Iridaoxacyclohexadiene-Bridged Mixed-Valence Iridium

Article pubs.acs.org/Organometallics

Iridaoxacyclohexadiene-Bridged Mixed-Valence Iridium Cyclooctadiene Complex: Oxidative Addition and Hydrogen-Transfer to Coordinated Cyclooctadiene Itzia Irene Padilla-Martínez,‡ Marisol Cervantes-Vásquez,† Marco Antonio Leyva-Ramirez,† and M. Angeles Paz-Sandoval*,† †

Departamento de Química, Centro de Investigación y Estudios Avanzados del IPN, Avenida IPN # 2508, Col. San Pedro Zacatenco, México D.F. 07360, México ‡ Unidad Profesional Interdisciplinaria de Biotecnología del Instituto Politécnico Nacional, Avenida Acueducto s/n, Barrio La Laguna, Ticomán, México D.F. 07340, Mexico S Supporting Information *

ABSTRACT: The systematic exploration of the synthesis of heteropentadienyl metal complexes leads us to study the metathesis reaction of [(η4-COD)Ir(μ2-Cl)]2 with lithium 2,4dimethyloxopentadienide, which affords the dinuclear Ir0−IrII compound (η4-COD)Ir[η1:1-μ2-η4-CHC(Me)CHC(Me)O)]Ir(η4-COD) (1) with a metal−metal bond. The COD ligands are coordinated η4 to each Ir center, whereas the oxopentadienyl ligand is bridging both Ir atoms, allowing the formation of a novel iridapyran complex with IrII and bonding η4 with Ir0. The addition of CO, PMe3, and PMe2Ph to the coordinatively unsaturated complex 1 has led, under mild conditions, to the corresponding dinuclear coordinatively saturated compounds (η4-COD)Ir[η1:1-μ2-η3-CHC(Me)CHC(Me)O)]Ir(η4-COD)(μ2-CO) (2) and (η4-COD)Ir[η1:1-μ2-η4-CHC(Me)CHC(Me)O)]Ir(η4-COD)(PR3) (R = Me, 3; PR3 = PMe2Ph, 4). Compound 3 showed a reversible reaction by dissociation of PMe3, recovering compound 1. The reaction of 1 with H2 and PMe3, PMe2Ph, and P(n-Bu)3 allows the isolation of cyclooctenyl derivatives (η4-COD)Ir[η1:1-μ2-η3-CHC(Me)CHC(Me)O)]Ir(μ2-H)(η1:η2-C8H13)(PR3) (R = Me, 5; R3 = Me2Ph, 6; R = n-Bu, 7), where the hydrogen promotes the formation of a metal-hydride, as well as hydrogen-transfer to one of the coordinated cyclooctadiene ligands. In the presence of molecular hydrogen, 4 leads also to the formation of 6 in better yield. The iridaoxacycle bridging ligand stabilizes these dinuclear iridium complexes, which easily undergo intermolecular insertion into activated C−H bonds. When the more sterically demanding phosphine P(i-Pr)3 is added in the presence of H2, a different reaction takes place, with the displacement of one COD ligand and the formation of (η4-COD)Ir(μ2-H)[η1:1-μ2-η3-CHC(Me)CHC(Me)O)]Ir(H)(Pi-Pr3)2 (8). The novel complexes 1−8 have been fully characterized, where 1 shows dynamic behavior in one of the COD ligands in solution and gives evidence of two different isomers present in the crystalline structure. Molecular structures of 1−3 and 5−8 have been determined by single-crystal X-ray diffraction studies.

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INTRODUCTION Heteronuclear substituents in acyclic unsaturated ligands have given clear evidence of a versatile and interesting chemistry with transition metals. In particular, the chemistry of the oxygen atom in α,β-unsaturated ligands is one of the most extensively studied; the results support the occurrence of the oxopentadienyl ligand preferentially as a terminal ligand in mononuclear compounds.1 Electron-rich oxopentadienyl-iridiumphosphine complexes, as kinetic products, have shown to have a propensity to undergo C−H bond activation, which generates novel metallacyclic products, such as iridaoxacyclohexadiene (iridapyran) and iridaoxacyclopentene derivatives.2 An interesting metallaoxabenzene (iridapyrylium) complex, [Ir(η1:1-CHC(Me)CHC(Me)O)]BF4, has been obtained from 2,4-dimethyliridapyran and 2 equiv of AgBF4.3 Reaction of lithium 2,4-dimethyloxopentadienide with [Cp*MCl2]2 (M = Rh, Ir) produces exclusively mononuclear compounds [Cp*M(Cl)(1−3-ηCH2C(Me)CHC(Me)O] (M = Rh, Ir). The chloro ligand can © 2014 American Chemical Society

be removed in the presence of AgX (X = BF4, PF6) to afford the corresponding cationic complexes [Cp*M(η5-CH2C(Me)CHC(Me)O][X] (M = Rh, X = BF4; M = Ir, X = PF6), while an organometallic polymer with a μ3-bridging iridaoxabenzene ligand is isolated if a bulkier 2,4-t-Bu-oxopentadienyl ligand is used.4 As an extension of the chemistry of the heteropentadienyl ligands, we decided to explore their reactivity with [(η4-COD)Ir(μ2-Cl)]2 (COD = cyclooctadiene), thus finding dimeric structures, which include μ2-bridging thia- and sulfinylpentadienyl ligands, as well as compound (η4-COD)Ir(μ2-Cl)(η1-μ2-η1:2-OSOCHCHCHCH2)Ir(η4-COD), which showed the dioxo-thiapentadienyl ligand bonding in an intermolecular fashion, as a sulfinato-O,S complex.5 Previously, the reaction of [(η6-C6Me6)RuCl2]2 with the trimethylsililoxybutadiene CH2CHCHCHOSiMe3 provides an unexpected Received: May 28, 2014 Published: October 22, 2014 6305

dx.doi.org/10.1021/om500392d | Organometallics 2014, 33, 6305−6318

Organometallics

Article

the corresponding coordinatively saturated complexes, is reported. Also, the treatment of this dinuclear unsymmetrical (iridapyran)(COD) complex 1 with molecular hydrogen in the presence of phosphines results in hydrogen-transfer to one of the coordinated cyclooctadiene ligands, which leads to the formation of η3-cyclooctenyl derivatives.

contrast, in which a dinuclear oxopentadienyl product, [(η6-C6Me6)Ru(η1:3-μ2-exosyn-CH2CHCHCHO)]2(BF4)2, has been isolated and structurally characterized. As far as we know, this is the first example of a complex bearing a μ2bridging oxopentadienyl ligand;6a a related reactivity study with CO, PR3, and PHPh2 has also been reported.6b Motivated by these results, it was decided to study the coordination of the oxopentadienyl ligand to [(η4-COD)Ir(μ2-Cl)]2 as part of a research program that would allow learning more about the bonding preferences and reactivity of these heteropentadienyl ligands. The findings showed the formation of a dinuclear iridium cyclooctadiene complex with a η1:1-μ2-η4iridaoxacyclohexadiene acting as a bridging ligand, which was interesting because there is no precedent of a bridging metallacycle that takes part in the formation of a novel twoelectron mixed-valence IrII−Ir0 compound. The multielectron activation of small-molecule substrates has been studied by Nocera et al. based on bidentate inorganic ligands which are able to support the intramolecular disproportionation of a symmetric binuclear metal core, such as the IrI−IrI dimer [(η4COD)Ir(μ2-Cl)2]2 to two-electron mixed-valence Ir II−Ir0 complexes.7 They demonstrated that iridium and rhodium mixed-valence complexes serve as platforms for a wide range of applications, such as C−H activation, reversible H2 addition, photocatalytic H2 production, multielectron photochemistry, and other organometallic chemistry.7 Dinuclear iridium complexes containing COD ligands have been studied to a great extent, and the most important precursor used has been the dichloro-bridged dimer [(η4-COD)Ir (μ2-Cl)]2.8 The capability of diiridium compounds to perform facile C−H activation has been widely demonstrated.8 A couple of interesting examples that are the result of the oxidative addition reactions associated with the metal−metal bond are (a) the reaction of the methylene-bridged dimer [(η4COD)Ir(μ2-CH2)]2 with diphenylacetylene to yield an iridium complex containing a bridging diphenylallyl ligand coordinated η1 and η3 in (η4-COD)Ir(μ2-CH2)[(η1-μ2-η3-(C(Ph)C(Ph)CH2)]Ir(η4-COD)9a and (b) the dinuclear dihydrido iridacyclopentadienyl complex (η4-COD)Ir(H)2(η1:1-μ2-η4-C4H4)Ir(η4-COD), as well as the trinuclear (η4-COD)Ir(μ2-H)(η1:1-μ3-η4-C4H4)[Ir(η4-COD)]2, where the triple-decker-like species can be cleaved by PMe3 to form dinuclear (η4-COD)(PMe3)Ir(η1:1-μ2-η4-C4H4)Ir(η4-COD).9b The versatility of the different coordination modes of bonding and hapticities adopted by the COD ligands has been demonstrated in several reactions involving dinuclear Ir(η4-COD) units10 as well as mononuclear Ir(η4-COD) compounds.11−16 Related dinuclear iridium compounds with hydride and phosphine ligands have also been prepared for a range of allyl and Cp* ligands, such as the thermolysis at higher concentrations of the allyl hydride compound Cp*IrH(η3-C3H5) in benzene, which leads to the oxidative addition product Cp*Ir(η1-C6H5)(η1-μ2-η3-CHCHCH2)(μ2-H)IrCp*, where the hydride and the η1,η3-allyl ligands are bridging both iridium atoms. The consequent reductive elimination of benzene from the dinuclear compound in the presence of donor ligands L, such as PMe3 and CO, affords the corresponding derivatives Cp*Ir(L)(η1-μ2-η3-CHCHCH2)IrCp*.17 Several X-ray structures containing the η1,η3-allyl ligand have been reported.17b In this work, the preparation of the coordinatively unsaturated dinuclear iridium complex (η4-COD)Ir(η1:1-μ2-η4CHC(Me)CHC(Me)O)]Ir(η4-COD) (1), which reacts with carbon monoxide and tertiary phosphines in order to produce

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RESULTS AND DISCUSSION

Synthesis and Spectroscopy of Dinuclear Compounds with Iridaoxacyclohexadiene and Iridaoxacyclohexadienyl Bridging Ligands. 1. Compound (η4-COD)Ir[η1,1-μ2-η4-CHC(Me)CHC(Me)O]Ir(η4-COD) (1). Treatment of [(η4-COD)Ir(μ2Cl)]2 in THF with 2 equiv of Li(2,4-dimethyloxopentadienide) at −78 °C resulted in the formation of the dinuclear unsymmetrical complex 1 in 88% yield. The whole reaction is described in Scheme 1. Scheme 1

Compound 1 was obtained as a dark red product after evaporation of the solvent and extractions with hexane. The 1H and 13C NMR data are summarized in Tables 1 and 2. At room temperature, the 1H NMR spectrum showed the expected signals for the oxopentadienyl ligand (δ 6.68, 4.97, 2.06, and 2.03 for H1, H3, Me2, and Me4, respectively). The signal at δ = 6.68 (d, 1.8 Hz) for the hydrogen at C1 was irradiated, and a nuclear Overhauser effect was observed at δ 4.03, 2.94, and 2.06; thus these protons were assigned to H6 and H5 of the COD ligand and the Me2 of the oxopentadienyl, respectively. Particularly informative were the signals at high field in the 13 C{1H} spectrum, which correspond to iridaoxacyclohexadiene carbon atoms C1−C4 at δ 127.0, 123.6, 86.1, and 151.0, in agreement with the formation of the “iridapyran” metallacycle. Several signals of the COD ligand, both in 1H and 13C NMR, appeared broad, suggesting the existence of a dynamic equilibrium in one of the COD ligands. The molecule was anchored at −50 °C; at this temperature, the four broad signals observed at δ 56.1, 64.1, 33.9, and 32.0, in the 13C NMR at room temperature, split into two pair of signals (Table 2), in agreement with unsymmetrical COD-coordinated ligands. The complete assignment was achieved by two-dimensional NMR experimental techniques. Strong exchange signals between H15 and H16 with H19 and H20, respectively, were observed in the NOESY experiment, at −60 °C, which pointed to the free rotation of COD coordinated to Ir0, instead of a conformational equilibrium. A dynamic process that results in the rotation of the COD methine protons has been reported.18 The absence of the characteristic CO vibration band in the IR strongly supports the proposed coordination mode. The nature of the bonding was confirmed through the single-crystal X-ray structure determination. Crystals of 1 were grown by slow cooling of a hexane solution, which produced almost redblack crystals. An ORTEP diagram is shown in Figure 1, where there is evidence of two positional isomers according to the iridaoxacyclohexadiene moiety with 50% occupancy. The crystalline structures are disordered. Crystal data and selected 6306


1.83 (s)

2.57 (s)

6.74 (br, s)

6.80 (s)

6.75 (s)

6.85 (s)

5.97 (s)

6.07 (s)

5.94 (s, br)

1c

2

2c

2e,f

3c

3e,f,g

6307

3h

2.05 (s)

2.53 (s)

2.51 (s)

2.55 (m)

6.11 (s)

8.00 (s)

8.00 (s)

8.03 (br, s)

4c

5

5f

6

2.03 (s)

2.13 (d, 2.3)

2.03 (s)

2.52 (s)

2.31 (s)

2.10 (s)

6.64 (s)

H2/Me2

2.06 (s)

1b

H1

6.68 (d, 1.8)

1

compound

H4/Me4

1.99 (s)

1.88 (s)

3.62 (s)

3.56 (s)

3.58 (s)

4.66 (s)

4.62 (s)

4.90 (s)

4.65 (s)

3.81 (s)

H5/H15

1.48 (s)

1.45 (s)

1.44 (s)

1.45 (s)

H6/H16

3.83 (m) 4.00 (t, 6.2)

H7/H17

2.13 (m) 2.38 (m)

2.27 (m) 2.40 (m)

2.61 (m)

3.79 (t, 8.5)

3.10 (br) 2.60 (m) 3.31 (m)

3.92 (br) 3.65 (m, 2H)

3.50 (m)

3.71 (m)

3.77 (t, 6.4)

3.71 (m)

3.59 (m)

3.66 (m) 3.20 (br)

2.61 (m) 3.22 (m)

3.74 (t, 7.1)

4.15 (m)

3.78 (m) 3.55 (m)

4.33 (t, 6.8) 3.29 (m)

2.10 (s)

(m)d (m) (m) (m, 2H)

1.86 (m)

1.22 (m) 1.90 (m, 2H) 2.37 (m)

1.37 (m) 1.93 (m, 2H) 2.40 (m)

2.55 (m) 2.75 (m)

2.08 (m) 2.49 (br) 2.67 (br)

2.13 (m) 2.61 (m)

2.57 (m, 2H)

1.93 1.45 1.60 2.08

(br) 3.25 (br) 2.18 (m, 2H) (ddd, 7.5) 4.28 (t, 6.6) 1.55−2.50 (m) (br) 3.76 (br) (m) 2.29 (dd, 6.7, 8.1) 1.36 (m) 1.60 (m) 3.13 (m) 3.97 (t, 7.0) 2.15 (m) 2.47 (dd, 6.3, 7.9) 3.10 (br)d 3.25 (m) 1.55 (m)

3.56 3.09 4.19 2.20

4.24 (br) 2.90 (br, m)

2.94 (ddd, 7.6) 4.03 (t, 6.2)

1.34 (s, br) 3.50 (br)

1.09 (s)

1.40 (s)

1.94 (s)

3.52 (d, 1.7) 1.48 (s)

3.81 (s)

4.55 (d, 2.0) 1.81 (s)

5.02 (s)

4.97 (d, 2.0) 2.03 (s)

H3

Table 1. 1H NMR Data of Compounds 1−8a H8/H18

H9/H19

3.83 (m) 4.66 (m)

4.68 (t, 7.3)

(m)d (m) (m) (m) (m) (m) (m, 2H) (m)

2.07 2.55 2.75 3.24 0.22 0.92 1.04 1.93 0.84 0.98 2.60 3.00 0.68

(m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m) (m)

2.49 (br) 2.67 (br)

2.21 (m) 2.96 (m)

2.20 1.24 1.81 2.08 2.20 2.15 2.57 3.27

1.30 (m)

1.45 (m)

4.16 (m)

3.10 (br) 1.40 (m)

1.49 (m)

4.37 (t, 6.9)

4.14 (br) 3.20 (br)

3.22 (m) 3.66 (m)

4.26 (m)

4.52 (t, 6.5)

3.33 (m) 4.17 (m)

3.84 (t, 7.0)

2.05 (m, 2H) 4.49 (br) 1.55−2.50 (m) 5.04 (t, 6.6) 3.76 (br) 2.20 (m) 4.20 (t, 6.9)d 2.94 (m) 1.20−2.80 (br)

2.10 (m, 2H)

2.18 (m)

H10/H20

(br) (m) (m) (m) (m) (m)

0.92 (m) 1.04 (m)

2.93 (m)

2.77 (br) 3.50 (br)

2.38 (m)

3.92 0.13 1.31 1.80 1.90 0.14

H11/H13

1.70 (m) 1.95 (m) 1.25 (m, 2H)

1.85 (m) 2.05 (m)

1.72 (m) 1.98 (m) 2.15 (m) 2.24 (m) 1.97 (m) 2.21 (m) 1.00−2.50 (m) 1.66 (m) 1.97 (br) 2.17 (br) 2.49 (br) 1.71 (m) 1.85 (m) 2.25 (m) 2.55 (m) 1.31 (m) 1.93 (m) 2.40 (m) 2.90 (m) 1.13 (m) 1.90 (m) 2.37 (m) 2.84 (m) 1.45 (m)

(br) (dd, 5.1, 7.9) 1.55−2.50 (m) (br) (m) 1.60 (m) 2.00 (m) (m) 2.15 (m) 2.20 (m) (m)d 2.50(dd, 7.7, 8.0) 3.25 (m) (m) 2.50 (m, 2H) 2.84 (m) (t, 6.9) 3.08 (m)

2.79 (m)

3.95

3.09

3.33

3.38

4.77 4.31 4.19 2.15

4.24 (br) 3.77(dd, 5.2, 7.7)

3.83 (m)

H12/H14

(m)d (m) (m) (m, 2H)

(m) (m) (m) (m) (m)

1.12 (m)

1.65 (m, 2H) 1.90 (m) 2.11 (m)

1.60 (m, 2H) 1.93 (m) ∼2.20 (br)

1.72 (m) 1.98 (m) 2.15 (m) 2.24 (m) 1.87 (m) 2.17 (m) 1.00−2.50 (m) 1.66 (m) 1.97 (br) 2.17 (br) 1.20 (br) 1.71 (m) 1.85 (m, 2H) 2.25 (m)

2.10 1.81 2.08 2.36

2.00 2.10 2.15 2.29 1.80

1.88 (m) 2.40 (m) 1.64 (br) 1.72 (m) 2.23 (m) 1.43 (m) 1.62 (m) 1.55−2.50 (m)

−11.33 (d, 31.8)

−11.57 (d, 32.7) 1.70 (d, 8.3)

−11.50 (d, 32.6) 1.69 (d, 8.5)

1.29 (d, 9.8) 7.08 (m) 7.27 (t, 7.7)

0.96 (d, 9.2)

1.29 (d, 9.4)

0.97 (d, 9.0)

Ir−H/PR3

Organometallics Article


2.43 (s)

6.49 (br, s)

8

a

2.62 (s)

8.24 (s)

7c

6308

3.61 (s)

3.58 (s)

3.59 (s)

H3

1.49 (s)

1.26 (s)

1.21 (s)

H4/Me4

3.64 (br)

4.29 (m)

3.40 (br)

3.90 (br)

H5/H15

H7/H17

2.96 (br)

H8/H18

1.42 (s)i

3.10 (br)

H9/H19

1.20 (m)i

1.20 (m)i

(m) (m)i (m) (m)i

1.82 (m, 11.0)

0.52 1.43 1.60 2.22

2.96 (br)

1.88 (m)i

1.16−1.80 (m) 4.21 (t, 9.0)i

1.18 (m)

0.88 (m) 1.12 (m)

1.82 (m, 11.0)

2.22 (m, 2H) 2.60 (m) 2.72 (m)

1.16−1.80 (m)

3.40 (br)

4.14 (t, 8.5)

2.22 (m)

2.38 (m)

3.89 (m)

3.10 (br)

H6/H16

H10/H20

1.30−2.50 (m)

H11/H13

(m) (m) (br)i (m) (m)

1.43 (m)i 3.64 (br)

0.87 1.83 4.21 1.02 1.24

2.22 (m) 2.19 (m) 2.32 (m)

1.79 (m)i 1.88 (m)i 1.95 (m)

1.16−1.80 (m)

0.48 (dd, 8.3, 8.8) 1.42 (m)i

1.45 (m) 1.86 (m) 3.90 (br)

Ir−H/PR3

1.80 (d, 8.6) 2.16 (d, 8.2) 1.30−2.50 (m) 7.41 (m, br) 7.43 (m, br) 7.68 (t, 7.6, 8.5) 1.19 (m) −11.16 (d, 31.9) 2.22 (m) 1.67 (d, 8.8) 1.16−1.80 (m) 2.04 (d, 8.3) 7.05−7.14 (m) 7.59 (t, 8.1) 2.48 (m) −11.5 (d, 28.1) 3.14 (m) 0.96 (t, 7.1) 1.43 (m)i 1.79 (m)i 1.88 (m)i 2.22 (m)i 2.19 (m) −31.1 (t, 17.2) 2.32 (m) −11.6 (dd, 19.2, 78.1) 1.06−1.22 (m)i 1.22−1.25 (m)i 2.51 (sept, 7.0, 2H)

H12/H14 2.38 (m)

In CDCl3. For numbering see Scheme 2. b−50 °C. cC6D6. dBroad signals of 2 (4.30, 4.90 ppm); 2C (5.10, 4.75, 4.25, 2.90 ppm). eCD2Cl2. f−60 °C. gIn mixture with 1. hToluene-d8. iOverlapped signals.

2.60 (s)

8.28 (s, br)

6c

H2/Me2

H1

compound

Table 1. continued



6309

91.0 28.3

90.3 28.4

92.6 28.6

132.5

123.1 (d, 10.4)

122.0 (br)

121.0 (br)

120.6 (d, 57.0)

120.8 (d, 55.0)

120.1 (d, 57.0)

118.0 (d, 54.5)

106.0 (d, 63.2)

2c

3c

3e

4g

5

5h

6

7g

8

a

90.7 28.7

130.1

2

C3

64.9

64.4 (d, 3.1)

64.7

64.5g

64.7

84.0

83.6

83.8

64.4

64.6

86.8

86.1

C4/Me4

208.5 30.5

211.5 30.2

211.7 30.4

212.1 30.4

211.2 30.1

151.0 26.3 146.8 25.9 207.8 30.3 208.3 30.8 102.7 (br) 21.9 (d, 1.1) 105.1 20.8 n.o.d 22.8

C6/C16

60.2 (d, 6.2)

56.3 (br) 53.2

56.3 (br) 50.8 (br)

55.5 (br)

55.5 (br) 54.8 (d, 5.4)

53.6 60.7

55.2 (br) 55.8

55.2 (br) 55.1 (d, 4.9) 57.6f (d, 5.2) 58.8 (d, 5.7)

58.8 (d, 5.7)

65.2 (br)

59.5 64.1 58.9 64.3 53.6 65.2 53.1 65.5 67.2 (d, 3.2) 68.7 (br) 67.5f 65.5 62.1

56.1 (d, 4.6)

n.o.d

(d, 4.4) (br)

(br) (br)

(br)

C5/C15 54.7 56.1 54.3 53.4 47.6 44.6 47.9 43.1 55.2 51.0 54.2 50.6 54.3

C7/C17

30.6 (br) 30.4

27.4

30.3 (br)

30.5 26.7

30.5 (br) 26.9

27.0

31.1

36.0 33.9 (br) 35.9 32.2 30.0 27.5 (br) 29.7 27.7 36.4 39.0 (br) 37.9 40.4 35.3

C8/C18

C9/C19

56.3 (br) 53.2

−1.3

40.3 (d ∼3.0)

30.6 (br) 30.4

55.5 (br)

44.9 −0.9

56.3 (br) 50.8 (br)

37.8 (d, 6.7)

55.5 (br)

57.7f 39.5

39.4 (d, 4.9)

55.2 (br)

−1.1 55.2 (br) −1.2

57.1

(d, 5.7) (br) (d, 6.9)

(br)

C10/C20 75.6 56.1 74.5 58.2 69.4 66.9 69.7 67.7 57.2 51.0 59.0 55.9 54.3

65.2 (br)

84.1 64.1 84.3 64.6 92.8 (br) 102.8 (br) 91.8 104.2 68.4 (d, 12.1) 68.7 (br) 67.5f n.o.d 62.1

30.3 (br)

39.0 38.0 (d, 9.4)

37.9 (d, 9.8) 39.6 (d, 4.5) 37.6 (d, 9.9)

37.8

33.3 33.9 (br) 33.3 33.8 27.9 27.5 (br) 27.8 27.5 35.5 39.0 (br) 34.4 39.1 36.1

37.8 (br) 37.2

24.2

37.5 (br)

29.2 23.6

37.4 (br) 24.5

24.8

(d, ∼2) (br)

(br)

(br)

C11/C13 28.2 32.0 27.7 30.6 35.6 38.4 36.7 39.1 29.6 31.0 29.7 30.7 28.1 37.8

In CDCl3. For numbering see Scheme 2. b−50 °C. cCD2Cl2, −60 °C. dNot observed. eToluene-d8, −90 °C. fOverlapped signal. gC6D6. h−60 °C.

91.2 28.3

125.8

C2/Me2

123.6 24.8 123.7 24.5 98.2 28.1 99.1 28.2 119.6 (d, 4.6) 24.7 118.2 24.2 116.4 (br) 24.0

1b

C1

127.0

1

compound

Table 2. 13C NMR Data of Compounds 1−8a

37.8 (br) 37.2

26.0

37.5 (br)

37.0 22.8

37.4 (br) 23.7

23.9

(d, ∼2) (br)

(br)

(br)

C12/C14 31.8 32.0 30.9 34.0 36.1 42.5 37.3 43.4 34.1 31.0 33.1 31.5 34.3 31.1 (s)/ (d, 25.4) (s)/ (d, 24.1) (s)/ (br) (d, 7.7, o) (m, p)f (s)/ (d, 29.5)

P δ/L

−36.8 17.4 128.2 128.7 138.0 −31.9 25.8 24.8 26.1 17.5 10.3 19.6 20.2 28.6 29.2

(s)/ (d, 34.0), 18.2 (d, 34.9), (d, 8.4, m) (s, p), 130.0 (d, 8.5, o), (d, 31.7, i) (s)/ (d, 24.6) (d, 12.3), (s), 13.8 (Me) (m, 17.7) (m, 12.2)/ (d, 26.9) (d, 13.8) (d, ∼19.0) (d, 23.7)

−51.0 (s)/ 18.2 (d, 30.1)

−54.4 13.6 −56.6 12.6 −46.6 11.0 129.4 128.1 −51.0 18.3

n.o.d

220.0

31



Organometallics

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Figure 1. Perspective view of isomers 1A and 1B. Hydrogen atoms have been omitted for the sake of clarity, except those of C1 and C3 in the oxairidacyclohexadiene ligand.

Table 3. Selected Bond Lengths (Å) of Compounds 1−3 and 5−8 C1−C2 C2−C3 C3−C4 C4−O1 C5−C6 C9−C10 C15−C16 C19−C20 C1−Ir1 O1−Ir1 C5−Ir1 C6−Ir1 C9−Ir1 C10−Ir1 Ir1−Ir2 C1−Ir2 C2−Ir2 C3−Ir2 C4−Ir2 Ir1−P1 C15−Ir2 C16−Ir2 C19−Ir2 C20−Ir2 Ir1−H12 Ir2−H12

a

1a

2b

3

1.348(19) 1.409(9) 1.415(9) 1.404(10) 1.404(8) 1.397(8) 1.355(7) 1.356(7) 2.039(18) 2.020(9) 2.138(5) 2.136(6) 2.122(6) 2.134(6) 2.8478(3) 2.252(16) 2.347(6) 2.238(6) 2.337(5)

1.392(5) 1.474(6) 1.448(6) 1.244(5) 1.446(6) 1.393(6) 1.409(6) 1.430(6) 2.033(4) 2.240(3) 2.124(4) 2.090(4) 2.275(4) 2.199(4) 2.7693(10) 2.221(4) 2.222(4) 2.175(4)

1.418(14) 1.453(14) 1.415(15) 1.340(12) 1.398(16) 1.377(15) 1.440(18) 1.421(17) 2.046(10) 2.079(6) 2.122(11) 2.169(10) 2.147(10) 2.156(9) 2.8675(7) 2.160(10) 2.259(10) 2.236(9) 2.359(10) 2.398(3) 2.144(11) 2.136(12) 2.122(11) 2.103(11)

2.111(6) 2.207(15) 2.104(6) 2.090(14)

2.165(4) 2.191(4) 2.133(4) 2.104(4) 2.075(4) Ir1−C23 2.106(4) Ir2−C23 1.173(5) C23−O2

1.7913

5

6

7

1.406(6) 1.458(7) 1.445(6) 1.243(6) 1.427(7) 1.531(6) 1.427(8) 1.424(9) 2.085(4) 2.208(3) 2.160(4) 2.141(4) 2.100(4)

1.413(5) 1.459(5) 1.429(5) 1.255(4) 1.422(5) 1.539(5) 1.441(6) 1.414(6) 2.089(3) 2.224(2) 2.169(3) 2.154(3) 2.100(4)

1.411(5) 1.457(6) 1.433(6) 1.254(5) 1.401(6) 1.544(6) 1.416(7) 1.402(7) 2.093(4) 2.202(3) 2.175(4) 2.149(4) 2.097(4)

2.9183(2) 2.160(4) 2.157(4) 2.193(4)

2.92064(17) 2.133(3) 2.158(3) 2.213(4)

2.9294(2) 2.121(4) 2.166(4) 2.234(4)

2.3492(12) 2.117(5) 2.094(5) 2.127(5) 2.144(5) 1.6165

2.3506(9) 2.106(3) 2.136(3) 2.153(4) 2.126(4) 1.83(4)

2.3864(11) 2.103(4) 2.140(4) 2.126(4) 2.120(4) 1.68(4)

1.77(4)

1.79(4)

8

Ir1−H12

1.403(5) 1.466(5) 1.415(6) 1.261(5) 1.507(6) 1.522(8) 1.444(6) 1.418(8) 1.499(6) 2.208(2) 1.864(4) 1.541(6) 1.862(4) 1.534(6) 2.9147(2) 2.174(3) 2.176(4) 2.221(4) 2.3155(9) 2.3578(9) 2.128(4) 2.114(4) 2.099(5) 2.126(4) 1.69(4)

Ir2−H12

1.88(4)

Ir1−H12D

1.54(4)

C2−C22 C13−C14

C14−C15 C5−P1 C5−C12 C10−P2 C10−C32

Ir1−P2

Isomer 1A. bOne of the two molecules in the asymmetric unit.

C3−C4 1.327(33); and C4−O1 1.317(16) Å].2a The sum of the internal angles in both structures were quite similar (711.2° vs 719.7°2a), but considering the expanded internal angles (average 123.5° vs 125.8°2a), which compensate for the O1−Ir1−C1 angle [93.2(6)° vs 90.7°2a], it is considered that there is a substantial tension into the rings. The iridaoxacyclohexadiene moiety showed a nonplanar six-membered ring [19.327(0.653) Å] as well as a long bond length of Ir2−C1 [2.252(16) Å] compared to other Ir2−C1 distances in compounds 2, 3, and 5−8 (vide infra, Table 3). The iridium−iridium distance of 2.8479(3) Å was within bonding distance, similar to the symmetrical-bridged (η4-COD)Ir[μ2-S2C2B10H10]Ir(η4-COD) [2.8608(11) Å],19 Cp*(H)Ir[μ2-(H)(BH4)]Ir(H)Cp* [2.823(1) Å],20 and Cp*Ir[μ2-(S)(C4H4)]IrCp* [2.818(2) Å]21 and other unsymmetrically

bond lengths and angles of isomer 1A are given in Tables 1S, 3, and 4 (see complete information on both isomers in the Supporting Information). An asymmetric structure was observed, with a fourcoordinate, slightly distorted square planar environment about the Ir1 center (IrII), without considering the metal− metal bond. Two of the coordinated positions correspond to the COD ligand, and another two, to the formed iridaoxacyclohexadiene. The Ir2 (Ir0) was coordinated to the bridging metallacycle through the η4-diene moiety and also to a second η4-COD ligand. The strong π-bond contribution in the metallacycle was contrasting with the alternating C−C bond lengths reported for the iridapyran compound Ir(H)[1,5-ηCHCHCHCO](PEt3)3 [C1−C2 1.350(21); C2−C3 1.449(31); 6310


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Table 4. Selected Bond Angles (deg) of Compounds 1−3 and 5−8 1a C1−C2−C3 C2−C3−C4 C3−C4−O1 C4−O1−Ir1 O1−Ir1−C1 C1−Ir1−C5 C1−Ir1−C6 C1−Ir1−C9 C1−Ir1−C10 O1−Ir1−C5 O1−Ir1−C6 O1−Ir1−C9 O1−Ir1−C10 Ir1−C1−C2 Ir1−C1−Ir2 C5−Ir1−Ir2 C1−Ir2−C2 C1−Ir2−C3 C1−Ir2−C4 C15−Ir2−C1 C15−Ir2−C2 P1−Ir1−C1 P1−Ir1−O1 P1−Ir1−C5

122.2(9) 127.6(6) 123.0(6) 121.1(6) 93.2(6) 94.5(5) 88.5(5) 149.8(4) 171.8(4) 150.7(3) 170.2(3) 92.7(3) 86.3(3) 124.0(12) 83.0(6) 137.62(15) 34.0(5) 65.0(5) 81.8(4) 163.9(15) 155.6(2)

a

116.9(3) 120.8(3) 123.7(4) 118.9(3) 87.57(14) 85.47(16) 87.73(16) 166.18(16) 151.69(17) 119.07(13) 159.03(14) 106.21(14) 78.70(14) 124.3(3) 81.09(13) 132.43(12) 36.51(14) 67.50(15) 90.21(15) 105.65(16)

157.32(16) C23−Ir1−C5

P1−Ir1−C6 P1−Ir1−C9 P1−Ir1−Ir2 O2−C23−Ir1 O2−C23−Ir2 Ir1−C23−Ir2 internal angles dihedral angles (deg) C1C2C3C4 C2C3C4O1

2b

81.75(16) C23−Ir1−C9

711.19 19.327 (0.653)

141.7(3) 135.2(3) 82.96(14) 692.12 13.003 (0.183)

3

5

6

7

8

117.0(9) 124.4(9) 124.1(9) 111.7(6) 91.1(3) 141.2(4) 179.0(4) 99.3(4) 89.5(4) 85.4(3) 89.4(4) 161.9(4) 158.7(3) 127.0(8) 85.9(4) 93.6(3) 37.3(4) 67.6(4) 79.8(4) 101.3(4) 123.3(4) 86.2(3) 81.3(2) 131.0(3)

117.5(4) 123.5(4) 125.5(4) 119.9(3) 88.33(14) 117.30(17) 79.03(18) 91.76(17)

117.3(3) 123.1(3) 124.7(3) 118.5(2) 87.43(12) 115.88(13) 78.37(13) 94.26(14)

117.4(3) 122.1(4) 125.1(4) 120.0(3) 87.37(13) 113.81(16) 76.92(16) 94.17(17)

89.82(15) 94.75(15) 175.12(15)

89.04(12) 95.48(12) 175.26(11)

88.74(14) 95.18(15) 174.54(15)

124.1(3) 86.84(15) 162.96(12) 38.01(17) 68.44(17)

123.1(3) 87.53(12) 161.61(9) 38.46(13) 68.68(14)

123.6(3) 88.07(15) 159.02(12) 38.42(15) 68.41(15)

170.08(19) 137.6(2) 147.84(12) 87.10(9) 94.52(13)

146.89(14) 110.93(14) 148.74(9) 82.82(7) 93.65(10)

148.80(18) 111.95(17) 149.55(11) 84.15(8) 95.22(12)

94.7(3) 84.6(3)

133.08(13) 95.38(13)

132.00(10) 97.88(10)

132.90(12) 97.03(13)

Ir2−Ir1−H12D

126.56(8)

100.20(3)

102.43(2)

103.55(3)

P1−Ir1−P2

117.3(3) 127.1(3) 127.1(3) 118.8(2) 89.89(12) 149.94(15) 95.70(17) 106.00(16) 109.54(13) 114.11(13) 138.11(3) 90.54(10) 95.25(7) 125.4(3) 86.72(13) 174.6(14) 37.62(14) 67.74(14) 89.2(13) 165.53(16) 143.33(15) 158.32(10) 93.62(7) 74.0(14) P1−Ir1−H12 94.4(13) 88.0(13) P2−Ir1−H12D 110.39(3)

695.34 27.883 (0.693)

698.77 14.882 (0.390)

694.11 17.919 (0.242)

695.62 16.556 (0.352)

C1−Ir2−C16 C1−Ir2−C19 C1−Ir2−C20 Ir1−P1−C5 Ir1−P2−C10 P2−Ir1−Ir2 P2−Ir1−C1 P2−Ir1−O1

P2−Ir1−H12

P1−Ir1−H12D

705.48 14.593 (0.342)

Isomer 1A. bOne of the two molecules in the asymmetric unit.

bridged diiridium complexes (η4-COD)Ir[μ2-F3CCCCF3]Ir(η2,3-C8H11) [2.850(3) Å]10a and (L)Ir(μ2-L2)Ir(Me)(Br)(MeCN) [L = R2PN(Me)PR2] [2.8290 (9) Å],7a and slightly shorter than that for hydride-bridging iridium−iridium atom centers in Cp*(η1-C6H5)Ir(η1:μ2-η3-CHCHCH2)](μ2-H)IrCp* [2.867(1) Å].17 There is a variety of interpretations of metal−metal bond distances with values in the range 2.603−2.984 Å,9,10,17,19−35 and even a very long Ir−Ir bond of 3.112 (1) Å has been justified in order to support the diamagnetism of the compound (η4-COD)Ir(Me)(μ2-pyrazole)2Ir(I)(η4-COD).32b In view of the X-ray analysis, as well as variable-temperature NMR studies, it is reasonable to conclude that compound 1 is an Ir0−IrII complex, which provides an interesting two-electron mixed valency by electronically and coordinatively distinctive adjacent iridium metal centers. The coordinative unsaturation of 1 is the cornerstone for the addition and oxidative addition reactions described below. 2. Addition Reactions of 1 with CO, PMe3, and PMe2Ph. The synthesis of compounds (η4-COD)Ir[η1:1-μ2-η3-CHC(Me)CHC(Me)O)]Ir(η4-COD)(μ2-CO) (2), (η4-COD)Ir[η1:1-μ2-η4-CHC(Me)CHC(Me)O)]Ir(η4-COD)(PMe3) (3), and (η4 -COD)Ir[η1:1 -μ2 -η 4 -CHC(Me)CHC(Me)O)]Ir(η 4COD)(PMe2Ph) (4) was carried out by mixing compound 1

and the corresponding Lewis bases suspended in saturated hydrocarbon solvents at low temperature, Scheme 2. An excess of CO was required for compound 2, while stoichiometric reactions with phosphines produced compounds 3 and 4. As expected, the addition reaction of 1 with PMe3 and PMe2Ph occurred at the coordinatively unsaturated IrII, while the Ir0 center was undisturbed, as seen in the crystal structure of 3, vide infra. NMR and IR spectra of the products 2−4 clearly indicated a different coordination mode of the bridging oxametallacycle ligand, where 3 and 4 maintained η4 and η1,1 bonds to the Ir0 and IrII, respectively. The phosphines coordinated to IrII in order to fulfill the 18e− in both metal centers appear as single resonances at 31P δ = −56.6 and −46.6 ppm for 3 and 4, respectively. Contrastingly, the 13C NMR spectrum of compound 2 showed the double bond CO character in the η3-iridaoxacyclohexadienyl bridging ligand with the consequent interconversion of the diene η4 of precursor 1 (vide supra) to an enyl η3 (C1−C4: 130.1, 98.2, 64.6, 207.8 ppm) bonding mode in 2. The IR spectrum of 2 also supports this η3-binding mode [ν(CO) 1594 cm−1] of the oxametallacycle bridging ligand, as well as confirmed the carbonyl ligand bridging the 6311


Organometallics

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Scheme 2. Addition and Oxidative Addition Reactions of Compound 1

iridium atoms, as observed from a strong ν(CO) absorption at 1798 cm−1. The 13C{1H} NMR of compound 2 showed at low temperature (CD2Cl2, −60 °C) 16 carbon resonances for the two chemically inequivalent, nonconjugated, η4-cyclooctadiene ligands. Contrastingly, 3 at the same temperature showed that one of these COD ligands was evidently bound in an unsymmetrical fashion, while the other COD was shown to be fluxional, as inferred from two sets of alkene and alkane resonances, which could be split at −90 °C. Unsymmetrically bridging aryl dinuclear iridium complexes,36 at room temperature, behaved similarly to 3. Compound 2 crystallized with two independent molecules in the asymmetric unit, and inspection showed that they were similar to each other. For clarity, only one will be described here, but the complete information is in the Supporting Information. The η3- and η4-binding mode of the oxametallacycle ligand was confirmed by X-ray crystallography

Figure 3. Perspective view of compound 3 drawn at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity, except those of C1 and C3 in the oxairidacyclohexadiene ligand.

described in Tables 1S, 3, and 4. The bridging CO in 2 was slightly nonsymmetric to the iridium atoms with bond lengths of 2.075(4) and 2.106(4) Å for Ir1−C23 and Ir2− C23, respectively. The Ir−P bond in 3 [2.398(3) Å] was quite similar to related compounds, such as (η4-COD)Ir(η1:2CH2CHCHCHSO2)PMe3 [2.398(2) Å]5 and 7 [2.3865(12) Å], and longer than those of 5 [2.3492(12) Å], 6 [2.3506(9) Å], and 8 [2.3578(9) Å], vide infra. As expected, 2 exhibited the shortest C−O bond [1.244(5) Å] for C4−O1 compared to 1.340(12) Å for 3. The metal−metal bond lengths of 2 and 3 were 2.7693(10) and 2.8675(7) Å, respectively, which are within the range of iridium−iridium intermetallic distances. Compound 2 is comparable to those observed in related diiridium complexes, such as (CNtBu)Ir(μ2L 2 )Ir(CN t Bu) 2 [2.7631(4) Å], 7 b (η 4 -COD)Ir[μ 2 (formamidinato)]Ir(OCOCF3)2(H2O) [2.774 (1) Å],22 (CNtBu)(Cl)Ir(μ2-L2)Ir(CNtBu)(Cl)2 [2.7774(3) Å],7b (L)Ir(μ2-L2)Ir(CH2CMe3)(Br) [2.7910(8) Å],7a (CNtBu)2Ir(μ2-L2)Ir(Cl)2 [2.7920(3) Å],7b where L = R2PN(Me)PR2, and (L)Ir(μ2L2)Ir(Cl)2 [L = [MeN(P(OEtF3)2] [2.7871(8) Å].7c Nonsymmetrical complexes, without hydrido-bridged ligands, show

Figure 2. Perspective view of compound 2 drawn at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity, except those of C1 and C3 in the oxairidacyclohexadiene ligand.

for compounds 2 (Figure 2) and 3 (Figure 3), respectively. Crystallographic data and bond lengths and angles are 6312


Organometallics

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bond lengths in a range between 2.643 and 2.8703 Å,7,9a,10,17,31,32a,34 while longer bond lengths (2.933−2.9577 Å) are observed for symmetric dinuclear iridium−iridium compounds.31,33 In solution of deuterated toluene, after 7 days, 3 showed a reversible reaction by dissociation of PMe3, recovering compound 1 (vide infra). Contrastingly, compound 4, under similar conditions, decomposed without evidence of dissociation of PMe2Ph. Compounds 3 and 4 are not stable in CDCl3. The lability of the PMe3 in 3 contrasts to the PMe3 adduct in Cp*Ir(PMe3)(η1-μ2-η3-CHCHCH2)IrCp*, which was heated to 100 °C without any evidence of PMe3 loss; instead an intramolecular C−H insertion was observed.17a It should also be mentioned that the coordination of MeCN in the unsymmetrical bimolecular core IrII−Ir0 with phosphazane ligands [Ir0,II(Me)(Br){(R2PN(Me)PR2)}3(MeCN)] showed that the usually weakly coordinated ligand could be removed only by prolonged exposure to vacuum. It was also shown that the H2 oxidative addition reaction proceeded only after the corresponding adduct had lost the MeCN.7a 3. Oxidative Addition Reactions of 1 in the Presence of Phosphines and Molecular Hydrogen. The addition of dihydrogen, along with several tertiary phosphines such as PMe3, PMe2Ph, and P(n-Bu)3, to the dinuclear unsymmetrical complex 1, in THF under mild conditions, resulted in hydrogen-transfer to one of the coordinated cyclooctadiene ligand with the formation of cyclooctenyl phosphine derivatives (η 4 -COD)Ir[η 1,1 -μ 2 -η 3 -CHC(Me)CHC(Me)O)]Ir(μ 2 -H)(η1:η2-C8H13)(L) (L = PMe3, 5; PMe2Ph, 6; P(n-Bu)3, 7), Scheme 2. These compounds were isolated as yellow solids in fair yields, due to the similar solubility of the cyclooctenyl derivatives 5−7 and the precursor 1, which prompted us to purify them through deactivated column chromatography, with the consequent decrease in the yield. Compound 6 is more easily obtained, in a pure form and in good yields, by reacting directly 4 with H2 in pentane, vide infra. A strong ν(CO) absorption at ∼1570 cm−1 in 5−7, as well as in compound 2 (1594 cm−1, vide supra), reflects the coordination of the oxygen atom to one of the iridium centers with the corresponding formation of the iridaoxacycle structures. The presence of the hydrido ligand in complexes 5−7 was not inferred from the IR, which contrasts with other dinuclear iridium compounds already reported.35,37 The proposed structures for 5−7, in solution, are supported by spectroscopic and analytical data in the Experimental Section; chemical shifts of 1H, 13C{1H}, and 31P{1H} NMR (Tables 1 and 2) were assigned according to Scheme 2 or the numbering of crystalline structures shown in Figures 4−6. In the 1H NMR of 5−7, the metal hydride resonances (∼−11.4 ppm) were observed as doublets due to the phosphorus coupling (JPH = 28−33 Hz), the coupling constant values, and the multiplicity, suggesting that the hydrides are not terminal and are acting as bridging ligands (see Supporting Information). The 31P {1H} NMR spectra showed single resonances at −51.0, −36.8, and −31.9 for 5, 6, and 7, respectively. The 13C{1H} spectra of 5−7 showed the characteristic carbonyl resonances for C4 at δ ∼212 ppm, whereas the chemical shift of C4 in the η4-binding mode of 1 was found at δ = 151 ppm. The resonance effects involving the oxygen lone pairs were observed at C3 (δ = ∼65), which proved to be the most negative ring carbon atom, followed by C2 (δ = ∼91) and C1 (δ = ∼120, d, ∼56 Hz). These chemical shifts of C3−C1 in η3-iridaoxacycle can be compared to the η4-iridaoxacyclohexadiene complex 1 (C3, δ = 86.1, C2, δ = 123.6, C1, δ = 127.0) and also to the

Figure 4. Perspective view of compound 5 drawn at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity, except the hydride and those of C1 and C3 in the oxairidacyclohexadiene ligand.



related “iridapyran” mononuclear complex mer-Ir[η1,1-CHC(Me)CHC(Me)O](PEt3)3(H), where the chemical shifts of C3, C2, and C1 are δ = 97.4, 127.4, and 108.7 ppm.2b Regarding these spectroscopic data, there is no doubt that in compounds 5−7 the iridaoxacycle bridging ligand has an η3-binding mode. In agreement with the hydrogen-transfer of the hydrideiridium-phosphine moiety to its coordinated cyclooctadiene, the 1H and 13C NMR spectra of 5−7 displayed typical chemical shift ranges of coordinated methines C5 and C6 and 6313


Organometallics

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H2 elimination, which should be favored if the oxidative addition of H2 occurred in a single site (IrII) to the binuclear core.7d However, there was no evidence of coupling between both hydrides. Then, it could not be determined if these hydrido ligands were in different metal centers. It should also be mentioned that the 1H NMR showed a 1.0:0.02:0.02 ratio for the corresponding singlets of H1 at 6.74 ppm and the hydrides at −8.1 and −22.3 ppm, respectively. The low intensity of these hydrido ligands compared to H1 suggests that the oxidative addition of H2, if it happened, was not really favorable in compound 1. Monitoring the reaction of 4 in the presence of H2, by 1H and 31P NMR in toluene-d8 at different temperatures (−40 to 25 °C), shows, after 18 h at room temperature, resonances assigned to 6 [ 1H δ = −11.24 (d, 31.8 Hz) and 31P δ = −37.3 ppm], 4 [31P δ = −46.8 ppm], and another unknown species [1H δ = −11.58 (dd, 21.5, 3.4 Hz) and 31P δ = −31.7 ppm] in 1.0:0.3:0.08 ratio. After 4 days 4 is totally consumed and 6 is the predominant compound, along with a couple of traces of hydrido ligands at δ = −11.56 (d, 22.3 Hz) and δ = −9.5 (d, 75.6 Hz). There is no evidence of dissociation of the PMe2Ph. These facts suggested that the activation of the molecular hydrogen in 4 could happen at the IrII center, only if the oxygen atom of the oxairidacyclohexadiene or one of the double bonds of the COD ligand at IrII is previously decoordinated. In this case, the attack of molecular hydrogen was expected to occur at the coordinatively and electronically 16e− unsaturated IrII-phosphine center in 1, prior to the cyclooctadiene activation that produces the corresponding cyclooctenyl-coordinated ligands. According to this, the tentative mechanism described in Scheme 3 is being proposed, where two plausible pathways for the oxidative addition of H2 and the protonation of the C−H bonds are considered in the absence and presence of phosphine. At first, the coordination of molecular hydrogen at the IrII center in compound 1 generates A, which could be transformed to a mixed-valent (Ir0−IrIV) intermediate B by oxidative addition on a single-site metal, IrII. The reversibility of the reaction could afford the elimination of H2, as already mentioned above, along with 1. A second pathway starts with 3 and 4, from which facile oxidative addition of H2 produces C or D by a 1,2-dihydride rearrangement as a result of a homolytic cleavage within the diiridium coordination sphere; one hydrogen atom migrates across the Ir−Ir metal with the concomitant η4 to η3 interconversion of the oxametallacycle bridging ligand. The insertion of the hydride to the cyclooctadiene ligand in C or D affords 5−7 with the corresponding coordination of the oxygen atom or the double bond of the cyclooctadiene ligand, respectively. The IrII−IrII compounds 5−7 could also be represented as I Ir −IrIII. Evidently, the higher electron density of IrII in 3 and 4, by coordination of the phosphine to the metal center, favors the facile oxidative addition of H2. This fact, along with the experimental observations that 5−7 were always in a mixture with 1 when almost simultaneous addition of PR3 and H2 was carried out, without previous isolation of the corresponding adducts, as well as the results of the monitored reaction between 1 and H2 through the 1H NMR, led us to propose that the coordination of the phosphine is determinant in the formation of 5−7, Scheme 3. Previous studies of two-electron mixed-valence diiridium compounds with bidentate diphosphazane7b,d and formamidinato22 ligands have shown formally IrI1→IrIII cores. In particular, the former inorganic ligand has

noncoordinated methylene carbons at C10. Particularly diagnostic were the low-frequency resonances of C9 in 13C NMR at δ = ∼−1.12. The solid-state structure of compounds 5−7 can be seen in Figures 4, 5, and 6, respectively. The crystal data and selected bonds lengths and angles are provided in Tables 1S, 3, and 4, respectively. Highly distorted hexacoordinated geometries at Ir1 were established for all crystalline structures, and in general the structural parameters for compounds 5−7 correspond fairly closely to each other. In the cyclooctenyl ligands, carbon C9 had the shortest bond, Ir1−C9 (∼2.10 Å), compared to Ir1−C5 (∼2.17 Å) and Ir1−C6 (∼2.15 Å), and C9 was opposite the oxygen atom, with a bond angle average of ∼175° for C9−Ir1−O1. The bond length C9−C10 (∼1.54 Å) confirmed the change in the hybridization at C10, where the average value of C9−C10 was ∼1.39 Å for compounds 1, 2, and 3. Typical bond distances for the allylic moiety in the η3oxairidacycles, C1−C2 (1.41 Å) and C2−C3 (1.46 Å), along with the corresponding long and short average values of C3−C4 (1.44 Å) and C4−O1 (1.25 Å), provided evidence of a more efficient π-electron delocalization in these bridging ligands, similar to other η3-oxodienyl-iridium derivatives.2b,4 The longest Ir1−Ir2 bond length was 2.9294(2) Å in 7; those in 5 [2.9183(2) Å] and 6 [2.92064(17) Å] were also longer than those of 1 [2.8479(3) Å], 2 [2.7693(10) Å], and 3 [2.8675(7) Å]. A similar trend was observed for Ir1−P1, where 7 [2.3864(11) Å] showed the longest bond length compared to 5 [2.3492(12) Å] and 6 [2.3506(9) Å]; these results were as expected according to the bulkiness of the three different phosphines PMe3, PMe2Ph, and P(n-Bu)3, with cone angles of 118°, 122°, and 132°, respectively.38 The iridium−iridium bond lengths of 5−7 were similar to those for monohydrido-bridged diiridium complexes, such as Ir(H)P(OEt)3[μ2-(H)(C10H14)]Ir(H)Cp* [2.9315(19) Å],24 Cp*Ir(H)[μ2-(H)(SOMeCH2)]Ir(H)Cp* [2.9414(4) Å],24 Cp*Ir(η1-C6H5)[η1-μ2-η3-(CHCHCH2)(μ2H)IrCp* [2.867(1) Å],17 Cp*Ir[μ2-(H)(Cl)]IrCp* [2.903(1) Å],28 and Cp*Ir[μ2-(H)(C6H4)(PPh2)]IrCp* [2.8901(4) Å],27 longer than Cp*Ir(H)[μ2-(H)(BH4)Ir(H)Cp* [2.823(1) Å],20 and shorter than those of Cp*Ir(H)[μ2-(H)(SORC6H4)]Ir(H)Cp* [2.9836(2) Å], 24 Ir(H) 2 (Pi-Pr 3 )[μ 2 -(H)(pz) 2 ]Ir(H)(Pi-Pr 3 )(MeCN) [2.9817(14) Å],35 and Cp*Ir(H)[μ2-(H)(PMe2C6H4)]Ir(H)Cp* [2.9782(4) Å].24 The planarity in the six-membered ring of 5−7 is on average 16.5°, which reflects less distortion than the one observed for 3 [27.883(0.693)°]. It should be noted that in the formation of 5−7 the phosphorus atom was coordinated to the Ir1 center and the protonation of the C−H of the cyclooctadiene ligand (C10) occurred at the same metal center. The results of the variable-temperature NMR studies involving 1 and 4 provide some insights into the H2 addition mechanism in each case: The reaction of 1 with H2 monitored at different temperatures (toluene-d8, −90 to 25 °C), through the 1H NMR, allowed the observation of two small hydrido singlets at −8.1 and −22.3 ppm and the full hydrogen inequivalence expected for compound 1, along with a singlet at δ = 4.30 ppm of the corresponding molecular hydrogen. No evidence of η4 to η3 interconversion of the oxairidacyclohexadiene ligand, or partial or full decoordination of the cyclooctadiene ligand, nor any sight of C−H activation in the cyclooctadiene ligand was observed at −90 °C. At 25 °C the 1H NMR spectrum, after 15 h, was almost identical to the pure compound 1, showing the characteristic dynamic behavior of the cyclooctadiene ligand, and without any detectable hydrido signals at low frequency. It thus seems that there is a reversible 6314


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Scheme 3. Two Plausible Pathways for the Oxidative Addition of H2 and the Protonation of the C−H Bonds

shown a variety of stable two-electron mixed-valence complexes with different electronic configurations.7b The high stability observed in the oxametallacycle and COD ligands was evident in all formed compounds 1−7, except for the COD ligand when the more sterically demanding phosphine P(i-Pr)3 was used. In this case, under identical conditions, the bis(phosphine) (η4-COD)(H)Ir[(η1:1-μ2-η3CHC(Me)CHC(Me)O)]Ir(μ2 -H)(η 1 :η 2 -C 8 H 13 )[P(i-Pr) 3 ]2 (8) was isolated in 46% yield. According to the structure of compound 8, it is proposed that the intermediate D is more likely involved in the formation of compounds 5−7 (see Scheme 3). The formation of compound 8, even under a stoichiometric reaction between 1 and P(i-Pr)3, did not show any evidence of an analogue complex of 5−7. The 1H NMR spectrum of 8 showed the presence of two hydrido ligands at δ −31.1 and −11.6 as a triplet and doublet of doublets with P−H coupling constants of 17.2 and 19.2 Hz, which were assigned as the terminal and bridging hydrido ligands, respectively. The assignment of complex 8 was based on previous studies where the trans effect is consistent with the chemical shifts.39 The 1H NMR spectrum displayed only one COD as a complicated group of signals between 1.20 and 3.64 ppm, and the 13C NMR spectrum showed two pairs of carbon resonances for the CH (δ = 53.2, 50.8) and CH2 (δ = 37.2, 30.4) of the COD ligand. Two-dimensional correlation NMR experiments allowed the assignment in which C1 (δ = 106.0, d, 63.2 Hz) and C4 (δ = 208.5) of the oxopentadienyl bridging ligand were shown to be at low frequency compared to 5−7. From the 31P NMR spectrum it was inferred that two P(i-Pr)3 were coordinated to one of the iridium atoms, along with couplings at δ = 17.5 (dd, 6.7, 8.7) and 10.3 (dd, 5.3, 8.7); similar 31P and 1H chemical shifts have been found in iridium hydrido phosphine carbonyl complexes where partial opening of the iridaoxapentadiene complexes Ir(H)Cl{η1:1-C(R)C(R)C(R)O}[(Pi-Pr)3]2 and [Ir(H)Cl{η1:1-OC(CHCH2)O}[(Pi-Pr)3]2

Figure 7. Perspective view of compound 8 drawn at the 50% probability level. Hydrogen atoms have been omitted for the sake of clarity, except the hydrides and those of C1 and C3 in the oxairidacyclohexadiene ligand.

occurred by treatment with CO.37 The structure of 8, with both phosphines and the iridaoxacyclohexadienyl bridging ligand coordinated to the iridium atom Ir1, was confirmed by crystallography (Figure 7). The structure consisted of a distorted octahedral geometry about the iridium atom Ir1 with C1, Ir2, and two P(i-Pr)3 ligands occupying the four equatorial sites and the O1 and hydrido ligand H12D occupying the axial sites. The Ir1−P1 and Ir1−P2 bond lengths were 2.3578(9) and 2.3155(9) Å, respectively. The triisopropylphosphine ligands in [Ir(H)(Cl) 2 (PH 3 )(Pi-Pr 3 ) 2 ] showed Ir−P bond lengths of 2.3708(6) and 2.3615(11) Å.40 The overall structural features of the Ir2 coordinated to both terminal cyclooctadiene and bridging iridaoxacyclohexadienyl ligands were similar to those of 5−7. 6315


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Article

Sigma-Aldrich, Strem Chemicals, Merck, and J. T. Baker, Co. (industrial grade). All compressed gases were obtained from Infra. Argon (>99.9%), nitrogen (>99.5%), and carbon monoxide (>99.5%) were used as supplied without purification. The 1H, 13C{1H}, and 31 1 P{ H} NMR spectra were referenced internally using the residual protio and carbon solvent resonances relative to tetramethylsilane with deoxygenated deuterated solvents. The external standard for 31P was H3PO4. High-resolution mass spectra were obtained by LC/MSD TOF with APCI as ionization source. Elemental analyses were performed at the Chemistry Department at Cinvestav. Infrared spectra were recorded using KBr pellets (4000−400 cm−1) and Nujol in PTFE (4000−200 cm−1). Melting points were determined and are uncorrected. Crystal Structure Determination. X-ray diffraction measurements were made at 173(2) K (1, 3, 5, 6, and 8), 150(2) K (2), and 293(2) K (7) on a CCD or CAD4 diffractometer, using graphitemonochromated Mo Kα radiation (λ = 0.710 73 Å). A summary of crystal data collection and refinement (SHELX 2014) parameters for compounds is given in Table 1S. The ellipsoids were drawn at 50% probability for all crystalline structures, except 7, with 30% probability ellipsoids. The hydrides as well as H1 and H3 of the bridging heterodienyl ligand were found by Fourier difference and refined without constraint, except for compound 1, where hydrogen atoms were fixed, and for compound 5, hydrogens H1, H3, H9, and H12 were first found by Fourier difference and later fixed by Uiso and constrained by the AFIX 3 command. Other hydrogens were found by geometry. The program SHELXLE42 was used in the refinement of compound 1. It was necessary to use many restraints in order to manage the high disorder in both isomers 1A and 1B. The thermal parameters were constrained with the command RIGU implemented in the new SHELXL 2014-7 version,43 along with the EADP restraint command for several carbon atoms in both isomers. The disorder in compound 1 was modeled by means of the SHELX command RESI, and the occupation was fixed to 0.5 for convergence in the refinement. The disorder in compound 7 was modeled with restraints for two chains of the n-butyl substituents in a 0.2414(57):0.7586(0.61) ratio. The subsequent full-matrix least-squares refinement proceeded, without any problem, until convergence in all cases. Synthesis of (1,2,5,6-η-COD)Ir[μ-(1−4-η-1,5-η-CHC(Me)CHC(Me)O)]Ir(1,2,5,6-η-COD) (1). The oxopentadienyl anion was prepared by adding 0.72 mL of mesityl oxide (6.3 mmol) to a lithium diisopropylamide solution, which was prepared with 8 mL of THF, 4.2 mL of n-BuLi 1.6 M in THF (6.72 mmol), and diisopropylamine (6.3 mmol), at the temperature of the ethanol−N2(liq) bath to room temperature. The recently prepared oxopentadienyl anion solution was added to 2.0 g (2.88 mmol) of [Ir(η4-COD)(μ-Cl)]2 in 40 mL of THF at the temperature of the ethanol−N2(liq) bath. The reaction mixture was warmed to room temperature, changing from orange to a red wine color, and after 2 h the solvent was evaporated under vacuum. The resulting solid was extracted with hexane until colorless. The deep red solution was evaporated under vacuum (if an oily product is obtained, it can be washed with cold methanol), to give a red wine solid in 88% yield (1.83 g, 2.63 mmol). Dark red wine crystals of 1 were grown by slow evaporation of a hexane solution at room temperature. The crystals melt at 151−152 °C as a wine red liquid. IR (KBr, cm−1): 2348 (w), 2274 (w,br), 1989 (w,br), 1810 (w,br), 1625 (w,br), 1569 (w,br), 1486 (m), 1442 (s), 1361 (s), 1321 (m), 1298 (w), 1261 (w), 1232 (w), 1152 (w), 1072 (m), 999 (s), 873 (vs), 809 (m), 685 (w), 650 (s), 602 (m), 511 (s), 473 (m). ESI + TOF: m/z 699.1801; error ppm 2.3221. DBE: 8.5. Anal. Calcd for C22H32OIr2: C, 37.92; H, 4.63. Found: C, 38.00; H, 4.36. Synthesis of (1,2,5,6-η-COD)Ir[μ-(1−3-η-1,5-η-CHC(Me)CHC(Me)O)]Ir(1,2,5,6-η-COD)(μ-CO) (2). (a) In a glass pressure reactor, 500.0 mg (0.72 mmol) of complex 1 dissolved in 15 mL of hexane was cooled to the temperature of an ethanol−N2(liq) bath and stirred under 1 atm of CO for 10 min or until an insoluble solid was precipitated. The reactor atmosphere was exchanged with N2, and the solid filtered. The resulting pale greenish solid was washed twice with 5 mL of hexane maintaining the temperature at −20 °C and

SUMMARY AND CONCLUSIONS The lithium oxopentadienide organometallic precursor showed the ability to drive this sort of conversion, affording the iridaoxacyclohexadiene bridging ligand, which allowed the isolation of unsymmetrical IrII−Ir0 binuclear compound 1. Compound 1 showed a reduced metal center, Ir0, without a vacant coordination site, and an IrII center with a vacant site; here, the electrophilicity of the latter dictated the reactivity of 1 against addition and oxidative addition reactions. Depending on electron counting formalisms, complexes 5−8 may be described as two-electron mixed-valence species in which there is a dative IrI−IrIII bond or, alternatively, as asymmetric 17e− species connected by a IrII−IrII bond formed by the pairing of electrons from each of the metal centers. This is in agreement with the diamagnetism observed in all compounds and confirmed by NMR. Furthermore, it should also be considered that π-ligands involved in compounds 1−8 improve efficient delocalization. The addition of tertiary phosphines to 1 afforded compounds 3 and 4. Compound 4 showed, in the presence of H2, an efficient and clean oxidative addition, facilitated by adjacent iridium metals that are electronically and coordinatively different, with the formation of hydrido ligands, where one of them promoted the insertion into a cyclooctadiene carbon sp2 bond, leading to σ,π-cyclooctenyl-coordinated derivative 6. This reactivity is contrasting with compound 3, which showed a reversible reaction by an easy dissociation of PMe3, recovering compound 1. The reaction of 1 with H2 along with tertiary phosphines led to the formation of 5−7 in a less selective process. These contrasting results were explained on the basis of the monitoring studies through NMR spectroscopy at different temperatures, where the relevance of the phosphine ligands in the oxidative addition was established. Essential for H2 reactivity at Ir0−IrII cores appears to be the ability of the ligand framework, in this case the iridaoxacyclohexadiene, phosphines, and COD, to maintain the electronic and steric asymmetry of the two-electron mixed-valence core without excessive reorganization as the hydrogen migrates among terminal and bridging coordination sites due to synergetic and cooperative effects. The steric bulkiness of the phosphine ligands, rather than their electronic nature, determines the dissociation of the cyclooctadiene ligand, as observed in 8. The results discussed above led to research on the activation of other donor molecules under similar conditions, and it was found that methyl iodide, as well as nitrogen donor ligands, such as piperidine, morpholine, or acetonitrile, and thiophene, as an example of a sulfur ligand, did not react with compound 1. The interest in the bimetallic heteropentadienyl-containing complexes is ongoing. Until now, astonishing differences have been found in analogous rhodium chemistry with heteropentadienyl ligands.

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EXPERIMENTAL SECTION

All experiments were carried out under an inert atmosphere by using standard Schlenk-type equipment. The solvents were dried by known procedures and distilled under nitrogen prior to use (diethyl ether and THF with Na/benzophenone; hexane from CaH2 and methanol from Mg/I2). The [Ir(η4-COD)(μ-Cl)]2 was prepared according to the literature procedure.41 The oxopentadienide lithium salt has been prepared as described in the synthesis of 1, vide infra, which is a sligthly different experimental technique than that previously reported. All other chemicals were used as purchased from Pressure Chemicals, 6316


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Article

dried under vacuum to give 430.0 mg (0.59 mmol) of complex 2 in 82% yield. (b) In a Schlenk tube 400.0 mg (0.57 mmol) of compound 1 was dissolved in 10 mL of hexane at −110 °C, and CO was bubbled. After 15 min there is a change from a red to a yellow-green solution. After partial evaporation of the solution, it turned red. It is important to maintain the presence of CO during all the evaporation processes in order to avoid regeneration of compound 1. Evaporation of the yellow solution, column chromatography under deactivated alumina, and elution of hexane afforded a yellow solution, which after evaporation gave a yellow-red solid. The solid was washed with hexane to give a mustard-yellow product in 65% (270.0 mg, 0.37 mmol) yield. Yellow crystals of 2 were grown by slow evaporation of diethyl ether at −20 °C. The crystals decompose at 132 °C without melting. IR (KBr, cm−1): 1798 (vs), 1594 (m), 1495 (w,sh), 1452 (m,sh), 1433 (m), 1363 (s), 1346 (m,sh), 1326 (m), 1287 (m), 1239 (w), 1200 (m), 1157 (w), 1077 (w), 1030 (w), 1002 (m), 923 (vw), 896 (m), 832 (w), 782 (w), 725 (w), 704 (vw), 620 (w), 551 (w), 510 (m), 482 (m). ESI + TOF: m/z 727.1735; error ppm 0.1489. DBE: 9.5. Anal. Calcd for C23H32O2Ir2: C, 38.11; H, 4.45. Found: C, 38.05; H, 4.55. Synthesis of (1,2,5,6-η-COD)Ir[μ-(1−4-η-1,5-η-CHC(Me)CHC(Me)O)]Ir(1,2,5,6-η-COD)(PMe3) (3). A solution of 250.0 mg (0.36 mmol) of complex 1 in 20 mL of pentane was cooled to the temperature of an ethanol−N2(liq) bath, and 0.037 mL (0.36 mmol) of PMe3 was added. The solution immediately turned yellow, from which a solid precipitated, and it was stirred for 10 min. The temperature of the reaction mixture was raised to 0 °C, and a solid was obtained from evaporation of the solvent at this temperature. The solid was dried under vacuum to give a mustard-yellow product in 83.0% yield (230.0 mg, 0.30 mmol). This compound must be stored at low temperature. The crystals melt dark red at 151−152 °C, which indicates the loss of PMe3 and the transformation to the dark red compound 1. Mustard-yellow crystals of 3 were grown from a saturated THF solution at −15 °C in a slight excess of PMe3. IR (KBr, cm−1): 2347 (w), 2272 (w,br), 1947 (w,br), 1812 (vw,br), 1705 (m), 1628 (m,br), 1588 (m,br), 1472 (s), 1426 (vs), 1357 (m), 1322 (vs), 1281 (s), 1234 (m), 1167 (s), 1076 (m,br), 1017 (m), 950 (vs), 876 (m), 835 (m), 805 (m), 735 (m), 679 (w), 602 (m), 512 (m), 494 (m), 459 (vw), 407 (vw). Mass spectra from ESI + TOF and FAB did not show the molecular ion. The ESI + TOF showed a peak at 699.1785; error 0.5026. DBE: 8.5, attributed to compound 1. Anal. Calcd for C25H41OPIr2: C, 38.85; H, 5.35. Found: C, 39.21; H, 5.54. Synthesis of (1,2,5,6-η-COD)Ir[μ-(1−4-η-1,5-η-CHC(Me)CHC(Me)O)]Ir(1,2,5,6-η-COD)(PMe2Ph) (4). A solution of 80.0 mg (0.11 mmol) of complex 1 in 10 mL of pentane was cooled to the temperature of an ethanol−N2(liq) bath, and 17.0 μL (0.11 mmol) of PMe2Ph was added. The solution immediately turned orange, and it was stirred for 15 min. The temperature of the reaction mixture was raised to 0 °C, and the orange solution was filtered at this temperature. Immediate evaporation of the solvent under vacuum affords an orange product in 83.0% yield (65.0 mg, 0.08 mmol). This compound must be stored at low temperature. The orange solid melts at 105−106 °C. IR (KBr, cm−1): 2346 (vw), 2237 (w,br), 1954 (m,br), 1879 (w), 1810 (w), 1695 (s, br), 1662 (s, br), 1585 (s, br), 1472 (vs), 1433 (vs), 1358 (s), 1320 (vs), 1265 (vs), 1234 (w), 1194 (vw), 1163 (vs), 1098 (vs), 1074 (vs), 1016 (vs), 939 (vs), 901 (vs), 804 (vs), 738 (vs), 736 (m), 694 (vs), 599 (s), 487 (vs), 408 (s). ESI + TOF: m/z 837.2383; error −2.1952 ppm. DBE: 11.5. Anal. Calcd for C30H43OPIr2·THF: C, 45.01; H, 5.68. Found: C, 45.13; H, 5.32. Synthesis of (1,2,5,6-η-COD)Ir[μ-(1−5-η-1,3-η-CHC(Me)CHC(Me)O)]Ir(μ-H)(1,2,5-η-C8H13)(PMe3) (5). In a glass pressure reactor, 250 mg (0.36 mmol) of complex 1 in 25 mL of THF was cooled to the temperature of an ethanol−N2(liq) bath, and 375 μL (0.39 mmol) of a 1 M solution of PMe3−THF was added. The temperature of the reaction mixture was raised to room temperature and then stirred under 1 atm of H2 for 1 h. The yellow solution was evaporated under vacuum, and the resulting solid was column chromatographed using deactivated alumina and eluted with hexane and diethyl ether in a 1:4 ratio. After solvent evaporation, 99.0 mg of complex 5 (0.13 mmol) was obtained from the first fraction as a bright yellow solid in 36% yield.

From the second fraction the starting complex 1 was recovered. The bright yellow crystals were grown by slow evaporation of a mixture of pentane and diethyl ether at −20 °C. Compound 5 turns red at 105 °C and melts at 151 °C. IR (KBr, cm−1): 2348 (w), 2275 (w,br), 2059 (w), 2035 (w), 1647 (w,br), 1572 (vs), 1449 (s), 1362 (s), 1314 (m), 1279 (m), 1198 (s), 1144 (m), 1088 (w), 1031 (w), 989 (m), 952 (vs), 891 (m), 849 (m), 811 (w), 724 (m), 671 (w), 637 (vw), 606 (m), 550 (w), 482 (w). ESI + TOF: m/z 777.2370; error −1.6921 ppm. DBE: 6.5. Anal. Calcd for C25H43OPIr2: C, 38.75; H, 5.59. Found: C, 38.89; H, 5.31. Synthesis of (1,2,5,6-η-COD)Ir[μ-(1−5-η-1,3-η-CHC(Me)CHC(Me)O)]Ir(μ-H)(1,2,5-η-C8H13)(PMe2Ph) (6). (a) The procedure is the same as described for 5, starting from 250.0 mg (0.36 mmol) of complex 1 and PMe2Ph (53.4 μL, 0.38 mmol) in 30 mL of THF. Evaporation of the solvent and washing the solid with pentane affords a mixture of 6 and 1. The mixture was chromatographed with deactivated alumina and elution with hexane. The first fraction collected was evaporated under vacuum, giving pure compound 6. The bright yellow crystals were grown by slow evaporation of pentane at −20 °C. The crystals melt at 101 °C. Yield: 30% (80.0 mg, 0.10 mmol). IR (KBr, cm−1): 2381 (vw,br), 2346 (vw), 1964 (w,br), 1814 (w,br), 1570 (vs), 1480 (m), 1452 (sh), 1436 (s), 1363 (s), 1351 (sh), 1316 (m), 1276 (s), 1201 (s), 1142 (w), 1091 (m), 1032 (sh), 988 (s), 940 (sh), 913 (vs), 836 (w), 800 (w), 780 (vw), 742 (s), 699 (s), 641 (w), 606 (m), 550 (w), 493 (s), 422 (s). ESI + TOF: m/z 839.2538; error ppm −0.1969. DBE: 10.5. Anal. Calcd for C30H45OPIr2: C, 43.05; H, 5.42. Found: C, 43.57; H, 5.10. (b) Compound 6 was also obtained in 69% yield, starting from complex 4 in the presence of 1 atm of H2, in pentane solution at −110 °C, while the temperature was raised to ambient. Then, the reaction mixture was stirred for 1 h. Filtration and evaporation of the solvent affords 6 (45.0 mg, 0.05 mmol). Synthesis of (1,2,5,6-η-COD)Ir[μ-(1−5-η-1,3-η-CHC(Me)CHC(Me)O)]Ir(μ-H)(1,2,5-η-C8H13)[P(n-Bu)3] (7). 7 was synthesized as described for 5, starting from 250.0 mg (0.36 mmol) of complex 1 and P(n-Bu)3 (89.0 μL, 0.36 mmol) in THF. Evaporation of the solvent afforded an amber-red oil, which after applying the sample to methylene chloride− hexane in a chromatographic column, with deactivated alumina, and eluting with hexane afforded a first fraction of a yellow solution, which was evaporated under vacuum, affording a bright yellow solid in 51% yield (115.0 mg, 0.13 mmol). Mp: 62 °C. The bright yellow crystals were grown by slow evaporation of diethyl ether at room temperature. IR (KBr, cm−1): 2369 (w), 2276 (w,br), 1975 (w,br), 1782 (w,br), 1662 (w,br), 1570 (vs), 1455 (vs), 1363 (s), 1314 (w), 1275 (m), 1231 (w), 1199 (s), 1146 (m), 1088 (s), 986 (s), 892 (s), 833 (w), 800 (w), 767 (w), 716 (m), 687 (m), 645 (w), 603 (m), 547 (m), 480 (m). ESI + TOF: m/z 903.3780; error ppm −1.2906. DBE: 6.5. Anal. Calcd for C34H61OPIr2: C, 45.31; H, 6.82. Found: C, 45.82; H, 6.82. Synthesis of (1,2,5,6-η-COD)Ir[μ-(1−5-η-1,3-η-CHC(Me)CHC(Me)O)]Ir(μ-H)(1,2,5-η-C8H13)[P(i-Pr)3] (8). 8 was synthesized as described for 5, starting from 100.0 mg (0.14 mmol) of complex 1, 255.0 μL (0.28 mmol) of a 1.12 M solution of P(i-Pr)3-THF, and 10 mL of THF. The resulting amber solid was chromatographed using deactivated alumina and diethyl ether and hexane as eluents in a 5:95 ratio. The canary-yellow crystals were grown by slow evaporation of diethyl ether at −20 °C. The crystals decompose at 66 °C and melt at 157 °C. Yield: 46% (60.0 mg, 0.07 mmol). IR (KBr, cm−1): 2369 (w), 2231 (m), 1996 (w,br), 1950 (w,br), 1799 (w,br), 1563 (vs), 1456 (vs), 1363 (s), 1316 (w), 1279 (m), 1248 (m), 1201 (m), 1150 (w), 1058 (m), 1032 (m), 990 (m), 911 (m), 885 (s), 797 (w), 733 (m), 693 (w), 645 (vs), 605 (m), 529 (s), 488 (w), 413 (vw). ESI + TOF: m/z 913.3764; error ppm 0.00606. DBE: 3.5. Anal. Calcd for C32H64OP2Ir2: C, 42.18; H, 7.08. Found: C, 41.20; H, 7.02.

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ASSOCIATED CONTENT

S Supporting Information *

1

H, 13C, and 31P NMR and IR spectra of compounds 1, 2, 4, 6, 8. X-ray crystallographic data in Table 1S, and the crystallographic information file (CIF) of compounds 1−3 and 5−8 (CCDC 6317


Organometallics

Article

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994759−994765). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Council of Science and Technology (Conacyt) (152280). I.I.P.M. thanks Conacyt (33438-E) and Secretariá de Posgrado e Investigación del Instituto Politécnico Nacional. We are very grateful to Dr. Ilia A. Guzei (Wisconsin University−Madison) for his constructive comments related to the X-ray crystallography. We thank V. M. Gonzalez-Diaz, M. T. Cortez-Picasso, and G. Cuellar for technical support in the NMR and ESI + TOF MS experiments.

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