Metal π Complexes of Benzene Derivatives. Germanium in the Periphery of Bis(benzene)vanadium and Bis(benzene)chromium. Synthesis and Structure of New Heterametallocyclophanes , 1
1997; American Chemical Society; Volume: 16; Issue: 21 Linguagem: Inglês
10.1021/om970249y
ISSN1520-6041
AutoresChristoph Elschenbroich, Eckhardt Schmidt, Rolf Gondrum, Bernhard Metz, Olaf Burghaus, Werner Massa, Sigrid Wočadlo,
Tópico(s)Ferrocene Chemistry and Applications
ResumoMono- 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,η6'-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.
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