Organometallics 1983,2, 355-356
355
Scheme I
Registry No. 1,82647-62-9;2, 82647-60-7; 3, 84081-57-2; (p-
H)RU~(CO),(~~-?’-C~CP~), 82647-61-8; OS~(CO),(~~-V’-CE CPh)(PPh,),82640-93-5; t-BuNC, 7188-38-7; n-BuNH,, 109-73-9;
Ru,7440-18-8; OS, 7440-04-2. Supplementary Material Available: Table I, atomic positions, Table 11, anisotropic thermal parameters, Table 111, bond lengths and angles for (p-H)(Ru3(C0),[C(CN-t-Bu)CPh], Table IV, atomic positions and thermal parameters, Table V, bond ;N-lr-L lengths and angles for 0s3(CO),[C(C(NH-t-Bu)(NH-n-Bu))CPh](PPh’), and listings of structure factor amplitudes for both compounds (44 pages). Ordering information is given on any masthead page. of a number of rhodium and iridium amides which not only may be readily prepared in high yields as crystalline solids but are thermally stable under inert atmosphere, both in the solid state and in solution. In addition, some of these Amides of Rhodium and Irldlum Stabilized as Hybrld complexes show unusual catalytic hydrogenation behavior Multidentate Ligands with simple olefins under very mild reaction conditions. Reaction of LiN(SiMezCH,PPhz)2 with a variety of Mlchael D. Fryzuk’ and Patricia A. MacNeli rhodium precursors in cold toluene or ether solutions, Department of Chemistry, University of British Columbia followed by extraction with hexane, results in high yields Vancouver, British Columbia, Canada V6T 1Y6 of the rhodium(1) amido phosphines 1-5 (eq 3). All of Received August 24, 1982 these complexes are highly air- and moisture-sensitive crystalline solids; they are typically recrystallized from Summary: A variety of rhodium and iridium amido phoshexane at -30 “C to give analytically pure products in phine derivatives have been isolated and fully character7 0 4 0 % yields. ized. These complexes are exceptionally stable, a unique (Rh(CO)zC1)2 feature of group 8 transition-metal amides, owing to the (Rh(COE)2Cd2 fiPp“2 incorporation of the amido function as a part of a “hybrid” Me,Si I LiN(SiMe2CH2PPh2), + [Rh(C2H4),C112 ligand. The catalytic homogeneous hydrogenation activity :N-RhL Rh( PMe3)4+CI Me& I of these rhodium and iridium species has also been inRh(PPhJ,CI 2h: (3) vestigated. ~
Although amides of the.“hard” early transition metals are well-known, such complexes of the “soft” later metals are very rare. The paucity of amide derivatives of the group 8 metals may be ascribed to unfavorable hard/soft pair interactions as well as kinetic instability. Attempts to isolate rhodium alkylamides were owing to decomposition via @ elimination of the metal-amide bond (eq 1). The incorporation of a ligand having no RhC1(PPh3),
LiNMez
RhH(PPhJ3
+ CH2=NMe
(1)
@-hydrogensresulted in the synthesis of the first rhodium amide2 (eq 2). However, although this complex is stable RhC1(PPh3)3
LiN(SiMe&
Rh(PPh3)2N(SiMe3)2(2)
under inert atmospheres in the solid state, decomposition, with concomitant elimination of HN(SiMe3)2,occurs at 25 “C in benzene solution (tip = 12 h). We have previously described3 the use of the hybrid ligand strategy in the design of novel transition-metal amido phosphine complexes. The term “hybrid” refers to a ligand system that contains both “hard” and “soft” donors linked in a chelating manner. To date, we have used this approach to prepare amido phosphine derivatives of Ni(11),Pd(11), Pt(II),4,5 Zr(IV), and Hf(1V) illustrating the versatile coordinating ability of this ligand type. We now wish to report the isolation and characterization ,6y7
(1) Diamond, S. E.; Mares, F. J. Organomet. Chem. 1977,142,C55.
(2)Cetinkaya, B.; Lappert, M. F.; Torroni, S. J. Chem. Soc., Chem. Commun. 1979,843. (3)Fryzuk, M.D.; MacNeil, P. A. J.Am. Chem. SOC.1981,103,3592. (4)Fryzuk, M. D.; MacNeil, P. A. Organometallics 1982,1, 918. (5)Fryzuk, M. D.; MacNeil, P. A. Organometallics 1982, 1, 1540. (6)Frvzuk, M. D.; Rettig, S. J.; Williams, H. D., submitted for publication in Inorg. Chem. (7)Fryzuk, M. D.;Williams, H. D. Organometallics 1983,2, 162.
L:
1
2 3 4 5
co
cyclooctene C2H4
PMe, PPh,
In all of these complexes, the hybrid ligand is coordinated in a tridentate fashion, binding to the rhodium center through both phosphines and the amide nitrogen, resulting in a square-planar, 16-electron species. The exclusive trans disposition of the chelating phosphines was established by the presence of a virtual triplet8 for the CH2Pprotons at -1.8 ppm in the IH NMR (Japp y 5 Hz). Further support for this trans configuration was given by the the chemical shift difference of 0.6-1.0 ppm between the ortho and para/meta protons of the P-phenyl substituents, when the spectrum is recorded in deuterated aromatic solvent^.^ Deuteriobenzene solutions of these complexes, sealed in NMR tubes under nitrogen, show no decomposition, even after several months at 25 “C. The analogous iridium derivatives may be prepared in a similar manner or, more simply, via reaction of the iridium cyclooctene amide (6) with the desired neutral ligand at room temperature in toluene (Scheme I). In contrast to the previous preparation of the rhodium analogues, the solvent used in the synthesis of the iridium amides is crucial; when diethyl ether is employed, inseparable mixtures of products are formed whereas the use of toluene results in high yields of the pure complexes. Once again, the lH NMR spectra of these derivatives indicate that all are square-planar complexes with trans disposed phosphines. It should be noted that only one other iridium amide complex, Ir(C0D)(N(SiMe3),](PEt3), has been prepared to date.1° Rhodium and iridium amides have also been synthesized ~~
~~~
(8)Brookes, P.R.; Shaw, B. L. J. Chem. SOC.A 1967,1079. (9)Moore, D. S.;Robinson, S. D. Inorg. Chim. Acta 1981,53,L171.
0 1983 American Chemical Society
Communications
356 Organometallics, Vol. 2, No. 2, 1983
incorporating bidentate hybrid ligands. The preparation of the cyclooctadiene derivatives 9 and 10 is very straightforward (eq 4);carried out at room temperature, {M(CODlC1)2
+
0CH3
LiN(CH2C,HS)(SiMe2CH2PPh21
R .T.
(4)
9 , M:Rh 10, M : I r
the products are obtained in virtually quantitative yields as analytically pure crystals. Although exceptionally air and moisture sensitive, these complexes, either as solids or in solution, undergo no decomposition (via p elimination) under inert atmospheres. As anticipated, some of these 16-electron Rh(1) and h(1) species are catalyst precursors for the homogeneous hydrogenation of simple olefins. For both the [Rh(COE)N(SiMezCHzPPhz)z](COE E cyclooctene) and [Rh(PPh,)N(SiMezCHzPPhz)z]systems, 1-hexene is efficiently hydrogenated to hexane under one atmosphere of hydrogen at 22 “C. Typical runsll were carried out in neat olefin, employing a substrate to catalyst ratio of approximately 1OOO:l. The hydrogenations were monitored by GLC” and indicate a rather unusual feature of these rhodium amido phosphines, that is, their surprisingly high isomerization activity. Assuming that hydrogenation proceeds through a dihydride intermediate (either via the well-established “hydride route” or “unsaturate routen13),only straightforward reduction of olefinic substrates would be expected, since most rhodium phosphine dihydride species show very little, if any, tendency toward olefin isomerization.14 However, when either [Rh(C0E)N(SiMe2CH2PPh2)21or [Rh(PPh3)N(SiMezCHzPPhz)z] is employed as catalyst precursor, the turnover number15 for isomerization of 1(10) Kermode, N. J.; Lappert, M. F.; Samways, B. J., presented in part at the International Conference on the Chemistry of the Platinum Group Metals, Bristol, England, July 1981. (11) (a) A typical run was carried out in a 250-mL heavy-walled flask, fitted with a Kontes 9-mm needle-valve inlet, attached directly to a vacuum line that had access to vacuum and purified hydrogen (passed through MnO on vermiculite and activated 4-A molecular sieves11b). Reaction temperature was maintained at 22 “C through the use of a glass water-jacket attached to a Haake temperature-controlling unit. The substrates (1-hexene and cis/trans-2-hexene) were purchased from Aldrich (Gold Label) and dried over activated 4-A molecular sieves, vacuum transferred, and freeze-pump-thawed several times. Any trace peroxides were removed by passing the dried olefins through a short column of activated alumina (Fisher 80-200 mesh). Samples were withdrawn via syringe and vacuum transferred away from the catalyst prior to GLC analysis. (b) Bafus, D. A.; Brown, T. L.; Dickerhoff, D. W.; Morgan, G. L. Rev. Sci. Instrum. 1962, 33, 491. (12) Column specifications: 60/80 Chromosorb P(AW)/20% tri-ocresyl phosphate, 20 f t X ‘ i sin. SS; column temperature, 40 “C; sample size, 0.5 fiL; detector, FID. (13) Collman, J. P.; Hegedus, L. S. ‘Principles and Applications of Organotransition Metal Chemistry”; University Science: Mill Valley, CA, 1980; Chapter 6. (14) Osborn. J. A.: Schrock, R. R. J . Am. Chem. SOC.1976,98.2134. (15) Turnover numbers given are those values averaged over a number ( > 5 ) of experimental runs and were calculated by using the expression: Turnover number = (mol substrate converted/mol catalyst)/unit time.
hexene to cisltrans-2-hexene (-70/h) is higher than for hydrogenation to hexane (-50/h). Similar behavior obtains for the rhodium and iridium bidentate amido phosphines; with [Ir(COD)((CHzC6H6)(SiMe2CHzPPhz)J1 the turnover number for hydrogenation is approximately 120/h as compared to -40/h for isomerization (the Rh analogue is about 4 times slower). Since no isomerization is observed in the absence of hydrogen, this process is clearly not occurring via oxidative addition of the olefin to form an allyl hydride intermediate (which can then reductively eliminate to produce internal olefins). Presumably then, for these systems, fl elimination of the coordinated alkyl intermediate to form internal olefins is a competing process with reductive elimination of the saturated alkane. The anomalous reactivity of these rhodium catalysts is further demonstrated by the observation that internal olefins such as 2-hexene are hydrogenated as rapidly as terminal ones; this is in contrast to the pronounced preference of terminal vs. internal olefins exhibited by classical Wilkinson-type hydrogenation systems.16 To complicate matters further, the [Ir(COE)(N(SiMezCHzPPhz)z)] derivative shows no evidence of isomerization and only straightforward reduction of olefins to alkanes under identical hydrogenation conditions; the turnover number, using 1-hexene as substrate, is comparable to that of its rhodium congener (-70/h). Although the origins of the unique catalytic activity of these rhodium and iridium hybrid ligand complexes are not fully understood, it is possible that it is a function of the ligand stereochemistry. It has been shown1’ that a facial coordination of the tridentate ligand is possible; therefore, it is conceivable that the rhodium complexes require a fac mer isomerism during the catalytic cycle which slows the reductive elimination step so that reversible elimination can occur. Another possibility is that the dihydride intermediate undergoes reductive elimination of the metal-amide bond to form a monohydride amino phosphine species which then acts as the active catalyst. The olefin isomerization ability of rhodium monohydride complexes has been well documented.16 We are at present further investigating these systems in order to gain more mechanistic information. Acknowledgment. Financial support for this research was generously provided by the Department of Chemistry and the Natural Sciences and Engineering Research Council of Canada. We also thank Johnson Matthey for the loan of RhC1, and IrC13. P.A.M. wishes to thank the Walter C. Sumner Memorial Foundation for a graduate scholarship.
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Registry No. 1, 84074-25-9; 2, 84074-26-0; 3, 84074-27-1; 4, 84074-28-2; 5, 84074-29-3; 6, 84074-30-6; 7, 84074-31-7; 8, 84074-32-8; 9, 84074-33-9; 10, 84074-34-0. Supplementary Material Available: Spectral d a t a (‘H NMR, 31PNMR, IR), analytical data for c o m p o u n d s 1-10, a n d hydrogenation profile g r a p h s (8 pages). Ordering information is given on a n y c u r r e n t m a s t h e a d page.
(16) James, B. R. In “Comprehensive Organometallic Chemistry”; Wilkinson, G., Ed.; Pergamon Press: New York, 1982; Vol. 5, Chapter 51. (17) Fryzuk, M. D.; MacNeil, P. A. Organometallics, in press.
