Hexaphenyl carbodiphosphorane adducts of heavier group 15 element trichlorides: syntheses, properties and reactivities

Carbodiphosphorane-Activated Distibene and Dibismuthene Dications

Low-valent antimony and bismuth have emerged as novel platforms for achieving reversible small-molecule activation at main-group metals. Although various examples of oxidative addition reactions at monomeric Sb(I) and Bi(I) have been reported, the chemistry of the heavy group 15 Sb(I)═Sb(I)/Bi(I)═Bi(I) double bonds toward small molecules remains largely unexplored. In this study, we present a straightforward synthesis of distibene and dibismuthene dications coordinated with a neutral carbodiphosphorane (CDP) ligand. The nonbonding interactions between the occupied p-orbital at the CDP ligand and the π-bonding orbital of the Sb═Sb/Bi═Bi bonds yield compounds with exceptionally small HOMO-LUMO gaps. In addition, the reduction of steric hindrance compared to known neutral derivatives stabilized with bulky aryl groups allows for better accessibility of the double bonds. This high reactivity is demonstrated in the oxidative addition of distibene to diphenyldisulfide as well as in [2+2] cycloadditions to alkynes. Additionally, the Sb═Sb bond reversibly adds to 2,3-dimethylbutadiene in a [4+2] cycloaddition reaction.

Geminal bimetallic coordination of a carbone to main-group and transition metals

The non-bonding carbone lone pair in geometrically-constrained antimony and bismuth carbodiphosphorane complexes readily complexed AuCl to afford rare examples of geminal bimetallic carbone coordination featuring a main-group metal.

Flexible coordination of carbodiphosphorane-based pincer ligands in chromium(0) carbonyl complexes

A series of chromium(0) complexes was obtained by subsequent irradiation of [Cr(CO)6] in the presence of [(Ph2P-CH2-PPh2)2CH]+. Depending on the reaction conditions and the duration of irradiation, complexes with different coordination modes of the potentially tridentate ligand can be isolated. Shorter irradiation times lead to the coordination of the terminal PPh2 groups and the formation of [(κ2P,P′-{Ph2P-CH2-PPh2}CH)Cr(CO)4]+ (2), whereas after longer irradiation duration, the formation of fac- and mer-[(κ3P,C,P′-{Ph2P-CH2-PPh2}CH)Cr(CO)3]+ (3) can be observed. In the presence of base, the neutral complex [(κ3P,C,P′-{Ph2P-CH2-PPh2}C)Cr(CO)3] (4) can be isolated, enabling the analysis of the central CDP group’s net donor strength through the C–O stretching vibration. Finally, the utilization of reductants like potassium graphite lead to the loss of hydrogen and generation of an anionic chromium(0) complex (5). Using quantum chemical methods, the stability of possible isomers is explored.

From carbones to carbenes and ylides in the coordination sphere of iridium

The carbodiphosphorane-based iridium pincer complex (2) is demonstrated to rearrange in chlorinated organic solvents under cleavage of a P-C-bond to give a chelating phosphine ylide ligand. A detailed mechanistic investigation reveals that these types of donor groups are prone for P-C-bond cleavage in the coordination sphere of transition metal hydrido complexes. Finally, complex 2 is demonstrated to be an efficient hydrogen-borrowing catalyst.

Cationic Phosphorus Compounds Based on a Bis(1-piperidinyl)-Substituted Carbodiphosphorane: Syntheses, Structures, and Csp3–H Activation

The use of the bis(1-piperidinyl)-substituted carbodiphosphorane (Ph₂(Pip)P)₂C (1) as an NCN ligand for the stabilization of phosphorus cations was studied. A simple ligand for halide exchange allowed the synthesis and isolation of a series of phosphorus monocations of the type [1-PR₂]⁺ (with R = Cl, Br, I, CyCl, Ph). These cations exhibit characteristic NMR and structural properties which nicely correlate with the charge at the central phosphorus atom and the interaction between the ligand and the PR₂ moiety. Halide abstraction from the monocations does not result in isolable dicationic compounds but in an unexpected intramolecular C_sp³–H activation in the piperidinyl group. DFT studies show that the selective activation of the CH₂ group next to the nitrogen atom instead of a CH group at the phenyl substituents proceeds via an iminium intermediate formed by hydride transfer from the carbon atom to the cationic phosphorus center. This observation clearly demonstrates the pronounced π acidity of the dicationic phosphorus species in comparison to compounds with a further π-donor substituent.

Design of non-ionic carbon superbases: second generation carbodiphosphoranes

A new generation of carbodiphosphoranes (CDPs), incorporating pyrrolidine, tetramethylguanidine, or tris(dimethylamino)phosphazene as substituents is introduced as the most powerful class of non-ionic carbon superbases on the basicity scale to date. The synthetic approach as well as NMR spectroscopic and structural characteristics in the free and protonated form are described. Investigation of basicity in solution and in the gas phase by experimental and theoretical means provides the to our knowledge first reported pK BH + values for CDPs in the literature and suggest them as upper tier superbases.