Organometallics 1986, 5, 2543-2550
2543
New Molybdenum and Iron Phosphoranides. Mechanism and Stereochemistry of the Rearrangement and Migration of a Phosphorus-Bound Allylic Group into an I ron-Bound Vinylic Group Pierre Vierling" and Jean G. Riess Laboratoire de Chimie Mol6culaire, Unit6 Associ6e au CNRS, Parc Valrose, 06034 Nice, France Received December 16. 1985
The series of phenylphosphoranidesof Mo, W, Ru, and Fe (4) has been successfully extended to their benzyl, vinyl, and allyl analogues 12 and 13, showing that the nature of the substituent at phosphorus in the bicyclic aminophosphoranes7 is not of prime importance in the isolatiop of metal phosphoranides. The iron allylphosphoranides 13b,c, and only these, are thermally converted into the vinyliron complexes 14b,c. These transformations occur stereoselectively,since 14b,c are formed, respectively, in a trans and cis configuration at the double bond. Chemical labeling of the allyl group in 13c allowed us to show that this conversion proceeds through insertion of iron into an allyl C-H bond, followed by a 1,3-proton shift to the terminal olefinic carbon atom, with concomitant P-C bond cleavage. This reactivity pattern differs both from the previously found phenyl group migration between phosphorus and iron, which implies only P-C bond rupture (1,2-sigmatropicshift mechanism), and from an ortho-metalation reaction, which implies only insertion of a metal into a C-H bond. In the present case, the anionic phosphoranide ligand in 13 is likely to increase the charge density on iron and hence its basicity, which allows this unexpected new phenomenon to take place. Introduction
Our current studies on the interplay between transition metals and phosphorus-basedligands, with the specific aim of developing new metal-induced phosphorus chemistry, led us to the first series of transition-metal phosphoranides 4'v2 and 53 (Scheme I). The chelated adducts 2 of the tautomeric phosphane form of 1 provided a relay to facilitate the abstraction of the proton initially located on phosphorus in 1. This intramolecular-intraligand approach proved effective in the synthesis of the phosphoranides 4 and was also successfully extended to cyclampho~phoranides.~ When applied to the iron analogue 2, this approach led however to an unexpected reversible migration of the phenyl group between phosphorus and iron (2 is 6), but it could be shown that the reaction 2 6 proceeds via the expected iron phosphoranide adduct 4 . 2 ~ ~ This reversible migration process exemplifies a metal-induced interconversion between a phosphorane and a phosphane derivative, i.e., between a hypervalent and a trivalent species via, formally, the reductive elimination or oxidative addition of benzene onto phosphorus. Also noteworthy is the fact that it is the same carbon atom of the phenyl group which is alternately bonded to the phosphorus and to the iron atom. The questions thus arose as to what the extent of this reactivity pattern is, and more specifically as to which substituents at phosphorus permit the observation of such a behavior, and also whether advantage could be taken of it as a means of forming metal-carbon bonds.
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(1) Jeanneaux, F.; Grand, A,; Riess, J. G. J.Am. Chem. SOC.1981,103, 4272. (2) Vierling, P.; Riess, J. G.; Grand, A. Inorg. Chem., in press.
(3) Wechter, J.; Mentzen, B. F.; Riess, J. G. Angew. Chem., Int. Ed. Engl. 1981,20, 284. (4) Dupart, J.-M.; Grand, A.; Pace, S.;Riess, J. G. J.Am. Chem. SOC. 1982,104,2316.
( 5 ) Vierling, P.; Grand, A.; Riess, J. G. J. Am. Chem. SOC.1981,103, 2466. (6) Hartgerink, J.; Vierling, P.; Le Borgne, G.; Riess, J. C .Vouu. J. Chim. 1986, 9, 707.
We investigated the behavior of bicyclic phosphoranes similar to 1, but with other substituents than a phenyl group at phosphorus, toward q5-CpMo(CO),C1 and q5CpFe(CO),Br. As reported in a preliminary communicat i ~ na, migration ~ reaction was also observed in the case of the allylphosphorane 7b, but it was the (a-viny1)iron compound 14b that was obtained instead of the (a-allyl) iron derivative 15b, which would have been anticipated if the same reaction as with the phenyl group had taken place. We wish now to report the isolation of the phosphoranides 12 and 13, to present a closer, detailed analysis of the reaction sequences involved, and to discuss the mechanism of the P-allyl to Fe-vinyl conversion. Results and Discussion Synthesis of the Chelated Cationic Adducts 10 and 11 (Scheme 11). Molybdenum Derivatives. The coordination behavior of the bicyclic phosphoranes 7a,b or 7d toward v5-CpMo(CO)&1is comparable to that of the previously reported phenylphosphorane 1.8 It results in the substitution of one carbonyl group and coordination of the tautomeric open form of 7 through phosphorus. This is attested by the IR spectra of the resulting compounds 8 which exhibit, in all cases investigated, two v ( C 0 ) absorptions and a 4") frequency at 3340 cm-', characteristic of the noncoordinated nitrogen site.8 The chelated cationic complexes 10 were obtained, as described for 2 (M = Mo) by a C1-/BPh4- anion exchange. Under these conditions, the coordination of the nitrogen atom is assisted and adducts 10a,b or 10d precipitate. The ca. 100 cm-l shift toward lower frequencies measured for the v(NH) of 10 with respect to that of 8 reflects this coordination of the nitrogen site. The 31Pand 'H NMR spectra show, respectively, one singlet for the coordinated phosphorus and one singlet for the protons of the cyclopentadienyl ligand. These data are very close to those (7) Vierling, P.; Riess, J. G. J. Am. Chem. SOC.1984, 106, 2432. (8) Wachter, J.; Jeanneaux,F.; Riess, J. G. Inorg. Chem. 1980,19, 2169.
0276-7333/86/2305-2543$01.50/0 0 1986 American Chemical Society
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A J q5-Cp(CO),MY
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L i Me
CP(CO),.,M
NaBPh,
Cp(CO),.qM
dacornposilion
H'
I
v(C0)" 28 1Oa 10b
1965-1885 1970-1885 1975-1895
Mo derivatives v(NH)* 6(31P(1Hl)b ~ ( ' H ( C P ) ) ~ 3220 3220 3240
198' 210' 209'
5.72' 5.31' 5.67'
v(C0)"
Z2
lla
Fe derivatives v ( N H ) ~ 6(31P{'H))b 6('H(Cp)) ( J H , Hz)' ~,
1960 1965
3240 3230
209' 222'
1965 1960
3220
:?++
llb
1oc
llc
3230 10d 41 12a 12b 12c 12d Av(CO)(l0-12) A6(2-4) A6 ( 10- 12)
1970-1895 1945-1850 1940-1850 1940-1850 1940-1850 20-45
3240
... ... ... ...
199'
5.75'
Ild 3220
44" 5 2" 49"
13a 13b 13c 13d
1910 1910 1910 1910 1910
Av(l1-13)
50-55
42
43" 154 156-160
A6( 11-13)
... ... ... ... ...
224 225
i
+
204e 223.8d 224.5c
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191'
7 3" 82" 80" 83.4 74"
4.85 (1.2)c 4.76 (1.5)' 4.36 (1.3)d 4.53 (1.3) + 4.73 (1.2Ie 4.83 (1.2) 4.84 ( 1 . 0 ) ' ~ ~
+
4.42 (1.3)d 4.72 (1.3) + 4.78 (1.5Ie
+ 83.3"
135 134-140
, for 6('H). In CH2Clzfor 6(31P);in CDzCl2for 6('H). e In CH3CN/CHzClzfor " In THF. KBr disks. 'In CHBCNfor I ? ( ~ ~inP )CD&N 6(31P);in CD3CN/CD2C12for 6('H). /All 6(31P('H))resonances are singlets. #Singlets for Mo compounds; doublets for Fe compounds.
measured for 2 (Table I), whose structure has been confirmed by X-ray analysis in the case of its PF6- salt.g Iron Derivatives. We have previously reported that the action of 1 on T ~ - C ~ F ~ ( C leads O)~B directly ~ to a mixture of the halogen-substituted cationic derivative analogous to g2 (main product) and of the carbonyl- and halogen-displaced derivative 2 (M = Fe; Br- in place of BPh4-). It was also shown that coordination on nitrogen, leading to 2, could be forced, starting from the analogue of 9, by expulsion of CO under UV irradiation, provided the bromide anion has been previously replaced by BPh4-.2 (9) Wachter, J.; Mentzen, B. F.; Riess, J. G., unpublished results.
The action of ligands 7 on ~ ~ - C p F e ( c o ) in ~ BTHF r led to the halogen-substituted compounds 9 in 8595% yields. The IR spectra of 9 exhibit two v(C0)absorptions and a 4") frequency at 3340-3380 cm-' characteristic of the noncoordinated nitrogen atom.8 The carbonyl- and bromine-substituted complexes analogous to 11 are also formed, but in very low yield. The chelated monocarbonyl cationic derivatives 11 were prepared by photolysis of a CH2CIZsolution of 9 (40-70% yields) after the bromide anion had been replaced by BPh4-. The IR data collected on the compounds isolated, with one v(C0) absorption and a v(NH) stretch at 3220-3240 cm-I (Table I) characteristic of coordinated nitrogen, agree with the proposed structure 11. Both P and N coordination in 1 la,b,d are preserved
N e w Molybdenum and Iron Phosphoranides
in CD2C12solution where the 31PNMR spectra exhibit respectively one singlet for the coordinated phosphorus and one doublet for the cyclopentadienyl protons. Similar patterns are observed in CD3CN solution for 1 l a only. In contrast, the , 'P and 'H NMR spectra recorded on CD3CN or CD2C12/CD3CNsolutions of l l b or l l d show two singlets for the coordinated phosphorus and two doublets for the cyclopentadienyl protons (Table I). This probably means that l l b , d coexist in solution with ll'b,d, respectively, where the ligand is monodentate through phosphorus and where nitrogen has been replaced by an acetonitrile molecule. The fact that only one species is detected in CH2C12excludes coordination of the double bond of the P-allyl or P-vinyl group to iron. A different situation is found in the case of l l c , where the ,'P spectra measured in CH3CN and CH2C12solutions are very similar, whereas in the 'H NMR spectrum the doublet observed for the cyclopentadienyl protons in CDzClzsolutions is split into two very close doublets in CD,CN solutions. This excludes a substitution of the coordinated nitrogen by an acetonitrile molecule as for 1 lb,d, which would result in very different chemical shifts in both ,'P and 'H NMR. Furthermore, the lH NMR spectra of llc, in CDzC12or CD3CN,show two well-separated doublets of doublets, the first located at 1.36 ppm (3JH,CH, 7 Hz, 3 J ~ p = 17.5 Hz) and the other at 1.32 ppm (,JH,CH, = 7 Hz, 3 J ~ , p= 20 Hz), assigned to two different methyl groups. These data are consistent with the presence in 1 IC of two asymmetric centers. The existence of two diastereoisomeric pairs of enantiomers for l l c is also apparent in the 13CNMR spectra recorded in CD2C12or CD3CN solutions for the signals of the CH=CH2 moiety: the diastereotopic CH carbon atoms appear as a singlet located at 133.1 pm and as a doublet at 132.7 ppm ( J c , p = 6 Hz) and the diastereotopic CH2 carbon atoms as two doublets centered at 120 and 119.3 ppm ( J c , p = 15 Hz for both). The diastereoisomers have indiscernible chemical shifts for the Cp, P-C, and CH, carbon atoms. The above results show that the nature of the substituent R at phosphorus in the phosphoranes 7 has little or no influence on their coordination chemistry with q5CpMo(C0),C18 while their reactivity toward q5-CpFe(CO),Br and the lability of the derivatives obtained depend strongly on R. The ease of displacement of a carbonyl group by P-coordination diminishes on going from phenylto benzyl-, allyl-, and vinylphosphoranes. These differences may be accounted for by the fact that phosphorus is more nucleophilic and basic in character in 7 than in 1, thus favoring halogen displacement. The cationic derivatives 11 are also sensitive to modifications of the substituents at phosphorus, the coordinated nitrogen atom being partially replaced by a donating solvent molecule in l l b , d and more strongly bonded to iron in lla,c and 2. Synthesis of the Metal Phosphoranides 12 and 13. Subsequent displacement of the proton from phosphorus, in 1, to nitrogen in the chelated adducts 2, through coordination of the tautomeric phosphane form of 1, and further reaction with a base, proved effective in the synthesis of the Mo, W,'8 Fe, and Ru2phenylphosphoranides 4 and 5. The question was then to know to what extent the nature of the substituents at phosphorus influence this reactivity pattern. We found that in THF at -80 "C the cationic derivatives 10 and 11 are quantitatively converted into the phosphoranides 12 and 13, respectively, by the action of CH3Li. The molybdenum complexes 12 were isolated in nearly quantitative yields, whereas the iron analogues 13 decompose during workup, precluding their complete pharac-
Organometallics, Vol. 5, No. 12, 1986 2545
terization. They are, however, stable in solution at temperatures below 0 "C. The neutral phosphoranides 12 and 13 exhibit CO absorptions shifted to lower frequencies with respect to the cationic derivatives 10 and 11, by 20-55 cm-', respectively, as expected from the increase in charge density at the metal (Table I). Concomitantly, the lowfield ,'P resonances of 10 and 11 are replaced by an upfield signal for 12 and 13. In the case of 13c, the two close 31P resonances measured are consistent with the diastereotopic character of the phosphorus atom. This variation in chemical shifts is considerable (A6 = 156-160 ppm for Mo and 134-140 ppm for Fe; Table I) and is comparable in magnitude to those which accompany the formation of the Mo, W, and Fe phenylphosphoranides 4 from their corresponding cationic adducts 2 (A6 = 154,142, and 135 ppm, re~pectively'-~), indicating the formation of a phosphoranide adduct rather than that of an amidophosphane complex analogous to 3. The formation of 3 has, indeed, been found to be accompanied by downfield A6's of -8, -13, and 0 ppm only in the P-phenyl Mo, W, and Ru series, the 31Pchemical shift thus remaining within the 160-220 ppm range characteristic of M(I1)-phosphane adducts. Such amido-phosphane adducts have not been detected during the abstraction of the proton from 10 or 11 even at -100 "C; if they exist, these species are of very short lifetime. However, as previously discussed for the P-phenyl iron derivative 4,2 a 16-electron species where the phosphoranide ligand would be monodentate through P (as in 13') or a fast exchange, even at low temperature), between such a species and the M-N-P phosphoranideadducts 13 and their isomeric M-0-P analogues of 5 cannot be excluded for derivatives 13a-c on the basis of the 31PNMR data.
-
R.
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13'
The formation of the P-allyl, -benzyl, or -vinyl phosphoranides 12 and 13 shows that the presence of a phenyl group on phosphorus, which could have been expected to stabilize the phosphoranide ligand by charge delocalization, does not appear to be of prime importance. The stability of these derivatives appears to be essentially related to the nature of the metal. The bicyclic nature of the ligand plays a more determinant part in the isolation of metal phosphoranides, as shown by our unsuccessful attempts6 to prepare the acyclic analogues of 12 or 13. This illustrates the importance of the transannular relationship of N and P in the flexible ligands 1 and 7. Rearrangement and Migration of the P-Allyl Group. One important aspect of the phenyl group migration phenomenon2p5was the formation of M-C bonds. We have, therefore, investigated the ability of the phosphoranides 12 and 13 to transfer the phosphorus-bonded organic group to the metal. Molybdenum Derivatives. Heating a THF solution of the molybdenum phosphoranides 12a-c under reflux led to a complex mixture of compounds, as shown by the 31PNMR spectra of the reaction solution. However, the presence of a ,'P resonance, among others, shifted upfield by 10-20 ppm with respect to those of 12a,b,d, suggests formation of the isomeric M-0-P phosphoranides analogous to 5: such an isomerization (4 5 ) has already been shown in the Mo and W phenylphosphoranide series'B2 to be accompanied by a similar variation in ,'P chemical shifts. No compound containing a Mo-R bond (R = benzyl, allyl, or vinyl) could be isolated by the usual
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I
2546 Organometallics, Vol. 5, No. 12, 1986
Vierling and Riess
Scheme 111. Mechanism of the Rearrangement and Migration of the P-Bound Allylic Group into the Fe-Bound Vinylic Group
13'
a b
c
R = benzyl R = allyl R = f?-rnethyl)allyl
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workup of the reaction mixture. those published for the related compound 16 (6 (13C) 136.5, Iron Derivatives. The iron P-benzyl and P-vinyl 152.4, and 23.8 ppm; Jcp = 37,0, and 3 Hz, respectively), phosphoranides 13a,d are also transformed rapidly into whose structure has been confirmed by X-ray diffraction several compounds when refluxed in THF, as attested by analysis.l0 The trans configuration at the double bond 31PNMR. A v(C0) absorption at 1930 cm-' in the crude is asserted by the magnitude of the JHIH2 coupling of 16 reaction mixture indicates (vide infra) that an analogue H2.l' of 6 or of 14b may have been formed. In contrast, a much cleaner reaction occurs when a THF solution of the allyl CplCO)Fe Cp(C0)fe Me, derivative 13b is heated. The CO vibration at 1910 cm-l of 13b is then seen to disappear, while a new CO stretch 'P(OPhI3 develops progressively at 1930 cm-'. At 60 "C the trans16 formation is complete within 1h. Adduct 14b is isolated Reaction Mechanism. The rearrangement of a Pas a yellow powder in 40% yield by column chromatogbonded allyl group into a Fe-bonded vinylic group is raphy (Si02/Et20)of the crude reaction product. Its particularly intriguing, especially since the 1,Zsigmatropic structure is unambiguously established by its spectroscopic shift mechanism established for the phenyl migration2 characteristics, which also exclude its being the initially cannot operate here. Its mechanism will be discussed in expected (a-ally1)iron derivative 15b. The conversion of view of the current interest in P-C bond cleavage by metal the phosphoranide ligand into the aminophosphane ligand complexes. Allylphosphorus compounds are known to as in 6, for which it has been proven by an X-ray structure undergo base-catalyzed isomerization into their 1determination,5 is established by the downfield 31Pchempropenylphosphorus analogues.12 By analogy with the ical shift of 136 ppm from 80 ppm for 13b to 216 ppm for phenyl migration,, the process observed here could 14b and by the 13C resonances of the NCH, and OCH, therefore consist either in a P-allyl to P-propenyl reargroups (two doublets at 54.6 and 54.4 ppm and two rangement in phosphoranide 13b, followed by the 1,2doublets at 69.3 and 69.1 ppm, respectively), these being sigmatropic migration of the resulting vinylic group from very close to those found for 6. P to Fe or in a 1,2 sigmatropic shift of the allyl group to The rearrangement of the P-bonded allyl group into a give the (a-ally1)iron species 15b followed by a a-allyl to Fe-bonded vinyl group is clearly attested by the lH and 13C NMR data. The 13C off-resonance spectrum of 14b displays two vinylic carbons at 133 (Cl) and 138 (C2) ppm, (10)(a) Reger, D. L.; McElligott, P. C. J. Am. Chem. Soc. 1980,102, each coupled with one proton, while the third carbon at 5923. (b)Reger, D. L.; Belmore, K. A.; Mintz, E.; Charles, N. G.; Griffith, E. A. H.; Amma, E. L. Organometallics 1983, 2, 101. 24.8 ppm belongs to a methyl group (Me2), definitely es(11) Pople, J. A.; Schneider, W. G.; Bernstein, H. J. High Resolution tablishing a CH=CH-CH3 pattern. Both these chemical Nuclear Magnetic Resonance; McGraw-Hill: New York, 1959. shifts and the coupling constants with phosphorus (JcIp (12) Horner, L.; Ertel, I.; Ruprecht, H. D.; Belovsky, 0. Chem. Ber. = 38, Jczp = 0, and J M ~ =~ 5P Hz) are also consistent with 1970, 103, 1582.
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