(Cyclopentadienyl)dihalogenochromium-Donor Compounds. Synthesis and NMR Investigation

A series of paramagnetic (S = 3/2) chromium half-sandwiches of the type CpCrX D (D = donor) were synthesized by starting from [CpCrX , Cp Cr, CpCrCl (THF), and Cp*Cr(CH [P(CH ]. Besides the parent cyclopentadienyl (Cp) the alkylated derivatives CH , (CH (Cp*), and C (CH were bound to chromium. The electronegative substituent was X = F, Cl, Br, I, and triflate, while the donors were three ethers, four ketones, dimethylsulfoxide, acetonitrile, methylisocyanide, pyridine, and seven molecules ER where E = N, P, As, Sb. The half-sandwiches were partly isolated and partly established in solution. The C and H NMR spectra showed strongly shifted signals which allowed to quantitatively investigate the equilibrium between CpCrX D and the anti ferromagnetic species [CpCrX . The NMR signals of CpCrX D and its substituted derivatives appeared in characteristic ranges thus providing a means of rapid identification. Considerable spin density was found to be induced on the ligands; it is negative in the Cp π system. As for the donors, inter- and intramolecular dynamic behavior as well as selective spin transfer to the γ protons of acetonitrile, methylisocyanide, and ketones was detected.