Ruthenium PCP–bis(phosphinite) pincer complexes

The reactions of [RuHCl(CO)(PPh₃)₃] with resorcinol bis(phosphinite) pincer ligands lead to complexes of the general formula [RuCl(PCP)(CO)(PPh₃)]; the crystal structure of one example has been determined. The structures of the bulky resorcinol 2-methyl-4,6-di-tert-butyl resorcinol and its mono-diisopropylphosphinite derivative were also determined. Reactions of [RuCl₂(PPh₃)₃] with resorcinol bis(phosphinite) ligands yield complexes of the type [RuCl(PCP)(PPh₃)], while the reaction of C₆H-2-Me-4,6-^tBu₂-1,3-(OPPh₂) with [RuHCl(CO)(PPh₃)₃] provides a PCP–pincer complex in which the ligand has undergone 2-methyl C–H activation.     

Unusual ruthenium hydride complexes supported by the [N(2-PPh2-4-Me-C6H3)2] pincer ligand

Complexes of Ru(II) containing the pincer ligand [⁻N(2-PPh₂-4-Me-C₆H₃)₂] (PNP^Ph) were prepared. The complex (PNP^PhH)RuCl₂ (1) was treated with 2 equiv AgOTf to produce the triflate complex (PNP^PhH)Ru(OTf)₂ (2). Complex 1 was also treated with an excess of NaBH₄ to give a bimetallic complex [(PNP^Ph)RuH₃]₂ (3). A number of methods, including X-ray crystallography, NMR spectroscopy, and computational studies, were used to probe the structure of 3. Addition of Lewis bases to 3 resulted in octahedral complexes containing a hydride ligand trans to a dihydrogen ligand.     

Aliphatic pincer-type POCOP ligands and their complexation behaviour with iridium: Crystal structure of an iridium(III) phosphinite complex

Reaction of 2 equivalents of 1,3-bis-(di-tert-butylphosphinito)-2-methyl-propane (1a) with [Ir(COD)Cl]₂ affords the first aliphatic diphosphinite PCP pincer complex with iridium, Ir(H){(t-Bu₂POCH₂)₂C(Me)}Cl (2). The poor yield of 2 is partly explained by the formation of a di-nuclear byproduct [IrCl(COD)]₂(μ₂-{(t-Bu₂POCH₂)₂CH(Me)}) (3). Reaction of 1,3-bis-(di-iso-propylphosphinito)-2-methyl-propane (1b) under the same condition does not give any cyclometallation, and reaction with IrCl₃·H₂O in DMF leads to complete decomposition of the pincer ligand under the formation of Ir(H)(i-Pr₂P(OH))₃(CO) (4), underpinning the comparatively low thermal stability of aliphatic phosphinite pincer systems.     

Synthesis, characterization and X-ray crystal structure of [Re(L4)(CO)3]Br · 2CH3OH (L4 = N,N-bis[(2-diphenylphosphino)ethyl]methoxyethylamine): A model compound for novel cationic Tc(I)-tricarbonyl radiotracers useful for heart imaging

This report describes synthesis and evaluation of cationic complexes, [^99mTc(CO)₃(L)]⁺ (L = N-methoxyethyl-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L1), N-[(15-crown-5)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L2) and N-[(18-crown-6)-2-yl]-N,N-bis[2-(bis(3-ethoxypropyl)phosphino)ethyl]amine (L3)) as potential radiotracers for heart imaging. Preliminary results from biodistribution studies in female adult BALB-c mice indicated that the cationic ^99mTc(I)-tricarbonyl complex, [^99mTc(CO)₃(L2)]⁺, has a significant localization in the heart at 60 min post-injection. To understand the coordination chemistry of these bisphosphine ligands with the ^99mTc(I)-tricarbonyl core, we prepared [Re(CO)₃(L4)]Br (L4: N,N-bis[(2-diphenylphosphino)ethyl]methoxyethylamine) as a model compound. [Re(CO)₃(L4)]Br has been characterized by elemental analysis, IR, ESI-MS, NMR (¹H, ¹³C, ¹H-¹H COSY, and ¹H-¹³C HMQC) methods, and X-ray crystallography. In solid state, [Re(CO)₃(L4)]⁺ has a distorted octahedron coordination geometry with PNP occupying one facial plane. The chelator backbone adopts a “chair” conformation with phosphine-P atoms at equatorial positions and the amine-N at the apical site. In solution, [Re(CO)₃(L4)]⁺ is able to maintain its cationic nature with no dissociation of carbonyl ligands or any of the three PNP donors.     

Gallium and indium compounds supported by a [PNP] pincer ligand

The new bis(phosphino)amido ligand, [MePNP^Ph], that incorporates (i) an ortho-tolylene linker between nitrogen and phosphorus and (ii) phenyl substituents on phosphorus, has been synthesized as its protonated derivative, [MePNP^Ph]H, via sequential treatment of (2-Br,4-Me-C₆H₃)₂NH with (i) BuⁿLi, (ii) Ph₂PCl and (iii) HCl. Deprotonation of [MePNP^Ph]H with BuⁿLi in THF affords the lithium derivative which has been isolated as both mono and bis THF adducts, [MePNP^Ph]Li(THF) and [MePNP^Ph]Li(THF)₂. Treatment of [MePNP^Ph]Li(THF)₂ with GaCl₃ and InX₃ (X = Cl, Br, I) gives a series of [MePNP^Ph]MX₂ complexes in which the [PNP] donor binds in a “T”-shaped manner and the metal has a distorted trigonal bipyramidal geometry. The reaction of [MePNP^Ph]Li(THF)₂ with “GaI” yields the Ga-Ga bonded complex [κ²-MePNP^Ph](GaI)(GaI)[κ²-MePNP^Ph] in which the [MePNP^Ph] ligand binds in a κ²-P,N manner. The bis(phosphino)amine [MePNP^Ph]H may also serve as a ligand and treatment of [MePNP^Ph]H with GaBr₃ affords [κ²-{[MePNP^Ph]H}GaBr₂][GaBr₄], in which the [MePNP^Ph]H ligand coordinates in a κ²-P,P manner such that the gallium adopts a tetrahedral geometry.     

Syntheses, characterization, density functional theory calculations, and activity of tridentate SNS zinc pincer complexes

A series of tridentate SNS ligand precursors were metallated with ZnCl₂ to give new tridentate SNS pincer zinc complexes. The zinc complexes serve as models for the zinc active site in liver alcohol dehydrogenase (LADH) and were characterized with single crystal X-ray diffraction, ¹H, ¹³C, and HSQC NMR spectroscopies and electrospray mass spectrometry. The bond lengths and bond angles of the zinc complexes correlate well to those in horse LADH. The zinc complexes feature SNS donor atoms and pseudotetrahedral geometry about the zinc center, as is seen for liver alcohol dehydrogenase. The SNS ligand precursors were characterized with ¹H, ¹³C, and HSQC NMR spectroscopies and cyclic voltammetry, and were found to be redox active. Gaussian calculations were performed and agree quite well with the experimentally observed oxidation potential for the pincer ligand. The zinc complexes were screened for the reduction of electron poor aldehydes in the presence of a hydrogen donor, 1-benzyl-1,4-dihydronicotinamide (BNAH). The zinc complexes enhance the reduction of electron poor aldehydes. Density functional theory calculations were performed to better understand why the geometry about the zinc center is pseudo-tetrahedral rather than pseudo-square planar, which is seen for most pincer complexes. For the SNS tridentate pincer complexes, the data indicate that the pseudo-tetrahedral geometry was 43.8 kcal/mol more stable than the pseudo-square planar geometry. Density functional theory calculations were also performed on zinc complexes with monodentate ligands and the data indicate that the pseudo-tetrahedral geometry was 30.6 kcal/mol more stable than pseudo-square planar geometry. Overall, the relative stabilities of the pseudo-tetrahedral and pseudo-square planar systems are the same for this coordination environment whether the ligand set is a single tridentate SNS system or is broken into three separate units. The preference of a d¹⁰ Zn center to attain a tetrahedral local environment trumps any stabilization gained by removal of constraints within the ligand set.     

A hexanuclear iridium complex with a novel binding mode of a PCP-pincer ligand

The hexanuclear iridium complex [η⁴-(COD)Ir]₂{η⁶-[κ⁴-C₆H₂(CH₂P^tBu₂)₂]Ir₂H₂Cl₃} (1) has been prepared by the reaction of [Ir(COD)Cl]₂ with the “PCP” ligand precursor, 1,3-C₆H₄(CH₂P^tBu₂)₂ (PCP-H). Characterization by X-ray diffraction reveals that complex 1 has an unusual structure in which metalation (C-H addition) of the ligand has occurred at the 4- and 6-positions of the PCP aryl ring. This is in contrast to the widespread reactivity of this ligand precursor in which a single metalation typically occurs at the 2-position, thereby allowing coordination of both phosphino groups to a single metal center to give the κ³-meridional pincer coordination. The complex can be viewed as being composed of a dimer of two bis-metalated (Ir(III)) PCP units, held together by two bridges of three chlorides each; the aryl ring of each of the PCP ligands of this hypothetical tetra-iridium dianion is then bound to a cationic [Ir(I)(COD)]⁺ unit.The structure discussed here crystallizes as the tetra(acetone) solvate in the monoclinic space group P2₁/n with lattice parameters a=14.4154(11) Å, b=15.4435(12) Å, c=19.5181(15) Å, b=99.996(1)° and V=4279.31(6) ų. Convergence to conventional R values of R(F)=0.041 and R_w(F)=0.092 was obtained for 445 variable parameters and 8085 reflections with F>4σ(F). Complex 1 also crystallizes as the octabenzene solvate in the orthorhombic space group Pbca, with lattice parameters a=16.4247(14) Å, b=24.1695(21) Å, c=28.0460(24) Å and V=11134(1) ų. Convergence of the orthorhombic phase to R(F)=0.038 and R_w(F)=0.084 was obtained for 595 variable parameters and 12 885 reflections with F>4σ(F).     

Organoosmium complexes of imidazole-containing chelate acceptor ligands

The complexes [(L)Os(η⁶-Cym)Cl](PF₆), Cym = p-cymene and L = bis(1-methylimidazol-2-yl)ketone (bik) or bis(1-methylimidazol-2-yl)glyoxal (big), were obtained and characterized with respect to spectroscopy, crystal structure (big complex) and (spectro)electrochemical behaviour at variable temperatures. DFT calculations confirm the structure of [(big)Os(η⁶-Cym)Cl]⁺ with imidazolyl-N-bonded Os^II in a boat-shaped seven-membered chelate ring with small N-Os-N angles (<84°). Reduction of this compound proceeds reversibly to a neutral complex of the α-semidione radical anion ligand big⁻; EPR and IR spectroelectrochemistry indicate very little participation from the heavy metal in the spin distribution. The analogous [(bik)Os(η⁶-Cym)Cl]⁺ could not be reduced reversibly to the ketyl radical complex but displayed a more reversible oxidation at high potential.     

Color tuning of iridium complexes - Part I: Substituted phenylisoquinoline-based iridium complexes as the triplet emitter

A series of new iridium complexes with isoquinoline derivative ligands were synthesized for application in organic light-emitting diodes (OLEDs). It is demonstrated that varying the substituents at the 2′- or 4′-positions of the isoquinoline ligand makes the color tuning possible. Because of the steric effect, the 6′-substituted complexes: bis[1-(6′-methyl)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6b1), bis[1-(6′-trifluoromethyl)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6b2), and bis[1-(6′-methoxy)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6b3) show red-shift effect with respect to the 4′-substituted complexes: bis[1-(4′-methyl)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6a1), bis[1-(4′-trifluoromethyl)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6a2), and bis[1-(4′-methoxy)phenylisoquinolinato-N,C^2′] iridium(III) (acetylacetonate) (6a3). All of these complexes are suitable for the red phosphorescent materials in OLEDs.     

Palladium(II) amido complexes with an unsymmetrical PNP′ pincer-type coordination and a new (E,E)-tetradentate diphosphinoazine coordination mode

Cationic palladium(II) complexes [PdCl{PR₂CH₂C(Bu^t)NNC(Bu^t)CH₂PR₂}]Cl, where R = isopropyl, cyclohexyl or tert-butyl, were synthesized by the reactions of the corresponding diphosphinoazines with bis(acetonitrile)palladium(II) dichloride. When bis(benzonitrile)palladium(II) dichloride was used instead, in the molar ratio of 2:1 to the diphosphinoazine, a new complex was isolated with the isopropyl ligand showing a previously unknown (E,E) tetradentate coordination mode. Crystal and molecular structure was determined by X-ray diffraction. The solid complex was a racemate of two axially chiral enantiomers and the chirality was preserved in solution. Reactions of the cationic complexes with triethylamine gave complexes [PdCl{PR₂CHC(Bu^t)NNC(Bu^t)CH₂PR₂}], containing deprotonated diphosphinoazines in ene-hydrazone unsymmetrical pincer-like configuration. The complexes represent several of the still rare examples of Pd(II) amido bis(phosphine) complexes with a chlorine atom covalently bonded trans to the amide nitrogen.     

Tripodal oxygen and tripodal nitrogen ligands in hydroformylation reactions: formation of novel rhodium(III) carbonyl bis(acyl) complexes

The rhodium(I) complexes TpmsRh(CO)₂ (1) and TpmsRh(cod) (2) of the tripodal nitrogen ligand tris(pyrazolyl)methanesulfonate, Tpms⁻=[(pz)₃CSO₃]⁻, catalyze the hydroformylation of 1-hexene. Addition of phosphine has a negative effect on the activity. The hydroformylation activity reaches a maximum at about 60 °C. At temperatures above 80 °C hydrogenation becomes an important secondary reaction. When the catalysis is performed at 60 °C in acetone with 1 or 2 as catalyst precursor all of the rhodium is recovered in the form of the rhodium(III) bis(acyl) complex TpmsRh(CO)(COC₆H₁₃)₂ (9). A similar behaviour is observed with rhodium(I) complexes bearing the tripodal oxygen ligand L_OMe⁻=[(cyclopentadienyl)tris(dimethylphosphito-P) cobalt O,O^′,O″]⁻. In this case all of the rhodium is transformed into L_OMeRh(CO)(COC₆H₁₃)₂ (10). These hitherto unknown bis(acyl) rhodium(III) complexes show the same catalytic activity as the rhodium(I) starting compounds.     

Diamidato-bis(diphenylphosphino) platinum(II) complexes: Synthesis, characterization, and reactivity in the presence of acid

The reaction of Pt(COD)Cl₂, where COD is 1,5-cyclooctadiene, with one equivalent of a diamidato-bis(phosphino) Trost ligand ((R,R)-2 = N,N′-bis(2-diphenylphosphino-1-benzoyl)-(1R,2R)-1,2-diaminocyclohexane, (R,R)-3 = N,N′-bis(2-diphenylphosphino-1-naphthoyl)-(1R,2R)-1,2-diaminocyclohexane, or (±)-4 = N,N′-bis(2-diphenylphosphino-1-benzoyl)-1,2-bis(aminobenzene)) in the presence of base afforded square planar diamidato-bis(phosphino) platinum(II) complexes (R,R)-2-Pt, (R,R)-3-Pt, (±)-4-Pt. Characterization of all complexes included the solution and solid state structure determination of each complex based on multinuclear NMR and X-ray analyses, respectively. Stability of the complexes in acid was examined on addition of HCl to (R,R)-2-Pt in chloroform and compared to the unreactive nature of the similar diamidato-bis(phosphino) complex 1-Pt (1 = 1,2-bis-N-[2′-(diphenylphosphino)benzoyl]diamino-benzene) in the presence of acid. Protonation of the bound amidato nitrogen atoms of (R,R)-2-Pt was observed along with decoordination of the nitrogen atoms from the platinum(II) center producing (R,R)-2-PtCl₂ in quantitative yield by NMR analysis. Confirmation of the product was made on comparison of the NMR spectra to that of authentic (R,R)-2-PtCl₂ prepared on reaction of Pt(COD)Cl₂ with (R,R)-2 in CH₂Cl₂ and characterized by single-crystal X-ray diffraction analysis and NMR spectroscopy. Results add to the knowledge of rich coordination chemistry of bis(phosphino) ligands with late transition metals, metal-amidato chemistry, and has implications in catalysis.     

Syntheses and characterization of Co(III) binuclear complexes with bis(catecholate) ligands containing an acetylene linker

Three binuclear Co(III) complexes with 5,5′-(buta-1,3-diyne-1,4-diyl)bis(3-tert-butylcatechol) (L1), 5,5′-(2,5-dimethoxy-1,4-phenylene)bis(ethyne-2,1-diyl)bis(3-tert-butyl-catechol) (L2) and 5,5′-(4,4′-(buta-1,3-diyne-1,4-diyl)bis(2,5-dimethoxy-4,1-phenylene))bis(ethyne-2,1-diyl)bis(3-tert-butyl-catechol) (L3) have been prepared. The triple bond-containing L1, L2 and L3 ligands were synthesized by a cross-coupling reaction. These complexes were characterized by elemental analyses, electrochemical measurements, ¹H NMR and UV-Vis spectra. In [Co₂(bpy)₄(L1)]²⁺, electrochemical oxidation of the complexes occurs at the bridges as two closely spaced one-electron couples. UV-Vis spectra reveal that chemical oxidation of [Co₂(bpy)₄(L1)]²⁺ using Ag⁺ occurs as a two-electron process forming [Co₂(bpy)₄(L1^Cat,SQ)]³⁺ or [Co₂(bpy)₄(L1^SQ,SQ)]⁴⁺. On the other hand, [Co₂(bpy)₄(L2)]²⁺ and [Co₂(bpy)₄(L3)]²⁺ exhibit different oxidation behavior under the same experimental conditions. In this report we discuss the role of the distance between the two metal atoms on the oxidative behavior of binuclear Co(III) complexes.     

Preparation of an unusual fluoroalkyl phosphinoyl chelate complex, {k-P,C,P,k-O-(CF3)2PCH2C6H3CH2P(CF3)O}2Pt2

Electron poor cationic complexes [(^CF₃PCP)Pt(L)]⁺ (where L = CO, NC₅F₅, or acetone) react with H₂O in polar solvents via selective hydrolysis of a single P-CF₃ substituent to afford the spectroscopically-characterized phosphinoyl-bridged complex {k³-P,C,P,k¹-O-(CF₃)₂PCH₂C₆H₃CH₂P(CF₃)O}₂Pt₂ (1) in good yield. X-ray diffraction confirms the presence of a six-member Pt-P-O-Pt-P-O ring in a chair conformation. The presumed intermediate aqua complex, (^CF₃PCP)Pt(H₂O)⁺, is stable in dichloromethane, but when dissolved in more polar solvents readily converts to 1.     

Hydroformylation of alkenes catalyzed by new dinuclear aryloxide- and carboxylate-bridged rhodium complexes

The new dinuclear aryloxide- and carboxylate-bridged rhodium complexes bis[μ-(2-methylphenolato)]bis[(η²:η²-cycloocta-1,5-diene)rhodium], di(μ-docosanoato)bis[(η²:η²-norborna-2,5-diene)rhodium] and bis[(μ-(adamant-1-yl)carboxylato]bis[(η²:η²-norborna-2,5-diene)rhodium] have been prepared. The complexes were tested as catalysts in the hydroformylation of styrene with a total pressure of CO/H₂ (1:1) of 1000 psi, at 25 and 60 °C, and displayed a regioselectivity towards the branched aldehyde of up to 97%. The same complexes as catalysts in the hydroformylation of 1-octene displayed a regioselectivity for the linear aldehyde of up to 55%.     

Mononuclear rhodium and iridium compounds with pyridyl-pyrazole ligands

Neutral [MCl(L₂)(Hpzpy)], [M(L₂)(pzpy)] and cationic [M(L₂)(Hpzpy)]CF₃SO₃ rhodium(I) or iridium(I) complexes [M = Rh or Ir; L₂ = diolefin or (CO)₂; pzpy = 3-(2-pyridyl)pyrazolate] have been prepared; the pzpy and Hpzpy ligands coordinate to the metal as bidentate chelate groups through one pyrazole nitrogen and the pyridine nitrogen atom. The reactivity of these complexes towards oxidative addition reactions of halogens, methyl iodide or triflic acid and towards displacement reactions has been studied. The neutral and cationic iridium(I) complexes are modest catalysts for the hydrosilylation of phenylacetylene with triethylsilane at 60 °C. The complexes have been characterised by analytical and spectroscopic data; their configuration has been confirmed by COSY and NOESY experiments and the molecular structure of [Rh(COD)(Mepzpy)(PPh₃)]CF₃SO₃ has been established by an X-ray diffraction study.     

Palladium(II) complexes of imidazolin-2-ylidene N-heterocyclic carbene ligands with redox-active dimethoxyphenyl or (hydro)quinonyl substituents

Four novel imidazolium salts, precursors to N-heterocyclic carbene (NHC) ligands, with 2,5-dimethoxybenzyl or 2,5-dihydroxybenzyl (i.e., p-hydroquinone) substituents have been prepared. The crystal structure of the hydroquinone-substituted imidazolium salt H₃L³Br reveals Br⁻?H-O bridged chiral chains of alternating [H₃L³]⁺ cations and Br⁻ counter-ions parallel to the x-axis. Palladium(II) complexes were accessible from reactions of the dimethoxyphenyl-substituted imidazolium precursors with palladium(II) acetate, but not from reactions of imidazolium cations with hydroquinonyl substituents. The crystal structure of the bis(dimethoxybenzyl)-substituted bis(NHC)Pd complex, cis-[PdBr₂(L²)] (2), is described. Puckering of the bis(NHC) ligand leads to a cleft in which an included molecule of dimethylformamide is situated. The cleft is closed by one of the dimethoxybenzyl groups which π-stacks with the dimethylformamide; the other dimethoxybenzyl group points away from the cleft and Pd(II) centre. Reaction of complex 2 with BBr₃ afforded the targeted bis(hydroquinone)-substituted bis(NHC)Pd(II) complex 3 (97% yield) which, in turn, was oxidised by 2,3-dichloro-5,6-dicyano-benzoquinone to the corresponding p-benzoquinone-substituted bis(NHC)Pd(II) complex 4 (98% yield). The cyclic voltammograms of the Pd(II) complexes 2-4 reveal waves that are attributed to an admix of the anticipated ligand-centred and [Pd(C-NHC)₂Br₂]-centred processes.     

Novel (oxazolinyl)phenyl phosphinite pincer ligand: Development of the first non-symmetrical, PCN type chiral palladium and platinum complexes

Chiral palladium and platinum complexes bearing non-symmetrical, PCN pincer ligand, 6-methoxy-3-(4′-isopropyl-2′-oxazolin-2′-yl)phenyl diphenylphosphinite [i-Pr-Phemox-OPPh₂], are first synthesized via oxidative addition of (i-Pr-Phemox-OPPh₂)Br 6 to Pd₂(dba)₃ · (CHCl₃) or Pt(dba)₂ and subsequent treatment with silver salts.     

Color tunable phosphorescent iridium complexes with substituted 2-phenylthiazoles as the cyclometalated ligands

Several new iridium complexes with substituted 2-phenylthiazoles as the cyclometalated ligands have been synthesized and characterized to try to investigate the effect of the size of the π system and substituent groups on physical properties. The complexes have the general structure of (C^∧N)₂Ir(acac), where the C^∧N are 2-phenylthiazole (ptz), 2-(4-methylphenyl)thiazole (mptz), 2-(4-ethylphenyl)thiazole (eptz). The absorption, emission, cyclic voltammetry and thermostability of the complexes were systematically investigated. The experimental results revealed that the maximum emission wavelength in CH₂Cl₂ at room temperature are in the range 542-547 nm, which is blue shift than that of the known iridium(III) bis(2-phenylbenzothiazolato-N,C^2′) acetyl acetonate (bt)₂Ir(acac) due to decreasing the size of the π system in the benzothiazole portion of 2-phenylbenzothiazole ligand.     

Strain in organometallics II: controlling the properties of tetra-coordinated iridium complexes using diastereomers of a bis(tropp) ligand system

The tetra-chelating ligands 1,2-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-ethane, bis(tropp^Ph)ethane, and 1,3-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-propane, bis(tropp^Ph)propane, were synthesised. For the binding of transition metals, these ligands offer two olefin moieties and two phosphorus centres and form mixtures of diastereomers with a R,S-configuration at the phosphorus centres (meso), or a R,R(S,S)-configuration (rac), respectively. meso/rac-bis(tropp^Ph)ethane was separated by fractional crystallisation and reacted with [Ir(cod)₂]OTf (cod=cylcooctadiene, OTf⁻=CF₃SO₃ ⁻) to give the penta-coordinated complex-cations meso/rac-[Ir(bis(tropp^Ph)ethane)(cod)]⁺, where the bis(tropp^Ph)ethane serves as tridentate ligand merely. One olefin unit remains non-bonded, however, a slow intra-molecular exchange between this olefin and the coordinated olefin unit was established (meso-[Ir(bis(tropp^Ph)ethane)(cod)]⁺: k<0.5 s⁻¹; rac-[Ir(bis(tropp^Ph)ethane)(cod)]⁺: k≈35 s⁻¹). The ligand meso/rac-bis(tropp^Ph)propane reacts with [Ir(cod)₂]OTf to give the corresponding complexes containing the tetra-coordinated 16-electron complex-cations meso/rac-[Ir(bis(tropp^Ph)propane)]⁺. The diastereomers were separated by fractional crystallisation. The complex rac-[Ir(bis(tropp^Ph)propane)]⁺ is reduced at relatively low potentials (E¹_1/2=−0.95 V, E²_1/2=−1.33 V versus Ag/AgCl) to give the neutral 17-electron complex [Ir(bis(tropp^Ph)propane)]⁰ and the 18-electron anionic iridate [Ir(bis(tropp^Ph)propane)]⁻, respectively. With acetonitrile, [Ir(bis(tropp^Ph)propane)]⁺ reacts to give the penta-coordinated complex rac-[Ir(MeCN)(bis(tropp^Ph)propane)]⁺ (K=45 M⁻¹, k_f=6×10³ M⁻¹ s⁻¹, k_d=1×10² s⁻¹) and with chloride to yield the relatively stable complex rac-[Ir(Cl)(bis(tropp^Ph)propane)] (k_d<0.5 s⁻¹). Compared to the rac-isomer, the meso-[Ir(bis(tropp^Ph)propane)]⁺ shows significantly cathodically shifted reduction potentials (E¹_1/2=−1.25 V, E²_1/2=−1.64 V versus Ag/AgCl), an acetonitrile complex could not be detected, and the chloro-complex, meso-[Ir(Cl)(bis(tropp^Ph)propane)], is much more labile (k_d≈20′000 s⁻¹). meso-[Ir(bis(tropp^Ph)propane)]⁺ reacts with one equivalent H₂ to give the trans-dihydride complex-cation, meso-[Ir(H)₂(bis(tropp^Ph)propane)]⁺, while the rac-isomer, rac-[Ir(bis(tropp^Ph)propane)]+, reacts with two equivalents H₂ to give rac-{Ir(H)₂(OTf)[(tropp^Ph)(H₂tropp^Ph)propane]}, a cis-dihydride complex containing a hydrogenated 10,11-dihydro-5H-dibenzo[a,d]cycloheptene unit, H₂tropp^Ph. The triflate anion in this complex is rather firmly bound and dissociates only slowly (k=29 s⁻¹). All differences between the different stereoisomers are attributed to the fact that the ligand backbone in the meso-isomer, meso-[Ir(bis(tropp^Ph)propane)]⁺, enforces a planar coordination sphere at the metal. On the contrary, already in the tetra-coordinated rac-[Ir(bis(tropp^Ph)propane)]⁺, the metal has a tetrahedrally distorted coordination sphere which does not impede the reduction to the d⁹-Ir(0) and d¹⁰-Ir(−1) complexes and allows more easily a distortion towards a trigonal bipyramidal (tbp) or octahedral structure for penta- or hexa-coordinated complexes, respectively. A comparison of the NMR data for iridium bonded olefins in equatorial or axial positions in tbp structures shows that the latter experience only modest metal-to-ligand back-donation, while the olefins in the equatorial positions have a high degree of metallacyclopropane character.