Reactivity of the carbodiphosphorane, (Ph3P)2C, towards main group metal alkyl compounds: coordination and cyclometalation

Boron Polycation Supported by Cyclic Bis(carbodiphosphorane)

A novel cyclic bis(carbodiphosphorane) ligand was prepared and investigated in coordination with group 13 elements, B, Al, and Ga. Al and Ga afforded dinuclear adduct where two metal centers were bridged by the bis(carbodiphosphorane) ligand. In contrast, the reaction with boron trichloride afforded a monomeric dicationic three-coordinate boron species composed of one boron moieties and one ligand. The structures of these products were determined by X-ray crystallography. In the dicationic boron compound, the sterically constrained cyclic structure enforced the boron center to acquire strained trigonal geometry with wide C-B-C angle of 140°. Furthermore, theoretical investigation with DFT and NBO suggested a significant contribution of tricationic two-coordinate boron resonance structure supported by two CDP ligands.

Theoretical Photoelectron Spectroscopy of Low-Valent Carbon Species: A ∼6 eV Range of Ionization Potentials among Carbenes, Ylides, and Carbodiphosphoranes

High-quality density functional theory calculations underscore a nearly 6 eV range for the ionization potentials (IPs) of neutral, low-valent carbon compounds, including carbenes, ylides, and zero-valent carbon compounds (carbones) such as carbodiphosphoranes (CDPs) and carbodicarbenes. Thus, adiabatic IPs as low as 5.5 ± 0.1 eV are predicted for CDPs, which are about 0.7-1.2 eV lower than those of simple phosphorus and sulfur ylides. In contrast, the corresponding values for N-heterocyclic carbenes are about 8.0 eV while those for simple singlet carbenes such as dichlorocarbene and difluorocarbene range from about 9.0 eV to well over 11.0 eV.

Synthesis of a low-valent Al4+ cluster cation salt

Low-valent aluminium compounds are very reactive main-group species and have therefore been widely investigated. Since the isolation of a stable molecular Al(I) compound in 1991, [(AlCp*)₄] (Cp* = [C₅Me₅]^-), a variety of highly reactive neutral or anionic low-valent aluminium complexes have been developed. By contrast, their cationic counterparts have remained difficult to access. Here, we report the synthesis of [Al(AlCp*)₃]⁺[Al(OR^F)₄]^- (R^F = C(CF₃)₃) through a simple metathesis reaction between [(AlCp*)₄] and Li[Al(OR^F)₄]. Unexpectedly, the [Al(AlCp*)₃]⁺ salt forms a dimer in the solid state and concentrated solutions. Addition of Lewis bases results in monomerization and coordination to the unique formal Al⁺ atom, giving [(L)_xAl(AlCp*)₃]⁺ salts where L is hexaphenylcarbodiphosphorane (x = 1), tetramethylethylenediamine (x = 1) or 4-dimethylaminopyridine (x = 3). The Al⁺-Al_Cp* bonds in the resulting [(L)_xAl(AlCp*)₃]⁺ cluster cations can be finely tuned between very strong (with no ligand L) to very weak and approaching isolated [Al(L)₃]⁺ ions (when L is dimethylaminopyridine).

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.