Organometallics 1996,14, 4962-4965
4962
Reactions of Methoxyallene and of Phenylallene with RhH(CO)(PPh&. Insertion of a C=C Bond into an Rh-H Bond, Giving (mAllyl)rhodium(I)Complexes Kohtaro Osakada," Jun-Chul Choi, Take-aki Koizumi, Isao Yamaguchi, and Takakazu Yamamoto" Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan Received May 15, 1995@ Scheme 1. Proposed Mechanism for Summary: Methoxyallene and phenylallene react with RhH(CO)(PPh& to give R ~ ( ~ / ~ - C H Z C H C H O M ~ ) ( C O ) - Polymerization of Monosubstituted N e n e Catalyzed by (n-Allyl)nickel(II)and -palladium(II) (PPhd2 (1) and Rh(r/3-CH2CHCHPh)(CO)(PPh3)2 (2)) Complexesa respectively. X-ray crystallography shows molecular structures having a n allylic ligand with syn OMe and Ph groups. The complexes undergo exchange of two CH2 allylic hydrogens on the N M R time scale through n-a-n rearrangement of the ligand. N M R studies on reaction mixtures of phenylallene and RhD(CO)(PPh& as well as of 2 and RhD(CO)(PPh& reveal irreversible insertion M of a C=C bond of phenylallene into an Rh-H or Rh-D M bond to give 2. a
Introduction
Several organotransition-metal complexes catalyze polymerization' of allene and substituted allene to give polymers having unique -C(=CHz)- or -C(=CHR)structural units in the main chain as well as syntheses of cyclic oligomers of these substrates.2 (n-Ally1)nickel(11) and -palladium(II) complexes are active catalysts for polymerization of monosubstituted allene to give products with high molecular weight or narrow polydispersity.lc,d The reaction is believed to proceed through repeated insertion of a double bond of allene into the bond between the metal center and the n-allylic end of the polymer chain (Scheme 11,because n-allyl complexes initiate the polymerization and also because a (n-allyl)nickel complex catalyzes the living polymerization of alkoxyallene with almost quantitative catalyst efficiency.ld Organorhodium(1) complexes also catalyze polymerization and oligomerization of allene.1b,2bleStoichiometric reaction of allene with RhH(CO)(PPh& was briefly reported to give Rh(r3-C3H5)(CO)(PPh3)23 through insertion of a double bond into the Rh-H bond. Low stability of the (n-ally1)rhodium product prevents a further investigation into the crystal structure of the complex Abstract published in Advance ACS Abstracts, September 1,1995. (1)(a) Otsuka, S.; Mori, K.; Iwaizumi, F. J . Am. Chem. Soc. 1965, 87, 3017. (b) Otsuka, S.;Nakamura, A. J . Polym. Sci., Polym. Lett. Ed. 1967,5,973. (c) Ghalamkar-Moazzam, M.; Jacobs, T. L. J. Polym. Sci., Polym. Chem. Ed. 1978,16,615.(d) Tomita, I.; Kondo, Y.; Takagi, K.; Endo, T. Macromolecules 1994,27,4413. (2) (a) Baker, R. Chem. Rev. 1973,73,487. (b) Otsuka, S.;Nakamura, A.; Minamida, H. J . Chem. Soc. D 1969,191.(c) Hoover, F.W.; Lindsney, R. V., Jr. J . Org. Chem. 1969,34,3051.(d) Scholten, J . P.; van der Ploeg, H. J. Tetrahedron Lett. 1972, 1685. (e) Otsuka, S.; Nakamura, A.; Yamagata, T.; Tani, K. J. Am. Chem. SOC.1972,94, 1037. (D Baker, G. K.; Green, M.; Howard, J. A. K.; Spencer, J. L.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1978,1839.(g) Hegedus, L.S.; Kambe, N.; Tamura, R.; Woodgate, P. D. Organometallics 1983, 2,1658. (3)Brown, C. K.; Mowat, W.; Yagupsky, G.; Wilkinson, G. J . Chem. Soc. A 1971,850. @
P = polymer chain.
Scheme 2. Possible Pathways for Insertion of Allene into an M-Y Bond
Y
M-Y
+
C=C=C'
/
\
H
as well as that on the detailed pathway of the reaction. Studies on the insertion of a double bond of allene into an M-X bond t o give a n-allylic complex (path i in Scheme 2): including the above reaction with RhH(C0)(PPh3)3, seem t o leave several mechanistic issues unclarified, such as whether the reaction gives rise to a minor amount of vinylic complexes through insertion in another direction (path ii in Scheme 2) and whether the insertion of a double bond is reversible. In this paper we report the results of reaction of monosubstituted allenes with RhH(CO)(PPh& t o give stable Rh complexes with n-allylic ligands. Full characterizations of the products and deuterium labeling experiments to reveal mechanistic details of the reaction as well as further reaction of the (n-ally1)rhodium complex with phenylallene are also described. (4)(a) Powell, P. Synthesis of q3-AllylComplexes. In The Chemistry ofthe Metal-Carbon Bond; Hartley, F. R., Patai, S., Eds.;Wiley: New York, 1982;pp 355-357. (b) Deeming, J. A.; Johnson, B. F. G.; Lewis, J . J. Chem. Soc. D 1970,598.(c) Chisholm, M. H.; Johns, W. S. Inorg. Chem. 1976,14,1189.(d) Stevens, R.R.; Shier, G. D. J . Organomet. Chem. 1970,21,495.(e) Hughes, R.P.; Powell, J . J. Organomet. Chem. 1972,34,C51.(0 Hughes, R.P.; Powell, J. J. Organomet. Chem. 1973, 60,409.(g) May, C. J.; Powell, J. J . Organomet. Chem. 1980,184,385.
0276-733319512314-4962$09.00/0 0 1995 American Chemical Society
Notes
Organometallics, Vol. 14, No. 10, 1995 4963
c21
Q 6c:c
c5 ,,c4
c3
5 C14
C13
c2
C15
-
C14
C32
Figure 1. ORTEP drawing of 1 at the 50% ellipsoid level. Figure 2. ORTEP drawing of 2 at the 50% ellipsoid level.
Results and Discussion
Reactions of methoxyallene and phenylallene with RhH(CO)(PPh& proceed smoothly to give the corresponding (x-allyl)rhodium(I) complexes Rh(q3-CH2CHCHOMe)(CO)(PPh3)2(1) and Rh(q3-CH2CHCHPh)(CO)(PPh& (21, respectively. H RhH(CO)(PPh&
\
+
,C=C=C
H
H
/ \
X
-PPh, Hb
\ pa-
H,
HC-C[(-WCO)(PPh,h ,C7-Hd
X
(1)
1: X-OM6 2: X = P h
Reactions of 1.2 equiv of phenylallene to the Rh complex a t room temperature and of 3.0 equiv of phenylallene at -30 "C result in formation of complex 2 in high yields, while the reaction of 3.0 equiv of phenylallene a t room temperature is accompanied by formation of small amounts of uncharacterized Rh complexes and oligomers of the substrates formed probably from further reaction of 2 in the reaction mixture with phenylallene. Molecular structures of 1 and 2 determined by X-ray crystallography are shown in Figures 1and 2, respectively. Both complexes have structures quite similar to each other and contain one CO ligand, two PPh3 ligands, and a n-allylic ligand with the usual Rh-P or Rh-C bond distances. The CO and PPh, ligands as well as central carbons of the allylic ligand constitute tetrahedral coordination around the Rh center. The allylic ligands of 1 and 2 have OMe and Ph substituents with syn orientations similar to many monosubstituted allyl complexes of transition metals. Selected bond distances and angles are summarized in Table 1. Two carbon-carbon bonds in the allylic ligand of 1 are similar to each other (1.407(5)A and 1.393(5)A), while the C3-C4 bond distance (1.404(5) A) of 2 is significantly shorter than the C2-C3 bond distance (1.438(5)
Table 1. Selected Bond Distances and Angles of 1 and 2 1 Rh-P1 Rh-P2 Rh-C1 Rh-C2 Rh-C3 Rh-C4 C2-C3 c3-c4 C4-02 02-C5 c4-c5
P1-Rh-P2 P1-Rh-C1 P1-Rh-C2 .Pl-Rh-C3 P1-Rh-C4 P2-Rh-C1 P2-Rh-C2 P2-Rh-C3 P2-Rh-C4 C1-Rh-C2 Cl-Rh-C3 Cl-Rh-C4 c2-c3-c4 C3-C4-02(C5)
Distances (A) 2.309(2) 2.399(1) 1.869(4) 2.179(4) 2.145(4) 2.233(4) 1.407(5) 1.393(5) 1.379(4) 1.392(5)
2
2.306(1) 2.401( 1) 1.876(4) 2.181(4) 2.132(4) 2.258(4) 1.438(5) 1.404(5) 1.484(5)
Angles (deg) 109.69(4) 97.7(1) 90.2(1) 111.6(1) 148.6(1) 106.7(1) 99.5(1) 117.8(1) 93.3(1) 148.1(2) 111.5(2) 95.7(2) 114.3(4) 125.6(4)
A). The difference between
111.17(4) 96.8(1) 90.7(1) 108.8(1) 145.1(1) 104.5(1) 97.4(1) 119.3(1) 97.8(1) 152.4(2) 114.0(2) 94.4(1) 116.0(4) 122.9(4)
the Rh-C2 and Rh-C4 bond distances of 2 (0.077 A) is larger than that of 1 (0.054 8).The above difference in the structural parameters between 1 and 2 can be attributed to significant n-conjugation of the C3-C4 bond of 2 with a phenyl group on the allyl ligand. Figure 3 shows the IH NMR spectra of 1 at 25 "C and a t -70 "C. The signals due t o two CH hydrogens of the allyl ligand, Hd and H,, appear a t 25 "C as two multiplets at 4.63 and 4.45 ppm, respectively, while a broad peak due to CH2 hydrogens is observed at 0.9 ppm. The 1H NMR spectra as well as the 13C{IH}NMR spectrum, showing one set of the peaks due t o allylic and OMe carbons, indicate the presence of a single isomer in the solution. It can be assigned to the isomer with a syn OMe substituent on the basis of the crystal structure of the complex. The peak at 0.9 ppm is
Notes
4964 Organometallics, Vol. 14, No. 10,1995
(a) 25 "C
Scheme 3. Possible Scheme for the Reaction of Substituted Allene Involving Reversible Insertion and Deinsertion of a Double Bond
OCH3
H
\
H
X H\C/
(b) -70 "C H2
OCH3
Scheme 4" H
Rh-H
I
5
"
~
'
1
4
"
"
I
'
3
'
'
'
I
'
2
"
~
"
"
1
~
"
+
w
\c=c=c{' H/ X
-
H I H, Cc ,, n HI
I
C/ x HI
Rh
~
0 PPm
Figure 3. 'H NMR (CDZC12, 400 MHz) of 1 (a) at 25 "C and (b) at -70 "C. Peaks with asterisks are due to EbO contained in the sample.
separated into two signals a t 1.20 and -0.08 ppm on cooling the solution to -70 "C. The temperaturedependent change of the NMR spectra is attributed to exchange of two CH2 hydrogens through n-o-n rearrangement of the allylic ligand on the N M R time scale. Although similar rearrangement through a (o-l-methoxyally1)rhodiumintermediate would cause isomerization from a syn t o an anti structure, the NMR spectra do not show peaks due t o an anti isomer, indicating much lower stability of the structure than syn isomer. The IH and 13C NMR spectra of 2 show peaks due to allylic hydrogens and carbons a t positions similar to those of 1. A J(H,Hd) value (9 Hz) larger than the J(HbH,) value (6Hz) at -70 "C indicates a syn orientation of the phenyl group in the allylic ligand unambiguously. Although the insertion of a double bond of phenylallene and methoxyallene into an Rh-H bond gives the n-allylic complex exclusively, the above results are not sufficient t o exclude partial formation of a propenylrhodium complex at the initial stage of the reaction followed by its conversion into the final product through ,&hydrogen elimination and reinsertion of a double bond into the Rh-H bond (Scheme 3). Previously we have revealed that allylic aryl sulfides react with RhH(PPh& to undergo rapid and reversible insertion and deinsertion of the C=C double bond into the Rh-H bond.5 Facile or reversible b-hydrogen elimination of alkylrhodium complexes is very common also.6 In order t o examine the reversibility of the insertion of a double bond of allene, deuterium labeling experiments were carried out by using RhD(CO)(PPh&. Reactions of methoxyallene and of phenylallene with RhD(CO)(PPh& give Rh(q3-CH2CDCHOMe)(CO)(PPh& ( 1 4 ) and Rh(q3-CH2CDCHPh)(CO)(PPh&(2-4, respectively. Deuterium is incorporated exclusively a t the (5)Osakada, K.; Matsumoto, K.; Yamamoto, T.; Yamamoto, A. Organometallics 1986,4, 857.
= Rh = Rh(CO)(PPh3),;X = OMe, Ph.
central carbon of the n-allyl ligand, as is confirmed by IH NMR spectra of the complexes showing no peak due to the central hydrogen as well as by the 2H NMR spectrum of 2-d showing a peak at 5.2 ppm a t 25 "C. The appearance of the 'H NMR peaks due to CHOMe and CHPh hydrogens as singlets also indicates selective deuteration at the central carbon of the allylic ligand. Reaction of equimolar 2 and RhD(CO)(PPh& for 5 h at room temperature does not cause deuteration of allylic hydrogens of 2 at all, indicating that no liberation of phenylallene from 1 through deinsertion occurs under the conditions. All these results agree with Scheme 4, involving irreversible insertion of a double bond of methoxyallene and phenylallene into the Rh-H bond to give (n-ally1)rhodiumcomplexes. The difference in reactivity toward deinsertion of a C-C double bond between alkyl and n-allyl ligands bonded t o a Rh center is attributed to high thermodynamic stability of n-allylic coordination preventing elimination of allene from a n-allylic ligand. A Ni complex having both ethyl and q3-allyl ligands, Ni(q3CsHs)Et(PPh3), causes ,&hydrogen elimination of an ethyl ligand rather than degradation of the allyl ligand to give Ni(q3-C3H5)H(PPh3),which undergoes subsequent coupling of hydrido and allyl ligands.' Both RhH(CO)(PPh& and 2 show similar activities as catalysts for the polymerization of phenylallene. Reactions of phenylallene in the presence of 5 mol % of the complexes at 60 "C give a MeOH-insoluble off-white solid. The lH NMR spectrum of the product shows somewhat broadened peaks a t 6.3 and 2.9 ppm in a ca. 1:2 peak area ratio, indicating the structure -[CH2C(6)(a) Werner, H.; Fraser, R. Angew. Chem., Int. Ed. Engl. 1979, H.;Fraser, R. J . Orgunomet. Chem. 1982,232, 351.(c) Byme, J. W.; Blaser, H. J.; Osborn, J. A. J. Am. Chem. SOC. 1976,97,3871.(d) Byme, J.W.; Kress, J. R.; Osbom, J. A.; Picard, L.; Weiss, R. E. J.Chem. Soc., Chem. Commun. 1977,662.(e) Yamamoto, T.;Miyashita, S.; Naito, Y.; Komiya, S.; Ito, T.; Yamamoto, A. Organometallics 1982, 1 , 808. (0 Brookhart, M.; Lincoln, D. M.; Bennett, M. A.; Pelling, S. J. Am. Chem. Soc. 1990, 112, 2691. (g) Brookhart, M.;Hauptman, E.; Lincoln, D. M. J.Am. Chem. SOC.1992, 114, 10394. (7)BBnnemann, H.; Grard, C.; Kopp, W.; Wilke, G. Pure Appl. Chem. 1971,23,265. 18, 157. (b) Werner,
Notes
Organometallics, Vol. 14,No. 10,1995 4965
Table 2. Crystal Data and Details of the Structure Refinement formula mw cryst size (mm) cryst syst
Z PXgroup b (A) c
(A)
a (deg) P (deg) y (deg)
v ('43)
z
T ("C) A (A) dcalcd (g p (cm-')
F(000) R
RW" no. of variables no. of unique rflns no. of obsd rflns (1'3dI)) " w = [dF0)1-2.
1
2
C4iH3702P2Rh 726.60 0.30 x 0.35 x 0.40 tri_clinic P1 (No. 2) 11.938(7) 15.725(8) 10.216(6) 90.85(5) 106.47(5) 107.16(4) 1746 2 23 0.710 69 1.381 6.03 748 0.034 0.030 415 6152 4902
C46H390P2Rh 772.67 0.35 x 0.40 x 0.40 triclinic Pi (No. 2) 12.078(3) 15.690(4) 10.958(2) 99.14(2) 109.15(2) 77.14(2) 1904 2 23 0.710 69 1.348 5.66 796 0.035 0.028 451 6700 4915
(=CHPh)],-. GPC traces of the polymers show that M , and M , are 1.8 and 2.0 x lo3 based on a polystyrene standard. Similar results between the reactions using RhH(CO)(PPh3)3and 2 indicate that RhH(CO)(PPh3)3catalyzed polymerization of phenylallene involves initial formation of 2 through insertion of a double bond into the Rh-H bond. Experimental Section Materials and Measurement. All the manipulations of the complexes were carried out under nitrogen or argon using standard Schlenk techniques. The solvents were dried by the usual method, distilled, and stored under nitrogen. IR spectra were recorded on a JASCO IR810 spectrophotometer. NMR spectra ('H and 13C)were recorded on JEOL EX-90 and -400 spectrometers. Elemental analyses were carried out on a Yanagimoto Type MT-2 CHN autocorder. Phenylallene, methoxyallene, and RhH(CO)(PPh3)3were prepared according t o the l i t e r a t ~ r e . ~RhD(CO)(PPh& ,~ was prepared by NaBD4 reduction of RhCl(CO)(PPh& in EtOD according t o the procedure for preparation of RhH(CO)(PPh&. lH and ?HNMR spectra of the complex in C6D6 indicated deuteration higher than 90% and no H-D scrambling between the hydrido ligand and PPh3 hydrogens in benzene solution. Reaction of RhH(CO)(PPh&with Methoxyallene. To a toluene (8 mL) solution of RhH(CO)(PPh& (290 mg, 0.32 mmol) was added methoxyallene (33 mg, 0.48 mmol) at room temperature. After the reaction mixture was stirred for 2 h, the solvent was removed under vacuum. The resulting oily material was washed repeatedly with hexane to give 1 as a yellow solid (160 mg, 69%). Similar reaction of the complex and methoxyallene in a 1:3 molar ratio at -30 "C gave 1 in higher yield (92%). IR (KBr): 1925 cm-l (v(C0)). lH NMR (400 MHz in CDzClz a t 25 " 0 : 6 7.7-7.0 (m, 30H, C6H5), 4.63 (8)Hallman, P. S.;Evans, D.; Osborn, J. A.; Wilkinson, G. J. Chem. Soc., Chem. Commun. 1967,305. (9) (a) Moreau, J. L.; Gaudemar, M. J.Orgummet. Chem. 1976,108, 159. (b) Roppe, W. Justus Liebigs Ann. Chem. 1955, 74, 596. (c) Hoff, S.; Brandsma, L.; Arens, J. K. Recl. Trau. Chim. Pays-Bas 1974, 27, 295.
= 7 Hz, J(HdRh) = 2 Hz), 4.45 (dddd, (dd, 1H, Hd, l H , Hc, J(HcHd) = J(HcHa) = J(HcHb) = 7 Hz, J(HcRh) = 2 Hz), 3.39 (s, 3H, OCHd, 0.9 (br, 2H, Ha and Hb). 'H NMR (400 MHz in CDzClz at -70 "c): 6 7.7-7.0 (m, 30H, C6H5), 4.30 (m, lH, HA, 4.26 (br, lH, Hd), 3.30 (8,3H, OCHs), 1.20 (dd, l H , Hb, J(HbH,) = 6 Hz, J(HbP) = 9 Hz), -0.08 (dd, l H , Ha,J(HaHc)= 8 Hz, &Hap) = 23 Hz). 13C(lH}NMR (100 MHz in C6D.5 at 25 "c): 6 201.9 (CO, J(CRh) = 72 Hz), 111.4 (CHO, J(CH) = 184 Hz), 69.4 (CH, J(CH) = 173 Hz), 58.1 (OCH3, J(CH) = 143 Hz), 35.2 (CH2, J(CH) = 153 Hz). The 'H and 13C(lH} COSY NMR spectra agreed well with the above assignment of the lH and 13C{lH}NMR peaks. Anal. Found (calcd) for C41H3702P2Rh C, 67.6 (67.8); H, 5.3 (5.1). Reaction of RhH(CO)(PPh&with Phenylallene. To a toluene (10 mL) solution of RhH(CO)(PPh& (430 mg, 0.47 mmol) was added phenylallene (65 mg, 0.56 mmol) at room temperature. After the reaction mixture was stirred for 2 h, the solvent was removed under vacuum. The resulting oily material was washed repeatedly with hexane to give 2 as a yellow solid (310 mg, 85%). IR (KBr): 1945 cm-l (v(C0)). lH NMR (90 MHz in C6D6 at 25 "C): 6 7.5-6.7 (m, 35H, C6H5), 5.15 (dddd, lH, Hc, J(HcHd) = 9 Hz, J(HcHa) = J(HcHb) = 7 Hz, J(HcRh)= 2 Hz), 3.70 (d, lH, Hd, J(HdHc)= 9 Hz), 1.6 (br, 2H, Ha and Hb). lH NMR (400 MHz in CDzCl2 at -70 "C): 6 7.7-7.0 (m, 35H, CsH51, 4.61 (br, Hc), 3.18 (ddd, Hd, J(HdHc) = 9 Hz, J(HdP) = 15 and 7 Hz), 1.53 (dd, Hb, J(HbHc) = 6 Hz, J(HbP) = 10 Hz), 0.54 (dd, Ha, J(HaHc)= 8 Hz, J(HaP) = 21 Hz). l3C(lH} NMR (100 MHz in C6D6 at 25 "c): 6 201.0 ( c o , J(CRh) = 72 Hz), 83.9 (CHPh), 71.1 (CH), 42.9 (CH2). Anal. Found (calcd) for C45H3902P2Rh C, 71.0 (71.5); H, 4.4 (5.1). X-ray Crystallographic Study. Crystals of 1 and 2 suitable for crystallography were obtained by recrystallization from Et20 at -20 "C. Crystal data and results of structural refinement were summarized in Table 2. The data were collected on a Rigaku AF'C5R diffractometer at ambient temperature (23 "C) using the o scan mode (28 5 50"). Correction for Lorentz and polarization effects and an empirical absorption correction (li,scan) were applied. The structure was solved by a common combination of direct methods (SAP1 91) and subsequent Fourier techniques. The positional and thermal parameters of non-hydrogen atoms were refined anisotropically, while hydrogen atoms were located by assuming the ideal geometry. Polymerization of Phenylallene. To a toluene (4 mL) solution of RhH(CO)(PPh& (46 mg, 0.050 mmol) and PPh (26 mg, 0.10 mmol) was added phenylallene (120 mg, 1.0 mmol) at room temperature. After the reaction mixture was stirred at 60 "C for 19 h, the solvent was reduced to ca. 1mL under vacuum. The resulting reaction mixture was slowly poured into MeOH (ca. 150 mL) with stirring. The resulting off-white solid was filtered, washed with MeOH repeatedly and dried in vacuo (44 mg, 38%). Polymerization using 2 as the catalyst gave the polymer product in 47% yield.
Acknowledgment. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, and Culture of Japan. We are grateful to Dr. Masako Tanaka for the crystallographic study. Supporting Information Available: Tables giving crystallographic data for complexes 1 and 2 (35 pages). This material is contained in many libraries on microfiche, immediately follows this article in the microfilm version of the journal, and can be ordered from the ACS; see any current masthead page for ordering information. OM9503510
