Synthesis and characterization of organoimido- and organoamido-rhenium(V) complexes. Crystal structures of [ReCl2(NC6H4PPh2-2)(HNC6H4PPh2-2)], [Re(8-HNC9H6N)2O(PPh3)][BPh4] and [Re(NPh)(NC5H3S-2-SiMe3-3)2(PPh3)][BPh4]

Abstract

The reaction of [ReCl₃O(PPh₃)₂] in toluene with 2-diphenylphosphinoaniline yielded the brown rhenium(V) amido/imido-complex [ReCl₂(NC₆H₄PPh₂-2)(HNC₆H₄PPh₂-2)]1. This represents the first example of a metal complex where a 2-aminophenylphosphine is fully deprotonated to give an N,P chelated imido-complex. The crystal structure of 1 shows a distorted-octahedral geometry with the imido-nitrogen trans to chloride whereas the amido-nitrogen is disposed trans to a phosphorus. The Re–N length of 1.988(4)Å for the amido nitrogen is consistent with protonation of the nitrogen in the chelated ligand. A Re–N bond length of 1.757(4)Å and a Re–N–C angle of 137.8(3)° for the deprotonated imide nitrogen imply substantial multiple bonding. The oxo-complex [Re(8-HNC₉H₆N)₂O(PPh₃)][BPh₄]2 was the unexpected product in the reaction of [ReCl₃O(PPh₃)₂] with 8-aminoquinoline in ethanol. It has a distorted-octahedral structure with two chelated amide ligands. The two quinoline-ring nitrogens as well as the two amido-nitrogens are arranged in a mutually cis configuration. The oxo and triphenylphosphine ligands occupy the remaining co-ordination sites. Reaction of [ReCl₃(NPh)(PPh₃)₂] in ethanol with the sterically hindered 3-trimethylsilylpyridine-2-thiol (Htspyt) yielded the green rhenium(V) phenylimido-complex [Re(NPh)(PPh₃)(tspyt)₂][BPh₄]3. Reaction of the unsubstituted pyridine-2-thiol (Hpyt) with the parent imido-complex yielded the analogous complex [Re(NPh)(PPh₃)(pyt)₂][BPh₄]4. The crystal structure of 3 reveals a distortedoctahedral configuration of the ligands about the central rhenium atom. The imide and phosphine ligands are cis with the remaining sites being occupied by the S,N chelated pyridinethiolate ligands. A ReN bond length of 1.725(8)Å and a Re–N–C bond angle of 166.0(6)° are indicative of the imide ligand functioning as a four-electron donor.