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

Abstract

Mono-and digerma[n]metallocyclophanes (n ) 1, 2) [(η 6 ,η 6′ -dimethyldiphenylgermane)M] (M ) Cr, 17; V, 18 • ), [(η 6 ,η 6′ -tetraphenylgermane)M] (M ) Cr, 20; V, 21 • ), and [(1,1,2,2tetramethyl-1,2-di-η 6 ,η 6′ -phenyldigermane)Cr] (24) were synthesized by means of lithiation and subsequent reaction with dichlorodimethylgermane or dichlorodiphenylgermane. Metalligand cocondensation of bromodimethylphenylgermane with chromium atoms followed by reductive coupling with lithium naphthalide gave the digermane complex 24. Additionally, the nonbridged derivatives [bis(trimethylgermyl-η 6 -benzene)M] (M ) Cr, 10d; V, 11 • ), [(trimethylgermyl-η 6 -benzene)(η 6 -benzene)Cr] (10m), and [bis(triphenylgermyl-η 6 -benzene)M] (M ) Cr, 14; V, 15 • ) were prepared and characterized by 1 H-and 13 C-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 13 C-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.

Photoinduced iron–cyclopentadienyl (Fe–Cp) bond cleavage reactions and photocontrolled polymerizations of strained [1]ferrocenophanes

“…In contrast, use of terpyridines led to polyferrocenylsilane formation or the cleavage of both Fe-Cp bonds [38]. Clearly subtle substituent effects play a key role in determining the products that arise from the photoinduced reactivity of the Fe-Cp bonds in ferrocenophanes and fascinating results are also likely for related species [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”

“…Since the discovery of the first example, sila [1]ferrocenophane in 1975 by Osborne and co-workers [1], strained [1]ferrocenophanes have attracted considerable attention and have inspired growing interest in a range of related species containing various d-and f-block metals, bridging elements, and even different p-hydrocarbon ligands [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. The angle created by the planes of the two cyclopentadienyl (Cp) rings in a ferrocenophane, generally denoted as a, represents a convenient qualitative measure of the degree of strain present [2].…”

Bis(benzene)chromium. 2. Its Discovery by E. O. Fischer and W. Hafner and Subsequent Work by the Research Groups of E. O. Fischer, H. H. Zeiss, F. Hein, C. Elschenbroich, and Others

“…Treatment of these complexes with pyridine-4-carboxaldehyde gave the radical cations, while a potassium mirror reduced them to the radical anions. 119 (In contrast to earlier workers, Elschenbroich calls the [(arene) 2 Cr] + cations "radical cations" in order to emphasize the presence of their one unpaired electron.) Also prepared in this manner were (1,4-(ClMe 2 Si) 2 C 6 H 4 ) 2 Cr and (ClMe 2 SiC 6 H 5 ) 2 Si.…”

Aryl Oligogermanes as Ligands for Transition Metal Complexes

“…So the molecular oligogermanium complexes bearing transition metals remain to be investigated in order to complete the series. To the best of our knowledge, only 6 articles describing complexes of arylmonogermanes with M(CO) 3 have been reported up to this day ,…”