摘要:
J . CHEM. SOC. DALTON TRANS. 1995 2323Heteroleptic Tripodal Complexes of Copper( 11): Towards aSynthetic Model for the Active Site in Galactose OxidasetHarry Adams, Neil A. Bailey, Cecilia 0. Rodriguez de Barbarin, David E. Fenton"and Qing-Yu HeDepartment of Chemistry* Dainton Building, The University of Sheffield, Sheffield S3 7HF, UKA series of copper(1r) complexes derived from tripodal ligands (HL) bearing pyridyl and phenolic armshave been synthesized and characterized. The molecular structures of complexes [CuL4(0,CMe)]-H,0and [CuL4( SCN)]*MeCO,Et {HL4 = 2-bis[2- (2-pyridyl)ethyl]aminomethyl-4-nitrophenol} were deter-mined by X-ray diffraction; the complexes exist as neutral, mononuclear species in the solid state. Theco-ordination geometry around the copper atom in each is a distorted square-based pyramid (z = 0.08 and0.1 1 ) where one pyridyl nitrogen occupies the axial position (Cu-N,, 2.27 and 2.20 A).Three liganddonor atoms comprising the square plane are unchanged but the fourth ligand is an exogenous donoratom from MeC0,- or SCN- respectively. Reference is made to the relationship of the structures tothat found at the copper(1i) centre at the active site of galactose oxidase.Galactose oxidase (GOase) is an extracellular metalloenzymesecreted by the fungus Dactylium dendroides. It catalyses thestereospecific oxidation of a broad range of primary alcoholsubstrates and possesses a unique mononuclear copper sitewhich catalyses a two-electron-transfer reaction during theoxidation of primary alcohols to the correspondingaldehydes.' The active site in GOase has been shown, by X-ray crystal structural analysis at 1.7 8, res~lution,~ to be quitedistinct from those in copper-containing enzymes such asascorbate oxidase and superoxide dismutase.At pH 4.5,consistent with spectroscopic features, the copper has a square-pyramidal co-ordination environment with an almost perfectsquare plane consisting of two histidine nitrogen atoms (His-496 and His-581), a tyrosine phenoxide oxygen (Tyr-272), andan oxygen atom from an exogenous acetate anion. At pH 7.0the copper site has essentially the same structure but the acetatehas been replaced by a water molecule; at a distance of 2.8 8,from the metal, this molecule is probably not co-ordinated sothat the site is best described as distorted tetrahedral with onlythe four protein residues attached to the metal.Until recentlyonly a limited number of investigations have consideredcomplexes which might structurally model the metal site inG 0 a ~ e . ~ Uma et have reported a series of mononuclearcopper(i1) complexes derived from tripodal ligands bearingphenolate, benzimidazolate and/or pyridine pendants; the X-ray structural analysis of one of their complexes revealed thepresence of an axial copper(i1)-phenolate bond which wasconsidered to mimic the axial copper(1r)-phenolate bond in theenzyme. In parallel with studies concerning the physical andchemical analysis of GOase, Whittaker et a/.* investigatedthe structures of several monocopper(i1) complexes derivedfrom the simple polyamine N,N,N',N",N"-pentamethyldiethyl-enetriamine and p-cresol, 2-methylsulfanyl- or 2-methylsulfinyl-p-cresol in order to gain insight into the co-ordinationchemistry associated with the assignment of the protein radicalto a novel tyrosine-cysteine covalent cross-link s t r ~ c t u r e .~We have used a series of tripodal compounds bearing pyridyland phenolic arms in a programme designed to search for smallmolecular models for the GOase site.' In the absence of anexogenous donor or in the presence of only weakly co-t Supplementury dutu uvuiluble: see Instructions for Authors, J . Cliern.Soc., Dalton Truns., 1995, Issue I , pp. xxv-xxx.R'ordinating anions, such as perchlorate, these compounds formdimeric copper(r1) complexes in which two copper(r1) atomsshare two phenolic oxygens from two ligands.In order toinhibit dimer formation and thus prepare the relatedmononuclear copper( 11) complexes, more strongly co-ordinatinganions than perchlorate and tetrafluoroborate have beenintroduced into the copper(n) co-ordination sphere. Forexample the acetate anion has been used in order to simulatethe basal interaction found at the copper(r1) site in GOase.ExperimentalReagents and solvents used were of commercial reagent quality.Purification of the pro-ligands was effected by flashchromatography with silica gel (40-63 pm). l o The identity andpurity of each was judged by TLC, 'H NMR, and massspectrometry. All elemental analyses were carried out by theUniversity of Sheffield Microanalytical Service.Infraredspectra were recorded as KBr discs using a Perkin-Elmer 17 I0IR Fourier-transform spectrophotometer (4000400 cm-'),electronic absorption spectra using a Philips PU8720 UVjVISscanning spectrophotometer operating in the range 220-880nm, 'H NMR spectra at 220 MHz on a Perkin-Elmer R34spectrometer, 13C NMR spectra (62.9 MHz) using a BrukerAM-250 spectrometer and positive-ion fast atom bombardment(FAB) mass spectra on a Kratos MS 80 spectrometer using a3-nitrobenzyl alcohol matrix unless otherwise stated2324 J. CHEM. SOC. DALTON TRANS. 1995CAUTlO N : Although no problems were encountered duringthe preparation of the perchlorate salts described below,suitable care and precautions should be taken when handlingsuch potentially hazardous compounds.Pro-ligand Synthesis.-Di[2-(2-pyridyl)ethyl]amine, and o-acetoxybenzyl bromide were synthesised according to literatureprocedures.' 9 l4[2-(2-Pyridyl)ethyl](2-pyrzdylmethyl)amine. 5 mol dmSodium hydroxide (4 cm3, 20 mmol) was added to(chloromethy1)pyridine hydrochloride (3.3 g, 20 mmol)dissolved in ice-water (15 cm3). The ensuing red solution wasadded dropwise to a stirred ice-water solution containing2-(2-aminoethyl)pyridine (2.45 g, 20 mmol). The clear yellowsolution was allowed to warm to 6OoC, changing to orange.5 mol dm-, Sodium hydroxide (4 cm3) was added in portionsduring 1 d. After cooling, the resultant mixture was extractedwith dichloromethane (2 x 50 cm3).The extracted solutionwas dried with MgS04, and evaporated to remove the solvent.A red-brown crude oil was recovered; vacuum distillation of theoil yielded 2.2 g of pure product (51.6%). NMR (CDCI,): 'H, 62.22 (s, 1 H, NH), 3.00 [m, 4 H, (CH,),], 3.85 (s, 2 H, CH,),7.00-7.55 (m, 6 H, aryl) and 8.45 (d, 2 H, pyridine); I3C, 6 37.1,49.1, 54.8, 121.2, 121.6, 121.8, 123.4, 136.4, 136.6, 149.2, 149.3,159.9 and 160.2.The pro-ligands HL' and HL2 were prepared by the methodof Karlin et al.; ' HL3 and HL4 were prepared in a similar wayand a representative procedure is described. A tetrahydrofuran( 100 cm3) solution containing [2-(2-pyridyl)ethyl](2-pyridyl-methyl)amine (2.13 g, 10 mmol), or di[2-(2-pyridyl)ethyl]amine(2.27 g), and triethylamine (20 mmol, 2.02 g) was stirred in anice-bath. To it, 2-chloromethyl-4-nitrophenol(10 mmol, 1.88 g)in tetrahydrofuran (50 cm3) was added dropwise while stirringthe solution rapidly.The solution was then allowed to warm toroom temperature with some accompanying precipitation oftriethylamine hydrochloride. The mixture was then heated toreflux for 2 h. After cooling, the suspension was filtered and thesolvent evaporated. The resultant crude oil was chromato-graphed with CH,CI,-MeOH (9: 1) to generate the pure pro-ligands HL3 (2.45 g, 67.2%) and HL4 (2.74 g, 72.3%).Spectroscopic data for the new pro-ligands: HL', 'H NMR(CDCI,) 6 2.95 [m, 4 H, (CH,),], 3.80 (d, 2 H, CH,), 6.70-7.60(m, 10 H, aryl), 8.45 and 8.55 (2 d, 2 H, pyridine); I3C NMR(CDCI,) 6 35.2, 53.6, 57.4, 59.3, 116.3, 119.1, 121.4, 122.2,122.3, 122.8, 123.2, 128.9, 129.3, 136.5, 136.8, 149.1, 149.2,157.6, 158.2 and 159.6; mass spectrum: m/z = 320 ( M ' , loo),227 (90), 212 (45) and 121 (74%); HL3, 'H NMR (CDCI,) 62.95 [m, 4 H, (CH,),], 3.75 (s, 2 H, CH,), 3.85 (s, 2 H, CH,),6.70-8.05 (m, 9 H, aryl), 8.35 and 8.45 (2 d, 2 H, pyridine); 13CNMR (CDCI,) 6 35.2, 53.3, 56.5, 58.6, 116.8, 121.5, 122.6,123.0, 123.2, 125.4, 125.8, 136.5, 137.0, 139.8, 148.9, 149.2,157.0, 159.3 and 164.3; mass spectrum: m/z = 365 ( M ' , 80),272 (95), 212 (90) and 121 (100%); HL4, 'H NMR (CDCI,) 63.05 [m, 8 H, (CH,),], 3.90 (s, 2 H, CH,), 6.75-8.05 (m, 9 H,aryl), 8.45 (2 d, 2 H, pyridine) and 9.90 (s, 1 H, OH); I3C NMR(CDCI,) 6 34.6, 53.0, 57.3, 116.5, 121.6, 122.1, 123.3, 124.9,125.3, 136.6, 140.0, 149.4, 158.9 and 164.5; mass spectrum:m/z = 379 ( M ' , loo), 286 (78), 274 (45), 228 (49), 114 (85), 106(40) and 94 (1 0%).Metal Complexation Reactions.-[( CuL ') ,] [C104],-H,0 1.The salt Cu(C104),~6H,0 (0.37 g, 1 mmol) in methanol (4 cm3)was added to a methanolic solution containing pro-ligand HL'(1 mmol, 25 cm3). Triethylamine (1 mmol) was added and theclear green solution heated to reflux for 2 h. On cooling, themixture was filtered to remove residual solids. The filtrate wasallowed to stand at room temperature for a few days duringwhich time a green precipitate developed. The solid wasrecrystallized from MeOH-MeCN. Yield 0.27 g (55.8%).[CuL'(O,CCMe,)]-H,O 2.The compound Cu(O,CCMe,),(0.27 g, 1 mmol), in methanol (4 cm3) was added to amethanolic solution (50 cm3) containing pro-ligand HL' (0.32g, 1 mmol); triethylamine (1 mmol) was added and the cleargreen solution was heated to reflux for 1 h. The resultantmixture was allowed to stand at room temperature for severaldays and then the solvent was removed in uacuo. The residuewas dissolved in dichloromethane (5 cm3), then diethyl ether( ~ 2 0 cm3) was added dropwise. The solution was allowed tostand at -20 "C overnight and blue crystals were collected(0.31 g, 64.2%).[(CuL2),][C1O4],~H,O 3. Pro-ligand HL2 (0.34 g, 1 mmol)and triethylamine (1 mmol) were dissolved in methanol (30cm3). The salt Cu(CI04),~6H,0 (0.37 g, 1 mmol) in methanol ( 5cm3) was added to the yellow solution which then turnedbrown.The mixture was heated at reflux for 4 h. After cooling,the resulting solution was filtered to remove residual solids.Dark green crystals were obtained either by leaving the filtrateto stand at room temperature for 3 d or by using diethyl ethervapour-diffusion techniques. Yield 0.36 g (72.3%).[(CuL2),][CF,S0,], 4. A solution of Cu(O,SCF,), (1mmol, 0.36 g) in ethanol ( 5 cm3) was added to an ethanolicsolution (25 cm3) containing pro-ligand HL2 (1 mmol) andtriethylamine (1 mmol). The dark brown solution was heated toreflux for 1 h. On cooling, some solid precipitated and wasfiltered off. A further period of standing gave a black-browncrystalline solid (0.38 g, 69.4%).[CuL2(CI)]-2H20 5 and [CuL2(N,)]-H,0 6.These com-plexes were synthesized by the literature procedure.[(CuL3),][CI04],-2H,0 7. The salt Cu(CI04),*6H,0 (1mmol) in methanol ( 5 cm3) was added to a methanolic solution(30 cm3) containing pro-ligand HL3 (1 mmol, 0.36 g). Theyellow solution turned to green and gave a green precipitate onaddition of triethylamine (1 mmol). The suspension was heatedto reflux for 1 h. After cooling, the resulting mixture was filteredto generate a green powder which was then recrystallized fromMeCN-MeOH (1 : 4). Yield 0.23 g (42.6%).[(CuL3),][BF4],-2H,0 8. Triethylamine (0.5 mmol) wasadded to a green methanolic solution (30 cm3) containing pro-ligand HL3 (1 mmol) and Cu(BF,),-H,O (1 mmol, 0.12 8).There was an immediate green precipitation which redissolvedwhen the suspension was heated to reflux.After refluxing for 2h the resulting solution was filtered and the filtrate allowed tostand at room temperature overnight. A blue-green crystallinesolid was collected (0.15 g, 55%).[CuL3(CI)]*H20 9. Copper(r1) chloride (0.14 g, 1 mmol) inMeOH ( 5 cm3) was added to a methanolic solution (30 cm3)containing pro-ligand HL3 (1 mmol). Triethylamine (1 mmol)was added and the mixture heated at reflux for 1 h. Aftercooling, the resulting mixture was filtered to remove residualsolids. The filtrate was then evaporated to dryness. Methanol ( 5cm3) was added to dissolve the residue and then ethyl acetate(30 cm3). This solution was allowed to stand at roomtemperature overnight.A green crystalline solid was collected,(0.34 g, 71.4%).[CuL3(0,CCMe,)]*H,0 10. This complex was synthesizedby a procedure analogous to that of 9 using Cu(O,CCMe,), (1mmol) instead of CuCI,. The resultant crude product wasrecrystallized from methanokthyl acetate (1 : 30), giving green-blue crystals (0.27 g, 53%).[(CuL4),][CIO4],~2H2O 11. The salt Cu(C1O4),~6H2O (1.5mmol) in MeOH ( 5 cm3) was added to a methanolic solution(40 cm3) containing pro-ligand HL4 (0.38 g, 1 mmol) andtriethylamine (1.5 mmol). The mixture was heated at reflux for1.5 h. After cooling, the resulting solution was concentrated to20 cm3 and allowed to stand at I "C overnight. The yellow-green solid generated was filtered off and recrystallized usingdiethyl ether vapour diffusion in its MeOH-MeCN (4: 1)solution to give small green crystals (0.41 g, 49.2%).[(CuL4),][BF,],-2H,0 12.Triethylamine (1 mmol) wasadded to a methanolic solution (35 cm3) containing pro-ligandHL4 (1 mmol) and Cu(BF,),-H,O (1 mmol). The mixture wasstirred at room temperature for 4 h. The resulting suspensioJ. CHEM. SOC. DALTON TRANS. 1995 2325was filtered to give a fresh green powder, which wasrecrystallized from MeCN-MeOH (1 : 6). Yield 0.40 g (71%).[CuL4(Cl)]*2H20 13. Copper(I1) chloride (1.5 mmol) inmethanol ( 5 cm3) was added to a methanolic solution (25 cm3)containing pro-ligand HL4 (1 mmol, 0.57 g) and triethylamine(1 mmol). A green precipitate emerged immediately and themixture was heated at reflux with stirring for 1 h.After coolingthe solid was filtered off and recrystallized from MeOH-MeCN( 1 : 5). Yield 0.38 g (49%).[CuL4(02CMe)].H20 14. A solution of Cu(O,CMe),-H,O( I mmol, 0.20 g) in hot EtOH (30 cm3) was added dropwise to asolution of pro-ligand HL4 (1 mmol, 0.38 g) in ethanol (30 cm3).The mixture was adjusted to pH z 8 with triethylamine thenheated to reflux for 2 h. After cooling, the resulting solution wasfiltered to remove residual solid impurity. The filtrate wasevaporated to near dryness and MeOH ( 5 cm3) was added todissolve the residue. Ethyl acetate (30 cm3) was added and thesolution was allowed to stand at room temperature for a fewdays until blue crystals developed (0.42 g, 8 1%).[CuL4(SCN)]-MeC02Et 15. Method A . Complex 11 (0.58 g,0.5 mmol) was dissolved in MeCN-MeOH (2: 1, 20 cm3).Sodium thiocyanate (1 mmol) in MeOH ( 5 cm3) was added andthe solution was then heated to reflux for 1 h.After cooling thesolution was concentrated to about 5 cm3 and ethyl acetate (25cm3) was added. Blue-green crystals were collected after leavingthe solution to stand at room temperature overnight (0.43 g,74%).Method B. Complex 14 (0.26 g, 0.5 mmol) was dissolved inmethanol (20 cm3). To the green solution was added NaSCN(0.5 mmol) in MeOH ( 5 cm3). The solution was heated at refluxfor 1 h during which time it changed to brown-green. Aftercooling the resulting solution was evaporated to near dryness.Methanol ( 5 cm3) was added to dissolve the residue then ethylacetate (20 cm3). The solution was allowed to stand overnight atroom temperature and the resulting crystals collected (0.23 g,All the complexes isolated were dried under vacuum oversilica gel and MgSO, and their elemental analyses are recordedin Table I .77%).Cr.vstullogru~h.y.-Crystal data and experimental conditionsfor complexes 14 and 15 are listed in Table 8.Complrs 14.A crystal having dimensions of0.60 x 0.55 x 0.40 mm was used to collect X-ray data at roomtemperature in the range 6.5 < 20 < 50.0" on a Stoe Stadi-2diffractometer by the o-scan method (0 d h d 11,O d k d 1 1,-29 < 1 < 28). The 4330 measured reflections yielded 3844unique and 3240 independent reflections with 1 Fl/o( 1 F1) > 4.0;all data were corrected for Lorentz and polarization effects butnot for absorption.The structure was solved using thePatterson heavy-atom method, which revealed the position ofthe copper atom. The remaining atoms were located by Fourier-difference maps. Refinement was by full-matrix least squares onF 2 . Hydrogen atoms were included in calculated positionsexcept for those of the water molecule which were found byFourier-difference map, and refined in riding mode withisotropic thermal vibrational parameters related to those of thesupporting atoms. Refinement converged at a final R (observeddata) = 0.0466 (wR, = 0. I227 for all 3844 unique reflections,307 parameters, mean and maximum 6/0 0.000, O.OOO), withallowance for the thermal anisotropy of all non-hydrogenatoms. Minimum and maximum final electron density -0.46and 0.57 e 8, '.A weighting scheme w = l/[02(Fo2) + (0.0662P)' + 2.66 P] where P = (Fo2 + 2Fc2)/3 was used in the latterstages of refinement. Complex scattering factors were takenfrom the program package SHELXTL 93 l 6 as implemented ona Viglen 486dx computer.Complex 15. A crystal having dimensions of0.75 x 0.60 x 0.10 mm was used to collect X-ray data at roomtemperature in the range 3.5 < 20 < 45.0" on a SiemensP4 diffractometer by the o-scan method (- I < h < 15,Table 1in parenthesesElemental analyses for the complexes with calculated valuesAnalysis (%)Compound1 [(CUL ),ICClO,I2*H2O4 C(CuL2),lCCF3S03128 [(cuL3)21 W 4 I 2-2H202 [CuL'(O,CCMe,)].H,O3 [(CUL'), [C104] 2*H,O7 [(CUL~),][CIO,]~-~H~O9 [CuL3(Cl)]-H,O10 [CuL3(0,CCMe3)]-H201 1 [ ( CuL4)2] [CIO,] ,-2H,O12 [(CUL~),][BF,],*~H,O13 [CuL4(Cl)]-2H,O14 [CuL4(0,CMe)].H2015 [ CuL4( SCN)].MeCO,EtC48.9 (49.0)59.8 (59.9)49.9 (50.0)48.7 (48.8)44.2 (44.1)45.4 (45.2)49.9 (50.0)54.5 (55.0)45.4 (45.2)46.5 (46.2)49.0 (49.2)52.9 (53.3)52.9 (53.2)H N4.4 (4.3) 8.8 (8.6)6.4 (6.2) 8.2 (8.4)4.4 (4.6) 8.2 (8.3)4.1 (4.1) 7.5 (7.7)4.1 (3.9) 10.1 (10.3)3.8 (4.0) 10.6 (10.5)4.3 (4.4) 1 1.6 (1 1.7)5.6 (5.5) 10.1 (10.3)4.2 (4.1) 9.9 (10.0)4.1 (4.2) 10.4 (10.3)4.9 (4.9) 10.5 (10.9)5.1 (5.1) 10.7 (10.8)4.8 (5.0) 12.1 (11.9)- 1 < k d 8, -27 < 1 < 26).The 4971 measured reflectionsyielded 3597 unique and 2752 independent reflections withIFl/o(IFI) > 4.0; all data were corrected for Lorentz andpolarization effects and for absorption based upon semiempiri-cal Y scans (maximum and minimum transmission coefficients0.991 and 0.670).The structure was solved by direct methodsand refined by full-matrix least squares on F 2 . Hydrogen atomswere included in calculated positions and refined in riding modewith isotropic thermal vibrational parameters related to thoseof the supporting atoms. Refinement converged at a final R(observed data) = 0.0702 (wR2 = 0.2081 for all 3597 uniquedata, 343 parameters, mean and maximum S/o 0.009, 0.165),with allowance for the thermal anisotropy of all non-hydrogenatoms; the solvent molecule atoms were restrained to havecommon anisotropic components within 0.025 standarddeviations.Minimum and maximum final electron density- 1.07 and 0.79 e A-3. A weighting scheme w = 1/[o2(FO2) +(0.1500 P)2] where P = (Fo2 + 2Fc2)/3 was used in the latterstages of refinement. The source of complex scattering factorswas as for complex 14.Additional material available from the Cambridge Crystallo-graphic Data Centre comprises H-atom coordinates, thermalparameters and remaining bond lengths and angles.Results and DiscussionCognisant that the copper(n) atom at the active centre of GOaseis present in a five-co-ordinated square-pyramidal environment,phenol-bearing tripodal ligands that result in the formation offive-co-ordinate complexes of copper(r1) with the donor atomsof the ligands occupying four of the five co-ordination siteswere employed in this study.Tripodal ligands capable offorming five-membered chelate rings have been shown toimpose a trigonal-bipyramidal geometry at copper(1r) with afifth ligand occupying the apical position trans to the tertiaryamino nitrogen atom of the tripod. -20 Sterically more flexibletripodal ligands that can form one or more six-memberedchelate rings favour the generation of a square-pyramidalgeometry where the fifth ligand occupies a basal position of thepyramid. 6.19.2 1-24 Consequently a series of tripodal ligandscapable of forming two or three six-membered chelate rings atthe metal and bearing a phenolic moiety, to resemble the aminoacid tyrosine, were employed in our investigations.In the presence of the weak base triethylamine, the phenolicgroup in the pro-ligand (HL) is readily deprotonated to formfive-co-ordinate copper(ir) complexes.If copper(I1) salts derivedfrom weakly co-ordinating anions such as perchlorate, tetra-fluoroborate or trifluoromethanesulfonate were used in thesyntheses the complexes formed tended to be dimers in whichtwo copper(I1) atoms share the phenolate oxygens from tw2326 J. CHEM. SOC. DALTON TRANS. 1995-~Table 2 Positive-ion FAB mass spectral assignments for complexesCompound(a) L = L'1 "2b(b) L = L23"4'5b6 b(c) L = L37 bg b9b10( d ) L = L41112"13'1415Anion (X-) [Cu,L,(X)]' [Cu,L, - HI+ [LCu,O - H]+ [Cu,L - 2H]+ClO,- 862 763Me,CCO,- 866 763C104- 876c1- 827N3 - 834CF3S03- 939c10, - 953BF4- 939c1- 890Me,CCO,C104- 980c1-MeCO, -SCN- 940BF4- 95485585585588 188245947550652044646046049 149 1505505[CUL] +38238 1395395395395427427427426440441440440440Where no value is given no peak was apparent over the background noise." Glycerol matrix.alcohol-trifluoroacetic acid matrix.3-Nitrobenzyl alcohol matrix. 3-Nitrobenzylligands. Addition of p-cresol, phenol or imidazole to the abovereactions followed by adjustment to pH z 9.0 using 3 mol dm-3NaOH to induce deprotonation of these ligands still gave onlythe dimeric products. Mononuclear copper(r1) complexes can beobtained in the presence of more strongly co-ordinating anionssuch as MeC0,-, CI-, Me,CCO,-, N,- and SCN-; evensimple addition of the sodium salts of the latter pair of anions toa solution containing the appropriate dimer leads to amonomeric product. When acetate was introduced into the co-ordination sphere of copper(I1) it was found to occupy a basalsite of the square-pyramidal environment (Fig. 1) so deriving astructural analogue for the basal plane of the copper(I1) site inGOase.Spectroscopic Characterization.-The principal peaks in thepositive-ion fast-atom bombardment (FAB) mass spectra of thecomplexes are reported in Table 2.The solvent molecules in thecomplexes are readily lost and not observed. For compounds 3,14 and 15 for which crystal structures have been solved thefollowing pattern emerged.For the dinuclear complex 3 amolecular ion peak was found at m/z 876, [Cu,L2,(C104)]+,together with a mononuclear fragment at m/z 395, [CuL2]',and two other dinuclear peaks at m/z 475 and 460 assigned to[L2Cu,0 - HI+ and [L2Cu, - 2H]+ respectively. Themononuclear complex 14 showed a parent peak at m/z 440assigned to [CuL"]' and with no evidence for dinuclearfragments. Complex 15 which was shown to have a monomericstructure gave peaks corresponding to both di- (m/z = 940,[CU~L~~(SCN)]+} and mono-nuclear species (mi. = 440[CuL"] +). Compounds 10 and 13 follow the same pattern as for14 but all of the other complexes give evidence of peaks, oftenweak, attributable to dinuclear complexes. It is thereforedifficult to assign structures with total certainty on the basis ofthe FAB mass spectrum.This propensity for higher aggregationin complexes in which there is a pathway for dimerization hasbeen noted previously.In the IR spectra (KBr disc) of the dimeric complexes distinctabsorptions corresponding to the unco-ordinated anions areobserved as strong bands at 1083 cm-' for BF,-, 1093 and 623Table 3 Carboxylate modes vasym and vsym in the IR spectra" forcomplexes 2,lO and 14Complex R in RC0,- vasym vsym2 Me,C 1562b 140010 Me,C 1568b 139614 Me 1562b 1387" In cm-l (KBr disc). Partly overlapping with ligand bands.cm for C104-, and 1257, 1150, 1030 and 637 cm-' forCF3S03-. For complexes in which the carboxylate is co-ordinated the antisymmetric and symmetric stretching modes ofthe carboxylate occur ca.1560 and 1400 cm-' (see Table 3),26the antisymmetric bands are partly overlapped by ligand bands.For complex 15 the strong band observed at 2093 cm-' isassigned to co-ordinated SCN - and the medium-intensityabsorption at 1736 cm-' is assigned to the ethyl acetate in themolecule. A band at 2041 cm-' for compound 6 is attributed toco-ordinated azide.'The electronic spectral data for the present complexes aresummarized in Table 4. The intense absorbance bandsoccurring in the range 370460 nm are assigned, by comparisonwith the spectral features of complexes of related ligands,'.' toequatorial 0 ~ --+Cufl charge-transfer transitions. For thecomplexes derived from HL3 and HL4 this charge-transfertransition shifts to higher energy (450 to 400 nm) and intensifiessignificantly; this is accounted for by the presence of thestrongly electron-withdrawing NOz group.The band at 405 nm( E = 2310 dm3 mol-' cm-') of complex 6 is ascribed to aN, -+CuI1 charge-transfer transition. ' The position of theligand-field bands suggests that in solution the Cu" atomsin the complexes, with the exception of 1 and 13, have similarsquare-pyramidal geometries. 7 * ' Complexes 1 and 13display lower-energy bands suggesting that changes haveoccurred in the geometry around copper(r1) and indicatingthe presence of a more trigonal-bipyramidal element ins ~ l u t i o n . ~ J. CHEM. soc'. DALTON TRANS. 1995 2327Table 4 Electronic spectra (hjnm, &/dm3 mol cm-' in parentheses) for the complexes in MeCNCompound1'2 '3'4'5'6 ''7'8'9101112'131415Ligand based a257 (12 600)287 (6 400)"253 (1 2 900)300 (4 300)d263 (13 000)262 (10 200)260 (1 1 200)240 (1 1 400)257 (13 200)256 ( 15 500)257 (17 100)257 (1 2 000)260 (14 600)258 (13 200)257 (7 800)260 ( I 1 000)259.2 ( 1 2 082)Charge transfer'405 (2 310)401 (25 800)400 (28 200)400 (30 000)404 (23 500)374 (21 600)374 (1 9 000)378 ( I 5 300)395 (19 000)385.8 (18 885)Ligand field438 (600) 780 (140)460 (400) 670 ( 1 10)439 (4 000) 660 (365)439 (3 150) 660 (350)440 (1 940) 670 (220)465 (1 380) 650 (260)655 (1 75)640 (165)680 (210)645 (140)495 (1 480) 675 (190)680 ( 150)760 (l60)/675 (320)665 (225)'' z I .O x 10 mol dm '.z 1.5 x 10 rnol dm-3. ' Concentrations were calculated based on the monomer. Shoulder. Data taken from ref. 15.HCONMez- MeCN ( 1 : 1) medium.Table 5 Selected bond lengths (A) and angles (") for complex 14 with estimated standard deviations (e.s.d.s)CU-O( 4)cu-O( 1 )CU-N( 4)Cu-N( 3)Cu-N( 1 )C u . - . 0 ( 5 )N( 1 )-C( 1 1N( 1 )-C( 5 )N( 2)-O( 3 )N( 2 )-O( 2 )O( 4)-Cu-O( 1 )0(4)-Cu-N(4)O( 1 )-Cu-N( 4)0(4)-Cu-N( 3)O( I )-Cu-N( 3 )N( 4)-Cu-N( 3 )0(4)-Cu-N( 1 )O( I tCu-N( 1 )N(4)-Cu-N( 1 )N(3)-Cu-N( I jC( 1 )-N( 1 )-C( 5 )C( I )-N( 1 )-CUC( 5)-N( 1 )-CUO( 3 )-N( 2)-O( 3 )1.970( 2)1.982( 3)2.046( 3)3.085(3)9.265(3)2.7 1 3( 2)1.338(5)I .340( 5 )1.227(4)1.230(4)85.53( 10)88.12(11)171.92( 1 1 )l67.38( 1 1 )93.16( 10)9 1.93 12)98.76( 12)90.31( 12)95.60( 13)93.79( 12)1 18.2(4)1 19.3 3)122.5(3)122.1(3)N(2)-C( 1 1 )N( 3)-C(7)N(3)-C( 15)N( 3)-C( 14)N(4)-C( 17)N(4)-C(21)O( 1)-C(8)0(4)-C(22)0(5>-C(22)C( 1 FC(2)C(7)-N(3)-C( 15)C( 7)-N( 3)-C( 14)C( 15)-N(3)-C( 14C(7)-N(3)-CuC( I 5)-N( ~)-CUC( 14)-N( ~)-CUC( 1 7)-N( 4)-C( 2 1C( 17)-N(4)-CuC(2 I)-N(4)-CuC( 8)-0( 1 )-cuC(22)-0( 4)-cuN( 1 )-C( 1 )-C( 2)C( 1 )-C(2)-C(3)C(4)-C(3)-C(2)0(3)-N(2)-C( 1 1 ) 119.0(3) C(3FC(4)-C(5)0(2)-N(2)-C( 1 1 ) 118.9(3)1.443( 5 )1.493(4)1.494(4)1.507(4)1.341(5)1.358(5)1.305(4)1.285(5)1.233(5)1.372(7)109.5( 3)109.0( 3)105.8(3)1 1 1.32)11 3.8(2)107.1(2)12 1.4(2)1 19.4( 3)129.6(2)107.3(2)l23.2(5)118.3(5)I19.5(5)119.0(5)119.0(3)C(2HJ3)C(3tC(4)C(4kC(5)C(5kC(6)C(6)-C(7)C(8 FC(9)C(8)-C(l 3)C(9)-C( 10)C( lO)-C( 1 I )C( I 1 )-C( 1 2)N( 1)-C( 5)-C(4)N( 1 )-C( 5)-C(6)C(4)-C(5)-C(6)C(5)-C(6)-C(7)O( 1 )-C( 8)-C( I 3)C(9)-C(S)-C( 13)C( 10kC(9)-C(8)C(9)-C( 10)-C( 1 1 )C( 1 2)-C( 1 1 )-C( 10)C( 1 3)-C( 12)-C( 1 1 )C( 12)-C( 13)-C(8)N( 3)-C( 7)-C(6)O( 1 )-C( 8)-C(9)C( 12)-C( 1 I)-N(2)C( 1 0)-C( 1 1 )-N(2)1.376(8)1 .370( 7)1.390(6)1 .506( 6)1.53 1( 5 )1.412(5)1.424( 5 )1.380( 5 )1.397( 5 )I .390( 5 )1 2 1.7(4)1 16.7( 3)1 2 1 .3 4)1 I3.3(3)1 13.7(3)120.6(3)121.0(3)118.4(3)121.8(4)118.5(4)12 1.4(3)118.8(3)119.8(3)120.2(3)119.6(3)C( 12)-C( 13)C( 1 3)-C( 14)C( 15)-C( 16)C( 16)-C( 17)C( 1 7)-C( 18)C( 1 8)-C( 19)C( 19)-c(20)C(20)-C(21)C(22)-C( 23)C( 12)-C( 1 3)-C( 14)C(8)-C( 13)-C( 14)C( 13)-C( 14)-N(3)N(3)-C( 15)-C( 16)C( 17)-C( 16)-C( 1 5 )N(4)-C( 17)-C( 18)N(4)-C( I7)-C( 16)C( lS)-C( 17)-C( 16)C( 17)-C( 18)-C( I 9)C(20)-C( 19)-C( 18)C( 19)-C( 20)-C( 2 I )N(4)-C(21)-C(20)O( 5)-C(22)-0( 4)0(5)-C( 22)-C( 23)0(4)-C(22)-C(23)1.388(5)1.494( 5 )1.519(5)1.499( 5 )1.380(5)1.390(7)1 .367( 7)1.377(6)1.517(5)119.1(3)12 1.0(3)116.0(3)114.0(3)1 10.4(3)I 15.7(3)122.2(4)1 18.8(4)119.2(4)11 9.8(4)I2 I .2(4)123.5(4)120.7(4)I 15.8(4)12 1.9(4)Structures qf' tlir Complexus-The crystal structure ofcomplex 3 has been reported previously.' The complex is adimer in the solid state; the molecular dication is centrosym-metric and comprises two related copper(r1) ions which areasymmetrically bridged by a pair of phenolic oxygen atomsfrom the two symmetry-equivalent tetradentate ligands.The molecular structures of complexes 14 and 15 are depictedin Figs.1 and 2 respectively. The atomic positional parametersare given, together with their standard deviations, in Tables 9and 10. Selected bond lengths and bond angles, with standarddeviations in parentheses, are presented in Tables 5 and 6.Tn the crystal structure of complex 14 the asymmetric unitcomprises one mononuclear copper(1r) complex molecule andone water molecule.The copper atom is bonded to the fourheteroatoms provided by the anionic ligand L4 and to theacetate anion in an approximately square-pyramidal co-ordination environment, in which atoms O(l), N(3), N(4) andO(4) make up the basal plane [root mean square (r.m.s.)deviation 0.061 A; with 0(1) -0.062, N(3) 0.056, N(4) -0.060,O(4) 0.066, N(1) -2.422 8, out of planarity with a very smallT = 0.076.28 The copper(r1) ion lies 0.161 a above this basalplane in the direction of N(l) and axially co-ordinates to thispyridine nitrogen [Cu-N(1) 2.265 A]. The acetate group isprimarily monodentate, Cu-0 1.970 1$, but the second oxygen isdirected back towards the metal with a long C u . . - Ointeraction of 2.71 3 8,.The pyridinyl and phenolate rings are planar (r.m.s.deviations 0.008, 0.008 and 0.01 2 A respectively), with anglesbetween six-membered ring planes of 78.4, 91.9 and 31.0'.Thenitro group is asymmetrically twisted by 7.0" with respect to thephenyl ring. Torsion angles of (amine) N-C-C-C (pyridine) are- 88.3 and - 78.7" respectively. The co-ordinated phenolat2328 J . CHEM. SOC. DALTON TRANS. 1995Table 6 Selected bond lengths (A) and angles (") for complex 15cu-O( 1 )Cu-N(4)Cu-N( 2)Cu-N( 1 )Cu-N( 3)s-C( 22)N( 1)-C(7)N( 1 )-C( 1 5 )N( 1 )-C(8)N(2)-C(14)O( 1 )-Cu-N(4)O( 1 )-Cu-N( 2)N(4)-Cu-N( 2)O( 1 )-Cu-N( 1 )N(4)-Cu-N( 1 )N(2)-Cu-N( 1 )O( 1 )-Cu-N( 3)N(4)-Cu-N( 3)N( 2)-Cu-N( 3)N( 1 )-Cu-N( 3)C( 7)-N( 1 )-C( 1 5)C(7)-N( 1 )-C(8)C( 15)-N( 1)-C(8)C(7)-N( I)-CUC( 15)-N( 1 )-CU1.938(4)2.0 1 2( 6)2.026( 5 )2.1 OO(4)2.205(5)1.603(7)1.502(7)1 .504( 7)1 .505( 7)1.35 1 (8)85.9(2)161.1(2)85.5(2)93.6( 2)1 67.9( 2)91.3(2)98.0(2)97.3 2)99.8(2)94.5(2)1 08 .O( 4)106.9(4)108.9(4)109.4(3)11 1.9(3)C(S)-N( l)-CuC( 14)-N( 2)-C( 10)C( 14)-N( ~)-CUC( 1 O)-N(2)-CuC(21)-N(3)-C(17)C( 2 1 )-N( ~)-CUC( I 7)-N( ~)-CUC(22)-N( ~)-CU0(2W(5)-0(3 )0(2FN(5)-C(4)0(3)-N(5)-C(4)C( 1 )-O( 1 )-cuO( 1 )-C( 1 )-C(2)O( 1 t C ( 1 FC(6)C ( 2 W 1 )-C(6)1.354(7)1.338(8)1 .345( 8)1 . 1 39( 8)1.213(8)1.256(8)1.458(8)1.31 l(7)1.396(9)1 1 1.7(3)118.1(5)12 1.0(4)119.5(4)119.9(6)1 18.3(4)12 1 .8(4)168.2(5)12 1.7(6)121 3 7 )1 I6.7(6)1 23.6( 4)120.2(6)120.8(6)1 19.0(6)1.41 l(9)1.372( 10)1.364( 10)1.382(9)1.388(8)1.499(8)1.518(9)1.498(9)1.35 1 (9)121.1(7)119.1(7)122.0(6)118.1(6)119.9(6)119.6(6)1 19.2(6)1 2 1 .3( 6)119.5(5)1 13.0(5)114.0(5)110.8(5)120.8(6)1 23.6( 6)115.4(5)C( 11)-C( 12)C( 12)-C( 1 3)C( 1 5)-C( 16)C( 16)-C( 17)C( 17)-C( 18)C( 18)-C( 19)C( 19)-C(20)C(2O)-C(2 1 )C( 1 3)-C( 14)C( IO)-C( 1 1 )-C( 12)C( 1 3)-C( 12)-C( 1 1 )C( 14)-C( 1 3)-C( 1 2)C( 1 3)-C( 14)-N( 2)N( 1 )-C( 1 5)-C( 16)C( 17)-C( 16)-C( 15)N( 3)-C( 1 7)-C( 18)N(3)-C( 1 7)-C( 16)C( 1 8)-C( 17)-C( 16)C( 19)-C( 18)-C( 17)C( 2 1 )-C(2O)-C( 19)C( 18)-C( 19)-C(20)N(3)-C(21)-C(20)N(4)-C(22)-S1.372(10)1.375( 1 1)1.350(9)1.533(8)1.49 l(9)1.397(9)1.359( 1 1 )1.397(11)1.379( 10)12 1.1(6)117.9(6)119.4(7)122.6(7)114.3(5)112.0(5)120.5(6)117.4(5)122.2(6)120.0(7)119.0(7)118.9(7)178.5(6)121.7(7)Cl14) _____ CClSI nFig.1 Molecular structure of complex 14, [CuL4(0,CMe)]-H,0oxygen is hydrogen bonded to a solvent water molecule[0( 1 ) O(6) 2.870,0( 1) H(6B) 1.90 A], which also links toa symmetry-related nitro group oxygen [0(6) - O(3) (+ - x, -; + y , ; - z ) 3.175 A, H(6A) =. .0(3) 2.33 .8.] through alonger, but angularly appropriate interaction.The asymmetric unit of structure 15 comprises amononuclear copper(r1) complex and one ethyl acetate solventmolecule. The copper atom is bound in a five-co-ordinateddistorted square-pyramidal environment provided by fourdonor atoms of ligand L4 and a NCS group, r.m.s.deviation ofbasal plane 0.044 A, deviation of Cu( I ) - 0.259 A towards axialN(3). The copper-donor atom distances within the s uare baselargest is for the axial position, 2.205 A. The SCN- ligand isco-ordination plane range between 1.938 and 2.100 x , and thenearly linear with N(4)-C(22)-S 178.5" and co-ordinates to thecopper(r1) through the nitrogen atom, C(22)-N(4)-Cu 168.2'.The phenyl and pyridinyl rings are planar (r.m.s. deviations0.007,0.008 and 0.005 A), and the deviations from planarity ofthe oxygen and nitrogen substituent atoms of the phenyl ringare small (-0.032 and -0.028 A). The nitro group isasymmetrically twisted by 5.6" from the plane of the phenylring.The angles between the pyridinyl and phenyl groups are87.9, 44.5 and 1 12.1" respectively. Torsion angles within(pyridinyl) C-C-C-N (amine) chelate groups are - 80.1 and- 86.6".Structural Comparison and Biological Relationship.-Acomparison of the structural parameters for complexes 3, 1J . CHEM SOC. DALTON TRANS. 1995 2329Fig. 2 Molecular structure of complex 15, [CuL4(SCN)]-MeC0,EtPyridineNPyridineN14 15Comparison of copper(I1) co-ordination environments Fig. 3Table 7 Comparison of some structural parameters for copper(r1) co-ordination spheresCompound T* r.m.s. deviation of Deviation of Cu Axial bond lengthbasal plane/A above plane/A Cu-N,,/A39 0.17 0.0936 l 5 014 0.08 0.06115 0.11 0.0440.271 2.1680.23 2.1620.161 2.2650.259 2.205* For perfect tetragonal and trigonal-bipyramidal geometries the values of T are zero and unity respectively; T being an index of the degree oftrigonality within the structural continuum between square-planar and trigonal-bipyramidal geometries.'*and 15 reveals that, except for minor differences, the threecompounds are closely similar with respect to the co-ordinationgeometry about the copper(r1) atom (Fig.3). Table 7 lists somestructural parameters of these complexes together with thosefor 6.15 In the present three complexes the geometries aroundcopper(rr) are best described as distorted square pyramidal witha small trigonal-bipyramidal component from t = 0.08 to 0.17.The present structures are very similar to that of the azidecomplex 6 but differ from that of the related copper(I1) chloridecomplex [CuLS(C1)],' in which two pyridyl nitrogens co-ordinate equatorially to copper(r1) and the phenolate occupiesthe apical position.It was proposed that the apical co-ordination of the phenolate was due to the introduction of theelectron-withdrawing NO2 group para to the phenolic group asin its absence phenolates had been found only to occupyequatorial positions. This may be related to the polarity rule,noted for main-group chemistry, which states that the moreelectronegative ligand will preferentially occupy the axialposition of a tetragonal based pyramid.29 This proposal is atodds with the structural information given here whereequatorially sited p-nitrophenolates are observed. We notehowever that in [CuL5(CI)] a 5,5,6-membered chelate ringsequence is observed at the copper(r1) atom whereas in 3,14 and15 6,6,6-membered chelate ring sequences are found and so it issuggested that steric factors are also involved and that thenature of the chelate rings formed may be more important thanhas previously been recognized.In complex 14 there is a discrete mononuclear square2330 J .CHEM. SOC. DALTON TRANS. 1995Table 8 Experimental details of the crystal structure determinations *ComplexFormulaMalAW AC I APi”ujA3DJg C M - ~F (000)p( Mo-Ka)/cm-’Total no.of unique dataObserved data [I Fl/o( I FI) > 4.01RwR2Goodness of fitLargest peakle A-* Details in common: blue; monoclinic, space group P2,ln; 2 = 4.14518.0210.095(2)24.525( 12)100.84(3)2367(2)1.45410769.738443 2400.04660.12271.0380.567C23H26CuN4069.734(4)15587.1414.8 15( 7)7.646(2)25.462( 7)105.95(3)2773(2)1.40612209.1359727520.07020.20811.0650.788c2 8 2 ,CuN,O,STable 9 Final fractional atomic coordinates ( x lo4) for complex 14Atom Y Y1800(1)273 5 (4)8207(3)2370(3)- 164( 3)3 569( 3)9275( 3)8 126(3j1130(3)448(4)3732(3)3066( 5 )3564(6)3689( 5)3365(5)2898(4)2573( 4)611(1)1859(3)399( 3)1939(3)1405(3)- 403(2)- 248(4)1195(3)- 888(2)- 1537(3)- 296 1 (3)1284( 5 )1975(6)3329(6)3939(5)3 173(4)3779(4)1306( 1 )700( 1 )3156(1)1961(1)1 l06(1)1499(1)3149(1)3527( I )813(1)1584(1)1 004( 2)251(2)- 153(2)- 101(2)357(2)757(2)1 279( 2)Y3247(4)467 1 (4)5972(4)7 I 3 1 (4)7019(4)5769(4)4584( 3)32 1 O( 4)1 1 55(4)- 127(4)- 90 l(4)- 2258(4)- 2860( 5 )-2113(5)- 772(5)572(4)9x5)V3040( 3)- 1 68( 3)- 749(4)-591(4)227(4)854(4)646( 3)I 173(4)2502(4)I 6 I 3( 4)1715(4)2 1 76( 5 )2358(5)2030( 5 )1 547( 4)- 1729(4)-3021(4)Z1807(2)1880(1)1847(2)2263(2)27 12(2)2750(2)2346( 1 )2437( 1 )2176(2)2086(2)1498(2)1367(2)8 I 2( 2)412(2)563(2)1099(2)809( 2 jTable 10 Final fractional atomic coordinates ( x lo4) for complex 15Atom Y V z4853 1)643 1 (2)4433( 3)6193(3)43 19(4)5 3 86( 4)269(4)3766(3)220( 3)2942( 4)2127(5)1261 ( 5 )1 197(4)I 98 1 (4)2864(4)3730(4)5244(4)601 l(4)- 427(4)2035( I )5967(3)41 l(6)1 150(7)280(7)3890(7)1235(9)3540(6)1 6 0 3 9)373(8)2998(8)3534( 10)294l( 10)1 85 I(8)1319(8)1881 (8)1364(8)1317(9)- 59( 8)1668( 1 )790( 1 )1935(2)965(2)1278(2)1630(3)1553(2)1268(3)204 1 (3)1 584( 3)1 193 3)121 l(3)1623(3)2026(3)2010(2)2444( 2)2704(2)%46( 2)2222(2)Y6638(4)7 57 7( 4)8 109( 5)7652( 5 )67 1 3( 5 )3980(4)45 15( 5)4246( 4)3919(5)3657(6)3721(6)4065(5)58 12(4)- 140( 7)877( 1 1 )1428(7)696( 7)- 757( 10)- 1319(12)Y1 184(8)724( 9)649( 10)871(9)- 2 I 53( 7)- 1456( 8)- 2539( 10)- 1837( 1 1)-28(11)4747(9)- 2527(20)-2351(19)- 1206(23)- 2020( 2 1 )957(9)- 1244(8)982( 10)- 2989(23)- 4622( 22)2476(2)2656(3)2298(3)1750(3)1583(3)1956(2)1596(3)1028(2)573(3)63(3)4(3)464( 3)1069( 2)358(4)1 182(4)471(7)700(4)665(6)413(8)pyramidal geometry with an equatorial acetate-copper(Ir) phenolate into such a system in order to move closer to abond.This structure, with an acetate oxygen trans to an aminenitrogen and a phenolate oxygen trans to pyridinyl nitrogen,may be compared with the ligand disposition in GOase wherethere is an acetate oxygen trans to a histidine nitrogen and atyrosine oxygen trans to another histidine oxygen in GOase(Fig. 3 ) . We are currently attempting to introduce an apicalstructural model for the natural system.AcknowledgementsWe thank the University of Sheffield for a Scholarship (to Q.-Y.H.) and the SERC and Royal Society for funds towards thepurchase of the diffractometerJ .CHEM. SOC. DALTON TRANS. 1995 233 1References1 G. Avigad, D. Amaral, C. Asensio and B. Horecker, J. Biol. Chem.,1962,237,2736.2 M. J. Ettinger and D. J. Kosman, in Copper Proteins, ed. T. Spiro,Wiley-Interscience, New York, 1982, p. 219.3 D. J. Kosman, in Copper Proteins and Copper Enzymes, ed. R.Lontie, CRC Press, Boca Raton, 1984, vol. 1, p. 1.4 N. Ito, S. E. V. Phillips, C. Stevens, Z. B. Ogel, M. J. McPherson,J. N. Keen, K. D. S. Yadav and P. F. Knowles, Nature (London),1991,350,87.5 N. Kitajima, Adu. Inorg. Chem., 1992,39, 1.6 R.Uma, R. Viswanathan, M. Palaniandavar and M. Lakshminaray-7 R. Uma, R. Viswanathan, M. Palaniandavar and M. Lakshminaray-8 M. M. Whittaker, Y.-Y. Chuang and J. W. Whittaker, J . Am. Chem.9 H. 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Soc., Dalton Trans., 1984, 1349.29 R. Luckenbach, Dynamic Stereochemistry of’ PentacoordinatePhosphorus and Related Elements, Georg Thieme, Stuttgart, 1973.Received 30th January 1995; Puper 5/00526
ISSN:1477-9226
DOI:10.1039/DT9950002323
出版商:RSC
年代:1995
数据来源: RSC