Unprecedented Tris-Phosphido-Bridged Triangular Clusters with 42 Valence Electrons. Chemical, Electrochemical and Computational Studies of their Formation and Stability

Abstract

This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(μ-PBu(t)2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e(-). The new species were obtained by an apparent bielectronic oxidation of the 44e(-) monohalides Pt3(μ-PBu(t)2)3(CO)2X with the corresponding dihalogen X2. Their X-ray structures are close to the D3h symmetry, similarly to the 44e(-) analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt3(μ-PBu(t)2)3I3, the redox potentials indicated that I2 can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e(-) intermediate [Pt3(μ-PBu(t)2)3(CO)2I](+) was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt3(μ-PBu(t)2)3I3, the transient 44e(-) species [Pt3(μ-PBu(t)2)3(CO)3](+) is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e(-) intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e(-) associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e(-) phosphido-bridged Pt3 clusters can be attributed to the simultaneous presence of three terminal halides.

The atomic level mechanism of white phosphorous demolition by di-iodine

“…On the other hand, the participation of I 2 in redox processes is rather general, a previous example studied by us being the oxidation of classic 44e − phosphide bridged Pt 3 clusters to 42e − derivatives with the reduced iodides as terminal ligands. 14 In our computational approach to the P 4 activation, the DFT-D functional was used, 15 since the dispersion forces help detecting particularly feeble adducts, some of which are endergonic and clearly disfavored by entropy. In particular, the latter highlights incipient Halogen Bonding (XB), still far from its canonic formulation emerging in frozen crystal structures, 16 which clearly indicate the occurrence of a major electron density redistribution.…”

Multinuclear Solid-State NMR and DFT Studies on Phosphanido-Bridged Diplatinum Complexes

“…Platinum diorganophosphanido complexes have been the object of intense study in the last years due to the rich chemistry they exhibit. − NMR spectroscopy is a powerful technique for investigating the structure and dynamics in solution of such complexes, owing to the presence of several different spin 1/2 nuclei in these molecules ( 1 H, 31 P, 195 Pt, 13 C, and in several cases 19 F). Although NMR studies on this kind of complexes have been performed for several decades, some issues about 195 Pt NMR and 31 P NMR remain unclear.…”

Synthesis and Spectroscopic and Spectroelectrochemical Characterization of a New Family of 44e– Tris-Phosphido-Bridged Palladium Triangles

“…In the presence of I − , which reacts with [Pt 3 (μ-PBu t 2 ) 3 (CO) 3 ] + to regenerate cluster 10, and of the oxidant, the reaction continues until complete conversion of Pt 3 (μ-PBu t 2 ) 3 (CO) 2 I into Pt 3 (μ-PBu t 2 ) 3 I 3 . 20 The results described here suggest that any 42e − Pd 3 species, including the hypothetical cluster Pd 3 (μ-PBu t 2 ) 3 I 3 which could simply be formed by the reaction of 9 + with I − , would not be easily isolable.…”

“…Moreover, after an exhaustive electrolysis, the CV of the solution shows two weak waves for reversible reductions in the cathodic region (−0.27 and −0.88 V), 21 that we may tentatively assign to the unstable cation 9 + . We recall that the redox potentials for the related reductions of [Pt 3 (μ-PBu t 2 ) 3 (CO)I 2 ] + , 11 + , the elusive platinum analogue of cation 9 + , were estimated to be +0.06 (11 +/0 ) and −0.47 (11 0/−1 ) V. 20 2.4.2. Cation 5 + .…”