Donor–acceptor complexes incorporating ferrocenes: spectroelectrochemical characterisation, quadratic hyperpolarisabilities and the effects of oxidising and reducing agents

Abstract

The donor–acceptor complexes [Fe(C₅H₅){C₅H₄QNHM(NO)(Tp^Me,Me)X}] {Tp^Me,Me = tris(3,5-dimethylpyrazolyl)borate; Q = nothing, M = Mo, X = Cl, Br, I; M = W, X = Cl; Q = C₆H₄, M = Mo, X = Cl, Br, I; M = W, X = Cl; Q = CHCHC₆H₄ or NNC₆H₄, M = Mo, X = Cl), which contain 16-valence electron metal nitrosyl centres, [Fe(C₅H₅){C₅H₄QpyMo(NO)(Tp^Me,Me)Cl}] (py = 4-pyridyl; Q = CHCH, CHCHCO, NCH and C₆H₄CHCH), [Fe(C₅Me₄H){C₅H₄CHCHpyMo(NO)(Tp^Me,Me)Cl}] and [Fe(C₅Me₄H)(C₅Me₄QpyZ)] {Q = CHCH or CHN, Z = Mo(NO)(Tp^Me,Me)Cl or W(CO)₅; Q2,4-CHCH(C₄H₂S)CHCH, Z = W(CO)₅ or Me⁺I⁻}, some of which contain 17-valence electron molybdenum nitrosyl centres, and [Fe(C₅Me₄H){C₅Me₄CHCH(C₄H₂S)CHCHpy}], have been characterised electrochemically, by their electronic spectra, and spectroelectrochemically. Hyper-Rayleigh scattering was used to determine the first hyperpolarisability, β, the data showing that (a) β is dependent on the metal in the acceptor fragment, (b) β increased when Cl or Br was replaced by I and (c) β increased when the number of methyl groups on the cyclopentadienyl rings increased. The β-values for comparable complexes containing {Mo(NO)(Tp^Me,Me)Cl} and {W(CO)₅} moieties were similar. Chemical oxidation of the ferrocenyl or chemical reduction of the molybdenum nitrosyl acceptor fragments in selected complexes caused a reduction of between 25% and 100% in the NLO response. X-Ray structural studies of [Fe(C₅H₅){C₅H₄NHMo(NO)(Tp^Me,Me)Cl}] (P) and [Fe(C₅Me₄H){C₅Me₄CHCHpyMo(NO)(Tp^Me,Me)Cl}] (P) are reported.