1975 461Synthesis and Characterization of Chromium(i1) Complexes of Tris-(2-diphenylphosphinoethyl)phosphine and 0-Phenylenebis(dimethy1-arsine)By Fabrizio Mani, Piero Stoppioni, and Luigi Sacconi,' lstituto di Chimica Generale ed lnorganica dell'-Universits di Firenze and Laboratorio per l a Stereochimica ed Energetica del Composti di Coordinazionedel C.N.R. Via J. Nardi 41, Firenze, ItalyThe preparation and properties of new high-spin five-co-ordinate and low-spin six-co-ordinate chrorniurn(l1)complexes are reported, [Cr(tdpep)X] [BPh,] [X = CI, Br, or I ; tdpep = tris(2-diphenylphosphinoethyl)phosphine]and [Cr(pdma),X,] [X = CI, Br, or I ; pdma = o-phenylenebis(dimethylarsine)] respectively.CHROMIUM(II) complexes so far reported are not verynumerous and most are high-spin octahedral species.lRecently, rare examples of chromium (11) complexes withtetrahedral and trigonal-bipyramidal3 geometries havebeen described.Studies of chromium (11) chemistryhave now been extended to include the complexingbehaviour toward chromium(I1) halides of ligandscontaining ' soft '-donor atoms, P and As, which havebeen shown to possess marked capacity for inducingspin pairing in some 3d metal ions.4In this paper we report the preparation and charac-terization of chromium( 11) complexes with the ligandstris(2-diphenylphosphinoethy1)phosphine (tdpep) ando-phenylenebis(dimethy1arsine) (pdma) .RESULTS AND DISCUSSION[Cr( tdpep)X] [BPh,] CompZexes.-Chromium(II) halidesreact with the ligand tdpep in the presence of sodiumtetraphenylborate to give blue crystalline products ofreported [Cr (Me,tren) Br] [hfe,tren = tris (2-dimet hyl-aminoethyl)amine] and [Cr(tdpea)X]+ [X = C1, Br, orI and tdpea = tris(2-diphenylphosphinoethyl)amine],species to which a five-co-ordinate trigonal-bipyramidalgeometry has been a~signed.~ On the basis of a one-electron splitting scheme of d orbitals in D3h symmetry,two spin-allowed transitions are expected for a high-spin d4 ion ( 5 0 ground term),5 and the two d-d bandsin the spectra of the present five-co-ordinate chromium-(11) complexes axe assigned as in Figure 1.The lowerintensity of the high-energy band agrees with thedipole-forbidden character of 5A1t+5E't transition instrictly D3h symmetry.A survey of the magnetic properties of five-co-ordinate chromium(II), iron(II), cobalt(II), and nickel@)complexes with the ligands tdpep and tdpea (Table 3)shows that spin-pairing tendency decreases in the orderNi > Co > Fe > Cr.The high-spin state of all five-co-ordinate chromium(r1) complexes so far reported,TABLE 1Analytical data for the complexesComplex Colour C H P Cr C H P CrFound (%) Calc. (%)r A\ r \[Cr(tdpep)Cl][BPhJ Blue 72.4 6.5 11-3 73.55 5.80 11.5[ Cr ( tdpep) Br] [ BPhJ Blue 69.5 6.4 11.0 70.65 5.60 11.05[Cr(tdpep) I][BPh4] Blue 67.0 5.6 10.4 67.8 5-35 10.6rCr(Pdma),C12] Red-brown 34-6 4.7[Cr(pdma) 2Br21 Red-brown 30-9 3.9CCr(pdma) 2121 Brown 27.5 3.67.4 34.55 4.656.5 30-65 4.106-7 27-35 3-667-506-656-90formula [Cr(tdpep)XJ[BPh,] (X = C1, Br, or I).Thesecomplexes axe high spin with effective magnetic momentsa t room temperature in the range 4-5-4.7 B.M., slightlybelow the spin-only value of 4.9 B.M. expected for fourunpaired e1ectrons.t The complexes are soluble in1,2-dichloroethane and behave essentially as 1 : 1electrolytes in this solvent. The electronic spectra ofthese complexes in 1,2-dichloroethane solution were allsimilar and did not differ from their solid-reflectancespectra. These spectra contain a maximum at ca.14000 cm-l (Table 2 and Figure 1) and a less intense,poorly resolved, band in the range 18 000-19 000 cm-l,and are strictly correlatable to the spectra of previouslyL. F. Larkworthy, K. C. Patel, and J. K. Trigg, J .Chem.SOC. ( A ) , 1971, 2766 and ref. therein; D. G. Holah and J. P.Fackler, jun., Inorg. Chem., 1966, 5, 479.D. E. Scaife, Austral. J . Chem., 1967, 20, 845; D. C. Bradley,M. B. Hursthouse, C. N. Newing, and A. J. Welch, J.C.S. Chem.Comm., 1972, 567.t 1 B.M. 21 9.27 x A m2.including [Cr(tdpep)I]+ which contains one of the mostnucleophilic donor-atom sets P,I, is therefore attribut-able to the e't and e' orbitals whose difference in energyis smaller than the spin-pairing energy. It has beennoted that a low-spin configuration for a d4 ion would befavoured more by a chromophore with C4* symmetrythan one with Dsh symmetry.6 However all attemptsto obtain chromium(I1) complexes with ligands which,on the basis of their steric requirements, tend to promotesquare-pyramidal geometry, were unsuccessful.[Cr(pdma),X,] ComfiZexes.-Complexes of most 3dmetals have long been known with this ligand, but to3 (a) M.Ciampolini, Chem. Comm., 1966, 47; (b) F. Mani andL. Sacconi, Inorg. Chim. Acta, 1970, 4, 365.4 (a) R. B. King, R. N. Kapoor, M. S. Singh Saran, and P. N.Kapoor, Inorg. Chem., 1971,10, 1851; (b) R. S. Nyholm and G. J.Sutton, J . Chem. SOC., 1958, 560, and ref. therein; C. H. Harris,R. S. Nyholm, and D. J. Phillips, ibid., 1960, 4379.C. Furlani, Co-ordination Chem. Rev., 1968, 8, 141; M.Ciampolini, Structure and Bonding, 1969, 6, 52.L. Sacconi, Co-ovdination Chem. Rev., 1972, 7, 352462IJ.C.S. Daltonchromium. Chromium(I1) halides react with theligand pdma to give brown crystalline products offormula [Cr(pdma),X,] (X = C1, Br, or I).TheseTABLE 2Physical data for the complexes10-3~/cm-1pen .I B. M. A b / (&/I mol-1 cm-1)e a % - Y 1 e[Cr (tdpep) Cl) [BPh,] 4.49 14 R 14.7,19.0 (sh)D 15.1 (560)[Cr(tdpep)Br] [BPh,] 4-70 14 R 14.3,18.1 (sh)18.1 (sh)D 14.8 (585),[Cr (tdpep) I J [ BPh,] 4.70 16 R 34.3, 18.7D 14.4 (440).18.7 (sh)15.4 (sh),> 2014.3, >20> 20(15*4), >17[Cr(pdma) 2C12.l 2-85 2.85 0 R 7.4, 8.8,[Cr(pdma) 3 r d 2.94 2.90 0 R 6.4, 7.9,[Cr(Pdma)zIzl 3.99 2.98 0 R 6.7, 13-3,[Mo(pdma) &121 2-85 R 8.5, 10.9,a Weiss constant. For cu. ~ O + M solutions at 20 OC. Thereference value in 1,2-dichloroethane was 19 S cm2 mol-l forBun,NBr. 6 R = Solid-state reflectance spectra, D = ab-sorption spectra in 1,2-dichloroethane. Ref.8.i . i + - 1 /A\ jI I////@--. I-;5 10 15 20 2516~8 I cm-1FIGURE 2 Reflectance spectra of [Cr(pdma),Cl,J, (-) and[Mo(Pdma)zC1,1 (-- - -4complexes are low spin with magnetic moments at roomtemperature ranging between 2.85 and 2.99 B.M., closeto the spin-only value of 2-83 B.M. expected for twounpaired electrons. The magnetic moments of thecomplexes measured between 84 and 298 K wereconstant within experimental error, with a Weissconstant of 0 K. The complexes are insoluble in thecommon organic solvents (C,H,, CHCI,, CH,CI,,ClCH,CH,Cl, MeOH, and EtOH were tried) but solublein MeNO, and EtNO,. Absorption spectra in the lattertwo solvents exhibit two intense bands at ca.15000and 21 000 cm-l, indicating almost complete oxidationof the chromium(I1) species. Reflectance spectra ofthe [Cr(pdma),X,j complexes (X = C1 or Br) exhibittwo maxima at ca. 7 000 and 8 000 cm-l and a poorlyresolved band at ca. 15000 and above 20000 cm-l(Figure 2 and Table 2). The spectrum of the iodo-derivative does not differ substantially from the formerspectra, but one asymmetric band appears at ca.7 000 cm-l and the band at ca. 13 000 cm-l is betterresolved. The positions of the absorption maximashift toward higher frequencies in the order I < Br <C1, in accordance with the relative positions of thehalogens in the spectrochemical series.For comparison purposes the previously reportedoctahedral complex [Mo(pdma),Cl,] * was prepared.The X-ray powder photograph of this complex ispractically indistinguishable from that of [Cr(pdma),Cl,].Moreover the reflectance spectrum of the molybdenum(r1)derivative in the region 5 000-25 000 cm-l is similarto the spectrum of the analogous chromium(I1) complex,apart from the absorption maxima being shifted towardhigher frequencies in the molybdenum( 11) complex.This shift is expected in the spectrum of a 4d metalcomplex when compared to that of a 3d metal.The8 J. Lewis, R. S. Nyholm, and P. W. Smith, J . Chem. Soc.,1962, 26921975low-intensity band which appeared at ca. 15 000 cm-lin the [Mo(pdma),Cl,] spectrum is presumably due to thepresence of traces of oxidation products of molybdenum(yellow [Mo(pdma),Cl,] quickly becomes dark brownwhen exposed to air and strongly absorbs at ca.15 OOOcm-l}, while the third band, which appeared in theregion of 13000-15000 cm-l in the chromium(I1)spectrum, is very likely masked in the molybdenum(I1)spectrum by a charge-transfer band which starts atca. 17000 cm-l. On the basis of these spectral andX-ray data, we conclude that [Cr(pdma),ClJ and[ Mo(pdma),Cl,] have similar octahedral geometries.Magnetic and spectral data of the [Cr(pdma),Brz] andrCr(pdma),I,] complexes were very similar to those ofthe chloro-derivative and indicate also an octahedralgeometry for these derivatives. The [Cr(pdma),XJcomplexes described here are among the few examplesso far reported of octahedral low-spin chromium (11)complexes.9EXPERIMENTALIn order t o prevent oxidation, all reactions and oper-ations were carried out under moisture-free nitrogen.The solvents were carefully deoxygenated by boiling andflushing with nitrogen before use. Anhydrous chromium-(11) halides 3b and o-phenylenebis(dimethy1arsine) (pdma) 10were prepared as already described.The ligand tris(2-di-phenylphosphinoe thyl) phosphine (tdpep) was obtainedfrom Pressure Chemical Co.chromium TetraphenyZbora2es.-A solution in n-butanolP. M. Lutz, G. J. Long, and W. A . Baker, jun., Inovg. Chem.,1969,8, 2629; A. Earnshow, L. F. Larkworthy, K. C. Patel, R. L.Carlin, and E. G. Terezakis, J . Chem. Soc. ( A ) , 1966, 611.HaZogeno[tris( 2-diphenyZ~hosphinoethyl)phosphine]-(20 cm3) of the appropriate anhydrous chromium(I1) halide(10-3 mol) was added to the stoicheiometric amount of theligand dissolved in methylene chloride (30 cm3).Thecomplexes were readily obtained after sodium tetraphenyl-borate (10-3 mol) dissolved in n-butanol (15 cm3) had beenadded to the solution. The crystalline products werecollected by filtration, washed several times with n-butanol-light petroleum, and dried in a stream of dry nitrogen.Attempts to prepare analogous complexes with the open-chain tetradentate ligand 3,6-diphenyl-3,6-diphosphaoctane-1,8-bis(diphenylphosphine) were unsuccessful.Dihdogenobis [o-~henyZenebis(dimethyZarsine)]chrorniumCompZexes.-A saturated solution in n-butanol of theappropriate anhydrous chromium(I1) halide (2 x mol)was added to the stoicheiometric amount of the ligand(4 x mol) in n-butanol (5 c d ) . The resulting bluesolution was cooled in ice and after a little time red-browncrystals separated. The Products were filtered off, washedwith n-butanol-light petroleum, then light petroleum, andfinally dried in a stream of nitrogen.Analytical data for the complexes are reported in Table 1.The complex [Mo(pdma) zC1,] was prepared for comparativepurposes as described by Nyholm and his co-workers.6All the complexes quickly decompose when exposed to air.Magnetic, spectrophotometric, conductivity, and X-raymeasurements were carried out using methods alreadydescribed.llWe thank Mr. P. Innocenti for technical assistance,Mr. F. Nuzzi for the analyses, and the Italian C.N.R. forfinancial support.[4/1086 Received, 4th June, 19741lo R. D. Feltham, A. Kasenally, and R. S. Nyholm, J . Orguno-l1 I. Bertini and F. Mani, Inorg. Chenz., 1967, 6, 2032.metallic Chem., 1967, 7, 285