Carbodiphosphorane Analogues E(PPh₃)₂ with E=C–Pb: A Theoretical Study with Implications for Ligand Design

Abstract

Quantum-chemical calculations at the BP86/TZVPP level have been carried out for the heavy Group 14 homologues of carbodiphosphorane E(PPh(3))(2), where E=Si, Ge, Sn, Pb, which are experimentally unknown so far. The results of the theoretical investigation suggest that the tetrelediphosphoranes E(PPh(3))(2) (1E) are stable compounds that could become isolated in a condensed phase. The molecules possess donor-acceptor bonds Ph(3)P→E←PPh(3) to a bare tetrele atom E, which retains its four valence electrons as two electron lone pairs. The analysis of the bonding situation and the calculation of the chemical reactivity indicate that the molecules 1E belong to the class of divalent E(0) compounds (ylidones). All molecules 1C-1Pb have very large first but also very large second proton affinities, which distinguishes them from the N-heterocyclic carbene homologues, in which the donor atom is a divalent E(II) species that possesses only one electron lone pair. Compounds 1E are powerful double donors that strongly bind Lewis acids such as BH(3) and AuCl in the complexes 1E(BH(3))(n) and 1E(AuCl)(n) (n=1, 2). The bond dissociation energies (BDEs) of the second BH(3) and AuCl molecules are only slightly less than the BDE of the first BH(3) and AuCl. The results of this work are a challenge for experimentalists.

Recent Advances in the Field of Main‐Group Mono‐ and Diatomic “Allotropes” Stabilised by Neutral Ligands

“…[30] Frenking has examined the properties of the as-yet-unknown NHC (14 E)-and phosphine (15 E)-stabilised E 1 complexes for E = Si-Pb. [13,31] The results revealed that in all cases two distinct lone pair orbitals are found about the E centres (Figure 7), and the L À E bonding is consistent with a "dative" (donor-acceptor) description. Both lone pairs were predicted to be chemically accessible for these species, as is Scheme 2.…”

“…The L-E-E-L compounds relate directly to homonuclear diatomics (EÀE, only stable for N 2 and O 2 in the native form for Groups [13][14][15][16], which is typically the starting point for discussions of molecular orbital (MO) theory in undergraduate education. The MO frameworks for the L-E-E-L complexes, particularly for elements from rows 3 and below have common arrangements as shown in Figure 1, with the level of electron population increasing by two with each group to the right.…”

“…Most researchers in the field have used a dative bonding model to describe their compounds; we have followed this precedent in the present review. This has apparently been met with some resistance, [13] and it is important to note that depicting these species by using a standard Lewis representation with lines rather than arrows is equally correct. Also of note is that a simple ligand exchange reaction from one L-E-L or L-E-E-L species to another (i.e., substituting L for a "stronger" ligand) has not been reported, which is one of the hallmark reactions of a dative bond.…”

Ein stabiles biradikaloides Singulett‐Siladicarben: (L:)2Si

“…[4] Trisilaallene haben eine gewinkelte Struktur und unterscheiden sich deutlich von ihren Kohlenstoffanaloga. Erklärungen zu diesen Unterschieden wurden von Frenking et al [5,6] verçffentlicht. In kürzlich verçffentlichen Artikeln von Bertrand et al, [7,8] Fürstner et al [9] sowie Frenking et al [10][11][12] konnten diese sowohl anhand experimenteller Untersuchungen als auch durch DFT-Rechnungen zeigen, dass das allenartige Molekül B (Schema 2) ebenso in der Struktur der Form C erhalten werden kann, wenn das zentrale C 0 -Atom an Liganden L gebunden wird, die als Donorliganden fungieren kçnnen.…”

“…[16c] Die berechnete Bindungslänge für das Si(NHC) 2 -Silylon beträgt (1.869 ) [5,6] und ist somit ein wenig kürzer als der in 2. Die C-N-Abstände zu den Carbenkohlenstoffatomen in 2 sind nahezu identisch mit denen in 1.…”