Reductive assembly of cyclobutadienyl and diphosphacyclobutadienyl rings at uranium

Abstract

Despite the abundance of f-block-cyclopentadienyl, arene, cycloheptatrienyl and cyclooctatetraenide complexes, cyclobutadienyl derivatives are unknown in spite of their prevalence in the d-block. Here we report that reductive [2 þ 2]-cycloaddition reactions of diphenylacetylene and (2,2-dimethylpropylidyne)phosphine with uranium(V)-inverted sandwich 10p-toluene tetra-anion complexes results in the isolation of inverted sandwich cyclobutadienyl and diphosphacyclobutadienyl dianion uranium(IV) complexes. Computational analysis suggests that the bonding is predominantly electrostatic. Although the c 4 molecular orbital in the cyclobutadienyl and diphosphacyclobutadienyl ligands exhibits the correct symmetry for d-bonding to uranium, the dominant covalent contributions arise from p-bonding involving c 2 and c 3 orbital combinations. This contrasts with uranium complexes of larger arenes and cyclo-octatetraenide, where d-bonding dominates. This suggests that the angular requirements for uranium to bond to a small four-membered ring favours p-bonding, utilizing 5f-instead of 6d-orbitals, over d-bonding that is favoured with larger ligands, where 6d-orbitals can become involved in the bonding.

Triamidoamine uranium(IV)–arsenic complexes containing one-, two- and threefold U–As bonding interactions

“…The bond topology analysis suggests that the U-As bonds are polarized, and in agreement with DFT and NBO analyses, confirms the presence of σ 2 , σ 2 π 2 and σ 2 π 4 U-As bonding interactions in 2c, 3c and 4′. Although it should be recognized that dipolar U n+ -As n− resonance forms will contribute to the electronic structure of these U-As linkages, the ellipticity values for σ 2 2c and σ 2 π 4 4′ are similar to those of ethane (0.0) and acetylene (0.0), whereas that of 3c lies between those of benzene (0.23) and ethylene (0.45) and exceeds the calculated value for the parent E-diarsene HAs=AsH (0.33) 63,74 .…”

“…Magnetic studies provide qualitative bracketing of the relative crystal field strengths of arsenide, arsinidene and arsenido ligands, and support the notion that the arsenido ligand in 4 exhibits the strongest point charge and crystal field at uranium(IV) compared to 2c and 3c, which are similar to each other, perhaps reflecting the polar nature of these U-As bonds. As in related nitride complexes 38,39 calculations suggest that uranium tends to deploy 5f orbitals more than 6d orbitals in the U-As bonds 74 . The complexes reported herein add to our understanding of actinideligand multiple bonds and soft uranium-ligand combinations more broadly and may in the future inform the design of new soft-donor ligands for the actinides.…”

Isolation of Elusive HAsAsH in a Crystalline Diuranium(IV) Complex

“…The calculated MDC q charges and MDC m spin densities at each uranium average +3.20 and −2.31, respectively, which suggests modest net donation of electron density to uranium(IV) from the ligands. [28] The arsenic MDC q charges average −1.12, which is consistent with the HAsAsH fragment carrying a formal −2 charge overall, which is a requirement of being bonded to two uranium(IV) [U(Tren TIPS )] + cations for charge neutrality. The calculated As–As Mayer bond order is 0.97, consistent with the As–As single bond suggested by the X-ray diffraction data, whereas the U–As Mayer bond orders average 0.34 and suggest polarized interactions; for comparison, calculated As–H, U–N amide , and U–N amine Mayer bond orders average 0.92, 0.82, and 0.22, respectively.…”

Radical anionic versus neutral 2,2′-bipyridyl coordination in uranium complexes supported by amide and ketimide ligands

“…[33][34][35][36][37][38][39][40][41][42] As part of our reactivity study, we decided to investigate the reactivity of arene-bridged inverted sandwich diuranium complexes with bipy to determine the factors influencing the formation of the resulting products, especially the oxidation state of the bipy ligand.…”