Phosphaethynolate
The phosphaethynolate
Synthesis
The first reported
Ten years later, in 2002, Westerhausen et al. published the use of Becker's method to make a family of alkaline earth metal
It was not until 2011 that the first stable salt of the phosphaethynolate anion was reported by Grutzmacher and co-workers [9] They managed to isolate the compound as a brown solid in 28% yield.[9] The structure of the stable sodium salt, formed by carbonylation of sodium phosphide, contains bridging PCO units in contrast to the terminal anions found in the previously reported structures.[9] The authors noted that this sodium salt could be handled in air as well as water without major decomposition; this emphasises the significance of the accompanying counter cation in stabilisation of PCO.[6][9]
.Direct
Ambidentate nature of the anion
The phosphaethynolate anion is the heavier
Computational studies carried out on the anion such as
Attack by oxygen
Coordination via the oxygen atom is favoured by
Attack by phosphorus
On the other hand, softer, more polarisable centres prefer to coordinate in a more covalent manner through the phosphorus atom.
Rearrangement of coordination character
There is one particular reaction studied by Grutzmacher et al. that exhibits the rearrangement of coordination character of PCO.[3] Initially when reacting the anion with triorganyl silicon compounds, it binds via the oxygen forming the kinetic oxyphosphaalkyne product.[3] The thermodynamic silyl phosphaketene product is generated when the kinetic product rearranges to allow PCO to coordinate through phosphorus.[3]
The formation of the kinetic product is charged controlled and thus explains why it is formed by oxygen coordination.
Reactivity of the anion
Extensive studies involving the phosphaethynolate anion have shown that it can react in a variety of ways. It has documented use in cycloadditions, as a phosphorus transfer agent, a synthetic building block and as pseudo halide ligands (as described above).
Phosphorus transfer agents
In these types of reactions, CO is released as the phosphaethynolate anion acts as either a mild
In 2014, Grutzmacher et al. reported that an
On the other hand, in the work published by Goicoechea and co-workers in 2015, the phosphaethynolate anion can be seen to act as a source of nucleophilic phosphide (P−).[16] The anion was seen to add across the Si=Si double bond of cyclotrisilene thus introducing a phosphorus vertex into its scaffold (after undergoing decarbonylation).[16]
Cycloaddition Reagents
After synthesising the potassium salt of the phosphaethynolate anion in 2013, Goicoechea et al. began to look into the potential of PCO towards
Cycloaddition reactions involving the phosphaethynolate anion have also been shown by Grutzmacher and co-workers to be a viable synthetic route to other heterocycles.
Synthetic building blocks
A large part of the research involving PCO is now looking into utilising the anion as a synthetic building block to derive phosphorus containing analogues of small molecules.
The first major breakthrough in this area came from Goicoechea et al. in 2013; they published the reaction between the PCO anion and ammonium salts which yielded the phosphorus containing analogue of urea in which phosphorus replaces a nitrogen atom.[4] The group predict that this heavier congener could have applications in new materials, anion sensing and coordination chemistry.[4]
Goicoechea and co-workers were also able to isolate the heavily sought after phosphorus containing analogue of isocyanic acid, HPCO, in 2017.[17] This molecule is thought to be a crucial intermediate in a lot of reactions involving PCO (including P-transfer to an imidazolium cation).[6][17]
Moreover, the most recent addition to this class of small molecules is the phosphorus containing analogue of
Other analogues
The other analogues of the phosphaethynolate anion all obey the general formulae E-C-X and are made by varying E and X. When changing either atom, unique trends amongst the different analogues become apparent.
Varying E
As 'E' is varied by descending group 15, there is a clear shift in the weights of the resonance structures towards the phosphaketene analogue .[11] This reflects the decrease in effective orbital overlap between E and C which in turn disfavours multiple bond formation. This increasing tendency to form double and not triple E-C bonds is also reflected in calculated E-C bond lengths .[14] The data from Table 1 is evidence of E-C bond elongation which correlates with the change from triple to double bond.[7]
ECO | E−C bond length (Å) | Delocalisation energy (kcal/mol) |
---|---|---|
NCO | 1.192 | 41.0 |
PCO | 1.627 | 44.0 |
AsCO | 1.740 | 64.0 |
In addition, NBO analysis highlights that the greatest electron
The shift towards the ketene isomer will also cause an increase in charge density on the elemental 'E' atom; this makes the elemental atom an increasing source of
Varying X
PCX | Resonance 'A' weight | Resonance 'B' weight |
---|---|---|
PCO | 51.5% | 38.4% |
PCS | 57.9% | 24.2% |
The simplest analogue that can be formed as 'X' is varied is PCS−. This anion was first isolated by Becker et al. by reacting the phosphaethynolate anion with carbon disulphide.[20] Unlike PCO, PCS shows ambidentate nucleophilic tendencies towards the W(0) complex mentioned above.[11]
This is the result of a reduced difference in electronegativity between E and X thus neither atom offers a substantial advantage over the other in terms of providing ionic contributions to bonding. As a result, the average electron density in PCS is spread over the entire anion [11]
whereas in PCO, most electron density is localised on the phosphorus atom as this is the atom which bonds to form the thermodynamically favourable product.References
- ^ a b c d e f Quan, Z. J. and Wang, X. C. (2014) 'The 2-phosphaethynolate anion: Convenient synthesis and the reactivity', Organic Chemistry Frontiers. doi:10.1039/c4qo00189c.
- ^ a b c Camp, C., Settineri, N., Lefèvre, J., Jupp, A. R., Goicoechea, J. M., Maron, L. and Arnold, J. (2015) 'Uranium and thorium complexes of the phosphaethynolate ion', Chemical Science. doi: 10.1039/c5sc02150b.
- ^ a b c d e f g h i j k Heift, D., Benko, Z. and Grützmacher, H. (2014) 'Is the phosphaethynolate anion, (OCP)-, an ambident nucleophile? A spectroscopic and computational study', Dalton Transactions. doi: 10.1039/c3dt53569j.
- ^ a b c Jupp, A. R., and Goicoechea, J. M. (2013) 'Phosphinecarboxamide: A Phosphorus-Containing Analogue of Urea and Stable Primary Phosphine', J. Am. Chem. Soc.. DOI:10.1021/ja4115693.
- ^ a b c d e f Becker, G., Schwarz, W., Seidler, N. and Westerhausen, M. (1992) 'Acyl‐ und Alkylidenphosphane. XXXIII. Lithoxy‐methylidenphosphan · DME und ‐methylidinphosphan · 2 DME — Synthese und Struktur', ZAAC ‐ Journal of Inorganic and General Chemistry. doi: 10.1002/zaac.19926120113.
- ^ a b c d e f g h i j k Grutzmacher, H., and Goicoechea, J. (2018) 'The chemistry of the 2‐phosphaethynolate anion', Angew. Chem. Int. Ed. doi:10.1002/anie.201803888.
- ^ a b c d Pyykkö, P. (2015) 'Additive covalent radii for single-, double-, and triple-bonded molecules and tetrahedrally bonded crystals: A summary', Journal of Physical Chemistry A. doi: 10.1021/jp5065819.
- ^ a b c Westerhausen, M., Schneiderbauer, S., Piotrowski, H., Suter, M. and Nöth, H. (2002) 'Synthesis of alkaline earth metal bis(2-phosphaethynolates)', Journal of Organometalic Chemistry. doi: 10.1016/S0022-328X(01)01267-0.
- ^ a b c d e Puschmann, F. F., Stein, D., Heift, D., Hendriksen, C., Gal, Z. A., Grützmacher, H. F. and Grützmacher, H. (2011) 'Phosphination of carbon monoxide: A simple synthesis of sodium phosphaethynolate (NaOCP)', Angewandte Chemie - International Edition. doi: 10.1002/anie.201102930.
- ^ a b c d e f g Jupp, A. R. and Goicoechea, J. M. (2013) 'The 2-phosphaethynolate anion: A convenient synthesis and [2+2] cycloaddition chemistry', Angewandte Chemie - International Edition. doi: 10.1002/anie.201305235.
- ^ a b c d e f g h i j k l Hou, G. L., Chen, B., Transue, W. J., Yang, Z., Grützmacher, H., Driess, M., Cummins, C. C., Borden, W. T. and Wang, X. Bin (2017) 'Spectroscopic Characterization, Computational Investigation, and Comparisons of ECX-(E = As, P, and N; X = S and O) Anions', Journal of the American Chemical Society. doi: 10.1021/jacs.7b02984.
- ^ a b c d e Alidori, S., Heift, D., Santiso-Quinones, G., Benkå, Z., Grützmacher, H., Caporali, M., Gonsalvi, L., Rossin, A. and Peruzzini, M. (2012) 'Synthesis and characterization of terminal [Re(XCO)(CO) 2(triphos)] (X=N, P): Isocyanate versus phosphaethynolate complexes', Chemistry - A European Journal. doi: 10.1002/chem.201202590.
- ^ a b Jupp, A. R., Geeson, M. B., McGrady, J. E. and Goicoechea, J. M. (2016) 'Ambient-Temperature Synthesis of 2-Phosphathioethynolate, PCS-, and the Ligand Properties of ECX-(E = N, P; X = O, S)', European Journal of Inorganic Chemistry. doi: 10.1002/ejic.201501075.
- ^ a b c Lu, Y., Wang, H., Xie, Y., Liu, H. and Schaefer, H. F. (2014) 'The cyanate and 2-phosphaethynolate anion congeners ECO-(E = N, P, As, Sb, Bi): Prelude to experimental characterization', Inorganic Chemistry. doi: 10.1021/ic500780h.
- ^ a b c d e f Tondreau, A. M., Benko, Z., Harmer, J. R. and Grützmacher, H. (2014) 'Sodium phosphaethynolate, Na(OCP), as a “p” transfer reagent for the synthesis of N-heterocyclic carbene supported P3 and PAsP radicals', Chemical Science. doi: 10.1039/c3sc53140f.
- ^ a b c Robinson, T. P., Cowley, M. J., Scheschkewitz, D. and Goicoechea, J. M. (2015) 'Phosphide delivery to a cyclotrisilene', Angewandte Chemie - International Edition. doi: 10.1002/anie.201409908.
- ^ a b c Hinz, A., Labbow, R., Rennick, C., Schulz, A. and Goicoechea, J. M. (2017) 'HPCO—A Phosphorus-Containing Analogue of Isocyanic Acid', Angewandte Chemie - International Edition. doi: 10.1002/anie.201700368.
- ^ a b Chen, X., Alidori, S., Puschmann, F. F., Santiso-Quinones, G., Benko, Z., Li, Z., Becker, G., Grützmacher, H. F. and Grützmacher, H. (2014) 'Sodium phosphaethynolate as a building block for heterocycles', Angewandte Chemie - International Edition. doi: 10.1002/anie.201308220.
- ^ a b c Szkop, K., Jupp, A. R., and Stephan, D. W. (2018) 'P,P‑Dimethylformylphosphine: The Phosphorus Analogue of N,N‑Dimethylformamide' J. Am. Chem. Soc. doi:10.1021/jacs.8b09266.
- ^ Tambornino, F., Hinz, A., Köppe, R. and Goicoechea, J. M. (2018) 'A General Synthesis of Phosphorus- and Arsenic-Containing Analogues of the Thio- and Seleno-cyanate Anions', Angewandte Chemie - International Edition. doi: 10.1002/anie.201805348.