title: Transmetalation of chromocene by lithium-amide, -phosphide, and -arsenide nucleophiles.
abstract: The pnictogen-centered nucleophiles LiE(SiMe3)2 (E = N, P, or As) substitute a cyclopentadienide ligand of chromocene (Cp2Cr), with elimination of lithium cyclopentadienide, to give the series of pnictogen-bridged compounds [(μ:η(2):η(5)-Cp)Cr{μ-N(SiMe3)2}2Li] (1) and [(η(5)-Cp)Cr{μ-E(SiMe3)2}]2, with E = P (2) or E = As (3). Whereas 1 is a heterobimetallic coordination polymer, 2 and 3 are homometallic dimers, with the differences being due to a structure-directing influence of the hard or soft character of the bridging group 15 atoms. For compound 1, the experimental magnetic susceptibility data were accurately reproduced by a single-ion model based on high-spin chromium(II) (S = 2), which gave a g-value of 1.93 and an axial zero-field splitting parameter of D = -1.83 cm(-1). Determinations of phosphorus- and arsenic-mediated magnetic exchange coupling constants, J, are rare: in the dimers 2 and 3, variable-temperature magnetic susceptibility measurements identified strong antiferromagnetic exchange between the chromium(II) centers, which was modeled using the spin Hamiltonian H = -2J(S(CrA)·S(CrB)), and produced large coupling constants of J = -166 cm(-1) for 2 and -77.5 cm(-1) for 3.
authors.affiliation: Institute of Inorganic Chemistry, University of Regensburg, Germany D-93040.
authors.forename: Sabine
authors.initials: S
authors.lastname: Scheuermayer
authors.forename: Floriana
authors.initials: F
authors.lastname: Tuna
authors.forename: Eufemio Moreno
authors.initials: EM
authors.lastname: Pineda
authors.forename: Michael
authors.initials: M
authors.lastname: Bodensteiner
authors.forename: Manfred
authors.initials: M
authors.lastname: Scheer
authors.forename: Richard A
authors.initials: RA
authors.lastname: Layfield