摘要:

J C'HFM so(' DALTON TRANS. 1986 202 IMetal Complexes of Sulphur-Nitrogen Ligands. Synthesis and Characterizationof Palladium(ii) Complexes of 3-( Mercaptomethy1)piperidineJoan Sola * and Ramon YanezDepartament de Quimica lnorganica, Universitat Autonoma de Barcelona, Beliaterra (Barcelona), Catalun ya,SpainThe complexes [Pd(HL)X,] [X = CI ( l a ) or Br ( I b)], [(PdLX),] [X = CI (2a), Br (2b), or I (2c)],and [Pd,L,] CI,*2H,O (3), where HL and L denote respectively 3- (mercaptomethy1)piperidine in itszwitterionic and anionic forms, have been prepared and characterized. Complex (3) has beenshown crystallographically to contain centrosymmetrical trinuclear cations where terminal PdL,units, containing cis-S,PdN, square-planar metal environments, are bound also in a square-planarfashion to a central palladium atom through bridging mercapto groups.The three planar metalenvironments exhibit equivalent dihedral angles. Complexes ( 2 ) exhibit trans mercapto- bridgeddimeric structures containing S,PdNX square-planar metal centres. Similar sulphur- bridged dimericstructures, with planar S,PdX, metal environments, are proposed for complexes (1 ). Complexes (2)and (3) are among the first known chelates of y-mercaptopiperidines.Previous reports from our laboratories have dealt with the co-ordination chemistry of y-mercaptoamines,' and we haverecently published some results concerning y-mercaptoalkyl-piperidine l i g a n d ~ . ~ ' These were attempts to enhance thechelating ability of one of the ligands previously studied, 4-mercapto- 1 -met hylpiperidine.which behaves as a unidentateligand.8 l o I n spite of the lower steric requirements of 2- and 3-(mercaptoalky1)piperidine ligands, no chelate compounds havebeen found with Ni", Cu', Ag', and Cd''.6In an extension of these studies to the second-row transitionmetals, and particularly to Pd", chelate complexes in which 3-(mercaptomethy1)piperidine (HL) behaves as a bidentate ligandhave been isolated for the first time.Experimental1.r. spectra were recorded on potassium halide or polyethylene(60% 180 cm ' ) pellets or Nujol mulls using Beckman 1.R.-20 Aand Perkin-Elmer 850 spectrophotometers. Electronic spectrawere recorded on Shimadzu UV 240 (20C-800 nm) andBeckman Acta VII (80&2 500 nm) spectrophotometers.Analytical data are given in Table 1.Palladium was determinedvolumetrically with ethylenediaminetetra-acetate (edta) andC, H, and N with a Perkin-Elmer 240 analyzer.3-(Mercaptomethyl)piperidine was synthesized following arecently reported method.' ' The racemic mixture was usedwithout separation of the enantiomers.Pwprrrutioti of Contplr.ues.-[ Pd( HL)Cl,] (la). The ligand(1.0 mmol) dissolved in water (8 cm3) with a few drops ofmethanol was added with stirring to an aqueous solution ofNa,[PdCl,] (10 cm', 1.0 mmol). A red microcrystalline pre-cipitate was collected, washed with water and ethanol, anddried under vacuum.[ Pd( H L)Rr,] ( 1 b). An aqueous solution of Na,[ PdCI,] ( 10cm3. 1.0 mmol) was added with stirring to a hot, saturated KBrsolution containing 1.0 mmol of HL in aqueous methanol (19: 1v'v, 20 cm-').'The reaction mixture was stirred at 8&85 C for30 min. A dark red microcrystalline precipitate was collected,thoroughly washed with hot water and then with ethanol, anddried under vacuum.[( PdLCl),] (2a). Upon addition of H L ( I .O mmol) dissolvedin aqueous methanol (19: 1 v,'v) to a saturated NaCl aqueoussolution containing Na,[PdCI,] ( I .O mmol) an orange-redTable 1. Analytical data for the palladium complexes with requiredvalues in parenthesesAnalysis(",)1H N Pd4.2 4.3 34.6(4.25) (4.5) (34.5)3.4 3.55 26.7(3.3) (3.5) (26.8)4.6 5.1 38.7(4.45) (5.15) (39.1)3.6 4.5 33.5(3.8) (4.4) (33.6)3.3 3.9 29.3(3.3) (3.85) (29.3)5.5 5.95 33.8(5.5) (5.9) (33.7)precipitate appeared.The reaction mixture was adjusted to pH8 with NaOH and then stirred for 30 min. A dark yellowprecipitate was filtered off and washed several times with hotwater until no chloride was detected in the washings. It wasdried in LICIC'UO over silica gel.[( PdLBr),] (2b). The same procedure as above was followedbut the Na,[PdCI,] solution was saturated with KBr. Anorange precipitate was obtained.[(PdLI),] (2c). An aqueous solution of Na,[PdCI,] (1.0mmol) was added with stirring to a saturated KI aqueoussolution containing HL (1.0 mmol) and the stoicheiometricamount of 0.02 mol dm-, NaOH. The mixture was stirredfor 30 min. The brown precipitate was collected, thoroughlywashed with hot water, and dried under vacuum.Complexes (2a)-(2c) are soluble in CHCl, and CH,CI,.[Pd3L,]CI,-2H,0 (3).An aqueous solution of Na,[PdCl,](1.0 mmol) was added with stirring to HL (1.3 mmol) dissolvedin 3.5 mol dm-3 aqueous NH,. If a small amount of precipitateappeared at this stage it was redissolved by adding some dropsof concentrated aqueous NH,. On standing, yellow crystalsappeared within a few days, which were collected and washedwith a small amount of ethanol.The same procedure can be used in the preparation of thecorresponding bromide compoundJ. CHEM. SOC. DALTON TRANS. 1986 2022Table 2. Selected i.r. bands (4 000-250 cm-') for palladium(rr) complexes(la)a (W (2a) (2b) (2c) (3)3 190w 3 180w3 090(sh) 3 080(sh)3 OSOs,br 3 040s,br1 590mb I 590sb3 160s 3 160s 3 160s 3 030s490s 490s 490s 482, 492d',s300m, (sh) 300s 300s 300s340m 340m 350m 345m 340m 360,340m275vs,br 270sa Spectrum recorded within the 4 000-1 80 cm-' range.Sharp. Doublet.Assignmentd H , )G(HAH)v(N-H) IV( Pd-N)V( Pd-S){;;;ateV( Pd-CI)Table 3. Electronic spectra * of palladium(ii) complexesComplex Solvent(la) CPd(HL)Cl,I Solid 36.1 , 31.7 , 26.0 , 22.2(W [IPd(HWr,l Solid 34.7 , 29.4 , 25.0 , 21.5(W C(PdLCIh1 CHCI, 36.8( 18 300), 32.3(6 OOO), 28.3(4 200), 23.8(800)(2b) [(PdLBr)zl CHCI, 35.3(19 700), 31.0(6 OOO), 27.5(4 500), 23.2(800)(k) C(PdLI),I CHCI, 34.0( 17 400), 29.4( 10 OOO), 26.3( 5 OOO), 22.7( 800)(3) [ Pd 3 L4]CI 1-2H 2 0 MeOH 39.7( 12 OOO), 35.6( 1 1 OOO), 29.1 ( 10 400)* In lo3 cm-' with &/dm3 mol-' cm-' in parentheses.Results and DiscussionSynthesis.-The preparative reactions are indicated inScheme 1.Reaction (iii) may be considered as a non-reversible(3)Scbeme 1. (i) X = CI or Br, HL; (ii) X = I, L-; (iii) X = CI or Br,NaOH, pH 8.0; (iv) X = CI or Br, 3 L-, 3.5 mol dm-3 NH,acid-base reaction in which amine groups, upon deprotonation,become co-ordinated to metal atoms, as it will be demonstratedlater. No appreciable reaction is observed on treatingcomplexes (2aH2c) with diluted acids. Reactions similar to(iii) but reversible have been shown to occur between cationicand neutral complexes of y-mercaptoamines,'* ' O the reactionproceeding in both directions without significant rearrangementof their common sulphur-bridged polymeric structures. Owingto the non-reversibility of reaction (iii), frameworks differentfrom the latter may be expected in our case.1.r.Spectra-Table 2 lists the principal i.r. bands. Complexes(la) and (Ib) are shown to contain protonated amine groupsand thus the ligands are in zwitterionic form (HL), co-ordinating only through the sulphur atom. The frequencies ofthe v(NH,) bands are indicative of weak hydrogen-bondinginteractions l 2 suggesting that the halide anions are not free butinvolved in metal co-ordination.A relevant feature of the complexes with the ligand in itsanionic form, (2a)--(Zc) and (3), is the shift of v(N-H) from3 280 cm-' for the free ligand to 3 160 cm-' for (2aH2c) and+3 030 cm-' for (3) showing that co-ordination via nitrogen istaking place.'j Owing to the non-sensitivity of v(N-H) incomplexes (2a)-(2c) towards the corresponding halide, theN-H groups are not appreciably involved in hydrogen- bondformation suggesting that halide anions are co-ordinated to thepalladium atoms.This is not the case for the complex (3), wherethe much larger shift of v(N-H) indicates, besides N-co-ordination, strong hydrogen-bonding interactions which pointto a counter-cation behaviour of the chloride anions.' 3*14Assignments of the metal-ligand vibrations (Table 2) confirmthe chelating behaviour of the ligand in complexes (2a)-(2c)and (3) as well as the existence of Pd-Cl bonds in (la) and (2a).While v(Pd-S)"-" and v(Pd-N) 18-20 are in good agreementwith other data reported, v(Pd-Cl) appears at rather lowerfrequencies than is usual.19q20Electronic Spectra-The electronic spectra of the complexes(Table 3), displaying a common pattern and showing no bandsabove 500 nm, are indicative of square-planar palladium(ri)environments.2 ' Strong ligand-to-metal charge-transfer (1.m.c.t.)absorptions appearing above 25000 cm-' overlap the spin-allowed d-d bands and make difficult the determination of thelatter. Thus we have been able to estimate no band other thanv1(22 200,21 500,23 800,23 200, and 22 700 cm-') correspond-ing to complexes (la), (1 b), and (2aH2c).The orders of decreasing energy, X = C1 > Br > 1,(2a) > (la), and (2b) > (lb), displayed by the d-d bands andalso by the charge-transfer transitions of complexes (la), (lb),and (2a)--(Zc) reflect the spectrochemical series as well as theoptical electronegativity of X,,,sZ3 and provide additionalsupport for the co-ordination of the halide anions in thesecompounds.Moreover, the highest energy c.t. absorptionsobserved for complex (3) account for the absence of Pd-CIbonds.Complexes with the Ligand in Anionic Form.-The structure of[Pd3L,]CI,.2H20 (3). The crystal structure of this compoundhas recently been published but only a general description wasgiven. The numbering system employed is depicted in Figure 1J. CHEM. soc DALTON TRANS. 1986 2023r-Figure 1. A view of the structure of [Pd3L4I2+, with the atom num-bering schemeThe structure consists of discrete trinuclear [Pd,L,I2 + cations,chloride anions, and water molecules.The shortest N-CIdistances (3.24, 3.15 A) account for significant N-H * * * CIhydrogen bonding l 4 as was indicated by the i.r. spectrum.Even though the cation closely approaches C,, symmetry,this is actually C,. The crystallographically imposed inversioncentre, which is located at the central palladium atom, causesthe cation to contain both enantiomers of the ligands. Two ofthese, respectively d and 1, co-ordinate each terminal palladiumatom giving rise to cis-S,PdN, environments. The centralpalladium atom is held to the terminal moieties throughbridging sulphur atoms of the mercapto groups, the five atomsof the PdS, environment lying rigorously on a plane due to theinversion centre at the metal atom.Both this plane and the alsoplanar S,PdN, units (largest deviation from mean plane 0.025A) determine dihedral angles of 133" thus imposing folding ofthe four-membered PdS,Pd rings along the S-S axis. Theserings have the syn-endo bridged conformation.**24 While thetwo crystallographically independent piperidine rings exhibit aregular chair conformation, the two six-membered chelate ringshave a slightly distorted one.Fackler 24 has discussed the relationships between somestructural parameters of these mercapto-bridged rings and theirinfluence on M-M interactions. According to his work, the largevalues of the Pd-Pd distance [3.217(1)A] and of the dihedralfolding ( 133.0 ) preclude any M-M interaction in our complex.Due to the fact that the S-S distance [2.982(6)A] is shorter thanthe normal S-S van der Waals non-bonding distance (3.2 A),significant bonding forces may be associated with it.,, Thevalues of these parameters lie between those found in somedimeric palladium complexes of y-mercaptoamines 5 * 7 and inthe complex [ 1 P~(SBU')(S,CSBU')},].~~Both types of palladium environments display significantdeviations from the square geometry.This is revealed by theS( 1)-Pd( 1)-S(2) angle of 80.0" as well as the mean value of theN-Pd-S angles (95.20, which are 14.0 and 6.8" respectivelylarger than S-Pd(2)-S and N-Pd-N. Both Pd-S distances[mean 2.319(5) and 2.291(11) A, respectively for Pd(1) antiPd(2)] and Pd-N [mean 2.O98( 17) A] are in good agreementwith other reported data (2.28-2.38 A for Pd-Ss*7*24-2' and2.02% 2.I8 A for Pd-N s*7*28p30 ). The planar PdS, environmentof an analogous PdNi heterometallic complex 27 exhibitsx* R n **+( b 1 R = C6H,,NH,Figure 2. Structures proposed for (a) [(PdLX),] (X = C1, Br, or I)(2a+(2c) and (h) [Pd(HL)X,] (X = CI or Br) (la) and ( l b )exactly the same S-Pd-S angles (80, 100") but slightly largerPd-S bond lengths (2.34 A).cis-S,PdN, Environments give rise to the splitting ofv(Pd-N) (482, 492 cm-').19[(PdLX),] (X = CI, Br, or I) (2aH2c). The stoicheiometryand spectral properties of these compounds, which indicate co-ordination oia N, S, and x , together with a strong tendency ofthe mercapto groups to behave as bridging l i g a n d ~ , ~ ' , ~ ~ leadto the assumption of a sulphur-bridged dimeric structurecontaining square-planar palladium environments.Besides theexperimental solubilities, the presence of an unique bandattributable to v(Pd-N) in the i.r. spectra of all these complexesas well as the sole v(Pd-CI) in that of complex (2a) point to atrans configuration ' [splitting of v( Pd-N) was observed forcomplex (3)]. Similarly to complex (3), these structures areexpected to be bent about the sulphur bridge [Figure 2 ( ~ ) ] . , ~Only the trans isomer has been analyzed crystallographicallyin related c~mplexes.~*~ A strong trans effect has been associatedwith sulphur l i g a n d ~ . ~ ~ . ~ , The low frequency of v(Pd-C1) forcomplex (2a) might be due to the trans effect of one of thebridging mercapto groups on the chlorine atom.Complexes with the Ligand in Zwitterionic Form, [ Pd( HL)X,](X = CI or Br) (la) and(lb).-Two structural possibilities maybe derived from the stoicheiometry and available spectral data,both containing square-planar palladium environments.Asulphur-bridged polymeric structure [{Pd(HL),),J2"+ with[PdX,]' as counter cation has already been suggested forsome palladium complexes of 4-mercapto- 1 -methylpiperidine. ' *A molecular dimeric structure [f Pd(HL)X,),], similar to thatproposed for complexes (2a)-(2c), may also be considered.A lower frequency for v6 corresponding to [PdCI,]'- thanin its usual range ( 3 3 6 3 2 7 would be expected inthe presence of a polymeric cation such as [{Pd(HL)2},]2"+.The large shift of 60 cm-' that would be required to reach thefrequency of 275 cm-' observed for complex (la) makes itunlikely that this band can be associated with v6.19 I n thisconnection, shifts up to only 15 cm-' have been found for v3 of[Cox,]' in [{Co(HL), ),][(COX,),], polymeric complexes ofCo" with 3-(mercaptomethy1)- l-methylpiperidine.3h Further-more, there is no absorption around 193 cm-' (v7 of [PdCl,]'-)or around 260 cm-' (v6 of [PdBr4]2-)'9 for complex (Ib)2024 J.CHEM. S O ( . . DAI-TOh TRANS. 1986Therefore, the i.r. data do not support an ionic polymericstructure for complexes (la) and (lb). The behaviour of thereaction (iii), already mentioned, also casts some doubt on thisassumption.Both arguments allow us to postulate the existence of dimericstructures in complexes (la) and (lb) with planar X,PdS, metalenvironments which probably determine a dihedral angle aboutthe S bridge [Figure 2(b)].24 The two i.r.-allowed v(Pd-CI) l 9due to the cis-CI,PdS, units in complex (la) would be obscuredby the broad and very strong absorption centered at 275 cm '.As in complex (2a), the trclns effect of the bridging mercaptogroups would account for the low value of this frequency. Asimilar structure but with tetrahedral metal centres has beencrystallographically demonstrated in the complex [(Zn( HL)-CI,) ,] where HL is 4-mercapto- 1 -methylpiperidine.*ConclusionsBy reacting 3-(mercaptomethy1)piperidine with [ PdX,]' saltswe have been able to prepare complexes with the ligand in itszwitterionic form and trinuclear and dinuclear S,N-chelates.These are among the first known chelate compounds containingy-mercaptopiperidine l i g a n d ~ .~Corresponding reactions of 2- and 3-(mercaptoalky1)-piperidines as well as of 3-(dimethylamino)propane- 1 -thiolwith nickel(r1) salts led to polymeric compounds where metal co-ordination was achieved only through sulphur atom^.^.^ Thehigher stability of Pd"-X compared with Ni"-X bonds, thegreater size of palladium(i1) ion, and, in our case, the softeningof the nitrogen atom in the piperidine ring37 seem to accountfor this different behaviour.ReferencesI J. C. Bayon, M. C . Brianso, J. L. Brianso, and P. Gonzalez, fnorg.Clicwi.. 1979, 18, 3478.2 H.Barrera, J. Suades, M. C . Pericaud. and J. L. Brianso, Pol~~lic~droti,1984, 3, 839.3 H. Barrera, J. C . Bayon, J. Suades, C. Germain, and J. P. Declerq,Polj.lterlron, 1984, 3, 969.4 H. Barrera, J. C . Bayon, P. Gonzalez, J. Sola, J. M. Vinas, J. L.Brianso, M. C . Brianso, and X. Solans, Polylicd-on, 1982, 1, 647.5 H. Barrera, J. L. Brianso. M. Font-Altaba, J. Sola, X. Solans, and J.Suades, Acru Crj~srullogr.. Sect. C, 1983, 39, 1653.6 H. Barrera. J. Sola, and J. M. Viiias, Trunsirion Met. Clieni., 1985, 10,233.7 H. Barrera and J. M. Vinas, Pol~hctlrot?. 198.5. 4, 2077.8 M. C . Brianso, J. L. Brianso, W. Gaete. J. Ros. and C. Suncr. J . C ' l w i i i .9 W. Gaete, J. Ros, X. Solans, and M. Font-Altaba, 111org. ('Iicwi.. 1984.10 R.M. Brunet, W. Gaete, P. Gonzlilez, and J. Ros, TruttsiiiotI .\lei.1 I H . Barrera. J. Sola. and J. M. Vinas. J . Cli(w~. R(,.\.. 1985. ( S ) 270.12 R. H. Nuttall, D. W. A. Sharp, and T. C. Waddington, J . Clrmr. Soc...13 Ch. A. Root and D. H. Busch, h r g . c/7~1., 1968, 7, 789.14 G. Pimentel and A. L. McClelland, 'The Hydrogen Bond,' FreemanI5 D. M. Adams and J. B. Cornell, J . Clivni. Soc. A , 1968, 1299.16 J. M. Burke and J. P. Fackler, h r g . Chem., 1972, 11. 2744.17 D. M. Roundhill, h r g . Clicwi., 1980, 19, 557.I8 C. W. Schlapfer and K. Nakarnoto. h r g . Chini. Actti. 1972, 6, 177; J.Suades, X. Solans, and M. Font-Altaba. Pol~~licrlron, 1984, 3, 1227.19 K. Nakamoto, 'Infrared Spectra of Inorganic and Co-ordinationCompounds,' 2nd edn..Wiley, New York, 1972.20 D. M. Adams. 'Metal-Ligand and Related Vibrations,' Arnold,London, 1967.21 Chr. K. Jorgensen, Itrorg. Chini. Actu RPL.., 1968, 2, 65.22 Chr. K. Jsrgensen, 'Absorption Spectra and Chemical Bonding inComplexes,' Pergarnon Press, Oxford. 1962.23 Chr. K. Jargensen. Prog. Inorg. Chcr?i., 1970. 12, 101.24 J. P. Fackler, Prog. ittorg. Chcni., 1976, 21, 55.25 N. R. Kunchur, At.rtr Cr~~.vtulfogr., Sect. B, 1968, 24, 1623.26 E. M. McPartlin and N. C. Stephenson. Actu Crjxrullogr., Sc2c.t. B,27 M. G. B. Drew, D. A. Rice, and K. M. Richards, J . Chcni. Soc., Dulton28 B. N. Dickinson, Z. Kristullogr., 1934, 88A. 281.29 S. E. Livingstone and J. D. Nolan, Inorg. Clicw., 1968, 7, 1447.30 J. M. Fowler and A. Griffiths, Acrn Crjxtullogr., Seer. B, 1978, 34.31 S. E. Livingstone, J . Clwnt. Soc., 1956. 1989, 1994.32 S. E. Livingstone, Q. R w . Chmi. So(,., 1965, 19, 386.33 M. A. Ali and S. E. Livingstone, C'oord. Chwi. RN., 1974, 13, 101.34 C. H. Perry, D. P. Athans, E. F. Young, J. R. Durig, and B. R.35 D. H. Brown, K. R. Dixon, C. M. Livingstone, R. H. Nuttall, and36 H. Barrera, L. Pinol. and J. Sola, unpublished work.37 J. M. Fowler and A. Griffiths, Actci Ct:t..vtuIIogr.. Sect. B, 1978, 34,Soc.. Dulton Trum.. 198 1. 852.23, 39.Climi., 1984, 9, 345.1960. 4965.and Co., San Francisco, 1960.1969, 25. 1659.Truns., 1980, 2075.1709.Mitchell, Speclrocliint. Actu, Part A, 1967. 23. I 137.D. W. A. Sharp, J . C ' l i ~ n i . Soc. A , 1967, 100.1712.R t w i r t d I 5th April 1985; Pcippr 5,62

ISSN:1477-9226    

DOI:10.1039/DT9860002021

出版商:RSC    

年代:1986

数据来源: RSC