Divalent Carbon(0) Chemistry, Part 2: Protonation and Complexes with Main Group and Transition Metal Lewis Acids

Abstract

Quantum-chemical calculations with DFT (BP86) and ab initio methods (MP2, SCS-MP2) were carried out for protonated and diprotonated compounds N-H(+) and N-(H(+))(2) and for the complexes N-BH(3), N-(BH(3))(2), N-CO(2), N-(CO(2))(2), N-W(CO)(5), N-Ni(CO)(3) and N-Ni(CO)(2) where N=C(PH(3))(2) (1), C(PMe(3))(2) (2), C(PPh(3))(2) (3), C(PPh(3))(CO) (4), C(CO)(2) (5), C(NHC(H))(2) (6), C(NHC(Me))(2) (7) (Me(2)N)(2)C==C==C(NMe(2))(2) (8) and NHC (9) (NHC(H)=N-heterocyclic carbene, NHC(Me)=N-substituted N-heterocyclic carbene). Compounds 1-4 and 6-9 are very strong electron donors, and this is manifested in calculated protonation energies that reach values of up to 300 kcal mol(-1) for 7 and in very high bond strengths of the donor-acceptor complexes. The electronic structure of the compounds was analyzed with charge- and energy-partitioning methods. The calculations show that the experimentally known compounds 2-5 and 8 chemically behave like molecules L(2)C which have two L-->C donor-acceptor bonds and a carbon atom with two electron lone pairs. The behavior is not directly obvious when the linear structures of carbon suboxide and tetraaminoallenes are considered. They only come to the fore on reaction with strong electron-pair acceptors. The calculations predict that single and double protonation of 5 and 8 take place at the central carbon atom, where the negative charge increases upon subsequent protonation. The hitherto experimentally unknown carbodicarbenes 6 and 7 are predicted to be even stronger Lewis bases than the carbodiphosphoranes 1-3.

Distinguishing Carbones from Allenes by Complexation to AuCl

“…This is in agreement with the calculated proton affinities of carbenes and carbones, which show that the first PAs of the two classes of compounds have similar values. [9] The DE int values also indicate that the TAAs that have been named "hidden carbones" [4,5] may have donor strengths that are comparable to carbodicarbenes. This is again in agreement with the calculated PAs.…”

“…Tetraaminoallenes (TAAs) have therefore been termed as "hidden" carbones. [4,5] We also calculated complexes of AuCl with carbon suboxide, C 3 O 2 [29] (6), as ligand, which is usually written with double bonds O=C=C=C=O. [29b,c] It has been shown that carbon suboxide, which has a quasi-linear equilibrium geometry with a remarkably shallow bending potential, [30] may also be seen as carbodicarbonyl C(CO) 2 .…”

Homoleptic Pnictogen–Chalcogen Coordination Complexes

“…62,66 The analogous triphosphenium cations have been considered as having the central phosphorus atom in the +1 oxidation state with formal bond orders to the adjacent phosphorus centers of either one (dative bond 13a, or single bond, 13b), 1.5 (13c), or two (13d). 57,67 Given the detailed treatment of both 12 and 13, an examination of the electronic structures of the dicationic chalcogen analogues was performed.…”

Hunting dimers

“…He could not keep himself from hypothesizing stability in the solid state for these. RH, inclined to view the carbones of GF [4][5][6][7][8] as nucleophilic carbenes, thought they would likely dimerize, a quintessential, highly exothermic reaction of carbenes. RH asked AYuR to examine some potential barrier-free dimerizations.…”

“…C/L between strong r-donors L such as PR 3 or NHC (N-heterocyclic carbene) and a divalent C(0) atom that possess two electron lone pairs at carbon rather than only one r lone pair in carbenes CR 2 [4][5][6][7][8].…”