Organometallics zyxwvu 1986,5, 839-845 839 exchange of carbonyl groups. As shown in Scheme I11 there zyxwvutsr are several plausible intermediates which would allow for carbonyl group migration between Fe and Rh. We favor the doubly bridged structure F since it is easily achieved from both isomeric C and D and it maintains the favored K -~~,~~-C,H, bonding functionality. Furthermore, the process is related to the well-established merry-go- round mechanism for carbonyl group migration in di- and polynuclear metal carbonyl compounds.32 An often ob- served feature in these systems is increased facility for carbonyl group migration upon phosphine s u b ~ t i t u t i o n . ~ ~ ~ ~ This is well illustrated in the present context as well. The parent pentacarbonyl la shows no line broadening in the 13C NMR spectrum up to 70 OC whereas in lb this tem- perature represents the coalescence point with an asso- ciated AGS343 of 15.4 kcal/”ol. Conclusion It is apparent from this first reactivity study on la that the bridging cycloheptatrienyl moiety is capable of ex- hibiting a variety of bonding capabilities. This flexible nature can be manifested in two distinct manners. The ability to create coordinative unsaturation is responsible for the facile carbonyl substitution reaction and may promote other reactions as well. The capacity for bonding (36) Mersalla, J. A.; Caulton, K. G. zyxwvutsrqpo Organometallics 1982, 1, 274. mode changes between the Fe-Rh framework and the p-C7H7 ligand is the reason for the movement of terminal CO group to bridging position and the associated CO scrambling processes. Further studies are underway to delineate the scope of the reactivity of la. The synthesis of related (p-C7H7)- MM’(CO)5 (M zyxwv = Fe, Ru, Os and M’ = Co, Rh, Ir) com- pounds are also being explored in order to probe the effect of the metal on the structure, fluxionality, and reactivity in this class of molecules. Acknowledgment. We thank the Natural Sciences and Engineering Research Council of Canada and the Univ- ersity of Alberta for financial support of this work and Johnson Matthey for generous loan of rhodium trichloride. F.E. acknowledges a Feodor Lynen research fellowship from the Alexander von Humboldt Foundation, Bonn, West Germany. Registry No. la, 51608-48-1; lb, 100190-09-8; 2a, 91868-00-7; 2b, 91855-30-0;3a, 91855-31-1; 3b, 91855-32-2; 3c, 91855-33-3;3d, 91855-34-4; 3e, 100190-10-1; 3f, 100190-11-2; Na(C,H,)Fe(CO),, 62313-81-9; [RhC1(COD)]2, 12092-47-6; Rh, 7440-16-6; Fe, 7439- Supplementary Material Available: A table of thermal parameters for lb (Table VIII) and listings of observed and calculated structure amplitudes for lb and 3b (31 pages). Ordering information is given on any current masthead page. 89-6. Synthesis, Molecular Structure, Solution Dynamics, and Reactivity of (gC,H,),M(p-PR,),Rh(q-indenyl) (M = Zr, Hf; R = Et, Ph)+ R. T. Baker” and T. H. Tulip Central Research & Development Department, E. zyxwvut I. du Pont de Nemours & Company, Experimental Station, Wilmington, Delaware 19898 Received June 13, 1985 The “metal-containing diphosphines”, Cp,M(PR2), (Cp = q-C5H5; M = Zr, Hf; R = Et, Ph), displace both coordinated ethylenes from (q-C,H,),Rh(+ndenyl), yielding the early-late heterobimetallic complexes Cp2M(p-PR2)zRh(q-indenyl). The molecular structure of Cp2Zr(p-PPh2)2Rh(q-indenyl) (IC), determined by X-ray diffraction, consists of edge-shared, pseudotetrahedral 16e Zr(IV) and distorted, square-planar Rh(1) centers with a planar ZrP,Rh bridging unit and a Zr-eRh separation of 3.088 (1) A. The indenyl ligand exhibits a pronounced “slip-fold” distortion toward v3-coordination and high barriers (14-15 kcal/mol) to indenyl rotation are observed by lH DNMR. Addition of CH31 to CpzM(p-PEtz)zRh(q-indenyl) affords the cationic d 0 4heterobimetallica [Cp,M&-PEt&Rh (CH3)(+denyl)]I. Red crystals of IC are monoclinic, R1/m (no. ll), with two molecules per unit cell of dimensions a = 9.700 (1) A, b = 18.855 (3) A, c = 10.185 (1) A, and /3 = 112.95 (1)O. The structure was refined to R = 0.029 and R, = 0.031 for 2928 observed reflections. Transition-metal complexes containing the v-indenyl ligand undergo ligand substitution much more readily than their 7-cyclopentadienyl analogs due to the stability of the the aromatization of the indenyl benzene ring.’ The re- (PR,), (cp = M I zr, ~f; R = Et, ph, cyclohexyl (CY)), contain both l e and 3e donor PR, ligands. Donation of both phosphorus lone pairs to a second metal center thus creates an electronically unsaturated early metal center in the resulting PR2-bridged heterobimetallic com- plex. We have previously described the binding of various metal carbonyl4and MLn5 fragments, where M = Ni, Pd, v3 bonding mode in the former, suggested to result from cently reported28 ‘‘metal-containing diphosphines”, Cp2M- (1) (a) Hart-Davis, A. J.; Mawby, R. J. J. Chem. SOC. A 1969,2403. (b) White, C.; Mawby, R. J.; Hart-Davis, A. J. Inorg. Chim. Acta 1970,4,441. (c) Jones, D. J.; Mawby, R. J. Ibid. 1972,6,157. (d) Eshtiagh-Hosseini, H.; Nixon, J. F. J. Less Common Met. 1978,61,107. (e) Caddy, P.; Green, M.; O’Brien, E.; Smart, L. E.; Woodward, P. Angew. Chem., Int. Ed, Engl. 1977, 16, 648; J. Chem. SOC., zyxwvutsrq ~alton Trans. 1980, 962. zyx (0 Caddy, P.; Green, M.; Howard, J. A. K.; Squire, J. M.; White, N. J. Ibid. 1981,400. (g) Bottrill, M.; Green, M. Ibid. 1977, 2365. (h) Gal, A. W.; van der Heijden, H. Angew. Chem., Int. Ed. Engl. 1981,20,978. (i) Diversi, P.; Giusti, A.; Ingrosso, G.;Lucherini, A. J. Organomet. Chem. 1981,205,239. 6) Rerek, M. E.; Ji, L.-N.; Basolo, F. J. Chem. SOC., Chem. Commun. 1983, 1208. (k) Rerek, M. E.; Basolo, F. J. Am. Chem. SOC. 1984, 106, 5908. (1) Casey, C. P.; OConnor, J. M. Organometallics 1985, 4, 384. ’Contribution no. 3775. 0276-7333/86/2305-0839$01.50/0 0 1986 American Chemical Society