Five-membered metallacycles of titanium and zirconium ? attractive compounds for organometallic chemistry and catalysis

Abstract

In these days a renaissance of metallacycles as an increasingly important class of organometallic compounds for synthetic and catalytic applications is evident, making such very attractive for a plethora of investigations. Titanocene and zirconocene bis(trimethylsilyl)acetylene complexes, regarded as three-membered metallacycles (1-metallacyclopropenes), present a rich chemistry towards unsaturated molecules. By elimination of the alkyne these complexes form by reaction with unsaturated compounds five-membered titana- and zirconacycles, all of which are relevant to stoichiometric and catalytic C-C coupling and cleavage reactions of unsaturated molecules.

Experimental and Theoretical Studies of Unusual Four‐Membered Metallacycles from Reactions of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes with the Sulfurdiimide Me3SiN=S=NSiMe3

“…Promising approaches for the stabilisation of highly strained structures include the introduction of metal centres or heteroatoms into the ring system. [2] This approach was very recently demonstrated by us for four-and five-membered azametallacycles [3,4] as well as for five-membered disilametallacycles [5] along with computational studies of the structures and bonding of the complexes. Bis(trimethylsilyl)acetylene complexes of group 4 metals of the type [CpЈ 2 M(L)(η 2 -ing the group 4 metal, nitrogen and sulfur.…”

“…In contrast, Stufkens and co-workers published a dinuclear manganese complex [(OC) 5 Mn 2 (CO) 3 (η 2 -tBu-N=S=N-tBu)] [8] displaying a cyclic Mn-N-S-N unit at one of the metal centres. Moreover, Rausch, Alt 2 ]} and the same sulfurdiimide. How-ever, the product obtained was only characterised spectroscopically.…”

Cycloaddition Reactions of a Chromium–Chromium Quintuple Bond

“…Alkyne and diene ligand have been successfully used as protecting ligands for low-valent Group 4 metallocenes by (for instance) the groups of Rosenthal, Erker, Beckhaus, and Mach. [13] If one uses a di-A C H T U N G T R E N N U N G atomic site of high bond order to activate such unsaturated molecules, cycloaddition reactions might be expected. We are interested in analogies of quintuple bonds to simple double and triple bonds.…”

“…Cr À Cr quintuple bonds can undergo similar (cycloaddition) reactions to those of well understood CÀC double and triple bonds. Considering the variety of reactions alkyne and diene complexes of Group 4 metallocenes can undergo, [13] we expect a rich chemistry of the cycloaddition product introduced here which we plan to study.…”

Zirconacycle-mediated synthesis of carbocycles

“…Zirconacycles (zirconacyclopentadiene, zirconacyclopentene and zirconacyclopentane) have several advantages over other metallacycles [9][10][11][12]: (i) they are easily prepared by coupling of alkynes and/or alkenes on reduced zirconocene, and (ii) they can be easily handled under normal conditions. Many excellent reviews on zirconacycles in organic synthesis have been already published .…”