Organometallics 1991,10, 2391-2398
dicate that the HOMO of the &electron precursor should be largely Ru-p3-C bonding in character, localized trans to the Ru-L(axial) bonds. The coupling constant to the equatorial 31Pnucleus, cis to the Ru-COMe bond, must be too small to be resolved (cf. the 31P-19COMe J,... value of 39 Hz in H3Ru3(COMe)(C0)6(PPh9)318 vs J& = 3.5 Hz in H3Ru3(COMe)(C0)7((PPh2)3CHI). I -
Acknowledgment- Purchase of a %"3 R3m/V diffractometer was made possible by a grant from the Chemical Instrumentation Program of the National Sci-
2391
ence Foundation (Grant No. 89-13733). This work was supported by the National Science Foundation through Grant No. CHE8900921 (J.B.K.). We thank Professor Robert D. Allendoerfer for assistance with the EPR measurements. Supplementary Material Available: Tables of distances and angles, anisotropic thermal parameters, and calculated positions of H atoms for (p-H)3R~3(p3.COMe)(C0)6(p3-(PPh2CH2)3CMe) and (p-H)3Ru3(p3-COMe)(C0),(pz-(PPhz)3CHJ~1.25CH2C12 (14 pages); tables of F,/F, values (56 pages). Ordering information is given on any current masthead page.
Pentadienyl-Iridium-Phosphine Chemistry.' Survey of the Reactions of Pentadienide Reagents with CII rL, Complexes John R. Bleeke,' Devran Boorsma, Michael Y. Chiang, Thomas W. Clayton, Jr.,t Tesfamichael Haile, Alicia M. Beatty, and Yun-Feng Xie Department of Chemistry, W8ShingtOn University, St. Louis, Missouri 63 130 Received January 22, 199 1
A s tematic stud of the reactions of four ClIrb complexes with pentadienide reagents has been carried out. reatment of 11r(PEt&3with potassium pentadienide produces (1,4,5-~-pentadienyl)lr(PEtS)s (21, while the reaction of C11r(PMe3)3with potassium pentadienide yields the analogous trimethylphosphine compound 5. In contrast, treatment of C11r(PMe3)3with potassium 2,4-dimethylpentadienideproduces an equilibrium mixture of (1,4,5-~p2,4-dimethylpentadienyl)Ir(PMe~)~ (3)and the metallacyclohexadiene complex fac-(1rCH2C(Me)=CHC(Me)=CH)(PMe3),(H) (4). The formation of 4 involves the intermediacy which intramolecularlyactivates a C-H bond on the end of 16e- (q1-2,4-dimethylpentadienyl)Ir(PMe3)3, of the pentadienyl chain. Vaska's complex, ClIr(PPhd,(CO), rea& with potassium 2,4-dimethylpentadienide to produce an equilibrium mixture of (1,4,5-q-2,4-dimethylpentadienyl)Ir(PPh3)2(CO) (6)and (1-3-q-2,4dimethylpentadienyl)Ir(PPh3)2(CO)(7). The analogous reaction involving*unmethylated pentadienide produces exelusively (l-&q-pe~~tadienyl)Ir(PPh~)~(CO) (8). This species undergoes a dynamic process in solution, which involves shuttling between q3- and 7'-pentadienyl bonding modes. Treatment of ClIr(PEG2(CO)with potassium 2,bdimethylpentadienide yields (1,4,5-q-2,4-dimethylpentadienyl)Ir(PEQ2(CO) (9), while the analogous reaction involving unmethylated pentadienide produces an equilibrium mixture of (1,4,5-q-pentadienyl)Ir(PEtS)z(CO)(10) and (1-3-q-pentadienyl)Ir(PEQ2(CO) (11). Molecular structures of compounds 2,3,6,and 8 have been determined by single-crystal X-ray diffraction studies. Crystal structure data for these compounds are as follows: 2, monoclinic, P2,/c, a = 15.489 (5) A, b = 11.453 (5) A, c = 15.769 (4) A, j3 = 101.83 ( 2 ) O V = 2738 (2) As 2 = 4, R = 0.038 for 3572 reflections with Z > 3u(Z); 3,monoclinic, ml/n, a = 8.958 (6) A, b = 20.308 (5) A, c = 11.970 (5) A, /3 = 93.14 (5)O, V = 2174 (2) A3,2 = 4, R = 0.037 for 3440 reflections with Z > 3u(Z); 6,monoclinic, P2,/n, a = 13.518 (5) A, b = 17.862 (6) A, c = 15.417 (5) A, j3 = 93.59 (3)O, V = 3715 (2) AS,2 = 4, R = 0.035 for 5003 reflections with Z > 3u(Z);8, monoclinic, P2,/c, a = 17.276 (7) A, b = 23.038 (8) A, c = 18.896 (5) A, j3 = 111.92 ( 2 ) O , V = 6977 (4) A3, 2 = 8, R = 0.049 for 6353 reflections with Z > 3 4 .
F
E
i
Introduction In an earlier paper? we reported that ClIr(PEtJ3 reacts with potassium 2,4-dimethylpentadienideto produce a , novel iridacyclohexadiene complex, (IrCH2C(Me)I =CHC(Me)=CH)(PEtS)&H)(1). This reaction proceeds through the intermediacy of 16e- (q1-2,4-dimethylpentadien~l)Ir(PEt~)~, which undergoes intramolecular oxidative addition a c r w an sp2C-H bond on the dangling terminus of the pentadienyl ligand. Compound 1 is the parent to a large family of unsaturated six-membered metallacycles,2including a rare metallabenzene complex ,
Scheme I
-4
(IdHTIC(Me)RCHRC(Me)&H)(PEt3)3.3 'Pew Postdoctoral Fellow.
In order to probe the generality of this novel synthetic route to unsaturated six-membered metallacycles and to 0276-7333/91/2310-2391$02.50/00 1991 American Chemical Society
Bleeke et al.
2392 Organometallics, Vol. IO, No. 7, 1991
Table I. Selected Bond Distances (A) and Bond Angles (deg) with Estimated Standard Deviations for
bL
(1,4,S-q-Pentadienyl)Ir(PEtl)l(2) Bond Distances c22
Ir-P(l) Ir-P(2) Ir-P(3) Ir-C(1) Ir-C(4)
2.319 (3) 2.333 (3) 2.339 (3) 2.161 (11) 2.139 (12)
Ir-C(5) C(l)-C(2) C(2)4(3) C(3)-C(4) C(4)-C(5)
2.112 (12) 1.502 (19) 1.329 (20) 1.489 (17) 1.454 (17)
Bond Angles
0
C36
Figure 1. ORTEP drawing of (1,4,5-~ppentadienyl)Ir(PEt~)~ (2).
further our understanding of (pentadieny1)iridium chemistry, we have undertaken a systematic study of the reactions of four C11rL3 precursors with potassium pentadienide and potassium 2,4dimethylpentadienide. We have discovered that, in addition to the metallacyclic products described above, these reactions can lead to the production of (l-3-q-pentadienyl)IrL3 and (1,4,5-q-pentadienyl)IrL3 complexes. Results and Discussion
A. Reaction of ClIr(PEt3)3with Potassium Pentadienide. As we reported earlier, treatment of CIIr(PE& with potassium 2,4-dimethylpentadienideleads cleanly to the production of the iridacyclohexadiene complex, (IrCHzC(Me)=CHC (Me)=CH) (PEt3)3(H) (l)? The initial product of this reaction is the fac isomer, which slowly (24 h) converts to the more thermodynamically stable mer isomer. In contrast, we now report that treatment of ClIr(PEt& with unnethylated pentadienide produces (1,4,5-q-per1tadienyl)Ir(PEt~)~ (2) (see Scheme I) in essentially quantitative yield. An ORTEP drawing of the molecular structure of 2 is shown in Figure 1; selected bond distances and angles are given in Table I. The 1,4,5-qpentadienyl bonding mode, which involves localized metal-alkyl and metal-olefin coordination, is relatively rare. To our knowledge, the only other pentadienyl complexes that exhibit this type of bonding are ($C6H5)2Ta(2,3-dimethylpentadieny1) and (q6-C5H&Ta(2,4-dimethyl~entadienyl).~ Compound 2 can perhaps best be viewed as a distorted octahedron in which the six coordination sites are occupied by C(l), C(4), and C(5) of the pentadienyl ligand and the three PEt, phosphorus atoms. Of course, the geometry is distorted because of the rigidity of the pentadienyl ligand. The a-bonded carbon atom, C(l), lies approximately trans to P(3) and cis to PO) and P(2). The *-bonded carbons C(4) and C(5) lie approximately in the Ir-P(l)-P(2) plane6 b
i
(1) Pentadienyl-Metal-Phcephine Chemistry. 23. For recent papers
in thie series, we: (a) Bleeke, J. R.; Haile, T.; Chiang, M.Y. Organometallics 1991,10,19. (b) Bleeke, J. R.; Wittenbrink,R. J. J. Organomet. Chem. lSSl,406,121. (c) Bleeke,J. R.; Wittenbrink, R. J.; Clayton, Jr., T. W.; Chiang, M.Y. J. Am. Chem. SOC.1990, 112,6539. (2) (a) Blaeke, J. R.; Pen , W.-J. Organometallics 1987,6, 1576. (b) Bleeke, J. R.; Peng, W.-J.; k e , Y.-F.; Chiang, M.Y. Organometallics 1990,9,1113. (3) Bleeke, J. R.; Me, Y.-F.; Peng, W.J.; Chiang, M.J. Am. Chem. Soc. 1980,111,4118. (4) Meleadez, E.; Arif, A. M.;Rheingold, A. L.; Emst, R. D. J. Am. Chem. SOC.ISM, 110,8703.
P(l)-Ir-P(2) P(l)-Ir-P(3) P(2)-Ir-P(3) P(1)-Ir-C(1) P(2)-1r-C(1) P(3)-1r-C(1) P(l)-Ir-C(4) P(2)-Ir-C(4) P(3)-Ir-C(4) C(l)-Ir-C(4) P(l)-Ir-C(5)
103.6 (1) 95.4 (1) 97.7 (1) 88.2 (3) 90.1 (3) 170.4 (3) 148.5 (3) 104.9 (3) 93.9 (3) 78.5 (5) 110.3 (3)
P(2)-Ir-C(5) P(3)-Ir-C(5) C(l)-Ir-C(5) C(4)-Ir-C(5) Ir-C(1)4(2) C(l)-C(2)4(3) C(2)-C(3)4(4) Ir-C(4)-C(3) Ir4(4)-C(5) C(3)-C(4)-C(5) Ir-C(5)-C(4)
144.9 (4) 88.4 (3) 81.9 (5) 40.0 (5) 110.1 (8) 118.0 (11) 117.5 (12) 110.0 (9) 69.0 (7) 115.7 (9) 71.0 (7)
and experience substantial back-bonding as evidenced by the relatively long C(4)-C(5) distance of 1.454 (17) A. In fact, the Ir-C(4)-C(5) interaction approximates a metallacyclopropane in which the iridium center is formally oxidized to Ir(II1). Hence, the stability of the 1,4,5-v pentadienyl bonding mode in 2 may result, in part, from the stability of d6 Ir(II1) in an octahedral coordination geometry. The 13C(lHJNMR spectrum of 2 exhibits the pattern of resonances that is characteristic of the 1,4,5-q-pentadienyl bonding mode. Uncomplexed carbon atoms C(3) and C(2) resonate far downfield a t 6 143.5 and 133.9, respectively. ?r-complexedatoms C(4) and C(5) resonate a t 6 36.6 and 20.9, respectively, and appear as doublets due to phosphorus coupling. Finally, u-bonded carbon atom C(1) resonates far upfield at 6 10.1 and appears as a doublet of triplets, coupled strongly to the trans phosphorus and weakly to the two cis phosphorus atoms. All three phosphorus atoms are inequivalent and appear as a secondorder ABC pattern in the 31P(1H)NMR spectrum. The signals show no tendency to coalesce upon heating to 80 "C. B. Reactions of ClIr(PMe3)3 with Potassium 2,4Dimethylpentadienide and Potassium Pentadienide. Treatment of C11r(PMeJ3 with potassium 2,4-dimethylpentadienide produces an equilibrium mixture of (1,4,5~-2,4-dimethylpentadienyl)Ir(PMe~)~ (3) and the metalla, cyclohexadiene complex, fac-(IrCHzC(Me)=CHC(Me)1 =CH)(PMe&(H) (4) (see Scheme I). Interconversion between 3 and 4 probably involves the intermediacy of (q1-2,4-dimethylpentadieny1)Ir(PMe& The iridium center in this 16e- species can either coordinate the terminal double bond of the pentadienyl (producing 3) or oxidatively add across a C-H bond on the end of the ql-pentadienyl (producing 4). Unlike its PEt, analogue, compound 4 does not isomerize from the fac to the mer geometry, apparently because of reduced steric strain in the fac geometry. In benzene at room temperature (20 "C), the equilibrium mixture slightly favors the metallacyclohexadiene complex (4:3 = 1.151). However, the position of the equilibrium can be pushed further toward the metallacycle by refluxing the mixture for short periods of time in polar solvents (e.g., acetone) and can be pushed toward the l,4,5-~ppentadienylcomplex by refluxing in nonpolar solvents (e.g., pentane). These isomerically enriched so(5) The mean deviation of atoms from the Ir-P(l)-P(2)4!(4)4!@) plane is 0.071 A.
Organometallics,Vol. 10, No.7, 1991 2393
Pentadienyl-Iridium-Phosphine Chemistry
Scheme I1
c22 c1
c33
Figure 2. ORTEP drawing of (1,4,5-~-2,4-dimethylpentadienyl)Ir(PMed3 (3). Table 11. Selected Bond Distances (A) and Bond Angles (de& with Estimated Standard Deviations for ( 1,4,S-q-2,4-Dimethylpntadienyl) Ir(PMe8) (3) Bond Distances Ir-P(l) Ir-P(2) Ir-P(3) Ir-Cl(1) Ir-C(4) Ir-C(5)
2.291 (3) 2.288 (2) 2.323 (3) 2.127 (8) 2.160 (8) 2.130 (8)
C(l)-C(2) C(2)4(3) C(2)4(6) C(3)-C(4)
1.469 (13) 1.334 (14) 1.506 (13) 1.480 (14) 1.465 (12) 1.495 (13)
Bond Angles P(l)-Ir-P(2) P(l)-Ir-P(3) P(2)-1~P(3) P(l)-IA(l) P(2)-1r-C(1) P(3)-1r-C(1) P(l)-Ir-C(4) P(2)-Ir-C(4) P(3)-1&(4) C(l)-Ir-C(4) P(l)-Ir4(5) P(2)-Ir-C(5) P(3)-Ir-C(5) C(l)-Ir4(5)
105.0 (1) 95.0 (1) 94.6 (1) 88.7 (3) 87.9 (2) 174.8 (2) 146.3 (2) 105.2 (2) 97.1 (2) 77.9 (3) 108.0 (3) 145.0 (3) 93.8 (2) 81.6 (3)
C(4)-Ir-C(5) Ir-C(1)-C(2) C(1)4(2)4(3) C(1)4(2)4(6) C(3)-C(2)-C(6) C(2)-C(3)4(4) Ir-C(4)-C(3) Ir-C(4)-C(5) C(3)4(4)4(5) Ir-C(4)-C(7) C(3)-C(4)4(7) C(5)-C(4)-C(7) Ir-C(5)4(4)
39.9 (3) 112.9 (6) 115.2 (8) 122.0 (9) 122.8 (10) 119.7 (9) 108.9 (6) 68.9 (5) 115.4 (8) 125.7 (7) 113.2 (8) 118.0 (8) 71.1 (4)
lutions yield spectroscopically pure crystalline samples of 4 and 3, respectively, upon workup. The molecular structure of 3 has been determined by single-crystal X-ray diffraction and is shown in Figure 2. Selected bond distances and angles are reported in Table 11. The structure of 3 bears a strong resemblance to that of 2. Once again, the coordination geometry is probably best described as a distorted octahedron in which C(1), C(4), C(5), P(1),P(2),and P(3) occupy the six coordination sites. C(l) lies directly trans to P(3) (C(l)-Ir-P(3) = 174.9 (2)O), an orientation that gives rise to very strong carbon-DhosDhorus couDline in the l3CI1HINMR spectrum . . (Jc(I)-p = 71.0 Hz). Metallacvcle 4 exhibits NMR spectra that very closely I I resemble those of fuc-(IrCH,C(Me)=CHC(Me)=CH)(PEt,),(H), which we reported earlierS2Particularly diagnostic is the W('H) NMR spectrum, which shows four d o d i e l d peaks between b 120 and 145for C(2), C(3), C(4), and C(5). C(5) is a broadly spaced doublet (J = 81.8 Hz) due to strong trans carbon-phosphorus coupling. Ring carbon atom C(1) (the methylene carbon) appears far upfield (6 -3.0) and is a broadly spaced doublet (J = 71.8 Hz) due to trans carbon-phosphorus coupling. The metal-hydride in 4 resonates at 6 -11.27 in the 'H NMR .
I
.
I
Figure 3. ORTEP drawing of (1,4,5-7-2,4-dimethylpentadienyl)Ir(PPh&( CO). (6).
spectrum and is a doublet (J = 160.3 Hz) of triplets (J = 20.9 Hz), confirming the fac orientation of the phosphines. The three PMe, ligands are all inequivalent and give rise to a complicated second-order ABC pattern in the ,lP(lH) NMR spectrum. Treatment of C11r(PMe3), with unmethylated pentadienide cleanly produces (1,4,5-7ppentadienyl)Ir(PMe3)3 (5) (see Scheme I). As in the reaction of ClIr(PEh), with potassium pentadienide, no metallacyclic products can be detected. C. Reactions of ClIr(PPh,),(CO) with Potassium 2,4-Dimethylpentadienideand Potassium Pentadienide. When Vaska's complex, ClIr(PPh,),(CO), is treated no metallacyclic with potassium 2,4-dimethylpentadienide, products are observed. This is perhaps not surprising, given the relative electron-poorness of the IrL, fragment in this case. Instead, an equilibrium mixture of (1,4,5-~2,4-dimethylpentadienyl) Ir (PPh,) 2( CO) (6) and (1-3-t)2,4dimethylpe11tadienyl)Ir(PPh&~(CO) (7) is obtained (see Scheme 11). Interconversion between 6 and 7 probably involves the intermediacy of (s1-2,4-dimethylpentadienyl)Ir(PPh&,(CO). The iridium center in this 16especies can coordinate the terminal double bond (producing 6) or the internal double bond (producing 7). At 20 "C in methylene chloride, the 1-3-?-2,4-dimethylpentadienyl compound predominates slightly ( 7 6 = 1.W but it is the 1,4,5-~pdimethylpentadienyl isomer that crystallizes from THF/pentane by using the slow diffusion technique. The molecular structure of compound 6, determined by a single-crystalX-ray diffraction study, is shown in Figure 3. Selected bond distances and angles are reported in Table 111. As with compounds 2 and 3, the coordination
Bleeke et al.
2394 Organometallics, Vol. 10, No. 7, 1991 Table 111. Selected Bond Distances (A) and Bond Angles (deg) with Estimated Standard Deviations for (1,4,5-tp2,4-Dimethylpe~ntadienyl)Ir(PPh~)~(CO) (6) Bond Distances Ir-P(l) 2.336 (2) C(l)-C(2) 1.506 (10) Ir-P(2) C(2)-C(2') 1.519 (13) 2.359 (2) C(2)-C(3) 1.309 (13) Ir-C(l) 2.143 (7) C(3)-C(4) 1.484 (12) Ir-C(4) 2.214 (8) C(4)-C(4') 1.498 (12) Ir-C(5) 2.141 (7) C(4)-C(5) 1.430 (11) Ir-C(6) 1.886 (7) P(l)-Ir-P(2) P(l)-Ir-C(l) P(2)-1r-C(1) P(l)-Ir-C(4) P(2)-Ir-C(4) C(l)-Ir-C(4) P(l)-Ir-C(5) P(2)-Ir-C(5) C(l)-Ir-C(5) C(4)-Ir-C(5) P(l)-Ir-C(6) P(2)-Ir-C(6) C(l)-Ir-C(6) C(4)-Ir-C(6)
Bond Angles 115.2 (1) C(5)-Ir-C(6) 88.1 (2) Ir-C(l)-C(2) 92.9 (2) C(l)-C(2)
