1674
Organometallics 1995, 14, 1674-1680
Phosphapentadienyl- Iridium-Phosphine Chemistry. Synthesis, Structure, and Spectroscopy of Phosphapentadienyl-BridgedIridium Dimers John R. Bleeke,* Alicia M. Rohde, and Kerry D. Robinson Department of Chemistry, Washington University, St. Louis, Missouri 63130-4899 Received December 7, 1994@ The reactions of new lithium phosphapentadienide reagents with ClIr(PRd3 have been investigated. Treatment of ClIr(PEt3)3 with lithium phosphapentadienide produced the phosphapentadienyl-bridged dimer [+-q1-phosphapentadienyl)Ir(PEt3)212 (1) as a 1.4:l mixture of trans (la) and cis (lb) isomers. The analogous reaction involving ClIr(PEt2Ph)3 produced [+-q1-phosphapentadienyl)Ir(PEt2Ph)212(2). Again, a 1.4:1 mixture of trans (2a) and cis (2b) isomers was obtained. The mechanism of trans cis isomer conversion was probed by means of a “crossover” experiment: pure samples of trans isomers la and 2a were combined and their conversion to the equilibrium mixture of trans and cis isomers was monitored. The absence of “mixed-dimer” products (i.e,, those containing both Ir(PEt3)2 and Ir(PEt2Ph)z moieties) in these reactions ruled out a trans cis isomerization mechanism involving monomeric (phosphapentadienyl)Ir(PR3)2 units and supported a mechanism involving dissociation of one iridium-phosphido bond, inversion a t the resulting terminal phosphido center, and re-formation of the iridium-phosphido bond. Treatment of ClIr(PEt3)s with lithium 2,4-dimethylphosphapentadienidegenerated [+-q1-2,4-dimethylphosphapentadienyl)Ir(PEt3)2]2 (3). Again, an equilibrium mixture of trans (3a) and cis (3b) isomers was obtained, but the presence of the bulky dimethylphosphapentadienyl ligand led t o a higher fraction of trans isomer (3a:3b = 8:l). The structure of 3a was confirmed by X-ray crystallography (triclinic, Pi,a = 11.756(4) b = 12.011(3) c = 17.716(7) a = 93.50(3)”,p = 92.89(3)”,y = 108.67(3)”,V = 2359.0(15)A3,2 = 2,R = 0.0277,R, = 0.0345).
-
-
A,
During the past 15 years, the chemistry of pentadienyl-metal complexes has been extensively investigated.2 The pentadienyl ligands in these complexes adopt a wide variety of bonding modes, and facile interconversion between these modes leads to interesting dynamic behavior and reactivity. In contrast, relatively little is known about heteropentadienyl ligands, i.e., analogues of pentadienyl in which one of the terminal CH2 groups has been replaced with a heteroatom. In order to learn more about heteropentadienyl ligands and their bonding preferences we have begun t o investigate a series of heteropentadienyl--iridiumphosphine complexes. Our general synthetic approach involves treating halo-iridium-phosphine precursors with anionic heteropentadienide reagents. Previously, we reported our findings in the ~xapentadienyl,~ thia~entadienyl,~ and a~apentadienyl~ ligand systems. We now describe the preparation of anionic phosphapentadienide reagents6 and the use of these novel reagents in the synthesis of phosphapentadienyl-iridium-phosphine complexe~.~ Abstract published in Advance ACS Abstracts, March 15, 1995. (1) Pentadienyl-Metal-Phosphine Chemistry. 29. For the previous paper in this series, see: Bleeke, J. R.; Luaders, S. T. Organometallics, in press. (2) For leading reviews, see: (a) Ernst, R. D. Chem. Rev. 1988,88, 1251. (b)Yasuda, H.; Nakamura, A. J. Organomet. Chem. 1986,285, 15. (c) Powell, P. Adu. Organomet. Chem. 1986, 26, 125. (3)(a)Bleeke, J. R.; Haile, T.; Chiang, M. Y. Organometallics 1991, 10, 19. (b) Bleeke, J. R.; Haile, T.;New, P. R.; Chiang, M. Y. Organometallics 1993, 12,517. (4) Bleeke, J. R.: Ortwerth, M. F.; Chiang, M. Y. Organometallics 1992, 11, 2740. @
A,
A,
Results and Discussion
A. Synthesis of Lithium Phosphapentadienide and Its Reactions with ClIr(PR& Complexes. Lithium phosphapentadienide was prepared in high yield by treating butadienylphosphines with n-butyllithium in diethyl etherhetrahydrofuran (THF) at -98 “C,followed by warming to room temperature. The 13C(lH} N M R spectrum of this orange, THF-soluble species showed four downfield peaks at 6 154.0(C4),142.0(C21, 122.0(C3),and 95.6 (Cl), with labeling as follows: H2
H4
The C4 peak was split into a doublet (J= 40 Hz)due to carbon-phosphorus coupling. Similarly, the lH NMR spectrum included five downfield signals at 6 6.90 (H4), 6.09 (H2),5.89 (H3), 4.12(HlantJ,and 3.87(Hlsm). The phosphido proton appeared at 6 1.88 and was split into a doublet of doublets as a result of large coupling ( J = 160 Hz) to phosphorus and small coupling (J= 12.5 Hz) ( 5 )Bleeke, J. R.; Luaders, S. T.;Robinson, K. D. Organometallics 1994,13, 1592. ( 6 )Recently, the first anionic phosphaallyl reagent was reported: 1993, 115, Niecke, E.; Nieger, M.; Wenderoth, P. J. Am. Chem. SOC. 69R9
( 7 ) A communication describing portions of this work has appeared: Bleeke, J. R.; Rohde, A. M.; Robinson, K. D. Organometallics 1994, 13, 401. (8) Cabioch, J. L.; Denis, J. M. J . Organomet. Chem. 1989,377,227.
0276-7333/95/2314-1674$Q9.QQ/Q0 1995 American Chemical Society
Phosphapentadienyl -Iridium-Phosphine
Chemistry
Organometallics, Vol. 14, No. 4, 1995 1675 Scheme 1
PEta
Isomer)
to H4. Finally, the 31P{1H}NMR spectrum showed a peak at 6 -107.1 (with respect to an external H3PO4 standard). In the absence of decoupling, this signal split into a doublet-of-doublets-of-doubletspattern, as a result of large one-bond coupling to the phosphido proton ( J = 160 Hz) and smaller couplings ( J = 26 and 5 Hz) to other hydrogens in the phosphapentadienide chain. Reaction of lithium phosphapentadienide with ClIr(PEt3)39in tetrahydrofuran at 0 "C, followed by warming t o room temperature, produced the deep red phosphapentadienyl-bridged dimer [b-+phosphapentadienyl)Ir(PEt&12 (1)in good yield (see Scheme 1). The 31P{1H} NMR spectrum of 1 clearly showed the presence of two solution phase isomers in a 1.4:l ratio. The major isomer (trans, la)exhibited a quintet (Jp-p = 19 Hz) at 6 68.0 (intensity 1) for the two bridging phosphido groups and a triplet (Jp-p = 19 Hz) at 6 -4.1 (intensity 2) for the four equivalent PEt3 ligands. The minor isomer (cis, lb) gave rise t o three equal-intensity multiplets at 6 66.4 (phosphido's), 1.0 (PEts's), and -10.0 (PEts's). The downfield 31PNMR chemical shifts of the bridging phosphido ligands (6 68.0 in la and 6 66.4 in lb) are typical for compounds containing a strong metal-metal interaction,1° while the small P-P coupling constants (19 Hz in la)are consistent with a tetrahedral geometry about each iridium center.'l The 13C and lH NMR signals of the phosphapentadienyl ligands in la and lb were very similar to those of the anionic phosphapentadienide reagent. The only major difference was the position of the lH NMR signal for the phosphido hydrogens, which were shifted dramatically downfield (to 6 8.83 in la and 6 8.58in lb) and appeared as a complex multiplet due to their participation in an AAXX' spin system. The X-ray crystal structure of la,which we reported earlier,7 showed the expected tetrahedral coordination geometry about each iridium center. Furthermore, the plane made by the two iridium centers and the two phosphido phosphorus atoms was oriented almost perpendicular t o the plane containing the two iridium centers and the four PEt3 phosphorus atoms; the dihedral angle was 94.6'. The Ir-Ir distance was 2.576(1)A,consistent with the presence of a double bond as required for each metal to achieve an 18e- count. The phosphapentadienyl ligand was essentially W-shaped with torsional angles of 179.2 and -175.5' for Cl-C2C3-C4 and C2-C3-C4-P1, respectively. The carboncarbon bond lengths showed the expected pattern of alternation. (9) Produced in situ by reacting [(cyclooctene)zIrC11zwith 6 equiv of PEt3 in tetrahydrofuran. (10)See, for example: (a) Garrou, P. E. Chem. Rev. 1981,81, 229. (b) Carty, A. J. Adv. Chem. Ser. 1982, No. 196, 163. (11)See, for example: (a) Kreter, P. E.; Meek, D. W. Inorg. Chem. 1983, 22, 319. (b) Jones, R. A,; Norman, N. C.; Seeberger, M. H.; Atwood, J. L.; Hunter, W. E. Organometallics 1983, 2, 1629. ( c ) Burkhardt, E. W.; Mercer, W. C.; Geoffroy, G. L. Inorg. Chem. 1984, 23, 1779.
U(C/.
Isomer)
While phosphido-bridged iridium dimers of this general structure are known,llaJZall contain dialkyl- or diarylphosphido groups. To our knowledge, this is the first example of a primary phosphido-iridium dimer and the first iridium system to exhibit cisltrans isomers. Perhaps the closest known analogue of 1 is [(p-P(H)(tbut))Rh(PMe3)&, reported by Jones et a1.llb However, this complex possesses two substituents on the bridging phosphido group which are very different in size and, as a result, it exists only as the less stericallyencumbered trans isomer. When a pure crystalline sample of trans isomer la was redissolved in benzene, it slowly (over a period of several days) isomerized back to the equilibrium mixture of cis and trans isomers. Two plausible mechanisms can be envisaged for the isomerization in nonpolar s01vents.l~The simplest is the dissociation of one iridium-phosphido bond, inversion a t the resulting terminal phosphido phosphorus center, and re-formation of the iridium-phosphido bond (see Scheme 2).14 While phosphorus inversion barriers are generally quite high, Gladysz15 has recently shown that the AG* for phosphorus inversion in terminal primary metal-phosphido complexes is remarkably low-in the range of 11-15 kcdmol. A second possible mechanism involves reversible dissociation of dimers into monomeric (phosphapentadienyl)Ir(PEt3)~complexes.16 In order to distinguish between these two mechanistic alternatives, we synthesized the diethylphenylphosphine analogue of 1,[$-+phosphapentadienyl)Ir(PEtzPh)& 2. Like 1,compound 2 crystallized from toluene as the trans isomer but slowly converted in benzene solution to a 1.4:l equilibrium mixture of trans (2a)and cis (2b)isomers. When crystalline samples of pure trans isomers la and 2a were dissolved together in benzene at room temperature, we observed the gradual formation of the cis isomers lb and 2b." However, no additional peaks due to the "mixed" dimer, (PEt3)zIrb+phosphapentadienyl)ZIr(PEtzPh)z, were detected in either the phosphido or phosphine region of the 31P (12)(a) Mason, R.; Sotofte, I.; Robinson, S. D.; Uttley, M. R. J. Organomet. Chem. 1972, 46, C61. (b) Bellon, P. L.; Benedicenti, C.; Caglio, G.; Manassero, M. J . Chem. SOC.,Chem. Commun. 1973,946. (c) Arif, A. M.; Heaton, D. E.; Jones, R. A,; Kidd, K. B:; Wright, T. C.; Whittlesey, B. R.; Atwood, J. L.; Hunter, W. E.; Zhang, H. Inorg. Chem. 1987,26, 4065.
(13) In polar solvents, a third mechanism involving deprotonatiod inversiodreprotonation of the bridging phosphido ligands may also be possible. See: Brown, M. P.; Buckett, J.; Harding, M. M.; LyndenBell, R. M.; Mays, M. J.; Woulfe, K. W. J . Chem. SOC.,Dalton Trans. 1991, 3097. (14)A slight variation on this mechanism would involve simultaneous dissociation of two iridium-phosphido bonds, leaving each phosphapentadienyl ligand coordinated to a single iridium center. The dimer would remain intact, held together by metal-metal bonds. (15) Zwick, B. D.; Dewey, M. A.; Knight, D. A.; Buhro, W. E.; Arif, A. M.; Gladysz, J. A. Organometallics 1992, 11, 2673. (16) An analogous mechanism has been postulated for the isomerization of a related rhodium dimer containing p-PMePh ligands.llC (17)The reaction was carried out in the dark to eliminate the slow photoassisted decomposition of 1 and 2.
Bleeke et al.
1676 Organometallics, Vol. 14, No. 4, 1995 Scheme 2
1a (trans isomer)
H'
\
1b (cis Isomer) Scheme 3
-"*WpH2
H1*?-$./cc,,.,
n-butyl Li
Hlanti H3
-C
NMR spectrum. This result rules out reversible dissociation of dimers into monomeric complexes under these rather mild conditions and supports the intramolecular process involving inversion a t the phosphido phosphorus center (cf., Scheme 2). B. Synthesis of Lithium 2,4-Dimethylphosphapentadienide and Its Reaction with ClIr(PEt3)s. Methylation of pentadienide or heteropentadienide reagents often has a dramatic effect on the chemistry of these species.ls In order to assess this effect in the phosphapentadienyl system, we set out t o synthesize lithium 2,4-dimethylphosphapentadienide. Since the precursor phosphine, (dimethylbutadienyl)phosphine, had not previously been reported, we first developed a synthesis for this precursor, as shown in Scheme 3. The diethyl (dimethylbutadieny1)phosphonate(A,Scheme 3) was produced using the general procedure developed by Teulade and Savignaclgfor the synthesis of vinylphosphonates. This species was then reduced to (dimethylbutadieny1)phosphine (B) with dichloroalane in tetraglyme and immediately collected at -196 "C, following the procedure developed by Denis et a1.8 Finally, treatment of this precursor phosphine with n-butyl(18)See, for example: (a) Bleeke, J. R.; Boorsma, D.; Chiang, M. Y.; Clayton, T. W., Jr.; Haile, T.; Beatty, A. M.; Xie, Y.-F. Organometallics 1991, 10, 2391. (b) Reference 3b. (19)Teulade, M.-P.; Savignac, P.; Aboujaoude, E. E.; Lietge, S.; Collignon, N. J . Organomet. Chem. 1986, 304, 283.
lithium at -98 "C, followed by warming t o room temperature, yielded the desired lithium 2,4-dimethylphosphapentadienide (C) as an orange solid. The 13C{lH) NMR spectrum of lithium 2,4-dimethylphosphapentadienide, like that of its unmethylated analogue, exhibited four downfield resonances between 6 160 and 100 for the carbon atoms in the phosphapentadienyl chain ( C l , C2, C3, and C4). The peaks due to carbons C4 and C3 were split into doublets (J = 44 Hz and J = 16 Hz, respectively) as a result of carbonphosphorus coupling. In addition, two methyl resonances (C5 and C6) appeared in the upfield region of the spectrum. The IH NMR spectrum showed the expected downfield signals for H3 and the Hl's at 6 5.73 and 4.16,respectively. The methyl peaks appeared at 6 1.97 and 1.65, while the phosphido proton resonated at 6 2.06 and was split into a well-separated doublet (J = 160 Hz) due t o phosphorus coupling. In the 31P{1H) NMR spectrum, the phosphido phosphorus appeared as a singlet at 6 -75.0. When coupled to protons, the signal split into a broad doublet with the expected P-H coupling of 160 Hz. Treatment of C11r(PEt3)39with lithium 2,4-dimethylphosphapentadieriide led to the production of [@-ql2,4-dimethylphosphapentadienyl)Ir(PEt3)z12(31,the 2,4dimethylphosphapentadienyl analogue of 1. The 31P{'H} NMR spectrum of the product showed an equilibrium
Phosphapentadienyl -Iridium -Phosphine Chemistry
Organometallics, Vol. 14, No. 4, 1995 1677
Line 2
~
~
~
io. 0
~
'
~
9.8
~
~
9.6
~
Line 5
'
~
9.4
~
~
9.1
~
~
9.0
~
~
8.11
~
~
8.6
'
I
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Figure 1. lH NMR signal (at 500 MHz) for the phosphido (P-H) protons in [(~-~~-2,4-dimethylphosphapentadienyl)Ir(PEt3)2]2 (3a). The complex signal, which consists of six "lines" labeled 1-6 above, arises from the fact that the phosphido protons are part of an AAXX' spin system, where A and A' are the phosphido protons and X and X' are the phosphido phosphorus atoms. mixture of trans (3a) and cis (3b) isomers, but the presence of the bulky dimethylphosphapentadienyl ligand led to a higher fraction of trans isomer (3a:3b = 8:l). The trans isomer gave rise t o a downfield quintet (Jp-p= 20 Hz) of intensity 1 (phosphido groups) and an upfield triplet (Jp-p= 20 Hz) of intensity 2 (PEta's), while the cis isomer gave rise to three equal-intensity signals, one in the downfield (phosphido)region and two in the upfield (PEt3) region. The I3C and 'H NMR spectra of 3 closely resembled those of the lithium 2,4dimethylphosphapentadienide reagent, with one exception: the phosphido protons were shifted downfield (to 6 9.31 for 3a) and appeared as a complex multiplet due to their participation in an AAXX' spin system, where A and A are the phosphido protons and X and X are the phosphido phosphorus atoms.20 The phosphido proton signal for 3a (at 500 MHz) is reproduced in Figure 1. It consists of six "linesn,a pair of quintets at 6 9.56 and 8.96, and a broad quartet with peaks at 6 9.97, 9.37, 9.14, and 8.54. Normally, the AA' pattern of an AAXX' spin system consists of ten lines,21but ours reduces to six because JA-A (the coupling between the two phosphido protons) is vanishingly small. From the positions of the six lines, arbitrarily labeled 1 6 in Figure 1, the values of Jx-x,JA-X,and JA-x can be easily calculated. The separation between lines 1 and 3 yields a value of 300 Hz for Jx-x (the coupling between the two phosphido phosphorus atoms).22 Similarly, the separation between lines 2 and 5 yields a value of 300 Hz for JA-x J A - ~ .Finally, the separation between lines 1 and 4, together with the previously calculated value of Jx-x,allows calculation of a value Hence, 'JA-x(the coupling of 287 Hz for JA-x- J A - ~ . between a phosphido proton and the phosphido phosphorus to which it is directly bonded) is 293.5 Hz, while 3 J ~ -(the x coupling between a phosphido proton and the other phosphido phosphorus) is only 6.5 Hz. The quintet fine structure in lines 2 and 5 (J = 8 Hz) arises from coupling between the phosphido protons and the P centers on the four equivalent PEt3 ligands.
-
+
(20) The only other phosphido-bridged dimer for which this type of lH NMR pattern has been reported is Mnz(p-PPhH)z(CO)B:see ref 13. (21)Pople, J. A.; Schneider, W. G.; Bernstein, H. J. High Resolution Nuclear Magnetic Resonance; McGraw-Hill: New York 1959; p 141. (22) This P-P coupling is unusually large for phosphorus atoms in a tetrahedral geometry and must result, at least in part, from the fact that the two phosphido P centers are part of a four-membered ring.
Crystals of compounds 3a were grown from a saturated toluene solution of 3a,b a t -40 'C, and its solid state structure was determined by a single crystal X-ray diffraction study. The compound crystallized with two independent molecules in the unit cell. Each molecule resided on a crystallographically-imposed inversion center, making the two Ir(PEt3)z fragments and the two bridging 2,4-dimethylphosphapentadienyl ligands crystallographically equivalent. The ORTEP drawing of one of the independent molecules is presented in Figure 2, while important bond distances and angles are reported in the caption. A listing of atomic coordinates is given in Table 1. As expected, the coordination geometry about iridium was approximately tetrahedral. In fact, the average of the six P-Ir-P angles was 109.6'. However, the presence of the methyl groups (particularly C6) on the phosphapentadienyl chain caused some tilting of the iridium-phosphine plane (Irl/Irla/P2/P3/P2aP3a) in order t o minimize unfavorable steric contacts. This tilting was clearly seen in the individual P-Ir-P angles; Pl-Irl-P2 was expanded to 121.9(1)', while P1-IrP3 was contracted to 102.8(1)'. The dihedral angle between the iridium-phosphine plane (Irl/Irla/P2&'3/ P2a/P3a) and the iridium-phosphido plane (Irl/Irla/ Pl/Pla) was 104.8'. (The analogous dihedral angle for compound l a was 94.6O.I The Irl-Irla distance of 2.587(1) A was typical for an iridium-iridium double bond. The bond distances along the phosphapentadienyl chain were normal except for Cl-C2 and C2-C5, which were equal within experimental error (1.429(10) and 1.418(13) A) and intermediate between typical signal and double bonds. This strongly suggested the presence of a 2-fold disorder, wherein methylene group C1 and methyl group C5 shared the two terminal positions. As a result of steric contacts between the methyl substituents, the central angle in the 2,4dimethylphosphapentadienyl ligand (C2-C3-C4) expanded to 131.2(7)'. (The analogous angle in l a was 123.5(8)".) In addition, angles C5-C2-C3 and C3-C4C5 were expanded to 124.7(6) and 125.6(6)', respectively. In summary, we have synthesized new anionic phosphapentadienide reagents and have demonstrated that these reagents can be used to produce phosphapentadienyl-metal complexes via simple nucleophilic dis-
'
l
~
Bleeke et al.
1678 Organometallics, Vol. 14, No. 4,1995
la
c34
Figure 2. ORTEP drawing of [@-q1-2,4-dimethylphosphapentadienyl)Ir(PEt&]2(3a). This compound crystallized with two independent molecules in the unit cell. Molecule 1,along with its distances and angles, is shown here. Selected bond distances (A): Irl-Irla, 2.587(1); Irl-P, 2.294(2); Irl-Pla, 2.295(2); Irl-P2, 2.254(2); Irl-P3, 2.261(2); Cl-C2, 1.429(10); C2-C3, 1.459(9); C2-C5, 1.418(13); C3-C4, 1.351(8); C4-C6, 1.513(9); C4-P1, 1.831(6). Selected bond angles (deg): Pl-Irl-Pla, 111.3(1); Pl-Irl-P2, 121.9(1); Pl-Irl-P3, 102.8(1); Pla-Irl-P2, 102.2(1); Pla-Irl-P3, 122.4(1); P2-Ir-P3, 96.8(1);Irl-Pl-Irla, 68.7(1); Cl-C2-C3, 116.0(7); Cl-C2-C5, 119.3(6); C5-C2-C3, 124.7(6); C2-C3-C4, 131.2(7); C3-C4-P1, 119.9(5); C3-C4-C6, 125.6(6); C6-C4-P1, 114.5(4);C4-Pl-Ir1, 129.3(2); C4-Pl-Irla, 128.0(2). Table 1. Atomic Coordinates ( x 104) with Estimated Standard Deviations for Non-Hydrogen Atoms in [o(-~1-2,4-Dimethylpho~phapentadienyl)Ir(PEt~)~]~ (3aP X
Ir 1 PI P2 P3 CI c2 c3 c4 c5 C6 c2 I c22 C23 C24 C25 C26 C3 1 C32 c33 c34 c35 C36
397(1 ) 1572(1) 770(2) 947(2) 5821(7) 5039(6) 3891(6) 2914(5) 5416(8) 2801(7) 554(7) 605(IO) -131(7) - 1476(7) 2260(7) 3333(8) 2525(7) 3460(8) 676(8) 979(11) 238(8) - 1 124(8)
V
9132(1) 11079(1) 7803 1) 8446(2) 14142(7) 13319(6) 12585(5) 1 182 l(5) I3259(9) 11507(7) 8141(7) 7256(9) 6215(6) 5921(7) 7607(7) 8728(8) 8526(8) 9758(9) 9266(7) 892 l(9) 6875(6) 6474(7)
Z
I14(I) 235( 1) -708(1) 1186(I) 475(5) -94(4) 149(4) -250(3) -839(6) 1097(4) - 1680(4) -2334(5) -741(5) -899(6) -697(5) -745(6) 1406(5) 1443(6) 2032(4) 2816(5) 1364(5) 1330(5)
This compound crystallized with two independent molecules in the unit cell. Coordinates for the unique portion of molecule I are given here.
placement reactions. In the iridium-phosphine system described herein, the phosphapentadienyl ligand bonds preferentially in a bridging phosphide (p-71)mode. Other metal-ligand systemsare now under investigation in order to learn about phosphapentadienyl bonding preferences.
Experimental Section General Procedures. All manipulations were carried out under an inert atmosphere (Nz) using either drybox or Schlenk techniques. Solvents were stored under nitrogen after being distilled from the appropriate drying agents. Diethyl eth-
ylphosphonate (Pfaltz and Bauer) was distilled before use. The following reagents were used without further purification: IrCly3H20 (Johnson Matthey), cyclooctene (Aldrich), 2-propanol (EM Science), triethylphosphine (Strem), diethylphenylphosphine (Strem),triethyl phosphite (Aldrich), 1,4-dichlorotrans-2-butene (Aldrich), potassium hydroxide (Aldrich), anhydrous ethanol (Midwestern Grain), lithium aluminum hydride (Aldrich), aluminum chloride (Aldrich), n-butyllithium (Aldrich), lithium diisopropylamide (Aldrich), diethyl chlorophosphate (Aldrich),methacrolein (Aldrich). [(Cyclooctene)zIr(C1)1223and butadienylphosphine8 were prepared by the literature methods. Nuclear magnetic resonance experiments were performed on Varian XL-300 MHz and VXR-BOO MHz spectrometers. The 'H and 13CNMR spectra were referenced to tetramethylsilane, while 31Pspectra were referenced to external H3P04. Some 'H peak assignments were determined using COSY (homonuclear shift-correlated spectroscopy) experiments. Some 13C peak assignments were determined using APT (attached proton test), off-resonance 13C(off-resonance 'H-decoupled 13C NMR spectroscopy), and/or HMQC ('H detected multiple quantum coherence) experiments. One gram sealed ampules of deuterated NMR solvents were used without further purification (Cambridge Isotope Laboratories). In the NMR spectra reported below, carbon atoms were numbered starting at the end of the chain opposite from phosphorus. Microanalyses were performed by Galbraith Laboratories, Inc., Knoxville, TN. Synthesis of Lithium Phosphapentadiende. Under nitrogen, butadienylphosphine (2.0 g, 0.023 mol) was mixed with 50 mL of diethyl ether and 10 mL of tetrahydrofuran (THF) and cooled to -98 " c in a methanol/N2(1) bath. nButyllithium (14.4 mL of a 1.6 M solution in hexanes, 0.023 mol) was diluted with -10 mL of diethyl ether and added dropwise over a period of 30 min. A yellow/orange color formed immediately in the solution. After slowly warming to room temperature, the solution was stirred for 8 h and filtered through Celite. The solvent was then removed under vacuum, (23)Herde, J. L.; Lambert, J. C.; Senoff, C. V. In Inorganic Syntheses; Parshall, G . W., Ed.; McGraw-Hill: New York, 1974; Vol. 15,pp 18-20.
Phosphapentadienyl -Iridium-Phosphine
Chemistry
yielding lithium phosphapentadienide as a gummy orange solid (crude yield: 2.0 g, 95%). A free-flowing orange powder was obtained by washing the crude product with three 200 mL aliquots of diethyl ether. This powder was extremely airsensitive, burning upon exposure to the atmosphere. 'H NMR (de-THF, 25 "C): 6 6.90 (m, H4), 6.09 (m, H2), 5.89 (m, H3), 4.12 (d, JH-H= 16.1 Hz, Hlantl), 3.87 (d, JH-H= 9.6 = 12.5 Hz, P-HI. Hz, HlsW),1.88 (dd, J H - p = 160 Hz, JH-H 13C{lH}NMR (de-THF, 25 "C): b 154.0 (d, J c - p = 40 Hz, C4), 142.0 (s, C2), 122.0 (br s, C3), 95.6 (5, C1). 31P{'H} NMR (ds-THF, 25 "C): 6 -107.2 (6). 31PNMR (ds-THF, 25 "C): 6 -107.2 (ddd, JP-H = 160 Hz, 26 Hz, 5 Hz). Synthesisof [(lr-q1-Phosphapentadienyl)Ir(PEts)z1z (1). Under nitrogen, triethylphosphine (0.16 g, 1.3 mmol) was added dropwise t o a stirred solution of [(cyclooctene)~Ir(C1)]~ (0.20 g, 0.22 mmol) in 10 mL of tetrahydrofuran (THF). The volatiles were removed under vacuum, and the resulting residue was redissolved in 50 mL of THF and cooled to 0 "C. Lithium phosphapentadienide (0.041 g, 0.45 mmol) in 20 mL of THF was added dropwise, causing the solution t o turn a deep red color. After the mixture was stirred overnight, it was heated gently (at -50 "C) for 4 h. The volatiles were then removed under vacuum, and the residue was extracted with toluene. The resulting red solution was filtered and evaporated t o dryness, yielding 0.15 g (67%) of 1 as a 1.4:l ratio of trans to cis isomers (1a:lb). When this product was redissolved in a minimal quantity of toluene and the solution cooled to -40 "C, l a crystallized as red plates. Compound l a was air- and light-stable for up to 1 week in crystalline form, but solutions of 1 in toluene and benzene were air- and lightsensitive. Anal. Calcd for C ~ Z H ~ Z I ~ P ~ : H, 7.08. C,Z37.41; Found: C, 36.93; H, 6.64. NMR (CsDs, 25 "C): 6 8.83 (AAXX' Trans Isomer la. multiplet, l J ~ - pz= 300 Hz, V p - p = 300 Hz, 3 J H - p = 6.9 Hz, 1, P-H), 6.82 (br m, 1, H3), 6.70 (br m, 1, H4), 6.55 (br m, 1, H2), 5.21 (d, JH-H = 16.5 Hz, 1, HlantJ, 4.94 (d, JH-H= 9.6 Hz, 1,HlSw),1.35 (br m, 12, PEt3 CHz's), 0.98 (br m, 18, PEt3 CH3's). I3C{'H} NMR (CsDs, 25 "C): 6 145.4 (C4), 138.7 (C2), 129.5 (C31, 115.2 (Cl), 24.3 (PEt3 CHZ'S),9.0 (PEt3 CH3's). 31P(1H}NMR (CsDs, 25 "c): 6 68.0 (quintet, J p - p = 19.0 Hz, 1, phosphido P), -4.1 (triplet, J p - p = 19.0 Hz, 2, PEt3's). Cis Isomer lb (Peak Positions Obtained from a Mixture of la and lb). 'H NMR (CsDs,25 "C): 6 8.58 (AAXX' multiplet, 'JH-P = 300 Hz, U - p % 300 Hz, % - P 6.9 Hz, 1, P-H), 7.14-6.48 (m's, 3, H4, H3, H21, 5.17 (d, JH-H = 17.0 = 9.0 Hz, Hl,,,), 1.35 (br m, 12, PEt3 Hz, HlantJ,4.96 (d, JH-H CHz's), 0.98 (br m, 18, PEt3 CH3's). W{'H} NMR (C&, 25 "C): 6 146.7 (C4), 138.7 (C2), 129.8 (C3), 115.0 (Cl), 25.1 (PEt3 CHZ'S),23.2 (PEt3 CHZ'S),9.3 (PEt3 CH~'S),8.7 (PEt3 CH3's). 31P{1H}NMR (CsD,3,25"C): 6 66.4 (br m, 1, phosphido P), 1.0 (br m, 1, PEt3), -10.0 (br m, 1, PEt3). Synthesis of [(lr-q1-Phosphapentadienyl)Ir(PEtzPh)~1z (2). Compound 2 was synthesized and isolated in a manner directly analogous t o the synthesis of compound 1, using diethylphenylphosphine in place of triethylphosphine. Yield: 60%. Trans Isomer 2a. 'H NMR (C&, 25 "C): 6 9.03 (AAXX' multiplet, l J ~ - p 300 Hz, 2 J p - p = 300 Hz, 3 J H - p % 6.9, 1, P-H), 7.67-7.00 (m's, 10, PEtzPh Ph's), -6.95 (br m, partially obscured by PEtzPh Ph's, 1, H3), 6.70 (br m, 1, H4), 6.58 (m, = 14.1 Hz, 1, Hl,,,,), 5.08 (d, JH-H = 9.6 1, H2), 5.31 (d, JH-H Hz, 1,Hl,,,), 1.85-1.18 (m's, 8, PEtzPh CHz's), 0.85 (br m, 6, PEtzPh CHs's), 0.67 (br m, 6, PEtzPh CH3's). 31P{1H}NMR (C&, 25 "C): 6 71.1 (quintet, JP-P = 18.5 Hz, 1, phosphido PI, -2.1 (triplet, J p - p = 18.5 Hz, 2, PEtzPh's). Cis Isomer 2b. 31P{1H}NMR (CsDs,25"C): 6 71.1 (br m, 1, phosphido P), 5.3 (br m, 1, PEtzPh), -10.1 (br m, 1, PEtzPh).
Organometallics, Vol. 14,No. 4, 1995 1679
Synthesis of Diethyl (Dimethylbutadieny1)phosphonate [CHz=C(Me)CH=C(Me)P(O)(OEtz)zl. A slurry of lithium diisopropylamide (LDA) (11.0 g, 0.103 mol) in 70 mL of THF and 70 mL of pentane was cooled t o -78 "C. Diethyl ethylphosphonate (8.14 g, 0.049 mol) in 15 mL of THF was added via addition funnel. Stirring was maintained for 5 min, as the reaction temperature was allowed to return t o -78 "C. Diethyl chlorophosphate (8.89 g, 0.052 mol) in 20 mL of THF was added by cannulation. The reaction mixture was allowed to stir for 15 min a t -78 "C, and then the dry icelacetone bath was replaced with a -23 "C bath (CClddry ice) to complete the reaction (stirred -30 min at -23 "C). Methacrolein (3.85 g, 0.055 mol) in 10 mL of THF was added to the reaction mixture via cannula. The -23 "C bath was then removed, and the reaction was allowed to stir for 2 h. Water (35 mL) was then added to the reaction mixture, and the solution was transferred to a separatory funnel. The solution was extracted with Et20 (3 x 50 mL), and the organic layer was dried over NaZS04. Diethyl ether was removed by vacuum aspiration, leaving diethyl (dimethylbutadieny1)phosphonatebehind as a yellow liquid. This phosphonate product was further purified by distillation under vacuum. Yield: 7.06 g (66%)of spectroscopically pure light yellow liquid. 'H NMR (CsDcj, 22 "C): b 7.25 (d, JH-P = 25 Hz, 1, H3), 4.95 (s, 1,Hl), 4.89 (s, 1,H l ) , 3.95 (m, 4, OEt CHz's), 1.97 (d, JH-P = 15 Hz, 3, H ~ ' s ) ,1.62 (6, 3, H ~ ' s )1.06 , (t,JH-H = 7 Hz, 6, OEt CHis). 31P{'H} NMR (C&, 22 "C): 6 22.5 (s). Synthesisof (Dimethylbutadieny1)phosphine[CHz=C(Me)CH=C(Me)PHz]. Dichloroalane was prepared in situ by the addition of Ac13 (21.3 g, 0.16 mol) to lithium aluminum hydride (LAH) (2.02 g, 0.053 mol) in 250 mL of tetraglyme at -20 "C. This slurry was allowed to stir for 30 min as it warmed to room temperature. The dichloroalane solution was then placed under dynamic vacuum, connected to a trap cooled with liquid nitrogen (-178 "C). Diethyl (dimethylbutadienyllphosphonate (5.46 g, 0.025 mol) was added slowly (-30 min) to the AlHClz solution, and (dimethylbutadieny1)phosphine was isolated in the cold trap as it was formed (-8 h). This phosphine product was further purified by trap-to-trap distillation in a tube equipped with an airtight stopcock and quickly transferred to a -40 "C freezer. Yield: 2.3 g (81%) of spectroscopically pure colorless liquid. 'H NMR (CsDs, 25 "C): b 6.33 (d, J H - p = 17 Hz, 1, H3), 4.93 (s, 1,Hl), 4.76 (s, 1,Hl), 3.44 (d, J H - p = 194 Hz, 2, P-H's), , (s, 3, H5's). 1.88 (d, J H - p = 6 Hz, 3, H ~ ' s ) 1.62 31P{1H}NMR (CsDs, 25 "C): 6 -105.9 (SI. Synthesis of Lithium 2,4-Dimethylphosphapentadienide. Lithium 2,4-dimethylphosphapentadienidewas synthesized in a manner directly analogous to the synthesis of lithium phosphapentadienide. Yield: 92%. 'H NMR (de-THF, 25 "C): 6 5.73 (d, J H - p = 7.5 Hz, 1, H3), 4.16 (s, 2, Hl's), 2.06 (d, J H - p = 160 Hz, P-H), 1.97 (d, J H - p = 9.8 Hz, 3, H6's), 1.65 (s, 3, H5's). 13C{lH}NMR (de-THF, 25 "C): 6 159.8 (d, Jc-p= 44 Hz, C4), 143.6 (s, C2), 117.2 (d, J c - p = 16 Hz, C3), 103.2 (s, Cl), 26.4-25.8 (C5, C6). 31P{'H} NMR (de-THF, 25 "C): 6 -75.0 (s). 31PNMR (ds-THF, 25 "C): 6 -75.0 (d, 'Jp-H = 160 Hz). Synthesis of [(lr-q1-2,4-Dimethylphosphapentadienyl)Ir(PEt&]z (3). Compound 3 was synthesized in a manner directly analogous to Compound 1. The equilibrium ratio of the transxis isomers was 8:l. Yield: 40% crystalline 3a. Anal. Calcd for C3~HeoIrzPs:C, 39.91; H, 7.46. Found: c, 39.39; H, 7.51. Trans Isomer 3a. lH NMR (CsD6,25 "c): 6 9.31 ( A A x x ' multiplet, 'JH-P = 293.5 Hz, 'Up-p = 300 Hz, V H - p = 6.5 Hz, 1, P-H), 6.39 (inverted t, J = 18.6 Hz, 1,H3), 5.07 (s, 1, Hl), 5.03 (s, 1,H l ) , 2.46 (inverted t, J = 10.5 Hz, 3, H6's), 2.00 (s, 3, H5's), 1.41 (br m, 12, PEtz CHis), 1.00 (br m, 18,PEt3 CH3's). W{'H} NMR (CsDs,25 "C): b 145.1 (br s, C4 or c2), 143.1 (virtual triplet, Jc-p = 15 Hz, C2 or C4), 135.2 (virtual triplet,
Bleeke et al.
1680 Organometallics, Vol. 14, No. 4, 1995 = 21 Hz, C3), 113.8 (Cl), 24.1 (C5), 24.0 (PEt3 CHis), 20.8 (virtual triplet, J c - p = 15 Hz, C6), 9.0 (PEt3 CH3's). 31P{1H]NMR (C~DG, 25 "C): 6 109.2 (quintet, JP-P= 20.0 Hz, 1, phosphido P), -6.0 (triplet, J p - p = 20.0 Hz, 2, PEt,'s). Cis Isomer 3b (from a Mixture of 3a and 3b). 31P{1H} NMR (CeD6, 25 "C): 6 99.8 (m, 1, phosphido P), -0.5 (m, 1, PEt3), -16.5 (m, 1, PEt3). Single Crystal X-ray Diffraction Study. A single crystal of 3a (C36HgoIrzP6,red prism, 0.58 mm x 0.36 mm x 0.44 mm) was sealed in a glass capillary under inert atmosphere. Data were collected at 295 K on a Siemens R3mN diffractometer using graphite monochromated Mo Ka radiation (A = 0.710 73 A). All data reduction and refinement were done using the Siemens SHELXTL PLUS package on a Micro VAX I1 comp u t e ~ - .Crystal ~~ data and details of data collection and structure analysis are summarized as follows: triclinic, Pi, a = 11.756(4) A, b = 12.011(3) A, c = 17.716(7) A, a = 93.50(3)", fi = 92.89(3)", y = 108.67(3)", V = 2359.0(15) A3, 2 = 2, dcalcd = 1.511 g/cm3,p = 58.60 cm-l, 8-28 scanning technique, +h,&:k,ilcollected, 9422 reflections with 3" < 28 3dZ) used in refinement, semi-empirical absorption correction (midmax transmission factors = 0.4421/0.8876), R = 0.0277, R, = 0.0345, goodness-of-fit = 0.95. The positions of the iridium atoms were determined by direct methods. Remaining non-hydrogen atoms were found by successive full matrix least-squares refinement and difference Fourier map calculations. The iridium atoms, phosphorus Jc-p
(24) Atomic scattering factors were obtained from the following: International Tables for X-Ray Crystallography; Kynoch Press: Birmingham, England, 1974;Vol. IV.
atoms, and carbon atoms were refined anisotropically. The phosphido hydrogens were located and refined isotropically. Hydrogen atoms for the terminal methylene and methyl groups of the phosphapentadienyl ligands were not included in the structure solution due to ambiguity in assigning these groups (vide supra). The remaining hydrogen atoms on the phosphapentadienyl ligands and phosphine ligands were placed at idealized positions and assumed the riding model. A common isotropic U value was refined.
Acknowledgment. We thank the National Science Foundation (Grants CHE-9003159 and CHE-9303516) and the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research. A loan of IrC13.3H20 from Johnson-Matthey AlfdAesar is gratefully acknowledged. Washington University's X-ray Crystallography Facility was funded by the National Science Foundation's Chemical Instrumentation Program (Grant CHE-8811456). The High Resolution NMR Service Facility was funded in part by National Institutes of Health Biomedical Support Instrument Grant 1S10 RR02004 and by a gifi from Monsanto Co. Supplementary Material Available: Tables containing a structure determination summary, final atomic coordinates, thermal parameters, bond lengths, and bond angles, and ORTEP drawings for the two crystallographically independent molecules of compound 3a (11pages). Ordering information is given on any current masthead page. OM940934U
