Reaction of [Cp*Ti(N Xyl N)(N t Bu)(NH 2 t Bu)] with 1 molar equiv of diphenylhydrazine yielded the hydrazinediido complex [Cp*Ti(N Xyl N)(NNPh 2 )(NH 2 t Bu)] (1a), whereas the orange pyridine adduct [Cp*Ti(N Xyl N)(NNPh 2 )(py)] (1b) was obtained by reacting the imide [Cp*Ti(N Xyl N)(N t Bu)(NH 2 t Bu)] with diphenylhydrazine in the presence of pyridine. The tert-butylamine coordinated to the metal center in 1a could be removed by heating the solid at 60 °C and 10 -6 mbar for 72 h, yielding [Cp*Ti(N Xyl N)(NNPh 2 )] (1c). In the presence of pyridine or 4-dimethylaminopyridine (dmap) as neutral co-ligands the hydrazinediido complexes [Cp*Ti(N Xyl N)(NNMePh)(py)] (2a) and [Cp*Ti(N Xyl N)-(NNMePh)(dmap)] (2b) as well as [Cp*Ti(N Xyl N)(NNMe 2 )(dmap)] (3) were prepared. Upon replacement of dmap by the weaker donor ligand pyridine in the synthesis of the pyridine adduct analogous to 3, a mixture of [Cp*Ti(N Xyl N)(NNMe 2 )(py)] (4a) and the dinuclear complex [Cp* 2 Ti 2 (N Xyl N) 2 (µ-η 1 ,η 1 -NNMe 2 )(µ-η 1 ,η 2 -NNMe 2 )] (4b) was obtained. Reaction of the dimethylhydrazinediido complex 3 with phenylacetylene gave the Markovnikov cycloadduct, which had sufficient lifetime to allow its 1 H, 13 C, and 15 N NMR spectroscopic characterization in solution. All three hydrazinediido compounds 1a, 2a, and 3 were found to display remarkable activities in catalytic hydrohydrazinations at ambient temperatures. For catalyst loadings of 5 mol % complete conversions of the terminal alkynes and diynes with Markovnikov regioselectivities of over 99% selectivity were observed within 1 h.

A series of new titanium half sandwich complexes, containing a 2-aminopyrrolinato ligand {N(Xyl)N}(-) as the ancillary ligand, have been prepared and are shown to be pre-catalysts for the hydroamination of alkynes. The coordination of {N(Xyl)N}(-) to titanium was achieved by reaction of [Cp*TiMe(3)] with the protioligand N(Xyl)NH giving [Cp*Ti(N(Xyl)N)(Me)(2)] (). Upon reaction of complex with an excess of tert-butylamine, the imido complex [Cp*Ti(N(Xyl)N)(N(t)Bu)(NH(2)(t)Bu)] () was formed. The latter provided the preparative entry to the synthesis of a range of N-aryl substituted imido complexes. Imido ligand exchange with 2,6-dimethylaniline, 2,4,6-trimethylaniline as well as 2,6-diisopropylaniline gave the corresponding arylimido complexes in clean reactions. Reaction of the titanium imido complex [Cp*Ti(N(Xyl)N)(N(t)Bu)(NH(2)(t)Bu)] with terminal arylacetylenes, such as phenylacetylene and tolylacetylene, led to C-H activation and the formation of alkynyl/amido complexes, whereas the arylimido complexes and cleanly underwent {2 + 2} cycloaddition, giving the azatitanacyclobutene derivatives. A single-crystal X-ray structure analysis of the azatitanacyclobutene [Cp*Ti(N(Xyl)N){kappa(2)N(2,6-C(6)H(3)Me(2))CTol[double bond, length as m-dash]CH}] () provided the first crystallographically characterized Markovnikov cycloaddition product of an imidotitanium complex with a terminal alkyne. The mechanistic aspects of the hydromanination of alkynes with the new Ti half sandwich complexes were studied and established a reversible {2 + 2} cycloaddition step and the cleavage of the metallacyclic intermediate as the rate determining step in the catalytic cycle. The titanium half sandwich imido complexes were found to be active catalysts for the inter- and intramolecular hydroamination of a broad range of alkynes and omega-aminoalkynes.

The use of an amino-oxazolinate (NN(ox) = kappa2-2,6-dimethylphenylamido-4(S)-isopropyloxazoline) as a chiral analogue to amidinate ligands in the chemistry of titanium was found to lead to undesired side reactions. The reaction of 2,6-dimethylphenylamido-4(S)-isopropyloxazoline with [Ti(NMe2)4] afforded the bis(amidinato) complex [Ti(NN(ox))2(NMe2)2] (2) which was thermally converted to the ring-opened decomposition products [Ti(NN(ox)){kappa3-N(2,6-C6H3Me2)C(NMe2)NC(iPr)CH2O}(NMe2)] (3) and [Ti{kappa3-N(2,6-C6H3Me2)C(NMe2)-NC(iPr)CH2O}2] (4). The NMR spectra of 4 recorded at low temperature displayed two sets of resonances corresponding to two symmetric isomers in a 2:5 ratio, the probable geometries of which were established by ONIOM (QM/MM) simulations. To suppress ring opening of the oxazolines, their oxygen atom was formally replaced by a CH2 group in the synthesis of a series of amino-pyrroline protioligands 2-RN(H)(5-C4H5NR') (HN(R)N(R')). Their reaction with [Ti(NMe2)4] gave the thermally stable complexes [Ti(N(R)N(R'))2(NMe2)2], of which three derivatives were characterized by X-ray diffraction. They are stereochemically dynamic and undergo reversible ligand rearrangements in solution, for which the activation parameters were determined by variable-temperature (1)H NMR spectroscopy.

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.

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