Synthesis, spectroscopic and X-ray crystallographic properties of manganese compounds of keto- and enol-coordinated di-2-pyridyl ketone benzoyl hydrazone (dpkbh). Reactions of [Mn(CO)₅Br] with dpkbh

Abstract

Reactions between [Mn(CO)₅Br] and dpkbh in low boiling solvents in air gave fac-[Mn^I(CO)₃(κ²-N_py,N_im-dpkbh)Br]·H₂O, [Mn^IIBr₂(κ³-N_py,N_im,O-dpkbh)], and [Mn^II(κ³-N_py,N_im,O-dpkbh-H)₂]·0.5H₂O (N_im = imine nitrogen and N_py = pyridyl nitrogen). Crystallization of fac-[Mn^I(CO)₃(κ²-N_py,N_im-dpkbh)Br]·H₂O from dmso or CH₃CN produced dark red crystals of [Mn^II(κ³-N_py,N_im,O-dpkbh-H)₂]·nX (X = dmso, n = 1 and X = H₂O, n = 0.22). This is in contrast to the reaction of [Re(CO)₅Cl] with dpkbh in refluxing toluene to form fac-[Re^I(CO)₃(κ²-,N_py,N_py-dpkbh)Cl] which can be crystallized from CH₃CN, dmso or dmf to form fac-[Re^I(CO)₃(κ²-,N_py,N_py-dpkbh)Cl]·nX (X = CH₃CN, n = 0 and solvate = dmso or dmf, n = 1). Infrared spectral measurements are consistent with keto coordination of dpkbh to Mn(I) in fac-[Mn^I(CO)₃(κ²-N_py,N_im-dpkbh)Br]·H₂O and Mn(II) in [Mn^IIBr₂(κ³-N_py,N_im,O-dpkbh)] plus enol coordination of the amide-deprotonated dpkbh, to the Mn(II) center in [Mn^II(κ³-N_py,N_im,O-dpkbh-H)₂]·0.5H₂O. Electronic absorption spectral measurements in non-aqueous solvents indicate sensitivity of fac-[Mn^I(CO)₃(κ²-N_py,N_im-dpkbh)Br]·H₂O and [Mn^II(κ³-N_py,N_im,O-dpkbh-H)₂]·0.5H₂O to changes in their outer-shell environments. X-ray crystallographic analyses elucidated the identities of [Mn^IIBr₂(κ³-N_py,N_im,O-dpkbh)] and [Mn^II(κ³-N_py,N_im,O-dpkbh-H)₂]·nX and divulged weaker coordination of [dpkbh] to Mn(II) in [Mn^IIBr₂(κ³-N_py,N_im,O-dpkbh)] and stronger coordination of [dpkbh-H]⁻ to Mn(II) in [Mn^II(κ³-N_py,N_im,O-dpkbh-H)₂]·0.22H₂O. Low-temperature X-ray structural analyses were employed to account for the disorder in the structure of [Mn^II(κ³-N_py,N_im,O-dpkbh-H)₂] and the short NH bond distance observed in the structure of [Mn^IIBr₂(κ³-N_py,N_im,O-dpkbh)]. A PLATON Squeeze treatment was invoked to account for the fractional occupancy of lattice water in the structure of [Mn^II(κ³-N_py,N_im,O-dpkbh-H)₂].

Keywords:

• Synthesis
• manganese
• di-2-pyridyl ketone benzoyl hydrazone
• X-ray
• spectroscopy

Acknowledgements

The authors acknowledge the University of the West Indies for financial support, Dr. Ishmael Hassan, Mr. Orain Brown, Dr. Mark Lawrence and Mr. Orville Green for technical assistance, and the United States National Science Foundation for support of the X-ray diffraction facility at Colby College.