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

Abstract

[2 + 3] Cycloaddition reactions of the di(azido)-Pd II complex trans-[Pd(N 3) 2(PPh 3) 2] ( 1) with an organonitrile RCN ( 2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N 4CR) 2(PPh 3) 2] ( 3) [R = Me ( 3a), Ph ( 3b), 4-ClC 6H 4 ( 3c), 4-FC 6H 4 ( 3d), 2-NC 5H 4 ( 3e), 3-NC 5H 4 ( 3f), 4-NC 5H 4 ( 3g)]. The reaction of trans-[Pd(N 3) 2(PPh 3) 2] ( 1) with propionitrile ( 2h) also affords, apart from trans-[Pd(N 4CEt) 2(PPh 3) 2] ( 3h), the unexpected mixed cyano-tetrazolato complex trans-[Pd(CN)(N 4CEt)(PPh 3) 2] ( 3h′) which is derived from the reaction of the bis(tetrazolato) 3h with propionitrile, with concomitant formation of 5-ethyl-1 H-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(N 4CR) 2(PTA) 2] ( 5) [R = Ph ( 5a), 2-NC 5H 4 ( 5b), 3-NC 5H 4 ( 5c), 4-NC 5H 4 ( 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-1 H-tetrazole from the coordination sphere of trans-[Pd(N 4CPh) 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.