Über Substituenten-Einflüsse auf die Bindungsverhältnisse der Metall-Komplexe des Cyclobutadiens / The Influence of Substituents on Bonding Properties in Metal Complexes of Cyclobutadiene

Abstract

The syntheses of some p- substituted phenylcyclobutadieneirontricarbonyls are reported. Carbonyl stretching frequencies, 13C-H- and H-Η-coupling constants are discussed with respect to bonding properties. There is apparently no conjugative interaction between the π-electron systems of cyclobutadiene and the phenyl ring.

Cyclobutadienemetal complexes

“…The organic chemistry of the cyclopentadienyl ligand in (cyclopentadienyl)(tetraphenylcyclobutadiene)cobalt (63) was investigated rather extensively by Rausch the following: acetomercuration in the presence of perchloric acid as catalyst (to afford 160 and 161); Vilsmeier formylation with /V-methylformanilide and phosphorus oxychloride (to afford 162); Mannich-typeaminomethylationwithbis(dimethylamino)methane and phosphoric acid (to afford 163); and Friedel-Crafts acetylation using acetic anhydride and boron trifluoride (to afford 164, in trace amounts only) (see Scheme XXVIII). Interestingly, the Friedel-Crafts acylation of 63 with benzoyl chloride and aluminum chloride gave a product (~1% yield) in which substitution appeared to have occurred on a phenyl rather than the cyclopentadienyl ring.…”

“…In most instances the mass spectra of cyclobutadienemetal complexes were obtained in order to establish the molecular weight from the molecular ions (Ml), although in few isolated cases brief discussions pertaining to some of the other spectral features have also been reported. More detailed studies of fragmentations taking place under electron-impact conditions were reported for complexes such as Ph4C4Fe(CO)3 (2),309 Ph4C4CoQ [Q = cyclopentadienyl (63) and indenyl],309 C8H6Fe(CO)2L [L = CO, Ph3P, Ph3As, and Ph3Sb],191 of a coordinated cyclobutadiene [R4C4M+, where M indicates either metal and/or metal bonded to some other ligand(s)] occurs by a two-step sequence involving successive losses of two acetylene (R2C2) fragments. This characteristic fragmentation pattern, pathway A in Figure 4, has been found in virtually all of the available mass spectra of cyclobutadienemetal complexes.…”

“…The synthesis of para-substituted phenylcyclobutadieneiron tricarbonyl derivatives (28) was achieved by the reaction of 3.4dibromo-2-arylcyclobutene (29), 62,63 prepared from arylcyclobutene-1,2-dione (30), with Fe2(CO)9 (Scheme VI). The dione 30 used in this synthesis was obtained by the thermal addition of arylacetylene to trifluorochloroethylene followed by hydrolysis with concentrated sulfuric acid.…”

Selective 1,4-Addition of Arenes to 3-Chloro-3-cyclobutene-1,2-dione under Friedel−Crafts Conditions. Synthesis and Reactivity of 4-Aryl-3-chloro-2-hydroxy-2-cyclobuten-1-ones1

“…3-( p -Tolyl)-3-cyclobutene-1,2-dione (14b). Method C: yellow crystals; mp 158−160 °C dec (acetone), (lit . mp 166 °C); yield 1.00 g (58%); IR 1765 (vs, br), 1600 (m) (CO, CC) cm -1 ; 1 H NMR (CDCl 3 ) δ 2.43 (s, 3H), 7.34 (d, 2H, J = 8.1 Hz), 7.86 (d, 2H, J = 8.1 Hz), 9.45 (s, 1H); 13 C NMR (CDCl 3 ) δ 22.07, 124.79, 129.50, 130.35, 146.17, 177.14, 195.44, 195.75, 198.06; MS m/z (relative intensity) 172 (M + , 18), 116 (100), 89 (11).…”

“…3-(4-Chlorophenyl)-3-cyclobutene-1,2-dione (14f). Method C: yellow crystals; mp 179−181 °C dec (acetone), (lit …”