Synthesis and X-ray crystal structures of alkaline-earth metallocenes with pendant substituents

Deprotonation of [(2-C5H4N)CH2CMe2]C5H5 ( = HCppy) and CH3OCH2CH2C5H5 (= HCp§) with Ae[N(SiMe3)2]2 (Ae = Ca, Sr. Ba) in toluene produces the corresponding metallocenes, Cp'2Ae, in high yield. 1H NMR data reveal that the calcium complex (Cppy)2Ca does not bind tetrahydrofuran. The solid state structures of (Cppy)2Sr and (Cp§)2Ca were obtained by single crystal X-ray analysis, and found to be monomeric, with the Lewis base substituents on the cyclopentadienyl rings coordinated to the metal centers. Crystals of (Cppy)2Sr grown from toluene are orthorhombic, space group Pbcn, with a = 11.988(4) Å, b = 16.141(4) Å, 12.572(4) Å, V = 2433(1) Å3, Z = 4, R = 0.038, Rw = 0.043 based on 635 observed reflections. The complex possesses a bent metallocene geometry and contains a crystallographically imposed two-fold rotation axis passing through the strontium. The average Sr-C and Sr-N distances are 2.85(1) and 2.660(7) Å respectively, and the ring centroid-Sr-ring centroid angle is 141.1°. Crystals of (Cp§)2Ca grown from toluene are monoclinic, space group P 21/n, with a = 6.912(4) Å, b = 15.114(2) Å, c = 15.435(3), ß = l00.34(2)°, V = 1586.3(9) Å3, Z = 4, R = 0.041, Rw = 0.048 based on 1318 observed reflections. The complex also has a bent metallocene geometry, with average Ca-C and Ca-O distances are 2.670(6) and 2.407(3) Å respectively; the ring centroid-Ca-ring centroid angle is 136.6°