η 3 ‐Coordination and Functionalization of the 2‐Phosphaethynthiolate Anion at Lanthanum(III)**

Zwitterionic 2-Phosphaethene-thiolates [(LC)P=CS(LC/P)]+ as PCS Building Blocks (LC=NHC, LP=PR3)

The zwitterionic compounds [(LC)P=CS(LC/P)]+ (3+, LC=NHC, LP=PR3), featuring cationic substituents at the phosphorus and carbon atoms, are synthesized as their triflate salts at a multi-gram scale from the reaction of Lewis base adducts of CS2, namely LC/P-CS2 (4), with a combination of [(LCP)4][OTf]4 (1[OTf]4) and Ph3P. The feasibility of using 3+ as PCS building blocks is showcased in their reactions with representative electrophiles (MeOTf) and nucleophiles (MesMgBr, Ph3PCH2), leading to selective functionalization of the PCS core at the S- and P-terminus, respectively. Additionally, it is reported that 3+ can function as ambident nucleophiles with AgOTf (2 equivalents), affording unprecedented linear coordination polymer [Ag2(OTf)3-μ2:κP,κS-((LC)P=CS(PCy3))]+ (6 b), where the PCS moiety acts as a bridging ligand in transition metal complexes for the first time. Reduction of 3+ facilitates the cleavage of the P- and C-bound substituents leading to the formation of the [PCS]- anion. Moreover, cycloaddition reactions of 3+ with 1[OTf]4 are shown to selectively yield five- and eight-membered polyphosphorus heterocycles. Preliminary results suggest the possibility of activating the C-S bond in [(LC)P=CS(LC)]+, resulting in the formation of [(LC)P=C(LC)-P(LC)][OTf]2, 12[OTf]2, which may serve as a synthon for the PCP unit in future studies.

Cyano(triphenylsilyl)phosphanide as a Building Block for P,C,N Conjugated Molecules

The cyano(triphenylsilyl)phosphanide anion was prepared as a sodium salt from 2-phosphaethynolate. The electronic structure of this new cyano(silyl)phosphanide was studied via computational methods and its reactivity investigated using various electrophiles and Lewis acids, demonstrating its P- and N-nucleophilicity. The ambident reactivity is in agreement with computations. The silyl group also shows lability and therefore the cyano(silyl)phosphanide can be considered as a phosphacyanamide synthon, [PCN]2- , and serves as building block for the transfer of a PCN moiety.

Phosphorus and Arsenic Atom Transfer to Isocyanides to Form π-Backbonding Cyanophosphide and Cyanoarsenide Titanium Complexes

Decarbonylation along with E atom transfer from Na(OCE) (E=P, As) to an isocyanide coordinated to the tetrahedral Ti^II complex [(Tp^tBu,Me )TiCl], yielded the [(Tp^tBu,Me )Ti(η³ -ECNAd)] species (Ad=1-adamantyl, Tp^tBu,Me- =hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borate). In the case of E=P, the cyanophosphide ligand displays nucleophilic reactivity toward Al(CH₃ )₃ ; moreover, its bent geometry hints to a reduced Ad-NCP^3- resonance contributor. The analogous and rarer mono-substituted cyanoarsenide ligand, Ad-NCAs^3- , shows the same unprecedented coordination mode but with shortening of the N=C bond. As opposed to Ti^II , V^II fails to promote P atom transfer to AdNC, yielding instead [(Tp^tBu,Me )V(OCP)(CNAd)]. Theoretical studies revealed the rare ECNAd moieties to be stabilized by π-backbonding interactions with the former Ti^II ion, and their assembly to most likely involve a concerted E atom transfer between Ti-bound OCE^- to AdNC ligands when studying the reaction coordinate for E=P.