Michael Fryzuk

Professor

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Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Fun with ferrocene : synthesis of polyiron complexes using 1,1'-diaminoferrocene based ligands (2017)

Reactions of an amidophosphine supported ditantalum tetrahydride, ([NPNSi]Ta)₂(μ-H)₄ and COx (x = 1, 2) were studied and all products were fully characterized. Selective deuteration allows for the production of two deuterated isotopomers which were used in low temperature NMR and GC-MS experiments in order to support a computationally determined mechanism. Iron and cobalt complexes of a ferrocene linked bis(phosphinoamide) were synthesized and characterized by X-ray crystallography and Mössbauer spectroscopy. The cobalt complex contains a Co–Fe bond that was absent in the all-iron complex. The Co–Fe bond was further studied using DFT calculations, which suggest that the bond is comprised of donation from the iron center to the cobalt center (Fe → Co) and back donation from the cobalt center to antibonding orbitals in the ferrocene backbone (Co → fc*). A putative nickel complex supported by the same bis(phosphinoamide) ligand underwent a reductive elimination of the amidophosphine groups forming a new P-N bond. Reactions between the aforementoned iron complex and H₂, CO₂ and other electrophiles were studied and the products of these reactions were fully characterized. The products of these reactions show that the iron phosphinoamides can cooperativley activate a variety of bonds without changing the oxidation state at iron. Upon reduction, the iron complex forms an Fe–Fe bond while remaining in a high spin state. The cleavage of the N=N double bond of azobenzene was achieved under photolytic conditions using the same iron phosphinoamide and is thought to involve formation of a putative iron imido which migrates to the phosphinoamide groups. Due to the tendency of iron phosphinoamides to activate substrates using ligand cooperativity, an alternative ligand using amidophosphine donors was syntheisized and initial coordination studies were performed.

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The synthesis and reactivity of low-coordinate enamido-phosphinimine iron complexes (2017)

Unsymmetrical, bidentate ancillary ligand scaffolds containing enamido-phosphinimine donors (NpN) were developed for the synthesis of low-coordinate iron complexes. A variety of ligands varying in steric hindrance were synthesized through the modularity of the Staudinger reaction. Trigonal planar and dimeric tetrahedral iron bromide complexes were fully characterized and served as precursors for further reactivity. The reduction chemistry of NpN iron bromide complexes was investigated and a number of end-on bridging N2 complexes were characterized by X-ray crystallography. Analysis of the coordinated N2 bond length indicated that the NpN scaffold does not contribute to enhanced bond activation in comparison to well-established β-diketiminate iron N2 complexes. Additionally, an NpN ligand with an indene linker was synthesized with the intent of generating an anionic indenyl moiety that would contribute electron density to the Fe–N₂ backbonding interaction. Unfortunately, DFT results indicated that minimal enhancement to activation results from this effect. A reoccurring observation in the attempted synthesis of NpN dinitrogen complexes was that the P=N bond of the phosphinimine was susceptible to cleavage under reducing conditions. A low-coordinate, dimeric NpN iron hydride was synthesized and its reactivity with unsaturated substrates was explored. The products from hydride insertion into azobenzene, 3-hexyne, and 1-azidoadamantane were characterized and did not vary significantly from the analogous products reported for the reactivity of β-diketiminate iron hydrides. Surprisingly, the NpN iron hydride displays unprecedented reactivity towards hexafluorobenzene, affording an NpN iron fluoride complex and pentafluorobenzene as products. The NpN iron hydride is a precatalyst for catalytic hydrodefluorination of perfluorinated aromatics in the presence of silane. Kinetic studies indicated that the rate-determining step during catalysis involved silane. Enamine-phosphazide intermediates were isolated during the Staudinger reaction and were stable to deprotonation and coordination to Fe(II) and Co(II) halides. The enamido-phosphazide iron bromide complex displayed unusual reactivity upon treatment with potassium triethylborohydride, affording a dimeric phosphinimido species with an Fe–Fe bond. Isotopic labeling studies indicated that cleavage of the phosphazide N–C(aryl) bond occurred through a radical process.

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Early metal complexes of an iminophosphorane containing ligand framework (2016)

A new tridentate, dianionic ligand containing two amido donors and a central iminophosphorane, [NNN]H₂, was synthesized as an adaptation from the [tolylNPN*]H₂ ligand framework. The [NNN] system was designed as an extension to the ortho-phenylene bridged [NPN*] frameworks, which have been studied extensively with zirconium and tantalum. Zirconium amido and chloride complexes stabilized by [NNN] were synthesized via protonolysis routes, and the zirconium dibenzyl complex was synthesized from the halide precursor. Reduction of the zirconium dichloride species with alkali metal reagents led to cleavage of the iminophosphorane P=N bond. The LUMO of [NNN]ZrCl₂(THF) showed antibonding character of the iminophosphorane P=N, by DFT analysis. Steric calculations of [NNN]ZrX₂ complexes (G Value, %Vbur) showed increased steric hindrance of [NNN] relative to [NPN*] ligands. A neutral donor substitution competition experiment corroborated the steric calculations. Tantalum alkyl and alkyne complexes [NNN]TaMe₃ and [NNN]Ta(BTA)Cl were synthesized via salt metathesis reactions with the dipotassium salt of [NNN]. Treatment of [NNN]TaMe₃ with dihydrogen at elevated temperature led to cleavage of the iminophosphorane P=N bond, likely through reduced tantalum intermediate species. Treatment of [NNN]Ta(BTA)(benzyl) with dihydrogen did not generate tantalum-hydride species or hydrogenate the alkyne ligand. Addition of 4-isopropylphenylazide to [NNN]Ta(BTA)Cl led to the tantalum-imido compound [NNN]Ta=N(4-iPrPh)Cl via displacement of the alkyne ligand, BTA. Alternative ligand systems were also examined. A tetradentate ligand [PNNP]H₂ with ortho-phenylene linkers and an ethylene tether was synthesized, and installed on zirconium amido and chloride precursors. Reduction of [PNNP]ZrCl₂ with potassium graphite was unsuccessful in attempt to activate dinitrogen. A redesigned ligand with a propylene tether could not be synthesized, through several routes. A tridentate, monoanionic ligand with ortho-phenylene linkers and silylamide functionality was designed based on the [NPN*] and silylamide [PNP] ligands. The tridentate framework could not be synthesized through several routes, however, a new bidentate ligand with a secondary silylamide ortho to a phosphine group, a first of its class, was synthesized.

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Cooperative ligand design for late transition metal coordination compounds (2015)

This thesis describes several cyclopentyl linked enamide phosphine ligands. Reactivity and mechanistic studies using coordination compounds featuring these ligands enable exploration of ligand cooperativity. Despite complex behavior in solution due to tautomerization, coordination of (NPN)DMP/DIPPH₂ to Rh generates RhCl{(NPN)DMP/DIPPH₂}(COE). Synthesis of RhCl{(NPN)DMP/DIPPH₂}(CO) and RhHCl₂{(NPN)DMP/DIPPH₂} is possible. NMR spectroscopy and in certain cases X-ray analysis establishes the diimine tautomer of the ligand coordinates to Rh in each case. Enamide phosphine complexes, Ir{(NP)DIPP}(COD) and Ir{(NP)DMP}(COD) are synthesized from simple imine phosphine ligands. Ir{(NP)DIPP}(COD) reacts with H₂ or PriOH to form [IrH₃{(NP)DIPPH}]₂. The imine tautomer of the ligand coordinates to Ir. Treating [IrH₃{(NP)DIPPH}]₂ with CO generates Ir{(NP)DIPP}(CO)₂. A proton from the imine ligand of [IrH₃{(NP)DIPPH}]₂ combines with an Ir hydride to release H₂. Observation of three intermediates, involved in conversion of [IrH₃{(NP)DIPPH}]₂ to Ir{(NP)DIPP}(CO)₂, suggests that tautomerization of the dissociated arm is involved in cooperative H₂ loss. Four imine phosphine ligands (R(NP)R'H), where the N-aryl groups (R) and the groups attached to P(R') are varied, are synthesized. Combining each ligand with RuHCl(PPri₃)₂(CO) and KOBut generates four enamide phosphine complexes: RuH{R(NP)R'}(PPri₃)(CO). Reacting RuH{R(NP)R'}(PPri₃)(CO) with H₂ generates RuH₂{R(NP)R'H}(PPri₃)(CO). The imine tautomeric form of the ligand coordinates to Ru in all four cases. The R' groups influence the rate of reaction and percent conversion to RuH₂{R(NP)R'H}(PPri₃)(CO). The mechanism for H₂ activation is explored using RuH{Pri(NP)Pri}(PPri₃)(CO). An intermediate is identified as RuH₂(H₂){Pri(NP)PriH}(PPri₃)(CO). The T₁,min value of a ¹H NMR resonance at δ -7.2 is 22 ms at 238 K (measured to 400 MHz), consistent with a Ru dihydrogen dihydride complex. The N donor of the enamine tautomeric form of the ligand is protonated by H₂ or D₂ and has dissociated from Ru. Tautomerization of the dissociated arm is involved in formation of the final product. Certain factors inhibit alcohol dehydrogenation catalysis for Ir{(NP)DIPP}(COD) and RuH{Pri(NP)Pri}(PPri₃)(CO). Two tridentate enamide phosphine ligands are developed in an effort to generate a catalyst. These ligands enable synthesis of RuH{(PNN)But}(CO) and RuH{(PNN)Pri}(CO). Exposing RuH{(PNN)But}(CO) to 1000 equivalents of benzyl alcohol yields a TON of 13 and TOF of 0.6 h-¹ after 22 hours. Nearly identical results are obtained for RuH{(PNN)Pri}(CO).

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o-Phenylene bridged diamidophosphine complexes of groups 4 and 5 metals for dinitrogen activation (2015)

A series of diamidophosphine donor sets (ipropNPN, tolNPN and phNPN) was prepared, whereby the arylamido groups have no ortho substituents. This allowed for the Buchwald-Hartwig arylamination to be replaced by a directed ortho metalation (DOM) process, sourcing commercial diarylamines. Amido and chloro complexes of Zr, Ti, Hf and Ta with these new diamidophosphine donor sets were prepared.Reduction of the zirconium dichlorides with KC₈ under N₂ gave the side-on dinitrogen complexes [ipropNPNZr(THF)]₂(µ-η²:η²-N₂) and [tolNPNZr(THF)]₂(µ-η²:η²-N₂) and of titanium dichloride gave the end-on complex [tolNPNTi(THF)]₂(µ-η1:η1-N₂). Compared to previously reported sterically encumbered [mesNPNZr(THF)]₂(µ-η²:η²-N₂), the zirconium complexes were more stable, with longer N-N bonds, less labile THF ligands and shorter Zr-O bond lengths. THF adduct displacement thus occurred less readily; for phosphine donors, displacement was at both zirconium centres i.e. [ipropNPNZr(PPhMe₂)]₂(µ-η²:η²-N₂), compared to the mesNPN analogue with an open site at one of the zirconium centres i.e. [mesNPNZr(PPhMe₂)](µ-η²:η²-N₂)[mesNPNZr]. For titanium, four different pyridine adduct species where observed in solution, but only one species was isolated wherein each THF was displaced by two pyridine molecules i.e. [tolNPNTi(Py)₂]₂(µ-η1:η1-N₂). These new dinitrogen complexes were found to be unreactive with H₂; for zirconium, the lack of an open site at one of the metal centres may explain lack of reactivity, and for titanium, the end-on dinitrogen bonding mode is not amenable to hydrogenolysis.The potassium salt of tolNPN with TaMe₃Cl₂ gave the trimethyl species tolNPNTaMe₃, but [tolNPNTaMe₄][Li(THF)₄] was isolated from tolNPNTaCl₃ with MeLi. Tantalum hydrides from trimethyl species and H₂ were unstable and did not form dinitrogen complexes, but mass spectra of tantalum trichlorides with KHBEt₃ and N₂ indicated dinitrogen hydrides [NPNTaH]₂(N₂) and further reaction with BEt₃. Reduction of tantalum trichlorides with KC₈ under N₂ gave mass spectra of dinitrogen complexes [NPNTaCl]₂(N₂), with no crystals isolated.

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The synthesis and reactivity of tantalum diamidophosphine complexes featuring an activated alkyne unit (2014)

A series of tantalum complexes supported by the diamidophosphine ligand [PhNPN*] were synthesized using Ta(alkyne)Cl₃(DME), Ta(V) reagents that feature a reduced alkyne unit: [PhNPN*]Ta(3-hexyne)X, and [PhNPN*]Ta(BTA)X (X = Cl, H, alkyl, N₃; BTA = bis(trimethylsilyl)acetylene). For these complexes, the bonding and reactivity at tantalum is best understood as a combination of both the high-valent ‘Ta(V)-alkenediyl’ and low-valent ‘Ta(III)-alkyne’ structural formalisms.The synthesis and reactivity of a series of Ta imide complexes, generated via the displacement of the alkyne ligand with an aryl azide from corresponding [PhNPN*]Ta alkyne complex is reported. In addition, the synthesis and attempted synthesis of Ta alkyne azide and nitride complexes are discussed. The further reactivity of the Ta imide complexes with aryl azides, and the synthesis of a triazenide moiety is presented.The reactivity of [PhNPN*]Ta alkyne monohydrides with a variety of small molecules was explored. These monohydride complexes combine with 2,6-dimethylphenyl isocyanide and phenylacetylene to form five-membered tantallacyclic products by coupling with the Ta-bound alkyne ligand. A kinetic study of the thermal rearrangement of a Ta alkyne phenylvinyl complex to the corresponding tantallacycle is included. The synthesis of formate and methylene diolate moieties via the reaction of carbon dioxide with multiple equivalents of Ta monohydride was also explored.The hydrogenolysis of [PhNPN*]TaMe₃, and several [PhNPN*]Ta alkyne alkyl and hydride complexes were investigated. The motivation for this work came from the remarkable reactivity observed by a previously reported Ta tetrahydride, ([NPNSi]Ta)₂(μ-H)₄ (1.71) with various small molecules, including N₂. An analogous tetrahydride complex, ([PhNPN*]Ta)₂(μ-H)₄, (5.4) was synthesized via the high-pressure hydrogenolysis of the [PhNPN*]Ta complexes. Unfortunately, the inertness of 5.4 with respect to N2 means that comparisons to the reactivity observed with 1.71 could not be made.The synthesis and structure of the Ta alkene hydride intermediates formed via low-pressure hydrogenolysis of the Ta alkyne complexes is presented. Possible mechanisms for the formation of these intermediates are discussed. The synthesis and proposed structure of a cationic [PhNPN*]Ta imide complex is presented, and potential catalytic applications of this complex are discussed. Newly synthesized compounds were structurally characterized by a combination of NMR spectroscopy and X-ray crystallographic studies.

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Development of group 4 and 5 complexes with N,O chelating supporting ligands as catalysts for the alpha-alkylation of amines (2013)

The use of stoichiometric, catalytic and theoretical methods in the development of an early transition metal catalyst for the α-alkylation of amines is described herein. The investigation is primarily focused on a series of mono(amidate) complexes of tantalum with varying steric and electronic properties. The amidate binding mode and catalytic activity of these complexes is significantly influenced by sterics. Corresponding bis(amidate) complexes are less active as catalysts for the α-alkylation of amines but offers a platform to study the hemi-lability of amidate ligands as well as tantalaziridine formation in these systems. A model 5-membered metallacycle is synthesized and characterized.Isotopic labeling studies with the most active mono(amidate) precatalyst reveal off-cycle reactions and suggest that tantalaziridine formation is rapid and reversible. Preliminary kinetic investigations implicate alkene insertion as the turnover limiting step, consistent with stoichiometric investigations. In addition, the use of radical probes in ligand backbones and an alkene substrate contradicts a one electron mechanism.Quantum chemical calculations are used to develop a theoretical model of the proposed catalytic cycle. The hemi-lability of amidate ligands is highlighted with the optimization of both κ¹(O) and κ²(N,O) minima and transition states. Here, protonolysis is calculated to be the turnover limiting step with small changes in geometry having a significant effect on the potential energy surface. The unlikelihood of a radical mechanism is supported by the computations of triplet species. A survey of established steric parameters has been completed for asymmetric amidate ligands to be used as a predictive tool for catalyst design. The calculated values can be related to the catalytic activity of mono(amidate) and axially chiral tantalum precatalysts. Diamide and diurea proligands featuring a neutral chalcogen atom tether are installed on zirconium and tantalum. The zirconium species form well-defined κ⁴(N,N,O,O) complexes with fluxional behaviour observed for the tantalum species in solution. No evidence of bonding is observed between the chalcogen donor and any metal centre. Fundamental differences in the redox potentials for ligands and complexes are investigated using cyclic voltammetry. The tantalum complexes are found to catalyze the α-alkylation of amines with the zirconium species being competent precatalysts for hydroamination.

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Phosphinoamide ligands for the synthesis of early transition metal organometallic complexes (2013)

Early transition metal hydrides are currently of great interest; they are intermediates in catalytic processes, and have demonstrated ability to activate small molecules. While these complexes are traditionally supported by cyclopentadienyl-type ancillary ligands, current efforts are focused on alternative architectures. In particular, chelating mixed-donor ancillary ligands are currently employed for the synthesis of metal hydride complexes. Bidentate phosphinoamide ligands ([ArNPiPr₂]¹- where Ar = 3,5-dimethylphenyl) were used herein for the synthesis of scandium, yttrium and zirconium organometallic complexes that were characterized using NMR spectroscopy and X-ray diffraction techniques. Mixed phosphinoamide-alkyl yttrium complexes were generated in solution as a mixture of products from reaction of ArNHPiPr₂ with Y(CH₂SiMe₃)₃(THF)₂. Using the same methodology, (ArNPiPr₂)₂Sc(CH₂SiMe₃)(THF) was prepared and reaction with H₂ or PhSiH₃ gave the ligand redistribution product (ArNPiPr₂)₃Sc(THF), along with insoluble materials. A ferrocene-linked diphosphinoamide ligand was developed ([fc(NPiPr₂)₂]²- where fc = 1,1′-ferrocenyl) and employed for the synthesis of a discandium dihydride complex which is bridged by both hydride and phosphinoamide ligands. Because of the insolubility of this discandium dihydride subsequent attempted reactions with CO, alkenes and alkynes were unsuccessful.Triphosphinoamide zirconium complexes (ArNPiPr₂)₃ZrX (X = Cl, Et, CH₂Ph, BH₄, PHPh) were prepared and proved to be poor precursors for the synthesis of a zirconium hydride complex. The ferrocene-linked diphosphinoamide ligand was used in the synthesis of zirconium organometallic complexes, fc(NPiPr₂)2ZrR₂ (R = Me, CH₂Ph, CH₂tBu, tBu). While these dialkyl zirconium complexes were unreactive with respect to H₂, they have been shown to undergo insertion of (2,6-dimethylphenyl)isocyanide to generate the expected iminoacyl complexes. The reactivity of the iminoacyl complexes has been examined and a thermally induced 1,2-hydrogen shift reaction was observed for the benzyl-substituted iminoacyl, to generate an amidoalkene complex; the kinetics of the transformation were studied and deuterium isotopic labelling experiments revealed a primary isotope effect for the migrating hydrogen. The electrochemical oxidation of ferrocene-linked diphosphinoamide scandium and zirconium complexes was examined using cyclic-voltammetry; irreversible oxidation of the ferrocenyl diphosphinoamide ligand in these complexes was observed.

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Synthesis and coordination chemistry of an N-heterocyclic carbene-containing tridentate ligand (2011)

One of the most exciting advances in transition-metal-catalyzed processes has been the move toward use of N-heterocyclic carbenes (NHCs) as ancillary ligands. The variation possible in NHC design is immense with one of the most important design aspects being the incorporation of NHC donors into polydentate arrays to generate tridendate pincer ligands. However, research into this class of compounds was limited until the isolation of the first stable crystalline NHC two decades ago. Therefore, understanding of the organometallic chemistry of this class of compounds remains limited in comparison to the closely related phosphine ligands. Thus, this thesis focuses on the preparation of a di-o-phenylene-bridged tridentate PCP donor set and the reactivity of coordination complexes of late transition metals containing this new ligand system. Incorporation of this tridentate ligand onto the group 10 triad of elements via oxidative addition proceeds smoothly to generate square-planar metal hydride complexes of the form [(PCP)MH][PF6] (where M = Ni(II), Pd(II) and Pt(II). Initiating reactivity studies of this series of complexes exposed a new type of non-innocent ligand ehaviour involving formation of a C-C bond between the carbene atom and an ethyl moiety. Isotopic labeling experiments and DFT calculations are used to provide mechanisticinsight into this process that is viewed as a possible source of catalyst deactivation in similar systems. Group 9 metal complexes of rhodium and iridium incorporating tridentate ligand arrays have achieved considerable success in the activation and functionalization of C-H bonds. To examine the reactivity of pincer complexes utilizing a central NHC donor a variety of new rhodium and iridium complexes were synthesized. A rhodium hydride species (PCP)RhH showed catalytic activity in the dehydrogenation of ammonia borane as well as in the ydrosilylation of terminal alkynes. Complexes consisting of both metal centres also exhibited ligand rearrangement processes that challenge the presumedstability of rigid tridentate ligand frameworks.

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Late transition metal complexes incorporating hemilabile mixed-donor N-heterocyclic carbene ligands (2010)

The discovery of N-heterocyclic carbenes (NHC) has dramatically affected the world of catalysis. Their inherent properties that make them excellent auxiliary ligands for catalytic processes have countless laboratories worldwide probing and exploiting every notable feature they possess. However, while there is no shortage of attention in this field of research, there has been considerably less interest in NHCs with an ability chelate to metals via a mixed-donor ligand architecture. Thus, this thesis describes the synthesis and application of a ligand set comprised of bidentate mixed-donor NHC ligands.The ligands prepared all contain a mesitylimidazol-2-ylidene core unit, but incorporate different donor-functionalized tethers. These mixed-donor NHC ligands are synthesized by using a strong base, such as KN(SiMe₃)₂, to deprotonate the imidazolium salt precursors. This strategy was used to effectively prepare 1-mesityl-3-(2-(mesitylamino)ethyl)imidazol-2-ylidene, Mes[CNH] and 1-mesityl-3-(2-aminoethyl)imidazol-2-ylidene, Mes[CNH₂]. Mes[CNH] was found to be a convenient proligand for the synthesis of various M-NHC (M = Rh, Ir, Ru, Pd, Ni, Fe, Ag, Li) compounds. These Mes[CNH]-M complexes demonstrated the hemilabile character of the Mes[CNH] ligand forming complexes that incorporated either a coordinated or uncoordinated amino tether. Mes[CNH]M(diene)Cl, Mes[CN]M(diene) and [Mes[CNH]M(diene)]BF₄(M = Rh, Ir; diene = 1,5-cyclooctadiene, 2,5-norbornadiene) were synthesized and investigated for their ability to perform hydrogenation and hydrosilylation reactions with various substrates. Mes[CNH]Ru(=CHPh)(PCy₃)Cl₂, Mes[CNH]Ru(=CHPh)(py)Cl₂ (py = pyridine) and Mes[CNH]Ru(=CHPh)(PMe₃)Cl₂ were also synthesized and fully characterized. The activity of the former two Ru complexes was studied for their ability to catalyze ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions. In addition, the phosphine dissociation rate of Mes[CNH]Ru(=CHPh)(PCy₃)Cl₂ was measured via magnetization transfer experiments and compared to other known Ru-benzylidene analogues.In addition to the amino-tethered NHC proligands, a phosphine analogue Mes[CP] was prepared and its reactivity with late transition metal complexes was investigated. While the free NHC-phosphine species could not be isolated, deprotonation of both the iminium and phosphine protons followed by the addition of [M(COD)Cl]₂ (M = Rh, Ir) yields Mes[CP]M(COD), which incorporates a bidentate NHC-phosphide ligand. Mes[CP]Ir(COD) was then investigated for its ability to perform hydrogenation and benchmarked to its Mes[CN]Ir(COD) analogue.

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