Iridium Half-Sandwich Complexes with Di- and Tridentate Bis

Article pubs.acs.org/Organometallics

Iridium Half-Sandwich Complexes with Di- and Tridentate Bis(pyridylimino)isoindolato Ligands: Stoichiometric and Catalytic Reactivity Astrid L. Müller, Tim Bleith, Torsten Roth, Hubert Wadepohl, and Lutz H. Gade* Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 276, 69120 Heidelberg, Germany S Supporting Information *

ABSTRACT: A series of κ2-(N,N)-coordinated bis(2-pyridylimino)isoindolato (BPI) complexes [Cp*Ir(BPI)Cl], which possess “three-legged piano-stool” structures, with the iridium atom being coordinated by the Cp* ligand 2 × N and Cl, were prepared via deprotonation of the BPIH ligands with either potassium hydride or LDA and subsequent reaction with [Cp*IrCl2]2 in THF. Cationic complexes [Cp*Ir(BPI)]+ containing κ3-(N,N,N)-coordinated BPI ligands were prepared as well as complexes with bidentate-coordinated BPI ligands, where the chloride ligand was substituted by either neutral or anionic ligands. Substitution in the orthoposition of the PBI ligands led to the formation of cycloiridated κ3-(N,N,C) species. Upon substitution of the anionic ligand by triphenylphosphine, a product was obtained with a hitherto unobserved κ2-(N,N) coordination of oMe-BPI to the metal center via the deprotonated nitrogen atom of the isoindole unit and one of the imine nitrogen atoms of the BPI ligand. A series of (para-cymene) osmium half-sandwich complexes with analogous structures and reactivities to their isoelectronic Cp*Ir(BPI) congeners were also prepared. Finally, it has been demonstrated that both Ir and Os complexes are catalytically active in the transfer hydrogenation of various ketones and imines.

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INTRODUCTION The coordination chemistry and reactivity of transition metal complexes is strongly influenced by their ancillary ligands, which define their steric and electronic properties as well as their stability.1 Monoanionic meridionally coordinating tridentate chelate ligands, frequently referred to as “pincers”, have been extensively studied as ancillary ligands in organometallic chemistry and molecular catalysis.2 Bis(2-pyridylimino)isoindoles (BPIH) are highly modular, readily accessible pincers that were first reported in 1952,3 while their coordination chemistry has been investigated since the 1970s.4 To date, BPI complexes with almost the whole range of transition metals have been reported.5−10 BPI ligands typically coordinate in a meridional tridentate (N,N,N) fashion to the metal center, as represented by complex A (Chart 1),8,9 although other denticities and coordination modes have also been observed.6,9,11,12 Various examples of applications of BPI complexes in catalysis have been reported, including catalytic oxidations with iron,13 cobalt,14 and ruthenium15 as well as the palladium-catalyzed hydrogenation of CC bonds.16 Recently, iridium(I) complexes of the general formula [(BPI)Ir(COD)] (B) (see Chart 1) have been employed in the catalytic epoxidation of a wide range of non-electron-rich olefins.9 In contrast to the κ3-(N,N,N) BPI-coordinated complexes A, the BPI ligand in B is coordinated in a κ2-(N,N) mode to the iridium center, due to the sterical demand of the COD ligand. To date, iridium(III) BPI complexes have not been reported, © XXXX American Chemical Society

Chart 1. Two Different Coordination Modes for BPI Ligands in Iridium(I) Complexes

although organometallic iridium(III) compounds in general display manifold reactivities and offer a range of applications.17 Pentamethylcyclopentadienyl (Cp*) iridium(III) half-sandwich complexes have played an important role in the development of organometallic chemistry. Although the first synthesis of [Cp*IrCl2]2 was reported in the late 1970s,18 the number of Cp*Ir complexes increased dramatically subsequent to the report of a convenient synthesis of this precursor Special Issue: Mike Lappert Memorial Issue Received: November 11, 2014

A

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Organometallics Scheme 1. Synthesis of the κ2-(N,N)-Chloro Complexes 1-Cl−5-Cl and Their Isomerization Behaviora

Reaction conditions: (i) Ligands 1 and 5: KH, THF, rt; [Cp*IrCl2]2, −78 °C. (ii) Ligands 2, 3, and 5: LDA, THF, −78 °C; [Cp*IrCl2]2, rt. (iii) 4Cl and 5-Cl: MeOH, rt, 30 min, to give 4[Cl] and 5[Cl]. (iv) 5-Cl: AgOTf, CH2Cl2, rt, in the dark, to give 5[OTf]. (v) 5-Cl: NaBPh4, MeOH, rt, to give 5[BPh4]. a

complex in 1990.19 Much of the early work in this field was devoted to investigations into C−H activation processes.20 More recently, the discovery that Cp*Ir complexes are excellent catalysts for hydrogen transfer reactions has given the field additional momentum. Complexes bearing additional chelating ancillary ligands proved to be particularly promising.21−30 In contrast, comparatively fewer compounds are known having additional tridentate ligands.31 In this paper, we report the preparation of Cp*-iridium halfsandwich complexes bearing BPI ligands in both bidentate and tridentate coordination modes, along with a study on the effect of varying substitution patterns on their coordination chemistry as well as the way this is reflected in the reactivity of the complexes. Subsequently, a series of (para-cymene) osmium(II) half-sandwich complexes, showing analogous structures and reactivities to their isoelectronic Cp*Ir(BPI) analogues, were synthesized, and both complexes were found to display catalytic activity in the transfer hydrogenation of various ketones and imines.

Figure 1. Molecular structure of [Cp*Ir(oMe-BPI)Cl] (1-Cl) (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity.

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complexes and correspond to the values reported for structurally related complexes.21−30 As usually observed for BPI metal complexes, the amido-like N(1)−Ir bond length is slightly shorter than the distance associated with the coordinated pyridyl arm N(3)−Ir.5−7,9 The C(4)−N(4) double bond of the uncoordinated pyridyl unit adopts an E configuration with a torsion angle N(1)−C(4)−N(4)−C(14) of −166.8(2)° (1-Cl), −169.4(2)° (2-Cl), and −174.7(2)° (3Cl). Consequently, one of the protons of the isoindole backbone is located directly above the anisotropy cone of the pyridyl ring, leading to a chemical shift of 1.30−1.90 ppm to higher field in the 1H NMR spectrum compared to the free ligand. The analogous effect was observed previously for κ2(N,N)-coordinated [(BPI)Ir(COD)] complexes.9 Upon stirring complexes 4-Cl and 5-Cl, which do not contain any substituents in ortho-position to the pyridinenitrogen of the BPI ligand (R4 = H), for 30 min in methanol, the orange suspension turned into a red solution. Removal of the solvent gave air-stable, red powders, whose NMR spectra showed a reduced set of signals for the BPI ligands, indicating

RESULTS AND DISCUSSION Synthesis of the Chloro Complexes [Cp*Ir(BPI)Cl] (1Cl−5-Cl) and Isomerization of ortho-Nonsubstituted (R4 = H) Complexes 4-Cl and 5-Cl. The κ2-(N,N)-coordinated [Cp*Ir(BPI)Cl] complexes 1-Cl−5-Cl were prepared via deprotonation of the BPIH ligands with either potassium hydride or LDA and subsequent reaction with [Cp*IrCl2]2 in THF (Scheme 1) and were isolated as orange, air-stable solids in good yields. The 1H and 13C{1H} NMR spectra of 1-Cl−5Cl indicate nonsymmetrical coordination of the BPI ligands, which was also confirmed by single-crystal X-ray structure analysis of complexes 1-Cl, 2-Cl, and 3-Cl. As a representative example, the solid-state structure of [Cp*Ir(oMe-BPI)Cl] (1Cl) is depicted in Figure 1; selected bond lengths and angles for all complexes are listed in Table 1. All three compounds possess “three-legged piano-stool” structures, with the iridium atom being coordinated by the Cp* ligand and the three donor atoms N(1), N(3), and Cl. The Ir− Cp* and Ir−Cl bond lengths are very similar for the three B

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Table 1. Selected Bond Lengths [Å] and Angles [deg] for the Molecular Structures of the Chloro Complexes [Cp*Ir(BPI)Cl] (1-Cl, 2-Cl, and 3-Cl) Ir−N(1) Ir−N(3) Ir−Cl(1) Ir−Cp*(a) N(1)−Ir−N(3) N(1)−Ir−Cl(1) N(3)−Ir−Cl(1) N(1)−C(1)−N(2)−C(9) N(1)−C(4)−N(4)−C(15) a

1-Cl

2-Cl

3-Cl

2.0673(17) 2.1551(17) 2.4235(5) 1.7912(9) 85.08(7) 86.41(5) 91.37(5) −15.7(4) −166.8(2)

2.057(2) 2.138(2) 2.4036(7) 1.790(1) 83.81(9) 85.88(7) 88.74(6) −17.7(5) −169.4(2)b

2.074(2) 2.139(2) 2.4166(8) 1.779(1) 83.17(8) 87.84(6) 89.52(6) 8.8(4) −174.7(2)c

Distance from Ir to Cp* plane. bN(1)−C(4)−N(4)−C(18). cN(1)−C(4)−N(4)−C(14).

Figure 2. Solid-state structures of the κ3-(N,N,N)-coordinated complex cations [Cp*Ir(BPI]+ 4[Cl] (left) and 5[Cl] (right) (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity.

Table 2. Selected Bond Lengths [Å] and Angles [deg] for the Molecular Structures in the Complexes [Cp*Ir(BPI)]X (4[Cl], 5[Cl], 5[OTf], 5[BPh4]) Ir−N(1) Ir−N(3) Ir−N(5) Ir−Cp*(a) Ir−[N,N,N]b N(1)−Ir−N(3) N(1)−Ir−N(5) N(3)−Ir−N(5) θc φd

4[Cl]

5[Cl]

5[OTf]

5[BPh4]

2.037(2) 2.115(2) 2.107(2) 1.790(2) 1.319(2) 77.67(9) 76.48(9) 96.07(9) 26.8(4) −27.0(4)

2.0276(19) 2.1160(18) 2.1123(19) 1.794(1) 1.283(1) 78.30(8) 79.05(8) 98.43(7) 17.9(3) −19.8(3)

2.0313(19) 2.1178(18) 2.1132(18) 1.790(1) 1.299(1) 77.98(7) 77.42(7) 97.86(7) 28.4(3) −23.9(3)

2.0341(19) 2.1251(18) 2.113(2) 1.795(1) 1.293(1) 77.37(8) 78.62(7) 98.42(7) 22.6(3) −22.9(3)

a

Distance from Ir to Cp* plane. bMolecular plane defined by N(1), N(3), and N(5). cTorsion angle C(1)−N(2)−C(9)−N(3). dTorsion angle C(4)−N(4)−C(14)−N(5).

their symmetric κ3-(N,N,N)-coordination and the formulation as 4[Cl] and 5[Cl] as represented in Scheme 1. To gain insight into the structural details of the complex geometry in the solid state, single-crystal X-ray structure analyses of both complexes were carried out (Figure 2). Selected bond lengths and angles are listed in Table 2. The Xray diffraction analysis of 4[Cl] and 5[Cl] established the structural details confirming the κ3-(N,N,N)-coordination of the BPI ligand at the iridium center and the presence of a nonbonded chloride counterion. As expected, the bond between the iridium atom and the neutral nitrogen atoms

N(3) and N(5) is slightly longer than to the anionic ligating nitrogen atom N(1). The iridium atoms are displaced by 1.319(2) Å (4[Cl]) and 1.283(1) Å (5[Cl]) from the molecular plane defined by the three nitrogens N(1), N(3), and N(5), which leads to two twisted pyridyl rings of the BPI ligands, relative to their isoindole backbone. The reaction of 5-Cl to 5[Cl] was found to take place quite rapidly in polar solvents, and it was of interest to establish whether it could be reversed in a nonpolar medium. Heating a toluene solution of 5[Cl], the reverse reaction was indeed observed and completed within 2 h. The reversibility of this C

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Organometallics Scheme 2. Reactivity of [Cp*Ir(oMe-BPI)Cl] (1-Cl) toward Neutral and Anionic Ligands

coordinated acetonitrile are observed more downfield from free acetonitrile. It was not possible to obtain single crystals of 1-MeCN[BPh4] suitable for X-ray diffraction analysis. However, by slow diffusion of n-pentane into a saturated solution in propionitrile, we could obtain crystals of the analogous propionitrile complex [Cp*Ir(oMe-BPI)(EtCN)]BPh4 (1EtCN[BPh4]), as determined by X-ray diffraction, which is shown in Figure 3 along with selected bond distances and angles. The propionitrile ligand coordinates almost linearly to the iridium center (Ir−N(6)−C(31) 171.5°) with an Ir−N(6) distance of 2.081 Å, which is within the normal range for such complexes.32 Whereas the Cp*Ir complex with the ortho-substituted oMeBPI ligand is incapable of forming a κ3-(N,N,N)-coordinated Cp*Ir(BPI) species because of the steric bulk of the two methyl groups, it was possible to generate a tridentate κ3-(N,N,C) coordination mode of the BPI ligand. The cyclometalated complex [Cp*Ir(oMe-BPI′)] (1-BPI′) was obtained as a dark brown solid in 64% yield from the reaction of the chloro complex [Cp*Ir(oMe-BPI)Cl] (1-Cl) with sodium hydroxide in acetonitrile at room temperature (Scheme 2). To gain insight into the structural details of the complex, single crystals of 1BPI′ were grown and characterized by X-ray diffraction. As shown in Figure 4, the BPI ligand coordinates as a dianionic ligand with the pyridyl nitrogen atom N(3), the amido nitrogen atom N(1) of the isoindole unit, and the cyclometalated carbon atom C(15) of the second pyridyl ring bonded to the iridium atom. Finally, the η5-coordinated Cp* ligand completes the coordination sphere of the half-sandwich complex. Due to the

isomerization reaction reflects the hemilabile character of the BPI ligands, which appeared to be promising for the application in catalytic reactions presented below. The κ3-(N,N,N)-coordination in the BPI derivatives could be specifically achieved through substitution of the chloride ligands by weakly coordinating anions. Whereas reaction of 5-Cl with silver triflate gave [Cp*Ir(tBu-BPI)]OTf (5[OTf]) (Scheme 1), stirring with sodium tetraphenylborate in methanol yielded [Cp*Ir(tBu-BPI)]BPh4 (5[BPh4]), which precipitated as a red solid from the reaction mixture. The solid-state structures of the cations determined by single-crystal X-ray structure analysis established molecular structures analogous to that of 5[Cl] (see Supporting Information). No influence of the counterion on the complex geometries was observed; selected bond lengths and angles are given in Table 2. Reactivity of the ortho-Methyl-Substituted Cp*Ir(oMe-BPI) Chloro Complex 1-Cl. We had observed that complexes 1-Cl and 2-Cl with ortho-substituted BPI ligands did not isomerize in polar solvents to the κ3-coordinated species and subsequently found that tridentate (N,N,N) coordination of the BPI ligand could not be induced by treating a solution of 1-Cl in methanol with chloride abstractors such as NaBPh4 or KPF6. However, using acetonitrile as the solvent generates the cationic solvate complex [Cp*Ir(oMe-BPI)(MeCN)]BPh4 (1MeCN[BPh4]), which was isolated as an orange, air-stable solid in 78% yield (Scheme 2). The NMR spectra of 1MeCN[BPh4] show similar signal patterns to the chloro complex 1-Cl, indicating the presence of the κ2-(N,N)coordinated BPI ligand. Furthermore, the signals of the D

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In order to gain insight into the formation of 1-BPI′, the reaction between 1-Cl and NaOH was carried out in deuterated acetonitrile and followed by NMR spectroscopy. The cycloiridation was found to proceed through an intermediate 1-X, which was formed within a few minutes after the addition of aqueous sodium hydroxide. In contrast to the observations by Bröring et al., the NMR spectra of 1-X indicate a κ2-(N,N)coordinated species (Figure 5). A possible intermediate, which

Figure 3. Molecular structure of the complex cation in 1-EtCN[BPh4] (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond distances [Å] and angles [deg]: Ir− N(1) 2.057(2), Ir−N(3) 2.134(2), Ir−N(6) 2.081(2), Ir−Cp* 1.821(1), N(1)−Ir−N(3) 83.45(9), N(1)−Ir−N(6) 82.72(9), N(3)−Ir−N(6) 88.15(9), Ir−N(6)−C(31) 171.5(2).

Figure 5. Aromatic section of the 1H NMR spectra after addition of NaOH(aq) to a solution of 1-Cl in CD3CN (a) after 5 min: mixture of 1-Cl and 1-X; (b) after 25 min: 1-X; (c) after 4 h: mixture of 1-X and 1-BPI′; (d) after 9 h: 1-BPI′.

is also in accordance with its 13C{1H} spectrum, might be the hydroxo complex [Cp*Ir(oMe-BPI)(OH)], resulting from abstraction of the chloro ligand. Unfortunately, all attempts to isolate this species failed, and 1-BPI′ was obtained after workup as the sole product. Next, we investigated the substitution of the chloride ligand of complex [Cp*Ir(oMe-BPI)Cl] (1-Cl) by other anionic ligands, a transformation that proved impossible to control for 5-Cl and only led to the formation of the tridentatecoordinated, cationic BPI complexes [Cp*Ir(tBu-BPI)]X (X = OTf, Br, I). Treating a solution of 1-Cl in acetone with sodium iodide readily afforded halide exchange and the generation of [Cp*Ir(oMe-BPI)I] (1-I) (Scheme 2). The molecular structure of 1-I is shown in Figure 6 along with selected bond distances and angles. It confirms a three-legged piano-stool configuration around the metal center similar to the one observed for the chloro complex 1-Cl, with an Ir−I distance of 2.7129 Å. Addition of triphenylphosphine and thallium hexafluorophosphate to a solution of 1-Cl in THF gave the cationic phosphine complex [Cp*Ir(oMe-BPI)(PPh 3 )]PF 6 (1PPh3[PF6]) as an air-stable, orange solid in 62% yield. The formulation of 1-PPh3[PF6] as depicted in Scheme 2 was confirmed by the observation of the molecular ion peaks [M − PF6]+ in the HR FAB mass spectra and an X-ray diffraction analysis (Figure 7). The molecular structure of 1-PPh3[PF6] illustrates a hitherto unobserved bidentate coordination of oMe-BPI to the iridium center via the deprotonated nitrogen

Figure 4. Molecular structure of the cyclometalated complex 1-BPI′ (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond distances [Å] and angles [deg]: Ir− N(1) 2.036(3), Ir−N(3) 2.182(3), Ir−C(15) 2.089(3), Ir−Cp* 1.824(1), N(1)−Ir−N(3) 79.41(10), N(1)−Ir−C(15) 80.95(11), N(3)−Ir−C(15) 104.55(11), C(4)−N(4)−C(14) 118.9(3), C(1)− N(2)−C(9) 120.1(3).

rigid structure of the BPI ligand, the interbond angles N(1)− Ir−N(3) (79.4°) and N(1)−Ir−C(15) (81.0°) are considerably smaller than the angle N(3)−Ir−C(15) (104.6°) between the iridium atom and the pyridyl nitrogens. The NMR spectra of 1BPI′ in CD2Cl2 are consistent with its structure in the solid state. As expected, resonances for nine aromatic protons are observed in the 1H NMR spectra, with the signals of the Ncoordinated side arm being detected at similar chemical shifts to those of the chloro complex 1-Cl. In the 13C{1H} NMR spectrum, the signal of the cyclometalated carbon atom is observed at 122.4 ppm. In recent studies by Wicholas and Bröring, an analogous κ3-(N,N,C)-coordination mode of the BPI ligand in square planar palladium complexes [Pd(oMeBPIH′)X] (X = Cl, OAc) has been described, resulting from sterical strain by terminal methyl groups.6,11 In these cases, the reaction proceeds through a symmetrical κ3-(N,N,N)-coordinated species, which is converted to the cyclopalladated complex by pyridine ring rotation and subsequent C−H activating of the heteroaromatic ligand.6 E

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mass spectra as well as elemental analysis were in accordance with the formation of [Cp*Ir(oMe-BPI)(N3)] (1-N3) (Scheme 2), containing an azido ligand and the BPI ligand in a bidentate binding mode. The characteristic ν(N3) band was detected at 2034 cm−1 in the IR spectrum (ν(NaN3) = 2140 cm−1).37 Single crystals of the azido complex 1-N3 were analyzed by Xray diffraction, and its molecular structure is depicted in Figure 8. There are two independent molecules in the unit cell, which

Figure 6. Solid-state structure of 1-I (thermal ellipsoids at 50% probability level, hydrogen atoms are omitted for clarity). Selected bond lengths [Å] and angles [deg]: Ir−N(1) 2.061(6), Ir−N(3) 2.158(5), Ir−I 2.713(1), Ir−Cp* 1.798(3), N(1)−Ir−N(3) 83.7(2), N(1)−Ir−I 86.92 (17), N(3)−Ir−I 95.25(18).

Figure 8. Molecular structure of 1-N3 (thermal ellipsoids at 50% probability level, only one of the two independent molecules is shown). Hydrogen atoms are omitted for clarity. Selected bond distances [Å] and angles [deg], values in square brackets refer to the second independent molecule: Ir(1)−N(1) 2.066(3) [2.064(3)], Ir(1)−N(3) 2.154(3) [2.142(3)], Ir(1)−N(6) 2.118(3) [2.119(3)], N(6)−N(7) 1.194(4) [1.193(4)], N(7)−N(8) 1.162(4) [1.158(4)], Ir−Cp* 1.790(2) [1.792(2)], N(1)−Ir(1)−N(3) 82.62(10) [83.81(11)], N(1)−Ir(1)−N(6) 84.98(11) [85.04(11)], N(3)−Ir(1)−N(6) 87.30(11) [86.86(11)], Ir(1)−N(6)−N(7) 121.2(2) [125.2(2)], N(6)−N(7)−N(8) 176.3(4) [174.4(4)].

mainly differ in the rotational orientation of the Cp* ligand and the free o-Me pyridyl arm. As expected, the azido ligand coordinates to the iridium center in a bent fashion (Ir−N(6)− N(7) 121° and 125°). The Ir−N(6) bond length of 2.12 Å lies within the normal range for similar complexes.38,39 Heating a solution of 1-N3 in toluene led to nonselective decomposition of the complex, whereas photolysis with a Hg lamp at room temperature selectively converted 1-N3 to [Cp*Ir(oMe-BPI)(N)] (1-N), which could be isolated as a dark green solid in 92% yield (Scheme 3). Single-crystal X-ray diffraction of 1-N indicated that photolysis of 1-N3 led to elimination of N2 and the formation of an essentially planar (rmsd 0.017 Å) five-membered iridacycle bearing a N−N chelate ligand (Figure 9). The new chelate ligand is coordinated to the iridium atom via the isoindole nitrogen atom N(1) and the nitrogen atom N(3) derived from the azido ligand, which is

Figure 7. Solid-state structure of the complex cation in 1-PPh3[PF6] (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted and the phenyl rings of the PPh3 ligand are represented by the ipso-C atoms for clarity. Selected bond lengths [Å] and angles [deg]: Ir−N(1) 2.131(3), Ir−N(2) 2.130(3), Ir−P(1) 2.3258(12), Ir−Cp* 1.821(2), N(1)−Ir−N(2) 61.22(13), N(1)−Ir−P(1) 87.25(10), N(2)−Ir−P(1) 91.46(10), N(1)−C(1)−N(2) 108.6(4), N(1)− C(4)−N(4) 120.7(4).

atom N(1) of the isoindole unit and one of the imine nitrogen atoms, N(2), of the BPI ligand. This may be due to the steric bulk of the PPh3 ligand and its interference with the orthosubstituted pyridyl ring of the BPI. Compared to the coordination via the pyridine nitrogen atom N(3) in, for example, 1-Cl, the unusual coordination via N(2) reduces steric strain between the phosphine ligand and the pyridyl ring of the coordinated side arm of the BPI ligand. The NMR spectra of 1-PPh3[PF6] are consistent with the unsymmetrical coordination mode of the BPI ligand as well as the presence of an unidentified, minor isomer (18%). Due to their reactivity, azido complexes of late transition metals represent interesting starting materials for the synthesis of new reactive compounds.33−35 Recently, the first terminal iridium nitrido complexes were prepared by Burger and Schneider via thermolysis or photolysis of the corresponding iridium azido complexes.36 When a methanolic solution of chloro complex 1-Cl and sodium azide was stirred for 2 h at room temperature, an orange solid was obtained. NMR, IR and

Scheme 3. Photolysis of Azido Complex 1-N3

F

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an iridium(I) diazenido (a) and an iridium(III) hydrazinediido species (b, c) represented in Scheme 4. Scheme 4. Resonance Structures of the Possible Binding Modes in 1-N

In order to further elucidate the electronic structure of the iridacycle, the complex was modeled by DFT. Two scenarios were considered in detail that are based on an 18 electron count for iridium: either Ir(I) is coordinated to a Cp* ligand and has two dative single bonds to an uncharged BPI ligand or Ir(III) receives six electrons from the two N-donors in addition to the six electrons shared with the Cp* ligand (see Scheme 4). For comparison, two reference molecules were considered, [Cp*Ir(NH)2] and [Cp*Ir(NH2)2(NH3)], which possess oxidation states of +I and +III, respectively. NPA showed a slightly positive charge for Ir in 1-N (+0.32e) that is in the usual range for Ir(III) complexes. With the help of NBO analysis, three nonbonding electron pairs were assigned to the Ir center in compound 1-N as well as in the Ir(III) reference compound, while in the Ir(I) reference four nonbonding pairs were found. Moreover, Wiberg bond indices (WBIs) for the Ir−N bonds showed that there is a multiple bond between the Ir center and N(3) (WBI: 1.107) and a single bond between Ir and N(1) (WBI: 0.658). Second-order contributions as well as the orientation of the orbitals indicate an iridacycle with delocalized electrons. All of these findings strongly support that the resonance structure corresponding to the Ir(III) complex c best represents the bonding (Scheme 4). This is also in good agreement with the previous interpretation for comparable iridacycles by Meyer et al. and Suzuki et al.38,41 In Figure 10 orbitals that contribute to the non-σ-bonding of the iridacycle are shown. As required for an aromatic ring, Ir contributes with its dxz-orbital to the π-system (see orbitals π(N(1)−Ir) and HOMO−1), while the filled dxy-, dx2−y2-, and dz2-orbitals are nonbonding at the iridium center. Since the interaction between the p-orbital at N(1) and the dxz-orbital at Ir is small, the antibonding MO to π(N(1)−Ir) is also occupied (HOMO−1). Therefore, the N(1)−Ir bond is best described as a single bond, but the lone pair at N(3) (HOMO−4) also has the appropriate symmetry to interact with the iridium center. This interaction, not explicitly depicted in the natural bond orbitals of Figure 10, renders the Wiberg bond index between N(3) and Ir larger than 1. Isomerization Behavior and Reactivity of the orthoFluorine-Substituted Cp*Ir(oF-BPI) Chloro Complex 3Cl. We found that there is a subtle influence of the substituent in ortho-position of the BPI pyridyl ring on the isomerization and reaction behavior of the Cp*Ir(BPI) complexes. The oFBPIH ligand (3) possesses a fluorine substituent in orthoposition, whose sterical demand lies between the ones of a proton and a methyl group. In analogy with the complexes 4-Cl and 5-Cl, we examined the isomerization of [Cp*Ir(oF-BPI)Cl] (3-Cl) in methanol-d4 by NMR spectroscopy. Instantaneously after dissolving the complex, the 19F{1H} NMR spectrum

Figure 9. Molecular structure of 1-N (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond distances [Å] and angles [deg]: Ir(1)−N(1) 1.994(3), Ir(1)− N(3) 1.926(3), Ir(1)−Cp* 1.823(2), N(2)−N(3) 1.378(4), N(2)− C(1) 1.334(5), C(1)−N(1) 1.352(5), N(1)−C(4) 1.419(5), C(4)− N(5) 1.274(5), N(1)−Ir(1)−N(3) 79.74(13), N(1)−C(1)−N(2) 112.8(3), N(3)−N(2)−C(1) 118.3(3), C(1)−N(2)−N(3)−Ir(1) −1.0(4), N(2)−C(1)−N(1)−Ir(1) −4.4(4), N(3)−N(2)−C(1)− N(1) 3.5(5).

bonded to the imino nitrogen atom N(2) of the BPI ligand. The NMR spectra of 1-N are consistent with its structure in the solid, and, in particular, the singlet of the Cp* protons in the 1 H NMR spectrum is observed at 2.01 ppm, hence 0.81 ppm downfield compared to the corresponding resonance in 1-N3. A similar chemical shift for the Cp* ligand was found for other Cp*Ir half-sandwich complexes with only an additional bidentate chelate ligand in their coordination sphere.34,38,40,41 Mayer and Suzuki previously reported that photolysis of Cp*Ir azido complexes [Cp*Ir(S2CNR2 or 2-Spy)(N3)] (S2CNR2 = N,N-dialkyldithiocarbamate; 2-Spy = 2-pyridinethiolate) afforded similar five-membered iridacycles by elimination of N2 and insertion of a nitrogen atom of the azide into the Ir−S or Ir−N(py) bond.38,41 The bond lengths of the planar chelate ring were described as intermediate between typical single and double bonds, and the metallacycles were interpreted as iridacyclopentadienyl-like moieties. The molecular structure of [Cp*Ir(oMe-BPI)(N)] (1-N) (see Figure 9) also provides support for an electron-delocalized fivemembered chelate ring. The bonds Ir(1)−N(1) (1.994 Å) and Ir(1)−Ir(N3) (1.926 Å) are shorter than Ir−N single bonds in iridium diazenido complexes (2.008−2.050 Å)42−44 but longer than the typical values for Cp*Ir(imido) complexes (∼1.73 Å).45 Furthermore, they were found to be similar to the reported Ir−N distances of the iridacycles characterized by Mayer and Suzuki (1.911 and 1.946 Å).38,41 The N(3)−N(2) distance (1.378 Å) is intermediate between single and double bonds involving the corresponding atoms (NN(diazenido): 1.20−1.28 Å; 42−44 N−N(hydrazine): 1.47 Å; 46 N−N(pyridazine): 1.346 Å47). Finally, the C−N bonds N(1)− C(1) (1.352 Å) and N(2)−C(1) (1.334 Å) were also found to lie in the normal range between amine and imine bonds (compare 1-N3: N(1)−C(4) 1.400(4) [1.405(4)] Å; N(2) C(1) 1.306(4) [1.296(4)] Å and N(4)C(4) 1.268(4) [1.283(4)] Å). In principal, the structure of compound 1-N appears to be best represented by the resonance structures of G

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Figure 11. 19F{1H} NMR spectrum: equilibrium between the (N,N)and the (N,N,N)-coordinated species 3-Cl and 3[Cl] at rt in methanol-d4.

Scheme 5. Isomerization Behavior of 3-Cl in Methanol and Synthesis of 3[BPh4] and 3-N3

Figure 10. Selected natural bond orbitals of 1-N. All orbitals depicted participate in the non-sigma-bonding of the iridacycle. HOMO, LUMO, and LUMO+1 are not shown, because they describe parts of the Ir−Cp* interaction.

displayed the two signals of the κ2-(N,N)-coordinated species 3-Cl (−53.91 and −71.01 ppm) as well as one signal of the κ3(N,N,N)-coordinated complex [Cp*Ir(oF-BPI)]Cl 3[Cl] (−52.23 ppm) (Figure 11). After 15 min, an equilibrium between the two species appeared, and the ratio of these two isomers changed with the temperature [ΔS = 39.3 ± 1.4 J K−1 mol−1, ΔH = 9.6 ± 0.5 kJ mol−1]. The experimentally determined thermodynamic data show that the κ2-coordinated species 3-Cl is enthalpically slightly favored in methanol. On the other hand, the κ3-coordinated, ionic species 3[Cl] is entropically strongly favored. Treatment of a solution of 3-Cl/3[Cl] in methanol with sodium tetraphenylborate led to the clean formation of κ3coordinated complex [Cp*Ir(oF-BPI)]BPh4 (3[BPh4]) as a red solid in 93% yield (Scheme 5). Single crystals suitable for X-ray diffraction were obtained by slow diffusion of n-pentane in a concentrated solution of 3[BPh4] in dichloromethane at 7 °C (Figure 12). The BPI ligand is again κ3-(N,N,N)-coordinated at the iridium atom, the bond angle N(3)−Ir−N(5) (104.80°) being slightly larger than in 5[Cl], 5[OTf], and 5[BPh4] (around 98°). This can be attributed to the stronger sterical

Figure 12. Molecular structure of the complex cation [Cp*Ir(oFBPI)]+ in 3[BPh4] (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ir−N(1) 2.056(2), Ir−N(3) 2.115(2), Ir−N(5) 2.187(2), Ir−Cp* 1.786(1), N(1)−Ir−N(3) 77.23(8), N(1)−Ir− N(5) 78.25(8), N(3)−Ir−N(5) 104.80(8).

H

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Organometallics repulsion between the pyridyl rings due to the fluorine substituents. Finally the κ2-coordination of oF-BPI could be enforced by treatment of a solution of 3-Cl/3[Cl] in methanol with sodium azide at room temperature. The product [Cp*Ir(oF-BPI)(N3)] (3-N3) was isolated as an orange, air-stable solid in 76% yield. The IR spectrum of 3-N3 proves the coordination of the azido ligand and exhibits the characteristic ν(N3) band at the same wavenumber as in 1-N3 (2034 cm−1). The NMR spectra display two sets of signals for the BPI ligand, indicating the presence of a κ2-(N,N)-coordinated BPI complex. The structural assignment based on the spectroscopic data could be confirmed by single-crystal X-ray structure analysis for azido complex 3-N3 (Figure 13).

Scheme 6. Synthesis of κ2-(N,N)- and κ3-(N,N,N)Coordinated Osmium Half-Sandwich Complexesa

Reaction conditions: (i) LDA, THF, −78 °C; [(p-Cym)OsCl2]2, rt. (ii) 7-Cl: MeOH, 30 min, rt, to form 7[Cl]. (iii) 7[Cl]: NaBPh4, MeOH, rt, to afford 7[BPh4]. a

Figure 13. Molecular structure of [Cp*Ir(oF-BPI)(N3)] (3-N3) (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ir− N(1) 2.0668(15), Ir−N(3) 2.1425(16), Ir−N(6) 2.1122(16), N(6)− N(7) 1.200(2), N(7)−N(8) 1.158(2), Ir−Cp* 1.785(1), N(1)−Ir− N(3) 82.75(6), N(1)−Ir−N(6) 87.53(7), N(3)−Ir−N(6) 84.44(6), N(6)−N(7)−N(8) 174.89(19), Ir−N(6)−N(7) 122.17(13).

Synthesis and Reactivity of Osmium(II) Half-Sandwich Complexes Bearing BPI Ligands. Given the interesting coordination chemistry and reactivity of the Cp*Ir(BPI) complexes, we synthesized a series of isoelectronic (paracymene) osmium(II) half-sandwich complexes (p-Cym)Os(BPI). Reaction of the protio ligands oF-BPIH (3) and tBuBPIH (5) with LDA and, subsequently, with the osmium precursor [(p-Cym)OsCl2]2 led to the formation of the complexes [(p-Cym)Os(BPI)Cl] 6-Cl and 7-Cl as dark red solids in 69% (6-Cl) and 82% (7-Cl) yield, respectively (Scheme 6). The 1H NMR spectra of 6-Cl and 7-Cl display the typical patterns of four diastereotopic doublets of the aromatic para-cymene protons between 6.12 and 5.62 ppm, due to the stereogenic osmium center. For compound 6-Cl, two signals are detected in the 19F{1H} NMR spectrum at −68.24 and −47.97 ppm, the latter representing the fluorine atom of the coordinated BPI pyridyl unit. The formulation of 6-Cl and 7-Cl as depicted in Scheme 6 was confirmed by the observation of the molecular ion peaks [M + H]+ in their HR DART mass spectra. Complex 7-Cl was found to isomerize in methanol, yielding the cationic, κ3-(N,N,N)-coordinated species [(pCym)Os(tBu-BPI)]Cl (7[Cl]) (Scheme 6), and addition of sodium tetraphenylborate gave [(p-Cym)Os(tBu-BPI)]BPh4 (7[BPh4]) via anion exchange. Single crystals of 7[BPh4] were obtained, and X-ray diffraction confirmed the tridentate

Figure 14. Molecular structure of the complex cation [(p-Cym)Os(tBu-BPI)]+ in 7[BPh4] (thermal ellipsoids at 50% probability level). Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Os−N(1) 2.0419(17), Os−N(3) 2.1231(17), Os−N(5) 2.1208(18), Os−Cym 1.679(1), N(1)−Os−N(3) 76.98(7), N(1)− Os−N(5) 77.83(7), N(3)−Os−N(5) 94.39(6).

coordination of the BPI ligand, similar to the corresponding [Cp*Ir(BPI)]X complexes 5[Cl], 5[OTf], and 5[BPh4], as illustrated in Figure 14. The Os−N(1) distance of 2.0419 Å is slightly shorter than the distances between the osmium center and the neutral pyridine nitrogen atoms N(3) and N(5) (2.1231 and 2.1208 Å), as observed in the Cp*Ir(III) complexes discussed above. Catalytic Transfer Hydrogenation of Ketones and Imines with Cp*Ir(BPI) and (p-Cym)Os(BPI) Complexes. The application of transfer hydrogenation catalysts based on half-sandwich Cp*Ir complexes was first reported in 1999 by I

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Organometallics Ikariya and Noyori.48 Since then, a multitude of diverse Cp*Ir systems has been published that are easily accessible and versatile precatalysts for this reaction.49 Complexes 1-Cl, 3-Cl, 5-Cl, and 7-Cl were tested as precatalysts for activity in the transfer hydrogenation of ketones and imines from iPrOH/ KOH at 80 °C. In a first screening of the catalytic performance, we examined the reduction of cyclohexanone and acetophenone with catalyst loadings of 5 mol %. Both ketones were converted to the corresponding alcohols in goodin the case of 3-Cl and 7-Cl in quantitativeyields within 1 or 2 h of reaction time (Table 3). The Cp*Ir(BPI) complex 3-Cl displayed the highest catalytic activity for both substrates and was used in the subsequent reactions.

Table 4. Transfer Hydrogenation of Various Ketones and Imines Catalyzed by 3-Cla

Table 3. Transfer Hydrogenation of Ketones Catalyzed by Cp*Ir(BPI) and (p-Cym)Os(BPI) Half-Sandwich Complexesa

NMR yield [%] entry

substrate

catalyst

t=1h

t=2h

1 2 3 4 5 6 7 8

cyclohexanone

1-Cl 3-Cl 5-Cl 7-Cl 1-Cl 3-Cl 5-Cl 7-Cl

68 >99 38 89 92 96 51 97

85

acetophenone

74 >99 98 >99 68 >99

a

Reaction conditions: Ketone (0.2 mmol, 1.0 equiv), KOH (0.1 mmol, 0.5 equiv), catalyst (0.01 mmol, 5 mol %), and 1,3,5-trimethoxybenzene (TMB) (0.05 mmol, 0.25 equiv) reacted in 1.0 mL of iPrOH at reflux temperature. Yields were determined by 1H NMR spectroscopy relative to TMB as internal standard.

Reaction conditions: Substrate (0.4 mmol, 1.0 equiv), KOH (0.2 mmol, 0.5 equiv), 3-Cl (0.004 mmol, 1 mol %), and 1,3,5trimethoxybenzene (TMB) (0.1 mmol, 0.25 equiv) reacted in 1.0 mL of iPrOH at reflux temperature. Yields were determined by 1H NMR spectroscopy relative to TMB as internal standard. bReactant was completely consumed.

Under the optimized reaction conditions (see Supporting Information) and a catalyst loading of 1 mol %, compound 3-Cl was tested in the hydrogen transfer of a series of ketones (Table 4), which were converted to the corresponding hydrogenated species in good yields. Transfer hydrogenation of imines afforded the corresponding amines in low to moderate yields. The lower activity of the Cp*Ir(BPI) catalyst in these reactions may be due to the fact that both imines and the generated amines can act as competing ligands and thus deactivate the catalytically active species (substrate and product inhibition).

ligand in a hitherto unobserved κ2-(N,N)-coordination of oMeBPI to the metal center via the deprotonated nitrogen atom of the isoindole unit and one of the imine nitrogen atoms of the BPI ligand. Furthermore, we synthesized a series of (paracymene) osmium half-sandwich complexes, showing analogous structures and reactivities to their isoelectronic Cp*Ir(BPI) congeners. Finally, we demonstrated that both Ir and Os complexes are catalytically active in the transfer hydrogenation of various ketones and imines.

CONCLUSIONS In summary, we have synthesized Cp*-iridium half-sandwich complexes bearing BPI ligands in various coordination modes. Starting from κ2-(N,N)-coordinated chlorido complexes [Cp*Ir(BPI)Cl], the effect of varying substitution patterns of the BPI ligands on the coordination chemistry was studied, showing a subtle influence on the reactivity of the complexes depending on the substituent in ortho-position of the pyridyl nitrogen atom. Cationic complexes [Cp*Ir(BPI)]+ containing κ3-(N,N,N)-coordinated BPI ligands were prepared as well as complexes with bidentate coordinated BPI ligands, where the chloride ligand was substituted by either neutral or anionic ligands. In this context, we also obtained the cycloiridated κ3(N,N,C)-coordinated compound 1-BPI′ as well as the phosphine complex 1-PPh3[PF6], which contains the BPI

General Procedures and Materials. All manipulations, except as indicated otherwise, were carried out under an inert gas atmosphere by using standard Schlenk techniques or a glovebox. Argon 5.0, purchased from Messer Group GmbH, was used after drying over Granusic phosphorus pentoxide (granulated). Solvents were dried over activated alumina columns by using a solvent purification system (M. Braun SPS 800) or according to standard literature procedures and degassed50 and stored in glass ampules under an argon atmosphere. Diethyl ether and n-pentane were distilled from sodium/potassium alloy, tetrahydrofuran and benzene from potassium, methanol from magnesium, dichloromethane and chloroform from calcium hydride, and toluene from sodium. The same procedures were used to dry the deuterated solvents. Degassed solvents were obtained by three successive freeze− pump−thaw cycles. NMR spectra were recorded on Bruker Advance II (400 MHz) and Bruker Advance III (600 MHz) spectrometers. Chemical shifts (δ) are reported in parts per million (ppm) and are

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EXPERIMENTAL SECTION

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Organometallics

22.5 (C10/C10′), 18.3 (C13′), 17.9 (C13), 9.12 (C(CH3) Cp*). HRMS (ESI+): m/z calcd for C36H40ClIrN5 ([M + H]+) 770.2596; found 770.2594. Anal. (%) Calcd for C36H39ClIrN5: C 56.20, H 5.11, N 9.10. Found: C 56.39, H 5.38, N 8.95. [Cp*Ir(oF-BPI)Cl] (3-Cl). The synthetic procedure of this compound was the same as that of 2-Cl, using oF-BPIH (3) (200 mg, 0.597 mmol) instead of pentBPIH to give 3-Cl as an orange, air-stable solid. Crystals suitable for an X-ray diffraction study were obtained from slow diffusion of n-pentane in a solution of 3-Cl in dichloromethane at 7 °C. Yield: 322 mg, 77%. 1H NMR (600.1 MHz, C6D6, 295 K): δ (ppm) = 8.08 (d, 3JHH = 7.5 Hz, 1H, H2), 6.96 (m, 3H, H1, H6, H7′), 6.78 (m, 1H, H7), 6.72 (m, 1H, H1′), 6.66 (m, 2H, H2′, H6′), 6.22 (d, 3 JHH = 7.9 Hz, 1H, H8′), 5.91 (d, 3JHH = 7.7 Hz, 1H, H8), 1.37 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, C6D6, 295 K): δ (ppm) = 163.5 (d, 1 JCF = 237.9 Hz, C9′), 162.8 (d, 1JCF = 232.9 Hz, C9), 161.9 (d, 3JCF = 7.02 Hz, C5′), 160.5 (C4′), 158.8 (C4), 156.0 (C5), 141.7 (d, 1JCF = 8.11 Hz, C7′), 140.8 (C3), 140.6 (d, 3JCF = 10.4 Hz, C7), 131.9 (C3′), 130.3 (C1), 129.7 (C1′), 124.1 (C2′), 121.7 (C2), 119.6 (d, 4JCF = 3.7 Hz, C6), 113.0 (d, 4JCF = 4.6 Hz, C6′), 103.1 (d, 2JCF = 31.2 Hz, C8), 102.0 (d, 2JCF = 36.8 Hz, C8′), 86.9 (C(CH3) Cp*), 9.1 (C(CH3) Cp*). 19F{1H} NMR (376.3 MHz, C6D6, 295 K): δ (ppm) = −52.3 (s, F), −68.3 (s, F′). HRMS (ESI+): m/z calcd for C28H26ClF2IrN5 ([M + H]+) 698.1469; found 698.1467. Anal. (%) Calcd for C28H25ClF2IrN5: C 48.24, H 3.61, N 10.04. Found: C 48.20, H 3.87, N 9.87. [Cp*Ir(Xyl-BPIMe)Cl] (4-Cl). The synthetic procedure of this compound was the same as that of 2-Cl, using Xyl-BPIHMe (4) (50.0 mg, 0.093 mmol) instead of pentBPIH to give 4-Cl as an orange, air-stable solid. Yield: 56.0 mg, 67%. 1H NMR (600.1 MHz, CD2Cl2, 295 K): δ (ppm) = 8.77 (s, 1H, H9), 8.23 (s, 1H, H9′), 7.98 (m, 2H, H7, H7′), 7.71 (s, 1H H2), 7.35 (s, 1H, H11′), 7.32 (d, 3JHH = 8.5 Hz, 1H, H6), 7.27 (s, 1H, H11), 7.09 (m, 3H, H6′, H13, H13′), 6.29 (s, 1H, H2′), 2.45 (s, 6H, H14/H14′), 2.44 (s, 6H, H14/H14′), 2.38 (s, 3H, H15), 2.10 (s, 3H, H15′), 1.58 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, CD2Cl2, 295 K): δ (ppm) = 162.1 (C5′), 161.9 (C4′), 159.8 (C4), 155.3 (C5), 151.8 (C9), 147.0 (C9′), 139.9 (C1′/C3′), 139.0 (C12/ C12′), 138.9 (C1), 138.7 (C12/C12′), 138.6 (C1′/C3′), 138.1 (C8/C8′), 136.6 (C7/C7′), 136.1 (C8/C8′), 136.0 (C7/C7′), 132.7 (C10), 131.8 (C10′), 130.2 (C3), 129.8 (C13), 129.1 (C13′), 125.5 (C2′), 124.6 (C11′), 124.3 (C11), 123.0 (C6), 122.2 (C2), 116.0 (C6′), 87.0 (C(CH3) Cp*), 21.3 (C14/C14′), 21.3 (C14/C14′), 20.5 (C15′), 20.1 (C15), 9.3 (C(CH3) Cp*). HRMS (ESI+) m/z calcd for C46H48ClIrN5 ([M + H]+) 898.3222; found 898.3160. Anal. (%) Calcd for C46H47ClIrN5: C 61.55, H 5.28, N 7.80. Found: C 61.56, H 5.66, N 7.70. [Cp*Ir(tBu-BPI)Cl] (5-Cl). The synthetic procedure of this compound was the same as that of 1-Cl, using tBu-BPIH (5) (111 mg, 0.270 mmol) instead of oMe-BPIH to give 5-Cl as an orange, airstable solid. Yield: 124 mg, 71%. 1H NMR (600.1 MHz, C6D6, 295 K): δ (ppm) = 8.55 (d, 3JHH = 6.3 Hz, H9), 8.52 (d, 3JHH = 5.4 Hz, H9′), 8.22 (d, 3JHH = 7.4 Hz, H2), 7,43 (d, 4JHH = 2.3 Hz, 1H, H6), 7.13 (m, 1H, H6′), 6.97 (m, 1H, H1), 6.78 (m, 2H, H1′, H8′), 6.61 (d, 3JHH = 7.7 Hz, 1H, H2′), 6.39 (dd, 1H, 3JHH = 6.3 Hz, 4JHH = 2.3 Hz, 1H, H8), 1.29 (s, 15H, Cp*), 1.00 (2, 9H, H11/H11′), 0.99 (2, 9H, H11/H11′). 13 C{1H} NMR (150.9 MHz, C6D6, 295 K): δ (ppm) = 163.2 (C7′), 160.5 (C5/C5′), 160.2 (C5/C5′), 160.1 (C4′), 158.5 (C4), 155.7 (C7), 152.7 (C9), 147.6 (C9′), 140.4 (C3′), 131.7 (C3), 129.0 (C1), 128.4 (C1′), 123.3 (C2′), 120.5 (C2), 118.9 (C6), 116.1 (C8), 114.8 (C8′), 112.6 (C6′), 85.4 (C(CH3) Cp*), 33.4 (C10/C10′), 33.3 (C10/C10′), 29.2 (C11/C11′), 28.9 (C11/C11′), 8.3 (C(CH3) Cp*). HRMS (ESI+): m/z calcd for C36H44ClIrN5 ([M + H]+) 774.2909; found 774.2916. Anal. (%) Calcd for C36H43ClIrN5: C 55.90, H 5.60, N 9.05. Found: C 55.51, H 5.65, N 8.58. [Cp*Ir(Xyl-BPIMe)]Cl (4[Cl]). Complex 4-Cl (30.0 mg, 30.4 μmol) was dissolved in methanol (2 mL), and the solution was stirred at rt for 30 min. By removal of the solvent under vacuum, the product 4[Cl] was isolated as a red, air-stable solid. Single crystals suitable for X-ray structure analysis were obtained by cooling a saturated solution of 4[Cl] in methanol to 7 °C. Yield: 27.6 mg, 92%. 1H NMR (399.9 MHz, CD3OD, 295 K): δ (ppm) = 8.90 (d, 4JHH = 2.2 Hz, 2H, H9), 8.29 (dd, 3JHH = 8.4 Hz, 4JHH = 2.3 Hz, 2H, H7), 7.85 (s, 2H, H2), 7.63

referenced to the residual proton or carbon signals of the solvents in the case of 1H and 13C{1H} NMR spectra.51 For 19F{1H} and 31P{1H} NMR spectra, H3PO4 and CCl3F were used as external standards, respectively. The following abbreviations were used: s (singlet), d (doublet), t (triplet), sept (septet), and m (multiplet). For atom numbering of the BPI ligands and the para-cymene ligand, see Supporting Information. High-resolution mass spectra were acquired on Bruker ApexQe hybrid 9.4 T FT-ICR (ESI, DART) and Jeol JMS700 magnetic sector (EI, FAB, LIFDI) spectrometers at the mass spectrometry facility of the Institute of Organic Chemistry of Heidelberg. IR spectra were recorded on an Excalibur 3100 FT-IR spectrometer by Varian as potassium bromide pellets. Elemental analyses were carried out in the Microanalysis Laboratory of the Heidelberg Chemistry Department. Unless otherwise stated, all chemicals were purchased from commercial suppliers and were used without further purification. The following compounds were synthesized according to literature procedures: oMe-BPIH (1),52 pentBPIH (2),53 Xyl-BPIHMe (4),9 tBu-BPIH (5),54 [Cp*IrCl2]2,19 [(p-Cym)OsCl2]2.55 For synthesis and characterization of oF-BPIH (3) and 1-X, see Supporting Information. [Cp*Ir(oMe-BPI)Cl] (1-Cl). To a solution of oMe-BPIH (1) (308 mg, 0.941 mmol, 1.0 equiv) in THF (12 mL) was added KH (188 mg, 4.70 mmol, 5.0 equiv). After stirring for 1 h the reaction mixture was cooled to −78 °C and [Cp*IrCl2]2 (413 mg, 0.518 mmol, 0.55 equiv) was added. The reaction mixture was stirred overnight at rt, and the solvent was removed in vacuo. The residue was extracted with toluene and filtered through a pad of Celite. After evaporation of the solvent, the crude product was washed with diethyl ether and n-pentane to afford the product 1-Cl as an orange, air-stable solid. Single crystals suitable for X-ray diffraction were obtained by slow diffusion of npentane in a solution of 1-Cl in dichloromethane. Yield: 593 mg, 91%. 1 H NMR (399.9 MHz, CD2Cl2, 295 K): δ (ppm) = 7.88 (d, 3JHH = 7.4 Hz, 1H, H2), 7.60 (m, 2H, H7, H7′), 7.42 (m, 1H, H1), 7.20 (m, 1H, H1′), 7.13 (d, 3JHH = 8.1 Hz, 1H, H6), 6.98 (d, 3JHH = 7.5 Hz, 1H, H6′), 6.94 (d, 3JHH = 7.3 Hz, 1H, H8), 6.78 (d, 3JHH = 7.8 Hz, 1H, H8′), 6.40 (d, 3JHH = 7.7 Hz, 1H, H2′), 3.03 (s, 3H, H10), 2.52 (s, 3H, H10′), 1.53 (s, 15H, Cp*). 13C{1H} NMR (100.6 MHz, CD2Cl2, 295 K): δ (ppm) = 162.5 (C5/C5′), 162.0 (C9), 160.5 (C4/C4′), 159.2 (C5/C5′), 158.2 (C9′), 157.5 (C4/C4′), 140.4 (C3′), 138.4 (C7/C7′), 138.1 (C7/C7′), 132.7 (C3), 130.4 (C1), 129.8 (C1′), 124.5 (C2′), 122.1 (C6), 121.7 (C2/C8), 121.6 (C2/C8), 117.9 (C6′), 112.3 (C8‘), 87.3 (C(CH3) Cp*), 29.4 (C10), 24.6 (C10′), 9.4 (C(CH3) Cp*). HRMS (ESI+): m/z calcd for C30H32ClIrN5 ([M + H]+) 690.1970; found 690.1967. Anal. (%) Calcd for C30H31ClIrN5: C 52.28, H 4.53, N 10.16. Found: C 52.39, H 4.23, N 9.72. [Cp*Ir(pentBPI)Cl] (2-Cl). A solution of LDA (39.4 mg, 0.368 mmol, 1.5 equiv) in THF (2 mL) was added to a solution of pentBPIH (2) (100 mg, 0.245 mmol, 1.0 equiv) in THF (6 mL) at −78 °C. After the addition was completed the solution was warmed to room temperature and stirred for another 30 min. Then the reaction mixture was added dropwise via cannula to a suspension of [Cp*IrCl2]2 (108 mg, 0.135 mmol, 0.55 equiv) in THF (4 mL), and the suspension was stirred overnight at room temperature. The solvent was removed in vacuo, and the residue dissolved in toluene and filtered over a pad of Celite. After drying in vacuo, the crude product was washed with diethyl ether and n-pentane to give 2-Cl as an orange, air-stable solid. Crystals suitable for an X-ray diffraction study were obtained from slow diffusion of n-pentane in a solution of 2-Cl in dichloromethane at 7 °C. Yield: 143 mg, 76%. 1H NMR (600.1 MHz, C6D6, 295 K): δ (ppm) = 8.23 (d, 3JHH = 7.6 Hz, 1H, H2), 7.10 (s, 1H, H6), 6.99 (m, 1H, H1), 6.85 (d, 3JHH = 7.5 Hz, 1H, H2′), 6.81 (m, 1H, H1′), 6.74 (s, 1H, H6′), 4.32 (m, 1H, H11a/H11b), 3.05 (m, 2H, H11′), 2.99 (m, 1H, H11a/H11b), 2.54 (m, 2H, H9′), 2.45 (m, 1H, H9a/H9b), 2.17 (m, 1H, H9a/H9b), 1.84 (s, 3H, H13′), 1.74 (s, 3H, H13), 1.79 (m, 4H, H10, H10′), 1.40 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, C6D6, 295 K): δ (ppm) = 166.1 (C12), 163.3 (C12′), 162.8 (C5′), 159.8 (C4′), 157.4 (C5), 157.2 (C4), 144.8 (C7/C8), 143.8 (C7′/C8′), 140.9 (C3′), 133.3 (C7/C8), 132.9 (C3), 129.7 (C7′/C8′), 129.5 (C1), 129.0 (C1′), 124.4 (C2′), 122.3 (C6), 121.3 (C2), 114.4 (C6′), 86.2 (C(CH3) Cp*), 39.2 (C11), 34.7 (C11′), 29.2 (C9), 28.6 (C9′), 22.8 (C10/C10′), K

DOI: 10.1021/om501138t Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

(ESI+): m/z calcd for C36H43IrN5 ([M − BPh4]+) 738.3148; found 738.3155. HRMS (ESI−): m/z calcd for C24H20B ([BPh4]−) 319.1664; found 319.1654. Anal. (%) Calcd for C60H63BIrN5: C 68.16, H 6.01, N 6.62. Found: C 68.04, H 6.14, N 6.62. [Cp*Ir(oMe-BPI)MeCN]BPh4 (1-MeCN[BPh4]). A mixture of 1-Cl (80.0 mg, 0.116 mmol, 1.0 equiv) and NaBPh4 (43.7 mg, 0.128 mmol, 1.1 equiv) in 5 mL of acetonitrile was stirred for 4 h at room temperature. The mixture was filtered through ALOX,; then the filtrate was evaporated to dryness. The residue was dissolved in dichloromethane and filtered over a pad of Celite to remove excess NaBPh4. Drying afforded the product 1-MeCN[BPh4] as an orange, air-stable solid. Suitable crystals for an X-ray diffraction study of the corresponding propionitrile complex 1-EtCN[BPh4] were obtained by slow diffusion of n-pentane in a saturated solution of 1MeCN[BPh4] in propionitrile. Yield: 63.3 mg, 78%. 1H NMR (600.1 MHz, CD2Cl2, 295 K): δ (ppm) = 7.91 (d, 3JHH = 7.4 Hz, 1H, H2), 7.66 (m, 2H, H7, H7′), 7.47 (m, 1H, H1), 7.31 (m, 8H, o-CH BPh4), 7.25 (m, 2H, H1′, H6), 7.03 (m, 2H, H6′, H8), 7.01 (m, 8H, mCH BPh4), 6.85 (t, 3JHH = 7.2 Hz, 4H, p-CH BPh4), 6.71 (d, 3JHH = 7.8 Hz, 1H, H8′), 6.44 (d, 3JHH = 7.7 Hz, 1H, H2′), 2.69 (s, 3H, H10), 2.48 (s, 3H, H10′), 2.38 (s, 3H, NCCH3), 1.51 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, CD2Cl2, 295 K): δ (ppm) = 164.5 (q, 1JBC = 49.3 Hz, ipso-CB BPh4), 161.6 (C5/C5′), 160.6 (C4‘), 159.5 (C9), 159.1 (C5/C5′), 158.8 (C9′), 157.8 (C4), 140.2 (C7/C7′), 139.5 (C3), 138.6 (C7/C7′), 136.2 (m, o-CH BPh4), 132.0 (C3′), 131.4 (C1), 131.0 (C1′), 126.0 (q, 3JBC = 2.7 Hz, m-CH BPh4), 124.9 (C2′), 123.3 (C6), 122.5 (C2/C8), 122.4 (C2/C8), 122.1 (p-CH BPh4), 121.5 (CN), 118.9 (C6′), 111.7 (C8′), 90.5 (C(CH3) Cp*), 29.3 (C10), 24.6 (C10′), 9.3 (C(CH3) Cp*), 3.7 (NCCH3). HRMS (ESI+): m/z calcd for C30H31IrN5 ([M − MeCN − BPh4]+) 654.2209; found 654.2192. HRMS (ESI−): m/z calcd for C24H20B ([BPh4]−) 319.1664; found 319.1660. Anal. (%) Calcd for C56H54BIrN5: C 66.33, H 5.37, N 8.29. Found: C 65.40, H 5.39, N 8.18. Due to cocrystallization with variable amounts of solvent, correct elemental analyses could not be obtained despite numerous attempts. [Cp*Ir(oMe-BPI′)] (1-BPI′). To a suspension of 1-Cl (96.5 mg, 0.140 mmol) in 4 mL of acetonitrile was added 0.1 mL of NaOH solution (0.3 M), and the reaction mixture turned to an orange solution and was stirred for 9 h. The solvent of the dark brown mixture was removed in vacuo; then, the residue was dissolved in 8 mL of toluene and washed with water (3 × 10 mL). Drying the organic phase over MgSO4 and subsequent evaporation of the solvent gave the cyclometalated compound 1-BPI′ as a dark green, air-stable solid. Single crystals suitable for an X-ray diffraction analysis were obtained from slow diffusion of n-pentane into a saturated solution of 1-BPI′ in dichloromethane at 7 °C. 1H NMR (600.1 MHz, CD2Cl2, 295 K): δ (ppm) = 8.24 (d, 3JHH = 7.5 Hz, 1H, H7′), 7.97 (m, 1H, H1/H1′), 7.77 (m, 1H, H1/H1′), 7.50 (m, 2H, H2, H2′), 7.43 (t, 3JHH = 7.6 Hz, 1H, H7), 7.91 (m, 2H, H6, H8), 6.73 (d, 3JHH = 7.5 Hz, 1H, H8′), 2.79 (s, 3H, H10), 2.48 (s, 3H, H10′), 1.31 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, CD2Cl2, 295 K): δ (ppm) = 164.0 (C4/C4′), 161.7 (C9), 161.0 (C5), 159.8 (C5′), 155.6 (C4/C4′), 152.6 (C9′), 150.9 (C7′), 139.9 (C3/C3′), 139.0 (C7), 138.4 (C3/C3′), 130.74 (C2/C2′), 129.7 (C2/C2′), 122.6 (C8), 122.4 (C6′), 121.6 (C1/C1′), 121.0 (C1/C1′), 120.6 (C6), 120.3 (C8′), 88.5 (C(CH3) Cp*), 30.7 (C10), 23.4 (C10′), 9.2 (C(CH3) Cp*). HRMS (FAB+): m/z calcd for C30H30IrN5 ([M]+) 653.2130; found 653.2157. Anal. (%) Calcd for C30H30IrN5: C 55.20, H 4.63, N 10.73. Found: C 55.33, H 4.85, N 10.65. [Cp*Ir(oMe-BPI)I] (1-I). To a solution of 50.0 mg of 1-Cl (58.0 μmol, 1.0 equiv) in 8 mL of acetone was added a solution of 20.8 mg of NaI (139 μmol, 2.5 equiv) in 2 mL of acetone. After stirring for 1 h the solvent was removed under reduced pressure and the crude product was dissolved in toluene. The solution was filtered through a pad of Celite, and the filtrate was evaporated to dryness to give 1-I as an orange solid. Single crystals suitable for an X-ray diffraction study were obtained by slow diffusion on n-pentane into a solution of 1-I in dichloromethane. Yield: 43.9 mg, 97%. 1H NMR (600.1 MHz, C6D6, 295 K): δ (ppm) = 8.08 (d, 3JHH = 7.4 Hz, 1H, H2), 7.10 (m, 2H, H6, H7′), 7.05 (m, 1H, H6′), 6.92 (m, 1H, H1), 6.77 (m, 1H, H7), 6.74 (m, 1H, H1′), 6.64 (d, 3JHH = 7.6 Hz, 1H, H2′), 6.56 (d, 3JHH = 7.2 Hz, 1H,

(d, 3JHH = 8.4 Hz, 2H, H6), 7.25 (s, 4H, H14), 7.15 (s, 2H, H13), 2.48 (s, 6H, H15), 2.35 (s, 12H, H14), 1.48 (s, 15H, Cp*). 13C{1H} NMR (100.6 MHz, CD3OD, 295 K): δ (ppm) = 163.9 (C4), 156.8 (C5), 151.3 (C9), 143.6 (C1), 141.0 (C7), 140.6 (C12), 138.9 (C10), 136.9 (C3), 136.3 (C8), 131.9 (C13), 126.0 (C6), 125.7 (C11), 124.8 (C2), 90.2 (C(CH3) Cp*), 21.5 (C14), 20.6 (C15), 9.2 (C(CH3) Cp*). HRMS (ESI+): m/z calcd for C46H47IrN5 ([M − Cl]+) 862.3461; found 862.3459. Anal. (%) Calcd for C46H47ClIrN5·3CH3OH: C 59.23, H 5.98, N 7.05. Found: C 59.04, H 5.54, N 7.54. [Cp*Ir(tBu-BPI)]Cl (5[Cl]). Complex 5-Cl (50.0 mg, 64.6 μmol) was dissolved in methanol (2 mL), and the solution was stirred at room temperature for 30 min. By removal of the solvent under vacuum, the product 5[Cl] was isolated as a red, air-stable solid. Single crystals suitable for X-ray structure analysis were obtained by cooling a saturated solution of 5[Cl] in benzene to 7 °C. Yield: 46.4 mg, 94%. 1 H NMR (399.9 MHz, CD2Cl2, 295 K): δ (ppm) = 9.68 (d, 3JHH = 6.2 Hz, 2H, H9), 7.93 (m, 2H, H2), 7.61 (m, 2H, H1), 7.49 (dd, 3JHH = 6.1 Hz, 4JHH = 2.3 Hz, 2H, H8), 7.45 (d, 4JHH = 2.3 Hz, 2H, H6), 1.47 (s, 15H, Cp*), 1.35 (s, 18H, H11). 13C{1H} NMR (100.6 MHz, CD2Cl2, 295 K): δ (ppm) = 165.8 (C7), 161.3 (C4), 156.5 (C5), 155.4 (C9), 138.4 (C3), 131.9 (C1), 122.5 (C2/C8), 122.4 (C2/C8), 121.8 (C6), 88.7 (C(CH3) Cp*), 35.5 (C10), 30.4 (C11), 9.4 (C(CH3) Cp*). HRMS (ESI+): m/z calcd for C36H43IrN5 ([M − Cl]+) 774.2909; found 774.2916. Anal. (%) Calcd for C36H43ClIrN5: C 55.90, H 5.60, N 9.05. Found: C 55.76, H 5.59, N 9.09. [Cp*Ir(tBu-BPI)]OTf (5[OTf]). Method A: To a solution of 5-Cl (60.0 mg, 77.6 μmol, 1.0 equiv) in dichloromethane (3 mL) was added AgOTf (20.0 mg, 77.6 μmol, 1.0 equiv), and the reaction mixture was stirred for 30 min in the dark. The solvent was removed in vacuo, and the residue dissolved in toluene and filtered over a pad of Celite. After drying in vacuo, the product 5[OTf] was precipitated in a mixture of dichloromethane/n-pentane as a red, air-stable solid. Yield: 64.7 mg, 94%. Method B: To a methanolic solution of 5[Cl] (60.0 mg, 0.078 mmol, 1.0 equiv) was added AgOTf, and the reaction mixture was stirred for 30 min in the dark. The solvent was removed in vacuo, and the residue dissolved in toluene and filtered over a pad of Celite. After drying in vacuo, the product 5[OTf] was obtained as a red, air-stable solid. Yield: 66.1 mg, 96%. Crystals suitable for an X-ray diffraction study were obtained by cooling a saturated solution of 5[OTf] in benzene to 7 °C. 1H NMR (399.9 MHz, C6D6, 295 K): δ (ppm) = 9.78 (d, 3JHH = 6.2 Hz, 2H, H9), 7.98 (m, 2H, H2), 7.90 (dd, 3JHH = 6.2 Hz, 4JHH = 2.1 Hz, 2H, H8), 7.56 (d, 4JHH = 2.1 Hz, 2H, H6), 7.05 (m, 2H, H1), 1.30 (s, 15H, Cp*), 1.03 (s, 18H, H11). 13C{1H} NMR (100.6 MHz, C6D6, 295 K): δ (ppm) = 165.6 (C7), 160.5 (C4/C5), 156.4 (C4/C5), 155.6 (C9), 138.7 (C3), 131.3 (C1), 123.0 (C8), 122.1 (C2), 121.5 (C6), 88.1 (C(CH3) Cp*), 34.9 (C10), 29.9 (C11), 8.7 (C(CH3) Cp*). 19F{1H} NMR (376.3 MHz, C6D6, 295 K): δ (ppm) = −77.26 (s, CF3). MS (ESI+): m/z (%) = 738.3 (100) [M − OTf]+. MS (ESI−): m/z (%) = 149.1 (100) [OTf] −. HRMS (ESI+): m/z calcd for C36H43IrN5 ([M − OTf]+) 738.3142; found 738.3154. Anal. (%) Calcd for C48H61F3IrN5O3S·0.5CH2Cl2: C 48.96, H 5.02, N 7.41. Found: C 48.90, H 4.96, N 6.98. [Cp*Ir(tBu-BPI)]BPh4 (5[BPh4]). Sodium tetraphenylborate (44.1 mg, 0.129 mmol, 1.0 equiv) was added to a solution of 5[Cl] (100 mg, 0.129 mmol, 1.0 equiv) in 4 mL of methanol and stirred for 15 min at room temperature. The precipitate was filtered off, washed with water (3 × 1 mL) and methanol (2 × 1 mL), and dried in vacuo to yield 5[BPh4] as a red powder. Crystals suitable for an X-ray diffraction study were obtained by slow diffusion of n-pentane in a saturated solution of 5[BPh4] in dichloromethane. Yield: 120 mg, 88%. 1H NMR (600.1 MHz, CD2Cl2, 295 K): δ (ppm) = 8.25 (d, 3JHH = 6.1 Hz, 2H, H9), 7.86 (m, 2H, H2), 7.58 (m, 2H, H1), 7.45 (d, 4JHH = 2.3 Hz, 2H, H6), 7.23 (m, 8H, o-CH BPh4), 7.17 (dd, 3JHH = 6.1 Hz, 4JHH = 2.3 Hz, 2H, H8), 6.93 (m, 8H, m-CH BPh4), 6.78 (t, 3JHH = 7.2 Hz, 4H, p-CH BPh4), 1.28 (s, 18H, H11), 1.26 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, CD2Cl2, 295 K): δ (ppm) = 166.2 (C7), 163.9 (m, ipso-CB), 161.3 (C4), 156.7 (C5), 151.0 (C9), 137.6 (C3), 135.9 (q, 3 JCB = 1.4 Hz, o-CH BPh4), 131.9 (C1), 125.6 (q, 2JCB = 2.8 Hz, m-CH BPh4), 122.6 (C6), 122.3 (C2), 121.7 (p-CH BPh4), 121.4 (C8), 88.4 (C(CH3) Cp*), 35.2 (C10), 29.9 (C11), 8.8 (C(CH3) Cp*). HRMS L

DOI: 10.1021/om501138t Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics H8′), 6.15 (d, 3JHH = 7.2 Hz, 1H, H8), 2.98 (s, 3H, H10), 2.47 (s, 3H, H10′), 1.36 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, C6D6, 295 K): δ (ppm) = 162.7 (C5′), 161.4 (C9), 159.8 (C4′), 159.5 (C5), 157.0 (C9′), 156.2 (C4), 140.4 (C3′), 137.4 (C7′), 137.0 (C7), 132.1 (C3), 129.8 (C1), 129.1 (C1′), 124.1 (C2′), 121.7 (C6), 121.5 (C2), 119.8 (C8), 117.2 (C8′), 113.4 (C6′), 87.4 (C(CH3) Cp*), 34.5 (C10), 24.5 (C10′), 9.4 (C(CH3) Cp*). HRMS (FAB+): m/z calcd for C30H32IIrN5 ([M + H]+) 782.1326; found 782.1304. Anal. (%) Calcd for C30H31IIrN5·CH2Cl2: C 43.01, H 3.84, N 8.19. Found: C 43.50, H 3.91, N 7.89. [Cp*Ir(oMe-BPI)PPh3]PF6 (1-PPh3[PF6]). A mixture of 1-Cl (50.0 mg, 72.5 μmol, 1.0 equiv), PPh3 (27.9 mg, 79.8 μmol, 1.1 equiv), and TlPF6 (20.9 mg, 79.8 μmol, 1.1 equiv) in 5 mL of THF was stirred for 1 h at room temperature. The crude product was dissolved in toluene and filtered through a pad of Celite. The filtrate was dried, and the residue was washed with diethyl ether (3 × 2 mL). Drying in vacuo afforded the product 1-PPh3[PF6] as an orange, air-stable solid. Single crystals suitable for X-ray structure analysis were obtained by slow evaporation of a concentrated benzene solution at 7 °C. Yield: 47.7 mg, 62%. 1H NMR (399.9 MHz, CD2Cl2, 295 K): δ (ppm) = 7.73 (m, 6H, o-CH PPh3), 7.66 (m, 2H, H7, H7′), 7.34 (m, 9H, m-CH, p-CH PPh3), 7.24 (m, 2H, H1/H1′, H2/H2′), 7.12 (m, 1H, H6/H6′), 7.06 (m, 2H, H1/H1′, H6/H6′), 6.85 (m, 2H, H8, H8′), 6.46 (d, 3JHH = 7.8 Hz, 1H, H2/H2′), 2.65 (s, 3H, H10/H10′), 2.56 (s, 3H, H10/H10′), 1.66 (d, 5 JHP = 1.8 Hz, 15H, Cp*). 13C{1H} NMR (150.9 MHz, CD2Cl2, 295 K): δ (ppm) = 174.7 (C4), 160.5 (C5/C5′), 158.5 (C9/C9′), 158.1 (C9/C9′), 155.7 (C4′), 152.4 (C5/C5′), 138.6 (C7/C7′), 138.2 (C7/ C7′), 135.4 (C3/C3′), 134.7 (d, 2JCP = 10.8 Hz, o-CH PPh3), 133.1 (C3/C3′), 131.4 (p-CH PPh3), 131.3 (C1/C1′), 130.2 (C1/C1′), 128.4 (d, 3JCP = 10.7 Hz, m-CH PPh3), 125.6 (C2/C2′), 124.1 (C2/C2′), 120.1 (C6/C6′), 118.9 (C6/C6′), 113.3 (C8/C8′), 112.2 (C8/C8′), 93.9 (d, 2JCP = 2.3 Hz, C(CH3) Cp*), 24.2 (C10/C10′), 23.9 (C10/C10′), 9.5 (C(CH3) Cp*) ppm. 31P{1H} NMR (161.9 MHz, CD2Cl2, 295 K): δ (ppm) = 17.9 (s), −144.5 (sept, 1JPF = 709.1 Hz, PF6). HRMS (FAB+): m/z calcd for C48H46IrN5P ([M − PF6]+) 916.3120; found 916.3125. Due to cocrystallization with variable amounts of solvent, correct elemental analyses could not be obtained despite numerous attempts. [Cp*Ir(oMe-BPI)(N3)] (1-N3). To a suspension of 1-Cl (100 mg, 0.145 mmol, 1.0 equiv) in methanol (4 mL) was added NaN3 (9.43 mg, 0.145 mmol, 1.0 equiv), and the mixture was stirred for 2 h at room temperature. Then, the reaction mixture was evaporated to dryness, and the residue was dissolved in toluene and filtered over a pad of Celite. The solvent was removed in vacuo to yield the azido complex 1-N3 as an orange, air-stable solid. Single crystals suitable for X-ray diffraction were obtained by slow diffusion of n-pentane in a solution of 1-N3 in dichloromethane. Yield: 89.8 mg, 89%. 1H NMR (600.1 MHz, C6D6, 295 K): δ (ppm) = 8.09 (d, 3JHH = 7.7 Hz, 1H, H2), 7.29 (d, 3JHH = 7.9 Hz, 1H, H6′), 7.12 (m, 2H, H6, H7′), 6.93 (m, 1H, H1), 6.82 (m, 1H, H7), 6.75 (m, 1H, H1′), 6.68 (d, 3JHH = 7.5 Hz, 1H, H2′), 6.57 (d, 3JHH = 7.5 Hz, 1H, H8′), 6.14 (d, 3JHH = 7.2 Hz, 1H, H8), 2.71 (s, 3H, H10), 2.48 (s, 3H, C10′), 1.26 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, C6D6, 295 K): δ (ppm) = 162.1 (C9′), 159.7 (C5), 159.1 (C4′), 158.9 (C9), 157.1 (C4), 155.9 (C5′), 139.7 (C3), 136.7 (C7′), 136.4 (C7), 131.7 (C3′), 129.0 (C1), 128.6 (C1′), 123.7 (C2′), 120.8 (C2), 120.6 (C6′), 119.1 (C8), 116.6 (C8′), 113.2 (C6′), 85.1 (C(CH3) Cp*), 26.6 (C10), 23.6 (C10′), 7.7 (C(CH3) Cp*). IR (KBr): ν̃ (cm−1) = 2034 (s, N3). HRMS (FAB+): m/z calcd for C30H31IrN8 ([M]+) 696.2301; found 696.2296. Anal. (%) Calcd for C30H31IrN8: C 51.78, H 4.49, N 16.10. Found: 52.00, H 4.57, N 15.34. [Cp*Ir(oMe-BPI)(N)] (1-N). An orange suspension of 1-N3 (50.0 mg, 71.9 μmol) in 2 mL of toluene was photolyzed with a Hg lamp at room temperature for 2 d, whereupon the reaction mixture turned into a green solution. The solvent was removed in vacuo to yield compound 1-N as a dark green solid. Single crystals were obtained from slow diffusion of n-pentane into a saturated solution of 1-N in toluene. Yield: 47.0 mg, 98%. 1H NMR (600.1 MHz, C6D6, 295 K): δ (ppm) = 7.90 (d, 3JHH = 8.0 Hz, 1H, H6), 7.31 (d, 3JHH = 7.9 Hz, 1H, H2), 7.19 (m, 1H, H7′), 7.08 (m, 2H, H7), 6.76 (d, 3JHH = 7.9 Hz, 1H, H6′), 6.71 (m, 1H, H1), 6.64 (m, 2H, H2′, H8′), 6.47 (m, 2H, H1′, H8), 2.46 (s,

3H, H10′), 2.18 (s, 3H, H10), 2.08 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, C6D6, 295 K): δ (ppm) = 162.6 (C5′), 159.7 (C4′), 158.0 (C9′), 156.4 (C5), 155.8 (C9), 155.4 (C4), 137.7 (C7), 137.4 (C7′), 133.4 (C3), 130.5 (C3′), 130.3 (C1), 126.3 (C2′), 125.9 (C1′), 121.7 (C8), 121.1 (C2), 177.7 (C8′), 177.1 (C6), 177.1 (C6), 111.2 (C6′), 87.2 (C(CH3) Cp*), 24.3 (C10′), 23.2 (C10), 10.3 (C(CH3) Cp*). MS (LIFDI+): m/z calcd for C30H31IrN6 ([M]+) 668.22; found 668.23. Anal. (%) Calcd for C30H31IrN6: C 53.95, H 4.68, N 12.58. Found: C 53.34, H 5.10, N 12.69. [Cp*Ir(oF-BPI)]Cl (3[Cl]). The κ2-(N,N)-coordinated complex 3-Cl (8.0 mg, 11.8 μmol) was dissolved in methanol-d4 (0.5 mL) and stirred at room temperature for 15 min. Within this time, an equilibrium between the κ2-(N,N) and κ3-(N,N,N) species 3-Cl and 3[Cl] has appeared with a ratio of 0.47:1 (3-Cl:3[Cl]). Compound 3[Cl] could not be isolated, and the NMR data were determined from the mixture of 3-Cl and 3[Cl]. 1H{19F} NMR (399.9 MHz, CD3OD, 295 K): δ (ppm) = 8.17 (m, 2H, H7), 7.99 (m, 2H, H2), 7.73 (m, 2H, H1), 7.48 (d, 3JHH = 7.9 Hz, 2H, H8), 7.35 (d, 3JHH = 8.0 Hz, 2H, H6), 1.37 (s, 15H, Cp*). 13C{1H} NMR (150.9 MHz, CD3OD, 295 K): δ (ppm) = 163.21 (d, 1JCF = 239.1 Hz, C9), 162.2 (C4), 155.5 (C5), 145.3 (m, C7), 139.7 (C3), 132.3 (C1), 122.3 (C2), 121.5 (C8), 108.4 (m, C6), 89.1 (C(CH3) Cp*), 8.0 (C(CH3) Cp*). 19F{1H} NMR (396.3 MHz, C6D6, 295 K): δ (ppm) = −52.23 (s, 2F). [Cp*Ir(oF-BPI)]BPh4 (3[BPh4]). Sodium tetraphenylborate (24.6 mg, 0.072 mmol, 1.0 equiv) was added to a suspension of 3-Cl/3[Cl] (50.0 mg, 0.072 mmol, 1.0 equiv) in 3 mL of methanol and stirred for 30 min at room temperature. The precipitate was filtered off, washed with water (3 × 1 mL) and methanol (2 × 1 mL), and dried in vacuo to yield 3[BPh4] as a red powder. Crystals suitable for an X-ray diffraction study were obtained by slow diffusion of n-pentane in a saturated solution of 3[BPh4] in dichloromethane. Yield: 65.6 mg, 93%. 1H NMR (600.1 MHz, CD2Cl2, 295 K): δ (ppm) = 7.90 (m, 2H, H2), 7.83 (m, 2H, H7), 7.61 (m, 2H, H1), 7.30 (d, 3JHH = 7.9 Hz, 2H, H6), 7.22 (m, 8H, o-CH), 6.98 (d, 3JHH = 8.0 Hz, 2H, H8), 6.92 (m, 8H, m-CH), 6.77 (t, 3JHH = 7.2 Hz, 4H, p-CH), 1.23 (s, 15H, H11). 13 C{1H} NMR (150.9 MHz, CD2Cl2, 295 K): δ (ppm) = 164.0 (q, 1 JCB = 49.5 Hz, ipso-CB), 163.1 (d, 1JCF = 255.9 Hz, C9), 162.0 (C4), 155.8 (C5), 144.8 (m, C7), 137.9 (C3), 135.9 (m, o-CH, BPh4), 132.4 (C1), 125.6 (q, 3JCB = 2.8 Hz, m-CH, BPh4), 122.7 (C2), 121.9 (C6), 121.7 (p-CH, BPh4), 108.2 (m, C8), 89.0 (C(CH3) Cp*), 9.1 (C(CH3) Cp*). 19F{1H} NMR (376.3 MHz, CD2Cl2, 295 K): δ (ppm) = −51.58 (s, 2F). HRMS (ESI+): m/z calcd for C28H25F2IrN5 ([M − BPh4]+) 662.1707; found 662.1705. HRMS (ESI−): m/z calcd for C24H20B ([BPh4]−) 319.1664; found 319.1634. Anal. (%) Calcd for C52H45BF2IrN5: C 63.67, H 4.62, N 7.14. Found: 62.82, H 4.73, N 7.22. Due to cocrystallization with variable amounts of solvent, improved elemental analyses could not be obtained despite numerous attempts. [Cp*Ir(oF-BPI)(N3)] (3-N3). To a suspension of 3-Cl/3[Cl] (30.0 mg, 0.043 mmol, 1.0 equiv) in methanol (1.5 mL) was added NaN3 (2.80 mg, 0.043 mmol, 1.0 equiv), and the mixture was stirred for 2 h at room temperature. The precipitate was filtered off, dissolved in benzene, and filtered over a pad of Celite. The solvent of the filtrate was removed in vacuo, and the crude product was washed with npentane to yield 3-N3 as an orange, air-stable solid. Single crystals suitable for X-ray diffraction were obtained by slow diffusion of npentane in a concentrated solution of 1-N3 in dichloromethane at 7 °C. Yield: 23.0 mg, 76%. 1H NMR (399.9 MHz, CD2Cl2, 295 K): δ (ppm) = 7.88 (d, 3JHH = 7.4 Hz, 1H, H2), 7.79 (m, 2H, H7, H7′), 7.44 (m, 1H, H1), 7.25 (m, 1H, H1′), 7.16 (d, 3JHH = 7.7 Hz, 1H, H6′), 7.98 (dd, 3JHH = 7.7 Hz, 5JHF = 2.0 Hz, 1H, H6), 6.71 (m, 2H, H8, H8′), 6.58 (d, 3JHH = 7.7 Hz, 1H, H2′), 1.59 (s, 15H, Cp*). 13C{1H} NMR (100.6 MHz, CD2Cl2, 295 K): δ (ppm) = 163.5 (d, 1JCF = 238.5 Hz, H9/H9′), 163.0 (d, 1JCF = 253.8 Hz, H9/H9′), 161.7 (C5/C5′), 161.5 (C4′), 159.7 (C4), 156.6 (C5/C5′), 142.6 (d, 3JCF = 8.3 Hz, H7/H7′), 142.3 (d, 3JCF = 10.4 Hz, H7/H7′), 140.8 (C3), 131.7 (C3′), 131.2 (C1), 130.4 (C1′), 124.6 (C2′), 122.0 (C2), 120.6 (d, 4JCF = 3.2 Hz, H6′), 113.6 (d, 4JCF = 4.9 Hz, H6), 104.2 (d, 2JCF = 31.5 Hz, H8/H8′), 103.1 (d, 2JCF = 36.8 Hz, H8/H8′), 87.4 (C(CH3) Cp*), 9.3 (C(CH3) Cp*). 19 1 F{ H} NMR (376.3 MHz, CD2Cl2, 295 K): δ (ppm) = −57.36 (s, M

DOI: 10.1021/om501138t Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics F), −69.65 (s, F′). IR (KBr): ν̃ (cm−1) = 2034 (s, N3). HRMS (FAB+): m/z calcd for C28H25F2IrN8 ([M]+) 704.1799; found 704.1814. HRMS (ESI−): m/z calcd for C24H20B ([BPh4]−) 319.1664; found 319.1634. Due to cocrystallization with variable amounts of solvent, correct elemental analyses could not be obtained despite numerous attempts. [(p-Cym)Os(oF-BPI)Cl] (6-Cl). A solution of LDA (30.5 mg, 0.285 mmol, 1.5 equiv) in THF (2 mL) was added dropwise to a solution of oF-BPIH (3) (63.6 mg, 0.190 mmol, 1.0 equiv) in THF (4 mL) at −78 °C. After the addition was completed the solution was warmed to room temperature and stirred for another 30 min. Then the reaction mixture was added dropwise via cannula to a suspension of [(pCym)OsCl2]2 (75.0 mg, 0.095 mmol, 0.55 equiv) in THF (4 mL), and the suspension was stirred overnight at room temperature. The solvent was removed in vacuo, and the residue dissolved in toluene and filtered over a pad of Celite. After drying in vacuo, the crude product was washed with diethyl ether (3 × 3 mL) and n-pentane (3 × 3 mL) to give 6-Cl as a dark red solid. Yield: 88.2 mg, 67%. 1H NMR (600.1 MHz, C6D6, 295 K): δ (ppm) = 8.06 (d, 3JHH = 7.5 Hz, 1H, H2), 6.94 (m, 3H, H1, H7′, H6′), 6.70 (m, 2H, H1′, H7), 6.58 (m, 2H, H2′, H6), 6.2 (dd, 3JHH = 7.8 Hz, 4JHH = 2.5 Hz, 1H, H8′), 5.92 (d, 3JHH = 5.4 Hz, 1H, H12b), 5.89 (m, 1H, H8), 5.84 (d, 3JHH = 5.4 Hz, 1H, H13b), 5.42 (m, 1H, H13a), 5.29 (d, 3JHH = 5.5 Hz, 1H, H12a), 2.19 (m, 1H, H15), 2.13 (s, 3H, H10), 0.84 (d, 3JHH = 6.8 Hz, 3H, H16a/H16b), 0.80 (d, 3JHH = 6.8 Hz, 3H, H16a/H16b). 13C{1H} NMR (150.9 MHz, C6D6, 295 K): δ (ppm) = 163.2 (d, 1JCF = 400.5 Hz, C9/C9′), 163.1 (d, 1JCF = 400.5 Hz, C9/C9′), 163.5 (C4‘), 162.9 (C5′), 158.2 (C4), 156.0 (C5), 141.8 (d, 3JCF = 7.8 Hz, C7′), 140.4 (m, C3, C7), 131.5 (C3′), 130.4 (C1), 129.7 (C1′), 124.0 (C2′), 122.6 (C2), 120.0 (d, 4JCF = 3.4 Hz, C6′), 112.7 (d, 4JCF = 4.5 Hz, C6), 102.2 (m, H8, H8′), 94.2 (C14), 92.1 (C11), 76.1 (C13a), 75.6 (C13b), 73.7 (C12a), 73.4 (C12b), 31.2 (C15), 22.4 (C16a/C16b), 22.0 (C16a/C16b), 18.4 (C10). 19F{1H} NMR (376.3 MHz, C6D6, 295 K): δ (ppm) = −47.97 (s, F), −68.25 (s, F′). HRMS (DART+): m/z calcd for C28H25ClF2N5Os ([M + H]+) 696.1381; found 696.1372. Anal. (%) Calcd for C28H24ClF2N5Os: C 48.44, H 3.48, N 10.09. Found: C 49.17, H 3.96, N 9.03. [(p-Cym)Os(tBu-BPI)Cl] (7-Cl). The synthetic procedure of this compound was the same as that of 6-Cl, using tBu-BPIH (5) (165 mg, 0.400 mmol) instead of oF-BPIH to give 7-Cl as dark red solid. Yield: 213 mg, 69%. 1H NMR (600.1 MHz, THF-d8, 295 K): δ (ppm) = 8.67 (d, 3JHH = 6.4 Hz, 1H, H9), 8.24 (d, 3JHH = 5.3 Hz, 1H, H9‘), 7.77 (d, 3 JHH = 7.5 Hz, 1H, H2), 7.28 (m, 1H, H1), 7.05 (m, 3H, H1′, H6, H8′), 6.95 (s, 1H, H6‘), 6.76 (d, 3JHH = 6.3 Hz, 1H, H8), 6.20 (d, 3JHH = 7.7 Hz, 1H, H2′), 6.11 (d, 3JHH = 5.2 Hz, 1H, H14b), 5.85 (d, 3JHH = 5.3 Hz, 1H, H15b), 5.66 (d, 3JHH = 5.2 Hz, 1H, H15a), 5.62 (d, 3JHH = 5.3 Hz, 1H, H14a), 2.45 (m, 1H, H17), 2.23 (s, 3H, H12), 1.31 (s, 9H, H11), 1.29 (s, 9H, H11′), 1.09 (d, 3JHH = 6.9 Hz, 3H, H18a/H18b), 1.04 (d, 3 JHH = 6.9 Hz, 3H, H18a/H18b). 13C{1H} NMR (150.9 MHz, THF-d8, 295 K): δ (ppm) = 164.3 (C5′), 164.0 (C4′), 162.2 (C7), 161.8 (C7′), 158.2 (C4), 157.9 (C9), 156.5 (C5), 149.2 (C9′), 141.3 (C3/C3′), 132.3 (C3/C3′), 130.3 (C1), 129.6 (C1′), 124.5 (C2′), 121.6 (C2), 120.6 (C6), 116.9 (C8), 116.1 (C8′), 113.1 (C6′), 94.2 (C16), 93.6 (C13), 77.2 (C14b), 76.3 (C14a/C15a), 76.2 (C14a/C15a), 73.7 (C15b), 35.2 (C10′), 35.0 (C10), 32.1 (C17), 30.3 (C11/C11′), 22.9 (C18a/C18b), 22.8 (C18a/ C18b), 18.6 (C12). HRMS (DART+): m/z calcd for C36H43N5Os ([M + H]+) 772.2822; found 772.2803. Anal. (%) Calcd for C36H42ClN5Os: C 56.12, H 5.49, N 9.08. Found: C 55.45, H 5.40, N 8.68. [(p-Cym)Os(tBu-BPI)]Cl (7[Cl]). Complex 7-Cl (40.0 mg, 51.9 μmol) was dissolved in methanol (2 mL), and the solution was stirred for 60 min at room temperature, whereupon the color changed from red to purple. By removal of the solvent under vacuum, the product 7[Cl] was isolated as a dark purple, air-stable solid. Yield: 36.8 mg, 91%. 1H NMR (600.1 MHz, CD3OD, 295 K): δ (ppm) = 8.98 (d, 3JHH = 5.8 Hz, 2H, H9), 7.88 (m, 2H, H2), 7.56 (m, 2H, H1), 7.39 (s, 2H, H6), 7.36 (d, 3JHH = 5.6 Hz, 2H, H8), 6.12 (d, 3JHH = 4.6 Hz, 2H, H15), 5.96 (d, 3JHH = 4.6 Hz, 2H, H14), 1.96 (sept, 3JHH = 6.7 Hz, 1H, H17), 1.63 (s, 3H, H12), 1.29 (s, 18H, H11), 0.93 (d, 3JHH = 6.8 Hz, 6H, H18). 13 C{1H} NMR (150.9 MHz, CD3OD, 295 K): δ (ppm) = 165.9 (C7), 163.1 (C4), 157.0 (C5), 154.2 (C9), 136.2 (C3), 131.6 (C1), 122.0 (C2), 121.0 (C6/C8), 120.6 (C6/C8), 96.8 (C16), 92.9 (C13), 76.5

(C15), 76.1 (C14), 34.7 (C10), 30.9 (C17), 29.0 (C11), 21.2 (C18), 16.7 (C12). HRMS (ESI+): m/z calcd for C36H42N5Os ([M − Cl]+) 736.3055; found 736.3050. Anal. (%) Calcd for C36H42ClN5Os: C 56.12, H 5.49, N 9.09. Found: C 55.29, H 5.49, N 8.53. Due to cocrystallization with variable amounts of solvent, improved elemental analyses could not be obtained despite numerous attempts. [(p-Cym)Os(tBu-BPI)]BPh4 (7[BPh4]). Sodium tetraphenylborate (8.88 mg, 0.026 mmol, 1.0 equiv) was added to a solution of 7[Cl] (20.0 mg, 0.026 mmol, 1.0 equiv) in 2.5 mL of methanol, and the mixture was stirred for 30 min at room temperature. The precipitate was filtered off, washed with water (3 × 1 mL) and methanol (2 × 1 mL), and dried in vacuo to yield 7[BPh4] as a dark purple powder. Crystals suitable for an X-ray diffraction study were obtained by slow diffusion of n-pentane in a saturated solution of 7[BPh4] in dichloromethane. Yield: 25.9 mg, 95%. 1H NMR (600.1 MHz, CD2Cl2, 295 K): δ (ppm) = 8.39 (d, 3JHH = 6.2 Hz, 2H, H9), 7.89 (m, 2H, H2), 7.63 (m, 2H, H1), 7.40 (d, 4JHH = 2.1 Hz, 2H, H6), 7.37 (m, 8H, o-CH), 7.13 (dd, 3JHH = 6.2 Hz, 4JHH = 2.2 Hz, 2H, H8), 7.04 (m, 8H, m-CH), 6.89 (t, 3JHH = 7.2 Hz, 4H, p-CH), 5.75 (d, 3JHH = 5.6 Hz, 2H, H15), 5.55 (d, 3JHH = 5.6 Hz, 2H, H14), 2.04 (sept, 3JHH = 6.9 Hz, 1H, H17), 1.62 (s, 3H, H12), 1.35 (s, 18H, H11), 0.99 (d, 3JHH = 6.9 Hz, 6H, H18). 13C{1H}NMR (150.9 MHz, CD2Cl2, 295 K): δ (ppm) = 166.0 (C7), 164.2 (q, 1JCB = 49.4 Hz, ipso-CB, BPh4), 162.5 (C4), 157.6 (C5), 153.2 (C9), 136.6 (C3), 136.1 (q, 2JCB = 1.4 Hz, o-CH, BPh4), 131.7 (C1), 125.8 (q, 3JCB = 2.8 Hz, m-CH, BPh4), 122.2 (C2), 122.1 (C6), 122.0 (p-CH, BPh4), 120.7 (C8), 96.7 (C16), 93.1 (C13), 76.5 (C15), 75.9 (C14), 35.2 (C10), 31.1 (C17), 30.0 (C11), 22.3 (C18), 18.0 (C12). HRMS (ESI+): m/z calcd for C36H42IrN5 ([M − BPh4]+) 736.3055; found 736.3057. HRMS (ESI−): m/z calcd for C24H20B ([BPh 4 ] − ) 319.1664; found 319.1656. Anal. (%) Calcd for C60H62BN5Os: C 68.36, H 5.93, N 6.64. Found: C 67.81, H 6.22, N 6.81. General Procedure for Catalytic Transfer Hydrogenation of Ketones and Imines. Screening of the Catalysts. Catalytic runs were performed in an inert atmosphere and by charging a flame-dried Schlenk flask with 5 mol % precatalyst 1-Cl, 3-Cl, 5-Cl, or 7-Cl, respectively. A solution of 1,3,5-trimethoxybenzene (TMB) (8.40 mg, 0.05 mmol, 0.25 equiv) as internal standard and KOH (semiconductor grade) (5.60 mg, 0.10 mmol, 0.5 equiv) in 1 mL of 2-propanol was added, and the mixture was stirred 5 min at room temperature. Subsequently, the ketone (0.20 mmol, 1.0 equiv) was added and the reaction mixture was placed in a preheated oil bath at 82 °C. Aliquots were withdrawn by syringe (0.1 mL) and quenched by mixing with CDCl3 (0.4 mL) in air at room temperature. After filtration through Celite, the solution was analyzed for conversion by 1H NMR. Transfer Hydrogenation of Ketones and Imines Using 3-Cl. Catalytic runs were performed in an inert atmosphere and by charging a flame-dried Schlenk flask with 1 mol % 3-Cl (2.72 mg, 0.004 mmol) and a solution of 1,3,5-trimethoxybenzene (16.8 mg, 0.10 mmol, 0.25 equiv) as internal standard and KOH (semiconductor grade) (11.0 mg, 0.20 mmol, 0.5 equiv) in 1 mL of 2-propanol. After the reaction mixture was stirred for 5 min, the substrate (0.40 mmol, 1.0 equiv) was added and the reaction mixture was placed in a preheated oil bath at 82 °C. Aliquots were withdrawn by syringe (0.1 mL) and quenched by mixing with CDCl3 (0.4 mL) in air at room temperature. After filtration through Celite, the solution was analyzed for conversion by 1 H NMR. DFT Calculations. All DFT calculations were carried out using the Gaussian09 program package.56 B3LYP was employed as functional.57 A def2-QZVPP basis set was used for all atoms of the iridacycle, while a def2-TZVPP basis was applied to adjacent atoms and a def2-SVP basis set was used for the other atoms. 58 For iridium, a pseudopotential for the core electrons was used as implemented in Gaussian 09 (MWB(60)), and the valence shell was described by a def2-QZVPP basis set. NBO analysis was performed using NBO 3.1 as implemented in Gaussian09 Rev. B.01. X-ray Structure Determinations. Crystal data and details of the structure determinations are listed in Tables S3−S5 of the Supporting Information. Full shells of intensity data were collected at low temperature with a Bruker AXS Smart 1000 CCD diffractometer (Mo N

DOI: 10.1021/om501138t Organometallics XXXX, XXX, XXX−XXX

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Kα radiation, sealed tube, graphite monochromator: complexes 3-Cl, 4[Cl], 5[Cl], 5[BPh4], 5[OTf], 1-I, 1-N3, and 1-N) or an Agilent Technologies Supernova-E CCD diffractometer (Mo or Cu Kα radiation, microfocus tube, multilayer mirror optics: all other complexes). Data were corrected for air and detector absorption, Lorentz, and polarization effects;59,60 absorption by the crystal was treated analytically60,61 (complex 1-Cl), numerically (Gaussian grid)60 (complexes 2-Cl, 1-EtCN[BPh4], 1-PPh3[PF6], and 1-N), or with a semiempirical multiscan method62−64 (all other complexes). The structures were solved by the heavy atom method combined with structure expansion by direct methods applied to difference structure factors65,66 (complex 1-I) or by the charge flip procedure67,68 (all other complexes) and refined by full-matrix least-squares methods based on F2 against all unique reflections.69,70 All non-hydrogen atoms were given anisotropic displacement parameters. Hydrogen atoms were generally input at calculated positions and refined with a riding model. Hydrogen atoms of solvent water in the structure of 5-Cl were located in a difference Fourier synthesis; the water molecule was then refined as a rigid group. When found necessary, disordered groups and/or solvent molecules were subjected to suitable geometry and adp restraints.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

Complete experimental procedures and characterization data of oF-BPIH (3) and 1-X; depictions of the molecular structures of compounds 2-Cl, 3-Cl, 5[OTf], and 5[BPh4]; NMR spectra from the isomerization of 5-Cl to 5[Cl]; determination of thermodynamic data of 3-Cl/3[Cl] in methanol; optimization of the reaction conditions of the catalytic transfer hydrogenation; atom labeling for NMR characterization of all compounds reported in this paper; coordinates determined by DFT calculations; listings of the crystal data and structural parameters of all compounds characterized by X-ray diffraction; CIF files giving crystallographic data for compounds 1-Cl, 2-Cl, 3-Cl, 4[Cl], 5[Cl], 5[OTf], 5[BPh4], 1-EtCN[BPh4], 1-BPI′, 1-I, 1-PPh3[PF6], 1-N3, 1-N, 3[BPh4], 1-N3, and 7[BPh4]. 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]. Fax: (+49) 6221-545609. Tel: (+49) 6221-548443. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS A.L.M. thanks Florian Mulks for help with the complex syntheses. T.B. thanks the Fonds der Chemischen Industrie for the doctoral Kekulé fellowship and the Studienstiftung des Deutschen Volkes for a doctoral fellowship. T.R. gratefully acknowledges the award of a Ph.D. grant from the Landesgraduiertenförderung (LGF Funding Program of the State of Baden Wü rttemberg). The computational studies were supported by bwGRiD, member of the German D-Grid initiative, funded by the Ministry for Education and Research and the Ministry for Science, Research and Arts BadenWürttemberg.

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DEDICATION Dedicated to the memory of Michael F. Lappert. O

DOI: 10.1021/om501138t Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/om501138t Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/om501138t Organometallics XXXX, XXX, XXX−XXX