Activation of the CH bond. Pentahydridobis(tertiary- phosphine)iridium and related complexes as homogeneous catalysts for hydrogen transfer involving monoolefins (original) (raw)
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Organometallics, 1997
Iridium complexes containing the TPPMS ligand (TPPMS) PPh 2 (m-C 6 H 4 SO 3 K)) have been prepared and studied in DMSO and H 2 O as a comparison to the PPh 3 analogues in toluene. Measurements of the pH of the complexes show that most are almost neutral, but Ir(CO)(H)(TPPMS) 3 is basic (pH) 10.7). The basicity of Ir(CO)(H)(TPPMS) 3 is confirmed by its reaction with H 2 O to give Ir(CO)(H) 2 (TPPMS) 3 +. In aqueous solution, reaction of trans-Ir(CO)(OH)(TPPMS) 2 with H 2 produces only fac-Ir(CO)(H) 3 (TPPMS) 2 not the usual mixture of facial and meridional isomers. This is attributed to a hydrogen-bonding interaction between the two cis-TPPMS ligands in H 2 O. Reaction of trans-Ir(CO)(Cl)(TPPMS) 2 with CO in water produces [Ir(CO) 2 (TPPMS) 2 + ]Cland [Ir(CO) 3 (TPPMS) 2 + ]Cl sequentially in a reaction that is pH dependent. Reaction of trans-Ir(CO)(OH)(TPPMS) 2 with CO results in products based on the water gas shift-reaction. These complexes of TPPMS are spectroscopically very similar to the PPh 3 analogues, but display significantly different reactions in H 2 O. Research aimed at catalysis in water or at a water/ organic solvent interface has greatly expanded in recent years. 1-5 The impetus derives from reducing the role of organic solvents and from easier separation of products. The advantages of water as a solvent in organic reactions were summarized as decreased price, increased safety, and simplified protection-deprotection processes, product isolation, and catalyst recycling. 5 Industrial production of butanal using rhodium catalysts with a water-soluble phosphine (P(m-C 6 H 4 SO 3 Na) 3
Journal of the …, 1993
IrHC12P2 (P = PiPr3) reacts rapidly with H2 at 25 OC to set up an equilibrium where Hz binds trans to the original hydride ligand (trans-2). A second slower reaction forms IrH(H2)C12P2 (cis-2), where the cis disposition of the chlorides, and also H cis to Hz, was established by neutron diffraction. This molecule (unlike trans-2), shows rapid site exchange between coordinated H and Hz. cis-2 can be induced to lose HCl to form Ir(H)2ClP2 (3). The structure of Ir(H)ZCl(PtBu2Ph)2, an analog of 3, was shown by neutron diffraction to have a planar HzIrCl in a Y shape, with C1 at the base of the Y and a H-Ir-H angle of only 73'. ECP ab initio calculations of IrHzCl(PH& show that the Y shape with a H-Ir-H angle close to the experimental value has the minimum energy. They also show that the trans-2 isomer of IrH(H2)Clz(PH3)2 is less stable than the cis-2 isomer by 10.3 kcal/mol. The Ir-Hz interaction is stronger in cis-2. The rotational barrier has been calculated in the two isomers as 2.3 (trans) and 6.5 (cis) kcal/mol. In agreement with the experimental structure, the H-H bond is found to eclipse preferentially the Ir-H bond in cis-2. The calculations also show that the Ir-H2 bond dissociation energy is greatkr in cis-2. It thus appears that the binding ability of a metal fragment not only depends on its ligands but is also linked in a subtle way to its stereochemistry. The J(HD) value for coordinated Hz in cis-2 is 12 f 3 Hz. The implication of this small value and of a Tl,i,(200 MHz) of 38 ms is an H/H distance of 1.07-1.35 A, which compares to the neutron diffraction distance of 1.11(3) A. The Ir-H distances of cis-2 are unprecedented in that the hydride-Ir distance (1.584( 13) A) is not shorter than the distances to the H2 hydrogens (1.537(19) and 1.550(17) A). One of the H2 hydrogens interacts with chloride of an adjacent molecule to give an infinite hydrogen-bonded polymer. An inelastic neutron scattering spectroscopic study on solid IrHCl~(Hz)(PiPr3)2 sets a lower limit on the rotational barrier of the Ir(Hz) unit of 2.0 kcal/mol. Ab initio calculations on IrHCl2(Hz)(PH3)2 yield a H-H distance in these two isomers of 0.81 and 1.4 A, respectively, showing that the moiety IrHClz(PH3)z with chlorides mutually cis is a much stronger reducing agent than that with chlorides trans (and thus H trans to Hz). Crystallographic data: For cis-2 (at 15K), a = 13.008(4) A, b = 11.296 (4) A, c = 16.095(4) A in space group Pna2l (2 = 4). For Ir(H)zC1(PtBu2Ph)2 (at 15K), a = 8.236(2) A, b = 17.024(6) A, c = 20.528(10) A, j 3 = 96.27(4)' in space group P21/c ( Z = 4).
Organometallics, 1994
The reactivity of the cis-dicarbonyl compound Ir(q1-OC(0)CH3)(CO)z(PCy3) (1) toward HSnPh3, HSiPhs, HSiEts, HzSiPhz, and H3SiPh is described. 1 reacts with HSnPh3 to afford Ir(SnPh3)(C0)3(PCy3) (2). The molecular structure of 2 was determined by X-ray investigations. Crystals of 2 are monoclinic, s ace group P21/n, with unit cell dimensions a = 14.643to the following R and R, values: 0.0192 and 0.0208 (6556 observed data). The coordination polyhedron around the iridium atom can be described as a trigonal bipyramid with the triphenylstannyl group and the tricyclohexylphosphine ligand occupying the axial positions, while the three carbonyl groups define the equatorial plane. 2 reacts with molecular hydrogen and HSnPh3. The first reaction gives IrH~(SnPh3)(C0)2(PCy3) (3) and the second one IrH(SnPh3)~(C0)2(PCy3) (4). The reactions of 1 with HSiR3 (R = Ph, Et) lead to mixtures of products, from which the complexes Ir(SiR3)(C0)3(PCy3) (R = Ph (5), Et (9)), IrHz(SiR3)-(CO)2(PCy3) (R = Ph (61, Et (7)), [I~HC~-O~CCH~)(CO)(PCY~)IZ (81, and IrH(q1-OC(0)CH3)-(SiR3)(CO)z(PCy3) (R = Ph (lo), Et (11)) can be isolated or spectroscopically detected. The reaction of 1 with 1 equiv of HzSiPhz gives I~Hz(S~(OC(O)CH~)P~Z)(CO)Z(PC~~) (12) along with small amounts of 8 and Ir(SiHPhz)(C0)3(PCy3) (15). In the presence of 2 equiv of Ha-SiPhz and HsSiPh, l affords IrH(SiHPh2)2(CO)z(PCy3) (13) and I~H (S~H Z P~) Z (C O) Z (P C Y~) (141, respectively. 13 in the presence of acetic acid evolves into 12 and IrHz(SiHPhz)(CO)z(PCy3) (16). 13 and 14 react with alcohols such as methanol, ethanol, 2-propanol, and phenol to give I~HZ(S~(OR)P~Z)(CO)Z(PCY~) (R = Me (171, Et (lS), 'Pr (19), Ph (20)) or IrHZ(Si(0R)z-Ph)(CO)z(PCy3) (R = Me (21), Et (221, 'Pr (23)). The key intermediates of these alcoholysis processes could be silylene species of iridium(II1). The formation of such intermediates may be a consequence of the trend that these types of compounds have to dissociate the tricyclohexylphosphine ligand. In addition, the spectroscopic characterizations of the complexes I~HZ(S~(OCH~)P~~)(CO)Z(P'P~~) (24), IrH(SiHPh2)2(C0)z(PiPr3) (251, and IrH2-(SiHPhz)(CO)z(PiPr3) (26) are also reported. (2) A, b = 13.048(1) A, c = 19.510(4) x , / 3 = 95.26(1)", and 2 = 4. The structure was refined
Vinylic C−H Bond Activation and Hydrogenation Reactions of Tp‘Ir(C2H4)(L) Complexes
Inorganic Chemistry, 1998
The substitution of one of the ethylene ligands of the complexes Tp′Ir(C 2 H 4) 2 (Tp′) Tp Me 2, 1*; Tp′) Tp, 1) by soft donors such as tertiary phosphines or carbon monoxide is a facile reaction that gives the corresponding Tp′Ir(C 2 H 4)(L) adducts. Spectroscopic studies support their formulation as five-coordinate, 18-electron species that possess a distorted trigonal bipyramidal geometry. This proposal has been confirmed by a single-crystal X-ray study carried out with the PMe 2 Ph complex Tp Me 2Ir(C 2 H 4)(PMe 2 Ph) (3b*). Related hydride derivatives of Ir(III) can be obtained either by hydrogenation of the Ir(I) adducts (in general, this gives Tp′IrH 2 (L) compounds) or by thermal activation of one of the C-H bonds of the coordinated C 2 H 4 ligand of the Tp Me 2Ir(C 2 H 4)(L) compounds. All these reactions can be understood by invoking the participation of transient, 16-electron (η 2-Tp′)Ir intermediates, but the thermodynamics of the [Ir](C 2 H 4) to [Ir]H(CHdCH 2) conversion does not require an overall change in the coordination mode of the Tp′ ligand.
Inorganic Chemistry, 2013
This work details the synthesis and structural identification of a series of complexes of the (η 5 -C 5 Me 5 )Ir(III) unit coordinated to cyclometalated bis(aryl)phosphine ligands, PR′(Ar) 2 , for R′ = Me and Ar = 2,4,6-Me 3 C 6 H 2 , 1b; 2,6-Me 2 -4-OMe-C 6 H 2 , 1c; 2,6-Me 2 -4-F-C 6 H 2 , 1d; R′ = Et, Ar = 2,6-Me 2 C 6 H 3 , 1e. Both chloride-and hydride-containing compounds, 2b−2e and 3b−3e, respectively, are described. Reactions of chlorides 2 with NaBAr F (BAr F = B(3,5-C 6 H 3 (CF 3 ) 2 ) 4 ) in the presence of CO form cationic carbonyl complexes, 4 + , with ν(CO) values in the narrow interval 2030−2040 cm −1 , indicating similar π-basicity of the Ir(III) center of these complexes. In the absence of CO, NaBAr F forces κ 4 -P,C,C′,C″ coordination of the metalated arm (studied for the selected complexes 5b, 5d, and 5e), a binding mode so far encountered only when the phosphine contains two benzylic groups. A base-catalyzed intramolecular, dehydrogenative, C−C coupling reaction converts the κ 4 species 5d and 5e into the corresponding hydrido phosphepine complexes 6d and 6e. Using CD 3 OD as the source of deuterium, the chlorides 2 undergo deuteration of their 11 benzylic positions whereas hydrides 3 experience only D incorporation into the Ir−H and Ir−CH 2 sites. Mechanistic schemes that explain this diversity have come to light thanks to experimental and theoretical DFT studies that are also reported.
Organometallics, 1999
The trisacetonitrile complexes [IrClH(P i Pr 3)(NCCH 3) 3 ]BF 4 (1) and [IrH 2 (P i Pr 3)(NCCH 3) 3 ]-BF 4 (2) have been prepared in one-pot reactions with high yields by reaction of the iridium-(I) dimers [Ir(µ-Cl)(coe) 2 ] 2 and [Ir(µ-OMe)(cod) 2 ] 2 with the phosphonium salt [HP i Pr 3 ]BF 4. The rates of exchange between free acetonitrile and the labile acetonitrile ligands of complexes 1 and 2 have been measured by NMR spectroscopy. This kinetic study has shown that both complexes readily dissociate one acetonitrile ligand trans to hydride, giving rise to fluxional five-coordinate intermediates. Substitution products 3-7 have been obtained by treatment of complexes 1 and 2 with CO and PMe 3. The structures determined for 3-7 can be rationalized on the basis of the steric requirements of the ligands, indicating that the products are formed by thermodynamic control. Ethene inserts reversibly into the Ir-H bond of 1 to give the compound [IrCl(Et)(P i Pr 3)(NCCH 3) 3 ]BF 4 (8), which has been used for the preparation of the stable ethyliridium(III) complexes [IrCl(Et)(P i Pr 3)(Py) 2 (NCCH 3)]BF 4 (9) and [Ir(η 2-O 2 CCH 3)Cl(Et)(P i Pr 3)(NCCH 3) 3 ] (10), respectively. The molecular structure of 10 has been determined by X-ray crystallography. The reaction of 2 with ethene, at low temperature, results in the sequential formation of the ethene complex [IrH 2 (η 2-C 2 H 4)-(P i Pr 3)(NCCH 3) 2 ]BF 4 (11) and the diethyl derivative [Ir(Et) 2 (P i Pr 3)(NCCH 3) 3 ]BF 4 (14). At room temperature in solution, 14 undergoes reductive elimination of ethane to form the iridium-(I) species [Ir(P i Pr 3)(NCCH 3) 3 ]BF 4 (15) and [Ir(P i Pr 3)(η 2-C 2 H 4)(NCCH 3) 2 ]BF 4 (16). These cations readily react with H 2 to regenerate 2, closing a cycle for ethene hydrogenation in which several participating species have been identified. The reaction of 2 with propene in solution also allows the characterization of products of propene coordination (17) and insertion (18). In this case, the species obtained after elimination of propane are products of allylic C-H activation: [IrH(η 3-C 3 H 5)(P i Pr 3)(NCCH 3) 2 ]BF 4 (19) and [IrH(η 3-C 3 H 5)(η 2-C 3 H 6)(P i Pr 3)-(NCCH 3)]BF 4 (20). The structure of complex 19 has been determined by X-ray diffraction, and the kinetics of dissociation of its two labile acetonitrile ligands have been studied by NMR spectroscopy. Complex 19 undergoes electrophilic activation of H 2 to give propene and reform the starting complex 2.
Cyclometalation at carbon adjacent to oxygen in platinum(II) and iridium(I) phosphine complexes
Journal of Organometallic Chemistry, 1979
at 125°C in 2-methoxyethanol yields a cyclometalated derivative, PtCl(t-Bu2PCHzOCHz)(t-BuzPCH3). Adding excess NaI and 1,8-bis(dimethylamino)naphthalene accelerates the reaction and gives the iodide-substituted analog. Under the same conditions, frans-PtCl,-(t-Bu,POCH2CH3)2 is also metalated at the methyl carbon atom. However, the slower rate of this reaction indicates that an a-oxygen atom has an electronic accelerating effect on the metalation process. Neither t-Bu,POCH, nor t-Buz-PCH2CH20CH3 &ve platinum(II) cyclometalated complexes; four-or six-membered chelate ring formation appears to be unfavorable. The t-Bu,PCH(CH3)-0CH3 ligand also does not yield a platinum(I1) metalated derivative. However, [IrCl(COT)2]2 (COT = cyclooctene) reacts at 25°C with both t-Bu2PCH20CH3 and t-Bu2PCH(CH3)0CH3, to form iridium(II1) metalated complexes by oxidative addition to the methyl C-H bond. These coordinatively unsaturated compounds react with CO, yielding octahedral iridium(II1) carbonyl hydride complexes.
Organometallics, 1991
Lithium(iminophosphorany1)methanide Li[CH2PPh2=N-Ca4-CH3-4] (2a) reacts with the rhodium and iridium complexes [ML Cll2 (M = Rh, L2 = COD, L = CO: M = Ir, L2 = COD) to yield the complexes [M(CH2PPh2=N-C8H4-bH -4 )L2] (3a, M = Rh, L2 = COD; 3c, M = Rh, L = CO, 3e, M = Ir, L2 = COD), in which the (iminophosphorany1)methanide ligand is coordinated as a u-N,u-C chelate, forming a new four-membered metallacycle. The molecular structure of 3a has been determined by X-ray crystallographic anal is. Compound 3a crystallizes in space group P2,/n with a = 31.877 (3) A, b = 12.932 (2) A, c = 13.579