Comparison of the molecular structures of trans-di(isothiocyanato)bis(triphenylphosphine)palladium(II) and trans-di(thiocyanato)bis(triphenyl phosphite)palladium(II)

Abstract

The molecular structures of trans-[Pd(NCS)₂(PPh₃)₂](I) and trans-[Pd(SCN)₂{P(OPh)₃}₂](II) have been determined by single-crystal X-ray diffractometry to investigate the roles of π-bonding and steric effects on the thiocyanate bonding mode. Crystals of (I) are triclinic, space group P with unit-cell dimensions a= 7.912(6), b= 11.659(7), c= 10.532(9)Å, α= 111.00(5), β= 87.51(8), γ= 106.36(6)°, Z= 1. Crystals of (II) are monoclinic, space group P2₁/c, with unit-cell dimensions a= 9.922(4), b= 10.096(8), c= 19.334(14)Å, β= 108.46(5)°, Z= 2. The structures were solved by heavy-atom methods and refined to R 0.036 [(I), 2 513 reflections] and 0.060 [(II), 3 089 reflections].

The thiocyanate ion is N-bonded in (I) and S-bonded in (II). Pd–P bond lengths are 2.3404(9) in (I) and 2.312(2)Å in (II), the significantly shorter length in the latter being attributed to decreased steric bulk and a lower σ-trans influence for the phosphite ligands. The Pd–S bond length [2.352(2)Å] in (II) appears to be anomalously long and inconsistent with a strong π-component to the bond. The presence of N-bonded thiocyanates in (I) is probably a result of intramolecular steric crowding rather than Pd–P π-bonding.