Coordination of N₂and Other Small Molecules to the Phosphorus Centre of RPW(CO)₅: A Theoretical Study on the Janus Facets of the Stabilization/Activation Problem

Abstract

Bonding of neutral terminal phosphinidene tungsten(0) complexes stabilized by ligands bound to phosphorus (ligand-to-P) have been studied using a large testbed of predominantly N-ligands. Most complexes (1 a-r,v-z and 2 l) exhibit a pyramidal P centre with a formal single ligand-to-P bond order. Three ligand-to-P complexes (1 s-u) exhibit planar sp -hybridization of P and P,N bonds featuring double bond character. All derivatives with C-ligands (1 v,x-z) exhibit a ligand-to-P bond strength intermediate between the P-N single and double bonded species. Remarkably, dinuclear complexes containing CN (1 p,w), N (1 r) and N (1-3 t) as bridging ligands between two phosphorus centres show intertwined terminal W(CO) fragments. In particular, the case of N bridging ligand (1-3 t) represents a noteworthy example of activation, displaying a weakened N,N bond and two sets of very strong P,N double bonds, the latter resembling the activation-picture of dinitrogen by transition metal complexes. Bond dissociation energies (BDEs) of ligand-to-P bonds do not show any correlation with a range of bond strength descriptors, but display some meaningful, roughly linear variation with the ligand softness. Based on Haaland's definition of dative bonding, a reasonable linear correlation of BDE with dativity (d ) and the dative covalence energy (DCE ) was found. A moderate correlation was also obtained with the vertical ionization potential of the ligand (I(L)) as well as with the ligands HOMO energy.

Terminal Phosphinidene Complex Adducts with Neutral and Anionic O-Donors and Halides and the Search for a Differentiating Bonding Descriptor

“…This clearly reveals the need of a more comprehensive study of the bonding features of L → P pnictogen bonds in II. A thorough exploration of the stabilization of electrophilic phosphinidene complexes (I) by adduct formation with C-and N-donor Lewis bases (II) was recently reported, highlighting the unveiled potential ability of I for uptaking and/or activating molecular dinitrogen, 23 similar to the recent report by Braunschweig using dicoordinate borylenes. 24 These investigations and discussions should be seen against the larger background of so-called unusual bonding in main-group element chemistry, 25a including various NHCstabilized or other Lewis base-stabilized low-coordinate acyclic as well as cyclic p-block element compounds.…”

“…The heterolytic BDE turns out to correlate almost linearly with the dativity index (Figure 6b) when excluding adducts with double-bond or partially double-bond PO character. The dativity index was also shown 23 to be proportional to the difference between the vertical electron affinity of the phosphinidene complex and the ionization potential of the ligand fragments in the adduct. Because the former is almost constant for all adducts, the latter is expected to correlate with the dativity index and, hence, with the BDE.…”

Access to 1,1′‐Bifunctional Phosphane Iron(0) Complexes via P–N Bond‐Forming Reactions and Selective P‐Functionalizations

“…The basic nature of the phosphanide anion 2′ an determines that initial interaction with an NH 3 molecule results in the formation of a van der Waals complex 2′ an · NH 3 (Scheme ), although no full proton transfer reaction was observed in the potential energy surface (PES). Instead, the nitrogen atom of NH 3 is nucleophilic enough to displace the chloride anion giving rise to 8′ , that can be viewed as a ligand‐stabilized phosphinidene complex, following a moderate barrier endergonic path (Figure ).…”

On the Mechanism of Trimethylphosphine-Mediated Reductive Dimerization of Ketones

“…Local correlation schemes of type LPNO (Local Pair Natural Orbital) for high level single-reference methods, such as CEPA (Coupled Electron-Pair Approximation), here the slightly modified NCEPA/1 version implemented in ORCA was used, were computed for comparison. Very close values between these two levels have been systematically reported for closed-shell systems with rmsd (root-mean-square deviation) typically below 0.2 kcal/mol, , and for this particular case amounts to 0.31 kcal/mol (0.37 kcal/mol with the def2-TZVPP basis set), taking the CCSD­(T)/def2-QZVPP level as reference for a set of 37 nonzero relative energy values (see the Supporting Information). Also, SCS-MP2 and PWPB95-D3 methods were checked for comparison, with rmsd values of 0.32/0.40 and 0.31/0.34 kcal/mol, respectively (def2-TZVPP/def2-QZVPP basis set).…”