Formation of Transient and Stable 1,3-Dipole Complexes with P,S,C and S,P,C Ligand Skeletons

Metal-catalyzed valence isomerization of a methylene(thioxo)phosphorane to a thiaphosphirane

We explored coordination chemistry associated with valence isomerization between a methylene(thioxo)phosphorane (MTP) and a thiaphosphirane. For this purpose, we developed the selective synthesis of a MTP by eliminating chlorodimethylphenylsilane from the corresponding chlorophosphine sulfide. Treatment of the MTP with an equivalent amount of pentafluorophenylgold(I) complex resulted in the formation of a thiaphosphirane gold(I) complex, which likely proceeds via an η2-P,C-MTP gold complex. The MTP undergoes a valence isomerization catalyzed by copper(I) chloride to furnish a transition metal-free thiaphosphirane. Computational studies proposed a plausible mechanism involving a Cu-assisted cyclization reaction.

Ring Strain Energy of Diheteropnictogeniranes El2 Pn (Pn=N, P, As, Sb)- Accurate versus Additive Approaches

Accurate ring strain energy (RSE) values for sixty-six parent pnictogeniranes having two other identical p-block elements, El2 Pn, have been reported. A decrease in RSE was observed to correlate with an increase in the p character of the AO used in endocyclic bonds, which is particularly remarkable on descending the groups 15 and 16. The latter also parallels higher -NICS(1) values, which seems not to be related with an increase in aromaticity, as pointed out by other NICS-related criteria, but to atom-centred diatropic currents mostly arising from the presence of lone pairs. Only in case of pnictogenaditrieliranes Tr2 Pn (Tr=B, Al, Ga), the decrease of -NICS(1) is related to a lower Hückel-type 2π-electron aromaticity on descending group 13. The use of an additive methodology based on atom-strain contributions enables estimation of RSEs for a large majority of all possible three-membered rings containing group 13-16 elements with modest accuracy (RMSE=4.371 kcal/mol), that could be remarkably improved by using bond-strain contributions (RMSE=1.183 kcal/mol) instead.

Challenging an old paradigm by demonstrating transition metal-like chemistry at a neutral nonmetal center

We describe nonmetal adducts of the phosphorus center of terminal phosphinidene complexes using classical C- and N-ligands from metal coordination chemistry. The nature of the L-P bond has been analyzed by various theoretical methods including a refined method on the variation of the Laplacian of electron density ∇2ρ along the L-P bond path. Studies on thermal stability reveal stark differences between N-ligands such as N-methyl imidazole and C-ligands such as tert-butyl isocyanide, including ligand exchange reactions and a surprising formation of white phosphorus. A milestone is the transformation of a nonmetal-bound isocyanide into phosphaguanidine or an acyclic bisaminocarbene bound to phosphorus; the latter is analogous to the chemistry of transition metal-bound isocyanides, and the former reveals the differences. This example has been studied via cutting-edge DFT calculations leading to two pathways differently favored depending on variations in steric demand. This study reveals the emergence of organometallic from coordination chemistry of a neutral nonmetal center.

Ring Strain Energies of Three-Membered Homoatomic Inorganic Rings El3 and Diheterotetreliranes El2Tt (Tt = C, Si, Ge): Accurate versus Additive Approaches

Accurate ring strain energies (RSEs) for three-membered symmetric inorganic rings El₃ and organic dihetero-monocycles El₂C and their silicon El₂Si and germanium El₂Ge analogues have been computed for group 14–16 “El” heteroatoms using appropriate homodesmotic reactions and calculated at the DLPNO-CCSD-(T)/def2-TZVPP//B3LYP-D4/def2-TZVP(ecp) level. Rings containing triels and Sn/Pb heteroatoms are studied as exceptions to the RSE calculation as they either do not constitute genuine rings or cannot use the general homodesmotic reaction scheme due to uncompensated interactions. Some remarkable concepts already related to the RSE such as aromaticity or strain relaxation by increasing the s-character in the lone pair (LP) of the group 15–16 elements are analyzed extensively. An appealing alternative procedure for the rapid estimation of RSEs using additive rules, based on contributions of ring atoms or endocyclic bonds, is disclosed.

Accurate ring strain energies (RSEs) are calculated for saturated three-membered homoatomic inorganic rings El₃ and diheterotetreliranes El₂Tt (Tt = C, Si, Ge). Aromaticity, lone-pair-induced strain relaxation for the group 15−16 elements, and bond stiffness are extensively discussed as main factors affecting the RSE. An attractive alternative procedure for fast estimation of the RSE using additive rules is proposed.

1,2σ3λ3-Oxaphosphetanes and Their P-Chalcogenides-A Combined Experimental and Theoretical Study

Although 1,2σ⁵λ⁵-oxaphosphetanes have been known for a long time, the “low-coordinate” 1,2σ³λ³-oxaphosphetanes have only been known since their first synthesis in 2018 via decomplexation. Apart from ligation of this P-heterocycle to gold(I)chloride and the oxidation using ortho-chloranil, nothing on their chemistry has been reported so far. Herein, we describe the synthesis of new 1,2σ³λ³-oxaphosphetane complexes (3a–e) and free derivatives (4a–e), as well as reactions of 4a with chalcogens and/or chalcogen transfer reagents, which yielded the P-chalcogenides (14–16a; Ch = O, S, Se). We also report on the theoretical results of the reaction pathways of C-phenyl-substituted 1,2 σ³λ³-oxaphosphetanes and ring strain energies of 1,2σ⁴λ⁵-oxaphosphetane P-chalcogenides.

Synthesis of azadiphosphiridine complexes. Theoretical studies on ring formation, the P-to-P' metal shift and the resulting nitrogen geometry

A set of azadiphosphiridine complexes 3a and 4b,c were synthesized in high selectivity using N-H and P-H deprotonation as key steps and RPCl₂ as substrates (R = NⁱPr₂ (a), -^tBu (b), Ph (c)). While complex 3a (P-NⁱPr₂) retained the P-W linkage of the starting material W(CO)₅{Ph₃CP(H)NH}, complexes 4b (P-^tBu) and 4c (P-Ph) revealed that a P-to-P' haptotropic shift of the W(CO)₅ group has occurred. Remarkably, complex 3a, bearing an unligated P-NⁱPr₂ unit, displays a planar ring N geometry while 4b,c showed a pyramidal geometry of the ring nitrogen atom. Theoretical studies on the ring formation including the P-to-P' haptotropic metal shift and the factors influencing the ring nitrogen geometry are reported.

Accurate Ring Strain Energy Calculations on Saturated Three-Membered Heterocycles with One Group 13-16 Element

Accurate ring strain energy (RSE) data for parent (CH₂)₂X rings are reported, where X are group 13-16 elements (El) in their lowest oxidation state, from the second to the sixth row, with their covalence completed by bonds to H. They are obtained from appropriate homodesmotic and hyper-homodesmotic reactions at different levels up to the CCSD(T) level, thus providing a benchmark of high-quality reference RSE values, as well as acceptably accurate faster lower-level options. Derivatives of indium, thallium, and lead cannot be properly described by a three-member ring connectivity, because they display a unique donor-acceptor structure from an ethylene π(C═C) orbital to an empty p orbital of a metallylene subunit. The RSE of groups 13 and 14 heterocycles increases on descending in the group (except for Ga and Ge), while it decreases for groups 15 and 16. The latter is presumably due to a strain-releasing mechanism favored by the increase of p-character at the sp³-type atomic orbital used by El in the endocyclic El-C bonds, %p(El)_El-C, originated by the tendency of the El lone pairs in groups 15-16 to increase their s-character. This strain-releasing mechanism does not exist in heavier tetrels, which keep almost unchanged the p-character in the endocyclic bonds at El, whereas for triels the p-character is still lower owing to their sp²-like hybridization. Remarkable linear correlations were found between the RSE and either the above-mentioned %p(El)_El-C, the distal C-C bond distance or the relaxed force constants for the endocyclic bond angles.

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

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.

"Low-coordinate" 1,2-oxaphosphetanes - a new opportunity in coordination and main group chemistry

While 1,2σ5λ5-oxaphosphetanes are well known intermediates from the Wittig-reaction, no 1,2σ3λ3-oxaphosphetanes have been described, so far. Herein, we present the first synthesis of 1,2σ3λ3-oxaphosphetanes derived from their κP-Mo(CO)5 complexes and first investigations towards metal coordination and P-oxidation. Bonding, ring strain energy and potential retro-[2+2] cycloaddition reactions of the 1,2-oxaphosphetane ring were studied by DFT methods.

Tin and Lead Phosphanido Complexes: Reactivity with Chalcogens

The reactivity of tin and lead phosphanido complexes with chalogens is reported. The addition of sulfur to [(BDI)MPCy₂] (M = Sn, Pb; BDI = CH{(CH₃)CN-2,6-iPr₂C₆H₃}₂) results in the formation of phosphinodithioates [(BDI)MSP(S)Cy₂] regardless of the conditions; however, when selenium is added to [(BDI)MPCy₂], a selenium insertion product, phosphinoselenoite [(BDI)MSePCy₂], can be isolated. This compound readily reacts with additional selenium to form the phosphinodiselenoate complex [(BDI)MSeP(Se)Cy₂]. In contrast, the addition of selenium to [(BDI)SnP(SiMe₃)₂] results in the formation of the heavy ether [(BDI)SnSeSiMe₃]. Differences in the solution and solid-state molecular species of tin phosphinoselenoite and phosphinodiselenoate complexes were probed using multinuclear solution and solid-state NMR spectroscopy.