来源: RSC
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