Organometallics 1995, 14, 842-847
842
31P,l3C, and lH NMR Studies on Chiral Allyl Ferrocenyldiphosphine Complexes of Palladium(I1) Paul S. Pregosin,” Renzo Salzmann, and Antonio T o p i Laboratorium fur Anorganische Chemie, ETH Zentrum, Zurich 8092, Switzerland Received August 29, 1994@
A series of complexes of the type [Pd(q3-allyl)(JOSIPHOS)ICF~S03, containing either the @-pinene,q3-CloH15, or the q3-C3H5 ligands and the new chiral 1,2-ferrocenyldiphosphine ligands, JOSIPHOS, have been studied using multidimensional NMR spectroscopy (JOSI}, (R1 = Cy, R2 = Ph, a; R1 = Ph, R2 = PHOS, 5, = (Cp)Fe{C5H3(1-CH(CH3)PR21)-2-PR22) Cy, b; R1 = Ph, R2 = Ph, c). A structural comparison based on NOE data for the cation [Pd(q3-CloH15)(5a)l+with NOE data from the analogous cations of S-BINAP and S,SCHIRAPHOS suggests that coordinated 5a intrudes more into the coordination sphere of the allyl ligand than do either S-BINAP or S,S-CHIRAPHOS. The nature of the chiral environment for 5a in [Pd(q3-CloHl5)(6a)1CF3S03,4d, is described. 2-D exchange spectroscopy for four cationic complexes of the type [Pd(q3-C3H5)(JOSIPHOS)1+,which contain different JOSIPHOS modifications, reveals a selective q3-q1-q3 isomerization, which, for the cations with 5a,b, involves opening of the Pd-C allyl bond cis to the PCy2 and trans t o the PPh2 moiety. The q3-q1-q3 selectivity is shown to be steric and not electronic in origin. 31P,13C, and lH NMR data are reported.
Introduction Organic reactions catalyzed by palladium,l and specifically those involving Pd-allyl intermediates, e.g., catalytic allylation2 PhCH(OAc)CH=CHPh
+
-CH(CO,Me),
chiral catalyst
PhCH{ CH(CO,Me),}CH=CHPh
+ OAc-
remain of synthetic interest. If the allylation is carried out using a palladium complex containing a chiral ligand such as a chelating diphosphine, the organic products which result often reveal substantial-to-excellent enantiomeric exce~ses.~ Recently, chiral chelating and mixed phosph~rus-nitrogen~~~ ligands have also been used with excellent results. Abstract published in Advance ACS Abstracts, December 15,1994. (1) (a) New Pathways for Organic Synthesis; Colquhoun, H. J.; Thompson, D. J., Twigg, M. V., Eds.; Plenum Press: New York, 1984. (b) Trost, B. M. ChemtractS.Org. Chem. 1988, 1 , 415.(c) Trost, B. M. Tetrahedron, 1977,33,2625.(d) Trost, B. M. Acc. of Chem. Res. 1980, 13,385.(e) Metallo-Organic Chemistry; Pearson, A. J., Ed.; John Wiley and Sons: New York, 1985.(DStary, I.; Kocovsky, P. J. A m . Chem. SOC.1989,111, 4981. (2)Consiglio, G.; Waymouth, R. M. Chem. Rev. 1989, 89, 257. Consiglio, G.; Indolese, A. Organometallics 1991,10,3425. Sawamura, M.; Ito, Y. J . Am. Chem. SOC.1992,114,2586. (3)Yamamoto, K.; Deguchi, R.; Ogimura, Y.; Tsuji, J. Chem. Lett. 1954,1657.Mackenzie, P. B.; Whelan, J.; Bosnich, B. J . Am. Chem. SOC.1985,107, 2046.Auburn, P. R.; Mackenzie, P. B.; Bosnich, B. J . Am. Chem. SOC.1985,107, 2033.Hayashi, T.;Yamamoto, A. Tetrahedron Lett. 1988, 29, 669. Hayashi, T.; Yamamoto, A,; Ito, Y.; Nishioka, E.; Miura, H.; Yanagi, K. J. Am. Chem. SOC.1989,111,6301. Sawamura, M.; Nagata, H.; Sakamoto, H.; Ito, Y. J. Am. Chem. SOC. 1992,114,2586. (4)(a) Pfalz, A. Acc. Chem. Res., 1993,26, 339. (b) von Matt, P.; Pfaltz, A. Angew. Chem., Znt. Ed. Engl. 1993,32,566. (c) Togni, A. Tetrahedron Asym. 1991,2, 683.(d) Tanner, D.Angew. Chem., Int. Ed. Engl. 1994,106, 625. (e) Sprinz, J.; Kiefer, M.; Helmchen, G.; Reggelein, M.; Huttner, G.; Zsolnai, L. Tetrahedron Lett. 1994,35, 1523.(0Dawson, G.; Frost, C. G.; Williams, J. M. J. Tetrahedron Lett. 1993,34,3149. @
The structural aspects of the intermediates which arise in the homogeneous allylation catalyzed by palladium(I1) complexes are important. It is known5-11 that NMR studies and especially lH NOE spectroscopy can determine subtle and gross molecular features in organometallic complexes of Pd(I1). For chiral compounds containing either BINAP or CHIRAPHOS, the ortho protons of the P-phenyl groups may be used as “reporters”to define the 3-D structure of the chiral Pdn-allyl catalyst p r e c u r s ~ r s . ~ , ~ In~part, J ~ J such ~ proximity effects deduced from NOE studies5-” have been used by Akermark and co-workers12to help shift the sydanti equilibria in some crotyl allyl complexes. Phase-sensitive lH-NOESY also provides exchange data,13 thus leading t o new6,8band selective6J4results for Pd-n-allyl isomerization dynamics. For [Pd(n-allyl)(5) (a) Pregosin, P. S.;Riiegger, H.; Salzmann, R.; Albinati, A.; Lianza, F.; Kunz, R. W. Organometallics 1994,13,83. (b) Pregosin, P. S.; Riiegger, H.; Salzmann, R.; Albinati, A,; Lianza, F.; Kunz, R. Organometallics, 1994,in press. (6)(a) Riiegger, H.;Pregosin, P. S.Magn. Reson. Chem. 1994,32, 297.(b) Pregosin, P. S.; Salzmann, R. Magn. Reson. Chem. 1994,32, 128. (7)Cesarotti, E.;Grassi, M.; Prati, L.; Demartin, F. J . Chem. SOC., Dalton Trans. 1991,2073. ( 8 )Albinati, A,; Ammann, C.; Pregosin, P. S.; Ruegger, H. Organometallics 1990,9, 1826.Albinati, A,; Kunz, R. W.; Ammann, C. J.; Pregosin, P. S.Organometallics 1991, 10,1800. (9)Giovanetti, J. S.; Kelly, C. M.; Landis, C. R. J . A m . Chem. SOC. 1993,115,4040. ( 1 0 ) A ” a n n , C. J.; Pregosin, P. S.;Ruegger, H.; Albinati, A,; Lianza, F.; Kunz, R. W. J . Organomet. Chem. 1992,423,415. (11)Riiegger, H.; Kunz, R. W.; Ammann, C.; Pregosin, P. S. Magn. Reson. Chem. 1992,29, 197. (12)(a) Akermark, B.;Hansson, S.; Vitagliano, A. J . Am. Chem. SOC.1990,112,4587.(b) Sjorgen, M.P. T.; Hansson, S.;Norrby, P.; Akermark, B.; Cucciolito, M. E.; Giordano, F.; Vitagliano, A. OrganoNorrby, P.; Sjorgen, M. P. T.; metallics 1992,11,3954.(c) Hansson S.; Akermark, B.; Cucciolito, M. E.; Giordano, F.; Vitagliano, A. Orgunometallics 1993,12,4940. (13)Hull, W. E. In Two-dimensional NMR Spectroscopy. Applications for Chemists and Biochemists; VCH: New York, 1987;p 153. (14)Breutel, C.; Pregosin, P. S.;Salzmann, R.; Togni, A. J . A m . Chem. SOC.1994,116,4067.
0276-733319512314-0842$09.00/0 0 1995 American Chemical Society
Allyl Ferrocenyldiphosphine Complexes of Pd(II)
Organometallics, Vol. 14, No. 2, 1995 843
Chart 1. Structural Units and Definitions
Chart 2. JOSIPHOS Ligands
Me,,Me
1
JOSIPHOS Ligands
3
2
JOSIPHOS, 5 Pd numbering system for q3cioH15
R1
R2
Sa Cy = cyclohexyl
Ph = phenyl
5b Ph 5c Ph
CY
5d phobyl
Ph
Ph
These ligands are S (on carbon) and R (on iron)
4 a, b = R- and S -BINAP
-
c = S,S CHIRAPHOS d = JOSIPHOS,Sa
(bidentate nitrogen ligand)]+,the suggestion,s based on 'H NOESY studies, that ring opening of the nitrogen chelate, followed by allyl isomerization, might explain apparent allyl rotation led t o an elegant proof by Backvall and co-workers.15 We have concentrated on Pd complexes with allyl ligands as shown in 1-4 (Chart l), using commercially available chiral auxiliaries. In this study we center on Pd(I1) allyl complexes of the novel chiral ferrocene-based ligand JOSIPHOS,165 (see Chart 21, and report on new structural and dynamic aspects. The ligands 6 possess two types of chirality and are effective chiral auxiliaries.
9 P
for the "phobyl"( (3.3.1]-9-phosphabicyclonon-9-yl, CgH14) complex there are two fused six-membered rings.
\ major isomer (1)
minor isomer (11)
View from behind the allyl towards the Pd. R1 = C6H11, R2 = C6H5.
Results and Discussion The new v3-CloH15 (/3-pinene) and v3-C3H5 allyl JOSIPHOS complexes were prepared as described previously (see Experimental Section) by removing C1- from the chloro-bridged allyl compounds, using either Ag+ or Tl+,followed by reaction with the appropriate ligand 5. N M R for the /3-Pinene-AllylComplex. For [Pd(v3-CloH15)(5a)ICF3S03,4d, there are two rotational isomers (only one face of the ,&pinene allyl can coordinate5JoJ1). With respect to a coordination plane defined by the Pd and two P atoms, there are two possible orientations for the v3-C1oH15ligand, and fragments of these structures are shown as follows: (15)Gogoll, A.; Ornebro, J.; Grennberg, H.; Backvall, J. E. J. Am.Chem. Soc. 1994,116, 3631. (16) (a) Togni, A.; Breutel, C.; Schnyder, A.; Spindler, F.; Landert, H.; Tijani,A. J.Am. Chem. Soc. 1994,116,4062.(b) Togni,A.; Breutel, C.; Soares, M. C.; Zanetti, N.; Gerfin, T.; Gramlich, V.; Spindler, F.; Rihs, G. Inorg. Chim. Acta 1994,222,213. (c) For 6d see: Abbenhuis, H. C. L.; Burckhardt, U.; Gramlich, V.; Kollner, C.; Pregosin, P. S.; Salzmann, R.; Togni, A. Organometallics 1996, 14, 759.
The C(CH312 bridge of the allyl is remote from the I'd-atom.
From 31PNMR the majodminor ratio is ca 1 O : l (see Table l), and we note that the major isomer has the larger part of the allyl hydrocarbon remote from the two cyclohexyl groups, i.e., the methine allyl carbon is pseudo-trans to the PCy2 moiety. The 'H NOESY spectrum, see Figure 1,was used t o assign the major isomer. One can recognize a strong NOE from the methine allyl proton, HC,t o the ortho protons of the P-phenyl ring. Further, the syn methylene allyl proton, Ha, is remote from the phenyls (no NOE's to these) but shows strong NOE's to the cyclohexyl protons. Additional NOE's support the structure assigned to the major i ~ 0 m e r . l The ~ ~ proton assignments17bfollow from this and the 31P,1Hcorrelation; see Table 2. There are several important structural conclusions which can be derived from the NOE analysis:
Pregosin et al.
844 Organometallics, Vol. 14,No. 2, 1995
1. The chiral pocket differs from that of S-BINAP in that the two phenyls do not occupy pseudo-axial and equatorial positions. On the basis of the strong NOE’s from both sets of ortho phenyl protons to the Cp proton H(30), we estimate that the substituted Cp ring approximately bisects the C(a)-P2-C(P) angle.
-Phenyl
ll
a-Phenyl
p 0
1
2. The six-membered chelate ring is in the form of a skew-boat, with the CH3 of the stereogenic side chain lying roughly parallel to the upper Cp ring:
2
4:
3
4
fragment of 6a
This conformation,which exists in the solid-state structure of [Pd(v3-C3H5)(5a)1CF3S03,16bplaces the CH3 close to an upper Cp ring proton and has the two cyclohexyl groups away from the lower v5-C5H5 ring (no NOE between these). Generally speaking, this ring conformation can change and for the new C3H5 allyl complex, 6d,16cmentioned later in the section on dynamics, the conformation is as follows:
fragment of 6d
In 6d the CH3 group is above the upper Cp plane and close to the aB-phenyl group (there is an NOE from the methyl to the ortho protons of this ring). Obviously, the chelate ring conformation can depend on the P substituents. 3. The JOSIPHOS phenyl groups in [Pd(v3C I O H ~ ~ ) ( ~ ~ ) Iintrude C F ~ Smore O ~ into the coordination sphere of the pinene-allyl group than in the analogous5 4b, and complexes [Pd(l;13-C~0H15)(S-BINAP)ICF3S03, [Pd(~3-C~~H1~)(S,S-CHIRAPHOS)ICF3S03, 4c. Under comparable conditions one finds strong NOEs from the JOSIPHOS phenyl groups to the allyl protons HC,Hd, and Hf, as shown by the arrows in Figure 1. For these same protons in the BINAP and CHIRAPHOS complexes we observed5J0J1 sometimes strong but often moderate-to-weak NOE’s t o these protons from the corresponding ortho phenyl protons. Clearly, in terms of its ability to intrude into the allyl coordination sphere,
PPm
Figure 1. Section of the IH 2-D NOESY for 4 indicating the selective NOE’s from the ortho a and /3 ring protons of the PPhz moiety to various aliphatic protons of the C10H16 allyl ligand. Specifically note the three arrows which indicate the cross-peaks arising from (top-to-bottom)Hf, Hd’, and the methine allyl proton Hc. These and other NOEs allow the major isomer to be correctly assigned and also allow us to develop a detailed structural picture for coordinated 6b (CDCl3, 500 MHz). JOSIPHOS is a “big“ ligand. The nature of, and the differences between, the chiral environments of a JOSIPHOS (and/or a BINAP) are important characteristics of these ligands and must be considered when rationalizing their effectiveness (or lack thereof) in, e.g., catalytic allylation.l6 A comparison the 13C chemical shifts for the terminal 4d, with allyl carbons of [Pd(y3-Cl~Hls)(5a)lCF3S03, those for (S and R) [Pd(q3-CloH15)(BINAPP)ICF3SO~, 4a,b, and [Pd(y3-CloH15)(S,S-CHIRAPHOS)ICF3SO3, 4c, is shown in Table 3. As the trialkylphosphine donor in 4d is expected to have a stronger trans-influence,18-20 (17)(a) There are numerous other NOES which support this assignment; e.g., Hd‘, one of the two protons immediately adjacent to the methine allyl HC, shows a strong NOE to the ortho protons of the phenyl group shown as “a”.Moreover, the NOE data allow us to readily differentiate between the two phenyl groups; e.g., the bridgehead proton Hf, which lies very close to the Pd atom, reveals a strong selective NOE to the ortho protons of the phenyl shown as “a”.(b) A comparison of Ha, Hb, and Hf within the two rotational isomers is particularly informative. In the major (minor) isomer, Ha appears at 4.28 (3.67), Hbat 3.00 (2.031, and Hf’ at -0.22 (+1.27). The changes in Hazbare consistent with the minor isomer having the allyl methylene close to the PPhz aromatic rings, once again, supporting the assignment. The shift for Hf, 6 = -0.22, the bridge-CHz proton close to the Pd atom, suggests that this has been placed directly above the a-phenyl ring. The lJ(C,H) value for this Hf’ suggests that it is not agostic. (18)Akermark, B.; Krakenberger, B.; Hansson, S.; Vitagliano, A. Organometallics 1987,6, 620.
Allyl Ferrocenyldiphosphine Complexes of Pd(II)
Organometallics, Vol. 14,No. 2, 1995 845
Table 1. 31PNMR Data for [Pd(lrl3-C1oH15)(5a)]CF3SO3 and [Pd(q3-C3H5)(5)1CF3S03,6
4
PA
58.5
PB
15.2
PA
58.5
PB
13.5
51.1
47.6
PB
29.9
47.4
51.1
34.9
PB
11.9
54.0
58.2
50.4
13.6
6iuaitm 49.3
47.2
48.7
29.6
6uWLlc PA
h
18.2
-
PA
d
6uniUu 58.6
34.1
58.8
11.2
6hmia.L PA
19.6
PB
10.4
6Lmilu 56.9
18.9
59.9
11.6
Table 2. ‘H and 13CN M R Datau for [Pd(g3-CloH15)(5a)lCF3S03 major isomer b C
d d‘
e f f g
h i “CP” CH3 CH
a
P
‘H
minor isomer
‘3C
‘H
‘3C
3.00 4.13 1.94 1.34 1.44 1.67 0.22 1.89 0.95 1.11 3.73 1.79 3.39
63.7 83.7 28.4 28.4 40.1 30.4 30.4 47.2 21.7 25.9
2.03 4.07 2.70 2.54 2.24 1.33 1.27 2.23 1.01 1.23
72.3 79.9
71.7 16.3 31.0
3.77 1.79 3.34
71.7 16.3 29.8
ortho-H 7.12 8.07
ortho-C 133.5 137.2
ortho-H 7.20 7.80
Ortho-C 132.6 136.3
63.7 73.7 74.7 67.1 60.0
C(3) 83.7 81.3 86.4 80.7 67.5
R
21.9 26.0
20.0 7.6 11.7 13.6 7.5
Chemical shifts are for CDC13 solutions at ambient temperature, relative to TMS, at 125 MHz. Major isomer.
and as the two terminal allyl carbons are in different (19) Clark, H. C.; Hampden-Smith, M. J.; Riiegger, H. Organometallics 1988, 7, 2085 and references quoted therein. (20)Appleton, T.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev. 1973,10,335. Motschi, H.; Pregosin, P. S.; Venanzi, L. M. Helu. Chim. Acta 1979,62,667. Motschi, H.; Pregosin, P. S. Inorg. Chim. Acta 1980, 40,141. Motschi, H.; Nussbaumer, C.; Bachechi, F.; Mura, C.; Pregosin, P. S. Inorg. Chim. Acta 1980, 63, 2071.
Pd
For the two rotational isomers of [Pd(v3-C3H5)(5a)l+, I11 and IV,one finds14 a selective ~ 7 ~ - ~ 7 ~ - 7 ,isomerization 7~ Fragments for the isomers of the C3H5complexes 6a
lR\
Y
Table 3. 13CN M R Dataa for the Terminal Allyl Carbons in [Pd(q3-Cl~H1~)(chelate)lCF3S03 Complexes C(1)
R
lROp-r
“Values (in ppm, relative to TMS) have been measured in CDC13 at 297K and at 500 MHz (‘H) and 125 MHz (I3C).
(S,R)-JOSIPHOS,5ab S-BINAP R-BINAP S,S-CHIRAPHOS 4,4’-dimethylbipyridine
-
L
Chemical shifts in ppm, relative to H3P04 for CDC13 solutions at 297 K and at 200 MHz. Coupling constants in Hz.
position
environments, the two 13C shifts will differ. Still, it is interesting that, for the JOSIPHOS derivative, the difference between C(1), trans to PPh2,63.7 ppm, and C(3),trans to PCy2,83.7 ppm, at 20.0 ppm, is the largest in the table. For the S- and R-BINAP complexes, the values are 7.6 and 11.9 ppm, respectively, whereas for S-CHIRAPHOS the difference is 13.6 ppm. For C(l), S pseudo-trans to the PPhz donor, the chemical shift of 63.7 ppm in 4d is at relatively low frequency, suggesting this PPh2 to be only a moderate donor. The corresponding 13C(l)position in the complex [Pd(v3-C10H15)(4,4’dimethylbipyridine)lCF&303is 60.0 ppm. The weakness of this PPh2 donor is probably best understood in terms of steric interactions between the allyl hydrocarbon and the PPh2 phenyl groups, as suggested above from the NOE data. Thus, the steric effects induce substantial changes in the electronic structure. This is presumably a general effect for ligand Sa and could be relevant in a discussion of its effectiveness as allylation catalyst.16 Allyl Dynamics. It is that allyl ligands can (but do not always) convert the syn and anti positions as shown:
RZ RZ IP,
H 111, major isomer, central C-H bond points towards Fe
IR\
-Pd ‘RRPH/
A
R*
-P, R2
IV, minor isomer, central C-H bond points away from Fe
involving opening of the Pd-C bond cis to the PCyz and trans t o the PPh2 moiety. This was the first example of this type of selectivity in a chiral phosphine complex and is interesting in that the trans influence of the PPhz aryl phosphine moiety is generally smaller20than that for the alkylphosphine PCy2 donor. As the steric bulk of the PCy2 group may play a role, we prepared the four v3-C3H5palladium complexes [Pd(v3-C&XJOSPHOS)l+, 6, with the JOSIPHOS ligands 5a-d24and studied the ~7~-47~-)7~ isomerization. The complexes 6, which differ in R1 and R2 and thus have different electronic and steric effects, include 5a and 5b in which the R1and R2 (21) Vrieze, K. In Dynamic Nuclear Magnetic Resonance Spectroscopy; Jackman, L. M., Cotton, F. A,, Eds.; Academic Press: New York, 1975. Cesarotti, E.; Grassi, M.; Prati, L.; Demartin, F. J. Organomet. Chem. 1989,370,407. (22) Faller, J. W. Determination of Organic Structures by Physical Methods; Nachod, F . C . , Zuckerman, J. J., Eds.; Academic Press: New York, 1973; Vol. 5, p 75. (23) Cesarotti, E.; Grassi, M.; Prati, L.; Demartin, F. J. Organomet. Chem. 1989,370, 407. (24) The JOSIPHOS ligand in ref 14 was R at carbon and S at the metal and not S a t carbon and R at the metal; however, for an q3C B Hallyl ~ this is not important. (25) The absence of observable exchange means only that exchange is relatively slow compared to the mixing time, 0.8 s, and not that there is no exchange. We have not attempted to warm the samples. (26) Weiss, R.; Verkade, J . G. Inorg. Chem. 1979, 18, 529. Vande Griend, L. J.; Verkade, J. G.; Pennings, J . F. M.; Buck, H. M. J.Am. Chem. SOC.1977,99, 2459 and references therein.
Pregosin et al.
846 Organometallics, Vol. 14,No. 2, 1995 Table 4.
NMR Dataa for the Terminal Allyl Carbons in the Complexes [Pd(t13-C3H5)(5)]CF3S03, 6
JOSIPHOS
trans to R1
trans to R2
ratio
5a
76.3 78.2 70.1 67.1 74.2 73.9 76.3 78.2
66.9 65.6 73.1 76.8 74.9 74.5 72.3 70.7
major, 1 minor, 0.5 major, 1 minor, 0.9 major, 1.0 minor, 0.8 major, 1.0 minor, 0.6
5b 5c
5d
Chemical shifts are for CDC13 solutions at ambient temperature, at 125 MHz.
PPm
5
3
4
Figure 2. Section of the phase-sensitive lH 2-D NOESY spectrum for the C3H5 allyl complex 6b. The “filled-in” cross-peaks arise from exchange, whereas the “open”crosspeaks arise from NOE’s. The four signals in the lower-left corner demonstrate exchange between the rotational isomers. The interpretation is shown in Scheme 1.The major rotational isomer has the C(2)-H bond pointing away from the Fe atom (CDC13, 500 MHz). Chart 3. JOSIPHOS Ligands 16a)
1 Cy2P.
I pd4 pph2
not dynamic at RT
I
(6b)
Ph2P, pd/
1 pcY2
not dynamic at RT
q3-ql-113 proceeds in both (a) and (b) such that the bond as to the PCyz opens.
No observable 113- ql- 113 isomerization at ambient temperature for (c) and (d).
Scheme 1. Sketch Showing the Exchange Pathways
substituents have been “exchanged”. We summarize the new exchange results in Chart 3 and show a section of the corresponding lH 2-D spectrum for [Pd(y3C3H5)(5b)lCF3S03,6b,in Figure 2. The specific selective exchanges for 6b are given, diagrammatically, in Scheme 1. The lower left corner of Figure 2 shows exchange between two central protons, H2. The remainder of the spectrum shows the specific, well-resolved
exchange cross-peaks (filled-in circles) for the eight protons, H’ and H3, four from each isomer. The open circle cross-peaks arise from NOE. There is no syn-anti exchange at C’, the carbon cis to the PCy2 moiety; however, the HIs proton of one isomer exchanges with the HIs proton of the other isomer. Exactly the same statement can be made for the H’” proton. There is syn-anti exchange at C3, the carbon cis to the PPhz moiety. The H35(or H3”)proton of one isomer exchanges with the H3” (or H35)proton of the other isomer. There is no syn-anti exchange within one isomer. From these results we see that there is selective formation of an +transition state, followed by rotation around the C(2)-C(3) bond and then re-formation of the v3-aiiyi. Consequently, for [Pd(v3-C3H5)(5b)l+, 6b, as for [Pd(v3-C3Hs)(6a)l+,6a, the Pd-C (terminal) bond which is cis to the PCyz fragment opens. This is despite the fact that in 6b there is a PCyz{Cp-type} donor as opposed to a PCyz(alky1) donor in 6a. For the cations [Pd(q3C3H5)(5c)I+,6c, containing R1 = R2 = Ph, and [Pd(q3C3H5)(5d)l+,6d, with Rzl = “phobyl” and R2 = Ph, we isomerization at ambient temobserve no ~~-5J-77~ p e r a t ~ r e . The ~ ~ result for 6d is pertinent in that, although the cyclic phobyl group represents two aliphatic R’ groups and is expected to be a donor comparable to other aliphatic substituents, it is a pinnedback26fragment and, thus, smaller. The measured rate of 113-~1-q3 isomeri~ationl~ is fast compared to the rate of catalytic allylation,16as previously noted.27 The absence of isomerization in the phobyl derivative, 6d, suggests that steric and not electronic effects are responsible for the selective q3-q1-q3 isomerization in 6. In the isomers of the q3-CloH15 cation, 4d, there is no q3-q1-q3 isomerization observable at ambient temp e r a t ~ r e Moreover, .~~ in studiesz8on Pd(I1) compounds involving the 1,3-diphenylallyl anion, PhCH-CHCHPh, one does not always observe syn-anti isomerization. Consequently, we again5 suggest that r3-C3H5 may not be a good model allyl for catalytic allylation. Apart from its small size, it shows a tendency to undergo a relatively rapid movement, a process which may be slower in other Pd(I1)-allyl complexes. Allyl lsC Data for 6. In Table 4 we show 13C data for the terminal allyl carbons in 6, 6 = 65.6-78.2 ppm. Due to the difference in trans-influence between the (27) Mackenzie, P. B.; Whelan, J.; Bosnich, B. J. Am. Chem. SOC. 1985,107,2046.Auburn, P.R.; Mackenzie, P. B.; Bosnich, B. J. Am. Chem. SOC.1986,107,2033. (28)von Matt, P.; Lloyd-Jones, D. C.; Minidis, A.; Pfaltz, A.; Macko, L.; Neuberger, M.; Zehndert, M.; Riiegger, H.; Pregosin, P.S. Submitted for publication in Helu. Chim. Acta.
Organometallics, Vol. 14, No. 2, 1995 847
Allyl Ferrocenyldiphosphine Complexes of Pd(II) Table 5. Selected 'H and
NMR Dahu for
[Pd(t13-C~H5)(5)1CF3S03, 6 position
1H
13c
6a,major (H2 "down" b) IS
la 2 36
3a "CP" a 3
a-I
4.37 2.29 5.84 4.87 2.86 3.64 1.74 3.51
6b, major (H2 "up") IS 4.73 la 3.36 2 5.36 3s 3.97 3a 2.60 "CP" 4.34 CH3 1.54 CH 3.89
76.3 76.3 121.9 66.9 66.9 70.9 15.0 29.8
la
2 3s 3a 3'CP" CH3 (31
4.63 2.91 6.31 4.07 3.03 3.59 1.30
4.24
6d, major (H2 "down") Is 4.33 la 2.87 5.95 2 5.03 3s 3.28 3a 3.72 "CP" 1.21 a 3 CH 3.59
13c
6a, minor (H2"up") 3.85 78.2 3.63 78.2 5.04 120.7 4.61 65.6 3.31 65.6 70.6 3.74 1.54
15.2
3.63
29.8
70.1 70.1 122.5 73.1 73.1 70.6 14.0 32.7
6b, minor (H2down") 67.1 4.63 67.1 3.00 121.3 5.58 76.8 3.58 76.8 3.15 4.31 70.6 14.0 1.52 32.7 3.64
74.2 74.2 124.7 74.9 74.9 71.3 17.1 31.8
6c, minor (H2 "up") 4.36 73.9 4.00 73.9 5.34 121.8 3.94 74.5 3.63 74.5 3.73 71.5 1.31 16.9 4.51 31.5
76.3 76.3 122.7 72.2 72.2 70.8 22.5 24.7
6d. minor (H2 "up") 78.2 3.77 78.2 3.49 121.8 5.34 4.73 70.7 70.7 3.62 3.80 70.8 1.06 22.5 3.56 24.9
6c, major (H2 "down") IS
1H
Chemical shifts in ppm. Coupling constants in Hz. The terms "up" and "down" refer to proximity of H2 to the a and /3 Ph's ("up" has the CH bond pointing away from the Fe atom).
donors,18 there is a marked separation of the two terminal carbons. 'I'ypical18chemical shifts are 70-79 ppm for model allyl complexes with chelating and monodentate aryl phosphines. In addition, Ozawa et aLZ9find d = 69.7 for the terminal carbons of the [Pd(q3-2-MeC3H4)(PMe3)21+ cation. Also, Nakamura and cow o r k e r ~report ~ ~ d = 55-58 for the neutral complexes [Pd(r3-C3H5)CH3(L)I,L = tertiary phosphine, thereby showing that a terminal methylene allyl carbon trans (29) Ozawa, F.; Son, T.; Ebina, S.; Osakada, K.; Yamamoto, A. Organometallics 1992,1 1 , 171. (30) Hayashi, Y.; Matsumoto, R; Nakamura, Y.; Isobe, K. J. Chem. SOC.,Dalton Trans. 1989,1519.
to a "PR3" can appear at lower frequency. We note that the difference,Ad, in the terminal carbon positions for the isomers in 8a is relatively large. Since for 5a-d,5a is the most effective of these chiral ligands in terms of enantioselectivity,16ait is tempting t o believe that this electronic differentiation, noted above for the analogous r3-CloH15 cation, may be important in the nucleophilic attack at the terminal carbon, i.e. enantioselectivity. Conclusions. The /?-pinene allyl complex 4d with JOSIPHOS ligand 5a has a sterically large chiral pocket, and the ligand intrudes markedly (much more so than S,S-CHIFLAPHOS)into the coordination sphere of the v3-allyl ligand. Coordinated 5 does not have marked axial/equatorial phenyl arrays but can show different chelate ring conformations as a function of R1 and/or R2. In 4d there are interesting terminal allyl 13C chemical shifts which hint at selective electronic q~ as a function effects. A selective ~ 7 ~ 7 l -isomerization of the P-substitutents is observed, with steric effects providing the driving force for the selectivity.
Experimental Section The NMR experiments were carried out using a Bruker
AMX 500 spectrometer on 0.02 mmol samples in CDC13. The frequencies 500.13, 202.47, and 125.75 MHz were employed for IH, 13C, and 31P, respectively. Standard pulse sequences were employed for the 1H-2D-NOESY,31 13C-1H,32and 31P1H33correlation studies. The phase-sensitive NOESY experiments used mixing times of 0.8 s. Ligand 5b was provided by Dr. F. Spindler, Ciba-Geigy AG, Basel, Switzerland. The C3H5 complexes of 5 were prepared as described by us previ0us1y.l~ The chloro-bridged dimer [Pd(r+CloH&1]2 was prepared according to the 1iterat1u-e~~ and recrystallized from CH2Cld hexane. This dimer (9.20 mg, 0.025 mmol) was dissolved in 2 mL of CHZC12, the mixture was then treated with solid (SP)JOSIPHOS (30.0 mg, 0.050 mmol), and the resulting solution was stirred for 10 h. AgCF3S03 (12.9 mg, 0.050 mmol) in 1 mL of MeOH was then added t o the yellow solution with immediate precipitation of a white solid. The suspension was then stirred in the dark for 1 h and filtered through Celite, and the solvent was distilled. The raw product was dissolved in a minimum of CHC13 and then treated with a 10-foldvolume of ether. Storage at -30 "C overnight affords orange crystals, which were (a)collected via decantation, (b) washed with ether, and (c) dried in Vacuo to afford 41 mg (81%)of product. Anal. Calc for C47H~eF303F3PzSFePd(985.25): C, 57.30; H, 6.04. Found: C, 57.18; H, 6.22.
Acknowledgment. P.S.P. thanks the Swiss National Science Foundation as well as the ETH for support and the Johnson-MattheyResearch Foundation, Reading, England, for the loan of precious metals. OM940688M (31)Sklener, V.; Miyashiro, H.; Zon, G.; Miles, H. T.; Bax, A. FEBS Lett. 1986,208,94. (32)Summers, M. F.; Marzilli, L. G.; Bax, A. J. Am. Chem. Soc. 1986,108,4285. (33)Jeener, J.:Meier. G. H.: Bachmann. P.: Emst. R. J. Chem. Phvs. 1979,71, 4546. (34) Trost, B. M.; Strege, P. E.; J. Am. Chem. SOC.1975,97, 2534. '
