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Experimental and Computational Investigations of Tautomerism and Fluxionality in PCP‐ and PNP‐Bridged Heavy Chalcogenides
Author(s) -
Elder Philip J. W.,
Chivers Tristram,
Thirumoorthi Ramalingam
Publication year - 2013
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201201378
Subject(s) - chemistry , tautomer , tellurium , chalcogen , electron paramagnetic resonance , crystallography , nuclear magnetic resonance spectroscopy , dihedral angle , toluene , selenium , spectroscopy , stereochemistry , computational chemistry , molecule , inorganic chemistry , hydrogen bond , organic chemistry , nuclear magnetic resonance , physics , quantum mechanics
The reaction of H 2 C(PCl 2 ) 2 with four equivalents of i PrMgCl produces H 2 C(P i Pr 2 ) 2 , which was treated with tellurium in boiling toluene, or selenium in toluene at room temperature, to give the monochalcogenides EP i Pr 2 CH 2 P i Pr 2 (E = Te, 4a ; E = Se, 4b ) in high yields. X‐ray structural determinations show that 4a and 4b exist as the CH 2 tautomers in the solid state with E–P–C–P dihedral angles of 56.1(2)° and 56.7(1)°, respectively. DFT calculations were carried out for the isolectronic series EPR 2 CH 2 PR 2 and EPR 2 NHPR 2 (E = Se, Te; R = Me, i Pr, t Bu, Ph) and for their non‐chalcogenated precursors in order to elucidate the factors that determine the preference for PH tautomers in some PNP‐bridged systems. Compounds 4a and 4b were also characterized by multinuclear ( 1 H, 13 C, 31 P, 77 Se, 125 Te) NMR spectroscopy. In solution, 4a exhibits fluxional behavior, which has been investigated by variable‐temperature and variable‐concentration multinuclear NMR spectroscopy. The observed behavior is consistent with an intermolecular tellurium transfer with an activation energy of 21.9 ± 3.2 kJ mol –1 ; consideration of selenium exchange in 4b indicates a much higher energetic barrier. DFT calculations provide insights into the pathway for the chalcogen exchange process in 4a (Δ E = 20.4 kJ mol –1 ). The outcome of reactions of 4a with selenium and n BuLi reflects the lability of the P‐Te functionality.