Steric and Electronic Parameters Characterizing Bulky and Electron

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Steric and Electronic Parameters Characterizing Bulky and Electron-Rich Dialkylbiarylphosphines Olivier Diebolt,†,‡ George C. Fortman,† Herve Clavier,†,‡,§ Alexandra M. Z. Slawin,† Eduardo C. Escudero-Adan,‡ Jordi Benet-Buchholz,‡ and Steven P. Nolan*,†,‡ † ‡

School of Chemistry, University of St-Andrews, St-Andrews KY16 9ST, U.K. Institute of Chemical Research of Catalonia (ICIQ), Avenida Països Catalans 16, 43007, Spain

bS Supporting Information ABSTRACT: The steric and electronic properties of several sterically demanding tertiary phosphines (dicyclohexylphosphino)biphenyl (2a), 2-dicyclohexylphosphino-20 -methylbiphenyl (2b), 2-dicyclohexylphosphino-20 ,60 -dimethoxybiphenyl (2c), 2-dicyclohexylphosphino-20 ,40 ,60 -triisopropylbiphenyl (2d), 2-diphenylphosphino-20 -(N,N-dimethylamino)biphenyl (2e), 2-di-tert-butylphosphino-20 -(N,N-dimethylamino)biphenyl (2f), and di(cyclohexyl)phenylphosphine (2g) have been studied by synthesizing and characterizing iridium complexes of types [IrCl(cod)(L)] (L = 2a-d) and cis-[IrCl(CO)2(L)] (L = 2a-d and 2g). The infrared stretching frequencies of the carbonyl complexes permit an estimation of the ligand donor properties (basicity) and suggest that the donor properties of ligands 2a-d reside between that of 2g and PCy3. The crystal structures of several [IrCl(cod)(L)] (L = 2a-d) and cis-[IrCl(CO)2(L)] (L = 2a-d and 2g) complexes are reported and used to quantify the ligand steric parameter.

’ INTRODUCTION Tertiary phosphines continue to play a major role as ancillary ligands in catalysis. As is a common theme in chemistry and other sciences, the simpler systems are studied and then expanded upon into more unique and specialized systems. In the case of tertiary phosphines, the symmetrical aryl and alkyl ligands such as PCy3, PPh3, and PiPr3 were first rigorously studied and then modified. One salient example is found in the work of Buchwald, whose replacement of one R group in PR3 structures with a biaryl group has resulted in a plethora of catalytically active organometallic complexes. The Buchwald group synthesized monodentate biphenyldiakyl phosphines in 1998.1 They have found applications in numerous fields of homogeneous catalysis.1-6 This is especially true of palladium-catalyzed carbon-carbon,7-13 carbonnitrogen,14,15 and carbon-oxygen16-18 bond-forming processes. The synthetic route leading to this ligand family allows modulation of the nature of the substituents appended to the architectural core and therefore permits fine-tuning of ligand steric and electronic parameters. The flexibility of their syntheses19 allows for a vast range of substitution and, thusly, a considerable array of their properties in catalysis (Figure 1). Tuning the R groups also permits a potential decrease in the reactivity of the ligand toward molecular oxygen.7 In addition, the R1, R2, and R3 substituents influence the size of the ligand but also allow arene coordination with the metal and can promote reductive elimination processes.20Although studies have been compiled on the effects of changing these R groups as a function r 2011 American Chemical Society

of catalytic efficiency, to date there has been no quantification of the influence of the nature of the R group on the basicity of the phosphine ligand itself. It is of great interest to study the properties of these ligands in order to better understand their activity in homogeneous catalysis. Recently our group has published work concerning the bonding enthalpies of a series of phosphines, which included the Buchwald phosphines, to the Au-Cl moiety as shown in eq 1.21 CH2 Cl

½AuðthtÞCl þ PR 3 sf ½AuðPR 3 ÞCl þ tht þ ΔHrxn 30 °C

ð1Þ It was deduced that the ΔHrxn was predominately influenced by the electron-donating abilities of the phosphine ligand. In the present contribution, we hope to extend this study of phosphine ligands on a very fundamental level. Pioneered by the work of Tolman,13,22,23 the electronic and steric properties of tertiary phosphines are now known to have a crucial impact on homogeneous catalysis. Their quantitative measurement is not trivial, and Tolman described two parameters:23 (1) the electronic parameter ν (or TEP), gauged by the infrared CO stretching frequencies of the [Ni(CO)3(L)] (L being the ligand of interest) complex; (2) the steric parameter θ (or cone angle), which allows for the quantification of the steric hindrance around the metal center. Although ν and θ do not fully Received: December 15, 2010 Published: February 14, 2011 1668

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Figure 1. General structure of the biaryl-containing tertiary phosphines.

describe the ligand behavior, they give an overview of their important properties. As mentioned above, Tolman chose to use [Ni(CO)3(L)] to examine the electronic parameter of L. Unfortunately, the starting material used in the synthesis of the nickel complexes, [Ni(CO)4], is extremely toxic and volatile. Moreover, in special cases, the reaction between [Ni(CO)4] and very bulky ligands L can lead to substitution of two carbonyl groups and the formation of three-coordinate [Ni(CO)2L].24,25 In these cases, the Tolman electronic parameter (TEP) cannot be measured. Alternatives to this nickel method have been investigated. Among them, carbonyl complexes of Rh, Cr, Mo, and W have been considered.26-34 Finally, the iridium system cis-[IrCl(CO)2L] was found to be the most general.35,36 The reactions take place in good yields, and the starting dimer [Ir(μ-Cl)(cod)]2 (1)37 (cod = 1,5-cyclooctadiene) is easily manipulated and generally less toxic. Its reaction with a coordinating ligand L (L generally is a 2 e- donor) leads to the monomeric species [IrCl(cod)L], which reacts with carbon monoxide to form the dicarbonyl species cis-[IrCl(CO)2L]. We wish to broaden the scope of phosphines for which this fundamental knowledge of steric and electronic parameters is known to the Buchwald phosphines by utilizing a similar strategy. Herein, we report the synthesis of [IrCl(cod)L] and cis-[IrCl(CO)2L] complexes where L is a series of unsymmetrical tertiary phosphines. Measurement of the carbonyl stretching frequencies of the latter complexes allowed for the first estimation of the electronic parameters associated with the Buchwald phosphines. Additionally, X-ray diffraction data on single crystals, for the above-mentioned complexes, are reported and allowed for a quantitative comparison of the steric bulk of these ligands.

’ RESULTS AND DISCUSSION To gauge the influence of the substitution around the ligands, the phosphines depicted in Figure 2 were selected. Phosphines 2a-d bear two cyclohexyl groups, their dissimilarity residing in the substitution around the second aryl moiety, R1, R2, and R3. Phosphines 2e and 2f, bearing phenyl and tert-butyl substituents, would permit observation of the influence of the group R. Of note, several unsuccessful attempts to synthesize [Ni(CO)3(L)] complexes with the Buchwald ligand series were conducted. These ligands simply appear to be too sterically demanding and do not afford simple products amenable to facile characterization. Therefore the selection of the iridium system appears to be the judicious choice. Finally, to permit a comparison, the steric and electronic properties of PCy2Ph (2g), as a model complex, were also investigated. Synthesis of [IrCl(cod)L] Complexes. The ligands shown in Figure 2 were reacted with [Ir(μ-Cl)(cod)]2 (1) in THF at room

Figure 2. Tertiary phosphines used in this study.

Scheme 1. Synthesis of [IrCl(cod)L] Complexes

temperature for 3 h (Scheme 1) and resulted in the square-planar d8 Ir(I) complexes [IrCl(cod)L]. Unfortunately, the phosphine 2f did not react with the starting dimer. Reactions with this ligand conducted overnight at 80 °C led to the recovery of the unreacted starting materials. The steric bulk conferred by the two tert-butyl groups may impede this reaction. Of note, 2b reacted slowly with [Ir(μ-Cl)(cod)]2 at room temperature, and the mixture had to be stirred at 60 °C to afford complete conversion. The obtained complex 3b is highly unsymmetrical in NMR, giving four different signals in 1H and 13C for the CH of the cyclooctadiene. Moreover, the 31P shift appeared very broad at room temperature, which suggests hindered rotation about the Ir-P bond in solution. Single crystals suitable for X-ray analysis were grown by slow evaporation of solvents at room temperature from saturated solutions containing the complex.38 The resulting structural solutions are displayed in Figure 3. Unfortunately, repeated attempts to crystallize complex 3e failed. The iridium atom adopts a square-planar geometry around the metal center in all structures obtained. Selected bond lengths and angles are given in Tables 1 and 2 respectively. 1669

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Figure 4. ORTEP representation showing weak Ir---H anagostic interaction in complex 3a.

Figure 3. ORTEP representation of [IrCl(cod)L] (3a-d). Hydrogens are omitted for clarity.

Table 1. Selected Bond Lengths (Å) for the [IrCl(cod)L] Complexes

a

complex

Ir-P (Å)

Ir-Cl

Ir-cod (av)a

Ir-cod (av)b

3a

2.3562(4)

2.3521(6)

2.123(2)

2.184(2)

3b

2.3577(3)

2.3625(3)

2.121(2)

2.182(2)

3c

2.3335(5)

2.3676(5)

2.117(2)

2.178(3)

3d

2.346(1)

2.359(1)

2.116(6)

2.178(8)

COD cis to phosphine. b COD trans to phosphine.

Table 2. Selected Angles (deg) for the [IrCl(cod)L] Complexes complex

P-Ir-Cl

P-Ir-Ccis-cod (av)

P-Ir-Ctrans-cod (av)

3a

92.504(17)

92.50(5)

161.26(5)

3b

93.682(10)

92.83(4)

161.3(4)

3c

90.335(17)

95.03(6)

161.5(1)

3d

89.64(5)

96.2(1)

161.3(2)

The Ir-P bond distances are similar in all complexes and fall within the range 2.33-2.36 Å. As expected, the CH2dCH2 trans to the Cl is slightly closer to the metal center than the CH2dCH2 trans to the phosphine. This is assuredly due to the π-basicity of the Cl ligand as opposed to the weakly π-acidic phosphine. Consequently, this would result in greater back-donation and a slightly higher bond order for the Ir-COD for the side trans to the chlorine ligand. Similar in character, structures of [IrCl(cod)(PEt3)]39 and [IrCl(cod)(PBz3)]40 have previously been published. No significant deviations from the norm appear to be present for the PR2R0 complexes presented herein. Interestingly for the Buchwald ligand series, each tertiary phosphine adopts a different spatial conformation. The complexes containing more substituted biphenyls (3c and 3d) tend

to direct the second phenyl ring away from the metal center, whereas the complexes with less substituted biphenyls (3a and 3b) appear to direct the second phenyl ring toward the metal. The common thread appears to be ortho substitution of the pendant aryl ring. Indeed, there appears to be a weak Ir---H anagostic interaction in these complexes. Complexes 3a and 3b contain Ir---H distances41 of 2.640 and 2.710 Å, where the H atom donor is the C-H that is ortho on the pendant aryl ring of the phosphine. As shown in Figure 4, the H atom appears to align along the z-axis, which is perpendicular to the coordination plane of the metal center. For complexes 3c and 3d the shortest Ir---H distances are 3.383 and 3.047 Å, respectively. Here the H atom is one-bonded to a cyclohexyl ring. These M---H distances are just beyond the generally accepted distance for an anagostic interaction.42 This highlights the effects of the substitution on the second aryl group of the biphenyl moiety on general molecular orientation (at least in the solid state). This possible coordination mode, although weak, may be a way to stabilize coordination complexes and help explain the unique reactivities displayed by complexes bearing members of this ligand family. It cannot, however, be discredited that these conformations are solely due to the steric bulk of the Buchwald ligands. The larger phosphines, 2c and 2d, may indeed adopt an orientation in which the biaryl ring faces away from the metal simply to reduce steric interactions with the metal center. In this case the apparent anagostic M---H interactions would be secondary in nature. Synthesis of cis-[IrCl(CO)2L] Complexes. Dichloromethane solutions of [IrCl(cod)L] placed under 1 atm of CO for 1 h resulted in clean substitution of the cyclooctadiene to form the corresponding greenish complexes 4a-d and 4g, cis-[IrCl(CO)2L] (see Scheme 2). Surprisingly, most of these dicarbonyl complexes are not stable toward air and need to be handled under inert atmosphere. Unfortunately, the carbonylation of 3e led to the formation of two unknown products. Attempts to isolate these products by crystallization or flash chromatography led to product decomposition. 31 P NMR chemical shifts differ, as expected, as a function of the ligand and range between 19.7 and 40.9 ppm (see Table 3). In contrast, the 13C signals corresponding to the carbonyl are very similar. The carbonyl carbon cis to the phosphine (trans to the 1670

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Cl) retained a chemical shift at approximately 169 ppm and 2 JCP = 12 Hz, while the carbon in trans position displayed a chemical shift at ca. 178 ppm and 2JCP = 115 Hz. Scheme 2. Synthesis of cis-[IrCl(CO)2L] Complexes

Table 3. Selected Chemical Shifts (ppm) of the cis-[IrCl(CO)2L] Complexes complex

δ 31P

δ C(cis-CO) (2JCP, Hz)

δ C(trans-CO) (2JCP, Hz)

4a

29.3

168.9 (12.1)

178.1 (115.1)

4b

32.8

168.8 (12.2)

178.3 (115.1)

4c

29.9

168.8 (12.4)

178.2 (115.1)

4d

40.9

169.4 (11.8)

178.1 (114.7)

4g

19.7

168.7 (12.4)

178.8 (115.7)

Single crystals suitable for X-ray analysis of 4a-d and 4g were obtained by slow evaporation of solvents from saturated solutions. ORTEP diagrams of the XRD data are shown in Figure 5, and selected bond lengths and angles are given in Tables 4 and 5. Compared to the cod complexes, the Ir-P bond is slightly longer for complexes 4a-d and 4g. Metal to CO back-donation is stronger than in the cod complexes, and thus there is less donation into the P-C σ* orbitals, which in turns causes the Ir-P bond distance to increase. Also lack of the spatial restriction introduced by the chelating cod ligand allows the bond angles to approach the classical 90° found in square-planar complexes. Additionally, the orientation of the biphenyl ring is the same as that found in the cod complexes. That is, the more substituted biphenyls are positioned away from the phosphorus and metal center, whereas the biphenyls with less substitution are directed toward the metal. Despite the fact that the shortest Ir---H distances are more uniform for complexes 4a-d (2.918-2.946 Å) than for 3a-d (2.640-3.383 Å), the H atoms closest to the metal center are the same as those in the cod complexes. That is, for complexes 4a and 4b, the H is attached to the pendant aryl ring, while for complexes 4c and 4d the H is bonded to a cyclohexyl ring. Again, it must be stated that the orientation of the biaryl rings may be solely due to ligand size. The larger ligands 2c and 2d may twist away from the metal center in an attempt to reduce steric pressure about the metal center. Comparison of metrical parameters between complexes 4a-d and 4g highlights no significant variation in bond angles or lengths about the Ir metal center as a function of the pendant aryl ring. There does not, however, appear to be any weak Ir---H

Figure 5. ORTEP representation of cis-[IrCl(CO)2L] complexes 4a-d and 4g. Hydrogens are omitted for clarity. 1671

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Table 4. Selected Bond Lengths (Å) for cis-[IrCl(CO)2L] Complexes 4a-d and 4g complex

a

Ir-P (Å)

Ir-COa

Ir-Cl

Ir-COb

4a

2.380(2)

2.348(2)

1.828(8)

4b

2.365(1)

2.328(1)

1.826(3)

1.896(8) 1.883(3)

4cc

2.385(3), 2.389(3)

2.359(3), 2.328(3)

1.85(1), 1.82(1)

1.88(1), 1.86(1)

4d

2.373(1)

2.347(1)

1.856(4)

1.900(4)

4g

2.373(2)

2.355(2)

1.855(8)

1.899(9)

CO cis to phosphine. b CO trans to phosphine. c Complex contains two independent molecules within the unit cell.

Table 5. Selected Angles (deg) for cis-[IrCl(CO)2L] Complexes 4a-d and 4g

Table 6 νCO, cm-1

av νCO, cm-1

TEP, cm-1a

PPh3b PCy2Ph (2g)

2002, 2085 1991, 2075

2043.5 2033.0

2068.9 2058.0

91.5(1)

PiPr3b

1986, 2077

2031.5

2059.2

88.8(5),

Cy-JohnPhos (2a)

1989, 2073

2031.0

2056.3

174.8(5) 174.9(1)

94.4(6) 91.0(2)

S-Phos(2c)

1987, 2070

2028.5

2054.1

PCy3b

1984, 2072

2028.0

2056.4

173.1(3)

90.7(4)

Me-Phos (2b)

1986, 2069

2027.5

2053.3

X-Phos(2d)

1985, 2070

2027.5

2053.3

IPrc ICyc

2067, 1981 2065, 1981

2023.9 2023.0

2051.5 2049.6

complex

P-Ir-Cl

P-Ir-COa

P-Ir-COb

COa-Ir-COb

4a

87.15(6)

91.8(2)

176.9(2)

91.4(3)

4b

87.81(11)

92.07(9)

174.19(9)

4cc

90.4(1),

89.9(3),

178.7(4),

4d

89.8(1) 88.33(3)

89.3(4) 91.9(1)

4g

90.09(7)

90.3(2)

ligand

a

CO cis to phosphine. b CO trans to phosphine. c Complex contains two independent molecules within the unit cell.

anagostic interaction in 4g. The closest Ir---H distance for complex 4g is 3.110 Å. To date, only one other related structure has been reported. Schumann et al. published the structure of cis-[IrCl(CO)2(PtBu3)] in 1979.43 The Ir-P bond length of cis-[IrCl(CO)2(PtBu3)] is slightly longer (2.43(1) Å) than that of structures of the carbonyl complexes reported herein (2.365(1)-2.385(3) Å). Most strikingly, the bond angles about the Ir metal center are somewhat more perturbed in cis-[IrCl(CO)2(PtBu3)] (P-IrCl = 94.8(5)o; P-Ir-cisCO = 98.2(15)o) than in complexes 4ad and 4g, suggesting that the unsymmetrical phosphine ligands studied herein are not as sterically demanding as the PtBu3 ligand. Infrared Spectroscopy and Derived Electron Donor Property. Measurement of the characteristic νCO stretching frequencies of the cis-[IrCl(CO)2(PR3)] complexes by FT-IR spectroscopy was performed. As expected, two bands of similar intensity (as typical of cis-CO in square-planar complexes) in the carbonyl region were observed. Complexes 4a-d displayed similar stretches in the ranges 1980-1989 and 20692073 cm-1, slightly lower than that of complex 4g, where νCO = 1991 and 2075 cm-1 were recorded. It is well known that changes in carbonyl stretching frequency are related to the electron-donating/withdrawing abilities of other ligands bound to the metal center. As such, we compared the carbonyl stretching frequencies of complexes 4a-d and 4g to other [IrCl(CO)2(L)] complexes (Table 6). From Table 6 it can be seen that all of the Buchwald family phosphines investigated appear to be more electron donating than PCy2Ph. Of the set, Cy-JohnPhos appears to be the least donating, while X-Phos ≈ Me-Phos are the most donating. The carbonyl stretches of 4b-d suggest that S-Phos, Me-Phos, and X-Phos are very similar in basicity to PCy3. These biaryl phosphines are less donating than the N-heterocyclic carbenes (NHCs) ICy and IPr.36a A method initially developed by Crabtree35 and later refined by our group36a allows for the determination of the Tolman electronic parameter (TEP) by correlation of the CO stretching

a

TEP values in italics calculated from linear regression derived in ref 36a. νCO for [IrCl(CO)2(L)] from ref 35. TEP values from ref 23. c νCO for [IrCl(CO)2(L)] from ref 36a. TEP values from ref 25. b

frequencies. The TEP can be calculated using the correlation shown in eq 2. TEP ¼ 0:847  ðνCOaverage Þ þ 336

ð2Þ

The results are shown in Table 6. It was found that the electronic parameters of the biaryl-containing phosphines fall between 2054 and 2056 cm-1. The estimated TEPs suggest a slightly different ordering of electron-donating ability but in general still imply a higher basicity than PCy2Ph and very similar to that of PCy3. It should be stated, however, that these derived TEP values are estimations at best, and the direct comparison of Ir complexes and the primary data they furnish should be a better gauge of their electronic parameter.44 The high electron-donating ability of the biaryl phosphines correlate well with catalytic performance, as is observed for the facile oxidative addition of aryl chlorides at room temperature for palladium catalysts bearing strong σ-donating ligands.45 Steric Parameter. The second parameter described by Tolman is the cone angle (θ). It is defined as a “cylindrical cone from the center of the P atom, which just touches the van der Waals radii of the outermost atoms of the model”.23 The phosphine ligands 2 are nonsymmetrical, and the corresponding symmetrical phosphines bearing three biaryl substituents (which would allow the calculation of θ) have not been reported. As an alternative, a computational method has been developed by Cavallo et al. that should be useful in the present system.46 The parameter %Vbur is defined as the amount of the volume of a sphere centered on the metal occupied by atoms of a ligand. The putative metal atom was positioned at 2.334 Å (the shortest bond length of all the structures obtained in this study; that of complex 3c) from the phosphorus atom, and the radius of the sphere was chosen as 3.5 Å. The calculated values for the complexes reported herein and of other relevant ligands are shown in Figure 6.47 1672

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Table 7. Calculated %Vbur Valuesb for Ligands 2a-d Using [AuCl(L)]c and [IrCl(CO)2Cl] Complexesa [AuCl(L)]c

[IrCl(CO)2(L)]

ligand

2.00 Å

2.28 Å

2.00 Å

2.28 Å

2a

51.0

46.7

40.2

35.0

2b

53.6

49.3

40.6

35.4

2c 2d

53.7 57.4

49.7 53.1

38.0 38.9

32.6 33.4

2g

38.0

32.7

36.8

31.6

a

The M-L distances of 2.00 and 2.28 Å were used to achieve consistency with ref 48. b Values calculated using ref 46b. c Values obtained from ref 48.

Figure 6. Selected %Vbur (%) calculated with Ir-P = 2.334 Å. Values in bold are based on the [Ir(Cl)(cod)L] X-ray structures, and values in italics are based on [Ir(Cl)(CO)2L] X-ray structures. Calculated using ref 46b. aValue based on XRD data from ref 43. bValues based on XRD obtained from ref 36a.

Upon examination of these data, the first observation is that all biaryl phosphines are relatively bulky (2a-d and 2g), the %Vbur being in the range 29-35%. Values determined from structures of [Ir(Cl)(cod)L] and cis-[Ir(Cl)(CO)2L] were found to vary by no more than 1.2%. Surprisingly, increasing the substitution (from 2a to 2d) decreases the steric factor. This may be the result of the aforementioned availability of the ortho H on the pendant aryl ring and subsequent weak Ir---H anagostic interaction. Indeed, the phosphines 2a and 2b have a %Vbur 35.0/33.8 and 34.1/34.4% (cod/(CO)2 complexes), respectively, whereas the substituted phosphines 2c and 2d have a lower buried volume value of approximately 31%. From the crystal structures in Figures 3 and 5, it can be stated that the more highly substituted biphenyl ligands shift the substituted ring away from the metal, whereas the second phenyl ring is angled toward the Ir center in the structures of 3a/b and 4a/b. Of the carbonyl complexes examined, PCy2Ph (2g) possesses the lowest %Vbur (30.6%). This is in line with the obvious difference of the lack of the pendant aryl group and additionally consistent with the lack of any significant Ir---H anagostic interaction in complex 4g. The structure of cis-[IrCl(CO)2(PtBu3)] has been reported.43 Using the same bond distance (2.334 Å), a value of 34.9% was calculated for the buried volume of PtBu3 in this iridium environment. This value is nearly identical to the one calculated for 2a. One advantage of the %Vbur calculation over Tolman’s cone angle is that it allows for a direct comparison between NHCs and phosphines. Again, using the bond distance of 2.334 Å, values were calculated for the reported structures36 of [IrCl(cod)(NHC)] and cis-[IrCl(CO)2 (NHC)], where

NHC = ICy, IMes, IAd, and IPr. Of the NHCs only the extremely bulky IAd ligand is of a similar size as the biarylphosphines examined here. Interestingly, the %Vbur of ligands 2a-d appears to be heavily dependent upon the metal center. For example, X-Phos was calculated to have a %Vbur of 57.4-53.1% for [Au(X-Phos)Cl].48 For complex 4d, using the same values for M-L distance as those used for the gold calculation, we obtained values of 38.9 and 33.5% for %Vbur. Shown in Table 7 is a comparison of %Vbur of ligands 2a-d in the complexes [IrCl(CO)2(L)] and [AuCl(L)]. The buried volume for all of the biaryl phosphines varies by more than 10% depending on whether the system is [AuCl(L)] or [IrCl(CO)2Cl]. Conversely, the %Vbur for PCy2Ph (2g) varies by less than 1.5%. This exemplifies a possible fluctionality of these biaryl ligands. These ligands can apply different steric pressures on the metal center depending upon the steric environment about the coordination sphere of the metal. Ligand flexibility has been shown to enhance catalytic activity,49 and this may help explain why these biaryl-containing phosphines have repeatedly been shown to be excellent ligands in catalytic systems.

’ CONCLUSION New iridium complexes bearing biaryl phosphine ligands [IrCl(cod)L] 3a-e and 3g have been successfully synthesized and characterized. Only the very bulky phosphine 2f did not react with the dimer 1. Placed under one atmosphere of carbon monoxide, 3a-d and 3g gave the dicarbonyl complexes cis-[IrCl(CO)2(L)] 4a-d and 4g. The carbonyl stretching frequencies of these complexes suggest that IPr > X-Phos ≈ Me-Phos ≈ PCy3 ≈ S-Phos > Cy-DavePhos > PCy2Ph . PPh3 in terms of electron-donating ability. The characterization of the complexes by XRD allowed for the calculation of %Vbur of these ligands in the square-planar environment. For the square-planar Ir systems studied here, some Buchwald phosphine ligand family members were found to have relatively medial %Vbur (29-35%). It was shown that increasing the substitution on the pendant aryl moiety caused a decrease in ligand %Vbur that may arise from weak M---H anagostic interactions between the ortho C-H pendant aryl moiety and metal center. Most interestingly was a substantial (>10%) change in %Vbur for ligands 2a-d between different metal complexes. This large change demonstrates that the biaryl phosphines are indeed flexible, and this important structural feature may help explain the attractive catalytic behavior of complexes that incorporate these ligands. 1673

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’ EXPERIMENTAL SECTION General Considerations. All reactions were carried out using standard Schlenk techniques under an atmosphere of dry argon or in an MBraun glovebox containing dry argon and less than 1 ppm oxygen. Ligands 2a-g were purchased from Sigma-Aldrich Chemicals. [IrCl(cod)]2 was graciously donated from Umicore. [IrCl(cod)(PCy2Ph)] was prepared following literature procedures.50 NMR solvents were dried over molecular sieves and degassed with argon before use. 1H, 13C, and 31P NMR spectra were recorded on a Bruker 400 or 300 MHz spectrometer at ambient temperature. IR spectra were recorded on a FTIR Bruker Tensor 27 with an ATR cell in CH2Cl2. Synthesis of [IrCl(cod)(2a)] (3a). In a glovebox, a round-bottom flask was charged with [Ir(μ-Cl)(COD)]2 (200 mg, 0.298 mmol), 2a (210 mg, 0.600 mmol), and dry toluene (10 mL). The solution was stirred at room temperature for 3 h, while the product precipitated. The solvent was evaporated, and 20 mL of acetone was added. The resulting suspension was filtered and washed with acetone, leading to 387 mg (94%) of a yellow microcrystalline product. 1H NMR (CDCl3): δ(ppm) 0.92-1.14 (m, CH2, 6H), 1.18-1.33 (m, CH2, 2H), 1.38-1.71 (m, CH2, 14H), 1.93-2.17 (m, CH2, 6H), 2.47-2.57 (m, CH-Cy, 2H), 2.74 (br s, CH-cod, 2H), 4.74-4.79 (m, CH-cod, 2H), 7.15-7.21 (m, Ph-H, 2H), 7.30-7.38 (m, Ph-H, 6H), 7.83-7.89 (m, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm) 26.4 (s, CH2), 27.9 (d, J = 9.7 Hz, CH2), 29.1 (s, CH2), 30.5 (d, J = 5.1 Hz, CH2), 31.7 (s, CH2), 33.6 (s, CH2), 36.0 (d, J = 23.1 Hz, CH-Cy), 53.4 (s, CH-cod), 87.2 (s, CH-cod), 87.4 (s, CH-cod), 126.2 (d, J = 7.3 Hz, CH-Ph), 127.2 (d, J = 34.1 Hz, C-Ph), 127.9 (s, CHPh), 128.0 (s, CH-Ph), 129.1 (s, CH-Ph), 130.1 (s, CH-Ph), 132.1 (d, J = 5.9 Hz, CH-Ph), 132.6 (d, J = 6.9 Hz, CH-Ph), 141.8 (s, Ph-C), 145.9 (d, J = 6.7 Hz, CH-Ph). 31P NMR (CD2Cl2): δ(ppm) 18.71. Anal. Calcd for C32H43ClIrP (MW 686.33): C, 56.00; H, 6.31. Found: C, 56.30; H, 6.32. Synthesis of [IrCl(cod)(2b)] (3b). In a glovebox, a roundbottom flask was charged with [Ir(COD)Cl]2 (200 mg, 0.298 mmol), 2b (217 mg, 0.600 mmol), and dry toluene (3 mL). The solution was stirred at 60 °C for 8 h. After this time, the volatiles were evaporated, and the resulting orange solid was dissolved in 3 mL of acetone. To this solution was added 15 mL of tert-butylmethyl ether to precipitate the product. Isolation by filtration leads to 319 mg (77%) of a yellow microcrystalline solid. 1H NMR (CD2Cl2): δ(ppm) 0.72 (m, CH2, 1H), 0.86-1.21 (m, CH2, 6H), 1.27-1.37 (m, CH2, 1H), 1.44-1.82 (m, CH2, 14H), 1.89-2.35 (m, CH2, 11H) (this multiplet contains a singlet integrating for three protons corresponding to CH3), 2.71 (pseudosept, J = 3.5 Hz, CH-cod, 1H), 2.89-2.97 (m, CH-cod, 1H), 4.59 (pseudosept, J = 3.7 Hz, CH-cod, 1H), 4.68 (pseudosept, J = 3.6 Hz, CH-cod, 1H), 6.97-7.03 (m, Ph-H, 1H), 7.05-7.14 (m, Ph-H, 2H), 7.14-7.24 (m, Ph-H, 3H), 7.25-7.35 (m, Ph-H, 2H), 7.53-7.51 (m, Ph-H, 1H), 7.75 (br d, J = 6.8 Hz, CH-Ph, 1H). 13C NMR (CD2Cl2): δ(ppm) 20.8 (s, CH3), 26.6 (d, J = 4.8 Hz, CH2), 27.8 (d, J = 11.1 Hz, CH2), 27.9 (d, J = 13.8 Hz, CH2), 28.0 (d, J = 11.1 Hz, CH2), 28.1 (d, J = 9.3 Hz, CH2), 29.0 (br s, CH2), 29.7 (br s, CH2), 30.7 (br s, CH2), 30.9 (d, J = 1.5 Hz, CH2), 32.8 (d, J = 4.7 Hz, CH2), 33.0 (d, J = 2.8 Hz, CH2), 34.2 (d, J = 3..2 Hz, CH2), 34.6 (d, J = 25.2 Hz, CH-Cy), 36.7 (d, J = 23.7 Hz, CH-Cy), 53.0 (s, CH-cod), 55.2 (s, CH-cod), 87.8 (d, J = 14.0 Hz, CH-cod), 88.0 (d, J = 12.3 Hz, CH-COD), 125.5 (s, CH-Ph), 125.7 (d, J = 10.1 Hz, CH-Ph), 128.3 (s, CH-Ph), 129.1 (br s, CH-Ph), 129.0 (br d, J = 1.7 Hz, CH-Ph), 131.0 (br d, J = 3.2 Hz, CH-Ph), 133.2 (d, J = 6.3 Hz, CH-Ph), 135.9 (br d, J = 14.6 Hz, CH-Ph), 136.1 (s, CPh), 141.4 (s, C-Ph), 145.0 (br s, C-Ph). 31P NMR (CD2Cl2): δ(ppm) 28.52 (br s). Anal. Calcd for C38H57ClIrPO (2 þ TBME) (MW 788.50): C, 57.88; H, 7.29. Found: C, 57.84; H, 6.69. Synthesis of [IrCl(cod)(2c)] (3c). In a glovebox, a round-bottom flask was charged with [Ir(cod)Cl]2 (100 mg, 0.149 mmol), 2c (122 mg, 0.298 mmol), and dry toluene (3 mL). The resulting solution was stirred at room temperature for 3 h. The solvent was then evaporated, and the

ARTICLE

resulting solid added with cold hexane. The resulting suspension was filtered and washed with cold hexane, leading to 211 mg (94%) of a yellow, microcrystalline solid. 1H NMR (CD2Cl2): δ(ppm) 0.62-0.85 (m, CH2, 2H), 1.02-1.22 (m, CH2, 4H), 1.30-1.86 (m, CH2, 16H), 1.94-2.27 (m, CH2, 6H), 2.55 (q, 2JHH = 10.5 Hz, CH-Cy, 2H), 2.99 (br s, CH-cod, 2H), 3.71 (s, CH3, 6H), 4.69 (br s, CH-cod, 2H), 6.68 (d, 2 JHH = 8.4 Hz, Ph-H, 2H), 6.92-6.99 (m, Ph-H, 1H), 7.35-7.45 (m, Ph-H, 3H), 7.66-7.75 (m, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm) 26.5 (s, CH2), 27.6 (d, JCP = 11.3 Hz, CH2), 28.2 (d, JCP = 11.7 Hz, CH2), 29.5 (m, CH2), 31.0 (m, CH2), 33.2 (m, CH2), 34.7 (d, 1JCP = 26.5 Hz, CH-Cy), 55.5 (s, CH3), 88.3 (d, 1JCP = 13.8 Hz, CH-Cy), 104.0 (s, Ph-CH), 125.0 (d, JCP = 12.1 Hz, CH-Ph), 126.3 (d, JCP = 31.0 Hz, C-Ph), 129.4 (d, JCP = 1.8 Hz, CH-Ph), 130.0 (s, CH-Ph), 134.0 (d, JCP = 5.8 Hz, CH-Ph), 136.5 (d, JCP = 18.0 Hz, CH-Ph), 139.4 (s, C-Ph), 158.3 (s, C-Ph). 31P NMR (CD2Cl2) δ(ppm): 37.01. Anal. Calcd for C33H45ClIrOP (MW 746.38): C, 54.71; H, 6.35. Found: C, 54.77; H, 6.43. Synthesis of [IrCl(cod)(2d)] (3d). In a glovebox, a roundbottom flask was charged with [Ir(COD)Cl]2 (100 mg, 0.149 mmol), 2d (142 mg, 0.298 mmol), and dry toluene (3 mL). The resulting solution was stirred at room temperature for 3 h. The solvent was then evaporated, and the resulting solid added with cold hexane. The resulting suspension was filtered and washed with cold hexane, leading to 175 mg (61%) of a yellow, microcrystalline solid. 1H NMR (CD2Cl2): δ(ppm) 0.72-2.58 (m, CH2-cod; CH2-Cy, CH3-iPr, 47H), 2.66-2.85 (m, 3H), 2.98 (sept, 2JHH = 6.9 Hz, CH-iPr, 2H), 3.23 (m, 1H), 4.73 (m, CH-COD, 1H), 7.08 (ddd, J = 7.6 Hz, J = 2.9 Hz, J = 1.7 Hz, Ph-H, 1H), 7.11 (s, Ph-H, 2H), 7.39 (tt, J = 7.5 Hz, J = 1.6 Hz, Ph-H, 1H), 7.47 (bt, J = 7.6 Hz, Ph-H, 1H), 7.86-7.97 (m, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm) 22.4, 22.9, 24.2, 25.9, 26.5, 26.7, 27.1, 27.5, 27.9, 28.3, 28.5, 29.5, 30.5, 31.0, 31.3, 31.7, 32.8, 33.8, 34.8, 35.6, 36.4, 36.8, 88.2 (s, CH-cod), 88.3 (s, CH-cod), 121.1 (s, CH-Ph), 121.7 (s, CH-Ph), 125.1 (d, JPC = 12.0 Hz, CH-Ph), 128.6 (d, JPC = 2.0 Hz, CH-Ph), 135.2 (d, JPC = 6.1 Hz, CH-Ph), 136.9 (s, C-Ph), 144.0 (s, C-Ph), 147.0 (s, C-Ph), 149.3 (s, CPh). 31P NMR (CD2Cl2): δ(ppm) 38.86. Anal. Calcd for C41H61ClIrP (MW 812.57): C, 60.60; H, 7.57. Found: C, 60.28; H, 7.45. Synthesis of [IrCl(cod)(2e)] (3e). In a glovebox, a round-bottom flask was charged with [Ir(cod)Cl]2 (100 mg, 0.149 mmol), 2e (114 mg, 0.298 mmol), and dry toluene (3 mL). The resulting solution was stirred at room temperature for 3 h. The solvent was then evaporated, and the resulting solid added with cold hexane. The resulting suspension was filtered and washed with cold hexane, leading to 139 mg (65%) of a yellow microcrystalline solid. 1H NMR (CD2Cl2): δ(ppm) 8.14 (ddd, J = 13.6 Hz, J = 7.6 Hz, J = 1.2 Hz, H-Ph), 7.78 (m, 2H, H-Ph), 7.497.16 (m, 10H, H-Ph), 7.10 (m, 3H, H-Ph), 6.68 (dd, J = 8.1 Hz, J = 0.9 Hz, 1H, H-Ph), 5.08 (m, 1H, CH-cod), 4.98 (m, 1H, CH-cod), 2.88 (m, 1H, CH-cod), 2.59 (m, 1H, CH-cod), 2.31 (m, 2H, -CH2-cod), 2.20 (s, 8H, N-(CH3)2 and -CH2-cod), 1.91 (m, 1H, CH2-cod), 1.80 (m, 1H, -CH2-cod), 1.57 (m, 2H, CH2-cod). 13C NMR (CD2Cl2): δ(ppm) 150.5 (s, C-Ph), 146.6 (d, JCP = 2.2 Hz, C-Ph), 140.4 (s, CH-Ph), 140.2 (s, CH-Ph), 136.7 (d, JCP = 12.3 Hz, CH-Ph), 134.9 (d, JCP = 10.4 Hz, CH-Ph), 133.1 (d, JCP = 6.6 Hz, CH-Ph), 132.8 (s, CH-Ph), 132.5 (d, JCP = 2.2 Hz, C-Ph), 130.8 (m, CH-Ph), 130.7 (m, CH-Ph), 130.4 (m, CH-Ph), 130.2 (m, CH-Ph), 130.0 (d, JCP = 2.3 Hz, CH-Ph), 129.8 (m, CH-Ph), 129.5 (m, CH-Ph), 128.6 (s, CH-Ph), 127.4 (d, JCP = 9.9 Hz, CH-Ph), 127.2 (d, JCP = 9.6 Hz, CH-Ph), 125.40 (d, JCP = 13.9 Hz, CHPh), 119.9 (s, CH-Ph), 117.4 (s, CH-Ph), 91.6 (d, JCP = 13.9 Hz, CHcod), 91.0 (d, JCP = 14.4 Hz, CH-cod), 53.7 (br s, CH-cod), 52.8 (br s, CH-cod), 42.8 (s, N-CH3), 33.9 (br s, CH2-cod), 33.07 (br s, CH2-cod), 30.2 (br s, CH2-cod), 29.3 (br s, CH2-cod). 31P NMR (CD2Cl2): δ(ppm) 27.76. Anal. Calcd for C34H48ClIrNP (MW 717.30): C, 56.93; H, 5.06; N, 1.95. Found: 56.83; H, 5.16; N, 2.05. Synthesis of cis-[IrCl(CO)2(2a)] (4a). A flask was charged with 3a (80 mg, 0.117 mmol) and dichloromethane (4 mL). A balloon filled 1674

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Organometallics with CO was connected to the flask. The orange solution rapidly turned yellow at room temperature. After 1 h, the solvent was evaporated and the resulting solid was washed with hexane (2  3 mL), affording 62 mg (84%) of a pale green powder. 1H NMR (CD2Cl2): δ(ppm) 0.97-1.16 (m, CH2-Cy, 6H), 1.21-1.36 (m, CH2-Cy, 2H), 1.39-1.53 (m, CH2Cy, 2H), 1.53-1.73 (m, CH2-Cy, 6H), 1.74-1.83 (m, CH2-Cy, 2H), 1.98-2.08 (m, CH2-Cy, 2H), 2.25 (m, CH-Cy, 2H), 7.15-7.19 (m, CH-Ph, 1H), 7.30-7.47 (m, CH-Ph, 7H), 7.67-7.74 (m, CH-Ph, 1H). 13 C NMR (CD2Cl2): δ(ppm) 26.5 (s, CH2-Cy), 27.5 (s, CH2-Cy), 27.7 (d, JCP = 2.1 Hz, CH2-Cy), 30.1 (d, JCP = 2.7 Hz, CH2-Cy), 31.3 (s, CH2Cy), 35.5 (d, JCP = 27.9 Hz, CH-Cy), 125.3 (d, JCP = 43.2 Hz, C-Ph), 127.1 (d, JCP = 9.1 Hz, CH-Ph), 128.3 (s, CH-Ph), 128.4 (s, CH-Ph), 130.2 (s, CH-Ph), 130.4 (d, JCP = 2.1 Hz, CH-Ph), 132.8 (d, JCP = 7.7 Hz, CH-Ph), 136.0 (d, JCP = 8.5 Hz, CH-Ph), 141.8 (d, JCP = 2.7 Hz, C-Ph), 147.1 (d, JCP = 6.8 Hz, C-Ph), 168.9 (d, JCP = 12.1 Hz, cis-CO), 178.1 (d, JCP = 115.1 Hz, trans-CO). 31P NMR (CD2Cl2): δ(ppm) 29.26. IR νCO (CH2Cl2): 2069.5, 1985.6 cm-1. Anal. Calcd for C26H33ClIrO2P (8 þ 1/4 CH2Cl2) (MW 634.17): C, 47.99; H, 5.06. Found: C, 47.82; H, 4.99. Synthesis of cis-[IrCl(CO)2(2b)] (4b). A flask was charged with 3b (80 mg, 0.114 mmol) and dichloromethane (4 mL). A balloon filled with CO was connected to the flask. The orange solution rapidly turned yellow. After 2 h, the solvent was evaporated and the resulting solid was washed with hexane (3  2 mL), leading to 61 mg (83%) of a yellow powder. 1H NMR (CD2Cl2): δ(ppm) 0.66-1.82 (m, CH2-Cy, 18H), 1.92-2.09 (m, CH2 and CH3), 2.10-2.23 (m, CH-Cy, 1H), 2.40-2.51 (m, CH-Cy, 1H), 7.06-7.11 (m, Ph-H, 1H), 7.13-7.32 (m, Ph-H, 4H), 7.35-7.44 (m, Ph-H, 2H), 7.77-7.87 (m, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm) 21.3 (s, CH3), 26.4 (d, JCP = 14.2 Hz, CH2-Cy), 27.2 (d, JCP = 13.9 Hz, CH2-Cy), 27.5 (d, JCP = 6.5 Hz, CH2-Cy), 27.6 (d, JCP = 7.0 Hz, CH2-Cy), 27.7 (d, JCP = 11.7 Hz, CH2-Cy), 29.1 (d, JCP = 1.7 Hz, CH2-Cy), 30.7 (br s, CH2-Cy), 30.8 (br s, CH2-Cy), 32.3 (d, JCP = 2.6 Hz, CH2-Cy), 34.5 (d, JCP = 28.3 Hz, CH-Cy), 35.9 (d, JCP = 27.6 Hz, CH-Cy), 125.4 (s, CH-Ph), 126.2 (d, JCP = 43.2 Hz, C-Ph), 126.7 (d, JCP = 10.4 Hz, CH-Ph), 128.7 (s, CH-Ph), 130.2 (s, CH-Ph), 130.4 (d, JCP = 2.2 Hz, CH-Ph), 131.3 (s, CH-Ph), 132.7 (d, JCP = 7.6 Hz, CH-Ph), 137.2 (s, C-Ph), 137.6 (d, JCP = 12.1 Hz, CH-Ph), 141.0 (d, JCP = 2.3 Hz, C-Ph), 146.1 (d, JCP = 5.2 Hz, C-Ph), 168.8 (d, JCP = 12.2 Hz, cis-CO), 178.3 (d, JCP = 115.1 Hz, trans-CO). 31P NMR (CD2Cl2): δ(ppm) 32.76. IR νCO (CH2Cl2): 2070.0, 1986.1 cm-1. Anal. Calcd for C27H35ClIrO2P (MW 650.21): C, 49.87; H, 5.43. Found: C, 50.06; H, 5.28. Synthesis of cis-[IrCl(CO)2(2c)] (4c). A flask was charged with 3c (80 mg, 0.107 mmol) and dichloromethane (4 mL). A balloon filled with CO was connected to the flask. Over 3 h, the orange solution turned yellow, slightly green. The solvent was then evaporated and the solid was washed with hexane. Drying the solid under vacuum led to 65 mg (88%) of a pale green product. 1H NMR (CD2Cl2): δ(ppm) 0.92-1.12 (m, CH2-Cy, 6H), 1.33-1.47 (m, CH2-Cy, 4H), 1.51-1.69 (m, CH2-Cy, 6H), 1.74-1.84 (m, CH2-Cy, 4H), 2.41 (qt, J = 9.7 Hz, J = 2.4 Hz, CHCy, 2H), 3.58 (s, O-CH3, 6H), 6.56 (d, JHH = 8.4 Hz, Ph-H, 2H), 7.00 (ddd, J = 7.5 Hz, J = 3.6 Hz, J = 1.5 Hz, Ph-H, 1H), 7.28 (t, JHH = 8.4 Hz, Ph-H, 1H), 7.34 (tt, J = 7.6 Hz, J = 1.4 Hz, Ph-H, 1H), 7.39 (tt, JHH = 7.4 Hz, JHH = 1.6 Hz, Ph-H, 1H), 7.78 (ddd, J = 11.4 Hz, J = 7.7 Hz, J = 1.1 Hz, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm) 26.5 (s, CH2-Cy), 27.6 (d, JPC = 11.5 Hz, CH2-Cy), 27.7 (d, JPC = 11.5 Hz, CH2-Cy), 30.0 (s, CH2Cy), 30.9 (s, CH2-Cy), 34.8 (d, JPC = 28.1 Hz, CH-Cy), 55.5 (s, O-CH3), 104.1 (s, CH-Ph), 119.0 (d, JCP = 2.9 Hz, C-Ph), 126.2 (d, JCP = 10.4 Hz, CH-Ph), 129.9 (d, JCP = 44.0 Hz, C-Ph), 130.0 (s, CH-Ph), 130.5 (d, JCP = 1.8 Hz, CH-Ph), 133.8 (d, JCP = 7.5 Hz, CH-Ph), 137.7 (d, JCP = 12.1 Hz, CH-Ph), 140.7 (d, JCP = 5.1 Hz, C-Ph), 158.4 (s, CPh), 168.8 (d, JCP = 12.4 Hz, cis-CO), 178.2 (d, JCP = 115.1 Hz, transCO). 31P NMR (CD2Cl2): δ(ppm) 29.88. IR νCO (CH2Cl2): 2069.1, 1985.7 cm-1. Anal. Calcd for C27H35ClIrO3P (MW 696.23): C, 48.30; H, 5.36. Found: C, 48.14; H, 5.46.

ARTICLE

Synthesis of cis-[IrCl(CO)2(2d)] (4d). A flask was charged with 3d (80 mg, 0.098 mmol) and dichloromethane (4 mL). A balloon filled with CO was connected to the flask. The color turnsed from orange to yellow. After 2 h, the solvent was evaporated, and the resulting yellow solid was washed with hexane (3  2 mL), leading to 66 mg (87%) of a pale green solid. 1H NMR (CD2Cl2): δ(ppm) 0.80-0.89 (d, 2JHH = 6.5 Hz, CH3, 6H), 0.93-1.08 (m, CH2, 4H), 1.13-1.25 (m, CH2, 4H and CH3, 12H), 1.35-1.76 (m, CH2, 12H), 2.40 (pseudo, 2JHH = 11.2 Hz, CH-Cy, 2H), 2.52 (sept, 2JHH = 6.7 Hz, CH-iPr, 2H), 2.85 (sept, 2JHH = 6.9 Hz, CH-iPr, 2H), 6.96-7.05 (m, Ph-H, 3H), 7.31-7.38 (m, Ph-H, 2H), 8.01-8.12 (m, Ph-H, 1H). 13C NMR (CD2Cl2): δ(ppm) 22.6 (s, CH3), 24.2 (s, CH3), 26.1 (s, CH), 26.1 (s, CH2-Cy), 27.2 (d, JCP = 13.0 Hz, CH2-Cy), 27.6 (d, JCP = 11.7 Hz, CH2-Cy), 30.9 (s, CH), 24.3 (d, JCP = 26.6 Hz, CH-Cy), 34.8 (s, CH), 121.6 (s, CH-Ph), 126.0 (d, JCP = 12.9 Hz, CH-Ph), 129.4 (d, JCP = 41.7 Hz, C-Ph), 129.6 (d, JCP = 2.1 Hz, CH-Ph), 134.6 (d, JCP = 7.4 Hz, CH-Ph), 136.4 (s, C-Ph), 139.3 (d, JCP = 19.4 Hz, CH-Ph), 144.0 (s, C-Ph), 147.1 (s, C-Ph), 149.7 (s, C-Ph), 169.4 (d, JCP = 11.8 Hz, cis-CO), 178.1 (d, JCP = 114.7 Hz, trans-CO). 31 P NMR (CD2Cl2): δ(ppm) 40.93. IR νCO (CH2Cl2): 2070.5, 1986.6 cm-1. Anal. Calcd for C35H51ClIrO2P (MW 762.42): C, 55.14; H, 6.74. Found: C, 55.14; H, 6.58. Synthesis of cis-[IrCl(CO)2(2g)] (4g). A flask was charged with 3g (215 mg, 0.352 mmol) and dichloromethane (6 mL). A balloon filled with CO was connected to the flask. The orange solution rapidly turned green at room temperature. After 1 h, the solvent was evaporated and the resulting solid was washed with pentane (2  3 mL), affording 145 mg (74%) of a pale green powder. 1H NMR (300 MHz, CD2Cl2): δ(ppm) 1.04-1.43 (m, CH2-Cy, 10H), 1.65-1.72 (m, CH2-Cy, 2H), 1.74-1.84 (m, CH2-Cy, 6H), 1.97-2.06 (m, CH2-Cy, 2H), 2.74-2.87 (m, CH2Cy, 2H), 7.47-7.57 (m, CH-Ph, 3H), 7.66-7.72 (m, CH-Ph, 2H). 13C NMR (75 MHz; CD2Cl2): δ(ppm) 26.3 (s, CH2-Cy), 26.9 (s, CH2-Cy), 27.1 (d, JCP = 2.0 Hz, CH2-Cy), 28.1 (d, JCP = 2.1 Hz, CH2-Cy), 28.8 (d, JCP = 1.6, CH2-Cy), 31.0 (d, JCP = 30.5 Hz, CH-Cy), 125.8 (d, JCP = 48.5 Hz C-Ph), 128.5 (d, JCP = 9.8 Hz, CH-Ph), 131.6 (d, JCP = 2.3 Hz CHPh), 135.2 (d, JCP = 9.0 Hz CH-Ph), 168.7 (d, JCP = 12.4 Hz, cis-CO), 178.8 (d, JCP = 115.7 Hz, trans-CO). 31P NMR (121 MHz, CD2Cl2): δ (ppm) 29.80. IR νCO (CH2Cl2): 2074.8, 1990.7 cm-1. Anal. Calcd for C20H57ClIrO2P (MW 558.11): C, 43.04; H, 4.88. Found: C, 42.95; H, 4.93.

’ ASSOCIATED CONTENT

bS

Supporting Information. Crystallographic information files (CIF) for all XRD structures. This material is available free of charge via the Internet http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Tel: þ 44 (0)1334 463698. Fax: (þ44) 01334 463 763. Present Addresses §

Universite Aix-Marseille, UMR CNRS 6263-Institut des Sciences Moleculaires de Marseille, Av. Escadrille Normandie Niemen, 13397 Marseille Cedex 20, France.

’ ACKNOWLEDGMENT We thank the ICREA, the ICIQ Foundation, the ERC (Advanced Researcher Award FUNCAT to S.P.N.), and the Ministerio de Educacion y Ciencia (Spain) for financial support. We are grateful to Umicore AG for their generous gifts of materials. S.P.N. is a Royal Society-Wolfson Research Merit Award holder. 1675

dx.doi.org/10.1021/om101174x |Organometallics 2011, 30, 1668–1676

Organometallics

’ REFERENCES (1) Old, D. W.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1998, 120, 9722–9723. (2) Bender, C. F.; Hudson, W. B.; Widenhoefer, R. A. Organometallics 2008, 27, 2356–2358. (3) Jimenez-Nu~nez, E.; Claverie, C. K.; Bour, C.; Cardenas, D. J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2008, 47, 7892–7895. (4) Kozhushkov, S. I.; Yufit, D. S.; Ackermann, L. Org. Lett. 2008, 10, 3409–3412. (5) Nieto-Oberhuber, C.; Perez-Galan, P.; Herrero-Gomez, E.; Lauterbach, T.; Rodriguez, C.; Lopez, S.; Bour, C.; Rosellon, A.; Cardenas, D. J.; Echavarren, A. M. J. Am. Chem. Soc. 2007, 130, 269–279. (6) Zou, T.; Pi, S.-S.; Li, J.-H. Org. Lett. 2008, 11, 453–456. (7) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J. Am. Chem. Soc. 2005, 127, 4685–4696. (8) Denmark, S. E.; Kallemeyn, J. M. J. Am. Chem. Soc. 2006, 128, 15958–15959. (9) Fox, J. M.; Huang, X.; Chieffi, A.; Buchwald, S. L. J. Am. Chem. Soc. 2000, 122, 1360–1370. (10) Hayashi, S.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2009, 131, 2052–2053. (11) Martin, R.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 3844– 3845. (12) Moradi, W. A.; Buchwald, S. L. J. Am. Chem. Soc. 2001, 123, 7996–8002. (13) Tolman, C. A. J. Am. Chem. Soc. 1970, 92, 2956–2965. (14) Ikawa, T.; Barder, T. E.; Biscoe, M. R.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 13001–13007. (15) Old, D. W.; Harris, M. C.; Buchwald, S. L. Org. Lett. 2000, 2, 1403–1406. (16) Anderson, K. W.; Ikawa, T.; Tundel, R. E.; Buchwald, S. L. J. Am. Chem. Soc. 2006, 128, 10694–10695. (17) Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadighi, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 4369–4378. (18) Torraca, K. E.; Kuwabe, S.-I.; Buchwald, S. L. J. Am. Chem. Soc. 2000, 122, 12907–12908. (19) Tomori, H.; Fox, J. M.; Buchwald, S. L. J. Organomet. Chem. 2000, 65, 5334–5341. (20) Martin, R.; Buchwald, S. L. Acc. Chem. Res. 2008, 41, 1461– 1473. (21) Fortman, G. C.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2010, 29, 3966–3972. (22) Strohmier, W.; Franz-Josef, M. Chem. Ber. 1967, 100, 2812– 2821. (23) Tolman, C. A. Chem. Rev. 1977, 77, 313–348. (24) Dorta, R.; Stevens, E. D.; Hoff, C. D.; Nolan, S. P. J. Am. Chem. Soc. 2003, 125, 10490–10491. (25) Dorta, R.; Stevens, E. D.; Scott, N. M.; Costabile, C.; Cavallo, L.; Hoff, C. D.; Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 2485–2495. (26) Barbeau, C.; Turcotte, J. Can. J. Chem. 1976, 54, 1603–1611. (27) Bitterwolf, T. E. Polyhedron 1988, 7, 409–415. (28) Carmona, E.; Sanchez, L. Polyhedron 1988, 7, 163–165. (29) (a) Lee, M.-T.; Hu, C.-H. Organometallics 2004, 23, 976–983. (b) Rosen, E. L.; Sanderson, M. D.; Saravanakumar, S.; Bielawski, C. W. Organometallics 2007, 26, 5774–5777. (c) Er, J. A. V.; Tennyson, A. G.; Kamplain, J. W.; Lynch, V. M.; Bielawski, C. W. Eur. J. Inorg. Chem. 2009, 1729–1738. (30) Stelzer, O.; Unger, E. Chem. Ber. 1975, 108, 1246–1258. (31) Herrmann, W. A.; Elison, M.; Fischer, J.; K€ocher, C.; Artus, G. R. J. Chem.—Eur. J. 1996, 2, 772–780. (32) K€ocher, C.; Herrmann, W. A. J. Organomet. Chem. 1997, 532, 261–265. (33) Mayr, M.; Wurst, K.; Ongania, K.-H.; Buchmeiser, M. R. Chem.—Eur. J. 2004, 10, 1256–1266. (34) Denk, K.; Sirsch, P.; Herrmann, W. A. J. Organomet. Chem. 2002, 649, 219–224.

ARTICLE

(35) Chianese, A. R.; Li, X.; Janzen, M. C.; Faller, J. W.; Crabtree, R. H. Organometallics 2003, 22, 1663–1667. (36) (a) Kelly, R. A.; Clavier, H.; Giudice, S.; Scott, N. M.; Stevens, E. D.; Bordner, J.; Samardjiev, I.; Hoff, C. D.; Cavallo, L.; Nolan, S. P. Organometallics 2008, 27, 202–210. (b) Díez-Gonzalez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612–3676. (c) Rosen, E. L.; Varnado, C. D.; Tennyson, A. G.; Khramov, D. M.; Kamplain, J. W.; Sung, D. H.; Cresswell, P. T.; Lynch, V. M.; Bielawski, C. W. Organometallics 2009, 28, 6695–6706. (d) Hudnall, T. W.; Bielawski, C. W. J. Am. Chem. Soc. 2009, 131, 16039–16041. (e) Varnado, C. D., Jr; Lynch, V. M.; Bielawski, C. W. Dalton Trans. 2009, 7253–7261. (f) Collins, M. S.; Rosen, E. L.; Lynch, V. M.; Bielawski, C. W. Organometallics 2010, 29, 3047–3053. (g) Hudnall, T. W.; Tennyson, A. G.; Bielawski, C. W. Organometallics 2010, 29, 4569–4578. (h) Tennyson, A. G.; Ono, R. J.; Hudnall, T. W.; Khramov, D. M.; Er, J. A. V.; Kamplain, J. W.; Lynch, V. M.; Sessler, J. L.; Bielawski, C. W. Chem. J. Eur. 2010, 16, 304–315. (37) The poorly soluble polymeric [Ir(CO)3Cl] can also be used as a starting material: Walter, H.; Frey, V. Chem. Ber. 1966, 99, 2607–2613. (38) CCDC 744632-744635 (3a-d), 746738 (4a), 744636 (4b), 746738 (4c), 744637 (4d), and 802800 (4g) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www. ccdc.cam.ac.uk/data_request/cif. (39) Brym, M.; Jones, C. Transition Met. Chem. (Dordrecht, Neth.) 2003, 28, 595–599. (40) Landaeta, V. R.; Peruzzini, M.; Herrera, V.; Bianchini, C.; Sanchez-Delgado, R. A.; Goeta, A. E.; Zanobini, F. J. Organomet. Chem. 2006, 691, 1039–1050. (41) The H atoms in the XRD structures are calculated on the basis of optimized geometries. (42) Typical anagostic bonds range from 2.3 to 2.9 Å. For more informatin see: Braga, D.; Grepioni, F.; Tedesco, E.; Biradha, K.; Desiraju, G. R. Organometallics 1997, 16, 1846–1856. (43) Schumann, H.; Cielusek, G.; Pickardt, J.; Bruncks, N. J. Organomet. Chem. 1979, 172, 359–365. (44) This statement should hold true even despite the XRD data, which implied a possible Ir---H anagostic interaction. This interaction may indeed increase the uncertainty in electron-donating abilities, but in solution, the steric pressure of the bulky ligands should be less. (45) Activation of aryl chlorides at room temperature by palladium catalyst (a) with PtBu3 see: Littke, A. D.; Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122, 4020–4028. (b) with NHCs, see: Navarro, O.; Kelly, R. A.; Nolan, S. P. J. Am. Chem. Soc. 2003, 125, 16194–16195. (46) Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.; Ragone, F.; Scarano, V.; Cavallo, L. Eur. J. Inorg. Chem. 2009, 1759–1766.(b) Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.; Ragone, F.; Scarano, V.; Cavallo, L. SambVca: A Web Application for the Calculation of the Buried Volume of N-Heterocyclic Carbene Ligands. https://www.molnac.unisa.it/OMtools/sambvca.php (accessed November 26, 2010). (47) Although no significant differences are observed, see SI Table S2 for %Vbur of ligands 2 in complexes 3 and 4 using the experimentally determined Ir-P distances. (48) Clavier, H.; Nolan, S. P. Chem. Commun. 2010, 46, 841–861. (49) (a) W€urtz, S.; Glorius, F. Acc. Chem. Res. 2008, 41, 1523–1533. (b) Lavallo, V.; Canac, Y.; Pr€asang, C.; Donnadieu, B.; Bertrand, G. Angew. Chem., Int. Ed. 2005, 44, 5705–5709. (c) Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F. J. Am. Chem. Soc. 2004, 126, 15195– 15201. (50) Bonnaire, R.; Horner, L.; Schumacher, F. J. Organomet. Chem. 1978, 161, C41–C45.

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