1588
Organometallics 1988, 7, 1588-1596
Pentadienyl-Metal-P hosphine Chemistry. 16.‘ Reaction Chemistry of (q3-2,4-Dimethylpentadienyl)Rh(PEt,), and (q3-2,4-Dimethylpentadienyl)Rh(PMe,), John R. Bleeke” and Andrew J. Donaldson Department of Chemistry, Washington University, St. Louis, Missouri 63 130 Received December 21, 1987
The reactions of (q3-2,4-dimethylpentadienyl)Rh(PEt3), (I) and (v3-2,4-dimethylpentadienyl)Rh(PMe3!z (2) with CH3+03SCF3-produce (175-2,4-dimethylpentadienyl)Rh(PEt3)2(Me)+O3SCF3(3) and (v5-2,4-d1methylpentadienyl)Rh(PMe3)2(Me)+03SCF3(4),respectively. The solid-state structure of 3 has been
determined by single-crystal X-ray diffraction. The complex crystallizes in the monoclinic space group
P2’/c with a = 11.310 (2) A, b = 13.507 ( 7 ) A, c = 18.226 (3) A, (3 = 95.97 ( 2 ) O , V = 2769 (3) A3,and 2 = 4. The coordination geometry of 3 is pseudooctahedral, with C(l), C(3), and C(5) of the 2,4-dimethylpentadienyl ligand and P(l), P(2),and C(8) (methyl carbon) occupying the six coordination sites. One of the phosphine ligands resides under the open “mouth” of the 2,4-dimethylpentadienyl ligand, while
the other phosphine and the methyl group occupy the coordination sites under the “edges” of the 2,4dimethylpentadienyl ligand. Upon heating in solution, the 2,4-dimethylpentadienyl ligand in 3 rotates with respect to the RhP,(Me) framework, exchanging the two phosphines, as well as the two ends of the 2,4-dimethylpentadienyl ligand. The energy of activation (Act)for this dynamic process, derived from variable-temperatureNMR studies, is 17.0 0.7 kcal/mol. Treatment of 3 and 4 with (Ph&N+Cl- produces (q3-2,4-dimethylpentadieny1)Rh(PEt3),(Me)(C1)( 5 ) and (q3-2,4-dimethylpentadieny1)Rh(PMe3),(Me)(C1) (6), respectively. Compound 5 crystallizes in the monoclinic space group P2,/c with a = 12.962 (3) A, b = 8.236 (2) A, c = 22.758 (6) 8,fl = 94.19 ( 2 ) O , V = 2423 (2) A3,and 2 = 4. The coordination geometry of 5 is pseudooctahedral with C(l), C(3) (2,4-dimethylpentadienylgroup), P(1),P(2),C(8) (methyl carbon), and C1 occupying the six coordinationsites. The phosphines are trans to the 2,4-dimethylpentadienylgroup, while the methyl and chloro ligands reside trans to one another. The q3-2,4-dimethylpentadienyl ligand has a syn geometry and is sickle-shaped. In solution, 5 undergoes a dynamic process involving isomerization of the 2,4-dimethylpentadienyl ligand from v3 to coordination (AG* = 13.0 f 0.5 kcal/mol). Treatment of 5 with 2 equiv of PMe3 produces 6 quantitatively. Treatment of 1 with HBF,-OEt, yields (v4-2,4-dimethylpentadiene)Rh(PEt&+BF,- (7),which reacts in situ with benzene and durene to release 2,4-dimethylpentadiene and produce (~f-benzene)Rh(PEt~)~+BF,(8) and (116-durene)Rh(PEt3)z+BF,(9), respectively. Compound 9 crystallizes in the monoclinic space group P2Jn with a = 8.349 (2) A, b = 10.843 (8) A, c = 29.535 (9) A, fl = 91.96 ( 2 ) O , V = 2672 (3) A3, and 2 = 4. In the solid state, the durene ring of 9 is nonplanar: the two unsubstituted durene ring carbon atoms are displaced out of the plane of the four methyl-substituted ring carbon atoms toward the rhodium center. Treatment of 2 with HBF,-OEtz yields an equilibrium mixture of (~5-2,4-dimethylpentadienyl)Rh(PMe3)z(H)+BF4(10) and (04-2,4-dimethylpentadiene)Rh(PMe&+BF,- (11). This mixture reacts with benzene and durene to produce ($ben~ene)Rh(PMe~)~+BF,(12) and ($-d~rene)Rh(PMe~)~+BF~(13), respectively.
*
Introduction During the past several years, there has been increasing interest in the synthesis, structure, spectroscopy, and reactivity of metal complexes containing the acyclic pentadienyl ligands2 Our principal interest is in the reactivity of (pentadieny1)M complexes, and, for this reason, we have focussed our efforts on a new class of electron-rich (pentadieny1)M complexes-the pentadienyl-metal-tertiary phosphine complexes.’ The tertiary phosphine ligands in these molecules serve three important functions. First, they promote electrophilic and oxidative addition reactions by increasing the electron density at the metal center. In so doing, they make it possible to introduce ligands such
as hydrides and alkyls and probe the interactions of these ligands with the pentadienyl group. Second, they promote q5 q3 and q3 9’ pentadienyl ligand isomerizations by stabilizing the resulting coordinatively unsaturated metal centers. This enhances the reactivity of the complexes toward nucleophilic addition and substitution reactions. Third, because the steric and electronic features of phosphine ligands can be readily varied, they make it possible to change the environment at the metal center and probe the effect of such variations on reactivity. Earlier, we reported the synthesis and dynamics of a new family of (~~-2,4-dimethylpentadienyl)Rh(PR~)~ complexes.lh We now wish to report reaction chemistry for two members of this family, (v3-2,4-dimethylpentadienyl)Rh(PEG), (1) and (~~-2,4-dimethylpentadienyl)Rh(PMe~)~ (2).
-
-
(1) The previous papers in this series are as follows: (a) Bleeke, J. R.; Kotyk, J. J. Organometallics 1983, 2, 1263. (b) Bleeke, J. R.; Hays, M. K. Ibid. 1984, 3, 506. (c) Bleeke, J. R.; Peng, W.-J. Ibid. 1984, 3, 1422. (d) Bleeke, J. R.; Kotyk, J. J. Ibid. 1985,4, 194. (e) Bleeke, J. R.; Peng, W.-J. Ibid. 1986,5,635. (f) Bleeke, J. R.; Stanley, G. G.; Kotyk, J. J. Ibid. 1986,5, 1642. (9) Bleeke, J. R.; Moore, D. A. Inorg. Chem. 1986,25,3522. (h) Bleeke, J. R.; Donaldson, A. J. Organometallics 1986, 5 , 2401. (i) Bleeke, J. R.; Hays, M. K. Ibid. 1987,6, 486. (i) Bleeke, J. R.; Kotyk, J. J.; Moore, D. A.; Rauscher, D. J. J. A m . Chem. SOC.1987,109,417. (k) Bleeke, J. R.; Hays, M. K. Organometallics 1987, 6, 1367 (1) Bleeke, J. R.; Peng, W.-J. Ibid. 1987, 6, 1576. (m) Bleeke, J. R.; Donaldson, A. J.; Peng, W.-J. Ibid. 1988, 7, 33. (n) Bleeke, J. R.; Rauscher, D. J.; Moore, D. A. Ibid. 1987,6, 2614. ( 0 ) Bleeke, J. R.; Hays, M. K.; Wittenbrink, R.
Results a n d Discussion Methylation of 1. Synthesis, Structure, and Dynamics of (q5-2,4-Dimethylpentadienyl)Rh(PEt,),(Me)+03SCF3-(3). Treatment of 1 with CH3+03SCF,results in methylation of the rhodium center and isomerization of the 2,4-dimethylpentadienylligand from q3 to $ coordination to produce yellow (v5-2,4-dimethyl~entadienyl)Rh(PEt~)~(Me)+O~SCF~(3) (see Scheme I).3
J. Ibid. 1988, 7, 0000. (2) (a) Ernst, R. D. Acc. Chem. Res. 1985, 18, 56. (b) Yasuda, H.; Nakamura, A. J . Organomet. Chem. 1985, 285, 15. ( c ) Powell, P. Adu. Organomet. Chem. 1986, 26, 125. (d) Lush, S.-F.; Liu, R.-S. Organometallics 1986, 5 , 1908.
(3) Treatment of ($-~yclopentadienyl)Rh(PR~)~ with CH31produces (~5-cyclopentadienyl)Rh(PR3)2Me*I-: Werner, H.; Feser, R.; Buchner, W. Chem. Ber. 1979, 112, 834.
0276-7333/88/2307-1588$01.50/0
1988 American Chemical Society
Organometallics,Vol. 7,No. 7, 1988 1589
Pentadienyl-Metal-Phosphine Chemistry Table I. Positional Parameters and Their Estimated Standard Deviations for Non-Hydrogen Atoms in (?‘-2,4-Dimethylpentadienyl)Rh(PEt~)~(CH*)+O~SCF~ (3) atom X V 2 0.21161 (3) 0.10311 (3) 0.19033 (2) 0.09274 (9) 0.2122 (1) 0.2135 (1) 0.19642 (8) 0.4030 (1) 0.0339 (1) 0.1162 (4) 0.0848 (6) -0.0072 (5) 0.1838 (4) 0.1187 (5) -0.0525 (5) 0.1145 (5) -0.0081 (5) 0.2547 (3) 0.0730 (5) 0.0865 (5) 0.2696 (3) 0.2136 (4) 0.0324 (5) 0.1554 (6) 0.1695 (7) -0.1554 (5) 0.1848 (4) 0.1208 (6) 0.3490 (4) 0.0863 (7) 0.2902 (6) 0.2125 (5) 0.2608 (3) 0.1415 (6) 0.1686 (6) 0.0029 (4) -0.0358 (4) 0.0910 (6) 0.2081 (7) 0.3591 (5) 0.2568 (5) 0.0704 (3) 0.3282 (5) 0.0057 (4) 0.3598 (6) 0.3267 (6) 0.0980 (5) 0.1244 (6) 0.170 (1) 0.4030 (6) 0.1505 (7) 0.1188 (5) 0.2075 (4) 0.5302 (5) 0.6552 (6) 0.0741 (7) 0.2155 (6) 0.4371 (6) -0.0502 (5) 0.2751 (3) 0.4374 (7) -0.0025 (7) 0.3503 (4) 0.1144 (4) 0.4262 (7) -0.0395 (6) 0.4975 (9) -0.1306 (7) 0.1231 (6) 0.7738 (6) 0.3607 (5) 0.9472 (4) 0.7053 (5) 0.8763 (3) 0.1923 (7) 0.8213 (4) 0.9644 (4) 0.1635 (6) 0.94217 (9) 0.7497 (1) 0.2420 (1) 0.6509 (6) 1.0081 (4) 0.2348 (6) 0.6745 (5) 1.0738 (3) 0.2770 (7) 1.0159 (4) 0.6230 (5) 0.1311 (6) 0.5767 (4) 0.2987 (7) 0.9962 (4)
Figure 1.
ORTEP
drawing of cation of (s5-2,4-dimethyl-
pentadienyl)Rh(PEt3),(CH3)+03SCF3(3). Scheme I”
$P;h
03SCF3-
Rh-p’
-
The q3 q5 isomerization of the 2,4-dimethylpentadienyl ligand enables the Rh(II1) center in cation 3 to attain a stable 18e count. An ORTEP drawing of the cation of 3, derived from a single-crystal X-ray diffraction study, is shown in Figure 1. Positional parameters of the non-hydrogen atoms are listed in Table I, while important bond distances and angles are given in Table 11. The overall coordination geometry of the cation of 3 is pseudooctahedral, with C(l), C(3), and C(5) of the 2,4-dimethylpentadienyl ligand, and P(1), P(2), and C(8) (methyl carbon) occupying the six coordination sites. The two phosphines reside in different chemical environments; P(1)sits under the open Ymouth” of the 2,4-dimethylpentadienylligand, while P(2) resides under a 2,4-dimethylpentadienyl “edge”. The methyl group occupies the other “edge” site. This geometry is
CI
5
“ p = Et3; p’ = PMe3. (a) CH3+03SCF3-. (b) (Ph3P)2N+C1-. (c) Ag+O,SCF 3 4 no. of parameters varied data/parameter ratio final RF" final RwFb
C21H44F303P2RhS
598.49
5
C2oHUClPZRh 484.88 R l / C
13.507 (7) 18.226 (3) 95.97 (2) 2769 (3) 4 yellow 0.2 X 0.3 X 0.6 1.436 Mo K a , X = 0.71069 8.310 none W
variable, 2-29 3.0 60.0 h,k,*l 8345 3986 280 14.2 0.050 0.066
C(2) or C(4)), 109.0 (d, J = 6.1 Hz, C(2) or C(4)),97.9 (d, J = 14.8 Hz, C(3)), 64.4 (d of d, J = 19.0 Hz, 3.8 Hz, C(l)), 33.5 (s, C(7)), 28.0 ( 8 , C(5)), 25.8 ( 8 , C(6)), 17.9 (d, J c -=~27.2 Hz, phosphine CH,'s), 16.8 (d, J c p = 25.2 Hz, phosphine CH,'s), 8.1 (s, phosphine CH,'s). 31P(1H]NMR (-80 "C, CDZClz): 6 23.8 (d of d, Jp-Rh = 180 Hz, J p - p = 43 Hz), 22.6 (d Of d, Jp-Rh = 176 Hz, Jp-p = 43 Hz). Conversion of 7 t o (q6-Benzene)Rh(PEt3),+BF4(8). Benzene (0.078 g, 1.0 mmol) was added to a solution of 7 (0.20 g, 0.39 mmol) in 10 mL of tetrahydrofuran, causing the color of the solution to change immediately from red-purple to red-orange. Evacuation of the volatiles left 8 as a yellow solid. Yield: 0.20 g (100%). Anal. Calcd for C18H36P2RhBF4:C, 42.88; H , 7.21. Found: C, 42.73; H, 7.03. 'H NMR (20 "C, (CD3),CO): 6 6.76 (s, 6, benzene CH's), 1.54 (m, 12, phosphine CHis), 1.20 (m, 18, phosphine CH,'s). 13C('H}NMR (20 "C, (CD3),CO): 6 100.8 (s, benzene CH's), 17.8 (virtual t, Jcp= 28.9 Hz, phosphine CHis), 8.6 (s, phosphine CH,'s). 31P(1H)NMR (20 "C, (CD3),CO): 6 41.2 (d, Jp-Rh = 199 HZ). Conversion of 7 to (~f-Durene)Rh(PEt~)~+BF~(9). Durene (0.053 g, 0.39 mmol) was added to a solution of 7 (0.20 g, 0.39 mmol) in 10 mL of tetrahydrofuran, causing the color to change gradually from red-purple to red. Evacuation of the volatiles left 9 as a red-brown solid. Yield: 0.21 g (100%). Anal. Calcd for CzHUP,RhBF4: C, 47.16; H, 7.93. Found C, 46.76; H, 8.12. 'H NMR (17 "C, CD,Cl,): 6 5.36 (s, 2, durene CH's), 2.35 (s, 12, durene CHis), 1.54 (quintet, J = 8 Hz, 12, phosphine CHis), 0.99 (d o f t , J = 16 Hz, 8 Hz, 18, phosphine CH,'s). 13C(1HJNMR (17 "C, CD,C12): 6 117.2 (durene Cs), 97.9 (durene CHs), 20.5 (virtual t, J c -= ~30.7 Hz, phosphine CH,'s), 19.0 (durene CH,'s), 8.2 (phosphine CHis). 31P(1H)NMR (17 "C, CD2C12):6 33.8 (d, Jp..Rh = 199 Hz). Protonation of (q3-2,4-Dimethy1pentadienyl)Rh(PMe3)), (2). S y n t h e s i s of (q5-2,4-Dimethylpentadienyl)Rh(PMe3),H+BF4- (10) a n d (q4-2,4-Dimethylpentadiene)Rh(PMe3),+BF4-(11). HBF4.0Eh (0.092 g, 0.57 mmol) in 5 mL of tetrahydrofuran at -30 "C was added with swirling to a solution of 2 (0.20 g, 0.57 mmol) in 5 mL of tetrahydrofuran a t -30 "C, causing the color of the solution to change immediately from red-orange to red-purple. Attempts to isolate solid 10 and 11 from this solution led to loss of 2,4-dimethylpentadiene and decomposition. However, the equilibrium mixture of 10 (30%) and 11 (70%) can be stored for a short time in tetrahydrofuran a t -30 "C and used in situ. NMR S p e c t r a for 10. 'H NMR (-35 "C, CD,C12): 6 5.72 (s,
12.962 (3) 8.236 (2) 22.758 (6) 94.19 (2) 2423 (2) 4 yellow 0.4 X 0.3 X 0.3 1.329 Mo Ka,X = 0.71069 9.362 psi scans 0.9993, 0.8953, 0.9565 9-28 variable, 4-29 3.0 45.0 h,k,*l 3378 2624 329 8.0 0.033 0.047
9 C22H44BF4P2Rh
560.25 R1/n 8.349 (2) 10.843 (8) 29.535 (9) 91.96 (2) 2672 (3) 4 red 0.6 X 0.15 X 0.15 1.392 Mo Ka, X = 0.71069 7.807 psi scans 0.9969, 0.8080, 0.8712 0-28
variable, 4-29 3.0 55.0 h,k,*l 5379 3563 246 14.5 0.083 0.124
1, H(3)), 3.65 ( s , l , H(l)s,,,), 3.14 (s, 1,H(5)*,,,), 2.17 (s, 3, H(6)'s), 1.76 (d, J = 8.9 Hz, 9, phosphine CH,'s), 1.39 (s,3, H(7)'s), -14.61 (m, 1, Rh-H). (Signals due to H(l)mt,,H(5Imt,, and one PMe, ligand are obscured.) 13C(1H)NMR (-35 "C, CD,Cl,): 6 125.0 (C(2)), 123.3 (C(4)), 93.1 (d, J = 12.0 Hz, C(3)), 70.8 (C(l)),56.6 (d of d, J = 32.4,7.5 Hz, C(5)), 27.9 (C(6))),26.6 (C(7)),22.6 (d, Jcwp = 34.3 Hz, phosphine CH3's), 20.5 (d, Jc-p= 29.8 Hz, phosphine CH3's). 31P{1H)NMR (-35 "C, CDzClz): 6 2.4 (d of t, Jp-Rh = 143 Hz, Jp-p c J p - H = 22 Hz, P(l)),-9.3 (d of d of d, Jp-Rh = 126 HZ, J p - p = 22 HZ, JP-H = 11 HZ, P(2)). NMR S p e c t r a for 11. 'H NMR (-35 "C, CD2C12):6 4.77 (s, 1, H(3)), 3.59 ( ~ ~H(l)a,.,J, 1, 2.68 (s, 1,H(I)mJ, 2.02 (5, 3, H(6)'s), 1.63 (s, 3, H(7)'s), 1.54 (d, J = 9.7 Hz, 9, phosphine CH3's), 1.44 (d, J = 10.4 Hz, 9, phosphine CH,'s), 1.09 (s, 3, H(5)'s). 13C(1H) NMR (-35 "C, CD2Cl,): 6 118.6 (C(2) or C(4)), 103.1 (C(2) or C(4)), 96.2 (C(3)), 63.6 (d, J = 14.7 Hz, C(l)), 33.0 (C(7)),27.8 (C(5)), 26.2 (C(6)), 19.3 (d, Jc-p= 28.4 Hz, phosphine CH3's), 18.1 (d, Jc-p= 28.2 Hz, phosphine CHis). 31P(*H)NMR (-35 "C, CDZCl2): 6 -12.9 (d of d, Jp-Rh = 170 Hz, J p - p = 50 Hz, P(l)),-16.1 (d of d, Jp-Rh = 182 Hz, J p - p = 50 Hz, P(2)). Conversion of 10/11 to ($-Benzene)Rh(PMe3),+BF4-(12). A procedure identical with that described earlier for the synthesis of 8, except with 0.17 g (0.39 mmol) of l O / l l , produced 0.11 g of yellow 12 (70% yield). Anal. Calcd for Cl2HZ4RhP2BF4:C, 34.31; H, 5.77. Found: C, 33.91; H, 5.23. 'H NMR (-35 "C, CD,C12): 6 6.42 (s,6, benzene CHs), 1.7 (m, 18, phosphine CH,'s). 13C('H)NMR (-35 "C, CD2C1J: 6 99.6 (benzene CHs), 15.4 (virtual t, Jc-p = 39.7 Hz, phosphine CH3's). 31P(1H)NMR (-35 "C, CD2C1,): 6 -5.0 (d, Jp-Rh = 199 Hz). Conversion of 10/11 t o (~f-Durene)Rh(PMe~),+BF,(13). A procedure identical with that described earlier for the synthesis of 9, except with 0.17 g (0.39 mmol) of l O / l l , produced 0.13 g of red-brown 13 (70% yield). Anal. Calcd for C16H3,P2RhBF4: C, 40.36; H, 6.79. Found: C, 40.08; H, 6.56. 'H NMR (18 "C, CD2Clz): 6 5.42 (s, 2, durene CH's), 2.33 (s, 12, durene CH3's), 1.44 (virtual m, 18, phosphine CH3's). l3C('H] NMR (18 "C, CD,Cl,): 116.7 (durene C's), 98.4 (durene CH's), 22.0 (virtual t, Jc-p = 34.5 Hz, phosphine CH3's), 18.7 (durene CH,'s). 13P('H} NMR (18 "C, CDZC12): 6 -1.8 (d, Jp-Rh = 200 Hz). X-ray Diffraction Studies of 3 a n d 5. Single crystals of 3, 5, and 9 were sealed in glass capillaries under an inert atmosphere. Data were collected a t room temperature on a Nicolet P 3 diffractometer, using graphite-monochromated Mo Ka radiation. All data reduction and structure refinement were done by using the Enraf-Nonius structure determination package (modified by
1596 Organometallics, Vol. 7, No. 7, 1988 B.A. Frenz and Assoc., Inc., College Station, TX) on a VAX 111780 computer.16 Crystal data and details of data collection and structure analysis are summarized in Table VII. In each case, the structure was solved by standard Fourier techniques, following the location of the rhodium atom from a Patterson map. For 3, all non-hydrogen atoms were refined anisotropically, while hydrogen atoms were added at idealized positions by using the program HYDRO and included in the structure factor calculations, but not refined. For 5, all nonhydrogen atoms except for the carbons in one PEt3 ethyl group (C(23)-C(23)’) were refined anisotropically. Atoms C(23) and C(23)’ each exhibited a twofold disorder, which we were able to model successfully by using a multiplicity of 0.5 for each site. Both seta of C(23) atoms (labeled C(23)A and C(23)B in Tables I11 and IV and C(23)’ atoms (labeled C(23)C and C(23)D) were refined isotropically. All hydrogen atoms except for those on the disordered ethyl group were located on difference Fourier maps. The positions of these hydrogen atoms (except for H(62)) were refined and were included in the structure factor calculations. For 9, all non-hydrogen atoms except the boron and the four fluorines in the BF4- group were refined anisotropically. The fluorine atoms exhibited very large isotropic thermal parameters consistent with a disorder problem. However, independent sets of fluorine atoms (in sites of partial occupancy) were not resolvable in the electron density maps. Therefore, a disorder could not be modeled, and the boron and four fluorine atoms were refined isotropically a t full occupancy. All hydrogen atoms were added a t idealized positions by using the program HYDRO and included in the structure factor calculations, but not refined. Solution Dynamics of Compounds 3 and 5. Samples were dissolved in (CD3),C0 or C2D4C12,and NMR spectra were recorded over the temperature range -80 to 80 “C. The exchange rate constant, k,, a t the coalescence temperature for each exchange process1’ was calculated by using the formula
k, =
dAv)
2112
where Au is the difference in frequency between the two exchanging sites in the stopped exchange limit.Is This exchange rate constant was then used to determine the free energy of activation, AG*, a t the coalescence temperature, T,, from the Eyring equation
(16) Atomic scattering factors were obtained from: International Tables for X-Ray Crystallography; Kynoch Birmingham, England, 1974;
VOl. IV. (17) The coalescence of the 13C NMR signals due to pentadienyl methyl carbons C(6) and C(7) was used to calculate the rotational barrier in 3, while the coalescenceof the H(l)mtiand H(1), signals in 5 wag used to calculate AG* for the v3 q1 q3 fluxional process. (18)Pople, J. A.; Schneider, W. G.; Bernstein, H. J. High Resolution Nuclear Magnetic Resonance; McGraw-Hill: New York, 1959; p 223.
Bleeke a n d Donaldson where k’= Boltzmann’s constant, h = Planck’s constant, and R = ideal gas c ~ n s t a n t . ’ ~
Summary From this study, several salient features of the reactivity of (q3-2,4-dimethylpentadienyl)Rh(PR3)2 complexes have emerged. First, the electron-rich metal center reacts readily with electrophiles such as CH3+and H+. These electrophilic additions are accompanied by shifts of the 2,4-dimethylpentadienylligands from the v3-bondingmode to the v5-bondingmode, generating 18e Rh(II1) products. Second, pentadienyl ligand shifts give rise to nucleophilic addition and substitution chemistry. For example, the nucleophilic additions of C1- to [ (v5-2,4-dimethylpentadienyl)Rh(PRJ2(Me)]+complexes proceed via 16e intermediates, which are generated by q5 q3 pentadienyl ligand shifts. Similarly, q3 q1 q3 ligand shifts are responsible for both the dynamic behavior and the nucleophilic substitution chemistry exhibited by (a3-2,4-dimethylpentadienyl)Rh(PEt3),(Me) (Cl). Third, the hydride ligands that result from protonation of (q3-2,4-dimethylpentadienyl)Rh(PR3)2 complexes exhibit a high aptitude for migration to the termini of the 2,4dimethylpentadienyl groups. The resulting [ (q4-2,4-dimeth~lpentadienyl)Rh(PR~)~]+ complexes, when treated with arenes, lose 2,4-dimethylpentadieneand are converted to [(v6-arene)Rh(PRJ2]’complexes. In contrast to hydride ligands, methyl ligands show no tendency to migrate.
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Acknowledgment. Support from the National Science Foundation (Grant CHE-8520680) is gratefully acknowledged. Washington University’s High Resolution NMR Facility was funded in part by National Institutes of Health Biomedical Research Support Instrument Grant 1 S10 RR02004 and by a gift from Monsanto Co. Registry No. 1, 104779-57-9;2, 104779-56-8;3, 114422-97-8; 4, 114422-93-4;5, 114422-90-1;6, 114422-91-2;7, 114422-81-0;8, 114443-22-0; 9,114422-83-2; 10, 114422-95-6;11, 114422-85-4;12, 114422-87-6;13,114422-89-8;CH3+03SCF
