Reactivity of a Terminal Ti(IV) Imido Complex toward Alkenes and Alkynes:  Cycloaddition vs C−H Activation

Abstract

This paper describes the reactivity of the base-free titanium imido complex Cp* 2 TidNPh (1) (Cp* ) pentamethylcyclopentadienyl) toward alkenes and alkynes. Complex 1 reacts with ethylene and acetylene to generate the azametallacycles Cp* 2 Ti(N(Ph)CH 2 CH 2 ) (2) and Cp* 2 Ti(N(Ph)CHdCH) (3), respectively. In the case of ethylene, the cycloaddition is readily reversible, and 2 was characterized spectroscopically under an ethylene atmosphere. We have also examined the reactivity of 1 toward phenyl-and trimethylsilylacetylene and have found that 1 activates the alkynyl C-H bond to give anilido-acetylide complexes Cp* 2 Ti(N(Ph)H)Ct CR (6, R ) Ph; 7, R ) SiMe 3 ). This reaction proceeds without observable intermediate metallacyclobutene complexes such as those observed previously for the reaction of the related oxo complex Cp* 2 Ti(O)pyr (pyr ) pyridine) with terminal alkynes. Thermolysis of azametallacyclobutene 3 results in formation of the novel ring-activated complex Cp*(η 5 ,η 1 -C 5 Me 4 CH 2 CHdCH)TiN(Ph)H (5).

Aiding Factors in the Formation of Azaplatinacyclobutane Rings – X‐ray and Crystal Structure of [Pt{CH(Ph)CH2NEt2‐κC,κN}(N,N,N′,N′‐tetramethylethylenediamine)]+ and of Its Open‐Chain Precursor

“…Elemental analyses were performed by using an Elemental Analyzer 1106 Carlo Erba instrument. 1 H NMR spectra were recorded with a DPX300 Advance Bruker instrument equipped with a probe for inverse detection and with z gradient for gradient-accelerated spectroscopy.…”

“…[1][2][3][4][5][6][7][8] The reaction sequence leading to their formation is very much dependent upon the nature of the metal involved. In the case of early transition metals, the azametallacyclobutanes are generated by [2+2] cycloaddition of an olefin to a metalla-imido moiety (M=NR).…”

“…In the case of early transition metals, the azametallacyclobutanes are generated by [2+2] cycloaddition of an olefin to a metalla-imido moiety (M=NR). [1] The reaction is generally reversible, and in the specific case of [Cp 2 (THF)Zr(=N-tBu)] reacting with norbornene, the formed azazirconacyclobutane was also structurally characterized. [1b] A different and more complex reaction pathway was proposed for the formation of an azatungstacyclobutane.…”

Asymmetric Hydroamination

“…The mechanism of alkene hydroamination is much less well understood than the mechanism of alkyne and allene hydroamination [91][92][93][94][95][96][97][98]. Based on the observationthat most neutral group 4 metal alkene hydroamination catalysts are unreactive toward secondaryaminoalkenesubstrates,amechanismanalogoustothatforalkyneandallene hydroamination involving metal imido species as catalytically active species has been proposed (Scheme 11.17) [83,84,88,89].…”

“…The metal imido species is generated via reversible a-elimination of an amine from a bis(amido) precursor. It can undergo a (most likely reversible) [93,95] [2 þ 2]-cycloaddition with the alkene moiety subsequently. The resulting azametallacyclobutane is protolytically cleaved to regenerate the metal imido species and release the hydroamination product.…”