Al₄(P^tBu₂)₆ − a Derivative of Al₄H₆ − and Other Al₄ Species: A Challenge for Bonding Interpretation between Zintl Ions and Metalloid Clusters

Abstract

The highly energetic molecule Al(4)H(6), with its distorted tetrahedral structure, was recently characterized via mass spectrometry and photoelectron spectroscopy investigations (Li, X.; et al. Science 2007, 315, 356). Here we present the preparation and structural investigation of the first analogous Al(4)R(6) cluster compound. In order to understand the bonding in this kind of Al(4) molecule, density functional theory and second-order Møller-Plesset perturbation theory calculations were performed. The results obtained are discussed in comparison with bonding in other Al(4) moieties, especially the aromatic bonding behavior in the dianionic planar Al(4)(2-) species (Li, X.; et al. Science 2001, 291, 859). Finally, on the basis of the results obtained for Al(4) species, a more general problem is discussed: the difference in bonding between Zintl ions and metalloid clusters.

K[Al4(PPh2)7PPh]: An AlII Phosphanide / Phosphinidene Intermediate on the Path to AlP Formation

“…[9,11] Although the alkyl substituent of the phosphanides differs, the Al/P frameworks in all three compounds have notably similarities in Al-P coordination and metric parameters. These structures are shown in the SI.…”

“…[9][10][11] The latter complex contains a naked P 3-ion that presumably results from a successive ligand-based decomposition process leading to the Al 3 P moiety. DFT studies showed how the ligand redox vs. disproportionation pathways followed different routes from the Al I precursors to give markedly different products.…”

Does Al4H 14 — cluster anion exist? High-level ab initio study

“…During the last three years, several novel alanes, both neutral and anionic, have been made and characterized. The emerging structural and electronic properties of alanes and their derivatives involving a small Al 4 cluster core have been notably the focus of the widespread interest [1, 2, 5, 6]. …”

“…Furthermore, the Al 4 H 6 cluster was suggested to be a high-energy density molecule, with the estimated heat of combustion (giving the Al 2 O 3 and water products) to be about 2.5 times greater than that for methane [1]. Various Al 4 R 6 and Al 4 R 5 X derivatives of Al 4 H 6 with the hydrogen atoms substituted by the bulky R groups and halogens X (R = P t Bu 2 ; X = Br,Cl) were subsequently prepared and structurally characterized [5]. …”

(Multi‐)Metallic Cluster Growth

“…The elucidation of mechanisms becomes more difficult as soon as several pathways need to be considered, for instance, upon observation of intermediates that occur in different types of reactions ( Figure 25). [64] The formation of [Al 4 R 6 ]( R 6 = Cl/Br + 5P tBu 2 or 6P tBu 2 )c an be viewed as ac omproportionation of [Al 2 R 4 ]a nd [Al 2 R 2 ], as ar eaction of monomeric [AlR 2 ]a nd [AlR], or as aradical reaction between two [Al 2 R 3 ]C radicals (as aproduct of [AlR 2 ]a nd [AlR] or upon elimination of R À from [Al 2 R 4 ]C À ). [Al 2 R 3 ]C was described earlieri nt he literature.…”