We report the synthesis, reactivity studies, and ring-opening polymerization of a tricarba[3]nickelocenophane. The resulting green polynickelocene (5) possesses a -(CH2)3- spacer between the nickelocene units and is shown to be of high molecular weight. SQUID magnetometry measurements indicate that 5 is a macromolecular material with an S = 1 repeat unit.
In order to gain insight into the mechanism for the thermal ring-opening polymerization of strained dicarba [2]ferrocenophanes, the thermal reactivity of selected examples of these species with different substitution patterns has been explored. When heated at 300 C dicarba[2]ferrocenophanes meso/rac-[Fe(h 5 -C 5 H 4 ) 2 (CHPh) 2 ] (meso/rac-7) and meso-[Fe(h 5 -C 5 H 4 ) 2 (CHCy) 2 ] (meso-13) were found to isomerize or to undergo disproportionation, respectively. These processes are apparently general for dicarba [2]ferrocenophanes with one or more non-hydrogen substituents at each carbon atom in the dicarba bridge and both appear to involve homolytic cleavage of the C-C bond in the bridge as a key step. In striking contrast, derivatives containing either one or no non-hydrogen substituents on the bridge such as {Fe 17) undergo thermal ringopening polymerization (ROP) under similar conditions (300 C, 1 h). Thus, thermolysis of 15 yielded polyferrocenylethylene {Fe[h 5 -C 5 H 4 ] 2 [CH(Ph)CH 2 ]} n (16a) with a broad molecular weight distribution (M w ¼ 13,760, PDI ¼ 3.27). Analysis of 16a by MALDI-TOF mass spectrometry suggested that the material was macrocyclic. Thermal treatment of linear polyferrocenylethylenes {Fe[h 5 -C 5 H 4 ] 2 [CH(Ph) CH 2 ]} n with narrow molecular weight distributions (prepared by photocontrolled ROP) at 300 C confirmed that the macrocycles detected form directly, and not as a result of depolymerization.Copolymerizations of 15 with 17 and of 15 with the deuterated species [Fe(h 5 -C 5 H 4 ) 2 (CD 2 ) 2 ] (d 4 -17) were conducted in order to probe the bond cleavage mechanism. Comparative NMR spectroscopic analysis of the resulting copolymers 18 and d 4 -18, respectively, and of homopolymer 16a, indicated that thermal ROP does not occur via a homolytic C-C bridge cleavage mechanism. A series of thermolysis experiments were conducted with MgCp 2 (Cp ¼ h 5 -C 5 H 5 ) at 300 C, which resulted in the isolation of ring-opened species formed from 15 and 17, and indicated that the Fe-Cp bonds can be cleaved under the thermal ROP conditions employed. The studies indicated that a chain growth process that involves heterolytic Fe-Cp bond cleavage in the monomers is the most probable mechanism for the thermal ROP of dicarba[2]ferrocenophanes.
The cationic homo-and heteronuclear sandwich complexes (η 5 -cyclopentadienyl)(ferrocenylethynyl-η 6 -benzene)ruthenium(II) hexafluoridophosphate (3a), (η 5 -cyclopentadienyl)-(ruthenocenylethynyl-η 6 -benzene)ruthenium(II) hexafluoridophosphate (3b), (η 5 -cyclopentadienyl)[1,4-bis(ferrocenylethynyl)η 6 -benzene]ruthenium(II) hexafluoridophosphate (4a), (η 5cyclopentadienyl)[1,4-bis(ruthenocenylethynyl)-η 6 -benzene]ruthenium(II) hexafluoridophosphate (4b), and (η 5cyclopentadienyl)[1,3,5-tris(ferrocenylethynyl)-η 6 -benzene]ruthenium(II) hexafluoridophosphate (5) were synthesized by means of Stille cross-coupling reaction using tri-n-butyl-(metallocenylethynyl)stannane as nucleophile and the appropriate (η 5 -cyclopentadienyl)(η 6 -iodobenzene)ruthenium(II) cations as electrophiles. As a catalyst, a Pd(0) complex, furnished with AsPh 3 ligands, was applied. The hitherto unknown iodobenzene complexes (η 5 -cyclopentadienyl)(1,4-η 6 -diiodobenzene)ruthenium(II) hexafluoridophosphate (1b) and (η 5 -cyclopentadienyl)(η 6 -1,3,5-triiodobenzene)ruthenium(II) hexafluoridophosphate (1c) as well as the described cationic homo-and heteronuclear sandwich complexes 3−5 were fully characterized and investigated with respect to the second-harmonic generation by hyper-Rayleigh scattering. For complexes 1b, 1c, 3a, and 5 X-ray structure determinations were performed.
Reaction of 4,5‐diazafluoren‐9‐one (dafone, 6) and zinc dichloride yields [(dafone)ZnCl2(H2O)] (11) in which the ZnCl2 moiety is coordinated to a single nitrogen atom and also to a molecule of water. Hydrogen bonding, not only to the uncomplexed nitrogen atom of dafone but also to the ketonic oxygen atom of a neighbouring molecule, leads to a zigzag chain structure. In contrast, reaction with anhydrous zinc iodide forms cis‐(dafone)2ZnI2 (12) in which the metal–nitrogen distances – 2.170(5) and 2.456(5) Å – are significantly different. Dafone, in the presence of dimethyl sulfoxide, reacts with K2PtCl4 to produce square‐planar (dafone)PtCl2(dmso) (13), whereas with K2PtBr6 the octahedral complex (dafone)PtBr4 (14) is formed in which the ligand chelates in a symmetrical fashion. Treatment of dafone with phenylethynyllithium furnishes 9‐phenylethynyl‐4,5‐diazafluoren‐9‐ol (7), which forms a square‐planar nitrogen‐bonded PtCl2 complex, 15. Reaction of 7 with Co2(CO)8 yields the (μ‐alkyne)hexacarbonyldicobalt cluster 17, which undergoes protonation at the nitrogen atom to form 20 rather than at the alcohol to form a cobalt‐complexed propargyl cation. Alkynol 7 also reacts with HBr by addition across the triple bond to form Z‐9‐[(2‐bromo‐2‐phenyl)ethenyl]‐4,5‐diazafluoren‐9‐ol (10). X‐ray crystal structures are reported for 6, 7, 10–15, 17 and 20, and their differing hydrogen‐bonding motifs are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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