Electronic structure of monodentate-coordinated diphosphine complexes. Photoelectron spectra of pentacarbonylmethylene bis(dimethyl phosphine)molybdenum and pentacarbonylethylene bis(dimethyl phosphine)molybdenum

Exploring Phosphine Electronic Effects on Molybdenum Complexes: A Combined Photoelectron Spectroscopy and Energy Decomposition Analysis Study

“…In Figure a–c, the position of this band is shifted to lower energies by increasing the alkyl size: from 9.84 eV for PMe 3 to 9.52 eV for PEt 3 , and 9.31 eV for P i Pr 3 . Note that the PMe 3 band position measured at 9.84 eV is in great accordance with the He­(I) spectrum of the same Mo complex of Lichtenberger and Jatchko who measured a band at 9.87 eV. , These energies have to be compared with those of the P-lone pair in the uncoordinated ligand. Experimental data on the P lone-pair band position could only be found for PMe 3 and PEt 3 in two works giving either 8.79 and 8.52 eV or 8.60 and 8.27 eV for PMe 3 and PEt 3 , respectively.…”

“…PES is thus able to provide direct and critical information on the molecular orbitals (MOs) of the complex and therefore of both the σ-donor and π-acceptor characters of the ligand. Using a molecular orbital interaction scheme, Lichtenberger was able to interpret and analyze the electronic effect influence on numerous ligands, including phosphines. ,,− Another approach, the quantitative analysis of ligand effects (QALE), , consists in the analysis of several experimental thermochemical and spectroscopic data of the complex and ligand to extract electronic parameters describing the stereoelectronic properties of the ligand. The QALE approach has demonstrated its ability for separating the σ and π contributions of the ligand, but it suffers of a few limitations.…”

Induced Acceleration of Phosphine Exchange in Metal Carbonyls by Pendant Groups of Coordinated Polyphosphines. Two Dangling Phosphine Arms Are Much Better Than One1

“…Electronic considerations would lead us to believe that the basicities of the nonequivalent phosphorus groups of (PPh 2 ) 2 CHCH 2 PPh 2 are quite similar, as each phosphorus atom has two phenyl substituents and is separated from other phosphorus atoms by either one or two methylene groups. For example, the p K a values of Ph 2 PCH 2 CH 2 PPh 2 and Ph 2 CH 2 PPh 2 are 3.86 and 3.81, respectively, and photoelectron spectroscopy studies show that Me 2 PCH 2 CH 2 PMe 2 and Me 2 PCH 2 PMe 2 are electronically nearly identical in LMo(CO) 5 complexes …”

Sterically crowded diphosphinomethane ligands: molecular structures, UV-photoelectron spectroscopy and a convenient general synthesis of tBu2PCH2PtBu2 and related speciesDedicated to Professor Roald Hoffmann on the occasion of his 65th birthday.Electronic supplementary information (ESI) available: photoelectron spectra for compounds 1–6, ORTEP diagrams for compounds 1–3 and 5–9+, calculated minimum structures (UB3LYP/6-31G**) and structural parameters for two forms of the radical cation dmpm. See http://ww

“…Assuming the validity of Koopmans' theorem (Àe j ¼ IP j ), which should be allowed in these organic systems, the first two ionisations correspond to the two canonical, non-degenerate, symmetryadapted highest occupied molecular orbitals, which are the linear combinations of the two P lone pairs, delocalised to some extent into the P-C and C-C bonds. Comparison with the values reported for monodentate PMe 3 (8.59 eV) 46 and P( t Bu) 3 (7.70 eV) 43 as well as the less bulky bidentate ligands bis(dimethylphosphino)methane (dmpm) (8.43 46 or 8.51 eV 45 ) and bis(dimethylphosphino)ethane (dmpe) (8.45 46 or 8.47 eV 45 ) shows that the diphosphines reported here are much more readily ionised than their methyl-substituted analogues, a For the asymmetrical molecules, the first P-C distance involves the phosphorous atom bearing tert-butyl groups (3, 4 and 5) or the P(III) phosphorous atom (8 + , 9 + ). b The dihedral angle is the torsion angle between a dummy atom located at the calculated centroid of the three carbon atoms bound to P1, P1, P2 and a dummy atom located at the calculated centroid of the three carbon atoms bound to P2.…”

“…In phosphorous chemistry, photoelectron spectroscopy (UV-PES) has been used to characterise the valence electronic structure of neutral phosphine ligands. [43][44][45][46] It has been shown that the lower the first (lone pair) ionisation energy of phosphine ligands, the better they are as donors in a coordinative bond. Photoelectron spectroscopy is thus one of the few physical measurements that can assess-at least in a qualitative sense-the electronic properties and behaviour of ligands in the absence of metals.…”