Ligands Based on Phosphine‐Stabilized Aluminum(I), Boron(I), and Carbon(0)

Abstract

As ystematic quantum chemical study of the bondingi nd 6 -transition-metalc omplexes, containing phosphine-stabilized, main-group-element fragments, (R 3 P) 2 E, as ligands( E = AlH, BH, CH + ,C ), is reported. By using energy decompositiona nalysis, it is demonstrated that as trong MÀ Eb ondi sa ccompanied by weakP ÀEb onds, and vice versa. Although the AlÀMb ond is, for example, found to be very strong,t he weak AlÀPb onds uggestst hat the corresponding metal complexes will not be stable towards phosphine dissociation. The interaction energies for the boron(I)-based ligand are lower,b ut still higher than those for two-carbonbased ligands.F or neutral ligands, electrostatic interactions are the dominating contributions to metal-ligand bonding, whereas for the cationic ligand as ignificant destabilization, with weak orbital and even weaker electrostatic metalligandinteractions, is observed. Finally,for iron(II) complexes, it is demonstrated that different reactivity patterns are expectedf or thef our donor groups:t he experimentally observedr eversible EÀHr eductivee limination of the borylenebased ligand (E = BH) exhibits significantly higherb arriers for the protonated carbodiphosphorane( CDP) ligand (E = CH) and would proceed throughd ifferent intermediates and transition states.F or aluminum, such reaction pathways are not feasible (E = AlH). Moreover, it is demonstrated that the metalh ydrido complexes with CDP ligandsm ight not be stablet owards reduction and isomerization to ap rotonated CDP ligand and areduced metal center.

Facial vs. Meridional Coordination Modes in ReI Tricarbonyl Complexes with a Carbodiphosphorane‐based Tridentate Ligand

“…Despite the retained planarity of the CDPmoiety in fac-3, the tilting of this donor group seems to be necessary for the realization of the facial coordination mode. A pronounced difference between the facial and meridional coordination mode is observed for the 13 C chemical shift of the central CDP-group, which indicates a more electron rich carbon atom of the CDP-moiety for the mer-isomer. Both isomers give rise to three bands between 1850 and 2060 cm À 1 in the IR spectrum for CÀ O-stretching vibrations, which show a typical pattern for each isomer.…”

“…The protonated CDP‐moiety (in fac ‐2 ) is a cationic ligand that solely acts as σ‐donor. A shortening of the Re−C CDP bond of 0.059–0.066 Å is observed upon removal of the proton from the CDP‐moiety, which might reflect the stronger σ‐donor and the π‐donor ability of the neutral CDP‐ligand as well as a reduced Coulomb repulsion between the central donor group and the cationic rhenium fragment relative to the protonated CDP‐ligand [13] . The lone pair generated by removal of the proton from the protonated CDP may be stabilized to a significant extent by π‐back bonding to the neighboring phosphine groups, which is indicated by shorter P−C CDP bond distances (Δ>0.1 Å).…”

“…A shortening of the ReÀ C CDP bond of 0.059-0.066 Å is observed upon removal of the proton from the CDP-moiety, which might reflect the stronger σ-donor and the π-donor ability of the neutral CDP-ligand as well as a reduced Coulomb repulsion between the central donor group and the cationic rhenium fragment relative to the protonated CDP-ligand. [13] The lone pair generated by removal of the proton from the protonated CDP may be stabilized to a significant extent by π-back bonding to the neighboring phosphine groups, which is indicated by shorter PÀ C CDP bond distances (Δ > 0.1 Å). In comparison to the C CDP À P bond distances in the previously reported complex [({Ph 3 P} 2 C)ReO 3 ] + (1.764-1.777 Å) [15] these bond distances in fac-3 and mer-3 are significantly shorter (1.676-1.704 Å), indicating a stronger delocalization of the CDP lone pair by π-back-bonding to the phosphine groups (negative hyper conjugation) in the reported rhenium(I) complexes.…”

“…[1][2][3][4] This description of the bonding situation is underlined by their ability to act as σand π-donor ligands [5][6][7][8] as well as μ 2 -bridging ligands in transition metal complexes [9,10] and between main group element Lewis acids. [11] In this context, CDPs were shown to be strong electron donating ligands, [12,13] which are suited to stabilize transition metal ions over a wide range formal oxidation states. [14,15] Due to their binding properties, CDP-based ligands were predicted to be superb substitutes for carbenes in Grubbs-II type metathesis catalysts and thus should lead to an increased catalytic activity.…”

The Pincer Platform Beyond Classical Coordination Patterns

“…The resulting ligands in complexes of similar to 14 are best described as neutral pincer‐type ligands containing three L‐type functions. [ 78,82,84 ]…”