Quantum Chemical Calculations on CHOP Derivatives—Spanning the Chemical Space of Phosphinidenes, Phosphaketenes, Oxaphosphirenes, and COP− Isomers

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.

CHNO isomers and derivatives – a computational overview

“…This was also true for the P-O bond in its phosphorus counterpart, oxaphosphirene. 12 No BCP was found for this very elongated N-O bond and therefore the structure lacks an RCP and can be categorized as a pseudocyclic molecule. The weakness of the N-O bond (Table 1) may be due to the fact that the single bond is formed with s-symmetry between the orthogonal p orbitals at both N and O, as shown in HOMOÀ1 (Fig.…”

“…Similar values were estimated using the computationally less costly def2-TZVP(-f) and def2-SVPD basis sets (31.98 and 36.73 kcal mol À1 , respectively), which are significantly lower than that computed at the singlereference DLPNO-CCSD(T)/def2-TZVPP level (42.78 kcal mol À1 ), where the latter is useful for comparative purposes with other reports typically employing this computational level. 12,20,21 Thus, it is worth mentioning the significantly lower RSE of 1a compared with oxaphosphirane 1 P a (49.08 kcal mol À1 ) at the DLPNO-CCSD(T) level, 12 which is in contrast to the known tendency to decrease the ring strain when replacing N by P in both saturated 20 and unsaturated three-membered rings (the computed RSE values for 2H-azirine and 2H-phosphirene are 41.19 and 32.57 kcal mol À1 , respectively 21 ). One tentative explanation may arise from the lower p character of the atomic orbital (AO) used by the O atom in bonding to C in 1 P a (68.3%) compared with 1a (73.0%), causing an enhanced ring strain, 20 which in turn results from the increase in p character of one the O lone pairs (LPs) in 1 P a compared with 1a (32.5 and 26.8%, respectively) while using almost pure p AOs for the other LPs and in bonding to the pnictogen atom (P or N).…”

“…There is no updated high-level study of all acyclic and cyclic CHNO isomers, nor is there a detailed analysis of their interconversion pathways, as very recently reported for the CHOP phosphaanalogues. 12 The same numeration scheme used in the latter has been kept in the present work in which state-of-the-art exploration of the potential energy surface (PES) of the parent CHNO isomers (a, R = H) and two other substituted derivatives with an electrondonating (b, R = CH 3 ) or -withdrawing (c, R = CF 3 ) group is reported. Also presented are the PES of anionic derivatives CNO À and of sixmembered (CHNO) 3 cyclotrimers.…”

Indirect Access to Carbene Adducts of Bismuth- and Antimony-Substituted Phosphaketene and Their Unusual Thermal Transformation to Dipnictines and [(NHC)2OCP][OCP]

“…Phosphorus-containing members of this family are phosphaketenes, R—P=C=O. 1 Although the first stable phosphaketene was reported nearly four decades ago, 2 the synthetic chemistry was experimentally challenging, and various products were thermally unstable. However, in the past decade, simple synthetic routes toward such compounds have emerged, which has resulted in the rapid development of the field.…”

Revealing electronic features governing hydrolysis of cephalosporins in the active site of the L1 metallo-β-lactamase

“…Equilibrium geometry congurations and corresponding calculated electron densities of reagents, intermediates, transition states and products of chemical reactions are analyzed by various approaches as QTAIM (Quantum Theory of Atoms in Molecules) [29][30][31][32][33][34][35][36][37][38][39][40][41] or conceptual DFT (Density Functional Theory) 23,36,[42][43][44] as well as diverse bonding descriptors. [33][34][35][36][37]45,46 Current studies of enzymatic reactions [47][48][49] also demonstrate an enhanced interest in the application of such combined methods in biochemistry. For example, the Fukui function interpreted the residue-residue interactions in biomolecular systems simulated by QM/MM method, 47 electrostatic potential allowed to identify regions of electrophilic/nucleophilic attack in the QM/MM structural models, 48,49 etc.…”