17
Organometallics 1995, 14, 17-19
Rhodium-Mediated Stoichiometric P=C Bond Cleavage and Catalytic Isomerization in Phosphacumulenes Marie-Anne David, Sara N. Paisner, and David S. Glueck" Department of Chemistry, Dartmouth College, 6128 Burke Laboratory, Hanover, New Hampshire 03755 Received November 17, 1994@ Summary: Reaction of Rh(PCyd2Cl (4a,Cy = cycloC&l~rlwith the phosphacumulenes Mes*P=C=X (X = 0 (l), X = NPh (2); Mes* = 2,4,6-(t-Bu)3C&l.d results in P=C bond cleavage to form [2,4-(t-Bu)zC&l~6-CMe2CH8H)l (5) a n d trans-Rh(PCy&Cl(CX) (6, X = 0; 7, X = NPh), respectively. In contrast, 4a and related Rh(I) PPh3 complexes are catalyst precursors for the rearrangement of Mes*P=C=CPhz (3)to its isomer [2,4-(tB U ) ~ C & ~ ~ ~ - C M ~ Z C H ~ C(8); H =theC intermediate P~.~I [Rh(PCy~[~(P,C)-Mes*P=C=CPh27C11,(9a),which is itself a n active catalyst for the isomerization, was isolated a n d characterized spectroscopically.
Scheme 1 t-Bu
P
II
c 11
X
1,x=o 2,X=NPh C Y 5 C ,' 1-BU
Rh
xc' 'PCY, H' We report that the reactions of the phosphacumu5 6,X=O 7,X=NPh lenesl Mes*P=C=X (X = 0 (11, X = NPh (21, X = CPh2 (3);Mes* = 2,4,6-(t-Bu)&sHd with Rh(1) phosphine complexes result in stoichiometric P-C bond cleavage Mes*P, which is known to undergo intramolecular in 1 and 2 and catalytic isomerization of 3 with partial cyclization, forming 5.6 Related P=C bond cleavage has been observed in 1 on reaction with Fe and W comcleavage of the P=C double bond. plexes.7 Reaction of 1 with Rh(PCy3)2C12 (4a; Cy = cycloIn contrast, 4a is a catalyst precursor for the isomerC&1) in THF at ambient temperature rapidly gives the known compounds [~,~-(~-Bu)zC~HZ(~-CM~ZCHZPH)I~ (5) ization of 3 to the phosphaindan derivative [2,4-(tand tran~-Rh(PCy3)2Cl(CO)~~ (6), while 2 and 4a afford BU)ZC~H~(~-CM~ZCHZPCH=CP~Z)I (81,which is appar5 and trans-Rh(PCys)aCl(CNPh) (7)(Scheme lh4 The ently produced by C-H activation of a tert-butyl methyl presence of a n isocyanide ligand in 7 is consistent with group with formation of a C-P bond and migration of the IR spectrum (YCN = 1991 cm-l with a shoulder a t the hydrogen to the central carbon of the phosphaal2050 cm-l) and the 13C NMR spectrum (6 166.5, dt, lene.8 The complexes Rh(PPh313Cl and [(PPh&RhClIz lJmc = 72 Hz, Vpc = 17 Hz, CNPh); the latter confirms (4b,cI9also act as catalyst precursors for this rearthe trans g e ~ m e t r y .These ~ results suggest that Rhrangement, which proceeds in benzene or THF at induced extrusion of CX (X = 0, NPh) from the phosambient temperature and proceeds more quickly on phacumulenes generates the reactive intermediate heating (Scheme 2). Control experiments show that 3 is stable under the reaction conditions in the absence of the Rh complexes and that neither PPh3 nor PCy3 Abstract published in Advance ACS Abstracts, December 15,1994. (1)For a review of phosphacumulene coordination chemistry, see: induces the isomerization. Nixon, J. F. Chem. Rev. 1988,88,1327-1362. Reaction of 500 mg of the phosphaallene 3 with 5 mg (2)(a) van Gaal, H. L. M.; Moers, F. G.; Steggerda, J. J. J. Orgunomet. Chem. 1974,65,C43-C45. (b) van Gaal, H. L. M.; van of 4c (146 equiv/Rh) in THF at 50 "C for 7 days affords den Bekerom, F. L. A. J . Orgunomet. Chem. 1977,134,237-248. the rearranged product 8 quantitatively, according to (3)Cowley, A. H.; Pakulski, M. Tetrahedron Lett. 1984,25,21252126. 31PNMR. White crystals of 8 are obtained in 78%yield @
(4)trcnur-Rh(PCys)&l(CNPh)(7). To a suspension of 4a (184mg, 0.26 mmol) in THF (1mL) was added 2 (100mg, 0.26mmol) dissolved in THF (2mL). The mixture was stirred a t room temperature and became a clear orange solution after a few minutes. The solvent was then removed under reduced pressure. The residual yellow solid was washed with cold petroleum ether, filtered on a frit, and dried under vacuum to give 154 mg of 7 (73% yield). An analytical sample was recrystallized from petroleum ether at -25 "C. The petroleum ether filtrate contained phosphaindan 6, identified by comparison of its NMR spectra to the literature values. In a separate experiment on a smaller scale (28mg (0.04mmol) of 4a),concentration of the petroleum ether filtrate and cooling to -25 "C gave 7 mg of 6 (64% yield). For 7 'H NMR (CD2C12)6 7.33-7.28(m, 2H), 7.24-7.19(m, lH), 7.12-7.09 (m, 2H), 2.37-2.29 (broad m, 6H), 2.05-2.01 (broad m, 12H), 1.79-1.65 (broad m, 30H), 1.30-1.11 (m, 18H);13C{'H} NMR (CD2C12) 6 166.5 (dt, lJmc = 72,2Jpc= 17 Hz, quat CN), 132.7 (quat Ph), 129.7 (Ph), 126.1 (Ph), 124.8(Ph), 34.0 (dd, 2Jmc = 'Jpc = 9 Hz, P-C-H), 30.6 (CH2), 28.3 (dd, = 2Jpc= 5 Hz, CH2), 27.2 (CH2); 31P{1H} NMR (CD2C12)6 38.5 (d, ' J ~ a p= 125 Hz); IR (KBr) 2915,2847,2652,2050 (shoulder), 1991,1590, 1490,1445, 1264,1173,1004,900,847,752, 736 cm-l. Anal. Calcd for C43H71ClNP2Rh: C, 64.36;H, 8.94. Found: C, 64.36;H, 8.97. ( 5 ) Jones, W. D.; Hessell, E. T. Organometallics 1990,9, 718-727.
(6)(a)Yoshifqji, M.; Sato, T.; Inamoto, N. Chem. Lett. 1988,17351738. (b) Cowley, A. H.; Gabbai, F.; Schluter, R.; Atwood, D. J.Am. Chem. SOC.1992,114,3142-3144. (7)(a) Cowley, A. H.; Pellerin, B.; Atwood, J. L.; Bott, S. G. J. Am. Chem. Soc. 1990,112,6734-6735.They also briefly describe a related CNF'h extrusion from 2. (b) Champion, D.H.; Cowley, A. H. Polyhedron 1986,4,1791-1792. (8)Related ring closures in organic Mes*-phosphorus compounds have been reported previously: (a) Bacereido, A.; Bertrand, G.; Mazerolles, P.; Majoral, J.-P. J. Chem. SOC.,Chem. Commun. 1981, 1197-1198. (b) Yoshifqji, M.; Shima, I.; Ando, K.; Inamoto, N. Tetrahedron Lett. 1983,24, 933-936. Related metal-induced rearrangements have been observed by Nixon and co-workers in the diphosphaallene Mes*P=C-PMes* on heating with iron or tungsten carbonyls, but in these cases the phosphorus-containing product is formed stoichiometrically and remains complexed to the metal: (c) Akpan, C. A.; Hitchcock, P. B.; Nixon, J. F.; Yoshifuji, M.; Niitsu, T.; Inamoto, N. J. Orgunomet. Chem. 1988,338,C35-C37. (d) Akpan, C. A. D. Phil. Thesis, University of Sussex, 1986. (9)Osbom, J. A.; Jardine, F. H.; Young, J . F.; Wilkinson, G. J.Chem. SOC.1966,1711-1732.
0276-733319512314-0017$09.0010 0 1995 American Chemical Society
Communications
18 Organometallics, Vol. 14, No. 1, 1995
Scheme 2 t-BU
I
Rh catalyst (4) a L = PCy3, n = 2 , x = 1
P
II
fCPhz
H, /
p-/ 'Me
f
*
\cf
\f;M='
bL=PPh3,n=3,x=l cL=PPh7.n = 2 . x = 2
CPhz
Scheme 3 Ph2C,, x Mes'PCCPhz L
x/2
C
Mes*P\R(c\(L I
[RhL,Cl]x (4) -Y L a L = PCys, n = 2, x = 1, y =l b L = PPh,, n = 3, x = 1, y =2 c L = PPh,, n = 2, x = 2, y = 2
L/
9a-b
'\Cphz
after recrystallization from petroleum ether.1° Elemental analysis and EI-MS show that 8 is an isomer of 3, and its structure was determined spectroscopically. In the lH NMR spectrum (CsDs), for example, there are four sets of peaks due to methyl protons in a 9:9:3:3 ratio. The vinylic proton resonates a t 6.86 ppm and does not show coupling to phosphorus, while signals for the methylene protons are a complex multiplet at 1.941.79 ppm (ABX spin system; 2 J = ~14.4 Hz; 2 J ~ = p 1 Hz, 2 J ~ = p 21 Hz).ll The CH2 carbon signal appears at 42.0 ppm (d, lJpc = 8.3 Hz) and the vinylic carbon at 135.3 ppm (d, lJpc = 27.5 Hz). When the reactions of 3 with PPh3 complexes 4b,c in THF are monitored by 31P NMR spectroscopy, the = 220 intermediate 9b (6 52.4 (dd, 2 J p p = 10 Hz; lJ~hp Hz, PPh3), -59.3 (broad dd, 2 J p p = 10 Hz; lJ~hp= 37 Hz, Mes*P=C=CPhz); Scheme 3) is observed, along with 3, product 8, both 4b and 4c, and PPh3. In both cases, once the supply of 3 is exhausted, the peaks due to the intermediate disappear. They reappear when more phosphaallene is added. In an analogous experiment,
4a is not seen, but PCy3, 3,and 8 are observed, along with the similar, longer lived intermediate 9a, which can be isolated directly from the reaction mixture. Alternatively, it can be prepared independently in 73% yield from the reaction of Rh(PCy3)2C1(prepared in situ from [Rh(COE)2C112 in petroleum ether or ether) with 3; this yields 9a as an air-stable red-orange precipitate (Scheme 3).12 Elemental analysis and integration of the lH NMR spectrum show that 9a has the formula Rh(PCy3)(Mes*P=C=CPh&l, while the IH and 13CNMR spectra show that the Mes* group remains intact. The 31P{1H} NMR spectrum (THF-ds) is similar to that observed for 9b (6 62.1 (dd, 2Jpp = 2 Hz, 'J~hp= 194 Hz, PCY~), -38.8 (dd, 2 J p p = 2 Hz, l J ~ h p= 37 Hz, Mes*P=C=CPh2)).13 The central carbon of the phosphaallene ligand resonates at 6 179.6 (dd, ~ J R=~27 c Hz, ~ J P =C 99 Hz).14An IR absorption at 1586 cm-l (KBr) may be assigned to an uncomplexed C-C bond.15 These observations are consistent with n(P,C)-coordinationof the phosphaallene ligand in 9a,b. Because of the low solubility of 9a in most organic solvents, we assume it exists in the solid state as a chloride-bridged dimer (Scheme 3).16 Com-
(12) COE = cyclooctene: van der Ent, A.; Onderdelinden, A. L. Inorg. Synth. 1973,14, 92-95. To a slurry of [(COE)2RhC112(41 mg, 0.057 mmol) in ether (4 mL) was added a solution of PCy3 (64 mg, 0.23 mmol) in 3 mL of ether. A red solution formed; it was filtered after -3 min. A solution of 3 (52 mg, 0.11 mmol) in 2 mL of ether was added to the filtrate. After 3 h red crystals formed; the mixture was cooled overnight at -25 "C to induce further crystallization. The yellow-orange supernatant was decanted, and the red crystals were washed with 4 x 2 mL of cold ether to give, after drying in vacuo, 73 mg (73%)of red crystals. This synthetic method avoids the use of sparingly soluble isolated 4a and allows precipitation of pure Sa under mild conditions. For Sa: 'H NMR (CD2C12) 6 8.23 (d, J = 7.5 Hz, 2H), 7.40-7.26 (m, 3H), 7.00 (2H), 6.93-6.88 (m, 3H), 6.74-6.71 (m, 2H), 2.18-1.50 (broad m, 22H), 1.40 (broad, 18H), 1.25-1.10 (broad m, 11H), 1.14 (9H); 13C{lH}NMR (CD2C12) 6 179.6 (dd, 'Jmc = 27 Hz, 'Jpc = 99 Hz, quat, F=C), 155.4 (quat, broad), 149.9 (quat), 142.0 (quat), 141.7 (quat, broad), 141.4 (quat), 132.7 (d, J = 102 Hz, quat), 130.2, 128.7, 128.2 (d, J = 3.8 Hz), 127.7, 127.4, 126.4, 122.9, 37.5 (quat), 35.5 (dd, z J ~ =c 5.5 Hz, 1Jpc = 25 Hz, P-C-H), 34.9 (quat), 32.1 (broad, CH3), 31.9 (broad, CHz), 31.4 (CH3),29.9 (CH2),28.4 (CH2), 28.2 (CHZ),26.9 (CHz); 31P{1H}NMR (THF-da) 6 62.1 (dd, 'JRW = 194 Hz, 2 J= ~ 2 ~ Hz), -38.8 (dd, 1J~hp= 37 Hz, 2 J p p = 2 Hz); IR (KBr) 3054,2924, 2849,2644,1586,1490,1441,1389,1361,1249,1198,1175,1122,1074, (10) [2,4.(t-Bu)zCsHz(6-CMezCH=CPha)l (6). An ampule 1030,1004,924,899,880,851,768,748,735,700,690,648,556,518, mmol), 3 (500 mg, 1.1 mmol), was charged with 4c (5 mg, 7.5 x 493, 451, 424 cm-l. The analytical sample cocrystallized with and 10 mL of THF, sealed under nitrogen, and heated in an oil bath dichloromethane and ether, which was quantitatively confirmed by at 50 "C. The extent of reaction was monitored by 31PNMR of aliquots integration of the 'H NMR spectrum. Anal. Calcd for of the orange solution; after 7 days the solvent was removed in vacuo C~oH&1P2Rh.0.35CH2Cl2.0.2C4Hl0O: C, 66.91; H, 8.22. Found: C, and the residue was recrystallized a t -25 "C from petroleum ether to 66.53:, H. 8.42. give 392 mg (78%)of 8, in three crops. An analytical sample was (13) (a) For comparison, in L2Pt[q2(P,C)-Mes*P=C=CPh21 (Lz = recrystallized from petroleum ether. For 8: mp 155 "C; 'H NMR (C6D6) (PPh3)2,Ph2PCHzCHzPPh2,(PEt&), the 1s5Pt-31P coupling constants 6 7.57-7.55 (m, lH), 7.44-7.42 (m, 2H), 7.24-7.19 (m, 3H), 7.13for the Mes*(P) nucleus are 192, 234, and 268 Hz, reipecthely.8d (b) 7.05 (m, 3H), 6.94-6.91 (m, 3H), 6.86 (lH, CH-CPhz), 1.94-1.79 (m, From the magnetogyric ratios of lg5Ptand lo3Rh,the magnitude of 2H, CHz, 2 J = ~14.4, 2 J p = ~ 1, 2 J p = ~ 21 Hz), 1.60 (9H), 1.40 (3H), lQ5Pt-Xcoupling is expected to be about 7 times that of lo3Rh-X (Kidd, 1.31 (9H), 1.17 (3H); l3C{lH} NMR (CD2Clz) 6 159.5 (d, J = 2.3 Hz, R. G.; Goodfellow, R. J.; In NMR and the Periodic Table; Harris, R. quat), 153.1 (d, J = 14.3 Hz, quat), 152.8 (quat), 150.4 (d, J = 19.2 Hz, K., Mann, B. E., Eds.; Academic: New York, 1978; p 249.) quat), 143.2 (d, J = 4.9 Hz, quat), 141.2, 141.1, 135.7 (d, J = 13.8 Hz, (14) For comparison, we prepared (PhzPCHzCHzPPhz)Pt[t2(P,C)quat), 135.3 ( d , J = 27.5 Hz, P-CHI, 130.7 (d, J = 3.8 Hz), 128.8,128.6, Mes*P=C=CPhz] as in ref 8d and obtained its 13C NMR spectrum in 128.1 (d, J = 2.7 Hz), 127.8, 122.4 (d, J = 4.9 Hz), 119.0 (d, J = 1.1 CDzClz. The central P=C=C carbon signal appears at 6 171.6 (ddd, Hz), 47.3 (d, J = 6.0 Hz, quat), 42.0 (d, J = 8.3 Hz, P-CHz),37.7 (d, lJ+c = 118 Hz, 2Jpc= 70 Hz, 2Jpc = 6 Hz; Pt satellites were too low J = 1.7 Hz, quat), 35.5 (quat), 32.8 (overlaps with next peak), 32.6 (d, J = 9.4 Hz), 32.3 (d, J = 5.0 Hz), 31.8; slP{lH} NMR (CD2Clz) 6 -22.2; in intensity to be observed). (15)Related absorptions at 1590,1600, and 1590 cm-l are observed 31PNMR (CeD6) 6 -20.5 (broad d, "J" = ca. 20 Hz); IR (KBr) 3052, 2956,1591,1554,1540,1491,1442,1394,1380,1360,1331,1244,1225, in the Pt-phosphaallene complexes of ref 8d. (16) Two spectroscopic observations suggest that Sa contains a n 1203,1164,1144,1129,1072,1030,986,952,930,902,880,852,841, agostic interaction between Rh and C-H bonds of the PCy3 ligand (for 810, 786, 770, 749, 713, 702, 656, 643, 621, 607, 559, 514, 483, 458, 428 cm-1; EI-MS mlz 454 (M*), 261 ((MH - Me - C2Ph2)+),57 (t-Bu). related complexes, see: Wasserman, H. J.; Kubas, G . J.; Ryan, R. R. J . Am. Chem. SOC.1986,108,2294-2301). The IR spectrum includes Anal. Calcd for C32H39P: C, 84.53;H, 8.66. Found: C, 84.57;H, 8.76. an absorption at 2644 cm-l, and the 13CNMR spectrum shows signals Catalysis by 4c is unaffected by the presence of metallic Hg, suggesting due to six different cyclohexyl carbons. In contrast, peaks due to four that the reaction is homogeneous and is not catalyzed by Rh metal; Cy carbons are observed for 6 and 7. Interaction of Rh with a C-H see: Whitesides, G. M.; Hackett, M.; Brainard, R. L.; Lavalleye, J.-P. bond on one PCy3 cyclohexyl group in Sa could make the six carbons P. M.; Sowinski,A. F.; Izumi, A. N.; Moore, S. S.;Brown, D. W.; Staudt, inequivalent. Rapid exchange (on the NMR time scale) between such E. M. Organometallics 1985, 4, 1819-1830. (11) The large difference in the two 2 J p couplings ~ has precedent a bond and the other two cyclohexyl groups by a 3-fold rotation could in the results for 6 , for which we find VPH= 15.3 and 1.8 Hz, make the three cyclohexyl groups equivalent. Unfortunately, we have not yet been able to obtain crystals suitable for X-ray analysis to check respectively. See also: Bentrude, W. G.; Setzer, W. N. In Phosphorus31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J. G., Quin, this assignment or to investigate related interactions in 6 and 7, which show IR peaks at 2654 and 2652 cm-l, respectively. L. D., Eds.; VCH: Deerfield Beach, FL, 1987; pp 365-389. --?
~
~~
Communications
plex 9a is readily soluble in CHzClz but decomposes at ambient temperature in this solvent, preventing molecular weight measurements. Isolated 9a is stable in solution in the presence of 3 and catalyzes its isomerization to 8. This reaction also proceeds smoothly in the presence of 1 equiv of PCy3. The isolation of 9a suggests that cumulenes 1 and 2 also initially bind to Rh with displacement of PCy3 to form the intermediates Rh(PCy3)[r2(P,C)-Mes*+C=XlC1 (X = 0, NPh), which are not observed under the reaction conditions. Mechanistic investigations of the role of such species in the P=C cleavage and isomerization reactions are in progress as part of a broader study of phosphacumulene coordination chemistry.
Organometallics, Vol. 14,No. 1, 1995 19
Acknowledgment. We thank Dartmouth College and the donors of the Petroleum Research Fund, administered by the ACS, for partial support of this work. We also thank Johnson Matthey/Alfa/Aesar for a loan of Rh salts. Supplementary Material Available: Text giving experimental details and spectroscopic data for complexes 5 and 6 and 31PNMR studies of catalysis by 4a-c and 9a (5 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. OM940876C
