Reactions of Titanium Hydrazinediido Complexes with Unsaturated Organic Substrates

Abstract

Reaction of [Cp*Ti(N Xyl N){N-NPh 2 }(NH 2 t Bu)] (1a) with 1 molar equiv of phenylallene resulted in the formation of a mixture of the two metallacyclic compounds [Cp*Ti(N Xyl N){κ 2 N(NPh 2 )-C(CHPh)CH 2 }] (2a and 2b) in a molar ratio of 3:1. Comparison of the 13 C and 15 N NMR resonances with the computed chemical shifts, along with an X-ray diffraction study of 2a, allowed the assignment of the diastereomers as the cycloadducts derived from a (3,2)-cycloaddition of the allene to the TidN bond. Upon reaction of 1a with phenylisothiocyanate, two complexes were formed in a 3:1 ratio. The major isomer, [Cp*Ti(N Xyl N){κ 2 -N(NPh 2 )C(NPh)S}] (4a), was isolated and identified by X-ray diffraction to result from a [2þ2] cycloaddition of the CdS bond in PhNCS to the TidN bond of the hydrazinediido unit, giving a four-membered metallacyclic ring with an S,N-coordination to the titanium center and an exocyclic CdN double bond. In the minor compound (4b) the two nitrogen atoms of the thiourea unit formed in the cycloaddition are coordinated to the titanium center. Isomerization between the cycloadducts occurs only in the direction 4b f 4a, and crossover experiments indicate a dissociative mechanism (via a retro-cycloaddition) for the rearrangement. The reaction of 1a with PhNCO gave analogous N,O-and N,N-coordinated cycloadducts. Finally, the N,N-dimethyl hydrazinediido complexes reacted unspecifically with most organic azides at ambient temperature. However, complex [Cp*Ti(N Xyl N){N-NMe 2 }(dmap)] (1c) underwent a clean and fast reaction with trimethylsilylazide to give the N-silylated η 2 -hydrazido(1-) titanium azide [Cp*Ti-(N Xyl N)(η 2 -NMe 2 -NSiMe 3 )(N 3 )] ( 8), in which the trimethylsilyl group of the azide is transferred to the hydrazido ligand, while the azide is terminally coordinated to the titanium center.

N-Substituted Iminocaprolactams as Versatile and Low Cost Ligands in Group 4 Metal Initiators for the Living Coordinative Chain Transfer Polymerization of α-Olefins

“…Complexes 1 – 3 are anticipated to adopt a C 1 -symmetric molecular structure if the [(R)­N imcap N] ligand is coordinated to the hafnium center in a κ 2 - N , N -bidentate fashion. However, 1 H NMR (400 MHz, benzene- d 6 , 25 °C) spectra recorded for all three complexes indicated a solution structure of higher symmetry that could potentially be due to either a different coordination geometry for the [(R)­N imcap N] ligand or, in keeping with our previous observations for the general class of II , a low energy barrier for metal-centered racemization that proceeds through a dynamic process involving “amidinate ring-flipping” of the [(R)­N imcap N] moiety. ,, Gade and co-workers have documented a similar dynamic process for their Cp*Ti­[κ 2 -( N , N )-2-aminopyrrolinato]­(Me) 2 complex.…”

“…As presented in Scheme , N-substituted iminocaprolactams ( III ) are a class of amidines that, as reported in 1948 by Benson and Cairns, can be obtained in high yield and with great structural diversity through simple condensation of primary amines with O -methylcaprolactim ( IV ), which in turn is produced through direct O- methylation of ε-caprolactam with dimethyl sulfate . Another attractive feature of this synthetic route to N-substituted iminocaprolactams is that a large number of different derivatives have already been reported as being stable compounds that can be easily purified by distillation or recrystallization. , On the other hand, and quite unexpectedly, we were surprised to find that no evidence appears to exist in either the academic or patent literature for efforts to develop the general class of iminocaprolactams as supporting ligands for metal complexes of any kind . , In this respect, the closest reported analogue of I is the (κ 2 - N , N )-2-aminopyrrolinato ligand, which can be viewed as a five-membered ring congener, that was recently introduced by Gade and co-workers in titanium complexes and later adopted by Barry and co-workers for aluminum complexes.…”

Zirconium and Hafnium Hydrazinediido Half-Sandwich Complexes: Synthesis and Reactivity

“…The 1 H NMR spectrum featured eight doublets and three septets (one consisting of two overlapping signals) corresponding to four diastereotopic isopropyl groups. In the 1 H− 13 C HMBC NMR spectrum, two signals in the 13 C NMR spectrum with shifts characteristic 14,16 for imino group carbon atoms (147.7 and 145.5 ppm) featured long-range coupling to the CHMe 2 protons of two isopropyl groups. The 15 N NMR spectrum displays eight resonances, which were assigned using 1 H− 15 N HMBC NMR spectroscopy (Figure 7).…”

“…6−15 Stoichiometric reactions with alkynes, 4,5,7,8,12 allenes, 14 and heteroallenes, such as isocyanates, 3,10,11,14 isothiocyanates, 10,11,14 carbon dioxide, 3,9,11 carbodiimides, 16 and carbon disulfide, 11 resulted in formal [2 + 2] cycloadditions. In some cases this initial reaction step was followed by Ti−X insertion, 10,17 or insertion into the N−N bond of the hydrazinediido unit, depending on the ancillary ligand.…”

C–H Activation in Diiron Bridging Vinyliminium Ligands: Reaction with CS2 to Form New Zwitterionic Complexes Acting as Organometallic Ligands

“…Examples are numerous and include insertion into M-O and M-N, [19] M-S, [20] M-H, [21] M-C [22] and M-M bonds in early-late heterodinuclear transition-metal complexes and bonds. [23] The reactions of CS 2 and SNCPh with M=N (double bond) [24] and M=C (metalcarbene interaction) [25] have also been reported. In all cases, the new ligands generated by insertion and rearrangement of XCS (X = S, NPh) are invariably coordinated to the metal centre through S (or N) atoms, more frequently as S,S-or S,N-chelating ligands.…”