* Synthesis of the first carboxy-functionalized phospholyl anion (4.03), from an in situ generated 2-ethoxycarbonylethylphosphinidene complex (4.01), through sequential insertion of two acetilenic units, decomplexation and exocyclic P-C bond cleavage in basic medium [pub009]:
* Oxidative activation of strained azaphosphirene complexes (4.04) to promote ring expansion reaction (RER) by reaction with nitriles. Theoretical calculations gave support to a ligand-centred radical reactivity (see spin density isosurfaces below) with the intermediacy of a nitrilium phosphane ylide complex radical cation (4.05·+), at least in case of reaction with moderately or strongly nucleophilic nitriles [pub034, pub045]. In absence of an external nitrile, dissociation of 4.05·+ can also provide the required second molecule of nitrile for a formal [3+2] cycloaddition leading to diazaphosphole radical cation complex 4.06·+ (R3 = R2). The high observed regioselectivity can be explained in the light of quantitative HSAB theory-derived relationships.
* Exploration of ring strain and endocyclic bond strength parameters for azaphosphiridines and their P(V)-derivatives and P-complexes (4.07), as well of possible endocyclic bond weakening mediated by N-complexation or N-protonation [pub061] and SET oxidation or reduction [pub071]. Changes that occurred on perturbation of the system were successfully followed by using the VBSD (variation of bond strength descriptors) methodology. For both azaphosphiridine and oxaphosphirane complexes (4.08) [pub073] SET reduction was revealed as a potentially useful approach for achieving P-decomplexation (4.09) (elusive so far by other techniques), except for the case of the P-trityl substituted systems that showed preference for the exocyclic P-C bond cleavage, thus resulting in the new potentially interesting building blocks azaphosphiridinide (4.10, E=NR3) and oxaphosphiranide (4.10, E=O) anions. Looking for superstrained systems the effect of structural attachment of a spiroring at C2 (4.11, n=0-3) was investigated [pub080]: strain seems to depend on deviation of the α angle from the ca. 115º value found in monocyclic (4.08) or unstrained spirocyclic (4.11, n=3) systems, in turn related to a roughly sp2 hybridization at C2, in line with Walsh cyclopropane description. Smaller spirorings (4.11, n=0-1) entails much smaller α angles which force lower s character of the exocyclic bonds and, consequently, higher s character for the endocyclic bonds, therefore rising the ring strain.
