* Deoxygenation of CO2 [pub075] and coordination of CO [pub087] by terminal phosphinidene complexes (R-P→M(CO)5) (5.01). The first one is accomplished through highly strained oxaphosphiranone complex 5.02 that sequentially extrudes CO and dimerizes.
The driving force for the overall exothermic deoxigenation process leading to phosphinidene oxide complex 5.03 is the remarkably high thermodynamic oxygen-transfer potential (TOP) exhibited by phosphinidene complexes 5.01, even higher than isonitriles:
The multi-faceted bonding of CO in molecular phosphorus compounds is described using calculated P-C bond strengths as a criterion. Full compliance matrices at coupled cluster level of several reference compounds as well as P≡CH, HP=CH2 and H2P-CH3 were calculated to obtain quantifiable data and enable comparison.
A comparative study of various CO bonding motifs in molecular compounds indicates that acyclic or cyclic diphospha-urea derivatives or isomers display P-CO bond strengths well below that of the P-C bond of H2P-CH3, thus providing insight into the bonding and the ease of CO extrusion, experimentally known for some cases. End-on addition of CO to neutral terminal phosphinidene complexes [M(CO)5PMe] proceeds in all cases exergonically, initially involving a van der Waals complex (shown).
Furthermore, calculated 31P NMR shifts and scalar 1J(P,E) couplings were correlated with P-CO and PC-O compliance constants as a tool for experimentalists.
* The reactivity of Li/Cl phosphinidenoid complexes was studied looking for optimal representation in agreement with experimental observations. For the case of the P-trityl pentacarbonyltungsten(0) complex 5.05. Neither the “naked” (unsolvated) (a) nor the 12-crown-4 complexed (b) structures represent properly the compound, but, rather, additional P···Li dissociation is required by either addition of an explicit molecule of the THF solvent (modelled by Me2O) (c) or by total solvation with four solvent (THF) molecules (d) [pub078].
The nucleophilic reactivity of such systems (several P-substituents) was pointed out by their behaviour towards a variety of electrophiles: N-methyl-3-thienylcarbaldimine (R: Tms2CH) [pub069], phosgene and aldehydes (R: Ph3C) [pub078], phosphite-substituted ketones (R: Tms2CH) [pub082], α-diketones (R: Tms2CH) [pub089], N-methyl-2-furylcarbaldimine (R: Cp*) [pub086] or N,N-dimethylcyanamide (R: Ph3C) [pub090]. In the two last cases, the R groups participate allowing the formation of a rearranged P-iminium- or –nitriliumphosphane ylid that further rearrange to a key aminophosphinidene complex stabilized by both through bond N→P electron donation and tiny intramolecular through space noncovalent interactions (NCIs) as well. The latter can be conveniently visualized by NCIplot isosurfaces. A full electronic description of differently substituted phosphinidene complexes and a discussion on how the electronic deficiency at P can be filled and turned into a nucleophilic reactivity is included.
