On the Mechanism of Trimethylphosphine ... - ACS Publications

Jul 5, 2018 - (Mulliken) electric charge separation (qC = −0.19 and +0.22 ..... Theory of Atoms in Molecules; Matta, C. F., Boyd, R. J., Eds.; Wiley...
0 downloads 0 Views 1MB Size
Download PDF
Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

pubs.acs.org/IC

On the Mechanism of Trimethylphosphine-Mediated Reductive Dimerization of Ketones Arturo Espinosa Ferao* Department of Organic Chemistry, Faculty of Chemistry, University of Murcia, Campus de Espinardo, 30071 Murcia, Spain

Downloaded via DURHAM UNIV on July 12, 2018 at 09:21:48 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

S Supporting Information *

ABSTRACT: High-level single-reference calculations reveal that trimethylphosphinemediated reductive dimerization of properly substituted (e.g., CF3) ketones proceeds via initial formation of an oxaphosphirane intermediate, with the oxygen atom occupying an equatorial position at phosphorus. In the “oxirane route”, this oxaphosphirane intermediate loses a trimethylphosphine oxide unit, thus behaving as a carbene transfer agent toward a second carbonyl molecule and giving rise to a carbonyl ylide that cyclizates to the corresponding oxirane. This in turn transfers the carbene unit to a second phosphine molecule, with loss of acetone, affording a phosphorane. The latter undergoes typical Wittig reaction to the final homocoupling product through the oxaphosphetane intermediate. The alternative direct conversion of oxaphosphirane into phosphorane constitutes the lowest energy path as it skips the highest barrier oxirane → phosphorane conversion. The oxirane route is favored by the use of polar solvents and electron deficient carbonyl components. The lowest barrier most exergonic process from oxaphosphirane is the pericyclic cycloaddition of the acetone C O bond along the endocyclic P−C bond, furnishing the stable 1,3,2-dioxaphospholane product.

■

reactions of this type have been used to obtain stilbenes,5 tetrathiofulvalenes (TTF),6 and isoindigo derivatives,7 whereas extended TTF derivatives,8 dithiafulvenes (DTF),8,9 and other nonsymmetric CC bonds10 can be achieved via heterocoupling of two different carbonyl units. The main disadvantage is that the method seems to be strongly dependent on the chalcogenone type (ketone/thione/ selenone)11 and of the substitution at the chalcogenone.12 On the basis of experimental observations, an early proposed mechanism for the reaction of thioketones with phosphites13 suggests initial chalcogenophilic attack of the P(III) reagent to afford an ylide AS (the subscript standing for the chalcogen atom type) which, in turn, reacts with a second thioketone, giving rise to 1,3,2-dithiaphospholane BS (Scheme 1). This loses a thiophosphate unit, yielding the three-membered thiirane CS that undergoes phosphite-mediated desulfurization

INTRODUCTION Carbon−carbon bond forming processes are of paramount relevance in organic synthesis. Pinacol coupling1 of two carbonyl units to furnish symmetrically substituted 1,2-diols is a classical representative of this type of reactions. The mechanism involves initial homolytic cleavage of the carbonyl π-bond in the presence of a reductive metal to give a metalbound ketyl radical. In the case of divalent metals, coupling of two such fragments can occur intramolecularly in a metalbridged bis-ketyl diradical species, affording the 1,2-diol chelate I (Figure 1). When appropriate transition metals are

Figure 1. Proposed intermediates in the pinacol and related coupling reactions.

Scheme 1. Proposed Mechanism for the P(III)-Mediated Reductive Dimerization of Chalcogenones According to Reported Observations

used in reductive conditions, the metal atom is inserted into the carbonyl π-bond, giving rise to a metallaoxirane2 II, representing an umpoled carbonyl unit that can thereafter react with a second non-umpoled carbonyl molecule. A related reaction is McMurry coupling3 in which two carbonyl units undergo reductive dimerization in the presence of TiCl3, or TiCl4 and a reducing metal such as zinc, to give an olefin. This reaction involves a polar rather than radical mechanism starting from a titanaoxirane II (M = TiCl2) as precursor for I, as demonstrated by Frenking through theoretical studies.4 Similarly, carbonyl compounds as well as their thia- and selena-analogues undergo reductive dimerization in the presence of P(III) reagents to give olefins. Homocoupling © XXXX American Chemical Society

Received: November 5, 2017

A

DOI: 10.1021/acs.inorgchem.7b02816 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Supporting Information). Also, SCS-MP233 and PWPB95-D334 methods were checked for comparison, with rmsd values of 0.32/ 0.40 and 0.31/0.34 kcal/mol, respectively (def2-TZVPP/def2QZVPP basis set). The B3LYP-D3 method (rmsd = 0.74/0.73 kcal/mol with def2-TZVPP/def2-QZVPP basis set) turned out to be the least accurate for the above-mentioned set of data. Electric charges were computed using the Mulliken population analysis.35 Bond strengths were indicated by using Mayer bond orders (MBO)36 computed at the B3LYP-D3/def2-TZVPP level. Bader’s AIM (atomsin-molecules) derived topological analysis of the electron density37 was conducted with AIMAll.38 Figure 3 was obtained with VMD.39

to the alkene via the sequential formation of betaine DS and 1,2-thiaphosphetane ES. The intermediacy of isomeric betaines AO and A′O in equilibrium14 has been used to explain the formation of isomeric 1,3,2- (BO) and 1,4,2-dioxaphospholanes (B′O), respectively, in the case of carbonyl compounds with electron deficient substituents,15 while formation of AO from the initially generated isomer A′O has been also recently suggested.5b Oxiranes (CO) have been isolated in the reaction of isatines with amino-substituted P(III) reagents and their formation alternatively explained via a carbene intermediate, generated from AO upon loss of the P(V) fragment.7c The likely intermediacy of such a carbene was confirmed by trapping with fullerene C60.16 Three-membered oxaphosphirane rings (FO) were proposed15b,17 as precursors for zwitterionic species AO/A′O; their existence was proved by early MO calculations (HF/3-21G*) for the reaction between formaldehyde and phosphorous acid18 and, very recently, as intermediates in the Perkow reaction of chloroacetone with trimethylphosphite.19 Heavier chalcogenaphosphiranes F were also experimentally reported.20 As carbonyl compounds (X: O) are, by far, the most common chacogenones, herein a single-reference high-level calculation of the potential energy surface (PES) for the reaction between acetone and trimethylphosphine is reported, including the effect of typical solvents used in this kind of reactions (toluene, THF, and CH2Cl2 were checked), providing the explanation for both the final product formation and the isolation of intermediates in some cases. Further studies will be devoted to heavier chalcogenones.

■

■

RESULTS AND DISCUSSION Main “Oxirane” Path. The approach of trimethylphosphine (2) to acetone (1) gives σ5,λ5-oxaphosphirane 3ax as the only product through a chelotropic reaction19 (Scheme 2), Scheme 2. Proposed Mechanism for the Trimethylphosphine-Mediated Conversion of Ketone 1 into Its Reductive Homocoupling Product 9

irrespective of the relative orientation of reagents, thus ruling out the existence of previously reported zwitterionic species (A/A′, Scheme 1) as initial intermediates. Compound 3ax features the O atom in axial position (dP−O = 1.797 Å; MBO = 0.693; no BCP found), in line with the well-known preferential location for the most electronegative P-substituent,40 the ring C atom occupying an equatorial position (dP−C = 1.769 Å; MBO = 1.006; ρ(r) = 0.1787 e/a03). Stepwise elongation of the P−O bond cleaves the ring back to its constituents 1 and 2, whereas P−C elongation promotes pseudorotation at P, affording the slightly less stable isomer 3eq (Figure 2) that locates the O atom in an equatorial position (dP−O = 1.627 Å; MBO = 1.138; ρ(r) = 0.1749 e/a03) and features a weakened axial P−C bond (dP−C = 1.842 Å; MBO = 0.904; ρ(r) = 0.1507 e/a03). This further confirms the inexistence of zwitterionic intermediates. One of the possible paths for reaction of 3ax, through its slightly less stable isomer 3eq, is the nucleophilic attack of 1 at the ring C atom (see the Supporting Information) with loss of trimethylphosphine oxide (5) to afford the carbonyl ylide 4, that has been described as a highly colored intermediate typically formed in the photodecomposition of oxiranes.41 This process can be formally viewed as a carbene transfer reaction from the oxaphosphirane 3eq to the nucleophilic O atom of the carbonyl unit 1, thus giving support to the experimentally observed carbene trapping reactivity in the presence of fullerene C60.16 Due to its 4π electron configuration, this oxirane valence isomer 4 features a HOMO in antiphase with respect to the termini of the π system (Figure 3), which determines the stereospecificity for its conversion into oxirane 6 through a very exergonic low-barrier conrotatory electrocyclization.42 As expected, carbonyl ylide 4 features a partially unsaturated C−O bond character (d = 1.321 Å, MBO = 1.177; ρ(r) = 0.2948 e/a03) in between the formal single bond in 6 (d = 1.443 Å, MBO = 0.927; ρ(r) = 0.2472 e/a03), and the formal

EXPERIMENTAL SECTION

Computational Details. DFT calculations were performed with the ORCA program package.21 All geometry optimizations were run in redundant internal coordinates with tight convergence criteria, in the gas phase, and using the B3LYP functional22 with the powerfully speeding up RIJCOSX algorithm23 and the Ahlrichs’ segmented def2TZVP basis set.24 The latest Grimme’s semiempirical atom-pairwise London dispersion correction (DFT-D3) was included in all optimizations and energy evaluations,25 taking into account the major part of the contribution of dispersion forces to the energy. Harmonic frequency calculations verified the nature of the computed species as minima or TS (transition state) structures, featuring none or only one negative eigenvalue, respectively. Moreover, all TS structures were confirmed by intrinsic reaction coordinate (IRC) calculations. From these optimized geometries, all reported data were obtained by means of single-point (SP) calculations using the more flexible and polarized def2-TZVPP or def2-QZVPP26 basis set. Reported energies include the zero-point vibrational term correction (see the Supporting Information) or the correction to the Gibbs free energy at the optimization level, and were obtained by means of the recently developed near linear scaling domain-based local pair natural orbital (DLPNO) method27 to achieve coupled cluster theory with single-double and perturbative triple excitations (CCSD(T)).28 This model chemistry, together with the def2-QZVPP basis set, constitutes the working level of theory along all the text. Where appropriate, solvent effects were computed using the COSMO solvation model.29 Local correlation schemes of type LPNO (Local Pair Natural Orbital) for high level single-reference methods,30 such as CEPA (Coupled Electron-Pair Approximation), here the slightly modified NCEPA/1 version31 implemented in ORCA was used, were computed for comparison. Very close values between these two levels have been systematically reported for closed-shell systems with rmsd (rootmean-square deviation) typically below 0.2 kcal/mol,19,32 and for this particular case amounts to 0.31 kcal/mol (0.37 kcal/mol with the def2-TZVPP basis set), taking the CCSD(T)/def2-QZVPP level as reference for a set of 37 nonzero relative energy values (see the B

DOI: 10.1021/acs.inorgchem.7b02816 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 2. Computed (DLPNO-CCSD(T)/def2-QZVPP) gas phase Gibbs free energy profile for the transformation of 1 into 9.

2, located 8.30 kcal/mol above the separated reagents, is considered as reference. Finally, phosphorane 7 reacts with a molecule of the carbonyl component 1 following a typical Wittig reaction mechanism44 through the 1,2-oxaphosphetane intermediate 8 and affording the alkene product 9. Only one oxaphosphetane isomer was located in the PES at the working level of theory, this featuring the O atom in an axial position around the P atom. Decomposition of the oxaphosphetane has a lower barrier (ΔGTS = 26.54 kcal/mol) than the transformation of 3eq into 4 or 7. 2. Carbonyl Heterocouplings. Although the full mechanism has been studied only for acetone as carbonyl component, the three only steps where the carbonyl unit is directly involved as reactant were additionally explored for a different ketone. With this aim, hexafluoroacetone 1F was chosen as well-defined electron deficient carbonyl reagent. The expected nucleophilic role of the carbonyl group (via the O atom) of acetone (1) in the reaction with intermediate 3eq (ΔGTS = 36.77 kcal/mol), the ring C atom acting as electrophilic center, agrees with the slightly higher energy barrier in the case of electron deficient 1F (ΔGTS = 39.27 kcal/ mol). Nevertheless, this is mainly due to a different mechanism as the ring C atom attacks nucleophilically (indeed HOMO in 3eq is essentially an endocyclic σ(C−P) bond mainly located at C) to the electrophilic carbonyl O atom in 1F, giving rise to the zwitterionic species 10F (Scheme 3) in an almost thermoneu-

Figure 3. Computed (B3LYP-D3/def2-TZVP) Kohn−Sham isosurface (0.04 au isovalue) for the HOMO in carbonyl ylide 4.

double bond in 1 (d = 1.209 Å, MBO = 2.134; ρ(r) = 0.4244 e/a03). Subsequent nucleophilic attack of phosphine 2 to one of the ring C atoms in oxirane 6 promotes consecutive C−O and C− C bond cleavage, leading to phosphorane 7 upon loss of a carbonyl unit 1. The later constitutes the rate-determining step for this path (ΔGTS = 48.12 kcal/mol), in agreement with the experimental isolation, in certain cases, of the oxirane intermediate. Worth mentioning is that no betaine intermediate has been located at the working level of theory upon reaction of oxirane 6 with phosphine 2 (vide infra), in contrast to common belief.43 Phosphorane 7 can be alternatively formed from the most reactive (unstable) oxaphosphirane isomer 3eq upon direct reaction with phosphine 2 attacking at the ring C atom with loss of phosphine oxide 5. Again, this entails a formal carbene transfer reaction from 3eq to the nucleophilic phosphorus center in the phosphine reagent, although a carbene species as such was never found as intermediate. The later 3eq → 7 direct path features a slightly higher energy barrier (ΔGTS = 38.86 kcal/mol) than the first step of the alternative stepwise 3eq → 4 → 6 → 7 conversion (ΔGTS = 36.76 kcal/mol) but skips the slowest 6 → 7 step (vide supra), therefore constituting the overall minimum energy (preferred) path to phosphorane 7 in the gas phase. Furthermore, this tiny preference for the conversion of 3eq into 4 over 7 (ΔΔGTS = −2.09 kcal/mol) is reversed as the solvent polarity increases (ΔΔGTS = −0.92/+0.36/+0.73 kcal/mol for toluene/THF/CH2Cl2, respectively), with respect to the gasphase reaction, and hence, the path through oxirane 6 is expected to be unfavored in dichloromethane and other polar solvents. The high energy content of the key initial oxaphosphirane intermediate constitutes the main drawback of the herein presented mechanistic proposal, although all relative energies are significantly reduced if the initial van der Waals complex 1·

Scheme 3. Proposed Mechanism for the Reaction of Ketone 1F with Oxaphosphirane 3eq

tral reaction (ΔG = −2.44 kcal/mol) (Figure 4). The electronic structure of 10F is supported by the Mulliken atomic charge variation at C with respect to 1F (Δq = −0.23 au) and at P with respect to 3eq (Δq = 0.10 au), as well as the remarkable pyramidalization at the tricoordinated C atom (sum of bond angles 333.3°). It features a short covalent P−O bond (d = 1.581 Å; MBO = 1.279; ρ(r) = 0.1924 e/a03) and a longer (noncovalent) essentially electrostatic P···O interaction C

DOI: 10.1021/acs.inorgchem.7b02816 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

12F. This dipolar species 12F then reacts with dipolarophile 1F, affording 1,3,2-dioxaphospholane 13F. The energy profile (Figure 4) shows the initial oxaphosphirane 3Fax formation as the rate-determining step and all subsequent being rather fast, in perfect agreement with the experimental observation of this reaction taking place at low temperature (observed even at −70 °C).15a Finally, in the third process involving the carbonyl component, the reaction of phosphorane 7 with the electron poor ketone 1F to give the fluorinated oxaphosphetane 8F, the process turns out to be barrierless and much more exergonic (ΔG = −29.01 kcal/mol) than the all-methyl case 7 + 1 → 8 (ΔG = −12.78 kcal/mol). This is due to the advanced C−C bond forming character of this step, therefore relying in the behavior of the carbonyl component as electrophile toward the nucleophilic phosphorane. Thus, this “oxirane route” would be favored in the case of electron deficient carbonyl components, in addition to when performing the reaction in the gas phase or apolar solvents (vide supra). 3. The 1,3,2-Dioxaphospholane Path. Insertion of a carbonyl C−O bond into the weakest endocyclic (axial) P−C bond of oxaphosphirane 3eq (Scheme 5)32c proceeds as

Figure 4. Computed (DLPNO-CCSD(T)/def2-QZVPP) gas phase Gibbs free energy profile for the transformation of 3eq and 1F into 4F.

(d = 2.480 Å; MBO = 0.115; no BCP found; qP = 0.62 au; qO = −0.41 au), the later preventing the formation of a P−C bond that would lead to 1,3,4-dioxaphospholane 11F. Moreover, 10F easily collapses (ΔGTS = 5.14 kcal/mol) by losing a Me3PO (5) unit to give the nonsymmetric carbonyl ylide 4F (Scheme 3) as precursor for the corresponding oxirane 6F (not computed). The proposed formulation for 4F is based in the significantly larger (CF3)2C−O distance (1.358 Å; MBO = 0.981; ρ(r) = 0.2613 e/a03) compared to that of the Me2C−O linkage (1.275 Å; MBO = 1.417; ρ(r) = 0.3323 e/a03), approaching typical values for purely C−O single and double bonds, respectively (e.g., 1.421 Å for methanol and 1.209 Å for acetone, at the same level), and the remarkable pyramidalization of the bis-trifluoromethyl-substituted C atom with respect to the planar dimethyl-substituted one (sum of bond angles 350.5° and 359.9°, respectively), featuring the expected (Mulliken) electric charge separation (qC = −0.19 and +0.22 au, respectively). On the contrary, the reaction of 1F with phosphine 2 turned out to be much faster, very low barrier (ΔGTS = 13.23 kcal/ mol) (Scheme 4, Figure 5), than the reference reaction of

Scheme 5. Proposed Alternative Mechanism for the Transformation of 3eq into 7

Scheme 4. Proposed Mechanism for the Reaction of Ketone 1F with Oxaphosphirane 3eq unprecedented pericyclic 2π(CO) + 2σ(P−C) cycloaddition and exergonically furnishes 1,3,2-dioxaphospholane 13. This conversion of 3eq into 13 has a lower barrier (ΔGTS = 31.34 kcal/mol) than the above-mentioned transformation into 4 (ΔGTS = 36.76 kcal/mol) (Figure 2), although the barrier difference (ΔΔGTS = 5.42 kcal/mol) computed in the gas phase decreases with solvent polarity (ΔΔGTS = 4.91/3.20/ 2.04 kcal/mol for toluene/THF/CH2Cl2, respectively), so that predominant formation of 13 over 4 might be expected, especially in the gas phase or apolar solvents and under kinetic control conditions. Nucleophilic attack of the phosphine 2 reagent to one of the ring C atoms in 13 promotes cleavage of the heterocycle to afford the antiperiplanar betaine 14, which is unstable as an isolated species (vide supra) but here is formed as the (stable) van der Waals complex (featuring four C−H··· O bonds) with phosphine oxide, 14·5. The phosphine oxidetemplated cleavage of the C−C bond in 14 furnishes phosphorane 7 (Scheme 5). Nevertheless, the high energy barrier required for the 13 → 14·5 step makes dioxaphospholane 13 kinetically (besides thermodynamically) stable and the reason why it can be easily detected or experimentally isolated,7c its transformation into the final alkene 9 requiring additional heating.5b Out of the kinetic control regime but below the temperature required for overcoming the 13 → 14·5 barrier, it can be expected that formation of the minor species 4 should constitute an alternative preferential transformation pathway to phosphorane 7 and hence to the final alkene 9.

Figure 5. Computed (DLPNO-CCSD(T)/def2-QZVPP) gas phase Gibbs free energy profile for the transformation of 1F and 2 into 13F.

acetone 1 (Figure 2), in agreement with the enhanced character as electrophile of the electron poor ketone 1F. Isomerization of the resulting oxaphosphirane 3Fax to 3Feq weakens the endocyclic P−C bond that easily cleaves up to D

DOI: 10.1021/acs.inorgchem.7b02816 Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

■

4. Formation of the Betaine. Cleavage of oxaphosphetane 8 can alternatively proceed by heteropolar fragmentation of the P−O linkage via rotation of the C−C endocyclic bond and leading to the gauge (synclinal) conformer of the betaine 14g (Scheme 6). Nevertheless, this process is remarkably

ACKNOWLEDGMENTS Technical support and the computational resources used from ́ the computation centre at Servicio de Cálculo Cientifico (SCC - University of Murcia) are deeply acknowledged.

Scheme 6. Formation of the gauche-Betaine 14g

DEDICATION Dedicated to Prof. Rainer Streubel on the occasion of his 60th birthday.

■ ■

ABBREVIATIONS PES, potential energy surface; MBO, Mayer bond order; TS, transition state; BCP, bond critical point; THF, tetrahydrofuran

endergonic and entails a higher energy barrier than the aforementioned retro-cycloaddition to 9 (and 5) (Figure 2) and hence is very unlikely to occur. Moreover, further increase of the P−C−C−O dihedral in 14g promotes cleavage of the central C−C bond into fragments 1 and 7.

■

■

CONCLUSIONS Trimethylphosphine-mediated reductive dimerization of properly substituted (e.g., CF3) ketones proceeds by initial chelotropic cycloaddition through an oxaphosphirane 3eq key intermediate. In the “oxirane route”, an oxirane 6 is formed upon cyclization of a carbonyl ylide 4, resulting from carbene transfer from intermediate 3eq (losing a trimethylphosphine oxide unit, 5) toward a second carbonyl molecule. A second carbene transfer from 6 (losing acetone) to another phosphine molecule is the rate-determining step of this route and affords phosphorane 7. This thereafter undergoes a typical Wittig reaction through the oxaphosphetane intermediate 8. The alternative direct P(III)-mediated deoxygenation of oxaphosphirane 3eq into phosphorane 7 constitutes the lowest energy path. Use of polar solvents (e.g., CH2Cl2) and electron deficient carbonyl components favors the oxirane route. The lowest barrier most exergonic process from 3eq is the pericyclic cycloaddition of the acetone CO bond along the endocyclic P−C bond, furnishing the stable 1,3,2-dioxaphospholane product 13, thus explaining isolation of these derivatives in some cases.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02816.

■

REFERENCES

(1) (a) Fittig, R. Ü ber einige Producte der trockenen Destillation essigsaurer Salze. Justus Liebigs Ann. Chem. 1859, 110, 17−23. (b) Wang, Z. Pinacol Coupling Reaction. In Comprehensive Organic Name Reactions and Reagents; John Wiley & Sons, Inc.: Hoboken, NJ, 2010. (2) Askham, F. R.; Carroll, K. M. Anionic zirconaoxiranes as nucleophilic aldehyde equivalents. Application to intermolecular pinacol cross coupling. J. Org. Chem. 1993, 58, 7328−7329. (3) McMurry, J. E.; Fleming, M. P. New method for the reductive coupling of carbonyls to olefins. Synthesis of β-carotene. J. Am. Chem. Soc. 1974, 96, 4708−4709. (b) Ephritikhine, M. A new look at the McMurry reaction. Chem. Commun. 1998, 2549−2554. (4) Stahl, M.; Pidun, U.; Frenking, G. On the Mechanism of the McMurry Reaction. Angew. Chem., Int. Ed. Engl. 1997, 36, 2234− 2237. (5) (a) Liu, W.; Tu, S.; He, T.; Zhao, Y.; Hu, H. The stereoselective synthesis of e-1,2-bis(3-indolizinyl)ethylenes by the reactions of 3thioformylindolizines with n-tributylphosphine. J. Heterocycl. Chem. 2008, 45, 1311−1314. (b) Petersen, J. F.; Tortzen, C. G.; Jørgensen, F. P.; Parker, C. R.; Nielsen, M. B. Phosphite-mediated conversion of benzaldehydes into stilbenes via umpolung through a dioxophospholane intermediate. Tetrahedron Lett. 2015, 56, 1894−1897. (6) Fabre, J. M. Synthesis Strategies and Chemistry of Nonsymmetrically Substituted Tetrachalcogenafulvalenes. Chem. Rev. 2004, 104, 5133−5150 and references cited therein. (7) (a) Bogdanov, A. V.; Bukharov, S. V.; Oludina, Y. N.; Musin, L. I.; Nugumanova, G. N.; Syakaev, V. V.; Mironov, V. F. A catalyst-free and easy nucleophilic addition of certain isatins to sterically hindered 2,6-di-tert-butyl-4-methylenecyclohexa-2,5-dienone. ARKIVOC 2013, iii, 424−435. (b) Bogdanov, A. V.; Musin, L. I.; Il’in, A. V.; Mironov, V. F. Novel 1-Aminomethylisatins: Peculiarities of the Synthesis and the Reaction with Tris(diethylamino)phosphine. J. Heterocyclic Chem. 2014, 51, 1027−1030. (c) Musin, L. I.; Bogdanov, A. V.; Krivolapov, D. B.; Dobrynin, A. B.; Litvinov, I. A.; Mironov, V. F. Effect of the Substituent on the Phosphorus Atom on the Reaction of Aminophosphines with 1-Alkylisatins. Russ. J. Org. Chem. 2014, 50, 822− 828. (8) (a) Müller, H.; Salhi, F.; Divisia-Blohorn, B. Bis-substituted Tetrathiapentalenes - Novel Building Blocks for Extended Tetrathiafulvalenes and Conducting Polymers. Tetrahedron Lett. 1997, 38, 3215−3218. (b) Schou, S. S.; Parker, C. R.; Lincke, K.; Jennum, K.; Vibenholt, J.; Kadziola, A.; Nielsen, M. B. On the Phosphite-Mediated Synthesis of Dithiafulvenes and π-Extended Tetrathiafulvalenes. Synlett 2013, 24, 231−235. (9) (a) Imakubo, T.; Iijima, T.; Kobayashi, K.; Kato, R. A new synthetic route to TTF-vinylogues. Synth. Met. 2001, 120, 899−900. (b) Leriche, P.; Roquet, S.; Pillerel, N.; Mabon, G.; Frère, P. New extended analogues of TTF via triethylphosphite-mediated reaction. Tetrahedron Lett. 2003, 44, 1623−1626. (c) Sorohhov, G.; Yi, C.; Grätzel, M.; Decurtins, S.; Liu, S.-X. A hybrid electron donor comprising cyclopentadithiophene and dithiafulvenyl for dyesensitized solar cells. Beilstein J. Org. Chem. 2015, 11, 1052−1059.

Energetics at different computational levels; energy profiles with lower basis set and with solvent (COSMO) efects; Cartesian coordinates and energies for all computed species (PDF)

AUTHOR INFORMATION

Corresponding Author

*Tel: +34 868 887489. Fax: +34 868 884149. E-mail: [email protected]. ORCID

Arturo Espinosa Ferao: 0000-0003-4452-0430 Funding

This work did not receive any financial support. Notes

The author declares no competing financial interest. E

DOI: 10.1021/acs.inorgchem.7b02816 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (10) Xia, Z.; Long, S.; Xiao, S.; Zou, X.; D’aurizio, A.; Panunzio, M. Microwave-Assisted Carbonyl−Carbonyl Coupling Route for the Preparation of a Useful Intermediate in the Synthesis of Carbapenems. Synth. Commun. 2009, 39, 2151−2160. (11) Fettouhi, M.; Ouahab, L.; Serhani, D.; Fabre, J. M.; Ducasse, L.; Amiell, J.; Canet, R.; Delhaes, P. Structural and physical properties of BEDO-TTF charge-transfer salts: κ-phase with CF3SO3−. J. Mater. Chem. 1993, 3, 1101−1107. (12) (a) Spencer, H. K.; Cava, M. P.; Garito, A. F. Organic metals: synthesis of benzotetrathiafulvalene. J. Chem. Soc., Chem. Commun. 1976, 966−967. (b) Gonnella, N. C.; Cava, M. P. Organic metals: A general synthesis of unsymmetrical tetrathiafulvalenes. J. Org. Chem. 1978, 43, 369−370. (13) McCullough, R. D.; Petruska, M. A.; Belot, J. A. Investigating the Synthesis of Unsymmetrical Tetrathiafulvalene Derivatives: Improved Yields by the Hidden Equivalent Method. Tetrahedron 1999, 55, 9979−9998. (14) Ramirez, F.; Gulati, A. S.; Smith, P. C. Reaction of tris(dialkylamino)phosphines with aromatic aldehydes. I. Nitrobenzaldehydes. Formation of 2,2,2-triamino-1,3,2-dioxaphospholanes and their conversion into epoxides. J. Org. Chem. 1968, 33, 13−19. (15) (a) Ramirez, F.; Smith, P. C.; Pilot, J. F.; Gulati, A. S. Reaction of tertiary phosphines with hexafluoroacetone and with o-quinones. Attack by phosphorus on carbonyl oxygen and isolation of 2,2,2trialkyl-2,2-dihydro-1,3,2-dioxaphospholanes. J. Org. Chem. 1968, 33, 3787−3794. (b) Kibardin, A. M.; Gazizov, T. K.; Efremov, Y. Y.; Zinin, V. N.; Musin, R. Z.; Pudovik, A. N. Reaction of trialkyl phosphites with 1,1,1-trifluoroacetone. Bull. Acad. Sci. USSR, Div. Chem. Sci. 1980, 29, 656−660. (16) (a) Romanova, I. P.; Bogdanov, A. V.; Mironov, V. F.; Larionova, O. A.; Latypov, S. K.; Balandina, A. A.; Yakhvarov, D. G.; Sinyashin, O. G. Fullerene C60 as an effective trap of acenaphthenone carbene generated in the reaction of acenaphthenequinone with hexaethyltriaminophosphine. Mendeleev Commun. 2009, 19, 306−308. (b) Romanova, I. P.; Bogdanov, A. V.; Mironov, V. F.; Shaikhutdinova, G. R.; Larionova, O. A.; Latypov, S. K.; Balandina, A. A.; Yakhvarov, D. G.; Gubaidullin, A. T.; Saifina, A. F.; Sinyashin, O. G. Deoxygenation of some α-dicarbonyl compounds by tris(diethylamino) phosphine in the presence of fullerene C60. J. Org. Chem. 2011, 76, 2548−2557. (17) Boisdon, M. T.; Barrans, J. Unexpected Reaction between Benzaldehyde and 2,4,4,5,5-Pentamethyl-l,3,2-dioxaphospholane leading to a Phospha(v)oxirane Dimer. J. Chem. Soc., Chem. Commun. 1988, 615−617. (18) Chang, J.-W. A.; Taira, K.; Urano, S.; Gorenstein, D. G. Stereoelectronic Effects on the Nucleophilic Addition of Phosphite to the Carbonyl Double Bond: Ab Initio Molecular Orbital Calculations on Reaction Surfaces and the α-Effect. Tetrahedron 1987, 43, 3863− 3874. (19) Espinosa Ferao, A. Comparative computational study on the reaction of chloroacetone with trimethylphosphite: Perkow versus Michaelis-Arbuzov reaction paths. J. Phys. Chem. A 2017, 121, 6517− 6522. (20) (a) Sase, S.; Kano, N.; Kawashima, T. Synthesis and Structure of the First 1,2σ5-Selenaphosphirane. J. Am. Chem. Soc. 2002, 124, 9706−9707. (b) Sase, S.; Kano, N.; Kawashima, T. Synthesis of the First Stable Pentacoordinate Selenaphosphirane. Phosphorus, Sulfur Silicon Relat. Elem. 2002, 177, 2039−2040. (c) Sase, S.; Kano, N.; Kawashima, T. Isolation of a cyclic intermediate in the reaction of a phosphorus ylide with elemental sulfur: Synthesis, structure, and reactivity of a 1,2σ5-thiaphosphirane. Chem. Lett. 2004, 33, 1434− 1435. (d) Takayuki, K. New Aspects in the Chemistry of Threemembered Ring Compounds Containing a Highly Coordinate Main Group Element. Chin. J. Chem. 2005, 23, 1267−1269. (21) (a) Neese, F. ORCA - An ab initio, DFT and semiempirical SCFMO package, Version 3.0.3; Max Planck Institute for Chemical Energy Conversion: Mülheim an der Ruhr, Germany, 2012. http://www.cec. mpg.de/forum/portal.php. (b) Neese, F. The ORCA program system. WIREs Comput. Mol. Sci. 2012, 2, 73−78.

(22) (a) Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648−5652. (b) Lee, C. T.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (23) Neese, F.; Wennmohs, F.; Hansen, A.; Becker, U. Efficient approximate and parallel Hartree-Fock and hybrid DFT calculations. A ’chain-of-spheres’ algorithm for the Hartree-Fock exchange. Chem. Phys. 2009, 356, 98−109. (24) (a) Schaefer, A.; Horn, H.; Ahlrichs, R. Fully optimized contracted Gaussian basis sets for atoms Li to Kr. J. Chem. Phys. 1992, 97, 2571−2577. (b) Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297−3305. (25) (a) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104−19. (b) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the damping function in dispersion corrected density functional theory. J. Comput. Chem. 2011, 32, 1456−1465. (26) (a) Schäfer, A.; Huber, C.; Ahlrichs, R. Fully optimized contracted Gaussian basis sets of triple zeta valence quality for atoms Li to Kr. J. Chem. Phys. 1994, 100, 5829−5835. Basis sets may be obtained from the Basis Set Exchange (BSE) software and the EMSL Basis Set Library: https://bse.pnl.gov/bse/portal. (b) Feller, D. The role of databases in support of computational chemistry calculations. J. Comput. Chem. 1996, 17, 1571−1586. (27) Riplinger, C.; Sandhoefer, B.; Hansen, A.; Neese, F. Natural triple excitations in local coupled cluster calculations with pair natural orbitals. J. Chem. Phys. 2013, 139, 134101−134113. (28) Pople, J. A.; Head-Gordon, M.; Raghavachari, K. Quadratic configuration interaction. A general technique for determining electron correlation energies. J. Chem. Phys. 1987, 87, 5968−5975. (29) (a) Klamt, A.; Schüürmann, G. COSMO: a new approach to dielectric screening in solvents with explicit expressions for the screening energy and its gradient. J. Chem. Soc., Perkin Trans. 2 1993, 220, 799−805. (b) Klamt, A. Conductor-like screening model for real solvents: a new approach to the quantitative calculation of solvation phenomena. J. Phys. Chem. 1995, 99, 2224−2235. (30) (a) Neese, F.; Wennmohs, F.; Hansen, A. Efficient and accurate local approximations to coupled-electron pair approaches: An attempt to revive the pair natural orbital method. J. Chem. Phys. 2009, 130, 114108. (b) Neese, F.; Hansen, A.; Wennmohs, F.; Grimme, S. Accurate theoretical chemistry with coupled pair models. Acc. Chem. Res. 2009, 42, 641−648. (31) Wennmohs, F.; Neese, F. A comparative study of single reference correlation methods of the coupled-pair type. Chem. Phys. 2008, 343, 217−230. (32) (a) Alfonso, M.; Espinosa, A.; Tárraga, A.; Molina, P. Multifunctional Benzothiadiazole-based Small Molecules Displaying Solvatochromism and Sensing Properties toward Nitroarenes, Anions and Cations. ChemistryOpen 2014, 3, 242−249. (b) Murcia García, C.; Espinosa Ferao, A.; Schnakenburg, G.; Streubel, R. CPh3 as a functional group in P-heterocyclic chemistry: elimination of HCPh3 in the reaction of P-CPh3 substituted Li/Cl phosphinidenoid complexes with Ph2CO. Dalton Trans. 2016, 45, 2378−2385. (c) Malik, P.; Espinosa Ferao, A.; Schnakenburg, G.; Streubel, R. Cycloaddition of P-C single bonds. Stereoselective formation of novel benzo-1,3,6,2trioxaphosphepine complexes via a ditopic van der Waals complex. Angew. Chem., Int. Ed. 2016, 55, 12693−12697. (d) Espinosa Ferao, A.; Streubel, R. Thiaphosphiranes and their complexes: systematic study on ring strain and ring cleavage reactions. Inorg. Chem. 2016, 55, 9611−9619. (e) Espinosa Ferao, A.; Streubel, R. A computational study on the stability of oxaphosphirane rings towards closed-shell valence isomerization. Eur. J. Inorg. Chem. 2017, 2017, 2707−2712. (f) Espinosa Ferao, A.; Streubel, R. Coordination of N2 and other small molecules to the phosphorus center of RPW(CO)5 - A F

DOI: 10.1021/acs.inorgchem.7b02816 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry theoretical study on the Janus facets of the stabilization/activation problem. Chem. - Eur. J. 2017, 23, 8632−8643. (33) (a) Grimme, S. Improved second-order Møller−Plesset perturbation theory by separate scaling of parallel- and antiparallelspin pair correlation energies. J. Chem. Phys. 2003, 118, 9095−9102. (b) Grimme, S.; Goerigk, L.; Fink, R. F. Spin-component-scaled electron correlation methods. WIREs Comput. Mol. Sci. 2012, 2, 886− 906. (34) (a) Goerigk, L.; Grimme, S. Efficient and accurate doublehybrid-meta-GGA density functionals - Evaluation with the extended GMTKN30 database for general main group thermochemistry, kinetics, and noncovalent interactions. J. Chem. Theory Comput. 2011, 7, 291−309. (b) Goerigk, L.; Grimme, S. A thorough benchmark of density functional methods for general main group thermochemistry, kinetics, and noncovalent interactions. Phys. Chem. Chem. Phys. 2011, 13, 6670−6688. (35) Mulliken, R. S. Electronic population analysis on LCAO−MO molecular wave functions. I. J. Chem. Phys. 1955, 23, 1833−1840. (36) (a) Mayer, I. Charge, bond order and valence in the AB initio SCF theory. Chem. Phys. Lett. 1983, 97, 270−274. (b) Mayer, I. Bond order and valence: Relations to Mulliken’s population analysis. Int. J. Quantum Chem. 1984, 26, 151−154. (c) Mayer, I. Bond orders and valences in the SCF theory: a comment. Theor. Chim. Acta 1985, 67, 315−322. (d) Mayer, I. In Modelling of Structure and Properties of Molecules; Maksic, Z. B., Ed.; John Wiley & Sons: New York, 1987. (37) (a) Bader, R. F. W. In Atoms in Molecules: A Quantum Theory; Oxford University Press: Oxford, U.K., 1990. (b) Bader, R. F. W. A quantum theory of molecular structure and its applications. Chem. Rev. 1991, 91, 893−928. (c) Matta, C. F.; Boyd, R. J. In The Quantum Theory of Atoms in Molecules; Matta, C. F., Boyd, R. J., Eds.; WileyVCH: New York, 2007; pp 1−34. (38) Keith, T. A. AIMAll, Version 14.06.21; TK Gristmill Software: Overland Park, KS, 2014. aim.tkgristmill.com. (39) Humphrey, W.; Dalke, A.; Schulten, K. VMD: Visual molecular dynamics. J. Mol. Graphics 1996, 14, 33−38. Home page: http:// www.ks.uiuc.edu/Research/vmd/. (40) (a) Ramirez, F.; Madan, O. P.; Heller, S. R. A Crystalline Tetraalkoxyalkylphosphorane from the Reaction of Trimethyl Phosphite with an α,β-Unsaturated Ketone. 3-Benzylidene-2,4pentanedione. P31 and H1 Nuclear Magnetic Resonance Spectra. J. Am. Chem. Soc. 1965, 87, 731−734. (b) Schmutzler, R. Chemistry and Stereochemistry of Fluorophosphoranes. Angew. Chem., Int. Ed. Engl. 1965, 4, 496−508. (c) Gorenstein, D. G.; Westheimer, F. H. Inhibited pseudo-rotation in a cyclic monoalkyphosphorane. J. Am. Chem. Soc. 1967, 89, 2762−2764. (d) Westheimer, F. H. Pseudo-rotation in the hydrolysis of phosphate esters. Acc. Chem. Res. 1968, 1, 70−78. (e) Gorenstein, D.; Westheimer, F. H. Nuclear magnetic resonance evidence for the pathways of pseudorotation in alkyloxyphosphoranes. J. Am. Chem. Soc. 1970, 92, 634−644. (f) Gorenstein, D. Barriers to pseudorotation in cyclic alkyloxyphosphoranes. J. Am. Chem. Soc. 1970, 92, 644−650. (41) (a) Becker, R. S.; Bost, R. O.; Bertoniere, N. R.; Smith, R. L.; Griffin, G. W. Spectroscopy and photochemistry of aryloxiranes. J. Am. Chem. Soc. 1970, 92, 1302−1311. (b) Minh, T. D.; Trozzolo, A. M.; Griffin, G. W. Low-temperature photochemistry of oxiranes. II. Formation of carbonyl ylides and their stereospecific interconversion with oxiranes. J. Am. Chem. Soc. 1970, 92, 1402−1403. (42) A careful inspection of 4 unveils instability of the wave function with respect to the closed-shell nature of its electronic structure in the gas phase, although resulted perfectly stable in the set of tested solvents (toluene, tetrahydrofuran, and dichloromethane). (43) Smith, M. B.; March, J. In March’s Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 6th ed.; John Wiley & Sons, Inc.: New York, 2007; p 1374. (44) Vedejs, E.; Marth, C. F. Mechanism of Wittig reaction: evidence against betaine intermediates. J. Am. Chem. Soc. 1990, 112, 3905−3909.

G

DOI: 10.1021/acs.inorgchem.7b02816 Inorg. Chem. XXXX, XXX, XXX−XXX