Distorted square planar nickel(II) carbonyl complexes containing terminal thiolate/selenolate ligands

Distorted square planar [Ni(CO)(SR)(n)(SePh)(3 - n)](-) (n = 0 (1), 3 (2), 1 (3) or 2 (4); R = Ph or C4H3S) complexes, were prepared by unique Cp-/PhS- (PhSe-) exchange reactions and oxidative addition. (SC4H3S)(2), [NiCp(CO)](2) and 2 equivalents of fac-[N(PPh3)(2)][Fe(CO)(3)(SC4H3S)(3)] in thf led to the isolation of [N(PPh3)(2)][Ni(CO)(SC4H3S)(3)] and [FeCp(CO)(2)(SC4H3S)]. Complex [Ni-0(CO)(3)(SePh)](-) was obtained upon chemical reduction of complex [Ni-II(CO)(SePh)(3)](-) with [BH4](-) under a CO atmosphere in thf. [Ni-II(CO)(SePh)(3)](-) was reobtained upon oxidative addition of diphenyl diselenide and benzeneselenol to [Ni-0(CO)(3)(SePh)](-) in thf. The mixed-chalcogenolate nickel(II) carbonyl complexes [Ni(CO)(SPh)(n)(SePh)(3 - n)](-) (n = 1 or 2) were prepared by PhSe-/PhS- ligand exchange reaction and oxidative addition of diphenyl disulfide to [Ni(CO)(3)(SePh)](-) individually. Complexes [Ni-II(CO)(SePh)(3)](-), [Ni-II(SC5H4N)(3)](-), [Ni-0(CO)(3)(SC5H4N)](-) and [Ni-0(CO)(3)(SePh)](-) are chemically interconvertible at ambient temperature. Coordinative addition of the metalloanion [Mn(CO)(5)](-) ([Fe(CO)(4)(SePh)](-)) to complex [Ni(CO)(SePh)(3)](-) and subsequent redox under a CO atmosphere led to formation of cis-[Mn(CO)(4)(SePh)(2)](-) (fac-[Fe(CO)(3)(SePh)(3)](-)) and [Ni-0(CO)(3)(SePh)](-). Nickel(II)/nickel(0) carbonyl thiolate complexes are more unstable thermally than the corresponding carbonyl selenolate complexes. Isotopic shift experiments demonstrate the lability of carbonyl ligand(s) of complexes 1-4 and [Ni(CO)(3)(SePh)](-) species. The vibrational spectroscopy of the Ni-II(CO) fragment (nu (CO) ranges from 2023 to 2043 cm(-1)) found in 1-4 may be regarded as a spectroscopic reference for the carbonyl binding site of [NiFe] hydrogenases and CO dehydrogenase.