J . CHEM. SOC. DALTON TRANS. 1983 1819Synthesis and Crystal and Molecular Structure of[ (rl-C5H5)Rh(p-C0)2Rh( PPh3)(q-C5H5)] t an Asymmetric BimetallicComplex with a Polar Rhodium-Rhodium BondFelice Faraone,+ Giuseppe Bruno, Sandra Lo Schiavo, Pasquale Piraino, andGabriella BombieriDepartment of Chimica lnorganica e Struttura Molecolare, Universita di Messina, Piazza S. Pugliatti,98 I00 Messina, lta l yTreatment of [{ Rh(q-C,H,) (CO)),(p-CO)] with PPh3, in saturated hydrocarbons, affords[ (q-C5H5) Rh(~-co)~Rh(PPh~) (q-C5H5)] which has been characterized by Lr., 1H n.m.r., and X-raydiffraction methods. The complex crystallizes in the triclinic space group P1, with a = 9.700(2),b = 11.076(2), c = 13.790(3) p\, a = 105.3(1), p = 109.6(1), y = 99.1(1)", and 2 = 2.On the basis of2 697 reflections with I 2 2.5 o(/), the structure has been refined to R 0.053 and R' 0.059. Themolecule possesses a near mirror plane defined by the Rh-Rh bond [2.673(1) A] and the phosphorusatom. The two carbonyl ligands form two different asymmetric bridges to the rhodium atoms[Rh(l)-C(19) 2.17(1), Rh(2)-C(19) 1.89(1), Rh(1)-C(20) 2.10(1), and Rh(2)-C(20) 1.90(1) A].The cyclopentadienyl ligands are in a cis position with an interplanar angle of 66.3" and both areperpendicular to the pseudo-mirror molecular plane. The co-ordination geometry about the two metal centresis different, being formally Rh(1) seven-co-ordinate and Rh(2) six-co-ordinate. The complex[(q-C,H,)Rh(p-CO),Rh(PPh,)(q-C,H,)] reacts with PPh3 to give the known [Rh(q-C5H5)(CO)(PPh3)J ;the same product can be obtained directly by reacting [{Rh(q-C,H,)(CO)),(p-CO)] with PPh3 in excess, inbenzene solution.Interest in the synthesis of bi- and poly-nuclear complexes oflow-oxidation state transition metals has arisen due to theirability to give, in principle, new modes of activation oforganic and inorganic molecules.' Such an ability is relatedto the possibility that a co-operative involvement of themetallic active sites occurs.'So far there is no clear evidence that the binuclear com-plexes behave differently from the mononuclear ones asregards the activation processes.2 In this respect the design ofnew types of binuclear complexes is interesting.We report on the synthesis and the crystal and molecularstructure of the unusual compound [(q-CsH5)Rh(p-CO)r-Rh(PPh3)(q-C5H5)]; this substance is an asymmetric di-rhodium complex containing 34 valence electrons andrepresents a new model for the activation of molecule^.^During the preparation of this paper some complexes of thesame type as [ ( T & H ~ ) R ~ ( ~ - C O ) ~ R ~ ( P P ~ ~ ) ( ~ - C ~ H ~ ) J havebeen r e p ~ r t e d .~ , ~ For their preparation a different route hasbeen followed.Results and DiscussionAddition of PPh3 to a solution of [{Rh(q-C,H,)(CO)),(p-CO)]in pentane afforded a green-brown crystalline complex, whichaccording to molecular-weight measurements in benzenesolution, analytical, i.r. and 'H n.m.r. data, must be formul-ated as [(r\-CsH5)Rh(p-CO),Rh(PPh,)(q-C5H5)J.The com-pound is stable indefinitely as a solid, but decomposesrapidly in chlorinated solvents; its solution in diethyl etheror benzene is stable over a long period of time. The i.r.spectrum (Nujol mull) showed bands at 1 815s and 1 760vscm-' revealing the presence of bridging carbonyl ligandst Di-~-carbonyl-l,2-bis(q-cyclopentadienyl)-l -triphenylphos-phinedirhodium(Rh-Rh).Supplementary data available (No. SUP 23619; 20 pp.): observedand calculated structure factors, thermal parameters, H-atom co-ordinates. See Notices to Authors No. 7, J . Chern. Soc., DaltonTrans., 1981, Index issue.Figure. The molecular structure of [(q-CsHs)Rh(p-CO)2Rh(PPh3)-(q-C5H5)], showing the atom-numbering schemeonly and bands at 830, 805, and 780 cm-' attributable to theout-of-plane bending of C-H modes of the C5H5 groupsq5-co-ordinated to the rhodium atoms.Two signals in the'H n.m.r. spectrum (C6D6) appeared as an asymmetricdoublet at S 5.03 [J(HRh) = 0.70 Hz] and as an asymmetrictriplet at 6 4.90 [J(HRh) = J(HP) = 0.68 Hz], indicating thenon-equivalent environment of the C5Hs groups. The values ofthe coupling constants are in the range normally found forcyclopentadienyl-phosphine-rhodium(1) complexes.6In order to define unambiguously the molecular structureof the prepared compound, [ ( T ~ C ~ H , ) R ~ ( ~ - C O ) ~ R ~ ( P P ~ , ) -(q-C5H5)], a single-crystal X-ray diffraction study was under-taken. The solid-state molecular structure of [(q-CSH5)-Rh(p-CO),Rh(PPh,)(q-CSHs)] is shown in the Figure togetherwith the atom-numbering scheme.Atomic parameters fro1820 J. CHEM. SOC. DALTON TRANS. 1983Table 1. Final fractional atomic co-ordinates ( x 10') for non-hydrogen atoms with estimated standard deviation in parenthesesX/a- 379(1)2 401(1)- 63(3)73 1 (1 0)1965(9)1 060(12)1675(12)-2 147(14)-2 872(13)-2 655(15)-1 870(16) - 1 474(14)4 938(12)4 218(16)3 439(15)3 637(16)4 591(16)Ylb2 257(1)2 020(1)3 410(2)325(8)4 604(7)1128(11)3 526(11)450( 1 3)1 174(20)2 406( 16)2 352(15)1177(13)2 552(16)2 410(16)1 139(21)513(14)1444(16)z/c2 952(1)3 944(1)1859(2)1 612(6)4 750(6)2 461(10)4 184(8)2 693(13)2 llO(13)2 929( 18)3 940(14)3 780(11)4 929(12)5 645(10)5 291(15)4 348(15)4 130(12)Xla-1 666(8) - 2 466(8)-3 681(8)- 4 096(8)-3 296(8)-2 081(8)7(7)- 712(7) - 748(7)- 65(7)654(7)690(7)1623(7)1 526(7)2 845(7)4 262(7)4 359(7)3 039(7)Ylb2 771(5)3 574(5)3 047(5)1 717(5)914(5)1 441(5)5 129(6)5 545(6)6 840(6)7 719(6)7 304(6)6 009(6)3 445(7)2 797(7)2 829(7)3 509(7)4 157(7)4 125(7)Z l c522(5)84(5)- 938(5)-1 521(5)-1 083(5)- 62(5)2 349(5)3 048(5)3 372(5)2 997(5)2 298(5)1974(5)1 543(5)497(5)295(5)I 141(5)2 187(5)2 388(5)Table 2.Interatomic distances (A) and angles (") with estimatedstandard deviations in parentheses(a) DistancesRh(1)-P(l )Rh( 1)-C( 19)Rh(2)-C(19)Rh( 1 )-C( 5 1 )Rh( 1)-C(52)Rh( 1 )-C(5 3)R h( 1 )-C( 54)Rh( 1 )-C( 5 5 )C(19)-0(1)PC(1)P-C( 1 3)C(5 1 )-C(52)C(5 1 )-C( 5 5 )C(52)-C( 53)C( 5 3)-C( 54)C(54)-C(55)(6) AnglesRh( 1)-C( 19)-Rh(2)Rh( 1)-C(19)-0( 1)Rh( l)-C(20)-0(2)P R h ( 1)-C( 19)Rh( 1 )-PC( 1)Rh(1)-PC(13)C(7)-PC( 13)C( 55)-C(5 1 )-C( 52)C( 5 1 )-C(52)-C( 53)C( 52)-c(53)-c(54)C( 53)-C( 54)-C( 5 5 )C( 5 1 )-C(55)-C( 54)2.281 (2)2.17( 1)1.89(1)2.28(1)2.26( 1)2.23(1)2.29(1)2.24(1)1.17(1)1.83 l(7)1.826(8)1.39(2)1.36(2)1.45(2)1.37(2)1.40(2)82.0(2)126.8(8)1 3 1.2( 8)88.4(3)110.9(2)117.3(3)103.1(3)109(1)105(1)108(1)108(1)109(1)R h( 1 )-R h(2)Rh( 1 )-C(20)Rh(2)-C(20)Rh(2)-C( 56)Rh(2)-C( 57)Rh(2)-C(58)R h( 2)-C( 59)Rh(2)-C(510)C( 20)-O( 2)P C ( 7 )C( 56)-C( 57)C(57)-C(58)C( 58)-C( 59)C(59)-C(510)C( 5 6)- C( 5 1 0)2.673(1)2.10( 1)1.90(1)2.26(1)2.29( 1)2.33(1)2.28(1)2.27(1)1.17(1)1.826(6)1.41(2)1.36(2)1.39(2)1.44(2)1.32(2)Rh( 1 )-C(20)-Rh(2)Rh(2)-C( 19)-0(1)Rh( 2)-C(20)-0 (2)P R h ( 1)-C(20)Rh(1)-PC(7)C(l)-PC(13)C( 1)-PC(7)C(57)-C(56)-C( 5 10)C( 56)-C( 57)-C( 5 8)C(57)-C( 58)-C(59)C(58)-C(59)-C(5 10)C(56)-C( 5 10)-C(59)83.6(4)150.9(9)144.7(9)87.7(3)115.9(2)104.7(3)103.4(3)111(1)107(1)107(1)109(1)105(1)the last cycle of refinement are given in Table 1.Interatomicdistances and bond angles are listed in Table 2 while selectedleast-squares planes and interplanar angles are given inTable 3.The structure is characterized by the short Rh-Rh distance[2.673(1) A], by the different co-ordination geometry of thetwo rhodium atoms (also implying a different co-ordinationnumber), and by the presence of asymmetric CO bridgingligands.The metals Rh(1) and Rh(2) are, respectively, form-ally seven- and six-co-ordinate. A particular shape cannot beused to describe the co-ordination geometry of the molecule.The Rh2(C0)2 frame is sigdcantly non-planar as shown byTable 3. Selected least-squares planes; distances of the atoms fromthe plane (A) are given in square bracketsPlane 1 : cyclopentadienyl ring (1)8.6492X + 3.3079Y - 7.05222 = 3.5852[C(51) -0.022, C(52) 0.002, C(53) 0.019, C(54) -0.033, C(55)0.0341Plane 2: cyclopentadienyl ring (2)6.9007X - 5.8904Y + 5.42922 = 4.5678[C(56) 0.013, C(57) -0.012, C(58) 0.007, C(59) 0.000, C(510)- 0.0081Plane 3: ring centroid Cp(l), Rh(l), P, Rh(2), ring centroid Cp(2)-2.1535X + 7.2360Y + 7.37842 = 3.8622[Cp(l) -0.000, Cp(2) -0.014, Rh(1) 0.031, Rh(2) -0.008, P-0.010, C(19) -1.458, C(20) 1.4160, O(1) -2.595, O(2)2.5511Plane 4: Rh(l), Rh(2), C(19)(carbonyl)3.9324X + 8.8819Y - 8.89812 = - 0.771 1[0(1) -0.08711Plane 5 : Rh(1)-Rh(2); C(20)(carbonyl)-5.0552X - 4.5223Y + 13.0862L = 3.0339[0(2) 0,01071Plane 6: Phenyl ring C(l)-C(6)Plane 7: Phenyl ring C(7)-C(12)Plane 8: Phenyl ring C(13)-C(18)Plane 9: Rh(l), Rh(2), C(19), C(20)-8.0743X - 2.1896Y + 10.7334Z = 1.29855.9208X - 1.5966Y + 7.03922 = 0.8387- 1.2591X + 10.7604 Y - 6.54722 = 2.4924-4.5008X - 7.1539 Y + 11.52742 = 1.7698[Rh(l) 0.189, Rh(2) 0.251, C(19) -0.217, C(20) -0.223, O(1) - 0.473, O(2) - 0.4721Angles (") between planes1-2 66.3 1-3 88.7 2-3 89.71-9 141.1 2-9 74.8 4-5 145.66-7 98.2 7-8 108.2 6-8 108.5the best mean plane calculated through these atoms [thedeviations: Rh(1) 0.189, Rh(2) 0.251, C(19) -0.217, andC(20) -0.223 .$I and by the dihedral angles of 142.7' betweenthe two fused RhCz planes and 145.6' between the two fusedCRhz planesJ.CHEM. SOC. DALTON TRANS. 1983 1821The unsymmetrical arrangement of the two carbonyls isinteresting. The Rh(2)-C(19) and Rh(2)-C(20) bond distancesof 1.89( 1) and 1.90( 1) A respectively are comparable and thesecarbonyls are closer to the six-co-ordinate Rh(2); their valuesare in agreement with those found in the trimer [{Rh(q-C,H,)-(CO>},].'~* The Rh(1)-C(19) bond distance is 2.17 A while theRh(l)-C(20) distance is 2.10 A.These values are not com-parable and are significantly larger than those of Rh(2)-C(19) and Rh(2)-C(20) above. This situation is very similarto that found in the Rh,(p-CO), frame of the trinuclearrhodium compound [Rh3(q-C,H,)3(p-CO)2(p3-CH)][CF3CO~]where the ' unsymmetrical ' bridge has Rh-C distances,Rh(2)-C(2) 1.914(9) A and Rh(1)-C(2) 2.202(11) A with aRh(1)-Rh(2) separation of 2.677(1) A [cf. Rh(2)-C(20) andRh( l)-C(20)].It is noteworthy that in both bridges of the present determin-ation the asymmetrical bonding is not accompanied by asignificant variation in the internal Rh-C(p-C0)-Rh angles[Rh( 1)-C( 19)-Rh(2) 82.0(2) and Rh( l)-C(20)-Rh(2) 83.6(4)"],with respect to the values given for symmetrical bridges whichare on average, 83".The Rh-C(p-C0)-0 angle deviatesconsiderably in both directions from the value of 137" ob-tained by an averaging of symmetrical bonding in a series ofrhodium complexe~,~ being Rh( l)-C(20)-0(2) 13 1.2(8),Rh(2)-C(20)-0(2) 144.7(9), Rh(1)-C(l9)-O(1) 126.8(8), andRh(2)-C( 19)-O( 1) 150.9'.With reference to these differences in bond distances andangles if we follow the Colton and McCormick lo classific-ation (for which when the difference in the M-C bondlengths is less than 0.3 A and the difference in the M-C-0angles is less than 20°, the bridging carbonyl group is asym-metric and when the differences are larger the carbonyl groupis semi-bridged) we should consider the bridging C(20)-O(2)carbonyl group as asymmetric, having a difference in theRh-C(20) bond distances of 0.2 A and a difference in theRh-C-0 angles of 13.5'.The second bridging carbonyl group,having a difference in the Rh-C(19) bond distances of 0.28 Aand a difference in the Rh-C-0 angles of 24.1", should beconsidered more as semi-bridging rather than asymmetricbridging. The second CO bridge is at the limit of the distinctionbetween the two types of bridging and we have consideredboth bridges as asymmetric.Tn this context the molecule provides an example of asym-metric carbonyl bridging ligands which can be explained, assuggested by Cotton in the case of semibridging carbonylligands, as buffers to the polar electron distribution on thetwo rhodium atoms.In fact, if we consider the rhodiumenvironment, we can count 18 electrons for Rh(1) and 16electrons for Rh(2). A Rh(1)-Rh(2) single bond is present, asindicated by the value 2.673(1) A, which is comparable toreported values in bridged dirhodium ~ t r u c t u r e ~ . ~ ~ ~ ~ ' ~ - ~ ~ Themetal-metal interaction in [(~-c,H,)Rh(p-co)~Rh(PPh~)-(q-C5H5)] can be regarded as arising from donation of anelectron pair from Rh(1) to Rh(2). The highly polar Rh(l)+Rh(2) bond produced would lead to asymmetric CO bridgingto mitigate the charge imbalance and to satisfy the Paulingelectroneutrality principle, as in the complex [V2(q-C5H5),-As shown in the Figure, which represents a view of thecomplex in the Rh(2)-O(1)-O(2) plane, apart from the PPh,ligand, the molecule exhibits an approximate mirror plane[Rh(l)-Rh(2)-P plane], about which there appears no par-ticular ligand crowding around the two metal centres whichcould add some other justification for the asymmetric bridgingcarbonyls.The cyclopentadienyl groups are in a cis position with aninterplanar angle of 66".This conformation is very close tothat observed in [(q-C5H,)MeRh(p-CO)2RhBr(q-C,H,)I(~-c0)2(c0)31.15where the molecule possesses a crystallographic mirrorplane. In this complex the rhodium atoms are symmetricallybridged by two carbonyl groups so that no difference incharge distribution on the rhodium atoms is present.TheRh-Rh bond distance [2.660(3) A] together with theRh-C(carbony1) bond distance [ 1.994(20) A] are in agree-ment with the present determination when we consider theaverage of the Rh-C(carbony1) distances. The Rh-C(CsHs)distances range from 2.23(1) to 2.33(1) 8, with averagedvalues for Rh(1)-C(C,H,) of 2.26 A and for Rh(2)-C(C,H5)of 2.29 A. These values are in agreement with the literaturereport^.^,'^*'^ The corresponding Rh-CSH5 separations forRh(1) and Rh(2), are respectively, 1.922 and 1.960 A. Thetwo C5H5 rings are planar in the limit of the errors with anaveraged value for the C-C distance of 1.39 A and for theC-C-C angles of 108".The packing diagram does not reveal particular inter-molecular interactions less than the sum of the normal van derWaals radii.The compound [(q-C,H5)Rh(p-CO),Rh(PPh3)(q-C5H5)]must be considered as an intermediate of the reaction of[(Rh(C,H,),(CO)>,(p-CO)] with PPh3 to give, as a finalproduct, the known complex [Rh(q-C,H,)(C0)(PPh3)]." I nfact [Rh(q-C,H,)(CO)(PPh,)] can be obtained directly from[(Rh(q-C5H,)z(CO)}2(p-CO)], by conducting the reaction inbenzene or dichloromethane solution, or from [(q-C5H5)-Rh(p-CO),Rh(PPh3)(q-C,H,)] in diethyl ether or benzenesolution. Differently from [(r&H,)Rh(p-CO),Rh( PPh3)-(q-C5Hs)], the complexes [(q-C, Me,)Rh(p-CO),Rh L( q -C5Me5)] (L = PMe2H or PMe,), recently obtained byreacting [{Rh(1&Me,)(p-C0)}~] with L, are inert towards anexcess of L and do not react to give the mononuclear com-pounds [ Rh( q -C5 Me5)(CO)L].The reaction of [{Rh(q-C,H5),(CO)},(p-CO)] with tertiaryphosphines is strongly influenced by the electronic propertiesand steric requirements of the ligand.Recently it has beenreported that [{Rh(q-C,H,)(CO)},(p-CO)] reacts with thephosphines PMe2Ph and P(OPh), to give the complexes[Rh,(q-C,H5),(p-C0)(CO)L] [L = PMe2Ph or P(OPh),] inwhich the CO groups are respectively bridging and terminallybonded ; these complexes have been studied by variable-temperature n.m.r. spectroscopy to establish solutiongeometries and the CO-fluxional mechanism. We observedthat P(C6H4Me-o)3, which shows a large steric requirement,failed to react, even under forcing reaction conditions, with[ { Rh(CsHs)(CO) >z(P-Co)l.Some recent literature reports indicate that the formation of'products requiring ring opening of the metallacyclic systemformed by Rh-CO-Rh is the most peculiar aspect of the[{Rh(~-CsH,)(CO)}2(p-CO)] rea~tivity.~*~~-*' However,depending on the nature of the reagents, the steps of reactionare rather different; as a matter of fact mono-, bi-, and tri-nuclear cyclopentadienyl-rhodium complexes have beenisolated.Unfortunately the kinetic and mechanistic aspects ofthese reactions are still unknown and therefore the experi-mental data cannot be rationalized. The formation of[(q-CsH5)Rh(p-C0)2Rh(PPh3)(q-C,H,)] in the reaction of[{Rh(q-CsH,)(CO)}2(p-CO)] with PPh3 indicates the possi-bility of a different route, with respect to those reported, inthe reactivity of [{Rh(q-C,H,)(CO)>z(p-CO)].-ExperimentalThe complex [(Rh(q-C,H5)(CO)}2(p-CO)] was prepared by amodification of a published procedure.8~22 Other reagentswere used as obtained from commercial sources.Infraredspectra were recorded with a Perkin-Elmer 457 spectromete1822 J. CHEM. SOC. DALTON TRANS. 1983using a polystyrene film for calibration. A WM 300 Bruker~spectrometer was used to obtain 'H n.m.r. spectra. Molecularweights were determined with a Knauer vapour pressureosmometer. Conductivity measurements were made with aWTW LBR conductivity meter. Elemental analyses wereperformed by the microanalytical laboratory of the OrganicChemistry Institute of Milan.Di-p-carbonyl-bis(~-cyclopentadienyl)(triphenylphosphine)-dirhodiiirmi.-A solution of [(Rh(q-C,H,)(CO)},(p-CO)] (0.1 5 g,0.357 mmol) in pentane was treated dropwise with a slightexcess of PPh3 (0.088 g, 0.38 mmol) in the same solvent.Afterca. 30 min the precipitated [(q-C5H,)Rh(p-C0),(PPh3)-(q-C5H,)] was formed almost quantitatively as green-browncrystals and isolated by washing with pentane and drying inoacuo (Found: C, 55.10; H, 3.90. C30H2502PRhZ requiresC, 55.05; H, 3.85%); v(C0) 1 815s and 1 760vs, br cm-'.'H N.m.r. (C6D6, 25 "c): 6 , 7.55-6.71 (m, 15 H, Ph), 5.03[d, 5 H, C5H5, J(HRh) 0.70 Hz], and 4.90 [t, 5 H, C5H5,J(HRh) = J(HP) = 0.68 Hz].Carbonyl(q-cyclopentadienyl)triphenylphosphinerhodiNnl( I).-Method A. To a benzene solution of [(Rh(q-C,H,)(CO)},-(p-CO)], triphenylphosphine in slight excess was added andthe reaction mixture left at room temperature with stirring.Monitoring the course of the reaction by i.r.spectra, only thev(C0) band of [Rh(q-C,H,)(C0)(PPh3)], as reaction product,was observed. The product was identified by comparing i.r.and n.m.r. spectra with those of an authentic sample."Method B. Triphenylphosphine, in benzene solution, wasadded to a solution of [(q-C,H5)Rh(p-CO)2Rh(PPh3)(q-C,H,)] in the same solvent. [Rh(q-C,H,)(CO)(PPh3)] wasformed almost immediately and identified by comparison withan authentic sample."Attenipted Reaction [{ Rh(C,H,)(CO)}z(p-CO)] withP(C6H4Me-o),.-A heptane solution (100 cm3) of [(Rh(q-C,H,)(CO)},(p-CO)] (0.20 g, 0.476 mmol) and P(C6H4Me-o)3(0.3 I9 g, I .047 mmol) was refluxed for ca.6 h. After this timethe starting rhodium complex was recovered entirely, showingthat the reaction did not occur.X- Ray Crystal Strirctirre.-Accurate unit-cell dimensionsand crystal orientation matrices, together with their estimatedstandard errors, were obtained from least-squares refinementof the 20, o, X , and cp values of 25 carefully centred high-angle reflections. Intensity data were collected at roomtemperature from a crystal of approximate dimensions0.09 x 0.12 x 0.13 nim on a Siemens-Stoe four circlediffractometer operating in the w/0 scan mode (scan width -=1.2", scan speed = 0.04" s-l) and by using graphite-mono-chromatized Mo-K, radiation. 5 202 Independent reflectionsup to 8 = 25" were measured, of which 2 697 had I 3 2.50(/),o(Z) being calculated from counting statistics.During the datacollection two standard reflections were measured every 120min to check the stability of the crystal and the electronics ofthe instrument. Intensities were corrected for Lorentz andpolarization effects and put on an absolute scale by Wilson'smethod.Crystal data. C30Hz50zPRhz, M = 654.3, Triclinic, spacegroup Pi, a = 9.700(2), b = 11.076(2), c = 13.790(3) A, cc == 1.677 g cm-j, 2 = 2, F(000) = 326, Mo-K, radiation,3, = 0.710 69 A, p(Mo-K,) = 13.3 cm-'.Structure solution and refinement. The molecular structureof the complex was solved by conventional Patterson andFourier syntheses. The refinement of the structural model,which was by the method of full-matrix least squares, was105.3(1), p = 109.6(1), y = 99.1(1)", U = 1295 Pi3, D,carried out allowing the Rh, P, 0, and C atoms of the cyclo-pentadienyl ring to vibrate anisotropically, while isotropicthermal parameters were applied to the phenyl carbon atomswhich were refined as rigid groups (symmetry D6,,, C-CI .395 A).Hydrogen atoms could not be located from electron-density difference maps and therefore were included in thescattering model in calculated idealized positions (C-H =0.95 A) with a common thermal parameter ( B = 7 A') but notvaried.The function minimized was CwA', in which w = 3.3088/lo2(Fo) + 0.001 Fo2] and A = IFo\ - IFc]; discrepancy indicesused were R = ( X ~ ~ F o ~ - ~ F c ~ ~ ) / E ~ F o ~ and R' = /Cw(~F0~ -~Fc~>'/~w~~F0~'~ *.Weighting-scheme analyses showed no seriousdependence of mean wA2 on either IFoI and h-'sin0. Thelargest peaks on the final difference map were in proximity ofthe rhodium atoms (maximum value 0.8 e A-')). Atomicscattering factors were taken from ref. 23. Allowance wasmade for the anomalous scattering of the rhodium andphosphorus atoms, using values of A f ' and Af" from ref. 23.The final conventional R value for the 2 697 observed reflec-tions with I > 2.5o(Z) was 0.053 (R' = 0.059). Final atomicparameters are presented in Table 1. All calculations werecarried out on the 1BM 4331 computer of the Centro diCalcolo Elettronico della Universita di Messina with theSHELX 76 program for crystal structure determination2'AcknowledgementsWe thank the C.N.R. and the Public Education Ministry forfinancial support.References1 A.J. Deeming, ' Transition Metal Clusters,' ed. B. F. G.Johnson, Wiley, New York, 1980; E. L. Muetterties, Science.1977,196, 839; G. L. Geoffroy, Acc. Chem. Rex, 1980,13,469;R. Poiblanc, Inorg. Chim. Acta, 1982, 62, 75 and refs. therein.2 J. Halpern, Inorg. Chim. Acta, 1982,62, 31 and refs. therein.3 F. Faraone, S. Lo Schiavo, P. Piraino, G. Bruno, and G. Bom-bieri, XXII Int. Conf. Coord. Chem., Budapest, Hungary, 1982,750; G. Bombieri, G. Bruno, F. Faraone, S. Lo Schiavo, and G .Tresoldi, Seventh European Crystallographic Meeting,Jerusalem, Israel, 1982, 200.4 H. Werner, Coord. Chem. Rev., 1982, 43, 165.5 H. Werner and B. Klingert, J .Organomet. Chem., 1982,233, 365.6 F. Faraone, G. Bruno, G . Tresoldi, G . Faraone, and G. Bombieri,7 M. S. Mills and E. F. Paulus, J . Organornet. Chem., 1967, 10, 33 I .8 F. Faraone, S. Lo Schiavo, G. Bruno, P. Piraino, and G . Bom-bieri, preceding paper.9 W. A. Herrmann, J. Plank, D. Riedel, M. L. Ziegler, K. Weiden-hammer, E. Guggolz, and B. Balbach, J . Am. Chem. Soc., 1981,103, 63.10 R. Colton and M. J. McCormick, Coord. Chem. Reu., 1980,31, 1 .11 F. A. Cotton, Prog. Inorg. Chem., 1976, 21, 1.12 C. J. Schaverien, M. Green, A. G. Orpen, and I. D. Williams,J . Chem. Soc., Chem. Commun., 1982, 912.13 W. A. Herrmann, C. Bauer, G. Kriechbaum, H . Kunkely, M. L.Ziegler, D. Speth, and E. Guggolz, Chem. Ber., 1982, 115, 878.14 R. J. Haines, E. Meintjies, and M. Laing, Inorg. Chim. Acta,1979,36, L403.15 F. A. Cotton, B. A. Frenz, and L. Kruczynski, J. Am. Chem.Soc., 1973, 95, 951.16 W. A. Hermann, C. K. R. Goddard, and 1. Bernal, J. Organomet.Chem., 1977, 140, 73.17 H. G. Schuster Woldan and F. Basolo, J . Am. Chem. Soc., 1966,88, 1657.18 J, Evans, B. F. G. Johnson, J. Lewis, T. M. Matheson, and J. R.Norton, J . Chem. SOC., Dalton Trans., 1978, 626.19 W. A. Herrmann, C. Kruger, R. Goddard, and I. Bernal,Angew. Chem., Int. Ed. Engl., 1977, 16, 334.J . Chem. SOC., Dalton Trans., 1981, 1651 and refs. thereinJ . CHEM. SOC. DALTON TRANS. 1983 182320 W. A. Herrmann, J. Plank, M. L. Ziegler, and P. Wulknitz,21 R. S. Dickson, C . Mok, and G. Pain, J . Organomet. Chem., 1979,32 J. Evans, B. F. G. Johnson, J. Lewis, and J. R. Norton, J .23 ‘International Tables for X-Ray Crystallography,’ 3rd edn.,24 G. M. Sheldrick, SHELX 76, Program for Crystal StructureReceived 1 6th November 1982 ; Paper 211 927Chem. Ber., 1981, 14, 716.166, 385.Chem. Soc., Chem. Commun., 1973, 79.Kynoch Press, Birmingham, 1974, vol. 4.Determination, University of Cambridge, 1976