Reactions of a Platinum (II) Agostic Complex: Decyclometalation

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Reactions of a Platinum(II) Agostic Complex: Decyclometalation, Dicyclometalation, and Solvent-Switchable Formation of a Rollover Complex Sarah H. Crosby, Guy J. Clarkson, and Jonathan P. Rourke* Department of Chemistry, Warwick University, Coventry, CV4 7AL U.K.

bS Supporting Information ABSTRACT: Good donor ligands react with an sp2 cyclometalated complex of platinum containing an agostic interaction, initially causing displacement of the agostic interaction and decyclometalation. Eventually, these complexes rearrange to give sterically less congested complexes containing an sp3 cyclometalated group. The same end products are observed even with poor donor ligands that do not displace the agostic interaction, and this, together with other results, suggests to us that the route to the end products goes via a different agostic species. These sp3 cyclometalated complexes can be made to dicyclometalate via the simple expedient of adding water/base. Finally, dissolution of the agostic complex in DMSO results in a reversible “rollover” reaction, giving a C∧C chelated ligand.

’ INTRODUCTION Agostic complexes are much sought after as part of the search for the selective and general transformation of unreactive C
H bonds to other functional groups1 and are widely invoked as intermediates in such reactions.2 Many metals have been investigated in the quest for such transformations: of particular relevance to this paper is the use of platinum.3 Agostic interactions have been invoked in the stabilization of the formally 14e T-shaped Pt(II) complexes,4 and such electrophilic centers ought to be ideally set up for subsequent C
H activation, where it is generally recognized that a preference exists for the activation of sp2 over sp3 C
H bonds.3 Our own contribution to this area includes a recent communication in which we described the synthesis and characterization of a platinum(II) complex that contained a unique bifurcated agostic interaction.5 “Rollover” complexes, where the normal N∧N chelation mode of a ligand such as 2,20 -bypridine is converted to a C∧N coordination mode can be thought of as the products of cyclometalation or C
H activation reactions. Rollover complexes have historical precedent, with the first platinum example being reported in 19856 and considerable further work being done by Zucca et al.7 In all these documented examples, the rollover is accompanied by loss of hydrocarbon, which presumably goes a long way toward providing the thermodynamic basis for the reaction to proceed: e.g., Scheme 1.7b Certainly, the release of hydrocarbons from these reactions makes the reverse rather unlikely, and the reverse has yet to be observed. More recently, some examples of rollover complexes detected in the gas phase have been reported.8 In that recent work, a “normal” N∧N-bound 2,20 -bipyridine complex was made to undergo collision-induced decomposition, which resulted in loss of methane and formation of a C∧N-bound rollover complex. Computational studies and isotopic labeling demonstrated that, r 2011 American Chemical Society

once formed, the rollover complex was able to reversibly abstract hydrogen from a coordinated dimethyl sulfide ligand. In this paper we now present details of the reaction pathways, X-ray structures of products, and additional reactivity of our previously described agostic complex, including a reversible rollover reaction that takes place at the platinum center in solution, one that is driven not by the release of a hydrocarbon but by the relief of steric strain.

’ RESULTS AND DISCUSSION Direct reaction of potassium tetrachloroplatinate with 2-tertbutyl-6-(4-fluorophenyl)pyridine, in ethanoic acid, activates one of the sp2 C
H bonds of the fluorinated phenyl ring to give a cyclometalated product containing an agostic interaction, 1. We can now report that the reaction of this agostic complex with 1 equiv of ligand to exchange the site of cyclometalation, activating an sp3 C
H bond to give complexes 2, is general (Scheme 2). Reactions take place in solvents such as acetone and chloroform, and new complexes containing triphenylphosphine and pyridine ligands, 2b and 2c, respectively, have been synthesized. Though complexes 2 might be thought to be rather sterically crowded, they do have the formulation depicted: a definitive confirmation of the structure of 2b in the form of an X-ray structure can now be reported (Figure 1). The platinum center of 2b in the X-ray structure is indeed rather crowded, and this induces significant distortions away from a perfect square-planar geometry. Thus, while the P
Pt
Cl angle of 88.5° is close to 90°, all other angles at the Pt center are between 6 and 12° away from ideal values of 90 or 180°. Bond lengths to the platinum are all slightly longer than those for Received: April 5, 2011 Published: June 13, 2011 3603

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Scheme 1

Scheme 2

related undistorted complexes.9 The coordination plane of the platinum is by no means flat: a plane defined by N1, Pt1, P17, and either C16 or Cl1 is reasonably flat, but the other coordinating atom (Cl1 or C16) is approximately 0.44 Å away from this plane. The reaction of 1 with DMSO in chloroform or acetone solution proceeds directly to 2a. In contrast, the reactions of 1 with pyridine or triphenylphosphine clearly initially form new complexes. NMR spectra show that addition of 1 equiv of pyridine to a solution of 1 results in the rapid formation of a complex that is still cyclometalated via the fluorophenyl ring (as shown by the coupling pattern of the protons there and by the presence of platinum satellites on the 19F resonance) and contains a coordinated pyridine but does not contain an agostic interaction. NOE measurements suggest that the coordinated pyridine is adjacent to the cyclometalated ring and distant from the tertbutyl group, and we have assigned the structure 3c to this new complex (Scheme 3). The new complex 3c is sufficiently longlived in solution for us to characterize it spectroscopically but, as will become clear, we were unable to isolate pure samples. Addition of another 1 equiv (or simply excess) of pyridine results in the formation of a further new complex, one with two added ligands coordinated per platinum (indicated by the integrals in the 1H NMR). The new complex maintains the sp2 carbon to metal bond (the couplings in the 1H NMR on this ring retain their pattern, and satellites are still present on the 19F resonance) and (from mass spectrometric data) appears to still contain a chloride. The two added ligands appear to be chemically identical (a single set of resonances in the 1H NMR for the coordinated pyridine), and we therefore assign them as mutually trans, with the complex having the formulation depicted as 4c (Scheme 3). When 2 equiv of triphenylphosphine is added to 1, the analogous complex 4b is formed very rapidly. Once again the integrals in the 1H NMR indicate two added ligands coordinated per platinum, and again the couplings in the 1H NMR on this ring retain their pattern and satellites are still present on the 19F resonance, indicating the complex maintains the sp2 carbon
metal bond. Again, the two added ligands appear to be chemically identical (a single resonance in the 31P NMR), and we therefore assign the formulation depicted as 4b (Scheme 3). In fact, 4b forms even when only 1 equiv of triphenylphosphine is added to

Figure 1. Molecular structure of 2b, with thermal ellipsoids at the 50% probability level and chloroform solvent removed for clarity. Selected bond lengths (Å) and angles (deg): Pt(1)
C(16), 2.033(2); Pt(1)
N(1), 2.1193(18); Pt(1)
P(17), 2.2078(6); Pt(1)
Cl(1), 2.4337(5); C(16)
Pt(1)
N(1), 78.13(8); C(16)
Pt(1)
P(17), 96.78(7); N(1)
Pt(1)
P(17), 174.69(5); C(16)
Pt(1)
Cl(1), 169.27(6); N(1)
Pt(1)
Cl(1), 96.79(5); P(17)
Pt(1)
Cl(1), 88.48(2); C(6)
N(1)
C(2), 119.79(19); C(6)
N(1)
Pt(1), 128.48(16); C(2)
N(1)
Pt(1), 111.47(15); C(2)
C(13)
C(15), 111.37(19); C(2)
C(13)
C(16), 107.24(19); C(15)
C(13)
C(16), 110.31(17); C(2)
C(13)
C(14), 108.87(17); C(15)
C(13)
C(14), 108.91(19); C(16)
C(13)
C(14), 110.12(19).

1, whereupon an equimolar mixture of 1 and 4b forms. Complexes 4b,c appear to be indefinitely stable, and we were able to fully characterize them. The formation of complexes 4b,c requires the breaking of the chelating pyridine nitrogen to platinum bond, compensated by the formation of a new metal to ligand bond. In the reaction of 3c to give 4c, it would seem that the replacement of one Pt
N bond by another Pt
N bond would be energetically neutral, but once we consider the relief of the steric strain from the fivemembered metallacycle and that caused by the proximity of the tert-butyl group, we can see why such a reaction would actually be favorable. With triphenylphosphine as the incoming ligand we can easily rationalize the formation of 4b from the unseen 3b on the basis of a stronger donor ligand (phosphine) replacing a weaker one (pyridine). Presumably the formation of this stronger bond, together with the relief of strain (further enhanced by the bulky triphenylphosphine), is sufficient to stabilize 4b with 3604

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Scheme 3

Scheme 4

Scheme 5

respect to 3b by a greater amount than 3b is stabilized with respect to 1, and thus the reaction of 1 with triphenylphosphine gives 4b directly; certainly reactions of this type have been seen before.10 We do not, however, see the decyclometalation reaction with DMSO nor, to the best of our knowledge, has anyone else. We do not even see the formation of complex 3a. Presumably a DMSO ligand is an insufficiently good donor to displace the agostic interaction and to give the sterically congested 3a,11 and certainly we would not have expected DMSO to displace the nitrogen of the pyridine to give complex 4a. Over a time scale of tens of hours at room temperature, complex 1 and 1 equiv of DMSO transforms into complex 2a, an equimolar mixture of 1 and 4b transforms into 2b, and 3c transforms into 2c. Though we have not performed an exhaustive kinetic analysis, it is apparent that the rates of formation of 2a
c are similar. It is worth noting, however, that the sp3 cyclometalated products are visible in the NMR spectra as soon as any spectra are run, making the isolation of pure 3c impossible. A comparison of complexes 2 and 3 (they are simply isomers of each other) shows that while complex 3 would be expected to have the stronger Pt
C bond, the complex will be very sterically congested, with the chloride ligand adjacent to the bulky tertbutyl group. By comparison, complex 2 might have the weaker Pt
C bond, but it will be significantly less sterically congested, with the chloride ligand adjacent to the phenyl ring: thus, complex 2 becomes the thermodynamically favored isomer. A DFT calculation shows that, in the case of L = pyridine, 2c is favored over 3c by some 33 kJ mol
1. At this point, it is worth noting that we have already established that complex 1 will exchange hydrogen for deuterium in both the tert-butyl group and the position meta to the fluorine at essentially identical rates (once normalized for the number of available hydrogens) when dissolved in deuterated ethanoic acid;

additionally we have established that there is an intramolecular hydrogen transfer from the tert-butyl group of 1 to the phenyl group of 2a.5 We have also recently proved the existence of an agostic interaction from the phenyl ring in a platinum complex containing a cyclometalated tert-butyl group of the same pyridine ligand used in this paper.11a Thus, the experimental evidence indicates that an isomeric form of 1 (shown as 5 in Scheme 4) ought to be accessible as an intermediate, and indeed DFT calculations suggest that 5 is only 25 kJ mol
1 higher in energy than 1. We can therefore envisage two possible routes into the formation of complexes 2 from the initial agostic complex 1: one where complex 3 is an intermediate (route A, Scheme 4) or one where 3 is simply an initial kinetic product (route B, Scheme 4). That the actual reaction steps are all reversible equilibria is demonstrated by the addition of an extra 1 equiv of triphenylphosphine to pure 2b, whereupon complex 4b slowly forms. Though we cannot definitively rule out the direct transformation of 3 into 2 and cannot definitively confirm the intermediacy of 5, we do feel the experimental evidence is more strongly in favor of the rate-determining formation of 5 from 1 followed by rapid formation of 2. The crucial step of the transformations will be the transfer of a hydrogen from the alkyl group, across the platinum to the aryl group: it seems self-evident that such a step ought to be easier from one agostic complex to another (i.e., from 1 to 5), rather than between ones in which the metal centers are congested with other ligands (i.e., from 3 to 2). A process of H transfer across the metal is strongly reminiscent of the σ-CAM mechanism proposed by Perutz and Sabo-Etienne.12 Addition of water to complexes 2 to induce a second cyclometalation13 is also general (Scheme 5): two further derivatives containing triphenylphosphine and pyridine ligands, 6b and 6c, respectively, have been synthesized and fully characterized. The X-ray structure of 6a is reported here for the first time (Figure 2). Bond lengths and angles are remarkably similar to those in the dicycloplatinated DMSO complex of 2,6-diphenylpyridine we reported some years ago.13a The presence of two cyclometalated rings results in some distortion around the central platinum, with the N
Pt
C bond angles both being close to 81°. 3605

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The DMSO ligands in 6a can be replaced by either triphenylphosphine or pyridine to directly give 6b and 6c, respectively, with no observable impurities. A new reaction was also observed: when complex 1 was dissolved in DMSO and left to stand over several days, two new complexes were formed in roughly equal yields with no other byproduct. The new products can be isolated from the DMSO solvent and characterized: they exhibit spectroscopic features very similar to each other, with only slight changes in chemical shifts in the NMR. The presence of platinum satellites on the 19F NMR signals indicates both species maintain the original Pt
C bond, and two signals of integral 6 (relative to the other signals) at 3.32 and 3.35 ppm in the 1H NMR, both with platinum satellites, indicate the presence of sulfur-bound DMSO ligands. Further study of the 1H NMR shows that the three signals of the pyridine ring in 1 have been replaced by two sets of only two (one of which exhibits platinum satellites) with two further broad resonances (relative integral one) at ∼10 ppm.

We therefore conclude that, in addition to the metalated fluorophenyl ring, we have metalated the pyridine ring at one of the carbons, to give two C∧C chelated complexes, and protonated the pyridine nitrogen (which maintains the overall neutrality of the molecules) (Scheme 6). We account for two sets of resonances in all the various NMR spectra as arising from the presence of two isomers. While we have not been able to fully separate the two isomers, and indeed it is likely that the two isomers are in slow equilibrium with each other (either via the starting material, or via ligand exchange), we have synthesized mixtures where the clear preponderance of one isomer over the other has allowed us to assign complete sets of NMR resonances to each isomer. The use of NOE (in particular finding which signals are affected by the DMSO signals) allows us to assign resonances definitively to the cis and trans isomers. Normally we would expect a strong preference for one isomeric form of organometallic complexes of platinum(II),10c,14 but the C∧C chelate in 7 means that both cis and trans isomers have to have both chloride and DMSO ligands trans to very similar carbon donors. There will be little steric preference for one isomer over the other, as the molecule is not crowded around the platinum. A DFT optimization of the both structures predicts a favoring of the cis over the trans by only 6 kJ mol
1, barely significant given the inherent uncertainties in DFT calculations. The rollover of C∧N cyclometalated pyridines to give C∧C complexes has never been observed before, implying that the simple replacement of the pyridine N
Pt bond by a pyridine C
Pt bond is unfavorable. Indeed, a DFT calculation on the isomerism of 8 to 9 (neither complex was actually made) depicted in Scheme 7 shows that 9 would be disfavored by some 47 kJ mol
1, relative to 8. This value of 47 kJ mol
1 is the value calculated with the solvation effect that arises from a solvent of dielectric constant 4.8 (i.e., CHCl3), and it drops to 36 kJ mol
1 when a solvent of dielectric constant 46.7 (i.e., DMSO) is used. Simplistically, we can understand this effect of solvent on the basis that the zwitterionic 9 will be more stabilized in more polar solvents.14c,15 The sensible comparison we need to make in our new rollover reaction is between 3a and 7, the analogues of 8 and 9 above. Now, in addition to the (unfavorable) replacement of one Pt
N

Figure 2. Molecular structure of 6a, with thermal ellipsoids at the 50% probability level. Selected bond lengths (Å) and angles (deg): Pt(1)
N(1), 2.008(3); Pt(1)
C(8), 2.077(3); Pt(1)
C(16), 2.102(4); Pt(1)
S(18), 2.1744(9); F(10)
C(10), 1.367(4); O(18)
S(18), 1.481(3); N(1)
Pt(1)
C(8), 80.54(13); N(1)
Pt(1)
C(16), 81.05(14); C(8)
Pt(1)
C(16), 161.20(15); N(1)
Pt(1)
S(18), 178.06(9); C(8)
Pt(1)
S(18), 101.20(10); C(16)
Pt(1)
S(18), 97.16(11); C(2)
N(1)
C(6), 123.3(3); C(2)
N(1)
Pt(1), 118.9(2); C(6)
N(1)
Pt(1), 117.8(2); O(18)
S(18)
Pt(1), 120.76(12); C(17)
S(18)
Pt(1), 108.50(15); C(19)
S(18)
Pt(1), 111.46(14).

Scheme 7

Scheme 6

3606

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Scheme 8

bond by a Pt
C bond in the formation of rollover 7, there is the (favorable) release of the steric strain caused by the close proximity of the tert-butyl group to the chloride, and this is presumably enough to drive the reaction to give rollover 7. In fact, as noted earlier, we never actually see 3a but instead see 2a, where the steric strain is already somewhat relieved by the exchange of sites of cyclometalation. Solutions of 7 in chloroform revert slowly to the sp3 cyclometalated complex 2a on a time scale of days (Scheme 8). This, then, begs the question as to why we even see the rollover complexes at all. Once again, DFT calculations are of assistance: while the formation of cis-7 and trans-7 are predicted to be favored over 2a by 12 and 6 kJ mol
1, respectively, in the polar DMSO, they are predicted to be disfavored by 4 and 11 kJ mol
1 in the nonpolar chloroform. Thus we are at the cusp of the relative stabilities of the isomeric complexes with the change of the solvent sufficient to drive the reaction one way or another: a polar solvent gives zwitterionic rollover complexes and a nonpolar solvent gives conventional N∧C chelates. Rollover reactions, whether reversible or not, have a hydrogen transfer step as a key part of their mechanism; indeed, the reaction depicted in Scheme 8 has two separate ones. Computational evidence8a suggests a mechanism along the lines of the σ-CAM process,12 and there seems no reason not to invoke an intramolecular mechanism. Thus, rollover reactions have the potential to offer considerable insight into C
H activation reactions such as those where competition results in differing products according to reaction conditions.16

’ CONCLUSIONS The chemistry of the agostic compound 1 is complex. However, most of the interesting aspects of its reactivity can be traced back to the presence of the large tert-butyl group responsible for the agostic interaction. Relief of steric strain caused by this group is sufficient to drive reactions in a number of different directions, dependent upon conditions. Thus, where there is a choice of reactions that relieve the steric strain we see the additional factor of solvent polarity coming into play. This gives us a unique reversible rollover reaction driven by a change of solvent. ’ EXPERIMENTAL SECTION All chemicals were used as supplied, unless noted otherwise. All NMR spectra were obtained on a Bruker Avance 300, 400, 500, or 600 MHz spectrometer in CDCl3 or d6-acetone; 1H and 13C shifts are referenced to external TMS, assignments being made with the use of decoupling, NOE, and the HMBC, HMQC, DEPT, and COSY pulse sequences. 19F chemical shifts are quoted from the directly observed signals and are referenced to external CFCl3. 1H
195Pt correlation spectra were recorded using a variant of the HMBC pulse sequence, with the 195Pt chemical shifts quoted taken from the 2D HETCOR spectra and

referenced to external Na2PtCl6. All accurate mass spectra were run on a Bruker MaXis mass spectrometer, and X-ray crystal structures were collected on an Oxford Diffraction Gemini four-circle system with Ruby CCD area detector. The syntheses of 1, 2a, and 6a have been reported previously,5 and the syntheses of 2b,c and 6b,c follow these procedures. Compound 2b. Yield: 89%. δH: 8.00
8.04 (2H, m, phenyl), 7.76 (1H, t, 3J = 8 Hz, pyridine), 7.53
7.59 (6H, m, PPh3), 7.25
7.31 (10H, m, pyridine and PPh3), 7.16 (1H, d, 3J = 7.6 Hz, pyridine), 7.10 (2H, t, 3 JH
H,H
F = 8.8 Hz, phenyl), 1.57 (2H, d, 3JH
P = 2.5 Hz, 2JH
Pt = 52 Hz, CH2), 1.35 (6H, s, Me). δC: 175.2, 163.8 (d, 1JC
F = 248 Hz), 159.6, 138.0, 137.1 (d, 4JC
F = 2 Hz), 134.5 (d, 2JC
P = 11.5 Hz), 131.3 (d, 1JC
P = 63 Hz), 131.1 (d, 3JC
F = 9 Hz), 130.1, 127.8 (d, 3JC
P = 10.7 Hz), 124.0, 119.6 (3JC
Pt = 35 Hz), 114.6 (d, 2JC
F = 22 Hz), 49.9, 33.0 (3JC
Pt = 40.6 Hz), 31.7 (d, 2JC
P = 4 Hz). δF:
112.4. δP: 16.0 (1JP
Pt = 4665 Hz). δPt:
4161 (d). HR-MS (ESI): m/z 684.1715, calcd for C33H30FNP194Pt ((M
Cl)þ) 684.1721. Anal. Found (calcd): C, 54.61 (54.96); H, 4.32 (4.19); N, 1.98 (1.94). Compound 2c. Yield: 94%. δH: 8.78 (2H, dd, 3J = 6.8 Hz, 4J = 1.5 Hz, pyridine), 8.05
8.08 (2H, m, phenyl), 7.74 (1H, t, 3J = 7.8 Hz, phenylpyridine), 7.63 (1H, tt, 3J = 7.5 Hz, 4J = 1.6 Hz, pyridine), 7.18 (1H, dd, 3J = 7.8 Hz, 4J = 1.4 Hz, phenylpyridine), 7.12
7.15 (2H, m, pyridine), 7.09 (2H, t, 3JH
H,H
F = 8.6 Hz, phenyl), 7.07 (1H, dd, 3 J = 7.8 Hz, 4J = 1.5 Hz, pyridine), 2.09 (2H, s, 2JH
Pt = 70 Hz, CH2), 1.54 (6H, s, Me). δC: 178.1, 163.5 (d, 1JC
F = 250 Hz), 161.1, 154.1 (2JH
Pt = 34 Hz), 137.4 (d, 4JC
F = 3.6 Hz), 137.0, 136.4, 130.6 (d, 3JC
F = 9.2 Hz), 125.1 (3JC
Pt = 51.6 Hz), 124.2, 119.8, 114.9 (d, 2 JC
F = 21.5 Hz), 50.4, 32.3, 27.6. δF:
111.9. δPt:
3003. HR-MS (ESI): m/z 501.1236, calcd for C20H20FN2194Pt ((M
Cl)þ) 501.1232. Anal. Found (calcd): C, 44.19 (44.66); H, 3.86 (3.75); N, 5.25 (5.21). Synthesis of 3c. Pyridine (0.0009 g, 1.090  10
5 mol, 1 equiv) was added to a solution of complex 1 (0.005 g, 1.090  10
5 mol, 1 equiv) in CDCl3 at room temperature. Characteristic NMR data are as follows. δH: 8.79
8.80 (2H, m, 3JH
Pt = 48 Hz, pyridine), 7.28 (1H, dd, 3 J = 8 Hz, 4J = 1 Hz, phenylpyridine), 7.27
7.41 (2H, m, pyridine), 6.73 (1H, td, 3JH
H,H
F = 8.6 Hz, 4J = 2.5 Hz, cyclomet ring), 5.91 (1H, dd, 3 JH
F = 9.4 Hz, 4J = 2.5 Hz, 3JH
Pt = 49 Hz, H adjacent to Pt), 1.77 (9H, s, tBu). δF:
111.3 (4JF
Pt = 64 Hz). δPt:
2849. Synthesis of 4b. Only details for 4b are given, as the synthesis of 4c followed a very similar procedure. Triphenylphosphine (0.011 g, 4.359  10
5 mol, 2 equiv) was added to a solution of complex 1 (0.010 g, 2.179  10
5 mol, 1 equiv) in CHCl3 at room temperature. The mixture was stirred (96 h) and the solvent removed to give the product in analytical purity. Yield: 96%. δH: 8.52 (1H, br d, 3J = 7.5 Hz, pyridine), 7.37
7.40 (13H, m, pyridine and PPh3), 7.25 (6H, t, 3J = 7.4 Hz, PPh3), 7.14
7.16 (12H, m, PPh3), 7.01
7.03 (2H, m, pyridine and phenyl), 6.31 (1H, dd, 3JH
F = 10 Hz, 4J = 2.6 Hz, 3JH
Pt = 62 Hz, phenyl), 6.04 (1H, td, 3JH
H,H
F = 8.5 Hz, 4J = 2.5 Hz, phenyl), 1.10 (9H, s, tBu). δC: 166.6, 160.8 (d, 1JC
F = 249 Hz), 159.4, 143.8 (d, 4 JC
F = 8 Hz), 139.2 (d, 3JC
F = 5 Hz), 133.6 (t, 2JC
P = 6 Hz), 129.0, 128.6 (t, 1JC
P = 28.3 Hz), 126.8 (t, 3JC
P = 5 Hz), 123.6 (d, 2JC
F = 17.5 Hz), 119.4, 114.8, 107.1 (d, 2JC
F = 21 Hz), 36.4, 29.1. δP: 21.6 (1JP
Pt = 3127 Hz). δPt:
4188 (t, 1JPt
P = 3146 Hz). HR-MS (ESI): m/z 982.2411, calcd for C51H4635ClFNP2194Pt ((M þ H)þ) 3607

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Organometallics 982.2399. Anal. Found (calcd): C, 62.32 (62.29); H, 5.07 (4.61); N, 1.83 (1.42). Compound 4c. Yield: 92%. δH: 8.57 (4H, dd, 3J = 7 Hz, 4J = 1.5 Hz, 2 JH
Pt = 40 Hz, pyridine), 7.56 (2H, tt, 3J = 7.7 Hz, 4J = 1.5 Hz, pyridine), 7.31 (1H, t, 3J = 7.6 Hz, phenylpyridine), 7.27 (1H, dd, 3J = 7.7 Hz, 4J = 1 Hz, phenylpyridine), 7.11 (1H, dd, 3J = 8.5 Hz, 4JH
F = 6.2 Hz, phenyl), 7.09 (1H, dd, 3J = 7.4 Hz, 4J = 1.2 Hz, phenylpyridine), 6.97 (4H, t, 3J = 7.1 Hz, pyridine), 6.90 (1H, dd, 3JH
F = 9.7 Hz, 4J = 2.7 Hz, phenyl), 6.61 (1H, td, 3JH
H,H
F = 8.5 Hz, 4J = 2.7 Hz, phenyl), 1.34 (9H, s, tBu) ppm. δC: 167.1, 160.7, 157.7 (d, 1JC
F = 249 Hz), 152.9, 142.2, 141.6 (d, 3JC
F = 4 Hz), 135.8, 134.2, 128.7 (d, 3JC
F = 8.4 Hz), 123.7 (3JC
Pt = 48 Hz), 121.6 (d, 2JC
F = 17 Hz), 119.2, 114.6, 109.0 (d, 2JC
F = 21 Hz), 36.8, 29.5. δF:
117.3 (4JF
Pt = 40 Hz). δPt:
2741. HR-MS (ESI): m/z 616.1413, calcd for C25H2635ClFN3194Pt ((M þ H)þ) 616.1420; 501.1232, calcd for C20H20FN2194Pt ((M
Cl
Py)þ) 501.1232. Anal. Found (calcd): C, 47.98 (48.66); H, 3.90 (4.08); N, 6.86 (6.81). Compound 6b. Yield: 87%. δH: 7.66 (1H, t, 3J = 7.8 Hz, pyridine), 7.58
7.63 (6H, m, PPh3), 7.52 (1H, dd, 3J = 8.5 Hz, 4JH
F = 5.2 Hz, phenyl), 7.40 (1H, br d, 3J = 8 Hz, pyridine), 7.29
7.31 (9H, m, PPh3), 6.93 (1H, br d, 3J = 8 Hz, pyridine), 6.58 (1H, td, 3JH
H,H
F = 8.7 Hz, 4 J = 2.8 Hz, phenyl), 6.38 (1H, dd, 3JH
F = 10 Hz, 4J = 2.5 Hz, 3JH
Pt = 30 Hz, phenyl), 1.48 (2H, d, 3JH
P = 1 Hz, 2JH
Pt = 40 Hz, CH2), 1.21 (6H, s, Me). δC: 179.1 (2JC
Pt = 61 Hz), 175.7 (dd, 3JC
F = 6 Hz, 2JC
P = 3 Hz), 164.7 (2JC
Pt = 52 Hz), 164.6 (d, 1JC
F = 254 Hz), 145.8 (4JC
F = 5.4 Hz), 138.2, 134.6 (d, 2JC
P = 12.3 Hz, 3JC
Pt = 41 Hz), 132.2 (d, 1JC
P = 58 Hz), 130.1 (d, 4JC
P = 2.3 Hz), 128.0 (d, 3JC
P = 10.7 Hz), 125.3 (d, 3JC
F = 7.7 Hz), 124.4 (d, 2JC
F = 14.6 Hz, 2JC
Pt = 61 Hz), 118.6 (d, 4JC
P = 2.3 Hz, 3JC
Pt = 33 Hz), 115.4 (d, 4JC
P = 2.3 Hz, 3JC
Pt = 27 Hz), 109.1 (d, 2JC
F = 23 Hz), 52.6 (d, 3JC
P = 3.8 Hz), 41.4 (d, 2JC
P = 5.4 Hz, 1JC
Pt = 461 Hz) 34.0 (3JC
Pt = 17.6 Hz). δF:
111.2 (4JF
Pt = 26.3 Hz). δP: 26.7 (1JP
Pt = 4117 Hz). δPt:
4110 (d). HR-MS (ESI): m/ z 684.1741, calcd for C33H30FNP194Pt ((M þ H)þ) 684.1721. Anal. Found (calcd): C, 57.36 (57.89); H, 3.87 (4.27); N, 2.10 (2.05). Compound 6c. Yield: 90%. δH: 8.93
8.94 (2H, m, pyridine), 7.73 (1H, tt, 3J = 7.8 Hz, 4J = 1.5 Hz, pyridine), 7.60 (1H, t, 3J = 8.0 Hz, phenylpyridine), 7.52 (1H, dd, 3J = 8.5 Hz, 4JH
F = 5.0 Hz, phenyl), 7.26
7.29 (3H, m, pyridine and phenylpyridine), 6.83 (1H, d, 3J = 7.9 Hz, phenylpyridine), 6.77 (1H, dd, 3JH
F = 8.5 Hz, 4J = 2.6 Hz, 3 JH
Pt = 28 Hz, phenyl), 6.68 (1H, td, 3JH
H,H
F = 8.8 Hz, 4J = 2.7 Hz, phenyl), 1.97 (2H, s, 2JH
Pt = 50 Hz, CH2), 1.36 (6H, s, Me). δC: 180.3, 178.1, 165.8 (d, 1JC
F = 253 Hz), 165.5, 153.6, 144.3, 136.9, 135.4, 126.0 (3JC
Pt = 48 Hz), 125.5 (d, 3JC
F = 8.2 Hz), 118.6, 117.7 (d, 2JC
F = 14.2 Hz), 115.2, 109.1 (d, 2JC
F = 24 Hz), 51.5, 42.2, 34.0. δF:
111.0 (4JF
Pt = 20 Hz). δPt:
2949 ppm. HR-MS (ESI): m/z 501.1231, calcd for C20H20FN2194Pt ((M þ H)þ) 501.1232. Anal. Found (calcd): C, 44.72 (44.66); H, 3.96 (3.75); N, 4.83 (5.21). Synthesis of 7. Complex 1 (0.010 g, 2.18  10
5 mol) was dissolved in DMSO (3 mL, excess) and left standing at room temperature for 3 weeks. The solvent was removed under high vacuum to give a yellow solid. trans-7. δH: 10.14 (1H, br s, N
H), 9.23 (1H, d, 3J = 7.7 Hz, 3JH
Pt = 64 Hz, py ring), 8.02 (1H, dd, 3JH
F = 10.2 Hz, 4J = 2.5 Hz, 3JH
Pt = 61 Hz, Ph ring), 7.14 (1H, dd, 3J = 8.5 Hz, 4JH
F = 5.0 Hz, Ph ring), 6.98 (1H, dd, 3J = 8.0 Hz, 4J = 2.0 Hz, py ring), 6.74 (1H, td, 3JH
H,H
F = 8.5 Hz, 4J = 2.7 Hz, Ph ring), 3.32 (6H, s, 3JH
Pt = 10 Hz, DMSO), 1.42 (9H, s, tBu) ppm. δC: 150.1 (2JC
Pt = 33.5 Hz, py ring), 124.7 (d, 3 JC
F = 8.5 Hz, 3JC
Pt = 71 Hz, Ph ring), 122.5 (d, 2JC
F = 19 Hz, Ph ring), 119.5 (3JC
Pt = 60 Hz, py ring), 111.8 (d, 2JC
F = 24 Hz, Ph ring), 44.3 (2JC
Pt = 25.5 Hz, DMSO), 36.3 (C), 29.1 (tBu) ppm. δF:
109.0 (4JF
Pt = 43 Hz) ppm. δPt:
4032 ppm. cis-7. δH: 10.14 (1H, br s, N
H), 8.99 (1H, d, 3J = 7.7 Hz, 3JH
Pt = 57 Hz, py ring), 8.34 (1H, dd, 3JH
F = 11 Hz, 4J = 2.5 Hz, 3JH
Pt = 70.5 Hz, Ph ring), 7.17 (1H, dd, 3J = 8.5 Hz, 4JH
F = 5.4 Hz, Ph ring),

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7.07 (1H, dd, 3J = 8.2 Hz, 4J = 2.0 Hz, py ring), 6.75 (1H, td, 3JH
H,H
F = 8.2 Hz, 4J = 2.6 Hz, Ph ring), 3.35 (6H, s, 3JH
Pt = 11.5 Hz, DMSO), 1.43 (9H, s, tBu) ppm. δC: 150.7 (2JC
Pt = 28.5 Hz, py ring), 125.3 (d, 3 JC
F = 9.5 Hz, 3JC
Pt = 76 Hz, Ph ring), 122.9 (d, 2JC
F = 20 Hz, Ph ring), 118.5 (3JC
Pt = 55 Hz, py ring), 110.5 (d, 2JC
F = 25 Hz, Ph ring), 44.6 (2JC
Pt = 29 Hz, DMSO), 36.4 (C), 29.2 (tBu) ppm. δF:
108.1 (4JF
Pt = 54 Hz) ppm. δPt:
4023 ppm. Data on the mixture of cis-7 and trans-7: HR-MS (ESI): m/z 500.0952, calcd for C17H21FNO194PtS ((M
Cl)þ) 500.0949. Anal. Found (calcd): C, 37.65 (38.03); H, 4.32 (3.94); N, 2.73 (2.61). X-ray Crystallographic Studies of 2b and 6a. Crystal data for 2b: the asymmetric unit contains the complex and two molecules of chloroform solvent, C35H32Cl7FNPPt, Mr = 959.83, monoclinic, space group P21/c, a = 16.0210(3) Å, b = 16.4039(2) Å, c = 15.4546(3) Å, β = 116.349(2)°; U = 3639.61(11) Å3 (by least-squares refinement on 11 844 reflection positions), T =100(2) K, λ = 0.710 73 Å, Z = 4, D(calcd) = 1.752 Mg/m3, F(000) = 1880, μ(Mo KR) = 4.445 mm
1, colorless block, crystal dimensions 0.20  0.10  0.10 mm, no crystal decay, θmax = 29.39°; hkl ranges
21 to þ22,
16 to þ22, and
21 to þ15; 18 996 reflections measured, 8628 unique reflections (R(int) = 0.0281), goodness-of-fit on F2 0.919, R1 (for 7067 reflections with I > 2σ(I)) = 0.0213, wR2 = 0.0372, 8628/2/423 data/restraints/parameters, largest difference Fourier peak and hole 0.660 and
0.912 e Å
3. Crystal data for 6b: C17H20FNOPtS, Mr = 500.49; monoclinic, space group Cc; a = 9.9679(2) Å, b = 18.6651(3) Å, c = 9.5993(2) Å, β = 111.176(3)°, U = 1665.37(6) Å3 (by least-squares refinement on 6729 reflection positions), T =100(2) K, λ = 0.710 73 Å, Z = 4, D(calcd) = 1.996 Mg/m3, F(000) = 960, μ(Mo KR) = 8.561 mm
1, colorless block, crystal dimensions 0.25  0.20  0.08 mm, no crystal decay, θmax = 29.20°; hkl ranges
9 to þ13,
25 to þ25, and
13 to þ10, 6952 reflections measured, 2742 unique reflections (R(int) = 0.0210), goodness-of-fit on F2 1.073, R1 (for 2711 reflections with I > 2σ(I)) = 0.0142, wR2 = 0.0344, 2742/4/209 data/restraints/parameters, largest difference Fourier peak and hole 0.624 and
1.097 e Å
3. In both cases, the structures were solved by direct methods using SHELXS,17 with additional light atoms found by Fourier methods. Hydrogen atoms were added at calculated positions and refined using a riding model, except the hydrogens on C16, which were located in a difference map. Their position was refined but given a distance restraint. Anisotropic displacement parameters were used for all non-H atoms; H atoms were given isotropic displacement parameters equal to 1.2 (or 1.5 for methyl H atoms) times the equivalent isotropic displacement parameter of the atom to which they are attached. DFT Calculations. All DFT calculations used the Amsterdam density functional (ADF) code, version 2008.01.18 The general features available in ADF have been described.19 Here, we have used scalar zeroorder regular approximation (ZORA) relativistic corrections with the OPBE functional20 and the supplied frozen-core, triple-ζ plus polarization ZORA basis sets. Solvation effects were included via the conductorlike screening model (COSMO) as implemented in ADF. Default SCF and geometry optimization convergence criteria were used.

’ ASSOCIATED CONTENT

bS

Supporting Information. Tables giving DFT optimized coordinates and energies for 1, 2a,c, 3c, 5, cis-7, trans-7, 8, and 9 and CIF files giving crystallographic data for 2b and 6a. This material is available free of charge via the Internet at http:// pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. 3608

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Organometallics

’ ACKNOWLEDGMENT We thank Warwick University for a WPRS award to S.H.C. and support from Advantage West Midlands (AWM) (partially funded by the European Regional Development Fund) for the purchase of a high-resolution mass spectrometer and the XRD system that was used to solve the crystal structures of 2b and 6a. ’ REFERENCES (1) (a) Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507. (b) Bergman, R. G. Nature 2007, 446, 391. (2) (a) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 6908. (b) Haller, L. J. L.; Page, M. J.; Macgregor, S. A.; Mahon, M. F.; Whittlesey, M. K. J. Am. Chem. Soc. 2009, 131, 4604. (3) Goldman, A. S.; Goldberg, K. I., In Activation and Functionalization of C-H Bonds; Goldberg, K. I., Goldman, A. S., Eds.; American Chemical Society: Washington, DC, 2004; ACS Symposium Series 885. (4) (a) Carr, N.; Dunne, B. J.; Orpen, A. G.; Spencer, J. L. J. Chem. Soc., Chem. Commun. 1988, 926. (b) Carr, N.; Mole, L.; Orpen, A. G.; Spencer, J. L. J. Chem. Soc., Dalton Trans. 1992, 2653. (c) Ingleson, M. J.; Mahon, M. F.; Weller, A. S. Chem. Commun. 2004, 2398. (5) Crosby, S. H.; Clarkson, G. J.; Rourke, J. P. J. Am. Chem. Soc. 2009, 131, 14142. (6) Skapski, A. C.; Sutcliffe, V. F.; Young, G. B. J. Chem. Soc., Chem. Commun. 1985, 609. (7) (a) Zucca, A.; Doppiu, A.; Cinellu, M. A.; Stoccoro, S.; Minghetti, G.; Manassero, M. Organometallics 2002, 21, 783. (b) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Soro, B.; Zucca, A. Organometallics 2003, 22, 4770. (c) Zucca, A.; Cinellu, M. A.; Minghetti, G.; Stoccoro, S.; Manassero, M. Eur. J. Inorg. Chem. 2004, 4484. (d) Zucca, A.; Petretto, G. L.; Stoccoro, S.; Cinellu, M. A.; Minghetti, G.; Manassero, M.; Manassero, C.; Male, L.; Albinati, A. Organometallics 2006, 25, 2253. (e) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Petretto, G. L.; Zucca, A. Organometallics 2008, 27, 3415. (f) Zucca, A.; Petretto, G. L.; Stoccoro, S.; Cinellu, M. A.; Manassero, M.; Manassero, C.; Minghetti, G. Organometallics 2009, 28, 2150. (8) (a) Butschke, B.; Schlangen, M.; Schr€oder, D.; Schwarz, H. Chem. Eur. J. 2008, 14, 11050. (b) Butschke, B.; Schwarz, H. Organometallics 2010, 29, 6002. (9) (a) Newman, C. P.; Casey-Green, K.; Clarkson, G. J.; Cave, G. W. V.; Errington, W.; Rourke, J. P. Dalton Trans. 2007, 3170. (b) Mamtora, J.; Crosby, S. H.; Newman, C. P.; Clarkson, G. J.; Rourke, J. P. Organometallics 2008, 29, 5559. (10) (a) Albrecht, M.; Dani, P.; Lutz, M.; Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 2000, 122, 11822. (b) Rodriguez, G.; Albrecht, M.; Schoenmaker, J.; Ford, A.; Lutz, M.; Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 2002, 124, 5127. (c) Crespo, M.; Granell, J.; Solans, X.; Font-Bardia, M. J. Organomet. Chem. 2003, 681, 143. (d) Crespo, M.; Solans, X.; Font-Bardia, M. J. Organomet. Chem. 1996, 509, 29. (11) (a) Crosby, S. H.; Clarkson, G. J.; Deeth, R. J.; Rourke, J. P. Dalton Trans. 2011, 40, 1227. (b) Conley, B. L.; Williams, T. J. J. Am. Chem. Soc. 2010, 132, 1764. (c) Crosby, S. H.; Clarkson, G. J.; Deeth, R. J.; Rourke, J. P. Organometallics 2010, 29, 1966. (12) Perutz, R. N.; Sabo-Etienne, S. Angew. Chem., Int. Ed. 2007, 46, 2578. (13) (a) Cave, G. W. V.; Alcock, N. W.; Rourke, J. P. Organometallics 1999, 18, 1801. (b) Cave, G. W. V.; Fanizzi, F. P.; Deeth, R. J.; Errington, W.; Rourke, J. P. Organometallics 2000, 19, 1355. (14) (a) Vicente, J.; Arcas, A.; Bautista, D.; de Arellano, M. C. R. J. Organomet. Chem. 2002, 663, 164. (b) Fornies, J.; Sicilia, V.; Larraz, C.; Camerano, J. A.; Martin, A.; Casas, J. M.; Tsipis, A. C. Organometallics 2010, 29, 1396. (c) Newman, C. P.; Clarkson, G. J.; Alcock, N. W.; Rourke, J. P. Dalton Trans. 2006, 3321. (d) Newman, C. P.; Deeth, R. J.; Clarkson, G. J.; Rourke, J. P. Organometallics 2007, 26, 6225. (e) Petretto, G. L.; Wang, M.; Zucca, A.; Rourke, J. P. Dalton Trans. 2010, 39, 7822. (f) Rourke, J. P.; Fanizzi, F. P.; Bruce, D. W.; Dunmur, D. A.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1992, 3009.

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