Group 4 Metallocene Mediated Homo- and Heterocoupling of Heteroaromatic Nitriles

Abstract

Coupling of different heterocyclic nitriles at group 4 metallocenes was investigated. The product of 2,6dicyanopyridine coupling at [Cp* 2 Ti] (1Ti) reacts with [Cp* 2 Zr(η 2 -Me 3 SiC 2 SiMe 3 )] to yield the novel trinuclear TiZr 2 complex 2, which further reacts with smaller heteroaromatic nitriles 2-cyanofuran and 2-cyanothiophene to form the homocoupling products 3Zr and 4Zr. Similar products were formed in the direct coupling of these nitriles at [Cp* 2 M] (M = Ti, Zr). Mixed 1-metalla-2,5-diazacyclopenta-2,4-dienes 5Ti and 5Zr can be accessed by using mixtures of both nitriles, or in the case of 5Zr by stepwise addition of different nitriles to [Cp* 2 Zr(η 2 -Me 3 SiC 2 SiMe 3 )]. Metallacycle transfer using titanocene complexes 3Ti and 4Ti and SOCl 2 yields the corresponding thiadiazole oxides 3SO and 4SO, as well as the mixed thiadiazole oxide 5SO, which were isolated and fully characterized. DFT calculations were done to further look into the process of nitrile exchange at metallocene. Article pubs.acs.org/Organometallics

Well-Defined Scandacyclopropenes: Synthesis, Structure, and Reactivity

“…These distances are apparently shorter than those found in the scandacyclopentadiene (av 2.273 Å) . The C1–C2 bond length (1.350(2) Å) is comparable with those in group 4 , and actinide metallacyclopropenes . In addition, the bond angles of C2–C1–C3 and C1–C2–C9 are 127.94(16)° and 130.19(15)°.…”

“…For example, transition and main-group metallacyclopropenes have been extensively studied because of the intrinsic interest in their structure, reactivity, and synthetic and catalytic applications (Scheme ). − Uranium and thorium metallacyclopropenes have also been reported recently by Zi et al However, to the best of our knowledge, well-defined rare-earth metallacyclopropenes have not yet been reported in the literature and targeted as new species for the community of rare-earth organometallic chemistry. This lack of rare-earth metallacyclopropenes is probably due to (i) the instability of the highly strained three-membered metallacycle, which renders it difficult to isolate and characterize, and (ii) the lack of variable oxidation states, which makes the classical oxidative addition of one alkyne to the low-valent rare-earth metal center unattainable.…”

Advantages of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes as Metallocene Sources Towards Other Synthetically used Systems

“…Such coupling reactions were later described for 2,6‐dicyanopyridine and very recently by Reiß, Beweries and coworkers for 2‐cyanofuran as well as 2‐cyanothiophene, giving several mixed tri‐ and tetranuclear complexes by homo‐ and heterocoupling using Cp* 2 M(η 2 ‐btmsa) (M=Ti, Zr) . When changing from aryl‐dinitriles to dicyanoalkyl adiponitrile, by a nitrile‐nitrile C−C coupling and subsequent protonation no 1‐titana‐2,5‐diaza‐cyclopenta‐2,4‐diene but a 1,4‐diazadiene complex was formed in a yield of 46 % (Scheme )…”

Multicomponent syntheses of 5- and 6-membered aromatic heterocycles using group 4–8 transition metal catalysts

“…However, a recent report has capitalized on the tail-to-tail coupling of nitriles on "Cp 2 Ti II ", 136,137 resulting in a formal [2 + 2 + 1 + 1] coupling of nitriles to tetrasubstituted pyrazines (Fig. 35) via Ti-to-Al transmetallation (cf.…”