摘要:

1. CHEM. SOC. DALTON TRANS. 1983 1217The Reactivity of Cyanogen towards Compounds containing ActiveHydrogens at Carbon Atoms. Part 3.' Synthesis of Bis[l -cyano-241 -iminoethyl)butane-I ,3=dionato]copper( 11) f rom Cyanogenand Bis(acetylacetonato)copper( 11) : Kinetics, Thermodynamicsand X-Ray Crystal Structure tBenedetto Corain," Marino Basato. and Giuseppinsi VisentinCentro di Studio sulla Stabilita' e Reattivita' dei Composti di Coordinazione, C. N.R.,Istituto di Chimica Analitica, 351 00 Padova, ItalyGiuseppe ZanottiCentro di Studio sui Biopolimeri, C.N.R., lstituto di Chimica Organica, 35700 Padova, ItalyThe complex [Cu(acac),] (acac = acetylacetonate) reacts with C2N2 under ambient conditions indichloroethane to give in high yield a compound of stoicheiometry [Cu(acacC,N,),].An X-raysingle-crystal analysis revealed that this is bis[l -cyano-2- (1 -iminoethyI)butane-l,3-dionato]copper(ii),apparently derived from bisC3- (cyanoiminomethyl) pentane-2,4-dionato]copper(ii) formed upon insertionof C2N2 into the methine C-H bonds in [Cu(acac),]. The kinetics of the cyanation process reveal thatit occurs in two distinct steps, which display similar second-order rate constants. The kinetic andthermodynamic role of the complex [Cu(acac),] is discussed.The reaction of cyanogen with P-dicarbonyl compounds inethanol is a base-catalysed process, known since 1898.' Thereaction (i) can be envisaged as an insertion of the C2Nzmoiety into the methine C-H bond of the organic substrateenolic form.This process may be of some synthetic interest in that itdoubles the degree of functionalization of the organic reagentby introducing the two groups C=NH and CZN.FH3CH, H/ \CH3 CH3H L~We have recently found la that this cyanoiminomethylationreaction can occur also at a metal-co-ordinated pentane-2,4-dionate ligand (acac-) (metal = Mn", Mn"', Fe", Co" 9 , Nil1or Cull), though the reaction is strongly dependent on themetal (it fails for Cr"' and Pd") and gives analytically pure [M-(acacCzN,),] only in the case of [Ni(acac)J and [Cu(acac)J.In view of the fact that this reaction of cyanogen is anovelty in its co-ordination chemistry lb and also becausethose acetylacetonate complexes found to be reactive withcyanogen catalyse not only the cyanation reaction mentionedabove but also the subsequent dimerization of the primaryorganic product to a heavily functionalized pyrimidine la (L)(Scheme I), we have studied in detail the mechanism of thereaction of [Cu(acac),] with CzNz and the thermodynamicsof the [Cu(acac),]/HLZ and [Cu(acacC,N,),]/Hacac ex-changes, which have been shown to be key steps in the copper-catalysed pyrimidine synthesis.' Further more the addition-insertion product [Cu(acacC,N,),] has been fully character-ized by X-ray analysis and other physical properties. For thiscopper(r1) complex a structure identical with that of [NiLa2]t Supplementary data atrailable (No. SUP 23551, 9 pp.): observedand calculated structure factors, positional and thermal parameters.See Notices to Authors No.7, J. Chem. SOC., Dalton Trans., 1981,Index issue.was proposed as the result of the similarity of the Debyespectra of the two species.The complex [NiLa2] is the primary product of the reactionof [Ni(acac)J with C2Nz; upon recrystailization at 60 "C itchanges into the more stable bis[l-cyano-2-(l-iminoethyl)-butane-l,3-dionato]nickel(ir) complex (hereafter referred to as[NiLB2]), for which the X-ray single-crystal structure was deter-mined. However, whether [NiLa2] is a real isomer or a dimor-phic form of [NiLB2] is still not unambiguously established."/c 0' 'CH,LScheme 1.ExperimentalSolvents were purified and dried by standard procedures. Inparticular, CH2C12 (Baker Bar) was treated with aqueoussodium carbonate, dried over sodium sulphate, and thendistilled.Cyanogen was a Union Carbide reagent and wasused as received. The preparation of stock solutions of CzNzand the determination of their concentrations were carriedout as described previ~usly.~Details for the preparation of [CuLp2] can be found else-where.* Crystals suitable for X-ray analysis were obtainedfrom a solution prepared from [Cu(aca~)~] (100 mg) in CHI-C12 (6 cm') containing CzNL (0.25 mol dm-9. The solution gavedark green crystals (94 mg) after 24 h at ca. 20 "C.Routine i.r. spectra were recorded on a Perkin-Elmer 257instrument; accurate ones on a 599 B model. Electronicspectra were recorded on a Perkin-Elmer A 72 spectrophoto-meter121 8 J. CHEM. SOC. DALTON TRANS. 1983X-Ray Structure Analysis of [CuLB2].-Crystal data (fromsingle-crystal diflractometry).Cl4HIJCuN4O4, M = 365.0,a = 11.460(7), b = 6.1 12(5), c = 5.61 1(4) A, u = 79.5(1), p =91.5(1), y = 104.0(1)", U = 375.0 A3, Z = 1, D, = 1.62 g~ m - ~ , F(000) = 187.0, h(Mo-K,) = 0.7107 A, ~ ( M o - K , ) =1.54 cm-l, space group P i .The intensities were collected on a Philips PWllOO four-circle diffractometer operating in the e/20 scan mode (scanwidth 1.0", scan speed 0.002" s-l); 1 320 independent reflec-tions up to 8 = 25" were measured, of which 1097 hadintensities greater than 2.5 times their standard deviation(CT, calculated from the counting statistics of the measure-ments). During data collection, two standard reflections weremeasured every 180 min to check the stability of the crystaland the electronics.The intensities were corrected for Lorentzand polarization factors, and an experimental absorptioncorrection was applied following the method proposed byNorth et a/.' A Fourier map was calculated by putting thecopper atom at the origin, and the rest of the molecule wasimmediately evident. The structure was refined by the full-matrix least-squares method, allowing the Cu, 0, and Natoms to vibrate anisotropically. The H atoms of the methylgroups were constrained to their normal geometry by usingthe group refinement procedure? The H atom bound to theimine nitrogen was not localized in the Fourier differencemap.Throughout the analysis the scattering factors of ref. 7 wereused; both real and imaginary parts of the anomalous dis-persion were included for copper only.The final R factor was 0.062 (R' = 0.066).The last cyclesof refinement were carried out by minimizing the quantityAll the calculations were carried out on the IBM 370/158&,,[(F')z - (F,)'], w = 3.52/[02(F) + 0.01 (F)2].computer of the University of Padova, with the SHELX 76system of programs.Experimental Kinetic Procedures and Mathematical Treat-ment.-Thermodynamics of the [Cu(aca~)~]/[CuL~~] system.Solutions of [Cu(a~ac)~] and of [CuLPz] were found to obeythe Beer-Lambert law in the concentration range employed.The coproportionation equilibrium constants were deter-mined by two different procedures.(a) The solutions of [Cu(aca~)~] and [CuLsz] were placed inthe two halves of a tandem cell and their total absorbance wasbalanced with a convenient reference.After mixing of thereaction solutions (in the tandem cell), the spectrum of themixture gave directly AA values at various wavelengths(AA = A,, - Ao). The absorbances at and before equilibr-ation are defined as in equations (1) and (2), where refersto [Cu(aca~)~], cB to [CuLBz], and EAB to [Cu(acac)LP].A. = cA{ 2[Cu(aca~)~]0}l/2 f &B(2[cuLPZ]O)1/2Here 2[Cu(aca~)~]~ and 2[CuLP2l0 are the concentrations ofthe solutions in the two halves of the cells; [Cu(aca~)~]~ and[CUL~,]~ are the initial concentrations after mixing; 2x is theconcentration of [Cu(acac)LP] at equilibrium; and I is the cellpathlength.(bj The measurements were performed with 0.1 cm cellscontaining, separately, [Cu(acac),], [CuLP,], and the mixtureobtained by mixing equal volumes of these two solutions.The two experimental methods gave consistent AA values,from which the equilibrium concentrations and the relatedequilibrium constant could be obtained as indicated in theDiscussion section.Reaction of 3-( Cyanoiminomethyl)pentane-2,4-dione (HL')with [Cu(aca~)~].-Tn order to calculate values for the equilib-rium constants of reactions (8) and (9) (see later) we employeda fitting method, i.e.we determined the concentration valuesof the various species involved which minimized the differencesbetween calculated and observed spectra of the mixture.Equation (3) was used, where x = concentration of [Cu-(acac)LP] at equilibrium, y = concentration of [CuLP2] atequilibrium, C = initial concentration of [Cu(a~ac)~], andC1 = initial concentration of HL".This fitting was applied at six different wavelengths (270-320 nm) characterized by large absorbance changes during thereact ion.Kinetics of Cyanation of [C~(acac)~].-The methodemployed to determine the reaction profiles can be sum-marized as follows.(a) Three particular h values were chosen: 305, 270, and340 nm.At 305 nm = CAB, whereas at 270 and 340 nmlarge absorbance changes are observed upon reaction.(b) From the absorbance values, at various times, at thethree chosen wavelength values, the actual concentration ofeach species was determined according to equation (4), whereC = initial concentration of [Cu(aca~)~], x = concentrationat a given time of [Cu(acac)LP], y = concentration at a giventime of [CuLP2], and I = cell pathlength.At 305 nm equation (4) reduces to A / / = Ao/l + y(cB -E ~ ) , which makes possible direct determination of y .Theuncertainty in y is indeterminate, whereas for [Cu(acac),] and[Cu(acac)LP] it may be represented by the differences betweenthe values of the concentrations calculated at 270 and 340 nm.Results and DiscussionSynthesis and Characterization of the Complex [Cu(acac-C,N,),].-The i.r. spectrum of the methylene chloridesolution under preparative conditions { [Cu(aca~)~] = 0.08mol dm-3; [CzNz] = 0.25 mol dm-3) displays the same twobands (at 3 330 and 1665 cm-') as a solution obtained bydissolving an authentic sample of [Cu(aca~C~N~)~].Thesolid compound displays i.r. bands at 3 270 (vN+), 2 225(vCrN), 1 635 (vCZN), and 1 555 cm-' (vcz0).The u.v.-visible spectra of the product in CH,CI, solutionand in the solid state (Nujol mull) are practically identical,indicating identical or very similar molecular structures inboth phases.* The product exhibits poor thermal stability:thermogravimetric analysis shows that it is stable in thenarrow temperature range 160-170 "C, under argon, beyondwhich thermal decomposition occurs. Mass measurementscarried out in the thermal stability temperature range giveclean spectra with a strong parent-ion peak (Found: M,365.0, Calc. M , 365.0). The magnetic moment, measured bythe Gouy method on solid samples, is 2.03 B.M.(1.88 xJ T-l) On the basis of these data and of analogy with a closelyrelated Ni" compound,'b two possible molecular structures [( 1)* The spectral data reported for this compound in ref. la refererroneously to the related Ni" species described in Part 1 (ref. lb).The correct figures are [h/nm (&/dm3 mol cm-')I : 270 (16 900).287 (17 900), and 344 (12 400)J. CIIEM. SOC. DALTON TRANS. 1983 1219c\H 3 p 3C N/Figure 1. Single-crystal X-ray structure of [CuLp2], with the atomicnumbering system used (hydrogen atoms not shown)and (2)] appear conceivable. An X-ray single-crystal analysisconfirmed structure (2). [CuLp2].The molecular structure of [CuLp2] is shown in Figure I . Thefinal structural parameters for non-hydrogen atoms arereported in Table I , and bond lengths and angles in Table 2.The molecule exhibits marked similarities to [NiLP2],lbdespite some significant differences.It possesses a centre ofTable 1. Final positional parameters (with e.s.d.s in parentheses)for non-H atoms in [CuLp2]Xla0.00.0466(5)0.1459(4)0.3 594(5)0.1246(6)0.1437(5)0.2405(5)0.2348(5)0.1 M7(6)0.3 3 40( 6)0.3 447( 6)0.4331(6)Ylb0.00.2508(9)0.1093(8)0.7239(9)0.71 07(9)0.4165( 10)0.4420( 10)0.2776(10)0.5925(11)0.2797( 12)0.6369(11)0.7420( 13)YIC1 .o1.1696(9)0.81 13(9)1.1569(9)1.4OO8( 12)1 .I 345(11)0.9664( 10)0.8 1 38( 1 0)1.28 1 4( 1 1)0.6422( 13)0.9758(11)0.7688(13)Table 2. Bond lengths (A) and angles (") in [CuLp2]1.910(4) C(l)-C(4) I .467(7) cu-O(1)1.913(4) C(3)-C(5) 1.505(8) c u-O( 2)O(l)-C(l) 1.303(6) C(2)-C(6) 1.477(7)0(2)-C(3) 1.263(6) C(6)-C(7) 1.504(8)C(l)-C(2) 1.436(7) C(4)-N(2) 1.135(7)C(2)-C(3) 1.423(7) C(6)-N( I ) I .220(7)O( I)-Cu-O(2)cu-O( 1 )-C( 1 )Cu-O(2)-C(3)O(l)-C( 1)-C(2)C( 1 )-C( 2)-C( 3 )C( 2)-C(3)-0(2)O( 1 )-C( I )-C(4)C(2)-C( 1 )-C(4)90.0(2) C(I)-C(4)-N(2) 168.0(6)127.7(4) C(l)-C(2)-C(6) 115.7(5)132.3(4) C(3)-C(2)-C(6) 124.2(5)126.6(5) C(5)-C(3)-C(2) 112.1(5)120.0(5) C(2)-C(6)-C(7) 123.5(5)123.4(5) C(2)-C(6)-N(I) 119.2(5)112.9(5) C(7)-C(6)-N(l) 117.2(5)120.5!5)Table 3.Some least-squares planes ' in the complex [CuLB,]. withtorsion angle and deviations (A) of atoms from the respectiveplanesPlane A: 0.455~ - 0.679~ + 0.5762 = 3.232c u 0.0 C(1)* 0.030O(1) 0.0 C(2)* - 0.004O(2) 0.0 C(3)* - 0.028C(6)* 0.060Plane B: 0.580.~ - 0.7753, + 0.2522 = 1.524N(l) 0.0 C(2)* - 0.047C(6) 0.0 C(7) 0.0Torsion angle between planes A and B: 20.8".' The equations of the planes are in the form Ax + By + Cz = D,in orthogonal 8, space with x parallel to a*, y parallel to c x a*, andz parallel to c.An asterisk denotes an atom not used in the planecalculation.symmetry; the copper atom shows an exact square-planarco-ordination geometry, the 0-Cu-0 angles being 90.0°,with the four oxygen atoms exactly in the same plane. Thetwo Cu-0 distances are very similar, despite the inductiveeffect of the CSN group, and are in good agreement with thevalues in other square-planar complexes of Cu" [1.90-1.91( 1) 8, in bis(3-phenylpentane-2,4-dionato)copper(r1)and 1.89--1.92( 1) A in bidethyl acetoacetato)copper(ii) '1.Bond distances and angles for the rest of the molecule aresimilar, within experimental error, to those in [NIL"].How-ever, significant differences can be seen in the conformationsof the two molecules; in [CuLp2] the CuOCCCO ring is nearlyplanar (Table 3), while in [NIL"] the OCCCO plane is tiltedby 52.6(1)" with respect to the ONiO plane. This fact, alon1220 J. CHEM. SOC. DALTON TRANS. 19831 6 tTable 4. Optical density changes at 368 nm as a function of therelative concentrations of [Cu(a~ac)~] and [CuLe2]Figure 2. Comparison of (a) the combined spectra of [Cu(a~ac)~]and [CuLe2] with (b) that of a solution obtained upon mixing equi-molar solutions of these reagents and with (c) the calculatedspectrum for quantitative conversion into iCu(acac)LB] { [Cu(aca~)~]~= [CuLB2l0 = 4.03 x mol drn-j, cell pathlength 0.439 cm x 2,reference CHIC&}with the C(2)-C(6) torsion angle of 21", suggests that someresonance could extend from the imino group to the 1,3-diketonate moiety.This is in agreement with the highersymmetry of the bond distances in [CuLB2] (as compared with[NiLB2]), despite the small difference between C( 1)-O( 1) andC(3)-0(2), which can be explained by the different sub-stituents on C(l) and C(3) atoms.The slightly different conformations of [CuLB2] and [NiLB2]could also explain the different crystal packing of the twocompounds, despite the similar molecular geometry.The observed structure of [CuLB2] contradicts the previousattribution for the same compound,'' which was based onthe close similarity of its Debye spectrum to that of [NiLa2].lbThese results cast doubt on the proposed structure of [NiLa2],and further investigations are required.Thermodynamics and Kinetics of the System [Cu(acac),]/C,-N2.-Ligand coproportionation reaction.In a preliminaryexperiment it was shown that equimolar solutions of [Cu-(acac),] and [CuLP2] (403 x mol dm-j) react rapidly( t , ca. 10 min) to give an equilibrium mixture with a u.v.-visible spectrum appreciably different from the sum of thespectra of the reagents (see Experimental section for details).This indicated the formation of a new species, considered tobe closely related to [Cu(a~ac)~] and [CuLD2] (Figure 2).Literature data for similar situations relevant to P-dike-tonate l 1 complexes show that under these conditions co-proportionation reactions take place to give mixed com-plexes, i.e.metal[P-diketonate (A)][B-diketonate (B)]. Thismeans that, in our case, reaction ( 5 ) apparently occurs.Attempts to isolate [Cu(acac)LP] in reasonably pure formwere unsuccessful, but its existence could be inferred from acareful spectrophotometric study of reaction (5) at variousvalues of [Cu(aca~)~]/[CuL~~].Table 4 reports the concentrations of the reacting com-plexes together with the relevant AA values obtained at 368nm (details of the methods are in the Experimental section).I n our treatment, AA is the difference between the absorb-ance of the mixture at (Aeq) and before (Ao) equilibration[equation (6)].This quantity is a function of the difference in1.03 x 10-42.01 x 10-44.95 x 10-4[C~(acac)~l~rnol dm-31.01 x 10-42.01 x 1 0 - 45.03 x 1 0 - 41.00 x 10-32.01 x 10-35.03 x 10-35.10 x 10-51.02 x 10-42.04 x 10-41.02 x 10-35.11 x1.98 x 10-54.94 x 10-51.98 x 10-44.94 x 10-49.89 x 1 0 - 41.98 x 10-34.94 x 10-32.48 x 10-44.97 x 1 0 - 49.94 x 10-42.48 x 10-34.97 x 1 0 - 3AAex,0.040 O0.044 O0.0460.0470.0460.046 O0.0740.1180.1500.1720.178 a0.0020.0090.0220.0330.0340.0400.0410.0430.0650.0890.1030.102AAn,,, =0.0450.0500.0520.0530.0520.0520.080.130.170.190.200.020.090.220.330.340.400.410.430.650.891.031.02a Cell pathlength 0.439 cm x 2.Cell pathlength 0.1 cm. Valuesnormalised to 1 cm pathlength.molar absorption coefficients of the product and the reagents,of x {the concentration of ' reacted ' [Cu(acac)J and [CuLB2]},AA = A,, - Ao = &XI (6)and of I (the cell pathlength); CAB refers to [Cu(acac)LB]},to [Cu(aca~)~], and to [CuLB2].The data in Table 4 show that for each series of reactionsthe AA figures increase with increasing initial [Cu(a~ac)~]concentration to reach a limiting value (AAll,) correspondingto complete conversion of the reagent present at lowerconcentration ([CuLB2] in our case) into the mixed species.From these values it is possible to calculate E from the relationE = AAlI,/(I[CuLP2]o) and, as a consequence, from knownvalues of and E ~ , the molar absorption coefficient of [Cu-(acac)LP].In this respect it is noteworthy that the EAB values deter-mined at various values of [CuLP2l0 and by different experi-mental methods (see Experimental section) are consistentwith an average figure of 2 042 f 74, suggesting the form-ation of a single compound, i.e.[Cu(acac)LP].At this point, the E value obtained, inserted in equation (6)allows one to calculate x and K for the coproportionationreaction (3, K = (2x)2/{([Cu(acac)z]o - x)([CuLe2]o - x ) } .To determine the K value for each set of data, only AAvalues in the range (0.2-0.8)AAli, were considered; out ofthis range the error in x becomes too high.Again, the consistency of the obtained K values (average10 & 3) supports the validity of the stoicheiometry indicated[reaction ( 5 ) ] .A further step in this treatment, relevant tothe following ligand exchange and cyanation studies, involvesthe calculation of the u.v.-visible spectrum of [Cu(acac)LB] inthe range 2 4 0 4 2 0 nm. In fact, from Figure 2 and by usinJ . CHEM. SOC. DALTON TRANS. 1983 1221A/nmFigure 3. Typical spectral changes observed upon addition of HL"to solutions of [Cu(acac),]the equation (6), one can calculate x from the experimentalAA value at 368 nm and then, by introducing the resultingx value, obtain the E values at other wavelengths from theexperimental AA values.Figure 2 also shows the calculated spectrum of [Cu-(acac)LP] at a concentration twice that of [Cu(aca~)~] and[CuLP2].As expected l2 this spectrum does not differ markedlyfrom the sum of the [C~(acac)~] and [CuLP2] spectra, althougha shift of 10 nm of the maximum around 300 nm is observed.Ligand exchange (with protonation) reactions. [Cu(aca~)~]reacts with HL" according to equations (8) and (9). Figure 3K1[Cu(aca~)~] + HLa [Cu(acac)LB] + Hacac (8)K2[Cu(acac)LP] + HLa __ [CuLPZ] + Hacac (9)shows the typical spectral behaviour observed in the range250-420 nm for these substitution reactions, which are fast(t+ ca. 5 min). Two runs were performed with [Cu(aca~)~]~ =5.1 x lo-' rnol dm-3 and 1 : 1 and 1 : 4 [Cu"] : HLa ratios.Inboth experiments and at all six investigated wavelengths (seeExperimental section) the difference between calculated andobserved absorbance figures was less than 4%. The procedureemployed led to values of K , = 0.83 i- 0.01, KZ = 0.10 &0.02, K,,z -- K,K2 =- 0.08 & 0.02, and to a value of 8 rfT 2 forthe coproportionation reaction constant. The excellent fittingobtained for the system described by equations (8) and (9) isa strong indication that the mixed complex is [Cu(acac)Lp] andnot [Cu(acac)L"], even though the spectra of these species maynot be very different.I2 This implies that the expectedpreliminary direct formation of [Cu(acac)La] is followed byfast isomerization to [Cu(acac)LP].A mechanism for this iso-nierization has been proposed already in the nickel(i1) case.IbWe have also investigated the [Cu(acac),]/HLa/[CuL~~]~Hacac system, starting from [CuLP2] and Hacac. Spectrophoto-metric studies (u.v.-visible) show clearly that [CuLp2] reactsrapidly (tm ca. 30 min) with Hacac, but no spectral fittingwas obtained in agreement with the reverse of equations (8)and (9) ([Cu"] = 5.2 x rnol dm-3; [Hacac] = 1-20 xmol dm-3). Then we studied the reaction between [CuLp2]and Hacac under preparative conditions, following it by i.r.spectroscopy. Analysis of the solution after addition ofHacac revealed that a species related to HLa (vN+ 3 460cm-') is immediately liberated from [CuLB2], and i.r. analysis ofthe solid residue left after evaporation indicated that HL",L (see Scheme l), and [Cu(aca~)~] (in similar proportions) arethe products of this evidently very complex reaction.These i.r. and preparative data suggest that the interactionof Hacac with [CuLPZ] cannot be seen simply as giving rise tothe reverse of equations (8) and (9), but as a more complexreacting system.Cyanation of [Cu(aca~)~] : preparative and kinetic aspects.When solutions of [C~(acac)~] ( 5 x rnol dm-3) are made0.6 rnol dm-3 in C2N2, the initial blue colour turns graduallyto green and a medium-strong i.r.band develops at 3 330cm-'. After about 24 h at room temperature, [CuLP2] beginsto separate in high yield.'"When a blue suspension of [Cu(aca~)~] in CHZCIZ (2.0mmol in 20 cm') is made 0.86 rnol dm-3 in C2Nz and stirredvigorously, the i.r.spectrum of the supernatant solution (0.1mm cell) displays a clear parallel development of two bands at1 525 and 1 560 cm-'. These bands are seen also in solutionsof [Cu(acac),] and [CuLp2] respectively; however that at 1 525cm-' cannot be due to [Cu(aca~)~] {its concentration is' buffered' by undissolved [C~(acac)~] for 40 min at ca.20 "C). The colour of the suspension turns gradually to greenand the intensity of the 1 525 and 1 560 cm-I bands beginsto decrease after cu. 45 min.These two observations indicate that under homogeneousphase conditions at {Cu"] = 5 x rnol dm-3 speciescontaining a >C=N-H group develop gradually. Underheterogeneous phase conditions, however, the data are morerevealing and strongly suggest that a species containing bothacac- and acac°C2N2- co-ordinated to CU" forms in solution.This complex is presumably the mixed [Cu(acac)Lp] species,which we have clearly deduced from the equilibration experi-ments discussed above and by the following kinetic evidence.Kinerics of the Cyanation of [Cu(a~ac)~].-The overallstoicheiornetric process (10) occurs in two well separatedconsecutive steps, (11) and (12).This system is complicated[Cu(aca~)~] + 3C2N2 ---t [CuLP2] (10)k l [Cu(acac)J + C2N2 ---t [Cu(acac)LB] (1 1)[Cu(acac)LP] + C2Nz -% [CuLP2] (12)by the occurrence of the coproportionation reaction (9,which is fast ( t , cn. 20 min) compared with processes (11)and (12). A typical spectral change observed upon reactionof C2Nz with [Cu(aca~)~] is shown in Figure 4.It was found most convenient to calculate kl and k2 byprevious determination of the concentration us.time profilesof [Cu(acac),], [Cu(acac)LP], and [CuLP2] (Figure 5). The actualconcentration of each species could be obtained by measuringthe absorbances at various times at three wavelengths {andby knowing that [Cu(aca~)~] + [Cu(acac)LB] + [CuLPl2 =[C~(acac)~l~).The behaviour shown in this and similar studies underdifferent conditions is qualitatively consistent with the pro-posed cyanation sequence and with the coexisting ligand co1222i 1.5J. CHEM. SOC. DALTON TRANS. 1983M mFm 4. Spectral changes upon cyanation of [Cu(aca~)~] by C2Nz ([Cu"] = 5.0 x lo'' mol0.01 cm)[C2N2] = 0.53 mol dm 'j; cell pathlengtht / minFigure 5.Concentration 0s. time profiles of (a) [Cu(aca~)~], (b) [Cu(acac)LB], and (c) [CuLB2] at [C2N2] = 0.53 mol dm-', [Cut'] = 5.0 x 10-mol dm-3proportionation equilibrium. In particular the relativelyshort induction period observed for [CuLB2] is in agreementwith the circumstance that [CuLB2] is formed not only bycyanation of [Cu(acac)L8], but also by fast ligand dispropor-tionation reactions of the mixed complex. Quantitative kineticinformation could be obtained from this type of study byworking with a suitable excess of C2N2 over Cu" and inselected time ranges where the kinetic rate law takes a simpli-fied form. A logarithmic plot of [Cu(acac)J concentration vs.time (conditions of Figure 5 ) exhibits a fairly good linearbehaviour for almost twice t+, thus furnishing the kobs.figurefor the first cyanation process {the same behaviour wasobserved with ten times lower initial [Cu(acac),] = 5 xlo-' moI dm-3}.The kobs. value for the second step was obtained by plottinglog ([CuLB2], - [CuLBZ],) vs. time, which again gives a goodpseudo-first-order plot at reaction times where the first step nolonger interferes.The kobs. value for the second step thus determined can beconsidered accurate, but kobs. for the first step is slightly alteredbecause of the formation of [Cu(aca~)~] from [Cu(acac)LB] (vialigand disproportionation), concomitant with the consumptionof [Cu(a~ac)~] due to CzN2 addition. An approximate estimateof this last effect indicates that the true cyanation rate of thefirst step may be 10% greater than the experimental one.The observed k&s. values for both steps depend linearlyupon C2N2 concentration as shown in Figure 6.The resulting second-order rate constants are kl = 7.4 xdm3 mol-' s-', i.e.kl N 2 k2 if stat-istical factors are considered. In other words, C2N2 exhibitsthe same reactivity towards [Cu(a~ac)~] and [Cu(acac)LP].A final, remarkable result is the effect of the quality of thesolvent on the reaction rate. Use of commercial CH2C12(HCI 0.001%; H20 0.02%) leads to a four-fold increase inreactivity of C2N2 for both stages, with respect to the use ofpurified CH2CIZ.The reported kinetic data for addition of CZNz to [Cu-( a ~ a c ) ~ ] are consistent with the rate law (13).This means thatand k2 = 1.7 x--d[Cu(a~ac)~]/dt = kl[C2Nz][Cu(acac)2] (1 3J. CHEM. soc. DALTON TRANS. 1983 1223ring-opening step is given by the observed fast exchangebetween [C~(acac)~] and [CuLB2] to give [Cu(acac)LB], and bythe comparably fast substitution with protonation reactionbetween [C~(acac)~] and HLa in purified CH2C12. Since it isgenerally acceptedIS that these exchange reactions of p-diketonate complexes proceed through this ring-openingprocess, it seems reasonable that the ' slow ' cyanogen addi-tion to [Cu(aca~)~] should imply this fast preliminary process.AcknowledgementsWe thank Mr. A. Ravazzolo for technical assistance.[CzNd / mol dm-3Figure 6. Dependence of kob. on C2N1 concentration for (a) thefirst and (b) the second reaction stepC2N2 is co-ordinated to [C~(acac)~] in the transition state.Asto the details of the mechanism, this observation implies (i)CzN2 attack on the metal centre, (ii) transfer of C2N2 to theco-ordinated ligand, (iii) rearrangement of the resulting cyano-iminoacetylacetonate ligand from a type La to a type L0 struc-ture. In principle, direct attack of C2N2 on the metal couldgive a five-co-ordinate reactive intermediate [C~(acac)~-(C2N2)],14 which changes rapidly into the cyanoimino-methyl derivative upon insertion of cyanogen into themethine bond, but the effect of the acidity of the medium(and/or water content) strongly suggests that an alternativemechanism could operate.It is known that the ligand ex-change reactions exhibited by some [M(acac)J type com-plexes involve preliminary acid- or water-assisted openingof a co-ordination arm, thus giving rise to a co-ordinatively' unsaturated ' metal complex. The remarkable kinetic effectdue to HCl and H20 in the solvent on the addition of C2N2to [Cu(a~ac)~] strongly suggests that end-on co-ordinationof CZN2 to a three-co-ordinate Cul* centre, rather than to afour-co-ordinate [Cu(aca~)~) moiety, may be the majorprocess.Indirect support for the importance of the fast preliminaryReferences1 (a) Part 2, B. Corain, C. Crotti, A. Del Pra, F. Filira, and G.Zanotti, Inorg. Chem., 1981,20,2044; (b) Part 1, B. Corain, A.Del Pra, F. Filira, and G. Zanotti, ibid., 1979, 18, 3523.2 W. Traube, Ber., 1898'31, 2938.3 M. Basato, B. Corain, A. Marcomini, G. Valle, and G. Zanotti,4 B. Corain, M. Basato, and G. Bontempelli, Anal. Chem., 1981,5 A. C. T. North, D. C. Phillips, and F. S . Mathews, Acta6 R. Eisenberg and J. A. Ibers, Inorg. Chem., 1965,4, 773.7 ' International Tables for X-Ray Crystallography,' Kynoch8 G. Sheldrick, SHELX 76 System of Computing Programs,9 J. W. Carmichael, L. K. Steinauf, R. L. Belford, J. Chem. Phys.,J . Organomet. Chem., submitted for publication.53, 124.Crystallogr., Sect. A , 1968, 24, 351.Press, Birmingham, 1974, vol. 4.University of Cambridge, 1976.1965,43, 3959.10 G. A. Barclay and A. Cooper, J. Chem. SOC., 1965,3746.11 N. A. Bailey, D. E. Fenton, M. V. Franklin, and M. Hall,J. Chem. SOC., Dalton Trans., 1980, 984; T. S. Moore andM. W. Young, J. Chem. SOC., 1932, 2694; M. F. Farona,D. C. Perry, and H. A. Kuska, Inorg. Chem., 1968, 7, 2415;L. F. Nicholas and W. R. Walker, Aust. J. Chem., 1970, 23,1135.12 A. M. Fatta and R. L. Lintvedt, Znorg. Chem., 1971, 10, 478.13 R. P. Eckberg, J. H. Nelson, J. W. Kenney, P. N. Howells, andR. A. Henry, Znorg. Chem., 1977, 16, 3128 and refs. therein.14 D. P. Graddon, Coord. Chem. Rev., 1969,4, 1.15 A. Watanabe, H. Kido, and K. Saito, Inorg. Chem., 1981, 20,1107, and refs. therein.Received 17th May 1982 ; Paper 218 1

ISSN:1477-9226    

DOI:10.1039/DT9830001217

出版商:RSC    

年代:1983

数据来源: RSC