Microwave synthesis of bis(tetrazolato)-PdII complexes with PPh3 and water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA). the first example of C-CN bond cleavage of propionitrile by a PdII Centre

Abstract

[2 + 3 Cycloaddition reactions of the di(azido)-PdII complex trans-[Pd(N3)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-FC 6H4 (3d), 2-NC5H4 (3e), 3-NC 5H4 (3f), 4-NC5H4 (3g). The reaction of trans-[Pd(N3)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 PdII. The [2 + 3 cycloadditions of [Pd(N3) 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 °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, 1H, 13C{1H} and 31P{1H} 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. © 2011 Elsevier B.V. All rights reserved.