Abstract
After many decades of intense research in low-coordinate phosphorus chemistry, the advent of Na[OCP] brought new stimuli to the field of CHOP isomers and derivatives thereof. The present theoretical study at the CCSD(T)/def2-TZVPP level describes the chemical space of CHOP isomers in terms of structures and potential energy surfaces, using oxaphosphirene as the starting point, but also covering substituted derivatives and COP− isomers. Bonding properties of the P–C, P–O, and C–O bonds in all neutral and anionic isomeric species are discussed on the basis of theoretical calculations using various bond strengths descriptors such as WBI and MBO, but also the Lagrangian kinetic energy density per electron as well as relaxed force constants. Ring strain energies of the superstrained 1H-oxaphosphirene and its barely strained oxaphosphirane-3-ylidene isomer were comparatively evaluated with homodesmotic and hyperhomodesmotic reactions. Furthermore, first time calculation of the ring strain energy of an anionic ring is described for the case of oxaphosphirenide.
Highlights
The chemistry of low-coordinate phosphorus compounds such as phosphinidenes (I), phosphaalkenes (II), and phosphaketenes (III) (Scheme 1) have received attention from experimentalists and theoreticians over many decades due to their particular bonding situation and reactivity [1,2,3,4]
An existing synthetic challenge is represented by oxaphosphiranes (VI) [6,7], only experimentally described as a ligand in transition metal complexes, being valuable due to a high potential in polymer chemistry, and oxaphosphirenes (VII) [8,9] (a 3-phosphinyl-1H-oxaphosphirene was computed as one of the possible CHOP isomers [10]) for which not even a attempt exists in the literature; the latter may stem from a degree of antiaromaticity [11]
The first stable derivative of a phosphaketene, possessing the general formula RP=C=O, was reported by Appel (R = Mes* = 2,4,6-tri-tert-butylphenyl) [12,13], and which remained the only derivative for a long time
Summary
The chemistry of low-coordinate phosphorus compounds such as phosphinidenes (I), phosphaalkenes (II), and phosphaketenes (III) (Scheme 1) have received attention from experimentalists and theoreticians over many decades due to their particular bonding situation and reactivity [1,2,3,4]. The first stable derivative of a phosphaketene, possessing the general formula RP=C=O, was reported by Appel (R = Mes* = 2,4,6-tri-tert-butylphenyl) [12,13], and which remained the only derivative for a long time. It was Grützmacher who described a novel approach to III using sodium phosphaethynolate Na[OCP] [14]. This new salt, bearing the OCP− (phosphaethynolate) anion [15,16], enabled a Molecules 2018, 23, 3341; doi:10.3390/molecules23123341 www.mdpi.com/journal/molecules
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