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Ligand substitution and electronic structure studies of bis(phosphine)cobalt cyclooctadiene precatalysts for alkene hydrogenation

Publication: Canadian Journal of Chemistry
28 September 2020

Abstract

Diene self-exchange reactions of the 17-electron, formally cobalt(0) cyclooctadienyl precatalyst, (R,R)-(iPrDuPhos)Co(COD) (P2CoCOD, (R,R)-iPrDuPhos = 1,2-bis((2R,5R)-2,5-diisopropylphospholano)benzene, COD = 1,5-cyclooctadiene) were studied using natural abundance and deuterated 1,5-cyclooctadiene. Exchange of free and coordinated diene was observed at ambient temperature in benzene-d6 solution and kinetic studies support a dissociative process. Both neutral P2CoCOD and the 16-electron, cationic cobalt(I) complex, [(R,R)-(iPrDuPhos)Co(COD)][BArF4] (BArF4 = B[(3,5-(CF3)2)C6H3]4) underwent instantaneous displacement of the 1,5-cyclooctadiene ligand by carbon monoxide and generated the corresponding carbonyl derivatives. The solid-state parameters, DFT-computed Mulliken spin density and analysis of molecular orbitals suggest an alternative description of P2CoCOD as low-spin cobalt(II) with the 1,5-cyclooctadiene acting as a LX2-type ligand. This view of the electronic structure provides insight into the nature of the ligand substitution process and the remarkable stability of the neutral cobalt complexes toward protic solvents observed during catalytic alkene hydrogenation.

Graphical Abstract

Résumé

Nous avons étudié les réactions d’auto-échange de diène dans le complexe à 17 électrons, formellement le précurseur du catalyseur cyclooctadiényl cobalt(0), le (R,R)(iPrDuPhos)Co(COD) (P2CoCOD, (R,R)iPrDuPhos = 1,2bis((2R,5R)-2,5-diisopropylphospholano)benzène, COD = 1,5cyclooctadiène) à l’aide du 1,5cyclooctadiène d’abondance naturelle et deutéré. L’échange de diène libre et coordonné a été observé à température ambiante dans une solution de benzèned6, et les études cinétiques indiquent un processus dissociatif. Le complexe P2CoCOD neutre tout comme le complexe cationique de cobalt(I) à 16 électrons [[(R,R)(iPrDuPhos)Co(COD)][BArF4] (BArF4 = B[(3,5(CF3)2)C6H3]4) ont subi un déplacement instantané du ligand 1,5cyclooctadiène par le monoxyde de carbone et ont formé les dérivés carbonyle correspondants. Les paramètres de l’état solide, la densité de spin de Mulliken calculée par la théorie de la fonctionnelle de la densité (DFT) et l’analyse des orbitales moléculaires évoquent une autre description du complexe P2CoCOD, où l’atome de cobalt(II) présente un faible spin et le 1,5cyclooctadiène agit comme ligand de type LX2. Cette façon de voir la structure électronique met en lumière la nature des processus de substitution de ligand et la stabilité remarquable des complexes neutres de cobalt à l’égard des solvants protiques que l’on observe au cours de l’hydrogénation catalytique de l’alcène. [Traduit par la Rédaction]

Introduction

Catalysis with Earth-abundant, first-row transition metals has witnessed a renaissance of interest recently due to potential economic and environmental advantages, as well as reactivity distinct from more widely used and studied precious metal catalysts.1 The asymmetric hydrogenation of carbon–carbon, carbon–oxygen, and carbon–nitrogen multiple bonds has received considerable attention. Examples of manganese, iron, cobalt, and nickel catalysts with high activity and enantioselectivities have been reported and, in some cases, offer performance or operating conditions superior to precious metals.2–4 Bis(phosphine)cobalt complexes have emerged as a powerful and versatile class of catalysts for asymmetric hydrogenation and offer remarkable properties such as stability in alcohol solvents and broad functional group tolerance.5 Compounds of this type have also been reported to be versatile catalysts for other catalytic transformations such as alkene hydroformylation6 and hydroacylation,7 alkene and alkyne hydrovinylation,8 [4 + 2] and [2 + 2] cycloadditions,9 and other C–C bond-forming reactions (Scheme 1).10
Scheme 1.
Scheme 1. Examples of catalytic chemistry promoted by bis(phosphine) cobalt complexes. [Colour online.]
High-throughput experimentation (HTE) has been an enabling technology for the rapid identification of in situ catalyst generation conditions and optimal ligands for asymmetric alkene hydrogenation. Two carbon-bridged, C2-symmetric chiral bis(phosphine)s in combination with cobalt(II) halides and alkyl lithium activating reagent emerged as effective for the hydrogenation of functionalized alkenes such as methyl 2-acetamidoacrylate.5a Greatly improved compatibility with essentially all of the 192 chiral bidentate ligands within the library was discovered when active cobalt catalysts were generated from zinc reduction in MeOH.5c A pilot-scale, 200 g asymmetric hydrogenation affording the epilepsy medication levetiracetam in 98.2% ee was performed with only 0.08 mol% loading of the cobalt catalyst. Isolation of well-defined Co(I) and Co(0) precatalysts generated from sequential one-electron reduction provided insights into catalyst activation pathways. The asymmetric hydrogenation of α,β-unsaturated carboxylic acids with diverse substitution patterns has also been achieved with the Co(0) precatalysts,5d wherein good functional group tolerance was observed and deuterium labeling studies supported an unusual homolytic H2 cleavage pathway with cobalt carboxylates.
To gain additional mechanistic insights, our laboratory has also been exploring the chemistry of well-defined organometallic cobalt precatalysts. Bis(phosphine)cobalt(II) dialkyls have been prepared and structurally characterized as low-spin, planar compounds and applied to the diastereoselective hydrogenation of hydroxyl alkenes.5b In the absence of substrate, stirring (R,R)-(iPrDuPhos)Co(CH2SiMe3)2 in methanol resulted in dehydrogenation of the alcohol and isolation of [(R,R)-(iPrDuPhos)Co]2(µ-CO)2.11 Related, formally cobalt(0) 1,5-cyclooctadiene complexes have been prepared either from the hydrogenation of the cobalt(II) dialkyl derivatives in the presence of COD or from reduction of the corresponding cobalt(II) dihalides in the presence of the diene.5b5d These compounds are one electron reduced variants of widely used bis(phosphine) rhodium(I) cations and are effective single component catalysts for the hydrogenation of a range of alkenes with high activity and enantioselectivity. Despite their anticipated reducing nature, the Co(0) precatalysts have shown unusual stability to protic solvents, as well as broad functional group tolerance.5c,5d
Recently, our laboratory reported the synthesis, structural characterization, and hydrogenation performance of [(R,R)-(iPrDuPhos)Co(COD)][BArF4] ([P2CoCOD]+), a pioneering example of a long-sought-after cobalt analogs of the rhodium cations.12 An idealized square-planar geometry at cobalt was identified in the solid-state structure of [P2CoCOD]+,12 and D2d-distorted tetrahedral geometry was observed for all neutral P2CoCOD compounds, a result of the formally Co(0), d9 configuration.5b5d The one-electron oxidized, cationic [P2CoCOD]+ exhibited much higher substitutional lability of 1,5-cyclooctadiene compared with the neutral P2CoCOD complex, where displacement of the diene by enamides and arenes for [P2CoCOD]+ was instantaneous and substitution by tetrahydrofuran-d8 also occurred over time.12 Although the neutral cobalt(0) precatalysts were highly active in protic solvents such as MeOH and i-PrOH for the asymmetric hydrogenation of enamides and unsaturated carboxylic acids, optimal performance for the cobalt(I) precatalysts was observed in aprotic solvents such as tetrahydrofuran for the asymmetric hydrogenation of methyl 2-acetamidoacrylate and (Z)-methyl-2-acetamidocinnamate, highlighting the distinct reactivity and tolerance of protons for the neutral and cationic cobalt intermediates during catalysis. Isolation of otherwise identical complexes separated by one-electron highlights the unique electronic properties offered by first row transition metals. Catalytic transformations including hydrogenation in potentially two different redox cycles, initiated from Co(0) and Co(I) precatalysts, are highly desired features unique to first-row metals and likely offer new reactivity and selectivity. Here, we describe a study in olefin substitution chemistry and electronic structures for both the neutral and cationic bis(phosphine) cobalt 1,5-cyclooctadiene complexes, P2CoCOD and [P2CoCOD]+, to better understand the basis of their distinct stability and reactivity profiles (Fig. 1).
Fig. 1.
Fig. 1. Examples of previously reported well-defined bis(phosphine)cobalt diene compounds.

Results and discussion

Kinetic studies of cyclooctadiene substitution reactions

The rate and mechanism of substitution of the cyclooctadiene ligands in both cobalt(0) and cobalt(I) was of fundamental interest and may provide insights into precatalyst activation and substrate coordination events. Our studies commenced with a self-exchange experiment between free and coordinated 1,5-cyclooctadiene with neutral P2CoCOD. Because of the paramagnetically shifted 1H NMR resonances of the formally cobalt(0) compound, 1,5-cyclooctadiene-d12 would provide additional spectroscopic handles for these experiments. The iron-catalyzed [4 + 4] cycloaddition of dienes, pioneered by tom Dieck13a and later optimized by Ritter13b and expanded by our laboratory,13c was well suited for the preparation of cyclooctadiene-d12 from commercially available 1,3-butadiene-d6. The targeted cobalt(0) diene complex, (R,R)-(iPrDuPhos)Co(COD-d12) (P2CoCOD-d12), was successfully synthesized following the previously reported procedure5c in 92% isolated yield. The natural abundance compound, P2CoCOD, exhibits paramagnetically shifted resonances in the benzene-d6 1H NMR spectrum at ambient temperatures that range from −80.23 to 34.35 ppm. Comparing these data with the analogous spectrum of P2CoCOD-d12 identified the six resonances corresponding to the coordinated cyclooctadiene (Supplementary Fig. S2).
With the P2CoCOD-d12 in hand, exchange with natural abundance 1,5-cyclooctadiene was explored (Fig. 2A). Addition of 20 equivalents of free 1,5-cyclooctadiene to a benzene-d6 solution of P2CoCOD-d12 and monitoring the progress of the reaction by 1H NMR spectroscopy established appearance of coordinated COD resonances over the course of 8 h at ambient temperature (Supplementary Fig. S7). Notably, the isotopic composition of the cyclooctadiene ligand also impacted the 1H NMR chemical shifts of the iPrDuPhos protons (Fig. 2B). The resolution of the 1H NMR resonances of the iPrDuPhos ligand in P2CoCOD and P2CoCOD-d12 provided a convenient measure for determining the degree of conversion for diene exchange. The reaction reached 10% and 50% conversions in approximately 4 and 27 h, respectively, and equilibrium was established after 96 h.
Fig. 2.
Fig. 2. (A) Diene self-exchange experiment between P2CoCOD-d12 and natural abundance 1,5-cyclooctadiene. (B) Stack plot of 1H NMR spectra of (R,R)-iPrDuPhos ligand resonances (partial) showing disappearance of P2CoCOD-d12 signals (square) and appearance of P2CoCOD signals (triangle) as an indicator of conversion. [Colour online.]
To determine the reaction order in both cobalt and 1,5-cyclooctadiene, initial rate (<10% conversion) measurements were performed. Three separate reactions: (A) P2CoCOD-d12 (32 mmol/L) and 1,5-cyclooctadiene (640 mmol/L); (B) P2CoCOD-d12 (32 mmol/L) and 1,5-cyclooctadiene (1280 mmol/L) and (C) P2CoCOD-d12 (64 mmol/L), and 1,5-cyclooctadiene (640 mmol/L) in benzene-d6 solutions were monitored by 1H NMR spectroscopy, and the formation of [P2CoCOD] product as a function of time is shown in Fig. 3. Doubling the concentration of 1,5-cycloctadiene did not result in a discernable acceleration in initial rate (A vs B), whereas an approximate two-fold enhancement in rate was observed when the initial P2CoCOD-d12 concentration was doubled (A vs C), establishing zeroth order behavior in [COD-d12] and 1st order in [P2CoCOD-d12], respectively (Fig. 3B). These findings support a dissociative substitution pathway where ligand coordination is fast compared with rate-determining cobalt–carbon bond breaking. Although 17-electron complexes have been reported to undergo associative substitutions through 19-electron intermediates,14 the steric properties of the ancillary ligands are known to dramatically influence the preferred substitution mechanism.15 The solid-state structure of P2CoCOD demonstrates that the iso-propyl groups on the rigid DuPhos ligand backbone impose steric hindrance above and below the P–Co–P plane, likely inhibiting formation a five-coordinate, 19-electron intermediate with two COD ligands coordinated in (η2, η2) and η2 arrangement. Substitution of P2CoCOD with 1,5-cyclooctadiene-d12 was also monitored and exhibited the same kinetic profile, suggesting there was no secondary kinetic isotope effect. An overall first order rate constant k = 6.6 (±0.5) × 10−6 s−1 was derived from the linear fits of the initial rates, supporting slow diene substitution. The entire reaction time courses for trials A–C were followed over 103 h until [P2CoCOD] plateaued and the equilibria were established (Fig. 3C). The increase in [P2CoCOD] slowed significantly at higher conversions, as the reverse reaction rate of the equilibrium became significant. Plotting conversions versus time for trials A–C showed similar traces but slightly different conversions (positions of final equilibrium) relevant to the initial [P2CoCOD-d12]:[COD] ratio (Fig. 3D).
Fig. 3.
Fig. 3. (A) Conditions and initial rates of ligand substitution. (B) Initial rate experiments, P2CoCOD concentrations versus time followed until 10% conversion. (C) Product concentrations versus time followed over entire reaction. (D) Conversion to product versus time followed over entire reaction. Trials A, B, and C reached equilibrium at 91% conversion (initial concentration [P2CoCOD-d12]:[COD] = 1:20), 94% conversion (initial concentration [P2CoCOD-d12]:[COD] = 1:40), and 88% conversion (initial concentration [P2CoCOD-d12]:[COD] = 1:10), respectively. [Colour online.]
The observation of a dissociative substitution mechanism for the 17-electron, neutral cobalt(0) complex prompted related studies on cyclooctadiene exchange with the 16-electron, cationic cobalt(I) complex, [P2CoCOD]+. The propensity of [P2CoCOD]+ to form the more stable 18-electron, η6-arene complexes [P2Co(arene)]+ precluded the use of benzene-d6 as solvent.12 Although [P2CoCOD]+ was also unstable upon prolonged standing at ambient temperature in THF-d8 due to solvent substitution and formation of high-spin, paramagnetic cobalt species,12 adding 20 equivalents of 1,5-cyclooctadiene-d12 to a THF-d8 solution of [P2CoCOD]+ and monitoring the reaction by 1H NMR spectroscopy after 10 min demonstrated that the reaction had reached equilibrium (Supplementary Fig. S8). No additional spectroscopic changes were observed until competing THF-d8 substitution occurred. Although no quantitative kinetic data could be obtained due to the fast rate of substitution, these observations clearly establish the substantial increase in the substitutional lability of [P2CoCOD]+ compared with its one-electron reduced analogue, P2CoCOD.

Cyclooctadiene substitution reactions with carbon monoxide

Substitution of the diene with stronger field ligands such as CO was also explored. Replacement of the 1,5-cyclooctadiene ligand by carbon monoxide with P2CoCOD was previously studied and afforded the coordinatively saturated, dimeric cobalt(0) dicarbonyl complex with bridging, terminal CO ligands and a cobalt–cobalt bond, [(R,R)-iPrDuPhosCo(η1-CO)(μ2-CO)]2 (Scheme 2A).11 The carbonylation of [P2CoCOD]+ was studied for comparison. Treatment of a diethyl ether solution of [P2CoCOD]+ with 1 atm CO resulted in an instant colour change from blue to orange. The product was isolated in 86% yield and X-ray diffraction established formation of the 18-electron cobalt carbonyl complex, [(R,R)-iPrDuPhosCo(η1-CO)3][BArF4] (Scheme 2B; Fig. 4). An idealized trigonal bipyramidal geometry at cobalt was observed. The 1H, 31P{1H}, and 13C{1H} NMR spectra (THF-d8, 298 K) of [(R,R)-(iPrDuPhos)Co(η1-CO)3][BArF4] suggest chemically equivalent phosphine atoms (singlet, 98.15 ppm) and carbon atoms of CO ligands (199.5 ppm) at ambient temperature (Supplementary Figs. S3–S5). The 1H and 13C NMR signals are consistent with an overall C2-symmetric environment for the ligand, despite the overall C1-symmetry of the molecule. This observation is consistent with those previously reported for η6-Ph(BPh3) and η2, κ1-methyl 2-acetamidoacrylate coordination.12 Solution infrared spectra (Et2O, 298 K) of [(R,R)-iPrDuPhosCo(η1-CO)3][BArF4] showed terminal CO stretching frequencies at 2079, 2035, and 2011 cm−1, which are higher than those of the neutral [(R,R)-iPrDuPhosCo(η1-CO)(μ2-CO)]2 (Scheme 2), consistent with weaker back-bonding to CO from Co(I)+ than the neutral, formal Co(0) center. The observation that both the neutral P2CoCOD and cationic [P2CoCOD]+ underwent fast and complete displacement of COD ligand by CO to afford coordinatively saturated carbonyl complexes highlight their substitutional lability to the stronger field ligand.
Fig. 4.
Fig. 4. Solid-state structure of [(R,R)-iPrDuPhosCo(η1-CO)3][BArF4] at 30% probability ellipsoids with H atoms and BArF4 anion omitted for clarity. [Colour online.]
Scheme 2.
Scheme 2. (A) Rapid substitution of P2CoCOD by CO and formation of bis(phosphine)cobalt dicarbonyl dimer.11 (B) Fast substitution of [P2CoCOD]+ by CO and formation of cationic bis(phosphine)cobalt tricarbonyl.

Electronic structure studies of [P2CoCOD]+ and P2CoCOD

The electronic structures of the neutral and cationic cobalt complexes were investigated by full molecule density functional theory (DFT) using the B3LYP functional. The qualitative d-orbital splitting diagrams for [P2CoCOD]+ are shown in Fig. 5A. The HOMO is principally dz2 in character as expected for a square-planar d8 metal complex with σ-donating phosphines and π-accepting alkene (diene) ligands.16 The qualitative d-orbital splitting diagram and the Mulliken spin density plot for P2CoCOD are likewise presented in Figs. 5B and 6. The spin density distribution on cobalt approximates the shape of the dz2 orbital, suggesting dz2 as the singly occupied molecular orbital (SOMO) of the S = 1/2 complex. This contrasts expectations for a cobalt(0), d9 complex where Jahn-Teller distortion resulting in a D2d geometry would be expected and the dxy, dxz, and dyz orbitals would have higher energies than dx2-y2 and dz2 orbitals and dz2 would be filled.
Fig. 5.
Fig. 5. Qualitative molecular orbital diagrams representing the corresponding orbitals possessing significant d-orbital character of (A) [P2CoCOD]+ and (B) P2CoCOD computed by DFT at B3LYP/def2-SVP/def2-TZVP level of theory. Calculations were initiated from optimized solid-state structures. [Colour online.]
Fig. 6.
Fig. 6. Spin-density plot for P2CoCOD obtained from the Mulliken population analysis (red, positive spin density; yellow, negative spin density). DFT calculation was performed at the B3LYP/def2-SVP/def2-TZVP level of theory. Calculations were initiated from optimized solid-state structure. [Colour online.]
A closer examination of the metrical parameters from the solid-state structure of P2CoCOD5c revealed that one alkene double bond of COD was longer than the other (1.417(3) Å vs. 1.396(3) Å), whereas the average Co–C bond length was shorter than the other (2.044(3) Å vs. 2.128(2) Å), indicating stronger back-bonding interaction and metallacyclopropane character17 of one “Co–C=C” bonds (Fig. 7A). The elongated C=C bond length is comparable with that (1.423 Å) of a structurally characterized cobalt ethylene complex, (PMe3)3Co(Ph)(η2-C2H4).18 By comparison, both alkene double bond distances of COD of the cationic [P2CoCOD]+ are 1.39(1) Å (Fig. 7A), suggesting weaker back-bonding from Co(I)+ and a lack of metallacyclopropane character. The solid-state structure of P2CoCOD showed distortion from an idealized D2d geometry towards a more square-pyramidal configuration, where the phosphines, cobalt, and one C=C bond of the cyclooctadiene define the basal plane and the other alkene is apical. A similar distortion towards square-pyramidal geometry and metallacyclopropane character have also been identified in the solid-state structures of (dppe)Co(COD)5b (dppe = 1,2-Bis(diphenylphosphino)ethane) and (R,R)-(BenzP*)Co(COD)5d ((R,R)-BenzP* = (R,R)−1,2-Bis(t-butylmethylphosphino)benzene) (Fig. 7A). As such, these formally P2Co(0)COD complexes are best described as five-coordinate, d7, cobalt(II) compounds with the cyclooctadiene being viewed as an LX2-type ligand. The four strong-field donors consisting of phosphines and alkyls occupy the xy plane and largely determine the relative d-orbital energies similar to those in a square-planar field with perturbation from the weaker field alkene donor coordinating through the z-axis and slightly raising the energies of the dz2, dxz, and dyz parentage orbitals. Accordingly, the spin density analysis and qualitative d-orbital splitting diagram suggest that the SOMO of the low spin, d7 cobalt complex has primarily dz2 character with contributions from the cyclooctadiene carbon p orbitals, whereas the dxz, dyz, and dxy orbitals are filled and dx2-y2 orbital is empty (Figs. 5B and 6).
Fig. 7.
Fig. 7. (A) Summary of bond distances of P2CoCOD complexes supporting the metallacyclopropane assignments. Bond distances of [P2CoCOD]+ are reported for comparison. (B) Truncated solid-state structure of P2CoCOD at 30% probability ellipsoids with H atoms omitted for clarity. [Colour online.]
In addition, the X-band EPR spectra of P2CoCOD, (dppe)CoCOD, (R,R)-(BenzP*)CoCOD and (R,R)-(PhBPE)CoCOD ((R,R)-PhBPE = 1,2-bis[(2 R,5 R)−2,5-diphenylphospholano]-ethane) all exhibit characteristic hyperfine coupling of one g tensor to the 59Co nucleus (I = 7/2) but no coupling to the 31P nuclei,5b5d indicating a lack of dx2-y2 character (phosphines are on the xy plane) of the SOMO and further supporting a d7 instead of d9 electronic configuration. Nevertheless, the relatively small g anisotropy for all P2CoCOD complexes5b5d compared with the large g anisotropy characteristic of square-planar, low spin, d7 cobalt(II) complexes, including (dppe)Co(CH2SiMe3)25b and (iPrmPNP)Co(X) (X = CH3, Cl and H, iPrmPNP is an L2X-type ligand),19 also suggest that the P2CoCOD compounds are electronically differentiated from low spin, planar L2CoX2 complexes. For a related structurally characterized P2Co(0)(η6-arene) precatalyst, (R,R)-(PhBPE)Co(η6-C6H6),5c DFT-computed Mulliken spin density distribution on cobalt approximate the shape of the dx2-y2 orbital (Supplementary Fig. S10), supporting a Co(0), d9 assignment for the η6-arene complex.
Taken together, the slow substitution rate of the 17-electron P2CoCOD may be attributed to the strong coordination of one cyclooctadiene C=C bond to the cobalt through strong π-back donation, resulting in a rate-determining alkene dissociation step. In addition, the shift of electron density from cobalt to the alkene fragment likely makes the metal less reducing and consequently less reactive towards protic solvents such as methanol. A stepwise substitution mechanism accounting for the overall dissociative process established from kinetic measurements is proposed in Scheme 3, where the transition states have primarily cobalt–carbon bond-breaking character. Dissociation of the apical alkene arm provided space for an incoming cyclooctadiene molecule affording a 17-electron bis(η2-cyclooctadiene) intermediate, whereas formation of a 15-electron mono(η2-cyclooctadiene) intermediate is less likely. Subsequent tautomerization between the apical and equatorial COD on the metallacyclopropane component and alkene dissociation generated the product. In comparison, oxidation by one electron to furnish the corresponding cation, [P2CoCOD]+, resulted in markedly higher substitutional lability and faster ligand self-exchange rate, likely originating from the electrophilicity of the cobalt(I) center and a stabilization effect from coordination of another alkene. An associative substitution for [P2CoCOD]+ is likely operative and occurs through an 18-electron intermediate. The planar geometry observed with [P2CoCOD]+ may also provide greater access of an incoming ligand from the apical direction, resulting in an increased rate of substitution.
Scheme 3.
Scheme 3. Proposed mechanism of ligand self-exchange reaction of P2CoCOD-d12 and COD. [Colour online.]

Conclusions

A dissociative substitution mechanism for the 17-electron, neutral P2CoCOD complex was established by kinetic studies on the self-exchange reaction between 1,5-cyclooctadiene and 1,5-cyclooctadiene-d12. Rapid displacement of 1,5-cyclooctadiene by carbon monoxide and formation of coordinatively saturated bis(phosphine)cobalt carbonyl complexes was observed for both P2CoCOD and the 16-electron cobalt cation, [P2CoCOD]+. Electronic structure studies and metrical parameters from the solid-state structures of P2CoCOD complexes support a cobalt(II)–metallacyclopropane assignment. The strengthened interaction within the metallacyclopropane and a more electropositive cobalt(II) center provide a rationale for the unusual protic stability of these formally cobalt(0) precatalysts.

Acknowledgements

H.Z. and P.J.C. acknowledge financial support from a National Science Foundation (NSF) Grant Opportunities for Academic Liaison with Industry (GOALI) grant (CHE-1855719). M.M.B. acknowledges an NIH F32 fellowship (F32 GM134610).

References

(1)
((a)) Chirik P. J. and Morris R. H. Acc. Chem. Res. 2015, 48 (9), 2495.
((b)) Mukherjee A. and Milstein D. ACS Catal. 2018, 8 (12), 11435.
((c)) Chen J. and Lu Z. Org. Chem. Front. 2018, 5 (2), 260.
((d)) Obligacion J. V. and Chirik P. J. Nat. Rev. Chem. 2018, 2 (5), 15.
((e)) Fürstner A. ACS Cent. Sci. 2016, 2 (11), 778.
((f)) Hayler J. D., Leahy D. K., and Simmons E. M. Organometallics. 2019, 38 (1), 36.
(2)
((a)) Zuo W., Lough A. J., Li Y., and Morris R. H. Science. 2013, 342 (6162), 1080.
((b)) Morris R. H. Acc. Chem. Res. 2015, 48 (5), 1494.
((c)) Morris R. H. Chem. Rec. 2016, 16 (6), 2640.
((d)) Morris R. H. Dalton Trans. 2018, 47 (32), 10809.
(3)
((a)) Li Y.-Y., Yu S.-L., Shen W.-Y., and Gao J.-X. Acc. Chem. Res. 2015, 48 (9), 2587.
((b)) Liu W., Sahoo B., Junge K., and Beller M. Acc. Chem. Res. 2018, 51 (8), 1858.
((c)) Wei D. and Darcel C. Chem. Rev. 2019, 119 (4), 2550.
((d)) Alig L., Fritz M., and Schneider S. Chem. Rev. 2019, 119 (4), 2681.
((e)) Ai W., Zhong R., Liu X., and Liu Q. Chem. Rev. 2019, 119 (4), 2876.
(4)
((a)) Shevlin M., Friedfeld M. R., Sheng H., Pierson N. A., Hoyt J. M., Campeau L.-C., and Chirik P. J. J. Am. Chem. Soc. 2016, 138 (10), 3562.
((b)) Liu Y., Yi Z., Tan X., Dong X.-Q., and Zhang X. iScience. 2019, 19, 63.
((c)) Du X., Xiao Y., Huang J., Zhang Y., Duan Y., Wang H., Shi C., Chen G., and Zhang X. Nat. Commun. 2020, 11 (1), 3239.
((d)) Li B., Chen J., Zhang Z., Gridnev I. D., and Zhang W. Angew. Chem. Int. Ed. 2019, 58 (22), 7329.
((e)) Xu H., Yang P., Chuanprasit P., Hirao H., and Zhou J. Angew. Chem. Int. Ed. 2015, 54 (17), 5112.
(5)
((a)) Friedfeld M. R., Shevlin M., Hoyt J. M., Krska S. W., Tudge M. T., and Chirik P. J. Science. 2013, 342 (6162), 1076.
((b)) Friedfeld M. R., Margulieux G. W., Schaefer B. A., and Chirik P. J. J. Am. Chem. Soc. 2014, 136 (38), 13178.
((c)) Friedfeld M. R., Zhong H., Ruck R. T., Shevlin M., and Chirik P. J. Science. 2018, 360 (6391), 888.
((d)) Zhong H., Shevlin M., and Chirik P. J. J. Am. Chem. Soc. 2020, 142 (11), 5272.
(6)
((a)) Hood D. M., Johnson R. A., Carpenter A. E., Younker J. M., Vinyard D. J., and Stanley G. G. Science. 2020, 367 (6477), 542.
((b)) MacNeil C. S., Mendelsohn L. N., Zhong H., Pabst T. P., and Chirik P. J. Angew. Chem. Int. Ed. 2020, 59 (23), 8912.
(7)
((a)) Chen Q., Kim D. K., and Dong V. M. J. Am. Chem. Soc. 2014, 136 (10), 3772.
((b)) Kim D. K., Riedel J., Kim R. S., and Dong V. M. J. Am. Chem. Soc. 2017, 139 (30), 10208.
((c)) Santhoshkumar R., Mannathan S., and Cheng C.-H. J. Am. Chem. Soc. 2015, 137 (51), 16116.
((d)) Yang J., Rerat A., Lim Y. J., Gosmini C., and Yoshikai N. Angew. Chem. Int. Ed. 2017, 56 (9), 2449.
((e)) Whyte A., Bajohr J., Torelli A., and Lautens M. Angew. Chem. Int. Ed. 2020, 59 (38), 16409.
(8)
((a)) Röse P. and Hilt G. Part 2. Synthesis. 2015, 48 (04), 463.
((b)) Jing S. M., Balasanthiran V., Pagar V. V., Gallucci J. C., and RajanBabu T. V. J. Am. Chem. Soc. 2017, 139 (49), 18034.
((c)) Biswas S., Page J. P., Dewese K. R., and RajanBabu T. V. J. Am. Chem. Soc. 2015, 137 (45), 14268.
((d)) Page J. P. and RajanBabu T. V. J. Am. Chem. Soc. 2012, 134 (15), 6556.
((e)) Hilt G. and Lüers S. Synthesis. 2002, 2002 (05), 609.
(9)
((a)) Pagar V. V. and RajanBabu T. V. Science. 2018, 361 (6397), 68.
((b)) Fiebig L., Kuttner J., Hilt G., Schwarzer M. C., Frenking G., Schmalz H.-G., and Schäfer M. J. Org. Chem. 2013, 78 (20), 10485.
(10)
((a)) Wu C. and Yoshikai N. Angew. Chem. Int. Ed. 2018, 57 (22), 6558.
((b)) Wang C., Monaco S. D., Thai A. N., Rahman M. S., Pang B. P., Wang C., and Yoshikai N. J. Am. Chem. Soc. 2020, 142 (29), 12878.
((c)) Whyte A., Torelli A., Mirabi B., Prieto L., Rodríguez J. F., and Lautens M. J. Am. Chem. Soc. 2020, 142 (20), 9510.
(11)
Zhong H., Friedfeld M. R., Camacho-Bunquin J., Sohn H., Yang C., Delferro M., and Chirik P. J. Organometallics. 2019, 38 (1), 149.
(12)
Zhong H., Friedfeld M. R., and Chirik P. J. Angew. Chem. Int. Ed. 2019, 58 (27), 9194.
(13)
((a)) Tom Dieck H. and Dietrich J. Angew. Chem. Int. Ed. Engl. 1985, 24 (9), 781.
((b)) Lee H., Campbell M. G., Hernández Sánchez R., Börgel J., Raynaud J., Parker S. E., and Ritter T. Organometallics. 2016, 35 (17), 2923.
((c)) Kennedy C. R., Zhong H., Macaulay R. L., and Chirik P. J. J. Am. Chem. Soc. 2019, 141 (21), 8557.
(14)
Shi Q., Richmond T. G., Trogler W. C., and Basolo F. J. Am. Chem. Soc. 1984, 106 (1), 71.
(15)
((a)) Zhao J., Goldman A. S., and Hartwig J. F. Science. 2005, 307 (5712), 1080.
((b)) Göttker-Schnetmann I. and Brookhart M. J. Am. Chem. Soc. 2004, 126 (30), 9330.
(16)
Börgel J., Campbell M. G., and Ritter T. J. Chem. Educ. 2016, 93 (1), 118.
(17)
((a)) Dewar M. J. S. Bull. Soc. Chim. Fr. 1951, 18, 71;
((b)) Chatt J. and Duncanson L. A. J. Chem. Soc. 1953, 2939–2947.
(18)
Klein H.-F., Groß J., Hammer R., and Schubert U. Chem. Ber. 1983, 116 (4), 1441.
(19)
Semproni S. P., Milsmann C., and Chirik P. J. J. Am. Chem. Soc. 2014, 136 (25), 9211.25,.

Supplementary Material

Supplementary data (cjc-2020-0352suppla.cif)
Supplementary data (cjc-2020-0352supplb.pdf)
Supplementary data (cjc-2020-0352supplc.pdf)

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Published In

cover image Canadian Journal of Chemistry
Canadian Journal of Chemistry
Volume 99Number 2February 2021
Pages: 193 - 201

History

Received: 14 August 2020
Accepted: 14 September 2020
Accepted manuscript online: 28 September 2020
Version of record online: 28 September 2020

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Key Words

  1. cobalt
  2. ligand substitution
  3. metallacyclopropane
  4. hydrogenation

Mots-clés

  1. cobalt
  2. substitution de ligand
  3. métallacyclopropane
  4. hydrogenation

Authors

Affiliations

Hongyu Zhong
Department of Chemistry, Princeton University, Princeton, NJ 08544, US.
Megan Mohadjer Beromi
Department of Chemistry, Princeton University, Princeton, NJ 08544, US.
Paul J. Chirik [email protected]
Department of Chemistry, Princeton University, Princeton, NJ 08544, US.

Notes

This paper is part of a special issue to honour Professor Robert H. Morris.
Dedicated to Prof. Robert H. Morris on the occasion of his 70th birthday.
Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from copyright.com.

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