Synthesis, Spectroscopy, Structure, and Reactivity of

Article pubs.acs.org/Organometallics

Synthesis, Spectroscopy, Structure, and Reactivity of Azapentadienyl-Rhodium-Phosphine and Azapentadienyl-IridiumPhosphine Complexes1 John R. Bleeke* and Wipark Anutrasakda Department of Chemistry, Washington University, One Brookings Drive, St. Louis, Missouri 63130, United States

Nigam P. Rath Department of Chemistry and Biochemistry, University of Missouri−St. Louis, One University Boulevard, St. Louis, Missouri 63121, United States S Supporting Information *

ABSTRACT: We report the synthesis, spectroscopy, structure, and reactivity of (1,2,3-η3)-(5-tert-butylazapentadienyl)Rh(PMe3)x (1, x = 2; 4, x = 3) and (1,2,3-η3)-(5-tert-butylazapentadienyl)Ir(PEt3)x (7, x = 2; 12, x = 3), which are produced by reacting [(cyclooctene)2M(μ-Cl)]2 with the appropriate amount of phosphine, followed by potassium tert-butylazapentadienide. Each of these compounds reacts with 1 equivalent of triflic acid to produce a monoprotonation product. Rhodium compounds 1 and 4 react at nitrogen to produce 2 and 5, respectively. Iridium compound 7 reacts at the metal center, generating an iridiumhydride product, 8, in which the azapentadienyl ligand coordinates in an unusual η3, η1-fashion, while compound 12 reacts at nitrogen to produce 13. The monoprotonation products have been treated with additional acid, and in each case the secondary site of electrophilic addition has been determined. Rhodium compounds 2 and 5 both react with a second equivalent of triflic acid at the metal center to produce unstable metal-hydrides. These species reductively eliminate protonated tertbutylcrotonaldimine and ultimately produce isolable octahedral Rh(III) complexes 3 and 6 after addition of a third equivalent of triflic acid. In contrast, when iridium compound 8 is treated with a second equivalent of triflic acid, addition occurs at nitrogen to produce diprotonation product 9. Similarly, 13 reacts with a second equivalent of acid at nitrogen, generating a product with a diprotonated nitrogen, 14. All of the compounds reported herein have been identified by NMR, while the structures of 2, 4, 5, 6, 12, 13, and 14 have been confirmed by single-crystal X-ray diffraction.

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uncoordinated. Earlier, we reported4 the synthesis of (1,2,3η3)-(5-tert-butylazapentadienyl)Ir(PMe3)3 and its reactivity toward the simplest electrophile, H+. We have also reported1 the syntheses of (1,2,3-η3)-(5-tert-butylazapentadienyl)Co(PMe3)2(L) (L = PMe3, P(OMe)3, and CO) and the reactions of these compounds with H+. In this paper, we broaden the scope of these previous studies and report the synthesis and reactivity of four related compounds, (1,2,3-η3)-(5-tert-

INTRODUCTION

Heteropentadienyl ligands (i.e., pentadienyl analogues in which one terminal CH2 group has been replaced by a heteroatom)2 have attracted increasing attention because of their ability to adopt a variety of bonding modes, a feature that can enhance the reactivity of their transition metal complexes.3 However, another interesting feature of heteropentadienyl ligands is their basicity due to the presence of nonbonding lone pairs on the heteroatom. Azapentadienyl ligands, in particular, have a strong tendency to react with electrophilic reagents when bonded to transition metals in ways that leave the nitrogen atom © 2013 American Chemical Society

Received: July 31, 2013 Published: October 9, 2013 6410

dx.doi.org/10.1021/om400765h | Organometallics 2013, 32, 6410−6426

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Scheme 1

butylazapentadienyl)Rh(PMe3)x (x = 2 or 3) and (1,2,3-η3)-(5tert-butylazapentadienyl)Ir(PEt3)x (x = 2 or 3). These molecules all possess two potential sites of reactivity for electrophiles, the nitrogen atom and the basic metal center. For each of the four compounds listed above, we have investigated the products obtained upon treatment with 1 equivalent of acid in order to determine the primary site for electrophilic addition. These monoprotonation products have then been treated with additional acid to ascertain secondary sites of reactivity. We have found that both the nitrogen atom and the metal center can serve as primary and secondary reaction sites, depending on the specific compound under investigation. Furthermore, when nitrogen serves as the primary site of reactivity, the protonated azapentadienyl ligand can adopt an η3-bonding mode, an η4-bonding mode, or a bonding mode that lies between these limiting structures. In this paper, we discuss the factors that determine where electrophilic addition occurs and address the question of why different ligand bonding modes are adopted.

in 1a and 1s. In 1a, H3 projects away from Rh while H4 projects toward it, while in 1s, H3 projects toward Rh while H4 projects away. The H1’s and H2’s have similar chemical shifts in both isomers, as expected. In the 13C{1H} NMR spectrum of 1a, C4 appears far downfield at δ 151.1, consistent with the fact that it is not coordinated to Rh. The remaining azapentadienyl carbons resonate at δ 102.7 (C2), 68.0 (C3), and 46.5 (C1). Both C3 and C1 show strong coupling to the 31P nuclei that lie approximately trans to them (JC3−P = 21.0 Hz, JC1−P = 25.4 Hz). The 13C{1H} NMR spectrum for 1s is very similar (see tabulated data in the Experimental Section). The 31P{1H} NMR spectrum of 1a shows two doublet of doublet patterns for the two inequivalent PMe3 ligands. The larger coupling (194.1 Hz for one phosphine and 187.0 Hz for the other) is due to rhodium, while the smaller coupling (35.9 Hz) is due to phosphorus. The syn isomer similarly exhibits two doublet of doublet patterns. There is no NMR evidence of fluxionality at room temperature. In the infrared spectrum of 1 (in Nujol mull), CN stretches appear at 1624.7 and 1604.1 cm−1. B. Monoprotonation of Compound 1. Synthesis, Spectroscopy, and Structure of (1,2,3-η3)(CH 2CHCHCHNH(tert-Butyl))Rh(PMe3) 2+ O3SCF3−, 2. Treatment of compound 1 with 1 equivalent of triflic acid in diethyl ether leads to the immediate precipitation of dark red 2, the monoprotonation product. The NMR spectra of 2 indicate that it is a single isomer in which the nitrogen atom has been protonated (see Scheme 1). In the 1H NMR, the NH signal appears at δ 8.32 and is a doublet due to strong coupling to H4 (JNH‑H4 = 14.4 Hz). This downfield chemical shift position for NH reflects significant positive charge at nitrogen. H4 resonates at δ 6.63 and is a doublet of doublets due to coupling to both NH and H3 (JH4−H3 = 11.7 Hz). H3 resonates at δ 4.79; its downfield chemical shift position strongly suggests that 2 adopts the anti ligand geometry. In the 13C{1H} NMR, C4 resonates at δ 136.0, modestly upfield from its position in 1a (δ 151.1), while the remaining azapentadienyl carbons are essentially unshifted from 1a. As in 1a, C3 and C1 show

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RESULTS AND DISCUSSION A. Synthesis and Spectroscopy of (1,2,3-η3)-(5-tertButylazapentadienyl)Rh(PMe 3 ) 2 , 1. Treatment of [(cyclooctene)2Rh(μ-Cl)]25 with 4 equivalents of PMe3, followed by at least 2 equivalents of potassium tertbutylazapentadienide,4,6 leads to the production of orange (1,2,3-η3)-(5-tert-butylazapentadienyl)Rh(PMe3)2 as a ∼50:50 mixture of anti and syn isomers, 1a and 1s, respectively (see Scheme 1). In the 1H NMR, the anti isomer, 1a, exhibits a downfield doublet at δ 6.59 due to H4. The doublet results from coupling to the adjacent H3 (JH4−H3 = 9.3 Hz). The remaining azapentadienyl signals appear as multiplets at δ 4.80 (H2), 4.35 (H3), 2.75 (H1), and 2.23 (H1). The 1H NMR spectrum of syn isomer 1s is similar but subtly different. The H4 signal is still a doublet (JH4−H3 = 9.0 Hz) but appears at a more downfield chemical shift position, δ 7.68. The H3 signal, in contrast, shifts upfield to δ 3.24. These shifts result from the orientations of H3 and H4 with respect to the rhodium center 6411


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coupling to the 31P nuclei that lie approximately trans to them: JC3−P = 12.1 Hz, while JC1−P = 18.8 Hz. The 31P{1H} NMR spectrum shows two doublet of doublet patterns with large couplings due to rhodium (194.7 and 176.1 Hz) and smaller couplings due to phosphorus (42.9 Hz). In the infrared spectrum, the CN stretch appears at 1607.3 cm−1. Single crystals of 2 are obtained by cooling a saturated acetone solution to −30 °C. The X-ray structure is presented in Figure 1, while selected bond distances are summarized in the

preponderance of spectroscopic and structural evidence supports resonance structure I as the dominant contributor to the bonding. Therefore, we have drawn 2 as a protonated η3azapentadienyl-rhodium complex in Scheme 1 and elsewhere. C. Further Protonation of Compound 2. Synthesis and Spectroscopy of (H)Rh(η1-O3SCF3)(η2-O3SCF3)(PMe3)2, 3. When compound 2 is dissolved in acetonitrile and treated with triflic acid, protonation occurs at the rhodium center, followed by reductive elimination of protonated tert-butylcrotonaldimine. Addition of another equivalent of triflic acid at rhodium leads to the isolated yellow rhodium product, (H)Rh(η1O3SCF3)(η2-O3SCF3)(PMe3)2, 3 (see Scheme 2).9 These same products are also observed when compound 1 is treated with excess triflic acid in acetonitrile. The identity of the protonated imine was confirmed by a comparison of its NMR spectra with those of an authentic sample, prepared by treating tert-butylcrotonaldimine with triflic acid.10 Interestingly, the protonated imine exhibits trans geometry about C2−C3 (JH2−H3 = 15.0 Hz), suggesting that the protonated azapentadienyl ligand isomerizes from anti to syn geometry before reductive elimination (A to B, Scheme 2). The rhodium product, 3, was identified from its NMR spectra. The hydride signal appears at δ −17.02 and is a triplet of doublets. The triplet coupling is due to the two equivalent PMe3’s (JH−P = 22.0 Hz), while the doublet coupling is due to rhodium (JH−Rh = 15.0 Hz). The magnitude of JH−P clearly indicates that the phosphines lie cis to the hydride.11 The equivalence of the two PMe3 ligands is clear from the 31P{1H} NMR spectrum, where they appear as a single rhodium-coupled doublet (JP−Rh = 118.4 Hz). In addition, the phosphines must reside cis to one another, because only in this geometry are they equivalent by symmetry. Consistent with the cis geometry is the observation that the PMe3 methyl H’s and methyl C’s exhibit characteristic “filled-in doublets” in their 1H and 13C{1H} NMR spectra, respectively.12a Finally, when 3 is treated with additional PMe 3 , it is converted to (H)Rh(η 1 O3SCF3)2(PMe3)3, 6, which is described in Results and Discussion Section F. D. Synthesis, Spectroscopy, and Structure of (1,2,3η3)-(5-tert-Butylazapentadienyl)Rh(PMe3)3, 4. Treatment of [(cyclooctene)2Rh(μ-Cl)]2 with 6 equivalents of PMe3, followed by at least 2 equivalents of potassium tertbutylazapentadienide, leads to the formation of orange (1,2,3η3)-(5-tert-butylazapentadienyl)Rh(PMe3)3 as a 85:15 mixture of anti and syn isomers, 4a and 4s, respectively (see Scheme 3). Compound 4 can also be obtained by treating 1 with one additional equivalent of PMe3. In the 1H NMR spectrum of the major anti isomer, 4a, H4 resonates at δ 6.52 and is a doublet due to coupling to H3 (JH4−H3 = 9.0 Hz), while the H3 signal appears at δ 3.75. As expected, the minor syn isomer exhibits a more downfield doublet for H4 (δ 7.48) and a more upfield signal for H3 (δ 2.75). In the 13C{1H} NMR spectrum of 4a, noncoordinated carbon C4 resonates far downfield at δ 155.5. The remaining coordinated azapentadienyl carbons appear upfield between δ 29.0 and 68.4. Similar shifts are observed for isomer 4s. The 31P{1H} NMR spectrum of 4a at −10 °C is a broad doublet (JP−Rh = 154.3 Hz) due to a facile fluxional process, probably rotation of the azapentadienyl ligand with respect to the RhP3 moiety.13 When the sample is cooled to −70 °C, some additional broadening of the signal is observed, but there is no clean separation of phosphine peaks. Similar behavior is observed for 4s. In the infrared spectrum of 4, the CN stretches appear at 1621.2 and 1602.6 cm−1.

Figure 1. Molecular structure of the cation in (1,2,3-η 3 )(CH2CHCHCHNH(tert-butyl))Rh(PMe3)2+O3SCF3−, 2, using thermal ellipsoids at the 50% probability level. The methyl H’s on the PMe3 ligands and on the tert-butyl group are not shown. Selected bond distances (Å): Rh1−P1, 2.2849(14); Rh1−P2, 2.2518(14); Rh1−C1, 2.217(5); Rh1−C2, 2.159(5); Rh1−C3, 2.215(5); C1−C2, 1.382(7); C2−C3, 1.445(7); C3−C4, 1.411(6); C4−N1, 1.316(6); C5−N1, 1.486(6).

caption. The structure clearly shows the anti (cis) geometry about C2−C3 (torsional angle C1−C2−C3-C4 = 17.7°) and the trans geometry about C3−C4 (torsional angle C2−C3− C4−N1 = 173.8(5)°), resulting in a sickle-shaped ligand. C4 and N1 lie 0.363 and 0.481 Å, respectively, out of the C1−C2− C3 plane. The bond distances of Rh to the three allyl carbons fall in the range 2.159(5) to 2.215(5) Å, while C4 resides 2.626 Å from Rh, just outside the normal bonding distance.7 The η3allyl fragment shows delocalized bonding (C1−C2 = 1.382(7) Å, C2−C3 = 1.445(7) Å), while C3−C4 (1.411(6) Å) is shorter than a normal C−C single bond and C4−N1 (1.316(6) Å) is slightly longer than a normal C−N double bond.8 These bond distances suggest that there may be a small contribution from the η4 resonance structure II (Chart 1), which may also explain why 2 exists only as the anti isomer. However, the Chart 1

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Scheme 2

Scheme 3

Compound 5 can also be obtained by treating 2 with one additional equivalent of PMe3. The NMR spectra of 5 indicate that it is a single isomer in which the nitrogen has been protonated (see Scheme 3). In the 1H NMR spectrum of 5, the NH proton is shifted significantly upfield (to δ 3.97) as compared to its position in 2 (δ 8.32), reflecting less positive charge at nitrogen. It appears as a doublet with a strong 12.0 Hz coupling to H4. H4 is likewise shifted markedly upfield (to δ 4.03) as compared to its position in 2 (δ 6.63). It appears as a doublet of doublets with coupling to both NH (12.0 Hz) and H3 (8.7 Hz). The remaining azapentadienyl hydrogens resonate at δ 5.15 (H3), 4.92 (H2), 1.52 (H1), and 0.22 (H1). The downfield chemical shift position of H3, along with its small coupling to H2 (J = 5.1 Hz), strongly suggests an anti geometry for the protonated azapentadienyl ligand. In the 13C{1H} NMR spectrum of 5, C4 is shifted significantly upfield (to δ 96.9) as compared to its position in 2 (δ 136.0). It appears as a quartet (J = 8.3 Hz) due to coupling to three equivalent 31P nuclei. (The phosphines are equivalent

When 4 is dissolved in a minimal quantity of pentane and cooled to −30 °C, orange crystals of 4a are formed overnight. The X-ray crystal structure of 4a is shown in Figure 2, while selected bond distances are summarized in the caption. The anti geometry and overall sickle shape of the ligand are evident from the torsional angles: C1−C2−C3−C4 = 35.5(7)° and C2−C3−C4−N1 = 162.0(4)°. C4 and N1 lie 0.692 and 0.933 Å, respectively, out of the C1−C2−C3 plane. The bond distances of Rh to the three allyl carbons fall in the range 2.087(4) to 2.222(5) Å, while the Rh−C4 distance of 3.032 Å is clearly nonbonding. The bond distances within the allyl moiety are delocalized as expected with C1−C2 = 1.424(7) Å and C2− C3 = 1.427(7) Å. The C3−C4 bond distance is 1.449(6) Å, while C4−N1 is 1.282(6) Å, typical for a C−N double bond. E. Monoprotonation of Compound 4. Synthesis, Spectroscopy, and Structure of (η4-(tert-Butylamino)butadiene)Rh(PMe3)3+O3SCF3−, 5. Treatment of 4 with 1 equivalent of triflic acid in diethyl ether leads to the immediate precipitation of dark red 5, the monoprotonation product. 6413


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Figure 2. Molecular structure of (1,2,3-η3)-(5-tertbutylazapentadienyl)Rh(PMe3)3, 4, using thermal ellipsoids at the 50% probability level. The methyl H’s on the PMe3 ligands and on the tert-butyl group are not shown. Selected bond distances (Å): Rh1−P1, 2.2772(12); Rh1−P2, 2.3202(13); Rh1−P3, 2.2640(13); Rh1−C1, 2.158(4); Rh1−C2, 2.087(4); Rh1−C3, 2.222(5); C1−C2, 1.424(7); C2−C3, 1.427(7); C3−C4, 1.449(6); C4−N1, 1.282(6); C5−N1, 1.479(6).

Figure 3. Molecular structure of the cation in (η4-(tert-butylamino)butadiene)Rh(PMe3)3+O3SCF3−, 5, using thermal ellipsoids at the 50% probability level. The methyl H’s on the PMe3 ligands and on the tert-butyl group are not shown. Selected bond distances (Å): Rh1−P1, 2.3068(6); Rh1−P2, 2.3191(5); Rh1−P3, 2.2910(5); Rh1−C1, 2.1740(17); Rh1−C2, 2.1246(17); Rh1−C3, 2.2457(17); Rh1−C4, 2.5083(18); C1−C2, 1.419(3); C2−C3, 1.418(2); C3−C4, 1.404(2); C4−N1, 1.369(2); C5−N1, 1.476(2); N1−H1, 0.83(2).

due to a fluxional process, vide inf ra.) The remaining azapentadienyl carbons appear at δ 78.6 (C3), 75.9 (C2), and 32.6 (C1). C1, like C4, shows coupling (J = 9.0 Hz) to three equivalent 31P nuclei. The 31P{1H} NMR spectrum of 5 consists of a broad Rhcoupled doublet at room temperature, but resolves into three well-defined doublet of doublet of doublet patterns (each 31P nucleus is coupled to Rh and the other two 31P’s) when cooled to −70 °C. This indicates that the fluxional process, probably a rotation of the protonated azapentadienyl ligand with respect to the RhP3 moiety, can be “frozen” at low temperature. The significant upfield shifts of NH, H4, and C4 observed in the 1H and 13C{1H} NMR spectra led us to expect a much larger contribution from the η4 resonance structure (IV, Chart 2) to the overall bonding picture in 5. In this structure, the

moiety (distances range from 2.1246(17) to 2.2457(17) Å) and a weaker interaction between Rh and C4 (2.5083(18) Å).7 The bonding within the allyl portion of the azapentadienyl ligand is fully delocalized, while C3−C4 (1.404(2) Å) and C4−N1 (1.369(2) Å) are also intermediate in length between typical single and double bonds.8 The hydrogen atom on nitrogen (H1) was located and refined. The H1−N1−C4 and H1−N1− C5 angles are 113.2 (17)° and 113.1(17)°, respectively, intermediate between tetrahedral (109.5°) and trigonal planar (120°). All of the spectroscopic and structural data cited above are consistent with the idea that both resonance structures III and IV are important contributors to the overall bonding picture in 5.14 In Scheme 3 and elsewhere, we have chosen to draw the structure of 5 with a dotted line from Rh to C4, emphasizing that this is a weak bonding interaction. However, other representations for the bonding are equally valid. F. Further Protonation of Compound 5. Synthesis, Spectroscopy, and Structure of (H)Rh(η1O3SCF3)2(PMe3)3, 6. When compound 5 is dissolved in acetonitrile and treated with triflic acid, protonation occurs at the rhodium center, followed by reductive elimination of protonated tert-butylcrotonaldimine. Addition of another equivalent of triflic acid at rhodium leads to the isolated yellow product (H)Rh(η1-O3SCF3)2(PMe3)3, 6 (see Scheme 4). The same products are observed when compound 4 is treated with excess triflic acid in acetonitrile. As before, NMR analysis of the protonated imine reveals that it has trans geometry about C2−C3, suggesting that the protonated azapentadienyl ligand isomerizes from anti to syn geometry before reductive elimination (D to E, Scheme 4). The 1 H NMR spectrum of the rhodium product shows a hydride signal at δ −17.11 with an apparent doublet of quartets splitting pattern (J = 22.0 Hz, 15.0 Hz). The magnitude of these

Chart 2

formal positive charge at Rh can be stabilized by the three e−donating PMe3 ligands. Our expectations were confirmed in the X-ray crystal structure of 5, which is presented in Figure 3. The structure clearly shows the anti geometry and the overall sickle shape of the azapentadienyl ligand. The relevant torsional angles are C1−C2−C3−C4 = 5.0(3)° and C2−C3−C4−N1 = 177.83(17)°. Carbons C1, C2, C3, and C4 deviate from planarity by an average of only 0.016 Å, while N1 lies just 0.075 Å out of that plane. The rhodium−carbon distances reveal strong interactions between Rh and the C1−C2−C3 allyl 6414


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Scheme 4

coupling constants indicates that the hydride ligand resides cis to any phosphines in the molecule.11 The 31P{1H} NMR exhibits two signals: a doublet of triplets (intensity = 1) due to a unique phosphine and a doublet of doublets (intensity = 2) due to two equivalent phosphines. In each case, the large doublet coupling (J = 118.8 and 88.4 Hz, respectively) is due to rhodium, while the smaller coupling (J = 32.3 Hz) is due to phosphorus. The fact that the hydride must lie cis to all of the phosphines (vide supra) implies that the two equivalent phosphines are mutually trans. This is supported by the observation of virtual triplet signals in the phosphine regions of both the 1H and 13C{1H} spectra.12b Yellow crystals of 6 were obtained from dichloromethane at −30 °C, and the X-ray crystal structure is presented in Figure 4. As predicted from the NMR analysis above, the three PMe3 ligands occupy meridional sites in octahedral 6. The hydride ligand lies cis to all three PMe3’s and trans to triflate. A second

triflate occupies the sixth site. As mentioned earlier, compound 6 is also produced upon treatment of compound 3 with PMe3. G. Synthesis and Spectroscopy of (1,2,3-η3)-(5-tertButylazapentadienyl)Ir(PEt 3 ) 2 , 7. Treatment of [(cyclooctene)2Ir(μ-Cl)]215 with 4 equivalents of PEt3, followed by at least 2 equivalents of potassium tertbutylazapentadienide, leads to the production of red-orange (1,2,3-η3)-(5-tert-butylazapentadienyl)Ir(PEt3)2, 7, as a 67:33 mixture of anti and syn isomers, 7a and 7s, respectively (see Scheme 5).16 In the 1H NMR, the anti isomer 7a exhibits a downfield doublet at δ 6.49 due to H4. The doublet results from coupling to H3 (J = 8.7 Hz). H3, in turn, resonates at δ 4.37. In the syn isomer, 7s, H4 is shifted downfield to δ 7.65, while H3 is shifted upfield to δ 3.00. These shifts result from changes in the proximity of H4 and H3 to the metal center, as discussed earlier for compound 1. In the 13C{1H} NMR spectrum of 7a, the azapentadienyl carbons are observed at δ 153.0 (C4), 92.1 (C2), 61.9 (C3), and 39.7 (C1). The signals for C3 and C1 show strong coupling to the 31P’s that reside approximately trans to them (JC3−P = 22.1 Hz, JC1−P = 25.9 Hz) in the square planar coordination geometry of 7a. Similar 13C{1H} NMR peaks are observed for the minor isomer, 7s. In the 31P{1H} NMR, each isomer gives rise to two equal-intensity doublets due to the PEt3 ligands. The doublets result from weak cis P−P coupling (JP−P = 4.0 Hz for 7a and 6.8 Hz for 7s). There is no evidence of fluxional behavior at room temperature. In the infrared spectrum of 7, the CN stretches occur at 1627.7 and 1610.4 cm−1. H. Monoprotonation of Compound 7. Synthesis and Spectroscopy of (1,2,3-η3,5-η1)-(5-tertButylazapentadienyl)Ir(H)(PEt3)2+O3SCF3−, 8. Treatment of compound 7 with 1 equivalent of triflic acid in diethyl ether leads to the formation of dark red 8, the monoprotonation product. The NMR spectra of 8 indicate that it is a single isomer in which protonation has occurred at the iridium center and the azapentadienyl ligand has coordinated in an unusual η3, η1 fashion involving both its allyl moiety and its nitrogen lone pair (see Scheme 5).17 In the 1H NMR spectrum, the metal hydride signal is observed at δ −28.79 and is a doublet of doublets due to coupling to two inequivalent PEt3’s. The coupling constants of 24.3 and 17.4 Hz indicate that the

Figure 4. Molecular structure of (H)Rh(η1-O3SCF3)2(PMe3)3, 6, using thermal ellipsoids at the 50% probability level. The methyl H’s on the PMe3 ligands are not shown. Selected bond distances (Å): Rh1−P1, 2.2217(4); Rh1−P2, 2.3693(4); Rh1−P3, 2.3475(4); Rh1− O1, 2.1944(10); Rh1−O4, 2.2464(11); Rh1−H1, 1.44(2). 6415


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Scheme 5

Scheme 6

hydride lies cis to both phosphines.11 Azapentadienyl hydrogen H4 appears unusually far downfield at δ 9.52 and is a singlet. In all of the other azapentadienyl complexes that we have studied, H4 couples strongly to H3 (typically J ≈ 9 Hz), so the absence of H4−H3 coupling in 8 provides an important structural clue. Simple modeling suggests that in the proposed η3, η1 structure, H4 and H3 would lie almost perpendicular to each other, resulting in minimal coupling.18 The remaining azapentadienyl hydrogens appear at normal chemical shift positions: δ 5.28 (H2), 4.64 (H3, doublet, coupled only to H2), 3.18 (H1), and 2.3 (H1). In the 13C{1H} NMR spectrum of 8, C4 resonates at δ 167.4, indicating that it is not coordinated to iridium. The remaining azapentadienyl carbons appear at δ 99.8 (C2), 52.8 (C3), and 35.9 (C1). Both C3 and C1 are strongly coupled to phosphorus (JC3−P = 19.4 Hz, JC1−P = 29.8 Hz), indicating that they lie approximately trans to phosphines. The 31P{1H} NMR

spectrum shows the expected pair of weakly coupled doublets (JP−P = 5.9 Hz) due to the two inequivalent cis PEt3 ligands. In the infrared spectrum of 8, the CN stretch is observed at 1620.3 cm−1. In order to eliminate the possibility that triflate is actually coordinated to iridium (in place of the azapentadienyl nitrogen), we carried out the reaction of 7 with HBF4·OEt2, an acid with a noncoordinating anion. As expected, the same product was obtained (except for the different anion). Furthermore, if triflate were coordinated to iridium, the compound would be neutral and should have solubility in diethyl ether and perhaps even pentane. Compound 8, on the contrary, is insoluble in these solvents. It is interesting to note that protonation of (1,2,3-η3)-(5-tertbutylazapentadienyl)Rh(PMe3)2, 1, occurs at nitrogen (vide supra) to produce 2, while protonation of (1,2,3-η3)-(5-tertbutylazapentadienyl)Ir(PEt3)2, 7, occurs at iridium to produce 6416


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Scheme 7

can be synthesized by the two-step procedure shown in Scheme 6. First, treatment of compound 8 with bis(triphenylphosphoranylidene)ammonium chloride (PPN+Cl−), a source of chloride, leads to the clean formation of orange (1,2,3-η3)-(5-tert-butylazapentadienyl)Ir(H)(Cl)(PEt3)2 as a ∼50:50 mixture of anti and syn isomers, 10a and 10s, respectively,19 along with production of PPN+O3SCF3−. Unlike cationic 8, neutral compound 10 shows good solubility in diethyl ether. In the 1H NMR spectrum of 10a, the hydride resonates at δ −23.48 and is an apparent triplet due to coupling to the two cis-phosphine ligands (JH−P = 15.0 Hz). H4 appears at δ 7.24 and is coupled strongly to H3 (J = 11.1 Hz), signaling that N is no longer bonded to Ir. H3 resonates at the relatively downfield chemical shift position of δ 4.67. In the syn isomer, 10s, the hydride is likewise a triplet due to phosphorus coupling, while H4 is shifted downfield (δ 7.61) and H3 is shifted upfield (δ 3.46). These shifts are fully consistent with our observations in other related systems. In the 13C{1H} NMR spectrum of 10a, uncoordinated carbon C4 appears far downfield at δ 172.7, while coordinated carbons C1 (δ 50.7) and C3 (δ 46.6) are strongly coupled to the 31P’s of phosphine ligands that lie approximately trans to them (JC1−P = 24.9 Hz, JC3−P = 23.8 Hz). In the 31P{1H} NMR spectrum of 10a, two weakly coupled doublets are observed for the inequivalent cis PEt3’s (JP−P = 6.2 Hz). Similar 13C{1H} and 31 1 P{ H} NMR signals are observed for 10s. In the infrared spectrum of 10, the CN stretch is observed at 1632.9 cm−1. Treatment of compound 10 with 1 equivalent of triflic acid in diethyl ether leads to protonation at nitrogen and the immediate precipitation of dark orange 11 as a 67:33 mixture of anti and syn isomers, 11a and 11s, respectively (Scheme 6). As expected, the NMR and IR spectra of 11 closely resemble those of 9 and are tabulated in the Experimental Section. K. Synthesis, Spectroscopy, and Structure of (1,2,3η3)-(5-tert-Butylazapentadienyl)Ir(PEt3)3, 12. Treatment of [(cyclooctene)2Ir(μ-Cl)]2 with 6 equivalents of PEt3, followed

8. This difference in regiochemistry reflects rhodium’s greater preference for 16e− square planar Rh(I) geometries and iridium’s propensity to adopt 18e− octahedral Ir(III) geometries. I. Further Protonation of Compound 8. Synthesis and Spectroscopy of (1,2,3-η 3 )-(CH 2 CHCHCHNH(tertbutyl))Ir(H)(η1-O3SCF3)(PEt3)2+O3SCF3−, 9. When 8 is treated with an additional equivalent of triflic acid, the nitrogen center is protonated (presumably after dissociating from Ir), and the coordination site formerly occupied by nitrogen is filled with triflate, producing yellow-orange 9 as an 85:15 mixture of anti and syn isomers, 9a and 9s, respectively (see Scheme 5). The same product can be obtained by treating compound 7 with 2 equivalents of triflic acid. In the 1H NMR spectrum of the major isomer, 9a, the hydride resonates at δ −31.32 and is an apparent triplet due to coupling to the two cis-phosphines. Although the two phosphines are chemically inequivalent (vide inf ra), they happen to couple identically to the hydride. The NH resonates at δ 11.30 and is a doublet due to coupling to H4 (JNH‑H4 = 15.9 Hz). H4, in turn, appears at δ 7.59 and is a doublet of doublets due to coupling to both NH and H3 (JH4−H3 = 11.1 Hz). The reappearance of the coupling between H4 and H3 confirms that N is no longer bonded to Ir. H3 resonates at the relatively downfield position of δ 4.82, as expected for the anti isomer. In the 13C{1H} NMR spectrum of 9a, C4 resonates at δ 171.3, clearly indicating that it is uncoordinated to Ir. C1 (δ 53.5) and C3 (δ 51.5) are strongly coupled to the 31P’s of phosphines that reside trans to them (JC1−P = 22.1 Hz, JC3−P = 24.3 Hz). The 31P{1H} NMR spectrum of 9a consists of two weakly coupled doublets (JP−P = 4.8 Hz) for the inequivalent cis-PEt3’s. In the infrared spectrum, the CN stretch appears at 1641.3 cm−1. J. Synthesis and Spectroscopy of a Chloro-Containing Analogue of 9, (1,2,3-η3)-(CH2CHCHCHNH(tert-butyl))Ir(H)(Cl)(PEt3)2+O3SCF3−, 11. A close analogue of 9 in which a coordinated chloro ligand has replaced the coordinated triflate 6417


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C−N double bond.8 Overall, the structure of 12a is very similar to that of (1,2,3-η3)-(5-tert-butylazapentadienyl)Rh(PMe3)3, 4a, described earlier in this paper. L. Monoprotonation of Compound 12. Synthesis, Spectroscopy, and Structure of (η4-(tert-Butylamino)butadiene)Ir(PEt3)3+O3SCF3−, 13. Treatment of compound 12 with 1 equivalent of triflic acid in diethyl ether leads to the immediate precipitation of light yellow 13, the monoprotonation product. Unlike monoprotonation of (1,2,3-η3)-(5-tertbutylazapentadienyl)Ir(PEt3)2, which occurs at the iridium center (vida supra), monoprotonation of 12 occurs cleanly at the nitrogen center (see Scheme 7).21 In the 1H NMR spectrum of 13, the NH proton appears at δ 2.41, substantially upfield from its position in monoprotonated (1,2,3-η3)-(5-tertbutylazapentadienyl)Rh(PMe3)2, 2 (δ 8.32), or monoprotonated (1,2,3-η3)-(5-tert-butylazapentadienyl)Rh(PMe3)3, 5 (δ 3.97), reflecting less positive charge at nitrogen. It is a doublet as a result of coupling to H4 (J = 9.9 Hz). H4 resonates at δ 2.59 and is also shifted upfield from its position in 2 (δ 6.63) or 5 (δ 4.03). It appears as a doublet of doublets due to coupling to both NH (J = 9.9 Hz) and H3 (7.5 Hz). In the 13C{1H} NMR spectrum, C4 resonates at δ 76.1, substantially upfield from its position in 2 (δ 136.0) and 5 (δ 96.9), suggesting that it is more strongly bonded to the metal center in 13. The C4 signal is split into a quartet by coupling to three equivalent (by fluxionality) phosphines (JC−P = 9.9 Hz). The 31P{1H} NMR of 13 at room temperature is a broad singlet due to a fluxional process (probably ligand rotation) that exchanges the phosphine positions. This process is fully arrested at −60 °C, where three well-separated 31P peaks are observed for the three PEt3 ligands. Light yellow crystals of 13 are obtained when a saturated acetone solution is cooled to −30 °C, and the X-ray crystal structure is shown in Figure 6. As anticipated from the NMR data, the structure of 13 reflects a larger contribution from the

by at least 2 equivalents of potassium tert-butylazapentadienide, leads to the formation of yellow (1,2,3-η 3 )-(5-tertbutylazapentadienyl)Ir(PEt3)3 as an 80:20 mixture of anti and syn isomers, 12a and 12s, respectively (see Scheme 7).20 Compound 12 can also be obtained by treating 7 with one additional equivalent of PEt3. In the 1H NMR spectrum of the major anti isomer, 12a, H4 resonates at δ 6.76 and is a doublet due to coupling to H3 (J = 8.7 Hz), which, in turn, resonates at δ 3.37. In the 13C{1H} NMR spectrum of 12a, C4 resonates at δ 160.1, while the iridium-bonded carbons appear at δ 47.2 (C2), 40.0 (C3), and 12.4 (C1). The C3 and C1 signals are quartets (JC3−P = 7.2 Hz, JC1−P = 8.3 Hz) due to coupling to the three equivalent (by fluxionality) phosphines. The 31P{1H} NMR spectrum of 12a at room temperature is a broad singlet, probably resulting from a facile rotation of the azapentadienyl ligand with respect to the IrP3 moiety. Upon cooling to −60 °C, the broad peak decoalesces to a complex multiplet of intensity 2 (most likely due to the two phosphines that sit under the azapentadienyl “backbone”) and a doublet of doublets of intensity 1 (probably due to the phosphine under the azapentadienyl “mouth”). Similar NMR behavior is observed for the minor syn isomer. In the infrared spectrum of 12, the CN stretch is observed at 1611.8 cm−1. Yellow crystals of 12a are obtained by cooling a pentane/ acetone solution of 12 to −30 °C, and the X-ray crystal structure is presented in Figure 5. The anti geometry and

Figure 5. Molecule structure of (1,2,3-η3)-(5-tertbutylazapentadienyl)Ir(PEt3)3, 12, using thermal ellipsoids at the 50% probability level. Hydrogens on the PEt3 ligands and on the tertbutyl group are not shown. Selected bond distances (Å): Ir1−P1, 2.2924(13); Ir1−P2, 2.3163(14); Ir1−P3, 2.2971(13); Ir1−C1, 2.170(5); Ir1−C2, 2.085(5); Ir1−C3, 2.215(5); C1−C2, 1.429(8); C2−C3, 1.453(7); C3−C4, 1.455(7); C4−N1, 1.266(7); C5−N1, 1.470(7).

overall sickle shape of the ligand is reflected in the torsional angles: C1−C2−C3−C4 = 45.8(7)° and C2−C3−C4−N1 = 153.7(5)°. C4 and N1 lie 0.884 and 1.254 Å, respectively, out of the C1−C2−C3 plane. The bond distances of iridium to the three allyl carbons fall in the range of 2.085(5) to 2.215(5) Å, while the Ir−C4 distance of 3.183 Å is clearly nonbonding. The bond distances within the allyl moiety are delocalized with C1− C2 = 1.429(8) Å and C2−C3 = 1.453(7) Å. The C3−C4 bond distance is 1.455(7) Å, while C4−N1 is 1.266(7) Å, typical for a

Figure 6. Molecular structure of the cation in (η4-(tert-butylamino)butadiene)Ir(PEt3)3+O3SCF3−, 13, using thermal ellipsoids at the 50% probability level. Hydrogens on the PEt3 ligands and on the tert-butyl group are not shown. Selected bond distances (Å): Ir1−P1, 2.3219(4); Ir1−P2, 2.3380(4); Ir1−P3, 2.3202(4); Ir1−C1, 2.1625(13); Ir1−C2, 2.1522(13); Ir1−C3, 2.2392(13); Ir1−C4, 2.3382(14); C1−C2, 1.447(2); C2−C3, 1.419(2); C3−C4, 1.4161(19); C4−N1, 1.4140(18); N1−C5, 1.4849(18); N1−H1A, 0.896(5). 6418


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η4 resonance structure (see VI, Chart 3) than either 2 or 5. The Ir−C4 bond distance in 13 is 2.3382(14) Å, well within the Chart 3

normal bonding range and significantly shorter than the Rh− C4 distances in 2 (2.626 Å) or 5 (2.5083(18) Å). The other three Ir−C distances in 13 range from 2.1522(13) to 2.2392(13) Å. The larger contribution from resonance structure VI is also reflected in the C4−N1 distance of 1.4140(18) Å. This is significantly longer than the corresponding C4−N1 distances in 2 (1.316(6) Å) and 5 (1.369(2) Å). The carbon−carbon distances within the butadiene moiety are delocalized and range from 1.4161(19) to 1.447(2) Å. The torsional angles reflect the sickle shape of the ligand and its planarity: C1−C2−C3−C4 = 0.68(19)° and C2−C3−C4−N1 = 176.20(12)°. The carbon atoms within the butadiene moiety (C1, C2, C3, and C4) exhibit an average deviation from planarity of only 0.004 Å, while N1 resides just 0.160 Å out of that plane. The hydrogen atom on nitrogen (H1A) was located and refined. The H1A−N1−C4 and H1A−N1−C5 angles are 111.3(13)° and 108.4(13)°, consistent with tetrahedral (sp3) geometry at nitrogen. All of the spectroscopic and structural data cited above point toward resonance structure VI being the dominant contributor to the bonding in 13. Therefore, we have drawn it as an η4butadiene-iridium complex in Scheme 7 and elsewhere. M. Further Protonation of Compound 13. Synthesis, Spectroscopy, and Structure of (η4-(tertButylammonium)butadiene)Ir(PEt3)32+(O3SCF3−)2, 14. Treatment of compound 13 with one additional equivalent of triflic acid leads to the immediate precipitation of light yellow 14, the diprotonation product, from THF. The NMR spectra of 14 indicate that the second protonation occurs at nitrogen, producing a tert-butylammonium-substituted butadiene compound, as shown in Scheme 7.21 The same product can be obtained by treating compound 12 with 2 equivalents of triflic acid. In the 1H NMR spectrum of 14, the two NH protons resonate at δ 7.03 and 6.78, far downfield from the NH shift position in monoprotonated 13 (δ 2.41). This downfield shift reflects the formal positive charge on nitrogen in 14. The hydrogens on the butadiene moiety resonate at δ 5.98 (H3), 5.19 (H2), 2.24 (H1), 1.48 (H4), and −0.14 (H1). In the 13 C{1H} NMR, the butadiene carbons are observed at δ 83.5 (C3), 75.4 (C2), 46.5 (C4), and 26.7 (C1). Both C4 and C1 are strongly coupled to phosphorus (JC4−P = 53.6 Hz, JC1−P = 34.2 Hz). The 31P{1H} NMR spectrum consists of three wellseparated phosphine peaks with no indication of fluxionality at room temperature. All of the NMR data suggest a “normal” η4butadiene ligand. This conclusion is confirmed by the X-ray crystal structure of 14, which is presented in Figure 7. The distances from Ir to each of the four butadiene carbons are essentially identical, ranging from 2.183(3) to 2.201(3) Å. The carbon−carbon bonds within the butadiene moiety are delocalized and range

Figure 7. Molecular structure of the dication in (η 4 -(tertbutylammonium)butadiene)Ir(PEt3)32+(O3SCF3−)2, 14, using thermal ellipsoids at the 50% probability level. Hydrogens on the PEt3 ligands and on the tert-butyl group are not shown. Selected bond distances (Å): Ir1−P1, 2.3418(8); Ir1−P2, 2.3230(8); Ir1−P3, 2.3581(8); Ir1− C1, 2.183(3); Ir1−C2, 2.195(3); Ir1−C3, 2.201(3); Ir1−C4, 2.192(3); C1−C2, 1.431(4); C2−C3, 1.403(4); C3−C4, 1.440(4); C4−N1, 1.477(4); N1−C5, 1.542(4).

from 1.403(4) to 1.440(4) Å, while the C4−N1 bond distance is 1.477(4) Å, normal for a C−N single bond.8 Torsional angle C1−C2−C3−C4 is 1.1(4)°, while torsional angle C2−C3− C4−N1 is 172.7(3)°, reflecting both the sickle shape of the ligand and its planarity. The average deviation of C1, C2, C3, and C4 from planarity is 0.004 Å, while N1 lies just 0.16 Å from that butadiene plane.

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SUMMARY In this study we have investigated the reactivity of four related compounds, (1,2,3-η3)-(5-tert-butylazapentadienyl)Rh(PMe3)x (1, x = 2; 4, x = 3) and (1,2,3-η3)-(5-tert-butylazapentadienyl)Ir(PEt3)x (7, x = 2; 12, x = 3), toward the simplest of electrophiles, H+. In each case, we have investigated the products obtained upon treatment with 1 equivalent of acid in order to determine the primary site of electrophilic addition. These monoprotonated products have then been treated with additional acid to ascertain secondary sites of reactivity. Our results are summarized in Scheme 8. The primary site of reactivity for compound 1 is the nitrogen atom, leading to monoprotonation product 2, in which the η3 bonding mode is retained and the rhodium center remains square planar and 16e−. In contrast, the primary site of reactivity for the iridium analogue, 7, is the iridium center, and metal-hydride 8 is the product. In this case, the azapentadienyl ligand adopts an unusual η3, η1 bonding mode in which the nitrogen atom is coordinated to iridium. The driving force for this reaction may be iridium’s preference for 18 valence electrons and an octahedral coordination geometry. Turning next to the tris(phosphine) starting materials, we have found that both rhodium compound 4 and iridium compound 12 react with H+ at nitrogen to produce monoprotonated products 5 and 13, respectively. However the bonding mode of the protonated ligand differs somewhat in these two products. In 12, the X-ray structure and NMR spectra point toward a dominant η4 resonance structure, and the protonated azapentadienyl is best viewed as an η4-tert6419


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Scheme 8

monoprotonated 13 with additional acid leads to a second protonation at nitrogen and production of the η4-(tertbutylammonium)butadiene species 14. Why does 13 react at nitrogen while 2 and 5 react at the metal center? This can be explained by recalling that resonance structure VI, where the formal charge resides on the metal rather than on nitrogen, dominates the bonding in 13. Hence, the second protonation occurs at N, because it bears less positive charge. Through this study, we have elucidated the preferred primary and secondary sites for electrophilic addition to a family of related azapentadienyl-rhodium and -iridium complexes. We are continuing to investigate heteropentadienyl-metal complexes with the goal of discovering interesting and unusual reactivity, both stoichiometric and catalytic.

butylaminobutadiene ligand. In 5, however, the Rh−C4 bond distance is very long (2.5083(18) Å), indicating a weak interaction, and the C4−N distance (1.369(2) Å) lies between those of normal C−N single and double bonds. Hence, the bonding mode in 5 can be viewed as intermediate between η3 (like 2) and η4 (like 13). It should be noted that in the η4 bonding mode formal charge resides on the metal center, where it can be neutralized by the electron-donating PR3 ligands. This is an important stabilizing effect, particularly in the tris(phosphine) systems. When monoprotonated rhodium compounds 2 and 5 are treated with additional acid, the second protonation occurs at rhodium. The resulting protonated azapentadienyl-Rh-hydride intermediates are unstable with respect to reductive elimination, so protonated tert-butylcrotonaldimine is released and octahedral Rh(III) compounds are isolated (after addition of a third equivalent of acid.) Why do these second protonations occur at rhodium rather than at nitrogen? This regiochemistry reflects the fact that the nitrogens already bear significant positive charge in 2 and 5, because resonance structures I and III are important contributors to the bonding (vide supra). The monoprotonated iridium compounds, in contrast, react with additional acid at nitrogen. In the case of monoprotonated compound 8, addition of acid produces the N-protonated η3tert-butylazapentadienyl product 9. Similarly, treatment of

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EXPERIMENTAL SECTION

General Comments on Experimental Techniques. All manipulations were carried out under a nitrogen atmosphere, using either glovebox or double-manifold Schlenk techniques. Solvents were stored under nitrogen after being distilled from the appropriate drying agents. Deuterated NMR solvents were obtained in sealed vials and used as received. [(Cyclooctene)2Rh(μ-Cl)]2,5 [(cyclooctene)2Ir(μCl)]2,15 and potassium tert-butylazapentadienide4 were prepared by literature procedures. RhCl3·3H2O (Pressure Chemical Co.), IrCl3· 3H2O (Pressure), cis-cyclooctene (VWR), trimethylphosphine (Aldrich), triethylphosphine (VWR), trifluoromethanesulfonic acid 6420


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(Aldrich), tetrafluoroboric acid-diethyl etherate (Aldrich), and bis(triphenylphosphoranylidene)ammonium chloride (Aldrich) were used as received. NMR experiments were performed on a Varian Unity Plus-300 spectrometer (1H, 300 MHz; 13C, 75 MHz; 31P, 121 MHz), a Varian Mercury-300 spectrometer (1H, 300 MHz; 13C, 75 MHz; 31P, 121 MHz), a Varian Unity Plus-500 spectrometer (1H, 500 MHz; 13C, 125 MHz; 31P, 202 MHz), or a Varian Unity-600 spectrometer (1H, 600 MHz; 13C, 150 MHz; 31P, 242 MHz). 1H and 13C spectra were referenced to tetramethylsilane, while 31P spectra were referenced to external H3PO4. HMQC (1H-detected multiple quantum coherence), HMBC (heteronuclear multiple-bond correlation), and COSY (correlation spectroscopy) experiments aided in assigning some of the 1H and 13C peaks. In all of the NMR spectra, carbon atoms and associated hydrogens are numbered by starting at the end of the chain opposite nitrogen. Mass spectra were obtained on a high-resolution quadrupole timeof-flight (Q-ToF) mass spectrometer (Maxis 4G) using electrospray ionization (ESI) as source. Infrared spectra were obtained on a PerkinElmer Spectrum BX FT-IR spectrometer. Microanalyses were performed by Galbraith Laboratories, Inc. (Knoxville, TN, USA). Synthesis of (1,2,3-η3)-(5-tert-Butylazapentadienyl)Rh(PMe3)2, 1. Trimethylphosphine (0.21 g, 2.8 mmol) was added dropwise to a cold (−30 °C) stirred solution of [(cyclooctene)2Rh(μ-Cl)]2 (0.50 g, 0.70 mmol) in 30 mL of tetrahydrofuran (THF). The mixture was slowly warmed to room temperature with stirring for 30 min. The resulting orange solution was cooled to −30 °C before addition of potassium tert-butylazapentadienide (0.46 g, 2.8 mmol) in 10 mL of cold (−30 °C) THF. After the mixture was warmed to room temperature and stirred for 3 h, the solvent was removed under vacuum. The residue was then extracted with pentane and filtered through Celite. Removal of pentane under vacuum yielded 1 as an orange oil. Yield: 0.45 g (85%). Note: anti and syn isomers of 1 exist in a 50:50 equilibrium mixture, making it difficult to assign some of the peaks to a particular isomer. For example, the 31P signals assigned below may actually belong to the other isomer. High-resolution ESI-MS: calcd for [M + H]+ (C14H32RhNP2+), 380.1138; found, 380.1125. IR (Nujol null): 1624.7, 1604.1 cm−1 (CN). Anti (50%) Isomer, 1a. 1H NMR (acetone-d6, 22 °C): δ 6.59 (d, JH4−H3 = 9.3 Hz, 1, H4), 4.80 (m, 1, H2), 4.35 (m, 1, H3), 2.75 (m, 1, H1), 2.23 (m, 1, H1), 1.3−1.45 (complex m, 18, PMe3’s), 1.02 (s, 9, tBu). 13C{1H} NMR (acetone-d6, 22 °C): δ 151.1 (d, J = 3.3 Hz, C4), 102.7 (d, J = 6.1 Hz, C2), 68.0 (apparent dt, J = 21.0 Hz, 6.6 Hz, C3), 55.3 (s, t-Bu C), 46.5 (ddd, J = 25.4 Hz, 7.7 Hz, 2.5 Hz, C1), 29.6 (s, tBu CH3’s), 22.0 (complex m, PMe3), 19.8 (complex m, PMe3). 31 1 P{ H} NMR (acetone-d6, 22 °C): δ −7.8 (dd, JP−Rh = 194.1 Hz, JP−P = 35.9 Hz, 1, PMe3), −13.0 (dd, JP−Rh = 187.0 Hz, JP−P = 35.9 Hz, 1, PMe3). Syn (50%) Isomer, 1s. 1H NMR (acetone-d6, 22 °C): δ 7.68 (d, JH4−H3 = 9.0 Hz, 1, H4), 4.97 (m, 1, H2), 3.24 (m, 1, H3), 2.91 (m, 1, H1), 2.23 (m, 1, H1), 1.3−1.45 (complex m, 18, PMe3’s), 1.15 (s, 9, tBu). 13C{1H} NMR (acetone-d6, 22 °C): δ 161.1 (d, J = 2.7 Hz, C4), 108.5 (d, J = 5.5 Hz, C2), 68.0 (apparent dt, J = 21.0 Hz, 6.6 Hz, C3), 55.7 (s, t-Bu C), 50.8 (ddd, J = 23.2 Hz, 7.2 Hz, 2.5 Hz, C1), 30.2 (s, tBu CH3’s), 22.0 (complex m, PMe3), 19.8 (complex m, PMe3). 31 1 P{ H} NMR (acetone-d6, 22 °C): δ −9.8 (dd, JP−Rh= 193.4 Hz, JP−P = 33.3 Hz, 1, PMe3), −13.5 (dd, JP−Rh = 186.9 Hz, JP−P = 33.3 Hz, 1, PMe3). Synthesis of (1,2,3-η 3 )-(CH 2 CHCHCHNH(tert-butyl))Rh(PMe3)2+O3SCF3−, 2. Compound 1 (0.37 g, 0.98 mmol) was dissolved in 15 mL of diethyl ether and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.74 mL, 0.98 mmol) was then added dropwise, causing a dark red precipitate to form immediately. The reaction mixture was stirred for 10 min before the resulting precipitate was filtered and washed with diethyl ether and pentane, giving a dark red powder. The powder was dissolved in a small quantity of acetone and cooled to −30 °C. Dark red crystals of 2 formed overnight. Yield: 0.41 (79%).

Anal. Calcd for C15H33RhNO3F3P2S: C, 34.03; H, 6.30. Found: C, 33.79; H, 6.14. IR (Nujol null): 1607.3 cm−1 (CN). 1H NMR (acetone-d6, 22 °C): δ 8.32 (d, JNH‑H4 = 14.4 Hz, 1, NH), 6.63 (dd, JH4‑NH = 14.4 Hz, JH4−H3 = 11.7 Hz, 1, H4), 5.26 (m, 1, H2), 4.79 (m, 1, H3), 2.92 (m, 1, H1), 2.46 (m, 1, H1),1.56 (d, JH−P = 9.0 Hz, 9, PMe3), 1.46 (d, JH−P = 8.7 Hz, 9, PMe3), 1.33 (s, 9, t-Bu). 13C{1H} NMR (acetone-d6, 22 °C): δ 136.0 (s, C4), 100.8 (d, J = 7.2 Hz, C2), 63.7 (dd, J = 12.1 Hz, 5.0 Hz, C3), 54.5 (s, t-Bu C), 51.5 (dd, J = 18.8 Hz, 7.2 Hz, C1), 28.6 (s, t-Bu CH3’s), 19.6 (d, JC−P = 28.1 Hz, PMe3), 17.4 (d, JC−P = 27.1 Hz, PMe3). 31P{1H} NMR (acetone-d6, 22 °C): δ −9.6 (dd, JP−Rh = 194.7 Hz, JP−P = 42.9 Hz, 1, PMe3), −14.6 (dd, JP−Rh = 176.1 Hz, JP−P = 42.9 Hz, 1, PMe3). Synthesis of (H)Rh(η1-O3SCF3)(η2-O3SCF3)(PMe3)2, 3. Compound 2 (0.14 g, 0.26 mmol) was dissolved in 5 mL of CH3CN and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.59 mL, 0.78 mmol) was then added, causing the solution color to change from dark red to yellow immediately. The volatiles were removed under vacuum. The residue was washed with diethyl ether and pentane and dried under vacuum, giving a yellow solid, 3. Yield: 0.11 g (79%). Note: This compound was also synthesized by treating compound 1 with excess triflic acid in acetonitrile. Because this product could not be fully separated from protonated imine (see Scheme 2), elemental analysis was not obtained. 1H NMR (acetonitrile-d3, 22 °C): δ 1.72 (“filled-in” d, JH−P = 11.7 Hz, 18, PMe3’s), −17.02 (t of d, JH−P = 22.0 Hz, JH−Rh = 15.0 Hz, 1, Rh-H). 13C{1H} NMR (acetonitrile-d3, 22 °C): δ 17.3 (“filled-in” d, JC−P = 39.7 Hz, PMe3’s). 31P{1H} NMR (acetonitrile-d3, 22 °C): δ 13.9 (d, JRh−P = 118.4 Hz, PMe3’s). Synthesis of (1,2,3-η3)-(5-tert-Butylazapentadienyl)Rh(PMe3)3, 4. Trimethylphosphine (0.32 g, 4.2 mmol) was added dropwise to a cold (−30 °C) stirred solution of [(cyclooctene)2Rh(μ-Cl)]2 (0.50 g, 0.70 mmol) in 30 mL of THF. The mixture was slowly warmed to room temperature with stirring for 30 min. The resulting light orange solution was cooled to −30 °C before addition of potassium tertbutylazapentadienide (0.46 g, 2.8 mmol) in 10 mL of cold (−30 °C) THF. After the mixture was warmed to room temperature and stirred for 3 h, the solvent was removed under vacuum. The residue was then extracted with pentane and filtered through Celite. The extract was evacuated to dryness and dissolved in a minimal quantity of pentane. The solution was cooled to −30 °C, producing orange crystals of 4 in a few days. Yield: 0.41 g (64%). Anal. Calcd for C17H41RhNP3: C, 44.83; H, 9.09. Found: C, 44.30; H, 9.13. IR (Nujol mull): 1621.2, 1602.6 cm−1 (CN). Anti (major, 85%) Isomer, 4a. 1H NMR (acetone-d6, 22 °C): δ 6.52 (d, JH4−H3 = 9.0 Hz, 1, H4), 4.50 (m, 1, H2), 3.75 (dd, JH3−H4 = 9.0 Hz, JH3−H2 = 5.7 Hz, 1, H3), 1.43 (m, 1, H1), 1.30 (br s, 27, PMe3’s), ∼1.1 (obscured, H1), 1.03 (s, 9, t-Bu). 13C{1H} NMR (acetone-d6, 22 °C): δ 155.5 (s, C4), 68.4 (s, C2), 62.1 (br s, C3), 54.9 (s, t-Bu C), 29.5 (s, t-Bu CH3’s), ∼29 (obscured, C1), 22.6 (br d, PMe3’s). 31P{1H} NMR (acetone-d6, −10 °C): δ −16.8 (br d, JP−Rh = 154.3 Hz, PMe3’s). Cooling to −70 °C leads to some broadening but no clean separation of peaks. Syn (minor, 15%) Isomer, 4s. 1H NMR (acetone-d6, 22 °C): δ 7.48 (d, JH4−H3 = 8.7 Hz, 1, H4), 4.76 (m, 1, H2), 2.75 (apparent t, J = 8.3 Hz, 1, H3), 1.58 (m, 1, H1), 1.30 (br s, 27, PMe3’s), 1.12 (s, 9, t-Bu), 0.75 (m, 1, H1). 13C{1H} NMR (acetone-d6, 22 °C): δ 162.9 (s, C4), 58.2 (br s, C3), 55.7 (s, t-Bu C), ∼33 (br s, C1), 29.3 (s, t-Bu CH3’s), 22.6 (br d, PMe3’s). C2 signal was not located. 31P{1H} NMR (acetone-d6, −10 °C): δ ∼−17 (partially obscured, PMe3’s). Synthesis of (η4-(tert-Butylamino)butadiene)Rh(PMe3)3+O3SCF3−, 5. Compound 4 (0.40 g, 0.88 mmol) was dissolved in 15 mL of diethyl ether and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.66 mL, 0.88 mmol) was then added dropwise, causing a dark red precipitate to form immediately. The reaction mixture was stirred for 10 min before the resulting precipitate was filtered and washed with diethyl ether and pentane, giving a dark red powder. The powder was dissolved in a small quantity of acetone and cooled to −30 °C. Dark red crystals of 5 formed overnight: Yield: 0.44 (83%). Anal. Calcd for C18H42RhNO3F3P3S: C, 35.70; H, 7.01. Found: C, 35.02; H, 6.80. 1H NMR (acetone-d6, 22 °C): δ 5.15 (dd, JH3−H4 = 8.7 Hz, JH3−H2 = 5.1 Hz, 1, H3), 4.92 (m, 1, H2), 4.03 (dd, JH4‑NH = 12.0 6421


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Hz, JH4−H3 = 8.7 Hz, 1, H4), 3.97 (d, JNH‑H4 = 12.0 Hz, 1, NH), 1.52 (obscured, 1, H1), 1.49 (d, JH−P = 8.4 Hz, 27, PMe3’s), 1.15 (s, 9, tBu), 0.22 (m, 1, H1). 13C{1H} NMR (acetone-d6, 22 °C): δ 96.9 (quartet of d, JC−P = 8.3 Hz, JC−Rh = 2.8 Hz, C4), 78.6 (d, J = 3.3 Hz, C3), 75.9 (d, J = 6.0 Hz, C2), 52.6 (s, t-Bu C), 32.6 (apparent quintet, JC−P = JC−Rh = 9.0 Hz, C1), 28.7 (s, t-Bu CH3’s), 19.9 (br d, JC−P = 23.1 Hz, PMe3’s). 31P{1H} NMR (acetone-d6, 22 °C): δ −13.8 (v br d, JP−Rh = 132.8 Hz, PMe3’s). 31P{1H} NMR (acetone-d6, −70 °C): δ −8.0 (ddd, JP−Rh = 133.8 Hz, JP−P = JP−P = 26.9 Hz, 1, PMe3), −9.5 (ddd, JP−Rh = 120.8 Hz, JP−P = 29.8 Hz, JP−P = 26.9 Hz, 1, PMe3), −17.8 (ddd, JP−Rh = 171.3 Hz, JP−P = 29.8 Hz, JP−P = 26.9 Hz, 1, PMe3). Synthesis of (H)Rh(η1-O3SCF3)2(PMe3)3, 6. Compound 5 (0.22 g, 0.36 mmol) was dissolved in 5 mL of CH3CN and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.83 mL, 1.1 mmol) was then added, causing the solution color to change from dark red to yellow immediately. The volatiles were removed under vacuum. The residue was then washed with diethyl ether and pentane and dried under vacuum, giving a yellow powder, 6. The powder was dissolved in a minimal quantity of dichloromethane and stored at −30 °C. Yellow crystals of 6 formed overnight: Yield: 0.21 g (91%). Note: This compound was also synthesized by treating compound 4 with excess triflic acid in acetonitrile. Anal. Calcd for C11H28RhO6F6P3S2: C, 20.96; H, 4.49. Found: C, 20.84; H, 4.75. 1H NMR (acetonitrile-d3, 22 °C): δ 1.74 (d, partially obscured, 9, PMe3), 1.71 (virtual t, JH−P = 7.2 Hz, 18, trans-PMe3’s), −17.11 (apparent d of quart, J = 22.0 Hz, 15.0 Hz, 1, Rh-H). 13C{1H} NMR (acetonitrile-d3, 22 °C): δ 18.6 (d, JC−P = 40.0 Hz, PMe3), 16.3 (virtual t, JC−P = 33.5 Hz, trans-PMe3’s). 31P{1H} NMR (acetonitriled3, 22 °C): δ 9.0 (dt, JP−Rh = 118.8 Hz, JP−P = 32.3 Hz, 1, PMe3), −9.6 (dd, JP−Rh = 88.4 Hz, JP−P = 32.3 Hz, 2, trans-PMe3’s). Synthesis of (1,2,3-η3)-(5-tert-Butylazapentadienyl)Ir(PEt3)2, 7. Triethylphosphine (0.26 g, 2.2 mmol) was added dropwise to a cold (−30 °C) stirred solution of [(cyclooctene)2Ir(μ-Cl)]2 (0.50 g. 0.56 mmol) in 30 mL of THF. The mixture was slowly warmed to room temperature with stirring for 30 min. The resulting orange solution was cooled to −30 °C before addition of potassium tertbutylazapentadienide (0.36 g, 2.2 mmol) in 10 mL of cold (−30 °C) THF. After the mixture was warmed to room temperature and stirred for 3 h, the solvent was removed under vacuum. The residue was then extracted with pentane and filtered through Celite. Removal of pentane under vacuum yielded 7 as a red-orange oil. Yield: 0.56 g (90%). High resolution ESI-MS: calcd for [M + H]+ (C20H45191IrNP2+), 552.2628; found, 552.2619. IR (Nujol mull): 1627.7, 1610.4 cm−1 (CN). Anti (major, 67%) Isomer, 7a. 1H NMR (acetone-d6, 22 °C): δ 6.49 (d, JH4−H3 = 8.7 Hz, 1, H4), 4.37 (m, 1, H3), 4.27 (m, 1, H2), 2.94 (m, 1, H1), 1.75−2.0 (complex m, 12, PEt3 CH2’s), 1.8 (partially obscured, 1, H1), 1.06 (s, 9, t-Bu), 0.95−1.15 (complex m, 18, PEt3 CH3’s). 13C{1H} NMR (acetone-d6, 22 °C): δ 153.0 (s, C4), 92.1 (s, C2), 61.9 (dd, J = 22.1 Hz, ∼4 Hz, C3), 55.1 (s, t-Bu C), 39.7 (dd, J = 25.9 Hz, 3.8 Hz, C1), 29.3 (s, t-Bu CH3’s), 21.7 (d, JC−P = 29.3 Hz, PEt3 CH2’s), 20.1 (d, JC−P = 29.3 Hz, PEt3 CH2’s), 8.6 (s, PEt3 CH3’s). 31 1 P{ H} NMR (acetone-d6, 22 °C): δ 11.6 (d, JP−P = 4.0 Hz, 1, PEt3), 8.3 (d, JP−P = 4.0 Hz, 1, PEt3). Syn (minor, 33%) Isomer, 7s. 1H NMR (acetone-d6, 22 °C): δ 7.65 (d, JH4−H3 = 8.7 Hz, 1, H4), 4.37 (m, 1, H2), 3.14 (m, 1, H1), 3.00 (m, 1, H3), 2.0 (partially obscured, 1, H1), 1.75−2.0 (complex m, 12, PEt3 CH2’s), 1.20 (s, 9, t-Bu), 0.95−1.15 (complex m, 18, PEt3 CH3’s). 13 C{1H} NMR (acetone-d6, 22 °C): δ 162.3 (s, C4), 97.8 (s, C2), 63.1 (dd, J = 21.6 Hz, ∼4 Hz, C3), 55.6 (s, t-Bu C), 45.3 (dd, J = 23.8 Hz, ∼4 Hz, C1), 29.7 (s, t-Bu CH3’s), 22.0 (d, JC−P = 31.5 Hz, PEt3 CH2’s), 19.2 (d, JC−P = 28.7 Hz, PEt3 CH2’s), 8.7 (s, PEt3 CH3’s). 31 1 P{ H} NMR (acetone-d6, 22 °C): δ 10.4. (d, JP−P = 6.8 Hz, 1, PEt3), 9.8 (d, JP−P = 6.8 Hz, 1, PEt3). Synthesis of (1,2,3-η3,5-η1)-(5-tert-Butylazapentadienyl)Ir(H)(PEt3)2+O3SCF3−, 8. Compound 7 (0.56 g, 1.0 mmol) was dissolved in 15 mL of diethyl ether and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.75 mL, 1.0 mmol) was then

added dropwise. After the reaction mixture was stirred for an additional 10 min, an oily solid was formed, together with a dark red solution. After removal of the liquid by decantation, the solid was washed with diethyl ether and pentane and dried under vacuum, giving a dark red solid of 8. Yield: 0.62 (89%). Note: Treatment of 7 with HBF4·OEt2 produced 8 as a BF4− salt. Yield: 82%. Anal. Calcd for C20H45IrBNF4P2: C, 37.49; H, 7.09. Found: C, 37.32; H, 6.78. IR (Nujol mull): 1620.3 cm−1 (CN). 1H NMR (acetone-d6, 22 °C): δ 9.52 (s, 1, H4), 5.28 (m, 1, H2), 4.64 (d, JH3−H2 = 6.6 Hz, 1, H3), 3.18 (d, J = 5.7 Hz, 1, H1), ∼2.3 (obscured, 1, H1), 2.0−2.4 (complex m, 12, PEt3 CH2’s), 1.23 (s, 9, t-Bu), 1.0−1.2 (complex m, 18, PEt3 CH3’s), −28.79 (dd, JH−P = 24.3 Hz, 17.4 Hz, 1, Ir-H). 13C{1H} NMR (acetone-d6, 22 °C): δ 167.4 (d, J = 4.4 Hz, C4), 99.8 (s, C2), 58.8 (s, t-Bu C), 52.8 (d, JC−P = 19.4 Hz, C3), 35.9 (d, JC−P = 29.8 Hz, C1), 29.2 (s, t-Bu CH3’s), 22.4 (d, JC−P = 34.8 Hz, PEt3 CH2’s), 21.7 (d, JC−P = 31.5 Hz, PEt3 CH2’s), 8.1 (d, JC−P = 3.8 Hz, PEt3 CH3’s), 8.0 (d, JC−P = 4.4 Hz, PEt3 CH3’s). 31P{1H} NMR (acetone-d6, 22 °C): δ −9.3 (d, JP−P = 5.9 Hz, 1, PEt3), −11.8 (d, JP−P = 5.9 Hz, 1, PEt3). Synthesis of (1,2,3-η3-CH2CHCHCHNH(tert-butyl))Ir(H)(η1O3SCF3)(PEt3)2+ O3SCF3−, 9. Compound 8 (0.44 g, 0.63 mmol) was dissolved in 20 mL of THF and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.47 mL, 0.63 mmol) was then added dropwise with stirring for 10 min, causing the solution color to change from dark red to yellow-orange. The volatiles were removed under vacuum. The residue was then washed with diethyl ether and pentane and dried under vacuum, giving a yellow-orange solid of 9. Yield: 0.40 g (75%). Note: This compound could also be synthesized by treating compound 7 with 2 equivalents of triflic acid. Yield: 68%. IR (Nujol mull): 1641.3 cm−1 (CN). Anti (major, 85%) Isomer, 9a. 1H NMR (acetone-d6, 22 °C): δ 11.30 (d, JNH‑H4 = 15.9 Hz, 1, NH), 7.59 (dd, JH4‑NH = 15.9 Hz, JH4−H3 = 11.1 Hz, 1, H4), 6.11 (m, 1, H2), 4.82 (m, 1, H3), 4.00 (m, 1, H1), 3.52 (m, 1, H1), 2.0−2.4 (complex m, 12, PEt3 CH2’s), 1.49 (s, 9, tBu), 1.0−1.2 (complex m, 18, PEt3 CH3’s), −31.32 (apparent t, JH−P = 15.5 Hz, 1, Ir-H). 13C{1H} NMR (acetone-d6, 22 °C): δ 171.3 (d, J = 4 Hz, C4), 97.4 (s, C2), 59.6 (s, t-Bu C), 53.5 (d, JC−P = 22.1 Hz, C1), 51.5 (d, JC−P = 24.3 Hz, C3), 27.1 (s, t-Bu CH3’s), 19.5 (d, JC−P = 34.8 Hz, PEt3 CH2’s), 18.9 (d, JC−P = 33.7 Hz, PEt3 CH2’s), 7.5 (d, complex m, PEt3 CH3’s). 31P{1H} NMR (acetone-d6, 22 °C): 1.0 (d, JP−P = 4.8 Hz, 1, PEt3), −4.6 (d, JP−P = 4.8 Hz, 1, PEt3). Syn (minor, 15%) Isomer, 9s. 1H NMR (acetone-d6, 22 °C): δ 11.45 (d, 1, NH), 8.51 (dd, JH4‑NH = 16.5 Hz, JH4−H3 = 10.5 Hz, 1, H4), 6.25 (m, 1, H2), 4.13 (m, 1, H3), 3.95 (m, 1, H1), ∼3.4 (m, 1, H1), 2.0−2.4 (complex m, 12, PEt3 CH2’s), 1.59 (s, 9, t-Bu), 1.0−1.2 (complex m, 18, PEt3 CH3’s), −31.92 (apparent t, JH−P = 15.5 Hz, 1, Ir-H). 13C{1H} NMR (acetone-d6, 22 °C): δ 174.3 (d, C4), 103.2 (s, C2), 58.7 (s, t-Bu C), ∼52.5 (C1), ∼49.5 (C3), 25.3 (s, t-Bu CH3’s). The PEt3 CH2 and CH3 signals were obscured. 31P{1H} NMR (acetone-d6, 22 °C): δ 1.7 (d, JP−P = 6.3 Hz, 1, PEt3), −4.0 (d, JP−P = 6.3 Hz, 1, PEt3). Synthesis of (1,2,3-η3)-(5-tert-Butylazapentadienyl)Ir(H)(Cl)(PEt3)2, 10. Compound 8 (0.44 g, 0.63 mmol) was dissolved in 20 mL of THF and cooled to −30 °C. Solid bis(triphenylphosphoranylidene)ammonium chloride (PPN+Cl−; 0.36 g, 0.63 mmol) was then added to the stirred solution of 8. After the reaction mixture was stirred for 5 min, 40 mL of pentane was added, causing PPN+O3SCF3− to precipitate out. The solution was filtered through Celite and evacuated to dryness, yielding 10 as an orange oil. Yield: 0.29 g (78%). High-resolution ESI-MS: calcd for [M + H]+ (C20H46191Ir35ClNP2+), 588.2394; found, 588.2392. Also observed fragment resulting from loss of tert-butylcrotonaldimine: calcd for [M − C8H15N + H]+, 463.1190; found, 463.1190. IR (Nujol mull): 1632.9 cm−1 (CN). Anti (50%) Isomer, 10a. 1H NMR (acetone-d6, 22 °C): δ 7.24 (d, JH3−H4 = 11.1 Hz, 1, H4), 6.04 (m, 1, H2), 4.67 (m, 1, H3), 3.61 (m, 1, H1), 2.96 (dd, J = 12.0 Hz, 6.9 Hz, 1, H1), 1.8−2.3 (complex m, 12, PEt3 CH2’s), 1.45 (s, 9, t-Bu), 1.0−1.2 (complex m, 18, PEt3 CH3’s), −23.48 (apparent t, JH−P = 15.0 Hz, 1, Ir-H). 13C{1H} NMR (acetone6422


Organometallics

Article

d6, 22 °C): δ 172.7 (s, C4), 92.2 (s, C2), 58.6 (s, t-Bu C), 50.7 (d, JC−P = 24.9 Hz, C1), 46.6 (d, JC−P = 23.8 Hz, C3), 27.7 (s, t-Bu CH3’s), 19.5 (d, JC−P = 35.4 Hz, PEt3 CH2’s), 19.2 (d, JC−P = 33.6 Hz, PEt3 CH2’s), 7.8 (d, JC−P = 3.3 Hz, PEt3 CH3’s), 7.4 (d, JC−P = 3.8 Hz, PEt3 CH3’s). 31P{1H} NMR (acetone-d6, 22 °C): −1.4 (d, JP−P = 6.2 Hz, 1, PEt3), −12.3 (d, JP−P = 6.2 Hz, 1, PEt3). Syn (50%) Isomer, 10s. 1H NMR (acetone-d6, 22 °C): δ 7.61 (d, JH3−H4 = 8.7 Hz, 1, H4), 5.54 (m, 1, H2), 3.46 (m, 1, H3), 3.29 (m, 1, H1), 2.56 (dd, J = 11.7 Hz, 6.9 Hz, 1, H1), 1.8−2.3 (complex m, 12, PEt3 CH2’s), 1.23 (s, 9, t-Bu), 1.0−1.2 (complex m, 18, PEt3 CH3’s), −25.18 (apparent t, JH−P = 15.1 Hz, 1, Ir-H). 13C{1H} NMR (acetoned6, 22 °C): δ 162.6 (s, C4), 96.6 (s, C2), 64.6 (d, JC−P = 27.7 Hz, C3), 56.6 (s, t-Bu C), 50.1 (d, JC−P = 27.6 Hz, C1), 28.7 (s, t-Bu CH3’s), 20.3 (d, JC−P = 33.2 Hz, PEt3 CH2’s), 18.5 (d, JC−P = 32.6 Hz, PEt3 CH2’s), 7.8 (d, JC−P = 3.3 Hz, PEt3 CH3’s), 7.5 (d, JC−P = 3.9 Hz, PEt3 CH3’s). 31P{1H} NMR (acetone-d6, 22 °C): δ −5.7 (s, 1, PEt3), −13.0 (s, 1, PEt3). Synthesis of (1,2,3-η3-CH2CHCHCHNH(tert-butyl))Ir(H)(Cl)(PEt3)2+ O3SCF3−, 11. Compound 10 (0.21 g, 0.36 mmol) was dissolved in 15 mL of diethyl ether and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.27 mL, 0.36 mmol) was then added dropwise, causing a dark orange precipitate to form immediately. The reaction mixture was stirred for 10 min before the resulting precipitate was filtered and washed with diethyl ether and pentane, giving a dark orange solid of 11. Yield: 0.22 g (81%). Anal. Calcd for C21H46IrNO3F3P2SCl: C, 34.11; H, 6.28. Found: C, 34.06; H, 6.02. IR (Nujol mull): 1639.1 cm−1 (CN). Anti (major, 67%) Isomer, 11a. 1H NMR (acetone-d6, 22 °C): δ 10.80 (br d, JNH‑H4 = 15.6 Hz, 1, NH), 7.25 (dd, JH4‑NH = 15.6 Hz, JH4−H3 = 11.7 Hz, 1, H4), 6.07 (m, 1, H2), 4.67 (m, 1, H3), 3.64 (m, 1, H1), 2.97 (m, 1, H1), 1.9−2.3 (complex m, 12, PEt3 CH2’s), 1.46 (s, 9, t-Bu), 1.0−1.2 (complex m, 18, PEt3 CH3’s), −23.40 (apparent t, JH−P = 15.0 Hz, 1, Ir-H). 13C{1H} NMR (acetone-d6, 22 °C): δ 173.4 (s, C4), 92.4 (s, C2), 58.7 (s, t-Bu C), 50.9 (d, JC−P = 25.4 Hz, C1), 46.3 (d, JC−P = 22.1 Hz, C3), 27.6 (s, t-Bu CH3’s), 19.4 (d, JC−P = 35.4 Hz, PEt3 CH2’s), 19.1 (d, JC−P = 33.7 Hz, PEt3 CH2’s), 7.8 (d, JC−P = 4.4 Hz, PEt3 CH3’s), 7.3 (d, JC−P = 3.8 Hz, PEt3 CH3’s). 31P{1H} NMR (acetone-d6, 22 °C): −1.2 (d, JP−P = ∼5 Hz, 1, PEt3), −12.2 (d, JP−P = ∼5 Hz, 1, PEt3). Syn (minor, 33%) Isomer, 11s. 1H NMR (acetone-d6, 22 °C): δ 8.31 (m, 1, H4), 6.26 (m, 1, H2), ∼3.6 (obscured, 1, H1), ∼3.6 (obscured, 1, H3), 3.16 (m, 1, H1), 1.9−2.3 (complex m, 12, PEt3 CH2’s), 1.55 (s, 9, t-Bu), 1.0−1.2 (complex m, 18, PEt3 CH3’s), −23.53 (apparent t, JH−P = 15.3 Hz, 1, Ir-H). NH signal was not located. 13C{1H} NMR (acetone-d6, 22 °C): δ 172.3 (s, C4), 99.2 (s, C2), 59.6 (d, JC−P = 24.4 Hz, C1), ∼58.8 (d, partially obscured, C3), 58.6 (s, t-Bu C), 27.3 (s, t-Bu CH3’s), 20.1 (d, JC−P = 36.0 Hz, PEt3 CH2’s), 18.4 (d, JC−P = 33.7 Hz, PEt3 CH2’s), 7.9 (d, JC−P = 4.5 Hz, PEt3 CH3’s), 7.4 (d, JC−P = 4.4 Hz, PEt3 CH3’s). 31P{1H} NMR (acetone-d6, 22 °C): δ 0.8 (s, 1, PEt3), −10.7 (s, 1, PEt3). Synthesis of (1,2,3-η3)-(5-tert-Butylazapentadienyl)Ir(PEt3)3, 12. Triethylphosphine (0.40 g, 3.4 mmol) was added dropwise to a cold (−30 °C) stirred solution of [(cyclooctene)2Ir(μ-Cl)]2 (0.50 g. 0.56 mmol) in 30 mL of THF. The mixture was slowly warmed to room temperature with stirring for 30 min. The resulting orange solution was cooled to −30 °C before addition of potassium tertbutylazapentadienide (0.36 g, 2.2 mmol) in 10 mL of cold (−30 °C) THF. After the mixture was warmed to room temperature and stirred for 3 h, the solvent was removed under vacuum. The residue was then extracted with pentane and filtered through Celite. The extract was evacuated to dryness and dissolved in a pentane/acetone mixture. The solution was cooled to −30 °C, producing yellow crystals of 12 overnight. Yield: 0.61 g (81%). Anal. Calcd for C26H59IrNP3: C, 46.54; H, 8.88. Found: C, 46.11; H, 8.71. IR (Nujol mull): 1611.8 cm−1 (CN). Anti (major, 80%) Isomer, 12a. 1H NMR (acetone-d6, 22 °C): δ 6.76 (d, JH4−H3 = 8.7 Hz, 1, H4), 4.19 (q, J = 4.8 Hz, 1, H2), 3.37 (br m, 1, H3), 1.6−1.9 (br m, 18, PEt3 CH2’s), 1.58 (br m, 1, H1), 1.02 (s, 9, t-Bu), 0.9−1.1 (br m, 27, PEt3 CH3’s), ∼0.9 (partially obscured, 1, H1). 13C{1H} NMR (acetone-d6, 22 °C): δ 160.1 (s, C4), 55.2 (s, t-Bu

C), 47.2 (s, C2), 40.0 (q, JC−P = 7.2 Hz, C3), 29.5 (s, t-Bu CH3’s), 23.9 (v br m, PEt3 CH2’s), 12.4 (q, JC−P = 8.3 Hz, C1), 8.5 (s, PEt3 CH3’s). 31 1 P{ H} NMR (acetone-d6, 22 °C): δ −26.8 (v br s, PEt3’s). 31P{1H} NMR (acetone-d6, −60 °C): δ −25.6 (complex m, 2, PEt3’s), −28.9 (dd, JP−P = 47.1 Hz, JP−P = 40.4 Hz, 1, PEt3). Syn (minor, 20%), Isomer 12s. 1H NMR (acetone-d6, 22 °C): δ 7.42 (d, JH4−H3 = 8.4 Hz, 1, H4), 4.32 (q, J = 5.1, 1, H2), 1.6 (br m, 1, H3), 1.6−1.9 (br m, 18, PEt3 CH2’s), 1.09 (s, 9, t-Bu), 0.9−1.1 (br m, 27, PEt3 CH3’s). H1 signals were obscured. 31P{1H} NMR (acetoned6, 22 °C): δ −24.1. (v br s, PEt3’s). 31P{1H} NMR (acetone-d6, −60 °C): δ −21.1 (complex m, 2, PE3’s), −29.5 (dd, JP−P = 55.8 Hz, JP−P = 42.9 Hz, 1, PEt3). Synthesis of (η4-(tert-Butylamino)butadiene)Ir(PEt3)3+O3SCF3−, 13. Compound 12 (0.43 g, 0.64 mmol) was dissolved in 15 mL of diethyl ether and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.48 mL, 0.64 mmol) was then added dropwise, causing a light yellow precipitate to form immediately. The reaction mixture was stirred for 10 min before the resulting precipitate was filtered and washed with diethyl ether and pentane, giving a light yellow powder. The powder was dissolved in a small quantity of acetone and cooled to −30 °C. Light yellow crystals of 13 formed overnight. Yield: 0.38 g (72%). Anal. Calcd for C27H60IrNO3F3P3S: C, 39.49; H, 7.38. Found: C, 39.20; H, 7.32. 1H NMR (acetone-d6, 22 °C): δ 5.20 (dd, JH3−H4 = 7.5 Hz, JH3−H2 = 4.5, 1, H3), 5.04 (apparent q, J = 4.5 Hz, 1, H2), 2.59 (dd, JH4‑NH = 9.9 Hz, JH4−H3 = 7.5 Hz, 1, H4), 2.41 (d, JNH‑H4 = 9.9 Hz, 1, NH), 2.11 (v br s, 18, PEt3 CH2’s), 1.76 (m, 1, H1), 1.16 (s, 9, tBu), 1.05−1.25 (m, 27, PEt3 CH3’s), −0.16 (br m, 1, H1). 13C{1H} NMR (acetone-d6, 22 °C): δ 80.2 (s, C3), 76.1 (q, JC−P = 9.9 Hz, C4), 66.0 (s, C2), 52.2 (s, t-Bu C), 28.5 (s, t-Bu CH3’s), 21.5 (v br m, PEt3 CH2’s), ∼21 (obscured, C1), 8.9 (br s, PEt3 CH3’s). 31P{1H} NMR (acetone-d6, 22 °C): δ −30.3 (v br s, PEt3’s). 31P{1H} NMR (acetoned6, −60 °C): δ −27.4 (d, JP−P = 10.8 Hz, 1, PEt3), −31.0 (d, JP−P = 19.3 Hz, 1, PEt3), −31.7 (dd, JP−P = 19.3 Hz, JP−P = 10.8 Hz, 1, PEt3). Synthesis of (η 4 -(tert-Butylammonium)butadiene)Ir(PEt3)32+(O3SCF3−)2, 14. Compound 13 (0.29 g, 0.35 mmol) was dissolved in 15 mL of THF and cooled to −30 °C. A cold 1.33 M solution of triflic acid in diethyl ether (0.26 mL, 0.35 mmol) was then added dropwise, causing a light yellow precipitate to form in a few minutes. The reaction mixture was stirred for 10 min before the resulting precipitate was collected by filtration and washed with diethyl ether and pentane, giving a light yellow powder. The powder was dissolved in a minimal quantity of dichloromethane and stored at −30 °C. Light yellow crystals of 14 formed overnight. Yield: 0.22 g (65%). Note: This compound was also synthesized by treating compound 12 with 2 equivalents of triflic acid. Yield: 62%. Anal. Calcd for C28H61IrNO6F6P3S2: C, 34.63; H, 6.34. Found: C, 33.79; H, 6.14. 1H NMR (methylene chloride-d2, 22 °C): δ 7.03 (br m, 1, NH), 6.78 (br m, 1, NH), 5.98 (br s, 1, H3), 5.19 (br s, 1, H2), 1.7−2.4 (m’s, 18, PEt3 CH2’s), 2.24 (obscured, 1, H1), 1.48 (obscured, 1, H4), 1.47 (s, 9, t-Bu), 1.0−1.3 (m, 27, PEt3 CH3’s), −0.14 (m, 1, H1). 13C{1H} NMR (methylene chloride-d2, 22 °C): δ 83.5 (dd, J = 5.5 Hz, 4.4 Hz, C3), 75.4 (br s, C2), 65.1 (d, J = 3.8 Hz, t-Bu C), 46.5 (apparent d of t, JC−P = 53.6 Hz, 3.8 Hz, C4), 26.7 (br d, JC−P = 34.2 Hz, C1), 25.0 (s, tBu CH3’s), 23.7 (d, JC−P = 31.4 Hz, PEt3 CH2’s), 23.2 (d, JC−P = 28.7 Hz, PEt3 CH2’s), 20.8 (d, JC−P = 30.4 Hz, PEt3 CH2’s), 10.1 (d, JC−P = 6.1 Hz, PEt3 CH3’s), 9.6 (d, JC−P = 6.1 Hz, PEt3 CH3’s), 9.2 (d, JC−P = 5.5 Hz, PEt3 CH3’s). 31P{1H} NMR (methylene chloride-d2, 22 °C): δ −23.9 (d, JP−P = 3.3 Hz, 1, PEt3), −31.8 (d, JP−P = 22.2 Hz, 1, PEt3), −33.3 (dd, JP−P = 22.2 Hz, JP−P = 3.3 Hz, PEt3). X-ray Diffraction Studies. Crystals of X-ray diffraction quality were obtained for compounds 2, 4, 5, 6, 12, 13, and 14. In all cases crystals of appropriate dimensions were mounted on MiTeGen microloops22 in random orientations. Preliminary examination and data collection were performed using a Bruker Kappa Apex II chargecoupled device (CCD) detector system single-crystal X-ray diffractometer equipped with an Oxford Cryostream LT device. All data were collected using graphite-monochromated Mo Kα radiation (λ= 0.71073 Å) from a fine focus sealed tube X-ray source. Preliminary unit cell constants were determined with a set of 36 narrow-frame 6423


Organometallics

Article

Table 1. X-ray Diffraction Structure Summary formula fw cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z cryst dimens, mm calcd density, g/cm3 radiation; λ, Å temp, K θ range, deg data collected h k l total decay no. of data collected no. of unique data Mo Kα linear abs coeff, mm−1 abs cor applied data to param ratio final R indices (obsd data)a R1 wR2 R indices (all data) R1 wR2 goodness of fit largest diff peak/hole, e Å−3 formula fw cryst syst space group a, Å b, Å c, Å α, deg β, deg γ, deg V, Å3 Z cryst dimens, mm calcd density, g/cm3 radiation; λ, Å temp, K θ range, deg data collected h k l total decay no. of data collected no. of unique data

2

4

5

C15H33F3NO3P2RhS 529.33 orthorhombic Pbca 12.999(3) 15.004(3) 23.641(5) 90 90 90 4610.7(17) 8 0.28 × 0.23 × 0.085 1.525 0.71073 100(2) 1.723−26.494

C17H41NP3Rh 455.33 triclinic P1̅ 8.240(2) 10.519(3) 13.854(4) 101.876(12) 91.596(11) 92.053(11) 1173.6(5) 2 0.35 × 0.17 × 0.15 1.289 0.71073 100(2) 1.98−25.55

C18H42F3NO3P3RhS 605.40 monoclinic P21/c 15.7407(9) 8.2928(4) 20.6824(12) 90 96.442(3) 90 2682.7(3) 4 0.41 × 0.30 × 0.14 1.499 0.71073 100(2) 2.246−32.360

−16 to 16 −18 to 18 −29 to 29 none obsd 60 519 4661 1.008 semiempirical 19.10



0.0549 0.1419

0.0482 0.1386

0.0315 0.0602

0.0568 0.1497 1.094 2.708, −1.302

0.0491 0.0665 1.025 0.818, −0.660 14·(CH2Cl2)2

0.0736 0.1521 1.038 1.244, −1.995 6·CH2Cl2

12

13·acetone

C12H30Cl2F6O6P3RhS2 715.20 monoclinic P21/c 12.7978(6) 9.0318(4) 24.2555(11) 90 97.805(2) 90 2777.7(2) 4 0.37 × 0.22 × 0.14 1.710 0.71073 100(2) 2.171−34.275

C26H59IrNP 670.85 monoclinic P21/c 9.9443(6) 18.4115(11) 17.1842(11) 90 97.046(4) 90 3122.5(3) 4 0.27 × 0.09 × 0.07 1.427 0.71073 100(2) 2.21−25.05

C30H66F3IrNO4P3S 879.00 monoclinic P21/n 20.3406(14) 9.5021(7) 22.0175(14) 90 115.453(3) 90 3842.5(5) 4 0.42 × 0.36 × 0.24 1.519 0.71073 100(2) 2.218−33.396

C30H65Cl4F6IrNO6P3S2 1140.86 monoclinic P21/n 20.7256(10) 11.6250(5) 21.3376(9) 90 115.415(2) 90 4643.4(4) 4 0.30 × 0.18 × 0.091 1.632 0.71073 100(2) 2.046−27.625

−20 to 20 −14 to 14 −37 to 38 none obsd 55 949 11 538

−11 to 11 −21 to 21 −20 to 19 none obsd 46 895 5524

−31 to 30 −14 to 14 −34 to 33 none obsd 151 286 14 868

−26 to 26 −15 to 15 −27 to 27 none obsd 86 005 10 724

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Organometallics

Article

Table 1. continued 6·CH2Cl2 Mo Kα linear abs coeff, mm−1 abs cor applied data to param ratio final R indices (obsd data)a R1 wR2 R indices (all data) R1 wR2 goodness of fit largest diff peak/hole, e Å−3 a

12

3.701 semiempirical 36.62


0.0285 0.0594

0.0326 0.0562

0.0184 0.0409

0.0280 0.0537

0.0397 0.0635 1.027 1.061, −0.752

0.0591 0.0636 1.047 1.188, −1.136

0.0227 0.0424 1.058 2.043, −0.568

0.0420 0.0582 1.025 1.101, −1.045

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scans. Typical data sets consisted of combinations of ω and ϕ scan frames with typical scan width of 0.5° and counting time of 15−30 s/ frame at a crystal to detector distance of 3.5−4.0 cm. The collected frames were integrated using an orientation matrix determined from the narrow-frame scans. Apex II and SAINT software packages23 were used for data collection and data integration. Final cell constants were determined by global refinement of reflections from the complete data set. Collected data were corrected for systematic errors using SADABS or TWINABS.23 Crystal data and intensity data collection parameters are listed in Table 1. Structure solution and refinement were carried out using the SHELXTL-PLUS software package.24 The structures were solved by direct methods and refined with full matrix least-squares refinement by minimizing ∑w(Fo2 − Fc2)2. All non-hydrogen atoms were refined anisotropically to convergence. Specific experimental details for individual structures are given below. For compounds 2, 4, 12, and 14, all H atoms were added in the calculated positions and were refined using appropriate riding models (AFIX m3). For 5 and 13, the H atoms on nitrogen (H1 and H1A, respectively) were located and refined freely. All other H atoms were added in the calculated positions and were refined using appropriate riding models. In 6, the H atom on rhodium (H1) was located and refined freely. All other H atoms were added in the calculated positions and refined using appropriate riding models. In 5, the rhodium atom exhibited a slight disorder and was split into two positions in a 98:2 ratio. Both atom positions were refined anisotropically. It is possible that the 2% rhodium disorder is due to a small amount of Rh(PMe3)4+O3SCF3− that cocrystallized with 5. In 6, one of the triflate ligands exhibited a 2-fold disorder (with one shared oxygen), which was successfully modeled. Similarly, the two chlorine atoms of the CH2Cl2 solvent molecule showed 2-fold disorder and was successfully modeled. In 14, one of the CH2Cl2 solvent molecules exhibited a 2-fold disorder, which was successfully modeled. In all structures except for 14, the largest residual peaks in the electron density difference maps were located near the heavy metal atoms. In 14, the highest residual peak was located near a disordered Cl atom.

ACKNOWLEDGMENTS The region X-ray Facility at the University of Missouri−St. Louis was funded in part by the National Science Foundation’s MRI Program (No. CHE-0420497).

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REFERENCES

(1) Pentadienyl-Metal-Phosphine Chemistry. 39. For Part 38, see: Bleeke, J. R.; Anutrasakda, W.; Rath, N. P. Organometallics 2012, 31, 2219−2230. (2) In principle, the heteroatom could be located anywhere along the five-atom chain. However, for the vast majority of heteropentadienylmetal complexes, the heteroatom resides in the terminal position, and our work has focused exclusively on “terminal” heteropentadienyl ligands. (3) For recent reviews of heteropentadienyl-metal chemistry, see: (a) Bleeke, J. R. Organometallics 2005, 24, 5190−5207. (b) PazSandoval, M. A.; Rangel-Salas, I. I. Coord. Chem. Rev. 2006, 250, 1071−1106. (4) Bleeke, J. R.; Luaders, S. T.; Robinson, K. D. Organometallics 1994, 13, 1592−1600. (5) Van der Ent, A.; Onderdelinden, A. L. Inorganic Syntheses; Wold. A.; Ruff, J. K., Eds.; McGraw-Hill: New York, 1973; Vol. 14, pp 92−95. (6) For synthesis of the analogous Li salt, see: Wolf, G.; Wurthwein, E.-U. Chem. Ber. 1991, 124, 889−896. (7) In general, a bond is indicated if the atom separation is less than r1 + r2 + 0.5 Å, where r1 and r2 are the covalent radii of the atoms in question. For Rh and C, the covalent radii are 1.350 and 0.770 Å, respectively, so r1 + r2 + 0.5 in this case equals 2.62 Å. This represents the maximum separation that would normally be considered a bonding interaction. However, the decision of whether to draw a bond is somewhat arbitrary and can hinge on other factors such as NMR chemical shifts and coupling constants. (8) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1−S19. (9) The η2-bonding mode for the triflate ligand has been previously observed in several related rhodium compounds: (a) Werner, H.; Bosch, M.; Schneider, M. E.; Hahn, C.; Kukla, F.; Manger, B.; Windmueller, B.; Weberndoerfer, M.; Laubender, M. J. Chem. Soc., Dalton Trans. 1998, 3549−3558. (b) Goikhman, R.; Milstein, D. Angew. Chem., Int. Ed. 2001, 40, 1119−1122. (10) NMR spectra for protonated tert-butylcrotonaldimine: 1H NMR (acetonitrile-d3, 22 °C): δ 11.4 (m, 1, NH), 8.41 (dd, JH4‑NH = 16.8 Hz, JH4‑H3 = 9.9 Hz, 1, H4), 7.44 (d of quart, JH2‑H3 = 15.0 Hz, JH2‑H1 = 6.9 Hz, 1, H2), 6.74 (dd, JH3‑H2 = 15.0 Hz, JH3‑H4 = 9.9 Hz, 1, H3), 2.15 (d, JH1‑H2 = 6.9 Hz, 3, H1’s), 1.50 (s, 9, t-Bu). 13C{1H} NMR (acetonitriled3, 22 °C): δ 168.2 (s, C4), 164.0 (s, C2), 124.5 (s, C3), 60.5 (s, t-Bu C), 27.3 (s, t-Bu CH3’s), 20.1 (C1). (11) The trans H−P coupling would be much larger. See: Crabtree, , R. H. The Organometallic Chemistry of the Transition Metals, third ed.; John Wiley and Sons: New York, 2001,; pp 260−−263.

ASSOCIATED CONTENT

S Supporting Information *

Tables, figures, and CIF files giving structure determination summaries, final atomic coordinates, thermal parameters, bond lengths, bond angles, and torsion angles for compounds 2, 4, 5, 6, 12, 13, and 14. This material is available free of charge via the Internet at http://pubs.acs.org.

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14·(CH2Cl2)2


I > 2σ(I).

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13·acetone


AUTHOR INFORMATION

Notes

The authors declare no competing financial interest. 6425


Organometallics

Article

(12) (a) Filled-in doublets result from coupling of the methyl groups to two chemically equivalent 31P nuclei that are weakly coupled to each other (as is the case for cis-phosphines). (b) Virtual triplets result from coupling of the methyl groups to two chemically equivalent 31P nuclei that are strongly coupled to one another (as is the case for transphosphines). See ref 11. (13) Alternatively, a Berry pseudorotation may be responsible, but the small “bite angle” of the allyl moiety makes this pathway more strained and, in our view, less likely. See: Albright, T. A.; Hofmann, P.; Hoffmann, R. J. Am. Chem. Soc. 1977, 99, 7546−7557. (14) We previously observed a similar “intermediate” structure for the monoprotonation product of (1,2,3-η3)-(5-tertbutylazapentadienyl)Co(PMe3)3. See ref 1. (15) Herde, J. L.; Lambert, J. C.; Senoff, C. V. Inorganic Syntheses; Parshall, G. W., Ed.; McGraw-Hill: New York, 1974; Vol. 15, pp 18− 20. (16) Attempts to make the bis(PMe3) analogue of 7 failed. Instead, the use of this smaller phosphine led to the production of (1,2,3-η3)(5-tert-butylazapentadienyl)Ir(PMe3)3. See ref 4. (17) This bonding mode has also been observed recently in several azapentadienyl-ruthenium complexes: Reyna-Madrigal, A.; MorenaGurrola, A.; Perez-Camacho, O.; Navarro-Clemente, M. E.; JuarezSaavedra, P.; Leyva-Ramirez, M. A.; Arif, A. M.; Ernst, R. D.; PazSandoval, M. A. Organometallics 2012, 31, 7125−7145. (18) (a) Karplus, M. J. Chem. Phys. 1959, 30, 11−15. (b) Karplus, M. J. Am. Chem. Soc. 1963, 85, 2870−2871. (19) We have previously reported the related reaction of (η5-2,4dimethyloxapentadienyl)Rh(PEt3)2(H)+ with PPN+Cl−: Bleeke, J. R.; Donnay, E.; Rath, N. P. Organometallics 2002, 21, 4099−4112. (20) In an earlier paper (ref 4), we reported the analogous reaction involving PMe3 instead of PEt3. In that case, we observed clean formation of the syn isomer as the kinetic product. This isomer then converted to an equilibrium mixture of anti and syn isomers (with anti as the predominant isomer) upon stirring in pentane for one hour at room temperature. In contrast, the PEt3 reaction produces the equilibrium mixture immediately; pure syn isomer cannot be obtained or even observed by NMR. (21) This is identical to what we previously observed in the analogous (1,2,3-η3)-(5-tert-butylazapentadienyl)Ir(PMe3)3 system. See ref 4. (22) MiTeGen LLC, PO Box 3867, Ithaca, NY. (23) Apex II, SAINT, SADABS, and TWINABS; Bruker Analytical XRay: Madison, WI, 2008. (24) Bruker-SHELXTL: Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.

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Synthesis, Spectroscopy, Structure, and Reactivity of

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