ARTICLE pubs.acs.org/Organometallics
Diastereomer Ratio of Products as a Mechanistic Probe in Epimerization and Ligand Exchange of Chiral-at-Metal [CpFe(Prophos)NCMe]X (X = I, PF6) Henri Brunner,*,† Hayato Ike,‡ Manfred Muschiol,† Takashi Tsuno,*,‡ Kazuhiro Koyama,‡ Takaki Kurosawa,‡ and Manfred Zabel†,§ † ‡
Institut f€ur Anorganische Chemie, Universit€at Regensburg, 93040 Regensburg, Germany Department of Applied Molecular Chemistry, College of Industrial Technology, Nihon University, Chiba 275-8575, Japan §X-ray structure analyses.
bS Supporting Information ABSTRACT: The diastereomers (RFe,RC)/(SFe,RC)-[CpFe(Prophos) NCMe]X (X = I, PF6), 5:95, differing only in the metal configuration, were prepared from (RFe,RC)/(SFe,RC)-[CpFe(Prophos)I] (95:5) in acetonitrile in the absence or presence of NH4PF6. The diastereomers interconverted by change of the Fe configuration in first-order reactions in CDCl3 at 293 K with half-lives of 216 min (iodide) and 96 min (hexafluorophosphate) in an SN1-type dissociation of the MeCN ligand, followed by pyramidal inversion of the 16-electron intermediates (RFe, RC)- and (SFe,RC)-[CpFe(Prophos)]þ and recombination with MeCN. In the presence of phosphite ligands there was MeCN/ligand exchange, the kinetics of which was measured. The rates of the MeCN/phosphite exchange decreased with increasing cone angle for P(OCH2)3CMe (101), P(OMe)3 (107), and P(OPh)3 (128). PPh3 (145) did not enter the vacant coordination site in the intermediates (RFe,RC)- and (SFe,RC)-[CpFe(Prophos)]þ. Phosphines such as Ph2PCH2CH2PPh2 and PBu3 bound only loosely to the intermediates. The phosphite complexes (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OR)3]X were configurationally stable at the metal atom. In the MeCN/phosphite exchange reactions the diastereomeric ratio of the products was constant, explained by an equilibrium between the intermediates in an energy diagram in which the barrier for the unimolecular pyramidal inversion was lower than the barriers for the bimolecular reactions of the intermediates with the phosphite ligands. A correlation between the major diastereomers (SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) and the diastereomers of the phosphite complexes with the same relative configuration and the favored envelope conformation of the Fe-Prophos chelate ring was corroborated, and a new correlation with the PP coupling constants of the Prophos ligand was established, including all the compounds of a former study.
’ INTRODUCTION The 16-electron intermediates (RRu,RC)- and (SRu,RC)-[CpRu(Prophos)]þ, formed in the dissociation of the RuCl bond in solutions of the half-sandwich complexes (RRu,RC)- and (SRu, RC)-[CpRu(Prophos)Cl] at ambient temperatures, retain their pyramidal geometry with the empty site in the remaining coordination position.1 The degree of retention of configuration at the metal atom in substitution reactions depends on the stability of the unsaturated intermediates toward pyramidal inversion. It is high for a basilica-type energy profile2 in which the barrier for pyramidal inversion is much larger than the barriers for addition of other ligands, as established for epimerization and ligand exchange in (RRu,RC)/(SRu,RC)-[CpRu(Prophos)Cl].1,2 In the present paper, inferred from the diastereomer ratio of substitution products, we demonstrate that epimerization and ligand exchange in (RFe, RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) follow an energy profile in which the barrier of pyramidal inversion of the r 2011 American Chemical Society
intermediates is lower than that of ligand addition to the intermediates (Scheme 1). Synthesis of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6). (RFe,RC)/(SFe,RC)-[CpFe(Prophos)I]3 (95:5) and an excess of NH4PF6 were dissolved in acetonitrile and stirred for 1 h at room temperature (Scheme 2). After removal of the solvent the residue was chromatographed at SiO2 with CH2Cl2/THF (100:1) or THF. The red-brown band contained (RFe,RC)/(SFe, RC)-[CpFe(Prophos)NCMe]PF6 (5:95). The preparation of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]I (5:95) was carried out without NH4PF6. Due to ion exchange effects, it did not elute completely with THF on a SiO2 column. However, it could be purified by chromatography on Celite. The formulas of Scheme 2 show only (R Fe ,R C )-[CpFe(Prophos)I] and Received: May 10, 2011 Published: June 14, 2011 3666
dx.doi.org/10.1021/om2003893 | Organometallics 2011, 30, 3666–3676
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Scheme 1. Energy Diagram for Epimerization and Ligand Exchange in (RFe,RC)- and (SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6)
(SFe,RC)-[CpFe(Prophos)NCMe]X, based on the ligand priority sequences I > Cp > PCHMe > PCH2 and Cp > PCHMe > PCH2 > NCMe.4,5 [CpFe(Prophos)NCMe]PF6 is air-stable in the solid state and in solution, whereas solutions of [CpFe(Prophos)NCMe]I decompose in air. Both salts are insoluble in alkanes and toluene, sparingly soluble in methanol, and well soluble in dichloromethane, THF, and acetonitrile. [CpFe(Prophos)NCMe]I may accumulate some [CpFe(Prophos)I]3 on standing. It is best to analyze diastereomer mixtures of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) in CDCl3 by 31P{1H} NMR spectroscopy. The two doublets of each of the two diastereomers are well separated and can easily be integrated. The equilibrium composition of both salts (RFe,RC)/(SFe,RC)[CpFe(Prophos)NCMe]X (X = I, PF6) is 5:95. The diastereomerically pure compounds (SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) were prepared by crystallization from CH2Cl2/ hexane. Crystals of (SFe,RC)-[CpFe(Prophos)NCMe]I 3 2(CH2Cl2) and (SFe,RC)-[CpFe(Prophos)NCMe]PF6 3 2(CH2Cl2) were suitable for X-ray analysis (Table 1). Only the cation of (SFe,RC)[CpFe(Prophos)NCMe]I 3 2(CH2Cl2) is shown in Figure 1, because the cation in the PF6 salt is very similar. Epimerization of (SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6). In CDCl3 diastereomerically pure (SFe,RC)-[CpFe(Prophos) NCMe]I epimerized at 293 K in a first-order reaction to the equilibrium composition (RFe,RC)/(SFe,RC)-[CpFe(Prophos) NCMe]I = 5:95 with kep = 3.21 103 (min1), corresponding to
Scheme 2. Synthesis of the Acetonitrile Complexes (RFe, RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6)
a half-life τ1/2 = 216 min for approach to equilibrium (Table 2). Using the equilibrium constant K = 5.4 102 the rate constants kf and kr for the forward reaction (SFe,RC) f (RFe,RC) and the backward reaction (RFe,RC) f (SFe,RC) could be calculated. Table 2 shows the temperature dependence of the rate constants and the activation parameters of the epimerization reaction. At 313 K the half-life for approach to equilibrium was down to 34 min. The equilibrium ratio decreased somewhat with increasing temperature. Interestingly, the epimerization of (SFe,RC)-[CpFe(Prophos) NCMe]PF6 at 293 K was faster by a factor of 2.25 than that of (SFe,RC)-[CpFe(Prophos)NCMe]I (Table 2). Addition of MeCN to CDCl3 solutions of (SFe,RC)-[CpFe(Prophos)NCMe]I increased the rate of epimerization (Table 2). Ratios CDCl3/MeCN of 99:1 and 10:1 resulted in 3- and 5-fold increases, respectively. Further increases to 10:2 and 1:1 and also the use of pure CD3CN did not change the epimerization rates. 3667
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Table 1. Crystallographic Data for [CpFe(Prophos)L]X Complexes (SFe,RC)-[CpFe(Prophos)- (SFe,RC)-[CpFe(Prophos)- (SFe,RC)-[CpFe(Prophos)- (SFe,RC)-[CpFe(Prophos)- (RFe,RC)-[CpFe(Prophos)NCMe]I 3 2(CH2Cl2)
NCMe]PF6 3 2(CH2Cl2)
radiation source (Å)
Mo KR (0.71073)
Mo KR (0.71073)
Mo KR (0.71073)
Mo KR (0.71073)
Cu KR (1.54184)
empirical formula
C34H34FeNP2,-
C34H34FeNP2,-
C35H40FeO3P3,I,2(CH2Cl2)
C35H40FeO3P3,F6P
C35H40FeO3P3,I 784.33
2(CH2Cl2),I
P(OMe)3]I 3 2(CH2Cl2)
P(OMe)3]PF6
P(OMe)3]I
2(CH2Cl2),F6P
fw
871.16
889.23
954.18
802.4
cryst syst
triclinic
triclinic
orthorhombic
monoclinic
monoclinic
space group
P1
P1
P212121
P21
P21
a (Å) b (Å)
9.333(3) 10.019(4)
9.543(4) 10.217(5)
10.772(5) 16.338(5)
10.169(4) 16.952(5)
9.53651(15) 17.08203(19)
c (Å)
11.415(5)
11.418(5)
23.351(5)
11.648(4)
11.01212(16)
R (deg)
88.191(17)
88.546(18)
90
90
90
β (deg)
68.322(15)
68.285(15)
90
116.418(13)
110.0613(17)
γ (deg)
71.573(14)
71.508(16)
90
90
90
V (Å)3
936.6(6)
975.5(8)
4110(2)
1798.3(11)
1685.06(4)
Z
1
1
4
2
2
Fcalcd (Mg/m3) abs coeff (mm1)
1.544 1.624
1.514 0.84
1.542 1.529
1.482 0.663
1.546 12.394
abs correct
multiscan
multiscan
multiscan
multiscan
semiempirical
transmn max./min.
0.8811/0.7698
0.8773/0.8238
0.6569/0.5152
0.9489/0.8733
1.00000/0.10808
F(000)
438
454
1928
828
796
cryst size (mm)
0.18 0.09 0.08
0.24 0.20 0.16
0.50 0.50 0.30
0.21 0.14 0.08
0.28 0.24 0.12
θ range (deg)
3.0327.48
3.0127.48
3.0427.48
3.1027.47
4.2762.30
reflns/unique
9297/6988
9600/7230
35 580/9274
17 651/7877
22 642/5262
Rint data/params
0.0511 6988/407
0.0764 7230/461
0.1421 9274/443
0.0831 7877/442
0.0910 5262/391
goodness of fit on F2
1.079
1.066
1.082
1.028
1.052
R1/wR2 (I > 2σ(I))
0.0494/0.0991
0.0607/0.1386
0.0816/0.1622
0.0645/0.1260
0.0481/0.1214
R1/wR2 (all data)
0.0647/0.1111
0.0892/0.1574
0.1102/0.1814
0.1052/0.1431
0.0498/0.1223
abs struct param
0.05(2)
0.03(2)
0.01(3)
0.03(2)
0.027(5)
largest diff peak and
1.211/0.705
0.476/0.467
1.638/1.215
0.521/0.431
1.626/1.396
813975
813976
813979
813980
813969
hole (e Å3) CCDC no.
(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]I
(SFe,RC)-[CpFe(Prophos)PO(OMe)2]
(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]PF6
radiation source (Å)
Cu KR (1.54184)
Mo KR (0.71073)
Mo KR (0.71073)
empirical formula
C34H37FeO3P3
C37H40FeO3P3,I
C37H40FeO3P3,F6P
fw
642.40
808.35
826.42
cryst syst
orthorhombic
orthorhombic
orthorhombic
space group
P212121
P212121
P212121
a (Å) b (Å)
9.0022(1) 19.6793(3)
9.7854(19) 16.627(3)
10.087(3) 16.516(3)
c (Å)
21.4058(3)
21.026(5)
21.551(6)
R (deg)
90
90
90
β (deg)
90
90
90
γ (deg)
90
90
90
V (Å)3
3792.19(9)
3421.0(12)
3590.3(16)
Z
4
4
4
Fcalcd (Mg/m3) abs coeff (mm1)
1.125 4.602
1.569 1.52
1.529 0.667
abs correct.
semiempirical
multiscan
multiscan
transmn max./min.
1.000000.65856
0.9702/0.7509
0.9008/0.8099
F(000)
1344
1640
1704
cryst size (mm)
0.27 0.23 0.13
0.20 0.11 0.02
0.33 0.22 0.16
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Table 1. Continued (SFe,RC)-[CpFe(Prophos)-
(SFe,RC)-[CpFe(Prophos)-
(SFe,RC)-[CpFe(Prophos)-
PO(OMe)2]
P(OCH2)3CMe]I
P(OCH2)3CMe]PF6 3.0327.48
θ range (deg)
3.0562.15
3.1027.47
reflns/unique
12 977/5803
32 732/7736
32 216/8179
Rint
0.0485
0.157
0.0842
data/params
5803/373
7736/406
8179/460
goodness of fit on F2
1.017
1.029
1.054
R1/wR2 (I > 2σ(I))
0.0444/0.1094
0.0713/0.0931
0.0539/0.1117
R1/wR2 (all data)
0.0521/0.1127
0.1250/0.1059
0.0830/0.1241
abs struct param largest diff peak and
0.000(5) 0.324/0.328
0.01(3) 0.577/0.658
0.01(3) 0.619/0.393
813981
813977
813978
hole (e Å3) CCDC no.
Figure 1. Structure of the cation (SFe,RC)-[CpFe(Prophos)NCMe]þ (left side) of the compound (SFe,RC)-[CpFe(Prophos)NCMe]I 3 2(CH2Cl2) and of the compound (SFe,RC)-[CpFe(Prophos)PO(OMe)2] (right side).
The epimerization of (SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) starts with the rate-determining cleavage of the FeNCMe bond (Scheme 1) to give the intermediate (SFe, RC)-[CpFe(Prophos)]þ and the ligand MeCN, which has a high dipole moment of 4.3 D.6 Ordered association of the ion and dipole may contribute to the negative entropy of activation, observed in this dissociation reaction (Table 2). Pyramidal inversion and reassociation of the intermediates with MeCN establish the (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) equilibria according to Scheme 1. In this paper the term “unsaturated intermediate” implies the inclusion of species such as [CpFe(Prophos)solvent]þ, containing weakly bound solvent molecules such as CDCl3 in fast exchange with other solvent molecules. As oxygen compounds are poor ligands for the CpFe(PP) fragment, water does not play a role in this type of chemistry. The increase of the rate of epimerization of (SFe,RC)-[CpFe(Prophos)NCMe]I in the presence of additional MeCN cannot be explained with the SN1 mechanism in Scheme 1. A contribution of another mechanism, such as chelate ring-opening followed by reaction with MeCN and recombination or reaction of (SFe,RC)-[CpFe(Prophos)NCMe]I with MeCN according to SN2 with inversion of the metal configuration or front-side addition and pseudorotation of the CpFe(Prophos) moiety, would account for these results. In the absence of additional MeCN such bimolecular reactions do not play a role, because the reactant MeCN, formed in the dissociation reaction, is present only in extremely small amounts.
Synthesis of the Phosphite Complexes (RFe,RC)/(SFe, RC)-[CpFe(Prophos)L]X (L = P(OMe)3, P(OCH2)3CMe, P(OPh)3, X = I, PF6). The phosphite complexes (RFe,RC)/(SFe,RC)-[CpFe-
(Prophos)L]X (Scheme 3) can be prepared in two different ways. (RFe,RC)/(SFe,RC)-[CpFe(Prophos)I] (95:5) and an excess of P(OMe)3 were stirred in toluene/methanol for 1 h at room temperature (Scheme 3) to give (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]I (13:87). Alternatively, (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 (5:95) with an excess of P(OMe)3 in dichloromethane can be used for the synthesis. In this case, however, the reaction time must exceed 10 half-lives of the epimerization of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6. After removal of the solvent the residue was chromatographed on SiO2 with CH2Cl2/ THF (100:1). The yellow band contained (RFe,RC)/(SFe,RC)[CpFe(Prophos)P(OMe)3]PF6 (17:83). The formulas of Scheme 3 show only (RFe,RC)-[CpFe(Prophos)I], (SFe,RC)-[CpFe(Prophos)NCMe]X, and (SFe,RC)-[CpFe(Prophos)L]X, based on the ligand priority sequence Cp > P(OMe)3 > PCHMe > PCH2. [CpFe(Prophos)P(OMe)3]X (X = I, PF6) are air-stable in the solid state and in solution. Both salts are insoluble in alkanes and toluene and well soluble in dichloromethane and THF. In the 31 1 P{ H} NMR spectra the phosphorus atoms of the diastereomers give a well-separated doublet of doublet system. Diastereomerically pure (SFe,RC)-[CpFe(Prophos)P(OMe)3]I was prepared by crystallization of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]I (13:87) from CH2Cl2/hexane. Crystals of (SFe,RC)-[CpFe(Prophos)P(OMe)3]I 3 2(CH2Cl2) were suitable for X-ray crystallography (Table 1). Its cation, shown in Figure 2 3669
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Table 2. Kinetics of the Epimerization of Diastereomerically Pure (SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) and Activation Parametersa
anion X
kep, min1
τep1/2, min
kforw, min1
kback, min1
5.4 102
3.21 103
216
1.64 104
3.05 103
5:95 5:95d
2
5.4 10 5.4 102
3
8.94 10 1.70 102
78 41
4
4.58 10 8.76 104
8.48 103 1.61 102
5:95e
5.2 102
1.66 102
42
8.25 104
1.57 102
5:95
f
5.8 10
2
2
4
1.52 102
5:95
g
5.6 10
2
3
1.88 102
6:94
b
5.9 10
2
4.25 10
4
7.23 103
7:93
b
7.5 10
2
1.01 10
3
1.35 102
9:91
b
9.8 10
2
3
1.87 102
temp K
equilibrium ratio (RFe,RC):(SFe,RC)
Kep
293
5:95b c
I
300 307 313 ‡
ΔH f = 90 ( 3 kJ mol ΔS‡f = 44 ( 8 J mol1 K1
Gibbs free energy
ΔG‡f = 103 ( 5 kJ mol1 293 300
2
1.99 10 7.65 10
3
1.45 10
3 2
2.05 10
1
activation enthalpy activation entropy PF6
1.61 10
5:95
b
7:93
b
8.90 10
43
1.06 10
35 91 48
1.83 10
34 ‡
1
ΔH r = 67 ( 3 kJ mol ΔS‡r = 97 ( 7 J mol1 K1 ΔG‡r = 96 ( 4 kJ mol1 5.2 10
2
7.1 10
2
3
7.19 10 1.87 10
2
96
3.58 104
6.83 103
3
1.75 102
1.25 10
37
a
1
(left side), closely resembles the cation of (SFe,RC)-[CpFe(Prophos)P(OMe)3]PF6 (not shown), whereas the cation of the diastereomer (RFe,RC)-[CpFe(Prophos)P(OMe)3]I (Figure 2, right side) has a conformation of the Fe-Prophos chelate ring different from all the other structures reported in this paper (see below). (RFe,RC)- and (SFe,RC)-[CpFe(Prophos)P(OMe)3]PF6 are configurationally stable at the metal atom. No epimerization was observed, even at higher temperatures. (RFe,RC)- and (SFe, RC)-[CpFe(Prophos)P(OMe)3]I also did not show signs of epimerization at room temperature. However, at elevated temperatures the iodide salts underwent MichaelisArbuzov rearrangement7 to give (RFe,RC)- and (SFe,RC)-[CpFe(Prophos)PO(OMe)2 ] (Scheme 4). In boiling toluene after 2 h (RFe, RC)/(S Fe,RC)-[CpFe(Prophos)P(OMe)3]I was completely rearranged, whereas (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)]PF6 was unchanged under the same conditions. At the lower temperature of boiling chloroform the rearrangement of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]I occurred to about 60% in 2 h. The rearrangement of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]I was stereospecific. As the chiral Fe center was not involved in the MichaelisArbuzov reaction, (RFe,RC)-[CpFe(Prophos)P(OMe)3]I rearranged to (RFe,RC)-[CpFe(Prophos) PO(OMe)2] and (SFe,RC)-[CpFe(Prophos)P(OMe)3]I to (SFe, RC)-[CpFe(Prophos)PO(OMe)2]. The yellow neutral complexes (RFe,RC)- and (SFe,RC)-[CpFe(Prophos)PO(OMe)2] are configurationally stable at the metal atom. The molecular structure of (SFe,RC)-[CpFe(Prophos)PO(OMe)2] is shown in Figure 1 (right side).
The reaction of the tied-back phosphite P(OCH2)3CMe8 with (RFe,RC)/(SFe,RC)-[CpFe(Prophos)I] (95:5) and (RFe, RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) (5:95) in dichloromethane paralleled that of P(OMe)3. The diastereomer ratio of the products (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]X (X = I, PF6) was 22:78 in both the iodide and the hexafluorophosphate series. The properties and spectra of the P(OCH2)3CMe derivatives are similar to the P(OMe)3 derivatives, including the diagnostic 31P{1H} NMR doublet of doublet patterns of the diastereomers. The diastereomerically pure compounds (SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]I and (SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]PF6 were obtained by crystallization from CH2Cl2/hexane. The data of their X-ray analyses are summarized in Table 1. The complex [CpFe(Prophos)P(OPh)3]PF6 is best prepared by treatment of [CpFe(Prophos)Cl]3 or [CpFe(Prophos)I]3 with P(OPh)3 and NH 4 PF 6 in THF. The reaction of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 (5:95) with P(OPh)3 in CDCl3 was extremely slow. It was not a clean reaction. During days at room temperature besides the signals of the expected exchange product new signals appeared, which we ascribe to compounds such as [CpFe{P(OPh)3}2X]9 formed in the replacement of Prophos by P(OPh)3. The reason for the slow reaction of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 with P(OPh)3 is its large cone angle10 of 128 (see below). Phosphine Complexes (RFe,RC)/(SFe,RC)-[CpFe(Prophos) L]X (L = PPh3, Ph2PCH2CH2PPh2, PBu3; X = I, PF6). In agreement with the steric considerations outlined above, PPh3 (cone angle 145) is so large that it did not enter the
31
1
Concentration of (SFe,RC)-[CpFe(Prophos)NCMe]X = 0.030.04 mol L ; reactions monitored by P{ H} NMR spectroscopy. Activation parameters at 300 K. b In CDCl3. c In CDCl3/MeCN (99:1, v/v). d In CDCl3/MeCN (10:1, v/v). e In CDCl3/MeCN (10:2, v/v). f In CDCl3/MeCN (1:1, v/v). g In CD3CN.
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Scheme 3. Synthesis of the Phosphite Complexes (RFe,RC)/(SFe,RC)-[CpFe(Prophos)L]X (L = P(OMe)3, P(OCH2)3CMe, P(OPh)3, X = I, PF6)
Scheme 4. MichaelisArbuzov Rearrangement of (SFe,RC)[CpFe(Prophos)P(OMe)3]I to Give (SFe,RC)[CpFe(Prophos)PO(OMe)2]
Figure 2. Cation (SFe,RC)-[CpFe(Prophos)P(OMe)3]þ (left side) of (SFe,RC)-[CpFe(Prophos)P(OMe)3]I 3 2(CH2Cl2) and cation (RFe, RC)-[CpFe(Prophos)P(OMe)3]þ (right side) of (RFe,RC)-[CpFe(Prophos)P(OMe)3]I.
vacant coordination site in the intermediates (RFe,RC)/ (SFe,RC)-[CpFe(Prophos)]þ. On addition of a 10-fold excess of PPh3 to a CDCl3 solution of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 (5:95) at room temperature, the 31P{1H} NMR signal of PPh3 stayed sharp. Differently, the 31P{1H} NMR signal of Diphos (Ph2PCH2CH2PPh2) broadened extensively (Figure 11S), while the 31P{1H} NMR signals of the two diastereomers (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 were unaffected (Figure 10S). This did not change on standing for hours. At temperatures below room temperature the 31P{1H} NMR signal of Diphos sharpened, whereas at higher temperatures it disappeared (Figure 11S). We assign small triplets at 99, 63, and 55 ppm at 323 K to complex [CpFe(Prophos)η1Diphos]PF6 (Figure 10S), and we explain the observed behavior by assuming a competition between MeCN and Diphos for the vacant coordination site, generated by the cleavage of the FeNCMe bond in (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6, including fast exchange of η1-Diphos and free Diphos. η1-Diphos has a cone angle similar to Ph2PMe (136) and Ph2PEt (139).11 Thus, phosphanes that are large ligands and good donors do not bind well to the [CpFe(Prophos)]þ fragment, because the binding pocket is relatively small and the Fe atom is an electron-rich center. The (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6/Diphos experiment definitely excludes opening of the chelate ring as the dominating mechanism that accounts for epimerization and ligand exchange in (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6. Diphos would enter an intermediate with η1-Prophos, and chelate ring closing should lead to a mixture of compounds with Prophos and Diphos chelate rings, which is not observed at ambient temperatures. Instead, Diphos is in competition with MeCN for the empty coordination position as outlined above. However, in the 31P{1H} NMR spectra of CDCl3 solutions of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 and excess Diphos at 323 K the small singlet of [CpFe(Diphos)-
NCMe]PF6 appeared at 98 ppm and increased somewhat at 328 K (Figure 10S). Heating CDCl3 solutions of (RFe,RC)(SFe,RC)[CpFe(Prophos)NCMe]PF6 and excess Diphos as well as [CpFe(Diphos)NCMe]Cl12 and excess (R)-Prophos at 328 K for hours produced mixtures of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 and [CpFe(Diphos)NCMe]PF6 (Figures 10S and 12S). Thus, Prophos/Diphos exchange is a slow high-temperature process starting from [CpFe(Prophos)η1-Diphos]PF6, not involved in epimerization and ligand exchange of (RFe,RC)/ (SFe,RC)-[CpFe(Prophos)NCMe]PF6 at ambient temperatures. (RFe,RC)/(SFe,RC)-[CpFe(Prophos)I] (95:5) was reacted with excess PBu3 in THF at 323 K for 15 h. After chromatography with THF [CpFe(Prophos)PBu3]I was isolated in the kinetically controlled diastereomer ratio 62:38 as yellow crystals. In solution [CpFe(Prophos)PBu3]I turned out to be configurationally labile at the Fe atom. In CDCl3 at room temperature the diastereomer ratio changed from 62:38 after 28 h to 71:29 and after 40 h to 83:17. The equilibrium composition is 95:5. Thus, the epimerization of [CpFe(Prophos)PBu3]I is much slower than that of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]I. In CDCl3 solution [CpFe(Prophos)PBu3]I undergoes ligand exchange. On addition of MeCN and P(OMe)3, the signals of the corresponding substitution products showed up in the spectra. Unfortunately, on standing in the 31P{1H} NMR spectra of solutions of [CpFe(Prophos)PBu3]I, signals of byproducts, some of them broad, and of the oxides of PBu3 and Prophos appeared. Therefore, accurate kinetics of the epimerization could not be determined. However, the slow dissociation of PBu3 from [CpFe(Prophos)PBu3]I is well in accord with the cone angle of PBu3 (132o)11 on one side and the electron-rich Fe center in [CpFe(Prophos)PBu3]I on the other side. Kinetics of the Ligand Exchange in (SFe,RC)-[CpFe(Prophos)NCMe]X. The kinetics of the MeCN/P(OMe)3 exchange in diastereomerically pure (SFe,RC)-[CpFe(Prophos)NCMe]I was measured with an 11-fold excess of P(OMe)3 in CDCl3 (Table 3). At 293 K the rate constant was k = 0.76 103 min1, corresponding to a half-life of τ1/2 = 912 min. In the 3671
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Table 3. Kinetics of theMeCN/L Exchange in (SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) in CDCl3a,b
X
ligand L
temp, K
k,c min1
τ1/2, min
(RFe,RC)/(SFe,RC)-[CpFe(Prophos)L]X
I
P(OMe)3
293
0.76 103 ( 0.7 105
912 ( 77
17:83
PF6
P(OMe)3
293
1.21 103 ( 0.2 105
572 ( 10
18:82
I
P(OCH2)3CMe
293 300
1.52 103 ( 0.5 104 4.74 103 ( 0.4 104
456 ( 16 146 ( 1
21:79 27:73
307
1.47 102 ( 0.1 103
47 ( 1
27:73
313
3.76 102 ( 1.6 103
18 ( 1
31:69
293
2.21 103 ( 0.7 105
313 ( 42
22:78
activation enthalpy ΔH‡ = 120 ( 1 kJ mol1 activation entropy ΔS‡ = 77 ( 1 J mol1 s1 Gibbs free energy ΔG‡ = 97 ( 1 kJ mol1 PF6
P(OCH2)3CMe
Kinetics determined using time-resolved 31P{1H} NMR spectroscopy. Complex ca. 10 mg (3.6 102 mol L1) and ligand (0.39 mol L1) in CDCl3 (0.4 mL). b Activation parameters for 300 K. c The constants k are disappearance rates of (SFe,RC)-[CpFe(Prophos)NCMe]X. a
PF6 salt the ligand exchange reaction of MeCN/P(OMe)3 was somewhat faster than in the iodide salt. The kinetics of the MeCN/P(OCH2)3CMe exchange in (SFe, RC)-[CpFe(Prophos)NCMe]I with an 11-fold excess of P(OCH2)3CMe8 in CDCl3 (Table 3) at 293 K was two times faster than that of P(OMe)3. In the temperature-dependent measurements the diastereomer ratio of the product (RFe, RC)/(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]I changed from 21:79 at 293 K to 31:69 at 313 K. We attribute the higher rate in the MeCN/P(OCH2)3 CMe exchange reaction (cone angle P(OCH2)3CMe 101)11 compared to the MeCN/P(OMe)3 exchange (cone angle P(OMe)3 107)10 to the smaller size of the tied-back ligand P(OCH2)3CMe.11 Interestingly, the MeCN/P(OMe)3 exchange reaction was so slow that starting with the diastereomerically pure major diastereomer (SFe,RC)-[CpFe(Prophos)NCMe]I, the minor diastereomer (RFe,RC)-[CpFe(Prophos)NCMe]I was building up during the reaction, a phenomenon not observed in the faster MeCN/P(OCH2)3CMe exchange reaction. The even larger ligands P(OPh)3 (cone angle 128) and PPh3 (cone angle 145) have been addressed before. At 293 K the rate of the MeCN/P(OMe)3 exchange was 4.2 times and that of the MeCN/P(OCH2)3CMe exchange 2.1 times slower than the rate of the epimerization of (SFe,RC)-[CpFe(Prophos)NCMe]I, indicating that the unimolecular pyramidal inversion is faster than the bimolecular reaction of the intermediates with the ligands P(OMe)3 and P(OCH2)3CMe present in large excess. This cannot be explained with a basilica-type energy profile as for [CpRu(Prophos)X] compounds.1,2 It requires an energy profile having a lower middle nave for pyramidal inversion, which governs epimerization and ligand exchange of complexes (RFe,RC)- and (SFe,RC)-[CpFe(Prophos)NCMe]I (Scheme 1).
Diastereomer Ratios in the MeCN/Ligand Exchange Reactions. In the MeCN/P(OMe)3 exchange reactions of (SFe,
RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) in CDCl3 at room temperature the diastereomer ratio of the products (RFe, RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]X (X = I, PF6) was 17:83 at all stages of the reaction. It was also 17:83 irrespective of whether (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]I or (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 was used as 5:95 or 0:100 mixtures and whether P(OMe)3 was used in 15fold excess in stoichiometric or substoichiometric amounts in accord with Scheme 1. That means barrier 1 for pyramidal inversion of the intermediates must be appreciably lower than barriers 2 and 20 for the bimolecular reactions of the intermediates (RFe,RC)- and (SFe,RC)-[CpFe(Prophos)NCMe]þ with P(OMe)3. Thus, on the basis of energy profile 1/2/20 the intermediates always react with their equilibrium concentrations, giving a constant product ratio (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]X (X = I, PF6) of 17:83. The results of the MeCN/P(OCH2)3CMe exchange reactions of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) in CDCl3 at room temperature were analogous to those of the MeCN/P(OMe)3 exchange. The diastereomer ratio of the products (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe] PF6 was 22:78 in all cases, corroborating the conclusions drawn from energy profile 1/2/20 in Scheme 1. Actually, the results of the MeCN/phosphite exchange reactions in (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) could be accounted for on the basis of a planar 16-electron intermediate [CpFe(Prophos)]þ. Such a planar structure had been suggested for [CpFe{PH3}2]þ, whereas [CpFe(CO)2]þ had been assigned a pyramidal structure.13 Calculations had shown that the barriers to pyramidal inversion of 16-electron intermediates are much lower for CpFeL2 than for CpRuL2 fragments.13,14 The height of the energy barriers for pyramidal 3672
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Table 4. Conformational Analysis of the Fe-Prophos Chelate Ring complex (SFe,RC)-[CpFe(Prophos)NCMe]I 3 2(CH2Cl2) (SFe,RC)-[CpFe(Prophos)NCMe]PF6 3 2(CH2Cl2) (SFe,RC)-[CpFe(Prophos)P(OMe)3]I 3 2(CH2Cl2)
— (PFePCHMe)
— (PFePCH2)
conformation type
23.4
1.0
22.1
0.9
envelope
19.8
6.1
envelope envelope
envelope
19.1
3.2
(RFe,RC)-[CpFe(Prophos)P(OMe)3]I
3.7
17.2
(SFe,RC)-[CpFe(Prophos)PO(OMe2]
22.8
0.4
envelope
(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]I
12.3
7.2
envelope
(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe] PF6
13.3
6.3
envelope
(SFe,RC)-[CpFe(Prophos)P(OMe)3]PF6
inversion of the intermediates and ligand addition to the intermediates cannot be measured directly. It is the diastereomer ratio of the products in epimerization and substitution reactions of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) that allows us to postulate and support the energy profile in Scheme 1. Conformations and Configurations. A correlation had been established between the conformation of the five-membered metalProphos chelate ring and the thermodynamic stability of major/minor diastereomers in equilibrium mixtures for a series of nine compounds of the type [CpM(Prophos)X].3,15 This correlation is corroborated by the structures of (SFe, RC)-[CpFe(Prophos)NCMe]X 3 2(CH2Cl2) (X = I, PF6), the parent compounds of the present study. The diastereomer ratio (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) of 5:95 corresponds to an energy difference of about 2.5 kcal/mol between the major and minor diastereomer at equilibrium (Scheme 1). The thermodynamically more stable diastereomers (SFe,RC)-[CpFe(Prophos)NCMe]X (X = I, PF6) adopt the favored envelope conformation (Table 4) in which the Fe atom, the two P atoms, and the C atom of the CH2 group are in a plane.3 The C atom of the CHMe group deviates from this plane, orienting its methyl group equatorially away from the complex (Figure 3, left side). As the diastereomers of the phosphite complexes do not interconvert, their thermodynamic stability cannot be derived from their equilibrium mixtures. However, the five structures with a (SFe,RC)-configuration in Table 1 have the same relative configuration as the major diastereomers in complexes that are configurationally labile at the metal center. Thus, these five structures together with eight structures of the previous report3 with the same relative configuration support the correlation with the favored envelope conformation of the M-Prophos chelate ring, shown in Figure 3, left side. One structure in this study with (RFe,RC)-configuration deviates from the preferred conformation (Figure 3, right side). In (RFe,RC)-[CpFe(Prophos)P(OMe)3]I the CH2 and CHMe groups change their roles compared to the favored conformation in Figure 3, left side. The C atom of the CH2 group occupies the position outside the PFePCHMe plane. The methyl substituent of the CHMe group is in an equatorial position and points away from the complex. The R-configuration of Prophos results in the λ-conformation of the chelate ring in all the compounds of Figure 3 which in enantioselective catalysis transmits the chiral information from the asymmetric carbon atom in the backbone via the phenyl “ears” of the PPh2 groups to the coordination sites at the metal center, where catalysis occurs.15,16
inverted envelope
Figure 3. Favored Fe-Prophos chelate ring in (SFe,RC)-[CpFe(Prophos)NCMe]PF6 3 2(CH2Cl2) (left side) and the exception in (RFe,RC)-[CpFe(Prophos)P(OMe)3]I (right side). At the P atoms only the ipso-C atoms of the phenyl rings are shown.
From the extended series of compounds of the type (RFe, RC)/(SFe,RC)-[CpFe(Prophos)X] another correlation is obvious. It links the configuration at the Fe atom and the PP coupling constants in the Prophos ligand. In [CpFe(Prophos)NCMe]X (X = I, PF6) the major (SFe,RC)-diastereomers by far have larger coupling constants (43.6 Hz) than the minor (RFe, RC)-diastereomers (31.7 Hz). All nine compounds of the previous study,3 which have the same relative configurations, show similar differences in the PP coupling constants, supporting the correlation. The only exceptions are the phosphite and phosphine complexes of this paper, in which the coupling constants of the two P atoms of the Prophos ligand have about the same magnitude in the (RFe,RC)-series and in the (SFe,RC)-series.
’ EXPERIMENTAL PART General Procedures. IR: JASCO FT/IR4100ST. 1H/31P{1H} NMR: Bruker Avance 400 (400/162 MHz, T = 293 or 300 K), TMS as internal standard and H3PO4 as external standard. MS: Finnigan MAT 95 (EI, 70 eV), MAT SSQ 710A, or ThermoQuest Finnigan TSQ 7000. All manipulations were carried out in purified nitrogen or argon.
(RFe,RC)/(SFe,RC)-(Acetonitrile)(η5-cyclopentadienyl)[propane-1,2-diylbis(diphenylphosphane-kP)]iron Iodide, (RFe,RC)/ (SFe,RC)-[CpFe(Prophos)NCMe]I. A solution of (RFe,RC)/(SFe,
RC)-[CpFe(Prophos)I] (95:5) (306 mg, 0.46 mmol) in a mixture of chloroform (20 mL) and acetonitrile (2.0 mL) was stirred for 30 min at room temperature. The solvent was removed and the residue was recrystallized from dichloromethane/hexane to give (RFe,RC)/(SFe, RC)-[CpFe(Prophos)NCMe]I (5:95) as red crystals in 88% (284 mg) yield. Diastereomerically pure crystals of (SFe,RC)-[CpFe(Prophos)NCMe]I 3 2(CH2Cl2) suitable for X-ray analysis were obtained by crystallization from dichloromethane/hexane. IR (KBr): ν 2260 cm1 (NC). 1H NMR (CDCl3, 293 K, major (SFe, RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets, if distinguishable): δ 7.927.19 (m, 20H, Ar-H), 4.29 (t, 5H, 3JPH = 1.2 Hz, Cp-H) [4.31 (t, 5H, 3JPH = 1.4 Hz, Cp-H)], 3.102.90 (m, 1H, CH), 2.382.26 (m, 1H, CH), 2.051.97 (m, 1H, CH), 1.91 (s, 3H, MeCN) [1.95 (s, 3H, MeCN)], 1.20 (dd, 3H, 3JPH = 10.8 Hz, 3JHH = 6.1 Hz, CH3) [0.70 (dd, 3H, 3JPH = 13.2 Hz, 3JHH = 7.3 Hz, CH3)]. 31P{1H} 3673
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Organometallics NMR (CDCl3, 293 K, major (SFe,RC)-diastereomer, minor (RFe,RC)diastereomer in brackets): δ 105.86 (d, 1P, 2JPP = 43.6 Hz) [107.45 (d, 1P, 2JPP = 31.7 Hz)], 83.28 (d, 1P, 2JPP = 43.6 Hz) [96.19 (d, 1P, 2 JPP = 31.7 Hz)]. MS (ES, CH2Cl2/MeCN): m/z 574 (cation, 5), 533 (100, cation MeCN). HRMS (LSI, glycerol): calcd for the cation C34H34Fe NP2þ 574.1512, found m/z 574.1508 (Mþ). Anal. Calcd for C34H34FeINP2 (701.3): C, 58.23; H, 4.89; N, 2.00. Found: C, 57.61; H, 4.70; N, 1.80.
(R Fe ,R C )/(S Fe ,R C )-(Acetonitrile)(η 5 -cyclopentadienyl)[propane-1,2-diylbis(diphenylphosphane-kP)]iron Hexafluorophosphate, (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6. To
(RFe,RC)-[CpFe(Prophos)I] (660 mg, 1 mmol) in acetonitrile (50 mL) was added NH4PF6 (1.8 g, 11 mmol). After stirring for 10 h at room temperature the solvent was removed. The residue was dissolved in dichloromethane. Excess NH4PF6 was extracted with water. Chromatography on silica with CH2Cl2/THF (100:1) gave an orange band, containing 650 mg (90%) of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)NCMe]PF6 (5:95). Diastereomerically pure red crystals of (SFe,RC)-[CpFe(Prophos) NCMe]PF6 3 2(CH2Cl2), suitable for X-ray analysis, were obtained by crystallization from dichloromethane/hexane. IR (KBr): ν 2266 cm1 (NC). 1H NMR (CDCl3, 293 K, major (SFe, RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets, if distinguishable): δ 7.837.33 (m, 20H, Ar-H), 4.24 (s, 5H, Cp-H) [4.21 (s, 5H, Cp-H)], 3.072.86 (m, 1H, CH), 2.161.94 (m, 2H, CH), 1.61 (s, 3H, MeCN) [1.69 (s, 3H, MeCN)], 1.18 (dd, 3H, 3JPH = 10.8 Hz, 3 JHH = 5.8 Hz, CH3) [0.67 (dd, 3H, 3JPH = 12.5 Hz, 3JHH = 6.8 Hz, CH3)]. 31P{1H} NMR (CDCl3, 293 K, major (SFe,RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets): δ 105.31 (d, 1P, 2JPP = 43.6 Hz) [108.36 (d, 1P, 2JPP = 31.7 Hz)], 83.41 (d, 1P, 2JPP = 43.6 Hz) [96.90 (d, 1P, 2JPP = 31.7 Hz)], 143.16 (sept, 1P, 1JPF = 712.8 Hz). MS (ES, CH2Cl2/MeCN): m/z 574 (cation, 100), 533 (39, cation MeCN). Anal. Calcd for C34H34F6FeNP3 (718.8): C, 56.76; H, 4.76; N, 1.94. Found: C, 56.45; H, 4.46; N, 1.89.
(RFe,RC)/(SFe,RC)-(η5-Cyclopentadienyl)[propane-1,2-diylbis(diphenylphosphane-kP)](trimethylphosphite-kP)iron Iodide, (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]I. To a solution of (RFe,
RC)/(SFe,RC)-[CpFe(Prophos)I] (95:5) (90 mg, 0.14 mmol) in dichloromethane (20 mL) was added P(OMe)3 (0.25 mL, 2.12 mmol), and the mixture was stirred for 2 h at room temperature. After evaporation of the solvent, the residue was washed with hexane. Diastereomer ratio of (RFe, RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]I = 17:83 (quantitative yield). Chromatography on silica with THF was possible without decomposition. Recrystallization from dichloromethane/hexane gave yellow crystals. Crystals of the major diastereomer (SFe,RC)-[CpFe(Prophos)P(OMe)3]I 3 2(CH2Cl2), suitable for X-ray analysis, were obtained by further crystallization from dichloromethane/hexane. 1 H NMR (CDCl3, 293 K, major (SFe,RC)-diastereomer, minor (RFe, RC)-diastereomer in brackets, if distinguishable): δ 7.737.18 (m, 20H, Ar-H), 4.51 (s, 5H, Cp-H) [4.48 (s, 5H, Cp-H)], 3.15 (d, 9H, 3JHP = 4.3 Hz, OCH3), 3.192.95 (m, 1H, CH), 2.152.04 (m, 2H, CH), 1.10 (dd, 3H, 3JPH = 11.5 Hz, 3JHH = 5.6 Hz, CH3). 31P{1H} NMR (CDCl3, 293 K, major (SFe,RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets): δ 169.60 (t, 1P, 2JPP = 89.2 Hz) [173.13 (dd, 1P, 2 JPP = 80.9 Hz, 2JPP = 91.6 Hz)], 104.95 (dd, 1P, 2JPP = 37.7 Hz, 2 JPP = 89.2 Hz) [93.73 (dd, 1P, 2JPP = 36.6 Hz, 2JPP = 80.9 Hz)], 75.71 (dd, 1P, 2JPP = 37.7 Hz, 2JPP = 89.2 Hz) [84.41 (dd, 1P, 2JPP = 36.6 Hz, 2JPP = 91.6 Hz)]. MS (ES, CH2Cl2/MeCN): m/z 657 (cation, 100). HRMS (LSI, glycerol): calcd for the cation C35H40Fe O3P3þ 657.1539, found m/z 657.1537 (Mþ). Anal. Calcd for C35H40FeIO3P3 (784.4): C, 53.59; H, 5.14. Found: C, 53.45; H, 5.33.
(RFe,RC)/(SFe,RC)-(η5-Cyclopentadienyl)[propane-1,2-diylbis(diphenylphosphane-kP)](trimethylphosphite-kP)iron Hexafluorophosphate, (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]PF6. Solutions of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)I]
ARTICLE
(95:5) (230 mg, 0.35 mmol) in toluene (10 mL) and NH4PF6 (700 mg, 4.5 mmol) in methanol (10 mL) were combined, and P(OMe)3 (0.6 mL, 5 mmol) was added. After stirring for 2 h at room temperature the solvents were evaporated and the residue was washed with petroleum ether several times to remove excess P(OMe)3. Excess NH4PF6 was removed by extraction with dichloromethane/water. Diastereomer ratio of (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]PF6 = 17:83 (quantitative yield). With 100:1 dichloromethane/THF (RFe, RC)/(SFe,RC)-[CpFe(Prophos)P(OMe)3]PF6 eluted as a yellow-orange band. Single crystals of (SFe,RC)-[CpFe(Prophos)P(OMe)3]PF6 for X-ray analysis were prepared by recrystallization from dichloromethane/hexane. IR (KBr): ν 841 cm1 (P-F). 1H NMR (CDCl3, 293 K, major (SFe, RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets, if distinguishable): δ 7.707.15 (m, 20H, Ar-H), 4.47 (s, 5H, Cp-H) [4.44 (s, 5H, Cp-H)], 3.801.82 (m, 3H, CH2CH), 3.09 (d, 9H, 2JPH = 10.4 Hz, OCH3) [3.25 (d, 9H, 2JPH = 10.6 Hz, OCH3)], 1.07 (dd, 3H, 3 JPH = 11.2 Hz, 3JHH = 5.9 Hz, Me) [1.21 (dd, 3H, 3JPH = 10.9 Hz, 3 JHH = 6.9 Hz, Me)]. 31P{1H} NMR (CDCl3, 293 K, major (SFe,RC)diastereomer, minor (RFe,RC)-diastereomer in brackets): δ 169.46 (t, 1P, 2JPP = 89.2 Hz, P(OMe)3) [173.01 (dd, 1P, 2JPP = 83.2 Hz, 2 JPP = 93.2 Hz, P(OMe)3)], 104.83 (dd, 1P, 2JPP = 37.2 Hz, 2JPP = 89.2 Hz) [93.57 (dd, 1P 2JPP = 37.7 Hz, 2JPP = 83.2 Hz)], 75.35 (dd, 1P, 2JPP = 37.2 Hz, 2JPP = 89.2 Hz) [84.22 (dd, 1P, 2JPP = 37.7 Hz, 2 JPP = 93.2 Hz)], 143.07 (septet, 1P, 1JPF = 713.5 Hz, PF6). MS (ES, CH2Cl2/MeCN): m/z 657 (cation, 100). HRMS (LSI, glycerol): calcd for the cation C35H40FeO3P3þ 657.1539, found m/z 657.1537 (Mþ). Anal. Calcd for C35H40F6FeO3P4 (802.4): C, 52.39; H, 5.02. Found: C, 52.42; H, 4.80.
(RFe ,RC)/(S Fe ,RC)-(η5 -Cyclopentadienyl)(dimethylphosphonato-kP)[propane-1,2-diylbis(diphenylphosphane-kP)]iron, (RFe,RC)/(SFe,RC)-[CpFe(Prophos)PO(OMe)2]. (RFe,RC)/
(SFe,RC)-[CpFe(Prophos)P(OMe)3]I (17:83) (100 mg, 0.16 mmol) was suspended in toluene (10 mL). After boiling for 2 h the solution had become clear. Removal of the solvent afforded (RFe,RC)/(SFe, RC)-[CpFe(Prophos)PO(OMe)2] (17:83) in quantitative yield. Recrystallization from warm petroleum ether (40/60) gave yellow crystals of (SFe,RC)-[CpFe(Prophos)PO(OMe)2], suitable for X-ray analysis. 1 H NMR (toluene-d8, 300 K, major (SFe,RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets, if distinguishable): δ 8.11 (t, 2H, 3 JHH = 8.2 Hz, 3JPH = 9.4 Hz, Ar-H) [8.38 (t, 2H, 3JHH = 7.6 Hz, 3 JPH = 9.2 Hz, Ar-H)], 7.86 (t, 2H, 3JHH = 8.7 Hz, Ar-H) [7.91 (t, 2H, 3 JHH = 9.2 Hz, Ar-H)], 7.617.14 (m, 16H, Ar-H), 4.824.64 (1H, m, CH) [4.184.05 (m, 1H, CH)], 4.59 (s, 5H, Cp-H) [4.54 (s, 5H, CpH)], 3.43 (d, 3H, 3JPH = 10.0 Hz, POMe) [3.70 (d, 3H, 3JPH = 10.2 Hz, POMe)], 3.22 (d, 3H, 3JPH = 10.1 Hz, POMe) [3.29 (d, 3H, 3 JPH = 9.9 Hz, POMe)], 3.122.94 (m, 1H, CH), 2.041.94 (m, 1H, CH), 1.18 (dd, 3H, 3JHH = 7.0 Hz, 3JPH = 10.9 Hz, Me) [1.27 (dd, 3H, 3 JHH = 6.4 Hz, 3JPH = 12.0 Hz, Me)]. 31P{1H} NMR (toluene-d8, 300 K, major (SFe,RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets): δ 131.30 (dd, 1P, 2JPP = 100.7 Hz, 2JPP = 103.8 Hz) [133.79 (dd, 1P, 2JPP = 93.1 Hz, 2JPP = 107.6 Hz)], 113.58 (dd, 1P, 2 JPP = 32.8 Hz, 2JPP = 103.8 Hz) [100.41 (dd, 1P, 2JPP = 33.6 Hz, 2 JPP = 93.1 Hz)], 85.66 (dd, 1P, 2JPP = 32.8 Hz, 2JPP = 100.7 Hz) [94.20 (dd, 1P, 2JPP = 33.6 Hz, 2JPP = 107.6 Hz)]. MS (EI, 70 eV): m/ z 642. Anal. Calcd for C34H37FeO3P3 (642.4): C, 63.57; H, 5.82. Found: C, 62.82; H, 7.04.
(RFe,RC)/(SFe,RC)-(η5-Cyclopentadienyl)(4-methyl-2,6,7trioxa-1-phosphabicyclo[2.2.2]octane-P1)-[propane-1,2-diylbis(diphenylphosphane-kP)]iron Iodide, (R Fe ,R C)/(S Fe ,R C )[CpFe(Prophos)P(OCH2)3CMe]I. A mixture of (RFe,RC)-[CpFe-
(Prophos)I] (100 mg, 0.15 mmol) and P(OCH2)3CMe (45 mg, 0.30 mmol) in chloroform (20 mL) was stirred for 3 h at room temperature. After evaporation of the solvent the residue was washed with ether to give 3674
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Organometallics (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]I (47:53) as a pale yellow powder in 93% (115 mg) yield. Diastereomerically pure crystals of (SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]I, suitable for X-ray analysis, were obtained by crystallization from chloroform/ether. 1 H NMR (CDCl3, 293 K, major (SFe,RC)-diastereomer, minor (RFe, RC)-diastereomer in brackets, if distinguishable): δ 7,777.33 (m, 20H, Ar-H), 4.45 (s, 5H, Cp-H) [4.54 (s, 5H, Cp-H)], 3.713.41 (m, 6H, CH2), 3.161.94 (m, 3H, CH2CH), 1.10 (dd, 3H, 3JPH = 12.0 Hz, 3 JHH = 6.4 Hz, Me) [1.36 (dd, 3H, 3JPH = 11.6 Hz, 3JHH = 6.8 Hz, Me)], 0.59 (s, 3H, Me) [0.62 (s, 3H, Me)]. 31P{1H} NMR (CDCl3, 293 K, major (SFe,RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets): δ 167.46 (dd, 1P, 2JPP = 83.2 Hz, 2JPP = 93.1 Hz) [167.27 (dd, 1P, 2JPP = 77.3 Hz, 2JPP = 95.1 Hz)], 103.78 (dd, 1P, 2 JPP = 38.6 Hz, 2JPP = 93.1 Hz) [96.81 (dd, 1P, 2JPP = 37.8 Hz, 2 JPP = 77.3 Hz)], 76.23 (dd, 1P, 2JPP = 38.6 Hz, 2JPP = 95.6 Hz) [85.46 (dd, 1P, 2JPP = 37.8 Hz, 2JPP = 95.1 Hz)]. MS (ES, MeCN): m/z 681 (cation, 100). HRMS (LSI, glycerol): calcd for the cation C37H40FeO3P3þ 681.1540, found m/z 681.1535 (Mþ). Anal. Calcd for C37H40FeIO3P3 (808.4): C, 54.91; H, 5.11. Found: C, 53.64; H, 4.82.
(RFe,RC)/(SFe,RC)-(η5-Cyclopentadienyl)(4-methyl-2,6,7trioxa-1-phosphabicyclo[2.2.2]octane-P1)-[propane-1,2diylbis(diphenylphosphane-kP]iron Hexafluorophosphate, (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]PF6. (SFe,RC)-
[CpFe(Prophos)NCMe]PF6 (10 mg, 0.014 mmol) and P(OCH2)3CMe (20.6 μL, 0.14 mmol) in chloroform were allowed to stand for 4 d. After evaporation of the solvent the residue was washed with ether to give (RFe,RC)/(SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]PF6 (18:82) as a pale yellow powder in 43% (4.8 mg) yield. Diastereomerically pure crystals of (SFe,RC)-[CpFe(Prophos)P(OCH2)3CMe]PF6, suitable for X-ray analysis, were obtained by crystallization from chloroform/ ether. IR (KBr): ν 841 cm 1 (PF). 1H NMR (CDCl3, 293 K, major (SFe,RC)-diastereomer, minor (RFe,RC)-diastereomer in brackets, if distinguishable): δ 7.687.34 (m, 20H, Ar-H), 4.44 (s, 5H, Cp-H) [4.52 (s, 5H, Cp-H)], 3.653.38 (m, 6H, CH2), 3.121.92 (m, 3H, CH2CH), 1.07 (dd, 3H, 3JPH = 12.0 Hz, 3JHH = 6.4 Hz, Me) [1.34 (dd, 3H, 3JPH = 10.9 Hz, 3JHH = 6.7 Hz, Me)], 0.52 (s, 3H, Me) [0.55 (s, 3H, Me)]. 31P{1H} NMR (CDCl3, 293 K, major (SFe,RC)diastereomer, minor (RFe,RC)-diastereomer in brackets): δ 167.33 (dd, 1P, 2JPP = 83.7 Hz, 2JPP = 93.2 Hz) [167.15 (dd, 1P, 2JPP = 79.3 Hz, 2JPP = 95.1 Hz)], 103.88 (dd, 1P, 2JPP = 39.6 Hz, 2JPP = 93.2 Hz) [96.76 (dd, 1P 2JPP = 37.2 Hz, 2JPP = 79.3 Hz)], 76.18 (dd, 1P, 2JPP = 39.6 Hz, 2JPP = 83.7 Hz) [85.42 (dd, 1P, 2JPP = 37.2 Hz, 2JPP = 95.1 Hz)], 143.06 (septet, 1P, 1JPF = 712.0 Hz, PF6). MS (ES, CH2Cl2/MeCN): m/z 681 (cation, 100). HRMS (LSI, glycerol): calcd for the cation C37H40FeO3P3þ 681.1540, found m/z 681.1552 (Mþ). Anal. Calcd for C37H40F6FeO3P4 (826.5): C, 53.78; H, 4.91. Found: C, 53.25; H, 4.92.
(η5-Cyclopentadienyl)[propane-1,2-diylbis(diphenylphosphane-jP](triphenylphosphite-kP)iron Iodide, [CpFe(Prophos) P(OPh)3]PF6. (RFe,RC)/(SFe,RC)-[CpFe(Prophos)Cl] (300 mg, 0.53
mmol), P(OPh)3 (260 μL, 1 mmol), and NH4PF6 (800 mg, 5 mmol) were stirred in THF (20 mL) for 3 d at room temperature. After removal of the solvent and extraction with dichloromethane/water a chromatography at silica with 100:1 dichloromethane/THF afforded a yellow band, containing the two diastereomers of [CpFe(Prophos)P(OPh)3]PF6 in a ratio of 72:28 in 50% yield (250 mg). 1 H NMR (CDCl3, 300 K, major diastereomer, minor diastereomer in brackets, if distinguishable): δ 8.076.83 (m, 29H, Ar-H), 6.12 (d, 6H, 3 JHH = 7.4 Hz, o-H of P(OPh)3) [6.376.35 (m, 6H, o-H of P(OPh)3)], 4.46 (s, 5H, Cp-H) [4.20 (s, 5H, Cp-H)], 3.322.25 (m, 3H, CH2CH), 1.11 (dd, 3JPH = 11.8 Hz, 3JHH = 6.6 Hz, Me) [0.99 (dd, 3H, 3JPH = 12.0 Hz, 3JHH = 6.3 Hz, Me)]. 31P{1H} NMR (CDCl3, 300 K, major diastereomer, minor diastereomer in brackets):
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δ 157.25 (dd, 1P, 2JPP = 80.1 Hz, 2JPP = 86.2 Hz) [161.63 (dd, 1P, JPP = 74.8 Hz, 2JPP = 84.7 Hz)], 101.63 (dd, 1P, 2JPP = 35.1 Hz, 2 JPP = 80.1 Hz) [85.89 (dd, 1P, 2JPP = 36.6 Hz, 2JPP = 74.8 Hz)], 74.06 (dd, 1P, 2JPP = 35.1 Hz, 2JPP = 86.2 Hz) [75.96 (dd, 1P, 2JPP = 36.6 Hz, 2JPP = 84.7 Hz)], 143.47 (septet, 1P, 1JPF = 712.7 Hz, PF6). MS (ES, MeCN): m/z 843 (cation), 574 (cation P(OPh3), 533 (100, cation P(OPh)3 MeCN). Anal. Calcd for C50H46F6FeO3P4 (988.7): C, 60.74; H, 4.69. Found: C, 60.47; H, 4.76. 2
(RFe,RC)/(SFe,RC)-(η5-Cyclopentadienyl)[propane-1,2-diylbis (diphenylphosphane-kP](tributylphosphine-kP)iron Iodide, (RFe,RC)/(SFe,RC)-[CpFe(Prophos)PBu3]I. To a solution of (RFe,
RC)/(SFe,RC)-[CpFe(Prophos)I] (95:5) (400 mg, 0.60 mmol) in THF (20 mL) was added PBu3 (3 mL, 12 mmol), and the mixture was stirred for 15 h at 323 K. After evaporation of the solvent the residue was dissolved in THF. Chromatography on silica with THF gave a green and a violet band (unreacted [CpFe(Prophos)I]). The orange-red band contained [CpFe(Prophos)PBu3]I. Yield: 170 mg (33%). Diastereomer ratio of [CpFe(Prophos)PBu3]I = 62:38. 1 H NMR (CDCl3, 300 K, major diastereomer, minor diastereomer in brackets, if distinguishable): δ 7.887.01 (m, 20H, Ar-H), 4.48 (s, 5H, Cp-H) [4.29 (s, 5H, Cp-H)], 3.321.78 (m, 3H, CH2CH), 1.740.86 (m, 21H, CH2CH2CH2 and Me), 0.79 (t, 9H, 3JHH = 7.2 Hz, Me). 31 1 P{ H} NMR (CDCl3, 300 K, major diastereomer, minor diastereomer in brackets): δ 102.4 (dd, 1P, 2JPP = 38.1 Hz, 2JPP = 45.02 Hz) [87.06 (dd, 1P, 2JPP = 37.4 Hz, 2JPP = 46.5 Hz)], 66.76 (dd, 1P, 2JPP = 38.1 Hz, 2JPP = 47.3 Hz) [79.28 (dd, 1P, 2JPP = 37.4 Hz, 2JPP = 45.8 Hz)], 29.04 (t, 1P, 2JPP = 46.6 Hz) [28.01 (t, 1P, 2JPP = 45.8 Hz)]. MS (ES, MeCN): m/z 735 (cation, 100). HRMS (ES): calcd for the cation C44H58FeP3þ 735.3095, found m/z 735.3092 (Mþ). Anal. Calcd for C44H58FeIP3 (862.6): C, 61.26; H, 6.78. Found: C, 60.02; H, 7.27. X-ray Analyses. Crystal and refinement data are given in Table 1. X-ray data were collected on a Rigaku RAXIS-RAPID imaging plate diffractometer using Mo KR (graphite monochromated, λ = 0.710 73 Å, fine focus tube, ω-scan) radiation at 173 K or an Oxford Diffraction Gemini Ultra diffractometer (Cu KR radiation, λ = 1.541 84 Å, ω-scan) at 123 K. The structures were solved by DIRDIF-2008,17 SIR97,18 or SHELX 9719 and refined by full-matrix least-squares on F2 by SHELX 97.19 All H atoms were included at calculated positions.
’ ASSOCIATED CONTENT
bS
Supporting Information. 1H and 31P{1H} NMR spectra of all new compounds, temperature-dependent 31P{1H} NMR spectra of a mixture of (RFe,RC)/(SFe,RC)-[CpFe(Prophos) NCMe]PF6 and Diphos, 31P{1H} NMR spectra of [CpFe (Diphos)NCMe]Cl and (RC)-Prophos, and CIF files giving crystallographic data for all the compounds listed in Table 1. This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*(H.B.) Fax: þ49-941-9434439. E-mail: henri.brunner@chemie. uni-regensburg.de. (T.T.) Fax: þ81-47-474-2579. E-mail: tsuno.
[email protected].
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