Electronic underpinnings of phosphido-bridged Pt-3 clusters and the questioned stereochemistry of a uniquely reported 46e(-) species

摘要

The compound H(PEt3)(3)Pt-3(mu-PPh2)(3) is the unique example of a 46e(-) phosphido-bridged triangular cluster, but its X-ray assigned stereochemistry appears questionable. In particular, the H-free P3Pt3(mu-P)(3) metal core is identical to that of the 46e(-) cation [(PEt3)(3)Pt-3(mu-PPh2)(3)](+) in two salts of the same publication. Also, the lack of a distortional effect due to the upright and strongly-bound hydride ligand is suspicious and intriguing aspects emerge from the inconsistent electronic structure. Although H(PEt3)(3)Pt-3(mu-PPh2)(3) is fully validated by IR and NMR spectra, DFT optimizations never reproduced the reported structure but highlighted a different stereochemistry not in contrast with the spectroscopic response. Here, a formal Pt(II) ion is almost separated with an essential square-planar coordination, completed by two trans-axial ligands (H and Et3P) perpendicular to the Pt-3 plane. Provided the chemical reliability of the in silico molecule, the crystals of the experimental structure have likely contents other than the hydridic cluster and the co-crystallized Ph2PH molecule. As a working hypothesis, the Pt-H and P-H linkages of the distinct components may have reacted together with H-2 release, and subsequent crstallization of the salt [(PEt3)(3)Pt-3(mu-PPh2)(3)](+)/[Ph2P]. This would explain the equal geometries of the putative 46e(-) cluster and the H-free 46e(-) cation. In the lack of any experimental X-ray dataset, the proposed crystal formulation could not be fully validated, but various aspects support its reliability. Essentially, the problem may arise from the misplacement of two H atoms (those of the mentioned Pt-H and P-H linkages), which does not affect the structural refinement but determines the chemical inconsistency. (C) 2014 Elsevier B.V. All rights reserved.