Organometallics 1996, 14, 1667-1673
1667
Synthesis and Reactivity of (q3-pentadienyl)Ir(PEt3)2and (q3-2,4-dimethylpentadienyl)Ir(PEt3)21 John R. Bleeke” and Scott T. Luaders Department of Chemistry, Washington University, St. Louis, Missouri 63130 Received November 7, 1994@ Treatment of [ClIr(PEt3)212 with potassium pentadienide or potassium 2,4-dimethylpentadienide produces (y3-pentadienyl)Ir(PEt& (1)or (y3-2,4-dimethylpentadienyl)Ir(PEt3)2 (2) in high yield. In solution, compound 1 exists as a 70:30 equilibrium mixture of antipentadienyl (la) and syn-pentadienyl (Is)isomers, while compound 2 exists exclusively in the anti form. Both la and 2 undergo a low-energy fluxional process that exchanges the ends of the antz-y3-pentadienyl ligand via a n 18e- y5-pentadienyl intermediate. Treatment of 1 and 2 with Lewis bases, L, leads t o the formation of known (pentadienyl)Ir(PEt&L complexes. In particular, addition of 1 equiv of PEt3 to 1 and 2 produces ((1,4,5-y)I
1
pentadienyl)Ir(PEt3)3 and mer-CH=C(Me)CH=C(Me)CH2Ir(PEt3)3(H), respectively, while addition of CO produces (( 1,4,5-y)-pentadienyl)Ir(PEt3)2(CO)/(( l-3-y)-pentadienyl)Ir(PEt3)2(CO) and ((1,4,5-y)-2,4-dimethylpentadienyl)Ir(PEt3)2(CO), respectively. Compounds 1 and 2 also react with Lewis acids. Hence, treatment with triflic acid produces (y5-pentadienyl)Ir(PEt3)2(H)+O3SCFg-(3)and (y5-2,4-dimethylpentadieny1)Ir(PEt3)2(H)+03SCF3(4), respectively, while treatment with methyl triflate generates (y5-pentadienyl)Ir(PEt&(CH3)+03SCF3- ( 5 ) and (y5-2,4-dimethylpentadienyl)Ir(PEt3)2(CH3)+O3SCF3(6),respectively. Compounds 3-6 adopt unsymmetrical structures in which one phosphine resides under a pentadienyl edge while the other phosphine is situated under the pentadienyl mouth. Compound 3 undergoes a fluxional process in solution that involves rotation of the y5-pentadienyl ligand with respect to the Ir(PEt&(H) fragment. Under this process, the two phosphines exchange positions and the two ends of the pentadienyl ligand become equivalent. Compounds 3-6 react with bis(triphenylphosphine)nitrogen(l+) chloride (PPN+Cl-), a source of C1-, to produce (syn-y3-pentadienyl)Ir(PEt3)2(H)(C1) (71, (syn-y3-2,4dimethylpentadienyl)Ir(PEt3)~(H)(Cl) (8),(syn-y3-pentadienyl)Ir(PEt&(CH3)(C1)(9), and (syny3-2,4-dimethylpentadienyl)Ir(PEt3)2(CH3)(Cl) (101,respectively. In these compounds, the phosphine ligands are situated trans to the pentadienyl ligands.
Introduction During the past decade, there has been increasing interest in the chemistry of transition-metal complexes containing the acyclic pentadienyl ligand.2 In part, this interest has been spurred by the pentadienyl ligand’s ability to adopt a variety of bonding modes (including r5, r3,and 7’ modes) and expectations that interconversions between these bonding modes will lead to interesting chemistry. We now report the synthesis of a pair of (pentadienylliridium bidphosphine) complexes whose solution-phase dynamic behavior and reaction chemistry illustrate the key role of facile pentadienyl ligand isomerizations.
Results and Discussion
A. Synthesis and Dynamic Behavior of (q3pentadienyl)Ir(PEt3)2(1) and (qs-2,4-dimethylpentadienyl)Ir(PEt& (2). Treatment of [C11r(PEt&123 with 2 equiv of potassium pentadienide4 or potassium 2,4-dimeth~lpentadienide~ leads to the production of Abstract published in Advance ACS Abstracts, February 15,1995. (1)Pentadienyl-Metal-Phosphine Chemistry. 28. Part 27: Bleeke, J. R.; Luaders, S. T.; Robinson, K. D. Organometallics 1994,13,1592. (2) For leading reviews, see: (a) Ernst, R. D. Chem. Reu. 1968,88, 1251. (b) Yasuda, H.; Nakamura, A. J . Organomet. Chem. 1986,285, 15. (c) Powell, P. Adu. Organomet. Chem. 1986,26,125. @
16e- (y3-pentadienyl)Ir(PEt3)2(1)or (y3-2,4-dimethylpentadienyl)Ir(PEt& in essentially quantitative yield (see Scheme 1). At room temperature, 1 exists as a 70:30 equilibrium mixture of anti (la) and syn (1s) isomers, while 2 exists exclusively in the anti form. The anti and syn isomers can be readily distinguished by the chemical shift of the H3 proton; H3 for the anti isomer is less shielded by the metal center and appears substantially downfield from H3 for the syn isomer.6 In solution, both 1 and 2 exhibit dynamic behavior. The lH NMR spectrum of 2 at room temperature consists of just four pentadienyl signals (Hlouter/H5outer, Hlinner/H5inner,H3, and the pentadienyl methyl groups) due to a rapid “end-to-end” fluxional process that exchanges the two sides of the pentadienyl ligand via (3) (a)This species was synthesized by reacting [(~yclooctene)2IrC112~~ with 4 equiv of PEts. (b) 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. (4)Yasuda, H.; Ohnuma, Y.; Yamauchi, M.; Tani, H.; Nakamura, A. Bull. Chem. SOC.Jpn. 1979,52,2036. (5)Earlier, we reported the synthesis of the analogous rhodium compound. See: Bleeke, J. R.; Donaldson, A. J. Organometallics 1986, 5,2401. (6)It is typical for “outer”allyl protons (such as H3 in la)to resonate downfield from “inner” allyl protons (such as H3 in IS). This effect is usually attributed to the inner protons’ closer proximity to the metal center: Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987;pp 175-180.
0276-733319512314-1667$09.00/0 0 1995 American Chemical Society
1668 Organometallics, Vol. 14,No. 4, 1995
Bleeke and Luaders
Scheme 1
(Is) isomers. At room temperature, l a and 1s are interconverting, probably via the mechanism outlined in Scheme 3, which involves sickle-shaped pentadienyl intermediate^.^ This interconversion, together with a rapid end-to-end fluxional process in the anti isomer (cf. Scheme 21, causes the following signals to coalesce:
1 4 [Cllr(PEt&
H2( la)/H4(la)/H2( ls)/H4(1s) H3( la)/H3(ls)
-2
Therefore, at room temperature, the lH NMR spectrum of 1 consists of just four broad signals in the pentadienyl region. As the sample is cooled to -30 "C, the anti z= syn interconversion slows down, causing the signals due to 1s to decoalesce from those due to la. Since 1s does not undergo end-to-end exchange at this temperature, seven separate signals are observed for its seven inequivalent protons. However, at -30 "C, la continues to undergo rapid end-to-end exchange and, therefore, only four 'H NMR signals ( H l o ~ + J H 5 oHlinneJH5imer, ~~r, H m 4 , and H3) are observed for it in the pentadienyl region. As the sample is cooled from -30 to -80 "C, the signals due to l a broaden somewhat but never fully decoalesce. On the basis of this behavior, AG* for the end-to-end fluxional process in l a is calculated to be less than 7.5 kcavmol. The interconversion of anti and syn isomers can also be conveniently monitored in the 31P{1H}NMR spectrum. Each isomer exhibits two peaks in the 31P{1H) NMR spectrum due to the two inequivalent phosphine ligands: the edge phosphines (P1 in Scheme 3) and the mouth phosphines (P2). At room temperature, all four signals are observable, although each of the anti signals is beginning t o coalesce with one of the syn signals. As the temperature is raised to 50 "C, coalescence progresses until only two signals are observed-one for the edge phosphines of l a and 1s and one for the mouth phosphines of the two isomers. Cooling the sample below room temperature causes the signals to decoalesce; at -80 "C, the stopped-exchange spectrum of four very sharp peaks is observed. B. Reactions of Compounds 1 and 2 with Lewis Bases. Not surprisingly, 16e- compounds 1 and 2 react readily with 2e- donor reagents, such as PEt3 and carbon monoxide, to produce 18e- species. As shown in Scheme 4, addition of PEt3 to 1 yields ((1,4,5-~)pentadienyl)Ir(PEt& (A) instantaneously at room temperature. Addition of PEta to 2 is a slower reaction but
18 (30%)
an ~5-pentadienylintermediate7 (see Scheme 2).8 Similarly, in the 13C{lH) NMR spectrum, only four pentadienyl signals are observed at room temperature: C11 C5, C2/C4, C3, and the pentadienyl methyl groups. The signals due to Cl/C5 and C2/C4 are quite broad but sharpen upon heating to 50 "C. However, as the sample is cooled and the fluxional process is slowed, the lH NMR signals due to HlouteJH5outer, HlinneJH5innerr and the pentadienyl methyl groups begin to "decoalesce", ultimately disappearing into the base line at -60 "C. Temperatures cold enough to observe reemergence of separate signals due to Hlouter, H5outer, Hlinner, HBinner, and the pentadienyl methyl groups could not be achieved. In the 13C{lH} NMR spectrum, a similar decoalescence is observed upon cooling, and separate peaks due to C1, C5, C2, and C4 do reemerge at -80 "C. From this behavior, the free energy of activation, AG', for the endto-end fluxional process in 2 is calculated to be 9.5 f 0.5 kcavmol. It should be noted that H3 and C3 are not affected by this process and hence their signals remain sharp over the entire temperature regime studied. Likewise, the phosphine ligands do not exchange under this process; one (P1in Scheme 2) remains under the pentadienyl edges while the other (P2) remains under the open pentadienyl mouth. Hence, separate 31P,lH, and 13CNMR signals are observed for the two PEt3 groups a t all temperatures. The NMR spectra for 1 are somewhat more compliI ultimately yields the iridacycle mer-CH=C(Me)CH=Ccated because of the presence of both anti (la) and syn Scheme 2
pl\ H3
C3
H1I L---
c2
c1
\p2
[I*:-
-
P1
-:
cz
p2
"-yl
Hlo
Me
-2
Hlo
Me
A
-
[tH4(10 J
Iridium Pentadienyl Complexes
Organometallics, Vol. 14, No. 4, 1995 1669
Scheme 3
p2
I450
Hll
c2L--;l \p2
b
la -
H1I
x H10
1s
Scheme 4
I ,Ir\
PEb
la
PEt3 (70%)
PEb
-
I ,Ir\
PEb
PEt3
1s (30%)
-2
PEt3
b
species have previously been isolated from the reactions (Me)CH2h(PEt3)3(H) (B)via a C-H bond activation of ClIr(PEt& or ClIr(PEt3)2(CO) with potassium penprocess. Similarly, treatment of 1 with CO leads to an tadienide or potassium 2,4-dimethylpentadienide.l0 equilibrium mixture of ((1,4,5-~)-pentadienyl)Ir(PEt3)2C. Reactions of Compounds 1 and 2 with Lewis (CO) and ((1-3-~)-pentadienyl)Ir(PEt3)2(CO) (C),while Acids. Compounds 1 and 2 also react cleanly with treatment of 2 with CO produces exclusively ((1,4,5-~)- electrophiles. As shown in Scheme 5, treatment of 1 2,4-dimethylpentadienyl)Ir(PEt&(CO) (D). All of these and 2 with 1 eauiv of triflic acid leads to electroDhilic (7) A similar fluxional process operates in the analogous rhodium system5 and in a series of isoelectronic (q3-cycloheptadienyljPdL2+ complexes (Mann, B. E.; Maitlis, P. M. J . Chem. Soc., Chem. Commun. 1976,1058). (8jIn Scheme 2, compound 2 and the proposed q5-pentadienyl intermediate (A) are drawn in projection to shown the orientation of the pentadienyl ligand with respect to the Ir(PEt3)z fragment.
(9)This “haptotropic rearrangement” has been examined theoretically for the isoelectronic (but hypothetical) species (q3-pentadienyl)Pt(PHa)z+: Silvestre, J.;Albright, T. A. J . Am. Chem. SOC.1985, 107,6829. (10)(a) Bleeke, J . R.; Peng, W.-J. Organometallics 1987,6, 1576. (b) Bleeke, J. R.; Boorsma, D.; Chiang, M. Y.; Clayton, T. W. Jr.; Haile, Organometallics 1991, 10,2391. T.; Beatty, A. M.; Xie, Y.-F.
Bleeke and Luaders
1670 Organometallics, Vol. 14,No. 4, 1995
Scheme 6
I rI,
PEta
PEta 1a (70%)
-
-
I /Ir\
PEt3
-
PEt3
I S (30%)
attack at the electron-rich iridium center and isomerization of the pentadienyl ligand to the y5 bonding mode, yielding the 18e- cationic complexes (y5-pentadienyl)Ir(PEt&(H)+03SCFg- (3)and (y5-2,4-dimethylpentadienyl)Ir(PEt3)2(H)+O3SCF3- (4), respectively." Similarly, compounds 1 and 2 react cleanly with methyl triflate to produce compounds 5 and 6, the methyl analogues of 3 and 4. All of these compounds possess the unsymmetrical structure shown in Scheme 5, in which one of the PEt3 ligands resides in the unique site under the open pentadienyl mouth, while the hydride or methyl ligand and the other PEt3 group occupy the remaining sites under the pentadienyl edges. This ligand orientation is apparent from the 31P(1H}NMR spectra of 3-6, wherein the two phosphines give rise to separate signals. The unsymmetrical structure is also reflected in the lH and 13C(lH} NMR spectra, where distinct signals are observed for the phosphine ligands and for each of the pentadienyl hydrogen and carbon atoms, although the signals for 3 are broad (vide infra). The hydride ligands in 3 and 4 resonate in the characteristic upfield region of the 'H NMR spectrum (6 -16.5 for 3 and 6 -17.3 for 4) and in each case appear as a pseudotriplet due to coupling to the 31Pcenters of the phosphine ligands. Similarly, the methyl ligands in 5 and 6 give rise t o characteristic upfield pseudotriplets at 6 0.5 and 0.2 in the lH NMR spectra. As mentioned above, the 'H NMR spectrum of 3 at room temperature exhibits broad signals in both the phosphine and pentadienyl regions; only the H3 peak is a sharp triplet. Likewise in the 13C(lH} NMR spectrum, only the C3 signal is sharp. We believe that this broadening is caused by a fluxional process that involves rotation of the 75-pentadienyl ligand with respect to the Ir(PEt&(H) fragment (see Scheme 6).12 Under this process, the two phosphines exchange positions and the two ends of the pentadienyl ligand become (11) Similar metal-centered protonations are observed in the analogous rhodium system but are followed by rapid migration of the hydride ligand to the pentadienyl ligand: Bleeke, J. R.; Donaldson, A. J. Organometallics 1988,7, 1588.
Scheme 6 p;'
Pi
H50
H1o
P2
-
Hlo
-3
equivalent. Of course, H3 and C3 are unaffected by this process. When the sample is heated to 50 "C in d6-acetone, additional line broadening occurs, although full coalescence of the exchanging signals is not achieved before the sample decomposes. Cooling the sample to -20 "C halts the fluxional process, and sharp stoppedexchange spectra are obtained. On the basis of this variable-temperature NMR behavior, AG* for pentadienyl ligand rotation in 3 must exceed 16 kcaymol. Unlike 3,compounds 4-6 show no NMR signal broadening at room temperature. D. Nucleophilic Addition of C1- to Cationic Compounds 3-6. Cationic compounds 3-6 all undergo clean nucleophilic addition at iridium when treated with C1- (from bis(tripheny1phosphine)nitrogen(1+)chloride) to produce (syn-y3-pentadienyl)Ir(PEt&(H)(Cl) (71, (syn-y3-2,4-dimethylpentadienyl)Ir(PEt&(H)(Cl) (81, (syn-y3-pentadienyl)Ir(PEt3)z(CH3)(C1)(S), and (syn-y3-2,4-dimethylpentadienyl)Ir(PEt3)z(CH3)(Cl) (lo),respectively (see Scheme 7). The syn geometry of the pentadienyl ligands in compounds 7-10 has been confirmed by carrying out NOESY (2DNOE) experiments. In each case, correlations are observed between Hlinnerand H3, requiring a ligand geometry in which (12)Similar fluxional processes have been observed in other (q5pentadieny1)metal complexes. See, for example: (a) Bleeke, J. R.; Stanley, G. G.; Kotyk, J. J. Organometallics 1986,5, 1642. (b) Bleeke, J. R.; Moore, D. A. Inorg. Chem. 198625,3522.(c) Bleeke, J. R.; Hays, M. K.; Wittenbrink, R. J. Organometallics 1968,7, 1417. (d) Bleeke, J. R.; Rauscher, D. J. Organometallics 1988,7,2328. (e) Newbound, T.D.; Stahl, L.; Ziegler, M. L.; Ernst, R. D. Organometallics 1990,9, 2962. (D Lin, W.-J.; Lee, G.-H.; Peng, S.-M.; Liu, R.-S. Organometallics 1991,1 0 , 2519.
Iridium Pentadienyl Complexes
Organometallics, Vol. 14, No. 4, 1995 1671
CI
-D these protons reside in close proximity. The orientation of the phosphine ligands trans to the pentadienyl ligands in 7-10 has been unequivocally established by the observation of substantial C-P coupling (-30 Hz) on pentadienyl carbons C1 and C3 in the 13C(lH) NMR spectra. As outlined in Scheme 7, these nucleophilic addition reactions probably proceed through the intermediacy of 16e- (anti-v3-pentadienyl)Ir(PEt3)2(L)+(L = H, CH3) species (A), which are attacked by C1-. The resulting anti isomers of compounds 7-10 (B;Scheme 7) then rearrange to the syn isomers via C3-bound yl-pentadienyl intermediates (Cand D; Scheme 7).13 In fact, when these reactions are monitored by NMR, the anti isomers (B)can be observed as intermediates, but these species cleanly convert to the thermodynamically preferred syn isomers over the course of several hours (compounds 9 and 10)or days (compounds 7 and 8).
Summary (pentadienyl)Ir(PEt& (1)and (2,4-dimethylpentadienyl)Ir(PEt& (2) adopt 16e- ground-state structures in which the pentadienyl ligands are coordinated to iridium in an v3 fashion. However, low-energy fluxional processes involving 18e- (v5-pentadienyl)Ir(PEt3)2intermediates occur in solution. Because compounds 1 and 2 are formally unsaturated (16e-1, they react readily with Lewis bases such as PEt3 and CO. However, t h e y also possess electron-rich metal centers a n d are reactive toward Lewis acids such as triflic acid and methyl triflate. The cationic products of these Lewis acid reactions undergo nucleophilic attack at iridium by C1-. Pentadienyl ligand interconversions play two key roles in this chemistry: (a)generating reactive sites at the metal center and (b) stabilizing intermediates and products. (13)Similar q3 t q1 t q3 interconversions are common in allylmetal chemistry.6
-C Experimental Section
General Procedures. All manipulations were carried out under an atmosphere of purified nitrogen in a Vacuum Atmospheres drybox or by standard Schlenk techniques. Solvents were stored under nitrogen after being distilled from appropriate drying agents. [(cyclooctene)~IrC1]~,3b potassium pentadienide-tetrahydrofuran,4 and potassium 2,4-dimethylpentadienide-tetrahydrofuran4 were synthesized using the literature methods. Triethylphosphine (Strem), carbon monoxide (Air Products), triflic acid (Aldrich), methyl triflate (Aldrich), and bis(triphenylphosphine)nitrogen(l+)chloride (PPN+Cl-; Aldrich) were used as received. NMR experiments were generally performed on a Varian XL-300 spectrometer (lH, 300 MHz; 13C, 75 MHz; 31P, 121 MHz). 'H and 13C spectra were referenced to tetramethylsilane, while 31Pspectra were referenced t o external H3P04. In most cases, lH assignments were made on the basis of COSY (lH-lH correlation spectroscopy) experiments, while 13C assignments were made using HMQC ( W - l H heteronuclear correlation spectroscopy) data. High-resolution MS data were obtained on a VG ZAB-SE mass spectrometer. Microanalysis were performed by Galbraith Laboratories, Inc., Knoxville, TN.
Synthesis of (rf-pentadienyl)Ir(PEts)z(1). Under ni(0.50 g, 5.6 x mol) was trogen, [(cyclooctene)~IrC1]~ dissolved in 50 mL of tetrahydrofuran (THF). To this solution mol), was added 4 equiv of triethylphosphine (0.26 g, 2.2 x generating an orange solution of [(PEt3)2IrCllz. ARer removal of the volatiles (THF and cyclooctene) under vacuum, the residue was redissolved in 50 mL of THF. Potassium pentadienide-tetrahydrofuran (0.20 g, 1.1 x low3mol) in 50 mL of THF was then added, causing the solution to turn dark red. After removal of the solvent under vacuum, the dark red residue was extracted with pentane and filtered through Celite. Removal of the pentane under vacuum yielded 0.46 g (83%) of compound 1 as a red oil. In solution, 1 existed as a 70:30 mixture of anti (la)and syn (Is)isomers. HRMS: exact mass calcd for C17H37lS3IrPz496.200, found 496.202. Room-TemperatureN M R Data for Equilibrating Isomers l a and 1s. Please refer to Scheme 1 for NMR atom
1672 Organometallics, Vol. 14, No. 4, 1995 labels. 'H NMR (CsDs, 22 "C): 6 4.92 (br m, 2, H2/H4), 4.63 (br m, 1, H3), 3.86 (br m, 2, HlouteJ'HSouter),3.44 (br m, 2, HlinneJHBinner), 1.84-1.55 (br m, 12, PEt3 CHis), 1.08-0.72 (br m, 18, PEt3 CH3's). 13C{1H}NMR (CsD6, 22 "c): d 114.0 (br m, C2/C4), 71.6 (br m, Cl/C5), 64.9 (d, J c - p = 20.3 Hz, C3), 23.2-20.0 (br m, PEt3 CHis), 9.0 (br s, PEt3 CH3's). 31P{'H} NMR (CsDe, 22 "C): 6 11.7, 10.9 (br humps, 1, PEts), 8.5, 7.6 (br humps, 1, PEtd. Low-TemperatureNMR Data for Isomer la (70%). 'H NMR (CsD&D3, -80 "C): 6 4.91 (m, 2, H2/H4), 4.58 (m, 1, H3), 3.83 (m, 2, HloutedH5outer),3.42 (br m, 2, HlinnedH5inner)y 1.81-1.45 (m, 12, PEt3 CHz's), 1.05-0.65 (m, 18, PEt3 CH3's). 31P(lH} NMR (CsD5CD3, -80 "C): 6 11.5 (s,1, PEta), 7.2 ( 6 , 1, PEt3). Low-TemperatureNMR Data for Isomer 1s (30%). lH NMR (CsD5CD3,-80 "C): 6 6.39 (m, 1, H4), 5.17 (m, 1, H5), 4.98 (m, 1, H5), 4.42 (m, 1,H2), 3.32 (m, 1, H3), 3.17 (m, 1, HlOukr),2.14 (m, 1, Hlimer),1.81-1.45 (m, 12, PEt3 CHz's), 1.05-0.65 (m, 18, PEt3 CHis). 31P{1H}NMR (CsD5CD3, -80 "C): 6 10.7 (s, 1, PEtd, 8.3 (s, 1, PEtd. Synthesisof (q3-2,4-dimethylpentadienyl)Ir(PEt3)~ (2). A procedure identical with that described above for 1 was employed, except that potassium 2,4-dimethylpentadienidetetrahydrofuran (0.23 g, 1.1 x mol) was used in place of potassium pentadienide. The yield of 2 as an orange oil was 0.50 g (85%). HRMS: exact mass calcd for C I ~ H ~ ~ ~ 524.232, found 524.230. Please refer to Scheme 1 for NMR atom labels. 'H NMR (C&, 20 "c): 6 4.16 (s, 1,H3), 3.76 (s, 2, HlouteJH5outer), 3.67 (s, 2, HlinneJ'H51nner),1.85 (s,6, pentadienyl CH3's), 1.77-1.56 (m, 12, PEt3 CHis), 1.00-0.87 (m, 18, PEt3 CHis). 13C{'H} NMR (C&, 20 "c): 6 125.3 (5, c2/ C4), 76.6 (s, Cl/C5), 68.5 (dd, J c - p = 26.0 Hz, 3.5 Hz, C3), 26.8 (s, pentadienyl CHis), 22.2 (d, J c - p = 29.0 Hz, PEt3 CH2), 20.6 (d, J c - p = 27.7 Hz, PEt3 CH2), 9.0 (9, PEt3 CH3), 8.9 ( 8 , PEt3 CH3). I3C{lH}NMR (CsD&D3, -80 "C, selected peaks): 6 149 (br s, C4), 106 (br s, C5), 101 (br s, C2), 68.5 (dd, J c - p = 26.0 Hz, 3.5 Hz, C3), 46 (br s, cl). 31P{1H} NMR (C6Dti, 20 "C): 6 11.6 (8, 1, PEt3), 8.5 (5, 1, PEt3). Reaction of Compound 1 with PEt3. Compound 1 (0.20 mol) was dissolved in 1 mL of ds-benzene in an g, 4.0 x NMR tube, and PEt3 (0.05 g, 4.0 x mol) was added, causing the solution color t o change rapidly from dark red to yellow. NMR spectroscopy showed quantitative conversion to ((1,4,5q)-pentadienyl)Ir(PEt3)3, which we reported previously.'O Reaction of Compound 2 with PEts. Compound 2 (0.20 g, 3.8 x mol) was dissolved in 1 mL of ds-benzene in an NMR tube, and PEt3 (0.05 g, 3.8 x mol) was added. NMR
Bleeke a n d Luaders mol) was added, and (-30 "C) triflic acid (0.06 g, 4.0 x the solution was stirred briefly. Addition of 20 mL of pentane caused 3 to precipitate out of the solution as a white solid. After removal of the solvent by decantation, the solid was washed with diethyl ether and pentane and dried under vacuum. Yield: 0.16 g (62%). Anal. Calcd for C1~H38F3Ir03P2S: C, 33.48; H, 5.94. Found: C, 33.18; H, 5.86. Please refer to Scheme 5 for NMR atom labels. 'H NMR ((CD3)2CO, 0 "C): 6 6.16 (m, 1,H3), 6.03 (br m, 1,H2), 5.76 (br m, 1,H4), 4.30 (m, 1,H5outer)r 3.20 (m, 1,Hlouter), 1.99 (m, 1,H5inner), 0.95 (m, 1, Hllnner),2.45-1.75 (m, 12, PEt3 CHz's), 1.38-0.78 (m, 18, PEt3 CHis), -16.50 (t,J H - p = 20.0 Hz, 1, Ir-HI. 13C{1H} NMR ((CD3)zCO,0 "C): 6 103.7 (9, C4), 100.7 (9, C2), 91.1 (d, J c - p = 9.1 Hz, C3), 58.9 ( 8 , C5), 43.1 (d, J c - p = 25.5 Hz, Cl), 22.6 (d, J c - p = 36.5 Hz, PEt3 CHis), 21.6 (d, J c - p = 34.6 Hz, PEt3 CHis), 8.4 (s,PEt3 CHis), 8.1 (s,PEt3 C H ~ S ) 31P{1H} . N M R ((CD&CO, 0 "C): 6 4.9 (br s, 1,PEts), -6.4 (br s, 1, PEt3).
Synthesis of (q6-2,4-dimethylpentadieny1)Ir(PEt3)zmol) was (H)+03SCF3-(4). Compound 2 (0.50 g, 9.6 x
dissolved in 20 mL of diethyl ether and cooled to -30 "C. Cold (-30 "C) triflic acid (0.14 g, 9.6 x mol) was added t o the solution, and upon swirling, compound 4 began t o precipitate out as a white solid. To complete the precipitation, the solution was stored at -30 "C for -20 h. After removal of the solvent by decantation, the solid was washed with diethyl ether and ~pentane ~ I ~ Pand Z dried under vacuum. Yield 0.48 g (74%). Anal. Calcd for C Z O H ~ ~ F ~ I ~C,O35.65; ~ P ~ SH,: 6.30. Found: C, 34.28; H, 6.31. Please refer to Scheme 5 for NMR atom labels. 'H NMR ((CD3)2CO,20 "C): 6 6.22 (s, 1, H3), 4.02 (s, 1, H50uter)~ 3.33 (s, 1, HlOukr),2.61 (s, 3, pentadienyl CH3), 2.56 (s, 3, pentadienyl CH3), 2.20 (m, 6, PEt3 CHz's), 1.98 (s, 1, H5inner), 1.89 (m, 6, PEt3 CHis), 1.06 (m, 18, PEt3 CHis), 0.88 (s, 1, Hllnner), -17.28 (t, J H - p = 21.4 Hz, 1, Ir-H). 13C{1H}N M R ((CD&CO, 20 "C): S 121.8 (s, C4 or C2), 117.5 ( 8 , C2 or C4), 91.2 (d, J c - p = 10.1 Hz, C3), 56.4 ( 8 , C5), 46.5 (d, J c - p = 28.4 Hz, Cl), 27.6 (s, pentadienyl CH3), 26.0 (s, pentadienyl CH3), 22.3 (d, J c - p = 31.4 Hz, PEt3 CHis), 21.8 (d, J c - p = 26.9 Hz, PEt3 CHz's), 9.1 (s,PEt3 CHis), 8.1 ( 8 , PEt3 CH3's). 31P{1H}NMR ((CD3)2CO,20 "C): 6 4.7 (d, J p - p = 10.5 Hz, 1, PEt3), -4.7 (d, J p - p = 10.5 Hz, 1, PEtd. Synthesis of (q6-pentadienyl)Ir(PEts)2(CHs)+OsSCF3(5). Compound 1 (0.20 g, 4.0 x mol) was dissolved in 20 mL of diethyl ether, and the solution was cooled to -30 "C. mol) was Cold (-30 "C) methyl triflate (0.07 g, 4.0 x added. The solution was swirled for several minutes and then stored at -30 "C overnight, causing 5 to precipitate out of the solution as an orange-yellow solid. After removal of the solvent by decantation, the solid was washed with diethyl ether and I pentane and dried under vacuum. Yield: 0.18 g (68%). Anal. monitoring showed a slow conversion t o mer-CH=C(Me)Calcd for C ~ & O F ~ I ~ O ~C, P 34.58; ~ S : H, 6.12. Found: C, 34.22; I H, 6.00. Please refer t o Scheme 5 for NMR atom labels. 'H CH=C(Me)CHzIr(PEt3)3(H),which we reported earlier.1° After NMR ((CD3)zCO, 22 "C): 6 6.48 (m, 1, H3), 5.57 (m, 1, H4), 20 h, the reaction was 90% complete. 5.25 (m, 1, H2), 3.98 (m, 1, H5outer), 3.01 (m, 1, Hlouter), 2.11 Reaction of Compound 1 with CO. Carbon monoxide (m, 1, H5,,,,,), 1.54 (m, 1, Hllnner),2.48-1.78 (m, 12, PEt3 was bubbled into a stirred solution of compound 1 (0.20 g, 4.0 CHz's), 1.28-1.01 (m, 18, PEt3 CHis), 0.49 (t, J H - p = 5.5 Hz, x mol) in 50 mL of tetrahydrofuran. Within several 3, Ir-CH3). 13C{1H)NMR ((CD&CO, 22 "C): 6 110.9 (s, C4), minutes, the solution color changed from dark red to yellow101.5 (8, C2), 91.5 (d, J c - p = 10.7 Hz, C3), 59.1 (9, C5), 47.6 orange. After removal of the volatiles under vacuum, the solid (d, J c - p = 31.9 Hz, Cl), 21.6 (d, J c - p = 35.5 Hz, PEt3 CHz's), residue was extracted with pentane and filtered through 18.7 (d, J c - p = 31.4 Hz, PEt3 CHis), 8.5 ( 8 , PEt3 CHis), -26.7 Celite. Removal of the pentane under vacuum yielded 0.15 g (br s, Ir-CH3). 31P{1H)NMR ((CD3)2CO, 22 "C): 6 -9.9 (d, (72%)of the previously reported equilibrium mixture of ((1,4,5J p - p = 8.5 Hz, 1, PEt3), -23.1 (d, J p - p = 8.5 Hz, 1, PEt3). v)-pentadienyl)Ir(PEt3)2COand ((1-3-v)-pentadienyl)Ir(PEt3)2(CO).'O Synthesis of (q6-2,4-dimethylpentadienyl)Ir(PEt3)r (C&)+03SCF3-(6). Compound 2 (0.60 g, 1.1x mol) was Reaction of Compound 2 with CO. Carbon monoxide dissolved in 20 mL of diethyl ether, and the solution was cooled was bubbled into a stirred solution of compound 2 (0.20 g, 3.8 to -30 "C. Cold (-30 "C) methyl triflate (0.19 g, 1.1 x x mol) in 50 mL of tetrahydrofuran. Within several mol) was added, and when the mixture was stirred for several minutes, the solution color changed from orange to light yellow. minutes, compound 6 began to precipitate as a light brown A workup procedure similar to that described above (Reaction solid. To complete the precipitation, the solution was stored of Compound 1 with CO) yielded 0.18 g (86%)of ((1,4,5-~)-2,4dimethylpentadienyl)Ir(PEt3)~(CO),which we reported earat -30 "C for -20 h. After removal of the solvent by lier.1° decantation, the solid was washed with diethyl ether and pentane and dried under vacuum. Yield: 0.53 g (67%). Anal. Synthesis of (q6-pentadienyl)Ir(PEts)2(H)+O3SCF3(3). Calcd for C Z ~ H ~ ~ F ~ I ~C, O 36.67; ~ P Z SH,: 6.46. Found: C, 36.36; mol) was dissolved in 20 mL Compound 1 (0.20 g, 4.0 x H, 6.38. Please refer t o Scheme 5 for NMR atom labels. 'H of diethyl ether, and the solution was cooled t o -30 "C. Cold
Organometallics, Vol. 14, No. 4, 1995 1673
Iridium Pentadienyl Complexes NMR ((CD&CO, 20 "C): 6 6.27 (m, 1,H3), 3.83 (m, 1, H50u*r), 2.63 (m, 1, Hlnuhr),2.44 (s, 3, pentadienyl CH3), 2.31 (m, 4, PEt3 CHz's), 2.14 (m, 4, PEt3 CHis), 2.07 (m, 1,H5inner),1.93 (s, 3, pentadienyl CH3), 1.66 (m, 4, PEt3 CHis), 1.05 (m, 18, PEt3 CH3's), 1.01 (m, 1, Hlinner),0.20 (t, J H - p = 5.4 Hz, 3, IrCH3). 13C{lH}NMR ((CD3)2CO,20 "C): 6 122.1 (s, C4 or C2), 121.3 (s, C2 or C4), 92.3 (d, J c - p = 11.4 Hz, C3), 57.0 (s, C5), 48.3 (d, J c - p = 34.9 Hz, Cl), 25.0 (s, pentadienyl CH3), 22.1 (s, pentadienyl CH3), 21.0 (d, Jc-P = 35.6 Hz, PEt3 CHZ),18.7 (d, J c - p = 30.3 Hz, PEt3 CHz), 9.3 (s, PEt3 CH3), 8.5 (9, PEt3 CHd, -18.5 (s, Ir-CH3). 31P{1H}NMR ((CD3)2CO,20 "C): 6 -9.6 (d, J p - p = 6.6 Hz, 1, PEt3), -21.8 (d, J p - p = 6.6 Hz, 1, PEt3). Synthesis of (syn-q3-pentadienyl)Ir(PEt&(H)(Cl)(7). Compound 3 (0.20 g, 3.1 x mol) was dissolved in 5 mL of tetrahydrofuran, and solid bis(tripheny1phosphine)nitrogen(1+)chloride (PPN+Cl-; 0.18 g, 3.1 x mol) was added. After the solution was swirled for several minutes, 30 mL of pentane was added, causing PPN+03SCF3- to precipitate out. The solution was then filtered and evaporated to dryness. The resulting solid was dissolved in tetrahydrofuran and the solution stirred for several days in order to convert the product entirely to the syn isomer. Removal of the THF under vacuum yielded compound 7 (0.12 g, 73%) as a light yellow powder. Anal. Calcd for C17H38ClIrP2: C, 38.37; H, 7.21. Found: C, 38.01; H, 7.15. Please refer to Scheme 7 for NMR atom labels. = 17.4 lH NMR (CsDs, 22 "C): 6 5.93 (m, 1,H4), 5.23 (d, JH-H Hz, 1, H5), 5.02 (m, 1, H2), 4.94 (d, JH-H = 9.9 Hz, 1, H5), 3.90 (m, 1, H3), 2.97 (m, 1,Hlou*r), 2.70 (m, 1, Hlinner),1.921.48 (m, 12, PEt3 CHis), 0.98-0.71 (m, 18,PEt3 CHis), -25.42 (t,JH-P = 15.0 Hz, 1, Ir-H). 13C{lH} NMR (C&, 22 "C): 6 143.7 (9, C4), 110.5 (s, C5), 94.7 (9, C2), 68.6 (d, J c - p = 28.8 Hz, C3), 46.4 (d, J c - p = 28.8 Hz, Cl), 21.0 (d, J c - p = 31.2 Hz, PEt3 CHis), 17.9 (d, J c - p = 31.2 Hz, PEt3 CHis), 8.1 (s,PEt3 CHis), 8.0 (s,PEt3 CH3's). 31P{1H}NMR (CsDs, 22 "C): 6 -7.3 (s, 1, PEt3), -16.4 (s, 1, PEt3). Synthesis of (syn-q3-2,4-dimethylpentadienyl)Ir(PEt3)2(H)(Cl) (8). Compound 4 (0.20 g, 3.0 x mol) was dissolved in 5 mL of tetrahydrofuran, and solid PPN+Cl- (0.17 g, 3.0 x mol) was added. After the solution was swirled for several minutes, 30 mL of pentane was added, causing PPN+03SCF3- to precipitate out. The solution was then filtered and evaporated to dryness. The resulting solid was redissolved in tetrahydrofuran and the solution stirred for several days t o convert the product entirely to the syn isomer. Removal of the THF under vacuum yielded compound 8 (0.13 g, 77%) as a light yellow powder. Anal. Calcd for C19H42ClIrP2: C, 40.73; H, 7.57. Found: C, 40.69; H, 7.50. Please refer to Scheme 7 for NMR atom labels. 'H NMR (CsDs, 22 "C): 6 5.11 (s, 1, H5), 5.07 (8, 1, H5), 3.85 (d, J H - p = 8.2 Hz, 1, H3), 3.34 (m, 1, Hlouter), 2.94 (m, 1, Hlinner), 2.45 (s, 3, pentadienyl CH3), 1.99 (s, 3, pentadienyl CH3), 1.90-1.50 (m, 12, PEt3 CHis), 1.07-0.79 (m, 18, PEt3 CH3's), -25.84 (t,JH-P = 16.0 Hz, 1, Ir-HI. 13C{lH}NMR (CsDs, 22 "C): 112.6 (s, C5), 70.4 (d, J c - p = 29.9 Hz, C3), 52.2 (d, J c - p = 29.9 Hz, Cl), 25.6 (s, pentadienyl CH3), 24.3 (5, pentadienyl CH3), 21.0 (d, J c - p = 30.7 Hz, PEt3 CHis), 18.8 (d, J c - p = 30.7 Hz, PEt3 CHis), 8.6 (s, PEt3 CHs's), 8.0 (s, PEt3 CH3's). Note: Carbons C2 and C4 were not observed. 31P{'H} NMR (CsDs, 22 "C): 6 -8.5 (d, J p - p = 3.0 Hz, 1, PEt31, -15.6 (d, J p - p = 3.0 Hz, 1, PEt3). Synthesisof (syn-q3-pentadienyl)Ir(PEt3)~(CHs)(C1) (9). Compound 5 (0.20 g, 3.0 x mol) was dissolved in 5 mL of tetrahydrofuran, and solid PPN+Cl- (0.17 g, 3.0 x mol) was added. After the solution was swirled for several minutes, 30 mL of pentane was added, causing PPN+03SCF3- to precipitate out. The solution was then filtered and evaporated to dryness. After redissolving in tetrahydrofuran and stirring for several hours, the pure syn isomer of 9 (0.13 g, 80%)was obtained as a light yellow powder. Anal. Calcd for C18H40ClIrPZ: C, 39.58; H, 7.40. Found: C, 39.21; H, 7.23. Please refer to Scheme 7 for NMR atom labels. 'H NMR (CsDs, 22 "C): 6 6.16 (m, 1, H4), 5.36 (dd, JH-H = 17.0, 2.5 Hz, 1, H5),
5.11 (dd, JH-H = 9.3 Hz, 2.5 Hz, 1, H5), 4.65 (m, 1, H3), 3.94 (m, 1, H2), 3.21 (m, 1,Hlouter), 3.14 (m, 1,Hlinner), 1.95 (m, 6, PEt3 CHz's), 1.82 (m, 6, PEt3 CHis), 1.05-0.80 (m, 18, PEt3 CHis), -0.08 (t, J H - p = 4.8 Hz, 3, Ir-CH3). 13C{IH} NMR (CeDs, 22 "C): 141.5 (9, C4), 110.9 ( 8 , C5), 110.1 (8,C2), 73.8 (d, J c - p = 30.2 Hz, C3), 46.7 (d, J c - p = 30.2 Hz, Cl), 18.1(d, J c - p = 29.6 Hz, PEt3 CHZ'S),15.9 (d, J c - p = 29.6 Hz, PEt3 CHis), 8.6 (s, PEt3 CHis), -34.7 (t,J c - p = 6.4 Hz, Ir-CH3). 31P{1H}NMR (C&, 22 OC): 6 -20.2 (br s, 1,PEt31, -29.6 (br 9, 1, PEt3). Synthesis of (syn-q3-2,4-dimethyl~n~~enyl)Ir(PEts)2(CH3)(Cl)(10). Compound 6 (0.20 g, 2.9 x mol) was dissolved in 5 mL of tetrahydrofuran, and solid PPN+Cl- (0.17 g, 2.9 x mol) was added. After the solution was swirled for several minutes, 30 mL of pentane was added, causing PPN+03SCF3- to precipitate out. The solution was then filtered and evaporated to dryness. After redissolving in tetrahydrofuran and stirring for several hours, the pure syn isomer of 10 (0.14 g, 84%) was obtained as a light yellow powder. Anal. Calcd for C2oH44ClIrP~: C, 41.83; H, 7.74. Found: C, 41.57; H, 7.54. Please refer to Scheme 7 for NMR atom labels. 'H NMR (CsDs, 22 "C): 6 5.11 (s, 1,H5), 5.06 (s, 1,H5), 4.43 (d, JH-P = 7.6 Hz, 1,H3), 3.21 (d, J H - p = 7.6 Hz, 1,Hlinner),3.00 (br s, 1, Hlnuer),1.98 (s, 3, pentadienyl CH3), 1.84 (s, 3, pentadienyl CH3), 2.10-1.70 (m, 12, PEt3 CHis), 1.08-0.70 (m, 18, PEt3 CH3's), 0.04 (t, J H - p = 5.4 Hz, 3, IrCH3). 13C{1H}NMR (CsDs,22 "C): 112.1 (s,C5), 72.1 (d, J c - p = 31.7 Hz, C3), 47.6 (d, J c - p = 31.7 Hz, Cl), 26.5 (s, pentadienyl CH3), 19.0 (s, pentadienyl CH3), 18.0 (d, J c - p = 29.4 Hz, PEt3 CHz's), 16.8 (d, J c - p = 28.1 Hz, PEt3 CH~'S), 9.0 (s, PEt3 CH3's), 8.5 (s, PEt3 CH3's), -32.0 (br s, Ir-CH3). Note: Carbons C2 and C4 were not observed. 31P{1H}NMR (C&, 22 "C): 6 -21.1 (d, J p - p = 5.7 Hz, 1, PEt3), -30.4 (d, J p - p = 5.7 Hz, 1, PEt3). Solution Dynamics of Compounds 1-3. Exchange rate constants, kc, at the coalescence temperature were calculated using the formula
k, =n(A~)/2~" where Av is the difference in frequencies between the two exchanging sites in the stopped-exchange limit.14 These exchange rate constants were then used to determine the free energy of activation, AG* at the coalescence temperature, T,, from the Eyring equation
k , = (k'/h)T,e-AG*/RTc where k' = Boltzmann's constant, h = Planck's constant, and R = ideal gas ~ 0 n s t a n t . I ~
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 IrCly3HzO from Johnson-Matthey AlfdAesar is gratefully acknowledged. Washington University's High Resolution NMR Service Facility was funded in part by National Institutes of Health Biomedical Support Instrument Grant 1 S10 RR02004 and by a gift from Monsanto Co. OM940845H (14) Pople, J. A.; Schneider, W. G.; Bernstein, H. J. High Resolution Nuclear Magnetic Resonance; McGraw-Hill: New York, 1959; p 223. (15)Lowry, T. H.; Richardson, K. S. Mechanism and Theory in Organic Chemistry; Harper and Row: New York, 1976; p 194.
