摘要:

J. CHEM. SOC. DALTON TRANS. 1982 1715Reactions of Palladium(ii) Ally1 Dimers with Palladium(ii) Complexescontaining -Bonded I ,2-Bis(imino)alkyl Groups. Crystal and MolecularStructure of the Zwitterionic Binuclear Compound [Pd(+2-MeC3H,)-(R1N=C(PdC12L)-CMe=NR2}] (L = PPh3, R1 = R2 = C,H,OMe-p)tBy Bruno Crociani and Roberta Bertani, lstituto di Chimica Generale, Via Archirafi 26, University of Palermo,ItalyTristano Boschi, lstituto di Chimica, Facolta di Ingegneria, University of Rome, ItalyGiuliano Bandoli, lstituto di Chimica e Tecnologia dei Radioelementi C.N.R., Area di Ricerca, Padova, ItalyThe 1,2-bis(iniino)alkylpalladium derivatives (A), R1N-CL’-CRJ-NR2 [ R l = R2 = C,H,OMe-p, R3 = Me, L‘ =trans-PdCIL, (L = para-substituted triarylphosphine or AsPh3) ; R1 = R2 = C,H,OMe-p, R3 = H or Ph, L‘ = trans-PdCI(PPh,),; R 1 = C6H,0Me-p, R2 = R3 = Me, L’ = frans-PdCI(PPh,),] reactwith [(PdC1(-q3-2-R4C3H4)}2] (R4 =H or Me) in the presence of NaC104 to yield the cationic binuclear complexes (B), [Pd(q3-2-R4C3H4)(R1N=CL’-CR3=NR2)] [CIO,], where the 1,2-bis(irnino)alkyl group acts as GO‘-”’ chelating ligand.In the absence ofNaCIO,, the reaction leads initially to the formation of the ionic compounds (C), [Pd(q3-2-R4C3H4) (R1 N=CL’-CR3=NR2)] [PdCI2(-q3-2-R4C3H4)], which in a subsequent slower stage reacts further with exchange of ancillaryligands between the cationic and anionic species, to give the zwitterionic binuclear complexes (D), [Pd(-q3-2-R4C3H4)(R1 N=CL“-CR3=NR2)] (L” = cis-PdCI,L), and [PdC1(-q3-2-R4C3H4)L]. A complex of type (C)[R1 = R2 = C6H40M$?-p, R3 = R4 = Me, L’ = PdCl(dppe), dppe = 1,2-bis(diphenylphosphino)ethane] can beisolated from the reaction of the corresponding derivative (A) with [fPdCl(q3-2-MeC3H4))21.The rates of ligandexchange depend markedly on the substituents R1, R2, and R3, on the nature of L, and on the solvent. Based onthese effects and on H n.m.r. spectral data, a mechanism is proposed, which essentially involves opening the five-membered 1,2-bis(imino) ring of the cation promoted by interaction with the anionic species in the intermediate(C). The ’H n.m.r. spectra of (D) indicate the presence of diastereoisomers which interconvert more or lessrapidly a t room temperature depending on the substituents R* or R3 and on the ligand L.The crystal and molecularstructure of a typical complex (D) (R’ = R 2 = C6H40Me-p, R3 = R4 = Me, L = PPh3) has been determined byX-ray diffraction analysis. Crystals are Orthorhombic, a = 20.224(5), b = 20.073(8), c = 19.829(9) A, spacegroup Pbca, and Z = 8. The structure has been solved by the heavy-atom method and refined by full-matrixleast squares to R = 0.086 for 1 795 diffractometer data (Mo-K, radiation). The structural data show that the-q3-allyl group is almost symmetrically bound to palladium and its plane forms a dihedral angle of 107.4’ with theplanar five-membered ring. The 1,2-bis(imino)propyI group is oo‘-NN‘ chelated to the Pd(r,3-2-MeC3H4) unitand the mean plane of the cycle makes a dihedral angle of 81.9” with the co-ordination mean plane of the cis-PdCI2(PPh3) group.The major features of the structure are represented by a short Pd-C(imino) bond [1.92(3) A],indicating a relevant x contribution, and by a close approach of the R3 substituent to the metal centre of the cis-PdCI2(PPh3) unit [Pd * * * C(methy1) 3.19 A].Ilu recent years the chemistry of polynuclear compoundshas attracted considerable attention for the inherenttheoretical interest and for the relevant catalytic im-plications. A general synthetic route to polynuclearnon-cluster Compounds involves the co-ordination reac-tion of metal complexes containing potentially ligatingfunctions, such as C-bonded acety1,l methosy(imino)-methyl,2 and pentane-2,4-dione groups or N-bondedpyrazolate * and P-bonded phosphinoyl l i g a n d ~ , ~ seefollowing page.Due to our interest in this field, we havepreviously studied the syntheses and the co-ordinatingabilities 6~ of C-bonded 1,2-bis( imino)alkylpalladium (11)derivatives of type (A) (following page).In general the reactions of (A) with transition metalsubstrates yield binuclear complexes in which the 1,2-bis(imino)alkyl group acts as a aa’-NN’ chelating biden-tate ligand.Only in a few cases, however, are trinuclear complexesobtained, which probably involve a oo’-NN’ bridging co-t p-[ 1 ’, 2’-Bis (p-methoxyphen yli mino) propyl-C1’( Pdl) : N,V’-( Pd2)] - 1,l-dichloro-2-( 1”-3”-~-2’’-methylallyl) -1-triphenyl-phosphinedipalladium.ordination mode of (:I) .7(l In sonie binuclear ~ 0 1 1 1 -pounds, migration of ancillary ligancls between the metalcentres is also observed.7c.dFollowing up this line of research and with 3 particularaim of elucidating the factors which affect the exchangeof ancillary ligands, we have carried out an investig-ation of the reactions of (A) with palladium(1r) ally1dimers, the results of which are reported herein.RESULTS AND DISCLTSSIONThe reactions of various 1,2-bis(irnino)alkyl~~alladiuni-(11) derivatives with [fPdC1(-q3-2-R4C,H4)),] (R4 = H orMe) are reported in Schemes 1 and 2.When an excess ofNaClO, is present, reactions (1) and (3) lead to the forin-ation of intensely coloured (from deep yellow to red-orange) cationic binuclear complexes (B) and (28), whichbehave as mono-monovalent electrolytes in MeOHsolutions (Table 1).The presence of an unco-ordinatedperchlorate anion in the solid is confirmed by the occur-rence of a strong broad band at ca. 1090 cm-l [v(Cl-0)]and a sharp strong absorption at ca. 625 cm-l [S(Cl-O)].Reaction (1) (Scheme 1) with compounds (5) or (6) yield1716 J. CHEM. SOC. DALTON TRANS. 1982cationic complexes of type (B) , contaminated by a certainamount of the products of types (D) and (E) of reaction(2). In the preparation of compound (14), the formationof the latter impurities can be minimized when thereaction mixture is worked-up as quick as possible (seealdehyde-N-methylimine) .g This is probably related tothe presence of stronger Pd-N bonds in the binuclearcationic compounds (9)-(17) and (28), with a conse-quently higher activation energy for the formation of amonodentate N-ligand intermediate involved in theExperimental section).The aa'-NN' chelation of the 1,2-bis(imino)alkyl group, indicated by the electronic and lH In the absence of NaClO,,n.m.r. spectra, affects the characteristic i.r. bands, [(PdC1(q3-2-R4C3H,)),] followsabove dynamic processes.HMe OMev(C=N) and v(Pd-CI), of the free ligands (A) in the sameway as previously observed"97 for other types of bi-nuclear complexes. In particular, the high-f requencyshift of v(PdX1) in (B) is due to the reduced trans-influence of the a-bonded organic moiety of (A) upon co-ordination, as can be inferred from the shortening of thePd-C1 bond distance of compound (1) in its adducts withCuC1, [(l) 2.41; CuCl,*(l) 2.36 A].6b37b On the otherhand, the v(Pd-C1) band in compound (27) (294 or 283crn-l),'a in which the chloride ligand is trans to a phos-phorus atom of the chelating group dppe [dppe = 1,2-bis(diphenylphosphino)ethanej, is essentially unaffectedby co-ordination [v(Pd-C1) = 297 or 285 cm-l in (as)].R LIThe lH n.m.r.spectra (Table 2) show that the allylgroups of (B) are q3-bound to the palladium centre whichis linked to the imino-nitrogen atoms and do not undergoany dynamic process at an appreciable rate in CD,CI, orCDC& solutions at 35 "C. This result is in contrast withthe fast syn-syn,anti-anti exchange of the allyl protons inthe cationic mononuclear complexes, [Pd(q3-2-RC3H,)Yj +(R = H or Me; Y = $-MeOC,H,N=CH-CMe=NC,H,-OMe-9): containing an asymmetric 1,2-bis(imino) ligand,and with the fast exchange of the non-equivalent terminalallyl carbons observed a t 23 "C for CD,Cl, solutionsof [Pd(qS-C3HS) (aqa)] + (aqa = 8-alkylquinoline-2-carb-iithe reaction of (A) witha quite different course,R 2/p=o\P=OMR2which eventually leads to the formation of the binuclearzwitterionic complexes (D) and the well known deriv-atives (E) [reaction (2)].Upon mixing of the reactants(1 : 1 molar ratio), the ionic intermediates (C) areimmediately and quantitatively formed, as indicated bythe electronic spectra in methanol, characterized by theintense metal-to-ligand charge-transfer (m.1.c.t.) bands ofthe cationic complexes (B), and by the lH n.m.r.spectrain CDCl,, which exhibit the typical signals of (B) and theanionic compounds [PdC1,(q3-2-R4C3H4)] -. The onlyrelevant difference occurs in the dynamic behaviour(syn-anti exchange) of the allyl group of the cationicspecies. The same spectral features are observed whenthe independently prepared complexes (B) and [AsPh,]-[PdCl,(q3-2-R4C3H4)] are mixed together in a 1 : 1 molarratio, under comparable experimental conditions. Atypical lH n.m.r. spectrum of the initial reaction mix-tures ( 1)-[(PdC1(q3-C,H5)},], or (10)-[AsPh,][PdC1,(q3-C,H5)], is reported in Figure 1. The signals H,, Hs, andHa are due to the q3-C3H5 group of the anion and com-pare well with those of the complex [AsPh4][PdCb(q3-C,H,)] {6(H,) = 5.5-5.0 (central proton); 6(H,) = 3.93[syrc protons, 3J(Hc-Hs) = 7.31; and S(HJ = 2.85p.p.m.[anti protons, 3J(H0-HB) = 12.3 Hz]}. The synand anti protons of the allyl groups of the cationicderivative (10) undergo a rather fast exchange, indicatedby their appearance as a doublet H' a t 3.14 p.p.m.[3J(Hc'-H') = 9.9 Hz], with a corresponding quintet H,'at 5.70 p.p.m. for the central allylic proton. The samedynamic process is also apparent from the lH n.m.r.spectra of the equimolar mixtures (A)-[(pdCl(~~-2-R4C3H4)},] (or (B)-[ AsPh,] [ PdC1,(q3-2-R4C3H,)]}, if thesubsequent ligand exchange reaction leading to (D)and (E) is sufficiently slow. For the initial mixture(1)-[{ PdCl(q3-2-MeC,H4),I (or (9)-[AsPh4] [PdCl,(q3-2-MeC,H,)]) in CDC1, at 35 "C, the syn and arcti protonsignals of the cationic species coalesce into a rather broadsinglet at 2.93 p.p.m., whereas those of the anion occur assharp singlets at 3.74 (syn) and 2.73 (anti), with the allylmethyl resonance at 2.02 p.p.m.{In [AsPh,][PdCI,(q3-2J. CHEM. soc. DALTON TRANS. 1982 1717R2I/ L N* ,C-R3C L - Pd - C,/ "A1L i ( i i 1L( B )( iii 1 1CL CH2\ Pi >C-R4C( CH2L( 2 )R 4M eHM eMeMeMeMeMeMeHSCHEME 1 (i) [[PdC1(q3-2-R4C3H,))J, NaClO, (excess) ; (ii) [/PdCl(q3-2-R4C3H,))J ; (iii) [AsPh J [PdCl8(qJ-2-R4C,H,)1718 J. CHEM. SOC. DALTON TRANS. 1982R(27)R = C6H40Me-p, L-L = dppe( i i )d1 I I I 16 5 4 3 28/p.p. m.FIGURE 1 Proton n.1n.r. spectrum in CDCl, a t 36 “C of the system (1)-[(PdCl(y3-C3H,))?1, or (10)- [AsPh,]lPdC1,(?3-C,H,)I, ( 1 : 1 molarratio) after 10 min from mixinJ.CHEM. SOC. DALTON TRANS. 1982 1719MeC3H,)] the corresponding signals are at 3.70,2.69, and ligands in the intermediates (C) of reaction (2). No1.99 p.p.m., respectively.} The characteristic 6(0-Me) exchange of ligands was observed in the reaction of (27)and G(C-Me) resonances of the co-ordinated 1,2-bis- with an equimolar amount of [(RhCl(cod)},] (cod =(imino)propyl group appear at 3.84, 3.74, and 2.38 cyclo-octa-l,5-diene).7~ The formulation of (29) isp.p.m., respectively, in good agreement with the corres- based on elemental analysis, conductivity, and spectralTABLE 1Analytical, physical, conductivity, and characteristic i.r. dataAnalysis * (yo)M.p." A -Compd.(O,/%) C186189-192170160-1 64164163193176167159164-166178179163180179187-189183- 186164171179-18114616016665.4(65.16)68.4(68.65)62.9(62.80)60.6(61.46)66.6(66.66)66.8(66.30)48.3(48.36)57.8(68.60)64.2(64.60)66.2(66.3)68.4(68.60)64.9(64.85)64.0(54.46)62.5(62.15)52.8(63.10)62.4(62.65)47.1(47.60)63.9(64.66)61.7(6 1.86)49.8(60.66)62.3(62.66)66.7(66.96)49.8(60.16)60.2(60.40)H3.6(3.60)6.9(5.76)6.4(6.25)4.6(4.66)4.7(4.60)4.6(4.40)3.6(3.40)6.0(6.16)4.6(4.80)4.3(4.40)4.4(4.45)4.4(4.60)4.3(4.40)4.34.5(4.46)4.2(4.30)3.8(3.70)4.8(4.90)4.6(4.66)4.2(4.26)4.4(4.30)4.3(4.40)4.4(4.46)4.6(4.65)(4.45)N2.4(2.45)2.6(2.70)2.5(2.60)2.6(2.70)2.2(2.30)2.3(2.36)2.02.1(2.16)1.92.3(2.35)2.12.5(2.60)2.6(2.65)2.6(2.60)3.1(3.16)3.2(3.26)2.8(2.86)3.0(3.06)2.7(2.90)2.9(3.00)3.2(3.26)2.8(2.96)3.4(3.66)2.3(2.30)(2.0)(2.00)(2.20)c121.7(2 1.50)3.6(3.46)3.2(3.15)3.6(3.40)6 .O(6.86)6.9(6.96)19.8(20.06)5.6(6.60)6.1(5.10)6.1(6.95)6.7(6.60)6.6(6.36)6.6(6.46)6.6(6.85)8.0(8.06)8.2(8.16)18.1(18.0)7.6(7.66)7.3(7.30)7.6(7.66)8.2(8.16)7.6(7.60)9.1(8.96)8.6(8.75)A (Q-1cm2mol-I)81.181.174.179.876.684.975.485.181.481.443.942.661.646.70.1 f0.2 f31.639.747.644.161.10.16M b,d1198(1 164.4)1016(1 031.9)1118(1 127.9)1 040(1 036.6)869(882.4)886(868.4)946(924.6)964(926.3)893(868.4)926792(944.4)(790.3)1.r. absorption (cm-l) - A rv(C=N) 01 620ms, 1 664ms1 624s, 1 662s1620ms, 1666s1620s, 1 660ms1580m, 1610 (sh)1680m, 1610 (sh)1 560m1680 (sh)1668m1562m1678m1676m, 1610 (sh)1676m, 1610 (sh)1581m1680m, 1516 (sh)1 680m1666m1680m, 1620 (sh)1 666m1680m, 1610 (sh)1 660m1676m1676mw, 1620 (sh)1681mv( Pd-Cl)270m265m265m274m309m308m312m3 16ms310m306mw302m300m302m297m or 286m297ms, 280ms300m, 280m300m, 284m296s, 280 (sh)294ms, 277ms291s, 280 (sh)298ms, 276ms294ms, 272ms298ms, 273ms298m, 270m,266 (sh)4 Uncorrected values, all compounds decompose on melting.6 Calculated values are given in parentheses. C Molar conductivitiesof 10-8 mol dm-a MeOH solutions, 293 K. 8 The assignmentof the Y(C=N) band of the binuclear complexes is tentative because of the occurrence of strong absorptions of the para-substitutedphenyl groups around 1 600 and 1 600 cm-l.* Molecular weight determinations by osmometry in 1,2-dichloroethane.f Molar conductivities of loms mol dm-8 1.2-dichloroethane solutions, 293 K.ponding chemical shift values of compound (9) (Table 2).The intermediacy of the ionic compounds (C) in reaction(2) is further supported by the isolation of product (29)from reaction (4) (Scheme 2).This can be easilyachieved because the exchange of ancillary ligandsbetween the cation containing a chelating dppe ligandand the anion of (29), if it occurs, proceeds at a consider-ably much slower rate than the exchange of monodentatemeasurements. The i.r. spectrum in the solid shows twointense v(Pd-Cl) bands of the anionic species at 270 and255 cm-l, which partly overlap with the v(Pd-Cl) absorp-tion of the cation. The electronic spectrum in MeOH at25 "C is characterized by strong m.1.c.t. bands with amaximum at 25 900 (e = 4 900 dm3 mol-l crn-l) andshoulders at 22 500 and 20 900 cm-l, and matches verywell with the spectrum of (28) in the same solvent. Th1720 J. CHEM. SOC. DALTON TRANS.1982lH n.m.r. spectrum in CDCI, confirms the presence ofboth the cationic and anionic species. Also in this case,the sy9z and anti allyl protons of the binuclear cation arerapidly exchanging so as to give rise to a slightly broadsinglet a t 2.92 p.p.m., whereas the q3-2-MeC,H4 system ofthe anion remains essentially unchanged. The dynamiclxhviour of the allyl groups of the cation in the inter-mediates (C), as well as in compound (29), may be reason-ably accounted for by an interaction with the anion,[PdCl,(q3-2-R4C,H,)1 --, probably through bridgingchlorides, wherebv n short lived cr-ally1 is formed lo (seebelow).R4 1This is also supported by tlic fact that the staticq3-allyl group of the binuclear cationic complex (28) ispromptly turned into a dynamic system, identical to thatof (29), upon addition of C1- ions (see Table 2).Thecation-anion interaction in (C) and in (29) does notinvolve exchange of tlie Pd(2-R4C,H4) unit between thetwo allyl species at a significant rate on the n.m.r. timc-scale, at variance with the behaviour of the systemsY-[{PdCl(q3-2-MeC3H4)},1 and [Pd( q3-2-hIeC3H,) Y ] -[C104]--rAsPh4] [PdC1,(q3-2-hfeC3H,)], where Y is ana-di-imine ligand of the type RN=CH-CH=NR (R =Rut or C,H40hfe-+) or RN=CMe-CMe-NR (R = C,H4-0Ale-p) * [sce reaction (h)]. In this case, the IH n.m.r.conductivity is observed, which probably arises fromionic dissociation of the Pd-Cl bonds weakened by thetram-influence of L and of the a-bonded I ,2-bis(imino)-alkyl group, and by the presence of a formal negativecharge on the palladium atom.The formulation of (D),suggested by spectral data, was confirmed by an S-raystructural analysis of complex (18), which will bediscussed later on.The i.r. spectra in the metal-chloride stretchingfrequencies region show two v(Pd-Cl) bands in the ranges300-291 and the 284-272 cm-l respectively, due to themutually cis chloride ligands of the unit PdC1,L. Thesame spectral feature was observed for the related deriv-atives (see below) [R = C,H,Ohfe-p; MX, = Rh(CO),,R h ( ~ o d ) , ~ " Pd(S,C,NMe,) and Pt(S,C,NMe,),'c andPd(pd) and Cu(pd) (pd = pentane-2,4-dionate) 11] antlappears to be diagnostic for this class of zwitterioriicbinuclear complexes containing the cis-PtlC1,L group.The course of reaction (2) can be monitored either byIH n.m.r. or by visible electronic spectra.The formationof the products (D) and (1.3) in a I : 1 molar ratio is clearlyindicated by the integration of the lH n.m.r. spectra ofthe mixtures when reaction (2) is completed. The ratesare markedly influenced by the nature of the solvent inthe order: benzene > chlorinated solvents (CH,C12,CHCl,, 1,2-dichloroet11ane) >> alcohols (RfeOH, EtOH) ;Y -1- [(PdCl(q3--2-hfeC,H4)],] 1' (~PdCI(~3-2-hIeC,H4)],Y)tJ i t [Pd(q3-2-MeC3H4)Y] + [PdCI,( q3-2-MeC3H4)] -spectra showed a fast scrambling of the Pd(q3-2-MeC,H4)group among the different allyl complexes, but gave noevidence of any syn-anti exchange of the allylic protons in~Pd(q3-2-hIeC,H4)Y]+. Such a difference may be relatedto the presence of stronger Pd-N bonds in the binuclearcomplexes (R) (as earlier discussed), which would makethe exchange of tlie Pd(q3-2-R4C,H,) unit between thecation and the anion of (C) energetically less favourablethan the dynamic process involving syi-a?iti exchange inthe allyl cation.Both products (D) and (E) of reaction (2) have beenisolated and characterized.The compounds (1;) areeasily identified by elemental analysis and by comparisonof their i.r. and lH n.m.r. spectra with those of authenticsamples prepared by bridge-splitting reactions of thedimers [(PdC1(q3-2-R4C3H4))2] with L. The zwitterionicbinuclear complexes (D) are monomers in 1,2-dichloro-ethane, where they are essentially non-conducting. InMeOH solution, however, an appreciable electricalby the neutral ligand L and the R2, R3 substituents inthe order: L = AsPh, > P(C,H,Cl-+), > PPh, >P(C,H,Me-fi), > P(C,H,OhIe-;h), (when R1 = R2 =C,H,OMe-;h and R3 = Me); R3 = H > Ph Ale (when1, = PPh, and R1 = R2 = C,H,OMe-fi); R2 = C,H,-OhIe-fi 9 hie (when 1, = PPh,, R1 = C,H40Me-p, antlR3 = hie).essentially reflects tlie differentstrength of tlic Pd-1, bonds, the effects of tlie substituentson tlie a-di-imine moiety arc, mainly related to the stabilityof the fivc-incmbcrecl ring of (R) and imply that ilPd-N bond brcaking (i.e.opening of the ring) is involvedin the step (C)+(U) + (E) of rcwiion (2). According tothe reaction mechanism which will be reported in detailin a forthcoming paper,], thc exchange of ligands occurspreferentially 7~ia a trinuclear transition state, arisingfrom the slow opening of the five-niemhered ring of thecationic substrate (R) upon interaction with the anion(see below).An analogous trinuclear transition state (orWhilc the influence oJ. CHEM. SOC. DALTON TRANS. 1982 1721transient) was proposed for the transfer of ancillaryligantls occurring i n tlrc rck:rction of (1) or (8) with[ T i t I(' 1 ( (Y MI)) 2'/ .7tlElectronic S$ectra.-The electronic spectra of thecomplexes (B) and (D) are characterized by a series ofoverlapping bands in the range 20 000-30 000 cni I ,which give rise to a rather broad absorption with amaxiniutn surrounded by one or more shoulders and withmolar absorption coefficients varying from 3 500 to 10 500d1n3 mol-l cni-1 (Figure 2).These bands have essentiallya nietal-to-ligand charge-transfer character (dFd - X*,.di-imine), as indicated by their dependence on thenature of the C- and N-substituents of the 1,2-bis-(imino)alkyl groups and by solvatochromic effect^.^. l4Whereas the neutral ligand L has only a little influenceon the position of the band maxima in both compounds(R) and (D), on passing from the cationic complexes (B)to the zwitterionic derivatives (D) [i.e. replacing thetrans-PdClL, by the cis-PdC1,L group] the m.1.c.t.bands undergo a shift to higher frequency of ca. 1500-2 000 cm-l, as can be seen from the spectra of the pairs(9), (18) and (14), (24) in Figure 2.A high-frequencyshift is also observed; when the R3 substituent ischanged in the order: Pli, H, Me [for example, the imax.of (25), (24), and (18) occur at 24 200, 24 900, and 25 500cm-l, respectively, in 1,2-dichloroethane] ; when theC,H40Me-$ group as R2 substituent is replaced by ainethyl group [5m,,,. of (9) and (16) at 23 500 and 25 700cni-l, respectively, in 1,2-dichloroethane] ; and when thepolarity of solvent is increased [Gmax. of (28), 25 800 in 1,2-dichloroethane and 26 400 cm-l in methanol]. Exceptfor the higher intensity of the m.1.c.t. bands of (14) and(U), due to the presence of a proton as R3 substituent,the spectra of the binuclear complexes in Figure 2 arequite similar to that of the mononuclear compound[ Pd( q3-2-hIeC,H,)Y] ;C104] (Y = $-MeOC,H,N=CMe-CMe=NC,H,Ohfe-fi), which was shown to contain aoo'-ILr-Y' chelating a-di-imine ligand.8 This indicatesthat the same five-membered metallocycle chromophoreis also present in derivatives of type (B) and (D), as wasconfirmed b\.the X-ray structural analysis of (18).pro to^ X.IIZ.Y. S$ectra.-The lH 1i.m.r. spectra of somerepresentative complexes are reported in Table 2. Ingeneral, tlic signals of the C- and N-substituents of the1 ,%bis(iniino)alkyl moieties are shifted downfield onco-ordination. This effect is particularly evident for theOnle-h and/or R3 =- Ph, the aromatic proton signals areR3 group, wlicn R3 = Me, since for R1 = R2 = C6114-partially masked by the intense phenyl resonances of L.In the complexes (A) with R3 = Me, 8(R3) occurs atrather high field, 1.29 -1.01 p.p.m.[the S(R3) values ofcompounds (1), 1.29, and (81, 1.01 p.p.m., are taken fromrefs. 7(a) and S(c)], owing to the through-space shieldingeffect of the phenyl ring current of the two mutuallytrans-L ligands,a whereas in the corresponding cationicderivatives (B) they are detected in the range 2.42-2.36I1.p.m. Such a marked downfield shift can be ascribedin part to a 0-N ligating mode of the imino-nitrogens {inthe mononuclear compound [Pd(q3-2-MeC3H4)Y] + (Y =$-MeOC,H,-N=CMe-CMe=N-C,H,OMe-fi) the 6 (C- Me)signal of the ao'-NN' chelating a-di-imine at 2.33 p.p.m.is only 0.23 p.p.m. to lower field from that of the freeligand8) and, to greater extent, to the change of coii-figuration (tmns+cis) of the 1,2-bis(imino)alkyl unitt tx:: ...XXXXh /nmFIGURE 2 Electronic spectra in 1,2-dichlorocthane at 25 "C ofcomplexes [Pd (q3-2-MeC,H,) (p-MeOC,H4N=CMe-CMe=NC8H4-OMe-p)][C104] (--) ; (9) (- - - -) : ( 1 4) ( a - ,) ; (1 8 )(--.-.-); and (24) ( x x x x )upon chelation, which brings the methyl protons into aposition very close to the palladium centre of the trans-PdClL, group above its co-ordination plane [Pd - .-C(methy1) distances of 3.37 and 3.19 A have been ob-served in CuC12*(1) '6 and (18), respectively]. It iswell established that protons closely approaching d8square planar metal centres above the co-ordinationplane undergo large downfield shifts, resulting from theanisotropy in the magnetic susceptibility of the metal.g*15A further deshielding of the R1, R2, and R3 protons isobserved on going from (B) to (D) (i.e.upon replacementof L by Cl-), which is essentially due to the reduceTABLE 2Proton 1i.in.r. data a1, 2-Bis(iiiiino)alkyl group(24)SolventCD,CI,CDCl,CDCI,CDCI,CDCl,CD,C12CDCI,CDCl,CDCl,CD,Cl,CD,CI,CDCI,CDCI,CDCI,CDCI,CDCI,CDCI,X-C6H4-P-Cl35or P-C,H,-7.7-7.2 (m) [30] 7.2-4.2 (m) [S]7.8-7.0 (m) [17] 6.9-6.7 (m)7.7-7.1 (m) [26] 6.9-5.9 (m)7.7-7.0 (m) [26] 7.0-6.2 (m) [6]7.7-7.0 (m) [14] 7.0-6.5 (m) [6]7.8-6.5 (m) [30] 9 6.4-6.2 (ni) [2] '17.8-6.5 (in) [10]7.8-7.0 (m) j17] 6.9-6.6 (ni) [6]7.8-i.0 (m) [32] 6.9-6.5 (m) [6]7.7-7.1 (m) [17] 7.1-43.8 (m) [GI7.8-6.3 (m) [43]7.9-6.4 (in) I2817.6-i.0 (ni) j l i ] 6.8--6.6 (m) ~ 2 18.0-6.4 (ni)8.0-6.4 (m)OCH,3.76 (s) [3]3.88 (s) [3]3.79 (s) [3]3.89 (s) [3]3.80 (s) [3]3.85 (s) [3]3.81 (s)\ -3.89 (s) [3]3.79 (s)J is]3.81 (s) [3]3.88 (s) ( 3 13.78 (s) [3j3.94 (s) [3]3.89 (s) [3]3.82 (s) 1 3 33.65 (s) 1313.82 (s) (313.84 (s) r:i]3.63 (s) [3]3.79 (s)3.73 (s)5.80 (s)3.76 (s)3.77 (s)3.81 (s)C-R32.42 (s) [3]2.9-6 (s) [3]2.97 (s) [3]1.28 (s) [3] f2.35 (s) [3]2.87 (s) [5] 'I2.40 (s) [3]2.90 (s) [3]2.99 (s) [3]7.80 (s) [l]8.88 (s) [l]ii2.98 ( s ) [3J2 .3 3 (s) d2.30 (s) d2.32 (s)-3.34 (s)CH,2.93 (s, br)2.86 (s) [l]2.76 ( s , br)2.80 (s, br)2.68 (s) [l]2.60 (s) [l]2.69 (s) [l]2.61 (s) [l]2.83 (s) [2]3.14 (sh)l3.01 (s) ill2.91 (s, br)2.92 (sh) 92.80 (s, br)2.69 (s) [l]3.04 (s, br)2.83 (s, br)2.76 (s, br)2.67 (s) [l]2.59 (s, br)2.81 (s, br)2.64 (s) [l]2.37 (s) [l]3.42 (s, br)3.13 (s, br)2.94 (s) [l]2.S6 (s) [l]3.31 (s, br)2.95 (s) [ l2.86 (s) [l]3.22 (s) [l]3.13 (s, br)2.91 (sh)2.94 (s, br)2.93 (s, br)3.30 (br) [ 3.39 (s) [:3J(N-CH,) 2.79 (br))2.63 ( b r )3.2-2.0 (m, br) v 3.1-2.7 '1(P-CH ,-)3.2 - 2.0 (m, br) 2.91 (s, br)(P-CH,-)3.2-2.0 (m, br) 3.70 (s)(P-CH,-) 2 69 (s)3.10 (s) I2.91 (s) [ l2.g.4 (s)l2.49 (s) I2.92 (s, br)a Chemical shift G/p.p.m., spectra recorded at 35 OC unless stated othcrwisc; s = singlet, m = niultiplet, br = broad.Integration valucsOverlapping AA'BB' signals of the C,H,OMe-$ groups (R1 and R2 substituents), the ortho protons of R1 being masked by the intense phenylAt 100 "C in 1,1,2,2-tetrachloroethane, the ally1 group signals occur at 2.82 (s) [?I, 2.70 (s) [ l l , 3.62 (s) [l], G(CH,); and at 1.89 (s) [R], 6(C-are present (see text).Molar ratio (compound) : AsPh,Cl >, 2 0 : 1. f The 6(C-R3) signal of the new complexes (3), (4), and (5) occurs atrespectively. 0 Overlapping signals. .4s-C,H5 + N-C,H,-- protons. j I n CD,CI, at -40 "C,at 3.45 (sh), 3.41 (s), 2.97 (sh), 2.92 (s), 2.85 (s), 2.77 (s), and 2.69 (s), and are partially masked by the G(N-CH,) and G(C-R3) resonancesrespectively.Masked by the P-C,H, -t N-C,H,- signals.The allylic methyl protons are detected as two sharp singlets at 2.06 and 1.92 i3.p.m.Signals of the [PdCl,(~j~-2-MeC,H,)j- anionJ. CHEM. SOC. DALTON TRANS. 1982 1723shielding effect of tlie phenyl ring current of the single J,liganci in the cis-PdC1,L unit,6b and probably also to adifferent charge distribution in the zwitterionic binuclearcomplexes. Such a downfield shift is of cn. 0.5 p.p.m.for R3 = Me and becomes remarkably large (1.08p.p.m.) for R3 = H. The change in chemical shift ofthe R2 protons (when R2 = Me) is illustrated by thcsequence: (8) 3.02,6c (16) 3.10, (26) 3.39 p.p.m.In general, the lH n.m.r. spectra of both types of bi-nuclear complexes (B) and (D) indicate the presence ofq3-allyl groups, characterized by distinct resonances forthe s y i t and anti protons, even though in most cases (for-q3-2-MeC3H4) the assignment proved to be ratherdifficult for the following reasons.(a) The s w and avti protons have chemical shiftsrather close to each other so that overlapping oftenoccurs.0-MeN -MeC- R4C-U3U1 I 14 3 28/p.p.mFIGITRE 3 Proto11 1i.ni.r.spectrum in CDCl, at35 "C of coniplex (16)(b) The asymmetric nature of the 1,2-bis(imino)alkylgroup (when RL = R2 = C,H,Ohfe-$ and R3 = Me) doesnot appreciably affect the two CH, ends of the ~3-2-MeC3H, system. For complexes (B) with a ' rigid'q3-2-MeC3H4 group, one would expect four signals, onefor each allyl proton, which may exhibit a fine structureresulting from coupling between non-equivalent protons(ABCD spectrum). Spectra of this type have beenobserved for compounds (14) and (15), where R3 = H andPh respectively, and also for complexes (16), where R1 =c,H,oMe-$~ and R2 = Me (see Figure 3). A commonfeature of these spectra is represented by the presence oftwo broader bands [at 3.55 and 2.82 p.p.m.for (16)],which upon accurate examination appear as unresolveddoublets and are tentatively assigned to the syn protonson the basis of coupling constant considerations (it isgenerally observed that the more significant coupling inallylic systems is that between the two syn protonsl6).In the analogue (17) the syn, anti assignment results fromthe different coupling constants with the central allylproton rS1p.p.m. (3-]/Hz) in CD2C1,, 3.76 (6.4) and 3.19(6.1) syii protons; 3.07 (13.3) and 2.90 (12.9) antiprotons].CICI--wLII- CI(IIb) IIMirrorplaneS c m m 3 (i) Interchange of diastereoisomers ( I ) (11)either through loss of configuration of the cis-PdC1,L unitor through rotation about the Pd-C bond; (ii) interchange ofdiastereoisoniers (ra) ( I I ~ ) and (Ib) (na) throughdynamic processes of the allyl group (see text)(IIa)(c) Because of restricted rotation about the Pd-C obond of the 1,2-bis(imino)alkyl group in the zwitterioniccomplexes (D), as can be inferred from the structuraldata of (18) on the basis of steric and electronic (relevantx contribution in the Pd-C bond) considerations, fourdiastereoisomers may be present in solution (Scheme 3).Due to the asymmetry of the PdCl(dppe) unit relative totlie co-ordination plane of the chelating or-di-imine,similar diastereoisomers may also occur for complex (28),whereas for derivatives (B), containing the tvans-PdC1L2group, only two enantiomers are possible, which are nottlistinguished by 'H 1i.m.r.spectra. The presence ofImth diastereoisomers (I) and (11) in solution is generallyindicated by the occurrence of two signals for the methylprotons of the 2-MeC3H4 ligand and, in a few cases, bytwo very close 8(C-R3) resonances [S(C-Me) 2.33 and 2.30p.p.m. for (28) in CDCl, at 35 "C; 8(C-H) 8.89 and 8.87p.p.m. for (24) in CD,C12 at -50 "C]. The integration an1724 J. CHEM. SOC. DALTON TRANS. 1982the broadness of the two allylic methyl bands of (18), (20),(22), (BG), and (28) show that isomers (I) and (11) arepresent in ca.1 : 1 ratio and interconvert rather rapidlyon the n.1n.r. time-scale at 35 "C. For complex (18) acoalescence temperature of ca. 70 O C has been observed i nI , I ,2,%tetrachloroetIiane. For the binuclear derivatives(23), (24), or (25), however, the interconversion rate ismuch higher as to give rise to a single 8(C-R4) at 35 "C.At a lower temperature (-50 "C) the allylic methyl sig-nal of (24) at 2.01 p.p.m. splits into two signals of equalintensity at 2.08 and 1.86 p.p.m., with a concomitantsplitting of 6(C-R3). Qualitatively, the rates depend onthe substituent R3 in the order Ph 2: H > Me, and ontlic ancillary ligand I, in the order AsPh, > P(C,H,Cl-$),> PPh,, all other things being equal.In the fastexchange limit, the terminal allylic protons of the 2-RIIeC3H, group appear as three separate resonances(singlets) of relative intensity 2 : 1 : I , the more intense o fwhich being slightly broad. This may be interpretedeither as an A4RCD spectrum with two coincident signalsor as two overlapping AA'BB' spectra. In any case, the( I ) 1' (11) interconversion does not involve any q3 orearrangement of the allyl moiety. In the slow exchangelimit, one would expect two more or less superimposedABCD patterns, one for each I'd(q3-2-hfeC3H4) grouplinked to the asymmetric chelating ligands which are notmirror images. This has been observed for complex (26)(R1 = C,H,OhIe-p, R2 = h k ) in CD2C12 at -40 "C,whereas, for the other derivatives with R1 = It2 =C,H,OMe-fi, the differences in chemical shift are sosmall that large overlapping occurs.The rate of(I) (11) interconversion is very much increased by asmall amount of C1- ions. As discussed earlier, in tliesystem (28)-AsPh,C1 this proceeds via a fast q3 odynamic process of the allyl group so that the syiz anda d i protons, and those of the R3 and R4 groups of thebinuclear cationic complex, coalesce into singlets at 2.91,2.32, and 1.93 p.p.m., respectively. In the mixture (18)-AsPh,Cl, however, a different mechanism is operating,since its spectrum at 35 "C (Table 2) is very similar tothat obtained for (18) in lJ1,2,2-tetrachloroethane at hightemperature. Various mechanisms can be proposed inorder to account for the above spectral observations.Tlie (I) (Ir) interconversion via path (i) of Scheme 3may involve either rotation of tlie chelated 1 ,%his-(imino)alkyl group about the Pd-C CY bond or loss ofconfiguration of the cis-PdCl,I, unit probably tlirough aPtl-C1 bond dissociation equilibrium (see previous clis-cuqsion).The ( I ) (11) interconversion TliQ path (iz)may involve cither rotation of the allyl group around itsbond axis to palladium, or cis-trans isomerization of theasyinmetric I ,2-bis(imino) ligand through cleavage of onePcl-N bond, or a ' flipping ' motion of the allyl ligand.Mechanisms involving complete dissociation of thcPd(q3-2-R4C3H4) unit or simultaneous occurrence of bothpath (i) and (ii) at comparable rate can be ruled out asthey would lead to onc AA'BR' pattern.The catalyticactivity of added C.1 ions may take place either blV path( i ) (attack of C1- on the cis-PdC1,L unit with loss ofconfiguration at the Pd centre) or by path (ii) [cleavageof one Pd-N bond upon attack of C1- on the Pd(q3-2-R4C,H4) unit, followed by cis-trans isonierization] .Crystal a i d Molecular S t r i d w e of ComfiIex (1 8) .- Inorder to establish definitely tlie formulation of thezwit terionic binuclear complexes (D), a single-crystal S-ray diffraction study of a typical representative com-pound, (18), was carried out.A PLUTO drawing l7 of the molecule is shown inFigure 4, which also gives the lalxlling scheme. SelectedFIGURE 4 Projection of complcs ( 1 8) viewed along theiioriiiai to the li\~c-memberetl chclntc ring including Ptl(2)intramolecular distances and angles with their estimatetlstandard deviations are listed in Table 3.The standarddeviations for all the distances and angles between lightatoms are rather high and reflect the low precision of thepositional parameters (see I<xperirnental section), owing tothe disorder at hieOH-H,O positions (in the unit cell thereare four hkOH and four H,O molecules of crystallizationper eight molecules of complex), thc relatively poorquality of the diffraction data, and thc limited nuinbcrof observed reflections. Because of the large uncertain-tics, comparison of lengtlis and angles is restricted to the' inner core ' of tlie complex. Altliough both diastcreo-isomers ( I ) and (11) of complex (18) are observed insolution (sec Scheme 3 and l'ablc Z ) , only the enantiomcrs( I ) precipitate during the crystallization process.Thcgeometry around the Pd( 1 ) atom is approximatelysquare planar and the five-membered chelate ring, in-cluding the Pd(2) atom, shows only very small deviationsfrom planarity. The Pd(2) co-ordination sphere alsoincludes a non-planar 2-methylally1 unit, with C(5J. CHEM. SOC. DALTONSelectcd iiitI-nmoleLularcoinplcs ( 1 8) withparenthesesl’d(I)-Cl( 1)Pd(1)-PPd(1)-C(1)Yd ( 1 )-C1( 2 )Pd (2)-C (4)Pd( 2)-C( 5)Pd (2)-C( 6)Pd(B)-N(l)Pd(2)-N(2)N (l)-C( 1)C( I)-C[?) c (2)-N (2)C(2)-C(3)N(l)-C(8)C( 11)-0( 1)( ) ( 1)-C( 14) s ( 2)-C ( 15}C(4)-C(fi)C ( 4)-c (7)(; (4)-C ( 5 )$ ( 2)-C ( 2 1 )C( 18)-0 ( 2 )1’-C nieaiiTRANS.1982TABLE 3distances (.$) anc~ angles (a) forestiinated standard deviations inC-C(phenp1) niedtiS ( 1) . * * N(2)I’d(1) * * * Pd(2)l’d(2) * . . C(1)C1( 1 )-I’d ( 1 )-C1(2)C1( 2)-Pd( 1)-P1’-Pd( 1)-C( 1)C’( l)-Pd(l)-Cl( 1)(:I( I)-Pd( 1)-PCl(%)-Pd( 1)-C( 1)N ( 1 )-I’d (2)-C( 5)N( I)-Pd(d)-C(4)N( l)-Pd(z)-C(G)N( l)-Pd(2)-N(2)5(2)-Pd(2)-C(4)h (2)-Pd(Z)-C(J)X(d)-Pd(2)-C(B)C( 5)-Pd (2)-C( 6)C( 5)-C(4)-C( 7)C( 4)-Pd( 2)-C( 5)C (4)-Pd (2)-C(6)I’d (2)-C(4)-C( 7)Pd( 2)-C (6)-C( 4)Pd (2)-C( 5)-C(4)C (5)-C(4)-C( 6)C (6)-C( 4)-C( 7)Pd( 2)-N( 1)-C( 1)Pd(Z)-N(l)-C(8)C( 1)-N( 1)-C(8)Pd(Z)-N(2)-C(2)Pd( 2)-N( 2)-C( 15)C (2)-N( 2)-C( 15)N( 1)-C( 1)-Pd( 1)N(1)-C(1)-C(2)Pd(l)-C(l)-C(2)C( 1)-C(2)-N( 2)N (2)-C( 2)-C( 3)C( 11)-0( 1)-C( 14)C( 18)-0(2)-C(2 1)C( 1)-C( 2)-C( 3)pd(ij-c(ij . --.Pd(2)C-C-C(pheny1) mean 120(2j ‘C(pheny1)-P-C(pheny1) iiican 104(2)2.36( 1)1.92(3)2.11(3)1.29(3)1.51 ( 3 )2.:?7( 1)2.26( 1)2.15(3)2.16(3)2.0 7 ( 3 )2.08( 2)1.55(4)1.25(3)1.48(3)1.34(4)1.45(4)1.43(4)1.51 (3)1.36(4)1.39(4)1.82(2)2.50(3)1.48( 3)1.53(4)I.40(3)4.88( 1 )2.08(3)(3 1 . q 3)s 9 . q 3)92( 1)88(1)I75.3( 3)179( 1)143( 1)114( 1)177(1)137( 1)170(1)107(1)37( 1)74(1):19( 1)ti5( 1)116(2)73(1)70(1)1 lO(2)124(3)125(R)124(2)123(2)114(2)118(2)119(2)135(2)106(2)119(2)118(2)118(2)125(2)118(2)169.4(7)123(2)120(2)(0.09 A) above the chelate ring plane and C(4), C(6)(-0.73, -0.02 A, respectively) below it.The plane ofthe allyl group makes an angle of 107.4’ with the Pd(2)co-ordinative plane, so that C(4) is tilted away fromPd(2). These structural features are normal for q3-%1725methylallyl complexes of palladium.18 The Pd( 1) andPd(2) co-ordiiiation plancs arc roughly normal (81 .O”)and C: (1) links tlic two ldancs. The distance Iwtweenthe pal~at~iuiii atoms is 6.88 A, wit11 a PCI(I)-C(I) - -Yd(2) angle of lli9.4”. U’itliin the allyl group the bondlengtlis and angles are similar to those found in theprevious 2-methylallyl palladium structures,*8.19 and tliegcometry of the groups out of the ‘ inner core ’ of thecomplex is normal. ‘I’he two rings of the p-methoxy-plienyl units arc at a dihedral angle of 24.4” and niakeiungles of 53.5 and 71.7” with the chelating ring, in linewith the values observed in tlie adduct Cuc‘l,*(’I’hc allyl moiety is +bonded to ”2) in ail cwentiallys~minictricril manner.?’lie 1,2-bis( i1iiino)propyl groupacts as a oo’-NN‘ cliclating ligand, with Pd(2)-N(sP2)bond lengtlis of 2.07 and 2.08 A, whicli arc rather longerthan tlie predicted value of 2.01 A [based upoii r(Ptlll) =1.31 and r ( N ) = 0.70 A (Pauling radii)].Z* However, tlicdifference (ca. 2o) is not significant and the observeddistances are very close to those reported for otlicrpalladium-imino-nitrogen bon~ls.~9 18c The PPh, liganciand the chelated 1,2-bis(iniino)propyl group have essen-tially the same structural trans-influence, as indicatedby the close Pd(1)-Cl(1) and Pd(1)-Cl(2) distances (2.36and 2.37 A, respectively).The Pd(1)-C(1) length ;1.92(3)A] is considerably shorter than the sum of covalent radiifor a Pd-C(sfi2) bond 2o and the values observed in othercomplexes containing a Pd-C (sP2) ~-boiid.~b.~(l Thismay be ascribed to a relevant x contribution (d - x*Imi,,) whicli would reduce tlie formal negative chargeon the cis-PdCl,(PPli,) metal centre. In tliib structureshort range palladium-hydrogen interact ions arc likelyto occur, as can be inferred froni the Y d ( 1) * * - C (9) (3.25and Pd(1) - * - C(3) (3.19 A) distances above and belowthe mean co-ordination plane. In particular, the inter-action of tlie C(3) methyl protons (which may reach amininium calculated distance of 2.5 A) is reflected in tlicrather low-field chemical shift (2.96 p.p.m.) of this groupin the lH n.m.r.spectrum of (18).This study rules out the alternative formulation ofcomplexes (D) (see below) whicli does not require an)’R*Iseparation of electrical charges arid can be related to thcstructures of other compounds with four-memberedN,C-chelating 1,2-bis( imino)alkyl groups.21v22EXPERIMENTALPhysical Measuvewzents.-lhe molecular weights weredctermincd using a Knauer osmonieter in 1,2-dichloro1726 J. CHEM. SOC. DALTON TRANS. 1982ethane a t 37 "C. Conductivity measurements were carriedout with a Philips PR9500 bridge at 20 "C. Proton n.m.r.spectra were recorded on a Varian EM-390 90 MHz spectro-meter with SiMe, as internal standard.Electronic spectrain solution were recorded with a Bausch-Lomb Spectronic210UV spectrophotometer in the range 650-250 nm a t 25O C , using quartz cells of 1 cin path length. Infrared spectrawere recorded with a Perkin-Elmer 597 instrument, usinghexachlorobutadiene mulls and NaC1 plates in the range4 000-1 300 cm-l, and Nujol mulls and CsI plates in therange 1700-250 cm-'. Microanalyses were performed byA. Rerton and G. Biasioli of the Microanalytical Laboratory,Institu to Radioelementi C . N. K., Padua.Preparation of the 1,2-Uis(iit.l ino)alk.yl~rcllntlzzclrl Deriv-utioes (A), (1)-(8) tcnd (27).--The coniplcscs (I), (6)-(8),and (27) have been prepared by previously describedmethods.sa*sc*6d$ The new compounds ( 2 ) - ( 5 ) , allcon t aining the 1 ,2- bi.j ( p - me t hox y phen y 1 i m in o) prop y 1 group ,have been obtained by the same synthetic procedure as for( l ) , using the appropriate ligand L instead of PPh,.Forcomplex (5) (L = AsPh,), the reaction takes ca. 12 h forcompletion, after addition of AsPh, t o the mixture resultingfrom the initial reaction between cis-[PdCl,(CNC,H,OMe-t)) ,]and HgMe, (molar ratio 21 1 : 1.5, 7 h).Due to the high solubility of (2) in benzene or CH,Cl,,n-hexane was added for precipitation. In all cases, afterelimination of the residual HgMeCl by sublimation, theproducts were conveniently purified by dissolving in theminimum volume of benzene (or CH,Cl,, depending onsolubility) and adding a double volume of ethanol.Themixture was concentrated a t reduced pressure until thecompounds began t o precipitate, and stored a t -20 "C t ocomplete the crystallization. [Yields based on theoreticalamount: (2) 70; (3) 83; (4) 68; ( 5 ) 60%.]Preparation of the Binuclear Cationic Complexes (B),(9)-( 17) and (28).-All these compounds have beenprepared by a general method, which is described in detailfor compound (9). The dimer [{PdC1(qR-2-MeC,H,)),] (0.1 g,0.25 mmol) dissolved in dichloromethane (ca. 40 cmJ) wastreated with (1) (0.48 g, 0.5 mmol) and then with a solutionof NaClO,*H,O (0.140 g, 1 mmol) in methanol ( 5 cniJ). Awhite precipitate of NaCl was immediately formed and thesolution became red-orange.After stirring for 15 min thereaction mixture was evaporated to dryness and the residuetreated with dichloromethane and charcoal. After filtr-ation, the clear solution was concentrated to a small volumea t reduced pressure and the product was precipitated byaddition of diethyl ether. The complex was purified byrecrystallization * from dichloromethane-diethyl ether (0.46g, 76%). High yields (75-907,) were also obtained forthe other cationic compounds. In the reaction with (6), thereactants were initially mixed together a t 0 "C. Afterstirring for 5 min, the mixture was worked-up a t roomtemperature as quick as possible to give a satisfactorilypure product, (14), in 650/, yield.Preparation of the Binucleav Zwittevionic Coniplexes (I)),(1 8)-(26) .-These compounds can be prepared in goodyields from the reactions of the 1,2-bis(imino)alkylpalladiuniderivatives (A) with [{PdC1(qJ-2-R4C,H,)},] ( R4 = H or Me;1 : 1 molar ratio) either in chlorinated solvents (usually 1,2-dichloroethane, but also dichloromethane, and chloroform)* General procedure: compounds were dissolved in the mini-mum volume of chlorinated solvent, the second solvent addeduntil incipient precipitation (stirring), and set aside for 12-24 h.or in benzene a t room temperature.Since the reactionrates are much higher in benzene, the use of this solvent isparticularly convenient for reactions which are exceedinglyslow in 1,2-dichIoroethane. For instance, the reactions of(d), ( t ) ) , and (3) require 8, 4, and 3 d respectively for com-pletion in 1,2-dichloroethane, whereas in benzene the reac-tion times are reduced to 48, 24, and 24 h, respectively.Another advantage of benzene is that the products (D)precipitate on forming.The two general methods will bedescribed in detail for the preparation of compound (1 8).Compound (1) (0.48 g,0 . 5 mmol) dissolved in 1,2-dichloroethane (ca. 40 (:in3) wasreacted with [{ PdCl(q3-2-MeC,H,)},] (0.2 g, 0.5 mmol). After24 11, the reaction mixture was treated with activated char-coal, filtered off, and the resulting orange solution con-centrated to a small volume a t rctluced pressurc. Theproduct (18) was precipitated almost quantitatively byaddition of diethyl ether. Hccausc of the presence of asmall amount of the second product, jl'dCl(q3-2-MeC,H,)-(PPh,)] (indicated by the 'H n.m.r.spectrum), complex (18)was recrystallized twice from the same solvents (0.32 g,72%). The mother-liquor from the first precipitation wasconcentrated to small volume. Upon addition of n-hexane,a yellow precipitate was obtained which was recrystallizedfrom 1,2-dichloroethane-n-hexane to give an analyticallypure sample of [PdC1(q3-2-MeC,H,) (PPh,)] (0.23 g, 50%,based on the theoretical amount) (Found: C, 57.3; H , 4.7;C1, 7.9. C,,H,,ClPPd requires C, 57.55; H, 4.85; C1,7.70). This compound was further identified by comparingits i.r. and IH n.m.r. spectra with those of an authenticsample prepared by the bridge-splitting reaction of [{ I'clCl(q~-2-MeC,H4) ),I with PPh,.The same procedure was used forthe preparation of (19) (reaction time 24 h, yield 757,) ; (20)(8 h, 84%); (23) ( 1 11, 70%) ; (24) ( 2 h, 767,); and ( 2 5 ) (5 h ,68%). In all cases, the second product (E) of reaction ( a ) ,[PdC1(q3-2-R4C,H,)IA], was isolated and identified e.g.,analysis of [PdCl(q3-2-MeC,H4){ P(C,H,Cl-p),}] (Found : C,46.8; H, 3.3; C1, 25.0. C,,H,,Cl,PPcl requires C, 46.95; H,3.40: C1, 25.20). The binuclear complex (18) can also beprepared from the reaction of the cationic compound (9)(0.6 g, 0.5 mmol) with [AsPh,][PdC1,(q3-2-MeC,H,)I (0.31 g,0.5 nimol) in 1,2-dichloroethane (20 mi3). After filtrationof the sparingly soluble salt [AsPh,] [ClO,], the reactionmixture was worked-up as described above.Complex ( 1 ) (0.48 g, 0.5 mtnol)was reacted with [{ PdCl(q3-2-MeC,H,)},] (0.2 g, 0.5 mmol)in benzene (40 cni3).A red-orange solution was initiallyobtained, from which yellow microcrystals of ( 18)*C,H,began to separate after a few minutes. The presence of amolecule of benzene of crystallization was indicated byelemental analysis (Found: C, 56.5; H, 4.8; X, 2.9; C1, 7.4.C4,H4,C1,N,0,PE'tl requires C, 56.25; H, 4.70; N, 2.90; C1,7.40%) and by g.1.c. analysis (gas liquid chromatography) ofa dichloromethane solution. The reaction mixture was setaside for 6 h and then diethyl ether (20 cm3) added in order tocomplete the precipitation. ,lfter filtration, the productwas recrystallized twice from 1,2-dichloroethane-diethylether, whereupon the benzene of crystallization is lost (0.33g, TCio/b).The niother-liquor from the first precipitationwas worked-up in the same way as for the reaction in 1,2-dichloroethane to yield 0.25 g of [PdC1(q3-Z-MeC,H,)-The same procedure was followed for the preparation of(21) (reaction time 24 h, yield 80%); (22) (48 h, 78%); and(26) (24 h, 75%).( a ) Reaction in 1,2-dickloroethalze.(b) Reaction in benzene.(PPh,)IJ. CHEM. SOC. DALTON TRANS. 1982Pvepnvation of the Ionic Cornpound (29).-Complex (27)(0.21 g, 0.25 mmol) was reacted with [{PdCl(q3-2-h4eC3H,)},]( 0 . 1 g, 0.25 mmol) in benzene (ca. 20 cm3). An iiiiniediatechange from yellow to orange occurred. After stirring for10 min, the yellow product (29) began to precipitate. Themixture was set aside (without stirring) for 30 min, and thenthe solid was filtered off and washed with cold benzene (0.16g, 53%).No further purification was required.TABLE 4Atomic co-ordinates ( x lo4) for complex (18), withestimated standard deviations in parenthesesX2 949(1)2 957(1)2 376(5)3 416(4)5 857( 12)4 616(18)3 233(13)2 131(12)2 854(15)2 183(14)1 638(15)3 693(16)2 681(18)3 627(19)3 899( 16)4 029( 16)4 676( 17)5 206(20)6 114( 16)4 451 (16)5 997(21)1 609(16)981 (1 7)421(16)418(18)9:30(15)1502(17)-722(17)2 920( 17)2 389( 17)2 Oll(19)2 163(18)2 694( 18)3 073(20)4 202(17)4 410( 18)5 006( 22)5 394( 18)5 186(21)4 590( 18)3 613( 16)3 080(19)3 190(20)3 833(21)4 366(20)4 256(19)3 830(28)3 054(5)-120(12)3 574(24)3 335(20)Y8 071(1)6 320( 1)8 771(6)8 MO(4)7 374(4)8 090( 13)5 005( 11)4 731(19)4 204(24)U 546(11)7 371(14)6 998(14)7 212(14)5 474( 19)6 057( 17)5 551(17)7 413(16)8 080( 17)7 889(20)7 %18(17)6 941(16)8 79'(23)6 144(16)6 462(16)6 059( 17)5 416(19)5 107(15)5 4821 17)5 310(16)7 824(15)7 647(16)7 037(18)6 614(17)6 708( 19)7 698(17)7 641(18)7 988( 19)8 872(18)8 042(18)6 514(16)6 085(19)5 440(20)6 225( 19)5 653(20)6 298(19)4 484(29)7 109(12)4 913(19)8 351(15)7 553(19)8 329(20)77 487(2)0 196(2)ti 698(6)8 608( 13)9 135(12)975(21)1209(26)8 685( 14)8 136(17)8 181(16)7 710(16)0 734(21)0 938(19)9 868(21)!I 306(22)8 614(17)8 703( 17)8 736(18)8 664( 20)8 598( 17)8 591(17)8 635(22)8 711(17)9 025( 18)9 186(19)8 998(20)8 705( 17)8 531(18)9 431(18)6 006( 17)5 870(20)4 845(21)5 561(22)6 410(20)5 742(22)5 539(2116 005(22)6 674(25)6 876(20)7 107(21)7 345(23)7 371(23)1778(331x 244(5)6 732(5)8 612(1S)3 '90(2l)4 981(22)7 OOl(18)7 477(24)7 133(20)* Occupancy factor: 0.5.S-Ray Cvystullogvaplzy of (18) .-Crystals of compound (18)were grown by very slow evaporation of a solution inMeOH-CH,Cl, ( 3 : 1 v/v). The plates showed a strongtendency to crack and t o twin.Eventually a cubic-shapedcrystal was found which was not cracked or twinned whichwas used for the structural determination [C3,H,,Cl,N20,-* For details see Notices to Authors No.7, J. Chem. SOC.,Dalton Trans., 1981, Index issue.1727PPd,(0.5PvIeOH*0.5H20), orthorhombic, a = 20.224(5),D, = 1.50 g cm-3, p = 10.9 cm-1 for Mo-K, radiation( A 2 0.7107 A), space group Pbca]. The cell parameterswere obtained with a Philips PW 1 100 computer-controlleddiffractometer from 25 strong reflections a t 20 i 28 < 27".Intensities were collected from the crystal of dimensions0.18 x 0.20 x 0.18 mm with graphite monochroinatedMo-K, radiation. An unique data set was collected outof 28 = 36" by the o-scan technique with a scan range of1.4 f 0.3 tan8 and a scan rate of 0.04" s-l; no reflection wassufficiently strong to require the insertion of an attenuatorfilter. The intensities of 3 256 independent reflectionswere measured; of these only 1 795 obeyed the conditionI 3- 3a(l) and were used in subsequent calculations.Theintensities were processed in the usual niaiiner.2d Noextinction or absorption corrections were applied. Thestructure was solved by the heavy-atom method. In theleast-squares refinement the function Cw( lFol - IF,I)? wasminimized, with unit wcight to each reflection.A wcigliting scheme based on counter statistics was un-successful, probably owing to systematic errors. In par-ticular, inspection of Fo/Fc values showed a rather pooragreement aniong weak reflections attributable to an un-sound signal-to-noise ratio of the scintillation counter. Thescattering factors used were those of ref.24. The majorcalculations for the analysis were made with the SHELX 76p-rograni.25 C'alpilatioiis were all perforiiiecl on the Consor-zio lnteruiiiversitario Italia Nord-Orientate C1X 7000coniputcr system. A number of cycles of block-diagonalieast-squares refinement with isotropic tliernial paranieters,follo\ved by difference syntheses, enabled location of all thenon-hydrogen atonis and led to convergence with R = 0.12.;i difference synthesis a t this stage showed evidence ofanisotropy in the motion of the heavy atonis together withthree unexpected peaks of 1.27, 1.16, and 0.98 e A-3. Thesepeaks were attributed to MeOH and H,O from the recrystal-lization mixture and the occupation factors for these siteswere fixed a t 0.5 in the successive refinement procedure.Thermal motions for these atoms are no greater than thoseobserved in the core of the complex.Further full-matrixrefincment, with anisotropic thermal parameters only forthe heavy atoms and with the plieiiyl carbon atoins of thePPh3 group constrained to fit a rigid regular hexagon toachieve a better ' observations-parameters ' ratio, convergedto R = 0.086. A final difference svnthesis sho\vetl maximano greater than 0.58 e'fable 4 shows the final position paranicters of tlic atonis;thermal parameters and thc observed and calculated struc-ture factors are listctl in Supplenientary Publication So.S U P 23207 (14 pp.).*b = 20.073(8), c = 19.829(9) A, U = 8 050 A', Z = 8,[ 1 / 14% Rccciued, 17th SeptetrtLev, 108 13REFERENCESC. M.Lukehart arid G. 1'. Torrence, Iiiorg. Ckcm., 1979, 18,3150; D. T. Hobbs and C M. Lukehart, Znorg. Ckern., 1980, 19,1811, and refs. therein.G. Minghetti, F. Bonati, and G. Banditelli, Inovg. Chem.,1976, 15, 2649.J . Lewis and C. Oldham, J. Chem. SOC. A , 1966, 1466; Y.Nakamura and K. Nakamoto, Inovg. Chem., 1975, 14, 63.4 G. Minghetti, G. Banditelli, and F. Bonati, Chem. Ind.(London), 1977, 123; J. Chem. SOC., Oalton Trans., 1979, 1851.ti R. P. Sperline and D. M. Roundhill, Inorg. Chem., 1977, 16,26121728 J. CHEM. SOC. DALTON TRANS. 1982(I (a) B. Crociani, M. Nicolini, and R. L. Richards, J . Ovgnna-?net. Chem., 1976, 104, 259; ( b ) B. Crociani, G. Bandoli, and D. A.Clemente, ibid., 1980,184, 269; ( c ) B.Crociani and R. L. Richards,ibid., 1978, 154, 65; ( d ) P. L. Sandrini, A. Mantovani, and B.Crociani, ibid., 1980, 185, C13.( a ) B. Crociani, M. Nicolini, and R. L. Richards, J . Chem.Soc., Dalton Trans., 1978, 1478; ( b ) B. Crociani, G. Bandoli, antl1). A. Clemente, J . Organornet. Chem., 1980, 190, C97; (c) 13.Crociani, M. Nicolini, and A. Mantovani, ibid., 1979, 177, 365;( d ) B. Crociani, U. Belluco, and P. L. Sandrini, ibid., 1979, 177,385. * B. Crociani, T. Boschi, and P. Uguagliati, Inorg. Cham. ,4cta,1981, 48, 9.A. J. Deeming, I. A. Rothwell, M. R. Hursthouse, and K. M.Rbdul Malik, J . Chem. Soc., Dalton Trans., 1979, 1899.lo K. Vrieze, in ‘ Dynamic Nuclear Magnetic ResonanccSpectroscopy,’ eds. L. B I . Jackman and F. A. Cotton, AcademicPress, New York, 1975, p. 441.l2 P. L. Sandrini, A. Mantovani, P. Uguagliati, and B. Crociani,Inorg. Chim. Acta, 1981, 51, 71.l3 B. Crociani, P. Uguagliati, R. Bertani, and L. Calligaro,Inorg. Chirn. Acta, 1980, 45, L75; B. Crociani, P. Uguagliati, U.Belluco, and M. Nicolini, unpublished data.l4 H. tom Dieck and I. W. Renk, Chem. Ber., 1971, 104, 110;H. tom Dieck, K. D. Franz, and F. Hohmann, ibid., 1975, 108,163; R. W. Balk, D. J. Stufkens, and A. Oskam, Inorg. Chim.r3cta, 1978, 28, 133; L. H. Staal, D. J . Stufkens, and A. Oskam,ibid., 1978, 26, 255.l6 H. van der Poel, G. van Koten, K. Vrieze, M. Kokkes, andB. Crociani, unpublished data.C. H. Starn, Inovg. Chim. A&, 1980, 39, 197, and refs.therein.l6 I. 1). Rae, B. 17. Rcichcrt, and B. 0. West, J . Ovganontct.Chem., 1974, 81, 227.l7 W. D. S. Motherwell, PLUTO I’rogram for Plotting RIolccularand Crystal Structures, Cambritlge C!ni\w-sity, 1976.l8 (a) C. R. Mason and -2. G. Whcclcr, J . Chcm. SOC. ‘ 4 , 1968,2849; ( h ) A . E. Smith, Acla Crystallop., 1066, 18, 331; (c) R . M.Gatehousc, B. 1.3. Keichcrt, illid 13. 0. West, Actn Crystallop.,Sect. B , 1974, 30, 6451.lD P. M. Bailey, E A . liclley, ;iii(1 1’. .I. Maitlis, J . Ovgaiiorrtrt.Chem., 1978, 144, C52; P. Henclriks, K. Olic, and I(. I’riezc,Cvyst. Stvuct. Commun., 1075, 4, 611; H. A . Graf, K. I-Iiittel, G.Nagorsen, and B. Rao, J . Organornet. Chkn., 1977, 136, 389; W. J C .Oberhannsli and I.,. F. Dahl, Ihid., 1965, 3, 43; M. R. Churchilland 13. Mason, Natirre (London), 1!)64, 204, 777; R. AIason and11. I<. Russell, Chem. Commiin., 1066, 26.2o L. Pauling, ‘ The Nature oE thc Chemical Bond,’ 3rd cdn.,Cornell IJniversity Press, Ithaca, New York, 1960, 13. 224.21 Y. Yamamoto and Y. Yamazaki, J . Ovganorrtet. Clieira., 1975,90, 329.22 J. M. Bassett, M. Green, J . .I. I(. floward, antl I:. C;. ’1.Stone, J . Chem. Soc., Dalton l‘vnws., 1980, 1779.23 J . Hornstra and B. Stul~bc, I’IV1100 1)ata ProcessingProgram, Philips Rcscarch Laboratories, Eindhovcn, Ncthcr-lands, 1972.24 D. T. Cronier and J . 13. Mann, Acta Crystull~~gi~., Srct. -4,1968, 24, 321.25 G. M. Sheltlrick, SHELX 76, program lor crystal structuredetermination, Carnbridgc University, 1976

ISSN:1477-9226    

DOI:10.1039/DT9820001715

出版商:RSC    

年代:1982

数据来源: RSC