Organometallics 1986,5, 383-385
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knowledge the donors of the Petroleum Research Fund, ration in 3 is 2.622 (4) A which is considerably longer than administered by the American Chemical Society for the the M w B separation in Mo(CO)~(BH~)-, 2.41 (2) A, and support of this research. R.T.P. and H.N. recognize suplonger than the sum of the estimated covalent radii, port for collaborative studies on borophane ligands pro2.44-2.49 A. Lastly, the Mo-H(lc) distance, 1.78 (3) A, vided by a NATO travel grant. is slightly shorter but within three standard deviations of a range of Mo-H-Mo bridge distances, 1.85-1.89 and Registry No. 2, 99641-85-7; 3, 99641-86-8; N B N ( S ~ M ~ ~ ) ~ , significantly shorter than the avera e Mo-(H-B) bridging 1070-89-9;(C6H5)P(C1)(N[Si(CH3),],J, 84174-75-4;Na(C5H5)Mo(CO)3, 12107-35-6; B2H6, 19287-45-7; H3B.THF, 14044-65-6; distance in Mo(CO)~(BH~)-, 2.02 PhPC12, 644-97-3. As a final structural point it is noted that the bridging hydride occupies a coordination position on the Mo atom; Supplementary Material Available: Listings of observed therefore, the C ~ M O ( C O ) ~ [P(X)(Y)] (H) fragment should and calculated structure factors, positional parameters, anisotropic be considered as a four-legged piano stool. The average thermal parameters, and bond distances and angles (21 pages). M-CO distance, 1.963 A, and O C - M d O angle, 78.5 ( 2 O ) , Ordering information is given on any current masthead page. compare favorably with the respective parameters in other C ~ M O ( C O ) ~complexes.25 L, The bonding in 3 has been examined with extended On the Metal Coordination In Base-Free Hiickel calculationsz6which reveal two principal interactions between the simplified fragments C ~ M O ( C O ) ~ P H ~Trls(cyciopentad1enyi) Complexes of the Lanthanolds. 2.' The X-ray Structure of and BH,. One high-lying occupied MO and the LUMO of the C ~ M O ( C O ) ~ fragment PH~ are chiefly bonding and (C5L5)3La*11:A Notably Stable Polymer Dlsplaylng antibonding combinations of a d orbital on the Mo atom More Than Three Different La-4 Interactions and the p orbital on the P atom that is perpendicular to Stefan H. Eggers, Jurgen Kopf, and R. Dieter Fischer' the PHz plane. While the bulk of the electron density in Institut fur Anorganische and Angewandte Chemie the bonding orbital is on the phosphorus atom, the LUMO Universitat Hamburg, 0-2000Hamburg 13, F.R.G. is primarily localized on the Mo atom.z7 The high-lying occupied MO of C ~ M O ( C O ) ~ P donates H ~ electron density Received July 30, 1985 into the BH, fragment LUMO, the p orbital on the B atom Summary: Crystalline base-free Cp,La (Cp = C5H5; perpendicular to the BH, plane, resulting in a B-P inmonoclinic P, space group ~ 2 , a; = 8.427 (5) A, b = teraction. The C ~ M O ( C O ) ~ PLUMO H ~ also accepts electron density from one of the degenerate HOMO'S of 9.848 (5) A, c = 8.456 (6) A, ,8 = 115.80 (6)'; Z = 2; the BH, group which lies in the BH, plane and is a bonding R = 0.077) forms polymeric zig-zag chains of distinct combination of a B atom p orbital with the s orbital of the (C5H5),La(p-q5:q2-C,H,) units involving two nonequivalent bridging hydrogen atom.28 (The other two H atom s terminal Cp ligands. The individual L a 4 distances clusorbitals also mix constructively with the other lobe of the ter predominantly around 2.6, 2.8, 2.9, and 3.0 A within B atom p orbital.) Mo-Hb bonding is enhanced and B-Hb the unexpectedly wide range 2.560-3.034 A. bonding is diminished (relative to the separated fragments) by this mixing of fragment MO's. Such appropriations of While the synthesis of base-free (C5H5),M complexes electron density are well-known for C-H bonds where a (including the first well-defined organo-rare-earth comwealth of structures has illuminated the preliminary stages pounds;2 M = Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, and of C-H bond a c t i ~ a t i o n . Furthermore, ~~ it is intriguing Yb)3dates back to 1954, the elucidation of the crystal and to note that the structure of 3 might be considered to molecular structures of representatives of this fundamental represent a trapped intermediate in the addition of a B-H class of compounds has turned out considerably more bond across the formal Mo=P bond. difficult than for the majority of their derivative^.^^^ In The formation and solid-state structure of 3 can be ra1969, a first report based on a crystallographic X-ray tionalized and understood with the bonding picture deanalysis suggested for Cp,Sm a rather complex situation scribed above. It remains to be demonstrated that the involving two different polymeric chains along with same structure prevails in solution. Detailed IR and NMR strongly disordered Cp ring^.^?^ While crystalline (C5studies of solutions of 3 are in progress, and additional H 5 ) 3 S involves ~ chains of well-defined ( T ~ - C ~ H ~ ) ~ S C ( I . L studies of the reactions of electrophilic reagents with 2 are 7':9'-C5H5) units,' the likewise polymeric compound (C5underway. H5)3Pr (1) is built up of zig-zag chains of distinct ( ~ 7 ~ C5H5)zPr(p-qx:q5-C5H5) units with 1 < x < 2.' Our conAcknowledgment. R.T.P. and J.V.O. wish to actinuing interest in the structures of Cp,Ln systems (Ln =
x.
(24) Love, R. A.; Chin, H. B.; Koetzle, T. F.; Kirtley, S. W.; Whittlesey, B. R.; Bau, R. J. Am. Chem. SOC. 1976,98,4491. (25) Curtis, M. D.; Han, K. R. Inorg. Chem. 1986,24, 378. (26) (a) Hoffmann, R. J. Chem. Phys. 1963,39,1397. (b) Hoffmann, R.; Lipscomb, W. N. Ibid. 1962,36, 2179; 1962,37, 2872. (c) Ammeter, J. H.; Burgi, H. B.; Thibeault, J. C.; Hoffmann, R. J.Am. Chem. SOC. 1978, 100, 3686. (d) Parameters: Summerville, R. H.; Hoffmann, R. J. Am. Chem. Soc. 1976,98,7240. (e) Both D S h BH, and BH3with observed bond lengths were used. Some averaging of experimental bond lengths and bond angles was necessary to impose C, symmetry. (0 Calculations performed with the interactive program EHT, by J. V. Ortiz. (27) The r Mo-P interaction is much less covalent in CpMo(CO),PH, than in 1, where the p orbital on the phosphorus atom is destabilized by the NR2 groups. (28) The same qualitative picture emerges whether the observed BH, geometry or an idealized D3h BH, geometry is employed in the calculations. (29) C-H-transition-metal bonds are reviewed in: Brookhart, M.; Green, M. L. H. J. Organomet. Chem. 1983, 250, 395. An extensive theoretical analysis is presented in: Saillard, J. Y.;Hoffmann, R. J.Am. Chem. SOC.1984,106, 2006.
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(1) Part 1: Hinrichs, W.; Melzer, D.; Rehwoldt, M.; Jahn,W.; Fischer, R. D. J. Organomet. Chem. 1983,251, 299. (2) For the most recent reviews on organolanthanoid chemistry, see: (a) Schumann, H. Angew. Chem., Znt. Ed. Engl. 1984, 23, 474. (b) Schumann, H.; Genthe, W. In 'Handbook on the Physics and Chemistry of Rare Earths", Gschneidner, K. A., Ed.; Elsevier: Amsterdam, 1984; Vol. 6, p 445. (c) Schumann, H. In 'Fundamental and TechnologicalAspects of Organo-f-Element Chemistry"; Marks, T. J., Fragalb, I. L., Eds.; D. Reidel Publishing Company, Dordrecht, Holland, 1985; p 1. (3) Wilkinson, G.; Birmingham, J. M. J. Am. Chem. SOC. 1954, 76, 6210, for further literature see ref 2. (4) For a review on organolanthanoid structures, see: Palenik, G. J. In "Systematics and the Properties of the Lanthanides"; Sinha, S. P., Ed.; D. Reidel Publishing Company: Dordrecht, Holland, 1983; p 153. (5) Wong, C.; Lee, T.; Lee, Y. Acta Crystallogr., Sect. B: S t r u t . Crystallogr. Cryst. Chem. 1969, B25,2580. (6) Most recently, a reinvestigation of the frequently questioned (see ref 1) structure of Cp,Sm6 has been attempted and turned out extremely difficult: Eggers, S.; Kopf, J.; Fischer, R. D., unpublished results. (7) Atwood, J. L.; Smith, K. D. J. Am. Chem. SOC.1973, 95, 1488.
0 1986 American Chemical Society
384 Organometallics, Val. 5, No. 2, 1986 C12'
Communications
A), appear, after correction for the appropriate radius of Ln(III),Scomparable with those of the short intramolecular Ln-C contacts of two recently examined (C5H5)*, Ln.-(CH,)Si(CH,),CHSi(CH,), systems.16 While distinct M-C(methy1) bonds may be ruled out in the latter case and although the sublimation enthalpy of 2 does not notably exceed that of 1 (nor the values of other Cp3Ln systems),1' there is increasing experimentalevidence of a more pronounced tendency of 2 (relative to 1) to form the sparingly soluble polymer, or to oligomerize in solution, rather than to add one Lewis base molecule, L. Thus, in CHzC12which cleaves Cp,Ln aggregates more readily than C6H618the solubility of 1 (11.4 mg/mL) exceeds that of 2 (0.6 mg/mL) by more than 1 order of magnitude. Actually, the 'H NMR spectrum of 2 in CD2C12displays two Cp proton resonances even at room temperature (6 6.25 and 6.09; Irel= ca. 2 and 3) whereas 1 gives rise to one singlet down to -40 "C (6 21.1).18 Hence, at least one (Cp,La). species might be sufficiently long-lived on the 'H NMR time scale, while the reverse seems to hold for the new adduct Cp,La.NHEt2,l9 the CHz resonance of which is, unlike that of its Pr homologue,20devoid of any diastereotopic splitting down to -70 "C. It has, moreover, been impossible to isolate adducts of 2 with Et2021and Et3N.19 While the crystalline Lewis base adducts of 1 and 2 like, e.g., 312and 413 usually involve three equivalent terminal q5-Cp ligands with rather close-lying individual Ln-C distances,z2one terminal Cp ligand of 2, and to a lesser extent of 1, too, shows a pronounced, and hitherto unp r e ~ e d e n t e d alternance ,~~ of its Ln-C distances: e.g., 2, (La-C)- = 2.560 (6), (La-C), = 2.999 (6), and (La-C),, = 2.805 A; 1,l (PPC),,.,~ = 2.590 (8), (Pr-C), = 2.910 (lo), (Pr-C)8v = 2.784 A.24 While the strikingly small value of (La-C),i, approaches the shortest individual Ln-C(Cp) distances so far reportedz5and would also correlate with those expected for genuine La-C u-bonds,26(La-C),,, I
Figure 1. ORTEP plot of [(CSHs)3La],.Selected bond lengths (in A) and angles (deg): La-C11 2.999 (6); La-C12, 2.949 (6); La-C13, 2.680 (6);La-C14, 2.560 (6);LaC15, 2.774 (5); La-C23, 2.947 (6); LaC24, 2.912 (5);LaC31, 2.897 (6);LaC32, 2.858 (6); LaC34,2.730(5);La"C21, 3.034 (6);La'%22,3.032 (6);La"C23 to La"C25 I3.713; Centl-LaCent2,111.5 (2); Centl-LaCent3, 114.9 (2); Cent2-La-Cent3, 116.5 (2); La'-La-"'', 114.8.
La-Lu) has primarily8 been focused on the La complex (C5H5),La(2), mainly for three reasons. (a) Owing to the maximal ionic radius in case of Ln(II1) = La(III),Snotable differences even between the structures of 1 and 2 might be envisioned. (b) While the literature is still devoid of any detailed description of the chemistry of 2, this compound belongs to the few commercially available organolanthanoidslOand has been claimed to be advantageous in arriving, e.g., at some prostaglandine precurs0rs.l' (c) The only X-ray studies of organo La complexes so far reported are those of the two base adducts of 2, CP,L~.THF'~(3) and C P , L ~ ( N C M ~ (4). )~'~ Following the original procedure: sublimed 2 was prepared in yields up to 89%.14 In contrast to an earlier attempt,I2single crystals suitable for an X-ray study were obtained aside major portions of amorphous material both during the stepwise high-vacuum sublimation of crude 2 (250-300 "C) and by resublimation (ca. 235 "C). The structure of 216 resembles that of 1' in view of a number of features, including the crystal system and the space group. Thus, 2 forms uniform nonlinear polymeric chains, carrying again adversely disordered Cp rings, but, in contrast to 1, 2 consists of well-defined (q5-C5H&La(kqz:q5-C5H5)units (Figure 1). The bridging Cp ring lies notably more remote from ita q5-bondedLn atom than the two terminal q5-Cp ligands: 2, Cent(Cp)-Ln = 2.705 (5) ((Lax), = 2.955), 2.555 (6), 2.532 (6) A; 1,".602 ((Pr-UaV = 2.875), 2.526, 2.488 A. The lengths of the two p-C-La' contacts of 2, 3.034 (6) and 3.032 (6) A (1,l 2.940 and 3.130 (8) A systematic survey of the mostly nonuniform structures of basefree Cp3Ln systems with Ln = La, Pr, Nd, Er, Tm, and Lu is going to be published in due course. (9) r(La)-r(Pr) = 0.06 A; see: Shannon, R. D. Acta Crystallogr. Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, A32, 751. (10) Together with Cp,Sm; Strem Chemicals Inc., No. 57-3000 and 62-3500. (11) Thus, unlike MCp (e.g., M = Li, Na, Tl), 2 reacts, e.g., with alkylsulfonates to give exclusively the 5-alkylcyclopentadienes:French Patents 2221424 (1973) and 2259089 (1974). (12) Rogers, R. D.; Atwood, J. L.; Emad, A.; Sikoric, P. J.; Rausch, M. D. J. Organomet. Chem. 1981,216, 383. (13) Li, X.-F.; Eggers, S.; Kopf, J.; Jahn, W.; Fischer, R. D.; Apostolidis, C.; Kanellakopulos, B.; Benetollo, F.; Polo, A.; Bombieri, G. Inorg. Chim.Acta 1985,100,183. (14) Reaction of 5.35 g (21.8 mmol) of LaCl, with 6.2 g (70.4 mmol) of NaCp over 8 h; the crude product was dried at 130 "C for 5 h; high vacuum sublimation (in Schlenk tube of 25-cm length and 3.5-cm diameter): 8 h, up to 220 OC; 8 h, up to 260 OC; 8 h, up to 300 "C. Color of sublimed 2: yellowish. Total yield: 6.5 g (19.4 mmol = 89%) of (C5H&La (maximal yield according to ref 3, 25%). (15) Crystal data (25 "C): monoclinic P, a = 8.427 (5) A,b = 9.848 (5) A, c = 8.456 (6) A,B = 115.80 (6)O,2 = 2, p = 1.757 g.cmV3,Syntex P2,, Mo K,, graphite monochromator, 4.5'< 26 < 500, full-matrix least-squares refinement (treating the ring C atoms exactly as described in ref 1) based on 1721 observed reflections ( I > 3 4 ) led after numerical absorption corrections to a final R (unweighted) of 0.0771 (anisotropic temperature factor, positions of H atoms calculated).
(16) . , (a) . Ln = Nd: Nd-.C = 2.895 (7) A. Nd-C(a-bond) = 2.517 (7) A. Mauermann, H.; Swepston, P. N.; Marks, T. J. Organometallics 1985,4, 200. (b) Ln = Y Y-C = 2.85 A, Y-C (a-bond) = 2.43 A. Teuben, J. H. In "Fundamental and Technological Aspects of Organo-f-Element Chemistry"; Marks, T. J., Fragali, I. L., Eds.; D. Reidel Publishing Company: Dordrecht, Holland, 1985; p 195. (17) Exception: Ln = Lu: (a) Devyatykh, G. G.; Borisov, G. K.; Krasnova, S. G. Dokl. Akad. Nauk SSSR 1972,203,110. (b) Devyatykh, G. G.; Borisov, G. K.; Zyuzina, L. F.; Krasnova, S. G. Dokl. Akad. Nauk SSSR 1973,212, 127. (18) Jahn, W. Ph. D. Thesis, Universitlit Hamburg, 1983. (19) Eggers, S. H.; Fischer, R. D., unpublished results. (20) Jahn, W.; Yunlu, K.; Oroschin, W.; Amberger, H.-D.; Fischer, R. D. Inorg. Chim.Acta 1984, 95, 85. (21) Completely white (in contrast to sublimed 2) and analyticallyvery pure 2 could readily be isolated from suspensions of 2 in OEtz. (22) For the structure of Cp,Pr(NCMe),, see ref 13. For the structure of Cp,Pr.THF, see: Fan, Y.; Lu, P.; Jin, Zh.; Chen, W. Sei. Sin., Ser. B (Engl. Transl.) 1984, 27, 993. (23) For comparison, for the sterically rather congested complex Ta(~5-Cp)(~2-CzH4)(PMezPh),C1, was found: (Ta-C),i, = 2.37 (1) A, (TaC), = 2.62 (3) A; here (Ta-C),, does not turn out drastically smaller than (Ta-C),, of less perturbed Cp,Ta"' systems ( n = 1 or 2). See: Atwood, J. L.; Honan, M. B.; Rogers, R. D. J. Cryst. Spectrosc. Res. 1982, 12, 205 and references therein. (b) The relative scattering of La-C in 2 also exceeds that of Th-C in the complex MezSi(C5Me4)2Th(CH2SiMe3)2 where a rather pronounced dispersion about the average ring C-C distance has been observed too: Fendrick, C. M.; Mintz, E. A.; Schertz, L. D.; Marks. T. J.: Dav. V. W. Ormnometallics 1984. 3. 819. (24j For the ;her termink Cp ligand of 2 were found: (La-C),,, = 2.730 (5) A, (La-C),, = 2.897 (6) A, (La-C),, = 2.818 A. (25) (Ln-C),. is, e.g., 2.582 (7) A in [Cp,Sm(SiMe,),l- (Schumann, H.; Nickel, S.; Hahn, E.; Heeg, M. J. Organometallics 1985,4, 800) and 2.48 (5) A in Cp,LuCl.THF (Ni, Ch.-Zh.; Zhang, Zh.-M.; Deng, D.-L.; Qian, Ch.-T. J . Organomet. Chem., in press. Qian, Ch.-T., personal communication). (26) See, for comparison, Nd-C(HSi,) of (CSMeS)1NdCH(SiMe3)z;16a however, (La-C),,, of 2 is smaller than Pr-C(N) of Cp3PrCN-c-C6Hll (2.68 A): Burns, J. H.; Baldwin, W. H. J. Organomet. Chem. 1976,120, 361.
Organometallics 1986,5, 385-386
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equals the comparatively long bridging contact La’-.p-C(CP). In summary, the coordination of La(II1)) in 2 is, probably due to optimal intra- and interchain packing, so irregular that any description in terms of either a common coordination polyhedron or a formal coordination number (in terms of integer electron pairs) appears inappropriate. Including all L w C contacts up to 3.035 A, the same total ligand hapticity of 17 as for 413 would result.
Acknowledgment. We gratefully appreciate grants (for S.E.) by the Allgemeiner Forschungspool der Universitat Hamburg and by the Deutscher Akademischer Austauschdienst (DAAD),Bonn. Dip1.-Chem. Holger Schultze kindly contributed a fraction of carefully sublimed 2. Registry No. 2, 1272-23-7. Supplementary Material Available: Tables of crystal data, atomic parameters and temperature factors, most important bond distances and angles, anisotropic thermal parameters, calculated hydrogen atomic parameters, and observed and calculated structure factors (15 pages). Ordering information is given any current masthead page.
On the Mechanism of the Hydrogenation/Dehydrogenation of a C, Fragment on a Triiron Cluster Site 1. K. Dutta, J. C. Vltes, and T. P. Fehlner” Department of Chemistty, University of Notre Dame Notre Dame, Indiana 46556 Received September 6, 1985
Summary: Deuterium tracer studies show that the proton-induced hydrogenation/dehydrogenation of a triiron vinylidene anion/triiron ethylidyne proceeds via a mechanism in which protonation/deprotonation takes place on the organic fragment while hydrogenation/dehydrogenation occurs on the triiron fragment. Evidence is presented for the formation of an unsaturated intermediate in the protonation step.
Reactions on ligands bound to metal cluster systems are of great interest as they can serve as realistic models for reactions occurring in heterogeneous phases.’ Presently, however, concepts of cluster reactivity are based extensively on the isolation and characterization of reasonably stable systems. Although the structure and bonding of such species provide a necessary foundation for an understanding of reactivity, they are no substitute for true mechanistic investigations.2 Recently we reported3 that the deprotonation of (p-H)3Fe3(CO)g(p3-CCH3)(I) results in the loss of H2and the formation of the vinylidene anion4 (1)Muetterties, E.L.; Rhodin, T. N.; Band, E.; Brucker, C. F.; Pretzer, W. R. Chem. Reo. 1979,79,91. (2) A recent report illustrates the danger of basing mechanistic ideas on stable, reasonable structures: Stoutland, P. 0.;Bergman, R. G. J.Am. Chem. SOC.1985.107.4581. (3)Vites, J. C.f Jacobsen, G.; Dutta, T. K.; Fehlner, T. P. J.Am. Chem. SOC.1985,107,5563. (4)Lourdichi, M., Jr.; Mathieu, R. Nouu. J. de Chim. 1982,6, 231.
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[ (p-H)Fe3(CO)gC=CHz-] (11) (eq 1). This reaction is quantitative at 25 OC. The reverse reaction takes place
H3Fe3(CO)gCCH3 + NR3
1 -1
HFe3(CO)gC=CHz- + HNR3+ + Hz (1) at 25 OC under 1 atm of H2 in 70% yield. As these two reactions constitute the formal dehydrogenation and hydrogenation of a C2fragment on a metal cluster framework under mild conditions and as the cluster system is a relatively simple one in terms of structure, we are investigating some aspects of the mechanism of the reaction. An obvious question raised by reaction 1 concerns the hydrogens removed as H+ and H2, viz, where do they come from in the forward reaction and where do they go in the reverse reaction ? On many clusters the protonation of metal-metal bonds is thermodynamically f a ~ o r e dhow,~ ever, this is not a mechanistic requirement. Indeed, examples of kinetically controlled protonation are knowna6 A direct way of answering this question is by isotopic labeling provided hydrogen scrambling in the products is slow relative to product characterization. As there was no evidence from ‘H NMR that the two types of hydrogen in I exchanged at room temperature, the conversion of I1 to I in the presence of H+ was investigated first. Treating a 1.0-mmol sample of K[HFe3(CO)gC=CH2] with H2in the presence of D+ yielded 0.7 mmol of I which, when analyzed by lH and 2H NMR, was shown to contain 85% of the D in the methyl group of the capping carbon. As demonstrated by the spectra in Figure 1, treating a similar sample of I1 with D2 in the presence of H+ yields selectively labeled I, i.e., HD2Fe3(CO)&CH3. The first labeling experiment suggests that the proton attacks the vinylidene fragment of I1 in preference to the iron base. This would produce an unsaturated intermediate, one possible representation of which is shown in Scheme I. Protonation at this position would weaken the coordination of the vinylidene double bond to the third iron, thereby opening a coordination site for Hzat the unique iron. This provides a route for the incoming H s of H2 to go directly to basal Fe-H-Fe positions to form I as we observe. If the unsaturated intermediate has a finite lifetime, it should be easily trapped by Lewis bases. Thus, we can rationalize the formation (p-H)Fe3(CO)g&-CO)(p3-CCH3), III,7awhich is produced on protonation in the presence of CO and which always constitutes the major byproduct of reaction -1. In the latter case, I11 is attributed to reaction of the intermediate with adventitious CO. (5)Deeming, A.J. “Transition Metal Clusters”; Johnson, B. F. G., Ed.; Wiley: New York, 1980. (6) Stevens, R. E.; Gladfelter, W. L. J.Am. Chem. Soc. 1982,104,6454. (7)Kolis, J. W.; Holt, E. M.; Shriver, D. F. J. Am. Chem. SOC.1983, 105,7307. (8) Vites, J. C.; Housecroft, C. E.; Jacobsen, G. B.; Fehlner, T. P. Organometallics 1984,3, 1591.
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