Synthesis and structural characterisation of tris(diphenylthiophosphinoyl)methane and tris(diphenylthiophosphinoyl)methanide complexes of rhodium and iridium; X-ray structures of [Rh(C8H12){η2-C(P(S)Ph2)3-S,S}] and [Ir(CO)2{gh2-C(P(S)Ph2)3-S,S}]

Abstract

Reactions of [MCl(cod)]2, M = Rh or Ir, cod = cyclooctadiene, with CH{P(S)Ph2}3 give the complex cations, [M(cod){CH(P(S)Ph2)3}]+, which are isolated in high yield as BF4− or ClO4− salts. These are the first reported examples of CH{P(S)Ph2}3 complexes in which the methine proton is retained after coordination. The high acidity of this proton is demonstrated by easy deprotonation to corresponding [M(cod){C(P(S)Ph2)3}] complexes. The 31P NMR spectrum of [Rh(cod){CH(P(S)Ph2)3}]BF4 remains a single line to −100°C whereas that of [Rh(cod){C(P(S)Ph2)3}] is resolved into two resonances at −60°C, suggesting that the former complex is 5-coordinate with an η3 (S,S,S) ligand and the latter 4-coordinate, η2 (S,S). The 4-coordinate structure is confirmed by X-ray diffraction studies of [Rh(cod){C(P(S)Ph2)3}] and [Ir(CO)2{C(P(S)Ph2)3}] which both show approximately square planar metal centers, η2 ligands with the third sulfur non-coordinated (“dangling”), and trigonal planar geometry at the central carbon of the tris(phosphinesulfide) ligand. [Rh(cod){C(P(S)Ph2)3}] and [Ir(CO)2{C(P(S)Ph2)3}] crystallize in the Pbca space group (Z = 8) with respective unit cells: a = 20.427(4) Å, b = 16.931(2) Å, c = 23.138(3) Å; and a = 22.140(6) Å, b = 22.317(5) Å, c = 14.792(3) Å. Line shape analysis for a variable temperature 31P NMR study of [Rh(cod){C(P(S)Ph2)3}] gives ΔGo‡ 46 ± 2 kJ mol−1 for the dynamic exchange of coordinated and non-coordinated sulfur.