Bis(isodiazene) and related complexes of molybdenum(VI). Syntheses and structures of [Mo(OTf)2(NNPh2)2(py)2], [MoCl(OTf)(NNPh2){NC5H3(CH2C(O)Ph2)2-2,6}], [{MoCl(NNPh2)2(µ-Cl)(NH2But)}2] and [MoTp′Cl(NNPh2)2] [OTf = O3SCF3, Tp′ = tris(3,5-dimethylpyrazolyl)hydroborate]

Abstract

Possible routes to [Mo(NNPh₂)₂R₂], where R = alkyl or aryl groups, have been investigated including the interaction of [MoCl₂(NNPh₂)₂(dme)] 1 (dme = 1,2-dimethoxyethane) with the standard alkylating agents LiR, RMgX, R₂Mg or R₂Zn under various conditions of solvent and temperature. There was, however, no evidence to suggest alkylation had taken place. Treatment of 1 with two equivalents of silver trifluoromethanesulfonate, silver triflate (AgOTf), in the presence of pyridine gave the golden-yellow bis(triflate) complex [Mo(OTf)₂(NNPh₂)₂(py)₂] 2 in good yield. In the presence of an excess of bipy (2,2′-bipyridine) the known dicationic species [Mo(NNPh₂)₂(bipy)₂]²⁺ was isolated as its PF₆^– salt. Attempts to replace triflate by alkyl groups in 2 were unsuccessful. A similar reaction of 1 with silver triflate in the presence of the bulky tridentate alkoxide 2,6-bis(2-hydroxy-2,2-diphenylethyl)pyridine (H₂L) led to loss of an NNPh₂ group (presumably as hydrazine) and formation of the green mono-isodiazene complex [MoCl(OTf)(NNPh₂)(L)] 3. The compound [Mo(CH₂CMe₂Ph)₂(NBu^t)₂] underwent partial imido ligand exchange with an excess of 1,1-diphenylhydrazine hydrochloride to give the brown bis(isodiazene) chloro-bridged dimer [{MoCl(NNPh₂)₂(µ-Cl)(NH₂Bu^t)}₂] 4. A chloride substitution reaction of 1 with potassium tris(3,5-dimethylpyrazolyl)hydroborate, (KTp′) afforded the bis(isodiazene) complex [MoTp′Cl(NNPh₂)₂] 5. The crystal and molecular structures of 2–5 have been determined. The complexes all contain linear isodiazene groups with Mo–N distances in the range 1.755(6) to 1.768(7) Å. In 2 the molybdenum(VI) centre has a pseudo octahedral geometry with axial pyridines and cis-triflate groups. In six-co-ordinate 3 the pyridinediolate ligand has a meridional donor atom arrangement with an equatorial isodiazene ligand. The binuclear compound 4 has slightly asymmetric chloro bridges coplanar with the terminal isodiazene ligands. Complex 5 is octahedral, having a facially co-ordinated Tp′ ligand and linear NNPh₂ ligands.