195533-15-4Relevant academic research and scientific papers
Metal π complexes of benzene derivatives. Germanium in the periphery of bis (benzene) vanadium and bis(benzene)chromium. Synthesis and structure of new heterametallocyclophanes
Elschenbroich, Christoph,Schmidt, Eckhardt,Gondrum, Rolf,Metz, Bernhard,Burghaus, Olaf,Massa, Werner,Wocadlo
, p. 4589 - 4596 (2008/10/08)
Mono- and digerma[n]metallocyclophanes (n = 1, 2) [(η6,η6-dimethyldiphenylgermane)M] (M = Cr, 17; V, 18?), [(η6,η6′-tetraphenylgermane)M] (M = Cr, 20; V, 21?), and [(1,1,2,2-tetramethyl-1,2-di-η6,η 6′-phenyldigermane)Cr] (24) were synthesized by means of lithiation and subsequent reaction with dichlorodimethylgermane or dichlorodiphenylgermane. Metal - ligand cocondensation of bromodimethylphenylgermane with chromium atoms followed by reductive coupling with lithium naphthalide gave the digermane complex 24. Additionally, the nonbridged derivatives [bis(trimethylgermyl-η6-benzene)M] (M = Cr, 10d; V, 11?), [(trimethylgermyl-η6-benzene)(η6-benzene)Cr] (10m), and [bis(triphenylgermyl-η6-benzene)M] (M = Cr, 14; V, 15?) were prepared and characterized by 1H- and 13C-NMR (10m, 10d, 14, 17, 20), cyclic voltammetry (CV) (10d, 11?14, 15?, 18 ?, 21?, 24), and EPR spectroscopy (10d?+, 11?, 14?+, 15?, 18?, 21?, 24?+). Crystals of 20 were subjected to a structure determination by X-ray diffraction, which disclosed a bending of the sandwich axis from linearity by 14.4°. The strain exerted on the coordinated benzene ring forces a pyramidal structure on the ipso-C leading to a markedly shielded 13C-NMR resonance. An EPR spectroscopic investigation of the vanadium derivatives reveals an increasing metal to ligand spin delocalization and the appearance of orthorhombic g and A tensors on bending the sandwich axis. While the redox potentials are virtually unaffected, when passing from the unstrained vanadium complexes 11? and 15? to the germa[1]vanadocyclophanes 18? and 21?, the transient monocationic species of the latter are destabilized dramatically. No evidence of ring-opening polymerization was observed on heating 18? to 165°C. Instead, metal-ligand cleavage occurs.
