Abstract
[2 + 3] Cycloaddition reactions of the di(azido)-Pd-II complex trans-[Pd(N-3)(2)(PPh3)(2)] (1) with an organonitrile RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N4CR)(2)(PPh3)(2)] (3) [R = Me (3a), Ph (3b), 4-ClC6H4 (3c), 4-FC6H4 (3d), 2-NC5H4 (3e), 3-NC5H4 (3f), 4-NC5H4 (3g)]. The reaction of trans-[Pd(N-3)(2)(PPh3)(2)] (1) with propionitrile (2h) also affords, apart from trans-[Pd(N4CEt)(2)(PPh3)(2)] (3h), the unexpected mixed cyano-tetrazolato complex trans-[Pd(CN)(N4CEt)(PPh3)(2)] (3h') which is derived from the reaction of the bis(tetrazolato) 3h with propionitrile, with concomitant formation of 5-ethyl-1H-tetrazole, via a suggested unusual oxidative addition of the nitrile to Pd-II. The [2 + 3] cycloadditions of [Pd(N-3)(2)(PTA)(2)] (4) (PTA = 1,3,5-triaza-7-phosphaadamantane) with RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N4CR)(2)(PTA)(2)] (5) [R - Ph (5a), 2-NC5H4 (5b), 3-NC5H4 (5c), 4-NC5H4 (5d)]. All these reactions are greatly accelerated by microwave irradiation (1 h, 125 degrees C, 300 W). Taking advantage of the hydro-solubility of PTA, a simple liberation of 5-phenyl-1H-tetrazole from the coordination sphere of trans-[Pd(N4CPh)(2)(PTA)(2)] (5a) was achieved. The complexes were characterized by IR, H-1, C-13{H-1} and P-31{H-1} NMR spectroscopies, ESI+-MS, elemental analyses and, for 3b, also by X-ray structure analysis. Weak agostic interactions between the CH groups of the triphenylphosphines and the palladium(II) centre were found. (C) 2011 Elsevier B. V. All rights reserved.