Cycloaddition and Cycloreversion Reactions of a Monomeric Ti(IV) Oxo Complex with Terminal and Internal Alkynes. A Reversible Oxametallacyclobutene/Hydroxoacetylide Interconversion

Alkyne Cycloaddition to a Titanocene Oxide as a Route to Cyclopentadienyl Modification

“…Cycloadditions of unsaturated organic molecules such as allenes and alkynes are well‐established routes to oxatitanacyclobutanes and oxatitanacyclobutenes 7. 8 However, further elaboration of these products and incorporation into useful synthetic schemes has yet to be realized. As part of our effort to develop new methods for the cleavage of early transition metal–heteroatom bonds in the context of N 2 functionalization,9 O‐atom and related group transfer processes,10 we have continued exploration of oxatitanacyclobutenes.…”

Kinetic Control and Multiple Mechanisms for CH Bond Activation by a ZrN Complex

“…A promising approach to the functionalization of unactivated hydrocarbons (RH) involves a 1,2‐RH‐addition across metalheteroatom multiple bonds [MX] (M=Groups 4–6, X=NR,1, 2 CR 2 ,3 CR,4 O5) to afford products of general structure [M(XH)(R)]. Extensive selectivity studies have been performed on Group 4 imido [M=NR′] systems that activate hydrocarbons under reversible conditions 1l–m.…”

“…The high relative rate for activation of tert ‐butylacetylene led us to speculate that 1 may activate alkynes by a mechanism distinct from that of direct 1,2‐RH‐addition via transition state 7 (Scheme , path a). In analogy to a TiO system,5 alkynes may undergo rate‐determining metallacycle formation (Scheme , k met , path b) with 2 to form intermediate metallacycle 8 , followed by rearrangement ( k rearr ) to provide 3 a . In a KIE competition study to form 3 a /[D 1 ]‐ 3 a , k H / k D was found to be 0.8.…”

Synthesis and carbonylation of oxotitanocyclobutanes derived from allene cycloaddition to a monomeric titanocene oxide

“…Brintzinger and Bercaw provided a seminal illustration of this approach with the introduction of the permethylcyclopentadienyl ligand into reduced titanium chemistry allowing observation of the first sandwich structure in the triad along with isolation and crystallographic characterization of the first example of a titanocene dinitrogen compound [13,19] This venerable ligand has also found application in the chemistry of titanocene oxide complexes such as [(g 5 -C 5 Me 5 ) 2 TiO], a metastable compound with a rare example of a terminal [Ti@O] linkage [20]. Despite its instability in the absence of pyridine, [(g 5 -C 5 Me 5 ) 2 TiO] exhibits a rich reaction chemistry undergoing cycloaddition with alkynes and allenes [21]. The oxatitanacyclobutanes derived from allene addition also proved unstable in solution being prone to additional modification from C-H activation of the cyclopentadienyl methyl groups [22].…”