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Reaction between equimolar amounts of trans-[PdCl(PPh3)2(CNR)][BF4] (R = t-Bu 1, Xyl 2) and diisopropylammonium azide 3 gives the tetrazolate trans-[PdCl(PPh3)2(CN4t-Bu)] (67%, 4) or trans-[PdCl(PPh3)2(CN4Xyl)] (72%, 5) complexes. 4 and 5 were characterized by elemental analyses (C, H, N), HRESI+-MS, 1H and 13C{1H} NMR spectroscopies. In addition, the structure of 4 was elucidated by a single-crystal X-ray diffraction. DFT calculations showed that the mechanism for the formal cycloaddition (CA) of N3- to trans-[PdCl(PH3)2(CNMe)]+ is stepwise. The process is both kinetically and thermodynamically favorable and occurs via the formation of an acyclic NNNCN-intermediate. The second step of the formal CA, i.e. cyclization, is rate limiting. Despite the fact that the substitution of CNMe by the N3- ligand is slightly thermodynamically favorable, we were unable to find paths on the potential energy surface for hypothetical CA between uncomplexed isocyanide and palladium-bound azide. Thus, we believe that the experimentally observed palladium tetrazolate complexes are, in fact, generated from the negatively charged uncomplexed azide and the positively charged metal-bound isocyanide species, and this reaction path is favorable from the viewpoint of Coulomb attraction.
Original language | English |
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Pages (from-to) | 521-527 |
Number of pages | 7 |
Journal | New Journal of Chemistry |
Volume | 40 |
Issue number | 1 |
DOIs | |
State | Published - 1 Jan 2016 |
ID: 7552408